Showing 1–50 of 121 results for author: Dong, C

Anomalous magnetocaloric effects in the quasi-one-dimensional antiferromagnet BaCo$_2$V$_2$O$_8$

Authors: Jiahao Yang, Chao Dong, Xinlong Shi, Zhuo Wang, Tiantian Li, Liusuo Wu, Junfeng Wang, Zhangzhen He, Liang Li, Yongkang Luo, Jianda Wu

Abstract: We investigate the transverse-field thermodynamics of the quasi-one-dimensional Ising-like antiferromagnet BaCo$_2$V$_2$O$_8$, whose tilted screw-chain geometry and anisotropic Landé $g$ tensor generate spatially modulated Zeeman couplings. Angle-resolved magnetocaloric-effect (MCE) measurements reveal a high-field temperature minimum near the transverse-field Ising critical field for… ▽ More We investigate the transverse-field thermodynamics of the quasi-one-dimensional Ising-like antiferromagnet BaCo$_2$V$_2$O$_8$, whose tilted screw-chain geometry and anisotropic Landé $g$ tensor generate spatially modulated Zeeman couplings. Angle-resolved magnetocaloric-effect (MCE) measurements reveal a high-field temperature minimum near the transverse-field Ising critical field for $H\parallel[110]$ that persists and shifts only weakly upon field rotation. Tensor-network calculations show that the rotation-induced staggered transverse field rapidly lowers the Ising critical field and that the magnetic Grüneisen ratio changes sign near the high-field temperature minimum, consistent with experiment. Our results establish that a dominant MCE response can persist away from the Ising critical region, suggesting a route to magnetic cooling by tailoring anisotropic Zeeman-coupling configurations in quantum magnets. △ Less

Submitted 25 August, 2026; originally announced August 2026.

Comments: 16 pages, 6 figures

Tilted $p$-wave magnet candidate CeNiAsO

Authors: Zhuo Wang, Zheng Liu, Shuo Zou, Hua-Xun Li, Jin-Xin Hu, Zhuolun Qiu, Ze Wang, Jiamin Gong, Lucheng Wei, Kangjian Luo, Hai Zeng, Meng Zhang, Chao Dong, Chuanyin Xi, Junfeng Wang, Jiakun Fang, Xiaotao Han, Guang-Han Cao, Liang Li, Yongkang Luo

Abstract: The unexpectedly small ordered moments of CeNiAsO, a candidate for correlated $p$-wave magnet, have posed a serious challenge to the precise determination of its magnetic structure, hindering the understanding of its fundamental properties. By leveraging the high sensitivity to local internal fields, our $^{75}$As nuclear quadrupole / magnetic resonance experiments reveal a commensurate antiferrom… ▽ More The unexpectedly small ordered moments of CeNiAsO, a candidate for correlated $p$-wave magnet, have posed a serious challenge to the precise determination of its magnetic structure, hindering the understanding of its fundamental properties. By leveraging the high sensitivity to local internal fields, our $^{75}$As nuclear quadrupole / magnetic resonance experiments reveal a commensurate antiferromagnetic order with a small out-of-plane moment $m_z\approx0.05$ $μ_{\mathrm{B}}$. This tilted magnetic configuration not only rotates the spin polarization axis away from the crystallographic $\mathbf{c}$-axis, but also enhances the non-relativistic spin splitting. We refer to this rare paradigm as a \textit{tilted $p$-wave magnet}. △ Less

Submitted 20 August, 2026; originally announced August 2026.

Comments: 7+10 pages, 4+9 figures

Bending-like stress induced by solder joint under uniaxial tensile testing in 2G-HTS tapes: Impact and optimization approach

Authors: Dean Liu, Yue Wu, Haoliang Xiang, Xiaofen Li, Caida Fu, Chiheng Dong, Yue Zhao

Abstract: The reversible stress limit (\mathit{R}_{rev}) of second-generation high-temperature superconducting (2G-HTS) tapes is a critical performance indicator, typically characterized through uniaxial tensile testing. In practice, the accuracy of the measured Rrev value is often compromised by stress concentration induced by the voltage tap solder joint. The present study investigates the underlying inte… ▽ More The reversible stress limit (\mathit{R}_{rev}) of second-generation high-temperature superconducting (2G-HTS) tapes is a critical performance indicator, typically characterized through uniaxial tensile testing. In practice, the accuracy of the measured Rrev value is often compromised by stress concentration induced by the voltage tap solder joint. The present study investigates the underlying interference mechanism using integrated experimental and numerical methods. Mechanistic analysis reveals that under uniaxial tensile loading, the local geometric inhomogeneity introduced by the solder joint induces an external, bending-like stress in the vicinity of the solder joint, transitioning from additional tensile stress in the zone adjacent to the joint to additional compressive stress in the zone remote from it. When the solder joint is attached to the front surface of the tape (the side closer to the superconducting layer), the superconducting layer experiences localized additional tensile stress, triggering premature damage and early \mathit{I}_{c} degradation. Consequently, an optimized back-surface soldering approach is proposed, which positions the superconducting layer in a localized compressive zone. Experimental validation demonstrates that the proposed approach effectively mitigates testing errors for various tape configurations. Notably, for the tape with a copper layer thickness of 5 μm, the measured \mathit{R}_{rev} increased from 546 MPa to 734 MPa, corresponding to a 42% increase, and moved closer to the actual value. The findings provide essential insights for the precision characterization of the electromechanical performances (EMPs) of 2G-HTS tapes. △ Less

Submitted 28 May, 2026; originally announced May 2026.

Ultra-Confinement of Polaritons in Single Atomic Layer Ag Photonic Quantum Dots

Authors: Xinyi Li, Tetyana Ignatova, Chengye Dong, Krishnan Mekkanamkulam Ananthanarayanan, Rinu Abraham Maniyara, Arpit Jain, Furkan Turker, Vinay Kammarchedu, Aida Ebrahimi, Joshua A. Robinson, Slava V. Rotkin

Abstract: Light scattering by two-dimensional (2D) van der Waals heterostructures (vdWHs) is immense, especially given their infinitesimal volume, thus enabling strong light-matter interactions. Surface 2D polariton waves manifest through large concentration of electromagnetic field in vertical direction, normal to their propagation. By confining vdWH materials into 2D photonic shapes, one can manipulate an… ▽ More Light scattering by two-dimensional (2D) van der Waals heterostructures (vdWHs) is immense, especially given their infinitesimal volume, thus enabling strong light-matter interactions. Surface 2D polariton waves manifest through large concentration of electromagnetic field in vertical direction, normal to their propagation. By confining vdWH materials into 2D photonic shapes, one can manipulate and compress light in lateral directions. Scattering-type scanning near-field optical microscopy is a perfect tool for direct imaging of the propagating polaritons and studying the properties of confined polaritons in nanostructures. Though, thus far the quantitative analysis, such the wavelength extraction, has been challenged for confined polaritons by incapability of mapping of the wave period on sub-wavelength scale and difficulty of identifying an adequate substrate's "background" to subtract. Here, an analytical approach is developed to reveal the local propagation constant of confined polaritons under abovementioned constraints and map it with the sub-wavelength resolution. Applied to analysis of the SiC/2D-Ag/EG (epitaxial graphene) photonic nanostructures, the technique uncovered that the polaritons are highly confined in both vertical ($\simλ$/50) and lateral directions ($\simλ$/40) by 2D metal. △ Less

Submitted 20 May, 2026; originally announced May 2026.

Collective quantum state at the atomic limit

Authors: Fan Zhang, Yanxing Li, Chengye Dong, Ninad Kailas Dongre, Viet-Anh Ha, Yu-Chuan Lin, Yiyuan Luo, Hyunsue Kim, Joshua A. Robinson, Feliciano Giustino, Fan Zhang, Chih-Kang Shih

Abstract: Collective quantum states are often associated with extended systems, where spatially extensive degrees of freedom enable emergent many-body behavior; whether such strongly correlated states survive at atomic dimensions remains a fundamental question. Tomonaga-Luttinger liquids provide a paradigmatic example of one-dimensional collective quantum matter characterized by spin-charge separation. Usin… ▽ More Collective quantum states are often associated with extended systems, where spatially extensive degrees of freedom enable emergent many-body behavior; whether such strongly correlated states survive at atomic dimensions remains a fundamental question. Tomonaga-Luttinger liquids provide a paradigmatic example of one-dimensional collective quantum matter characterized by spin-charge separation. Using low-temperature scanning tunneling microscopy and spectroscopy, we directly visualize quantized collective modes in atomically confined mirror twin boundary segments of monolayer WSe2. Distinct standing-wave branches associated with fractionalized spin and charge excitations persist in segments as short as one nanometer, establishing the atomic-scale confinement limit of Luttinger-liquid behavior. These ultrashort segments form a new class of many-body quantum dots whose discrete spectra arise from confined collective bosonic modes rather than single-particle electron states. When assembled into ordered chains, inter-dot coupling reshapes electron-like fundamental states while collective spin/charge excitations remain largely intact, revealing distinct coupling responses of emergent many-body modes. Our results demonstrate that collective quantum matter can persist and exhibit fundamentally distinct coupling behavior at atomic length scales, establishing a novel platform for engineering strongly correlated quantum phases from atomically confined building blocks. △ Less

Submitted 6 May, 2026; originally announced May 2026.

Ultrafast photo-thermoelectric currents in graphene junctions in the mid-infrared

Authors: Nina Pettinger, Michel Panhans, Johannes Schmuck, Sebastian Loy, Xiaoyi Zhou, Chengye Dong, Joshua A. Robinson, Sergey Zherebtsov, Christoph Kastl, Frank Ortmann, Alexander W. Holleitner

Abstract: Graphene is widely recognized for its ultrafast and broadband photocurrent response, but whether the broadband ultrafast characteristics are preserved at mid-infrared wavelengths with photon energies below the optical phonon energy remains an open question. Here, we investigate the carrier dynamics in graphene junctions under mid-infrared excitation using an ultrafast pump-probe photocurrent spect… ▽ More Graphene is widely recognized for its ultrafast and broadband photocurrent response, but whether the broadband ultrafast characteristics are preserved at mid-infrared wavelengths with photon energies below the optical phonon energy remains an open question. Here, we investigate the carrier dynamics in graphene junctions under mid-infrared excitation using an ultrafast pump-probe photocurrent spectroscopy. We utilize dual split gate devices to demonstrate that the photo-thermoelectric effect can dominate the photoresponse of graphene also for a mid-infrared femtosecond excitation. We observe that graphene retains its broadband photocurrent response in this spectral region, but the photocurrent relaxation time increases from ca. 2 ps below 8-9 micrometer up to 3 ps at longer mid-infrared wavelengths. The absence of a pronounced phonon bottleneck in the decay dynamics at room temperature suggests an efficient interplay of electron-electron and electron-phonon scattering even for photon energies below the optical phonon energy in graphene. The observed wavelength dependence of the photocurrent relaxation times is consistent with energy-dependent theoretical relaxation times as derived from a microscopic transport theory of graphene that includes electron-phonon coupling within a Holstein-Peierls Hamiltonian. △ Less

Submitted 13 March, 2026; originally announced March 2026.

Ultrafast Band-Gap Renormalization in Bilayer Graphene

Authors: Eduard Moos, Zhi-Yuan Deng, Hauke Beyer, Arpit Jain, Chengye Dong, Li-Syuan Lu, Joshua A. Robinson, Kai Rossnagel, Michael Bauer

Abstract: We demonstrate, by femtosecond time- and angle-resolved photoemission spectroscopy, that photoinduced interlayer charge transfer in a heterostructure consisting of Bernal-stacked bilayer graphene and a single atomic layer of silver on 6H-SiC(0001) transiently modulates the intrinsic potential landscape across the silver-graphene interface. This acts as an ultrafast optoelectronic gate that drives… ▽ More We demonstrate, by femtosecond time- and angle-resolved photoemission spectroscopy, that photoinduced interlayer charge transfer in a heterostructure consisting of Bernal-stacked bilayer graphene and a single atomic layer of silver on 6H-SiC(0001) transiently modulates the intrinsic potential landscape across the silver-graphene interface. This acts as an ultrafast optoelectronic gate that drives momentum-dependent band renormalizations, resulting in a transient band-gap opening on femtosecond timescales. Simultaneously, the photogenerated hot-carrier population enhances electronic screening, leading to subsequent closing of the band-gap beyond the thermal equilibrium value. These findings reveal two different mechanisms for photoinduced, reversible control of the electronic band structure in bilayer graphene -- interlayer charge transfer and hot-carrier-enhanced screening -- providing a general framework for the ultrafast control of electronic properties in graphene-based heterostructures. This opens up novel pathways for the realization of ultrafast optoelectronic devices and the exploration of correlated quantum phases in bilayer graphene under non-equilibrium conditions. △ Less

Submitted 20 February, 2026; originally announced February 2026.

Superconducting Decoherence and Thermal Quenching of the Josephson Diode Effect in Low-Dimensional Josephson Systems

Authors: F. Yang, C. Y. Dong, Joshua A. Robinson, L. Q. Chen

Abstract: Motivated by recent studies on superconducting (SC) diode nonreciprocity, we uncover a generic smooth SC-phase decoherence mechanism in low-dimensional Josephson structures. Contrary to the conventional single-energy-scale paradigm where Josephson coherence and diode nonreciprocity vanish simultaneously only at the SC gap-closing temperature, we demonstrate, within a fully self-consistent microsco… ▽ More Motivated by recent studies on superconducting (SC) diode nonreciprocity, we uncover a generic smooth SC-phase decoherence mechanism in low-dimensional Josephson structures. Contrary to the conventional single-energy-scale paradigm where Josephson coherence and diode nonreciprocity vanish simultaneously only at the SC gap-closing temperature, we demonstrate, within a fully self-consistent microscopic framework beyond mean-field theory, that SC phase fluctuations generically split these phenomena into distinct energy scales. As a result, rather than a single SC-normal transition, the system exhibits a sequence of distinct thermal crossovers upon heating: the diode effect disappears first at $T_η$, Josephson coherence is subsequently lost at $T_c$, and the SC gap collapses only at a higher temperature $T_s$. Using a bilayer SC system as a concrete example, we show that the separation between these temperature scales is not solely dictated by Josephson coupling, but is instead strongly and counterintuitively shaped by the in-plane disorder and carrier density. These findings reveal that smooth SC phase decoherence introduces a distinct and more fragile energy scale, with potential implications for layered superconductors such as cuprates and recently discovered nickelates, as well as for SC qubit platforms. △ Less

Submitted 8 March, 2026; v1 submitted 18 February, 2026; originally announced February 2026.

Unexpected type-II multiferroic phase in GdMnO3 under high magnetic fields

Authors: Ming Yang, Jun Chen, Junfeng Wang, Chao Dong, Chengliang Lu, Gang Xu, Jinguang Cheng, Jianshi Zhou, Shuai Dong

Abstract: Perovskite manganites with small A-site ions, as the first and canonical branch of type-II multiferroics, are ideal systems to exhibit magnetism-induced ferroelectricity. Despite their established magnetoelectric phase diagrams under low magnetic fields, here an unidentified phase with a large magnetism-induced polarization (up to 1500 μC/m2) is revealed in GdMnO3 under high magnetic fields up to… ▽ More Perovskite manganites with small A-site ions, as the first and canonical branch of type-II multiferroics, are ideal systems to exhibit magnetism-induced ferroelectricity. Despite their established magnetoelectric phase diagrams under low magnetic fields, here an unidentified phase with a large magnetism-induced polarization (up to 1500 μC/m2) is revealed in GdMnO3 under high magnetic fields up to 60 T. Based on multiprobe experiments, a complete phase diagram is constructed with successive polar-nonpolar-polar-nonpolar transitions. Such a nonmonotonic evolution is well mimicked by model simulation, while the spin-lattice coupling is the key ingredient for the reentrant ferroelectric phase. △ Less

Submitted 13 January, 2026; originally announced January 2026.

Remote epitaxial frustration

Authors: Taehwan Jung, Nicholas Hagopian, Anshu Sirohi, Quinn Campbell, Chengye Dong, Zachary T. LaDuca, Tamalika Samanta, Joshua Robinson, Paul M. Voyles, Jason K. Kawasaki

Abstract: Remote epitaxy relaxes the constraints of conventional epitaxy, to enable low defect density, chemically abrupt heterostructures and exfoliation of single crystalline membranes. However, definitive evidence for a true remote mechanism remains elusive because most experiments can be explained by alternative mechanism that are macroscopically indistinguishable from true remote epitaxy. Using GdAuGe… ▽ More Remote epitaxy relaxes the constraints of conventional epitaxy, to enable low defect density, chemically abrupt heterostructures and exfoliation of single crystalline membranes. However, definitive evidence for a true remote mechanism remains elusive because most experiments can be explained by alternative mechanism that are macroscopically indistinguishable from true remote epitaxy. Using GdAuGe films grown on graphene/SiC (0001), we present two signatures that cannot be explained by the leading alternatives to the remote mechanism: (1) a few atomic layer thick disordered interlayer at the GdAuGe/graphene interface and (2) a $30\degree$ rotated epitaxial relationship between the GdAuGe film and the SiC substrate. Density functional theory calculations indicate these signatures arise from remote epitaxial \textit{frustration}, a competition amongst epitaxy to the remotely screened substrate, to graphene, and to the graphene-induced interfacial reconstruction. Tuning the amplitudes and periodicities of these competing potentials provides new opportunities to intentionally disrupt long-range order. △ Less

Submitted 7 December, 2025; originally announced December 2025.

Point defects and their dynamic behaviors in silver monolayer intercalated between graphene and SiC

Authors: Van Dong Pham, Arpit Jain, Chengye Dong, Li-Syuan Lu, Joshua A. Robinson, Achim Trampert, Roman Engel-Herbert

Abstract: Point defects give rise to sharp modifications in the structures and electronic properties of two-dimensional metals, offering an atomic-level platform for fundamental studies and potential applications. In this work, we investigate atomic-scale defects in a two-dimensional silver monolayer intercalated between epitaxial graphene and SiC using scanning tunneling microscopy. Dark and bright defects… ▽ More Point defects give rise to sharp modifications in the structures and electronic properties of two-dimensional metals, offering an atomic-level platform for fundamental studies and potential applications. In this work, we investigate atomic-scale defects in a two-dimensional silver monolayer intercalated between epitaxial graphene and SiC using scanning tunneling microscopy. Dark and bright defects are identified as vacancies or substitutional impurities within the silver monolayer, each hosting a localized electronic state. Remarkably, under tunneling electron excitation at negative bias, the bright defects exhibit dynamic behaviors characterized by inelastic switching between two states. The switching can be reversibly controlled by the microscope tip, enabling the defects to function as atomic-scale two-level conductance switches. Analysis of defect switching reveals possible defect origins and the relationship between dark and bright defect species. Our findings establish a pathway to precise manipulation of defects in two-dimensional metals and uncover previously unexplored dynamics with potential use in nanoelectronics. △ Less

Submitted 4 February, 2026; v1 submitted 13 November, 2025; originally announced November 2025.

Comments: 33 pages, 5 main figures and 6 supplementary figures

Journal ref: Nano Lett., 26, 2, 902 (2026)

Defect-Mediated Phase Engineering of 2D Ag at the Graphene/SiC Interface

Authors: Arpit Jain, Boyang Zheng, Sawani Datta, Kanchan Ulman, Jakob Henz, Matthew Wei-Jun Liu, Van Dong Pham, Wen He, Chengye Dong, Li-Syuan Lu, Alexander Vera, Nader Sawtarie, Wesley Auker, Ke Wang, Bob Hengstebeck, Zachary W. Henshaw, Shreya Mathela, Maxwell Wetherington, William H. Blades, Kenneth Knappenberger, Ursula Wurstbauer, Su Ying Quek, Ulrich Starke, Shengxi Huang, Vincent H. Crespi , et al. (1 additional authors not shown)

Abstract: Atomically thin silver (Ag) films offer unique opportunities in plasmonic, quantum optics, and energy harvesting, yet conventional growth methods struggle to achieve structural control at the monolayer limit. Here, we demonstrate phase-selective synthesis of large-area, crystalline 2D Ag films via defect-engineered confinement heteroepitaxy (CHet) at the epitaxial graphene/silicon carbide (EG/SiC)… ▽ More Atomically thin silver (Ag) films offer unique opportunities in plasmonic, quantum optics, and energy harvesting, yet conventional growth methods struggle to achieve structural control at the monolayer limit. Here, we demonstrate phase-selective synthesis of large-area, crystalline 2D Ag films via defect-engineered confinement heteroepitaxy (CHet) at the epitaxial graphene/silicon carbide (EG/SiC) interface. By tuning graphene growth and post-growth defect introduction, two distinct Ag phases are achieved with disparate properties: a nearly commensurate Ag(1) lattice stabilized by vacancy and line defects in epitaxial graphene, and a denser Ag(2) phase preferentially grown with sp3-rich zero-layer graphene. Structural and spectroscopic characterization confirm lattice registry with the SiC substrate, while theoretical calculations reveal a thermodynamic preference for Ag(2) but an easier nucleation for Ag(1). Both phases are found to be semiconducting, with the Ag(2) phase exhibiting slightly enhanced n-doping of graphene. Notably, nonlinear optical measurements reveal a three-order magnitude difference in second-order susceptibility between the two phases, demonstrating promise for phase-tunable 2D metals in reconfigurable optoelectronic and metamaterial platforms. △ Less

Submitted 10 November, 2025; originally announced November 2025.

Atomically-resolved exciton emission from single defects in MoS$_2$

Authors: Lysander Huberich, Eve Ammerman, Gu Yu, Yining Ren, Sotirios Papadopoulos, Chengye Dong, Joshua A. Robinson, Kenji Watanabe, Takashi Taniguchi, Oliver Gröning, Lukas Novotny, Tingxin Li, Shiyong Wang, Bruno Schuler

Abstract: Understanding how atomic defects shape the nanoscale optical properties of two-dimensional (2D) semiconductors is essential for advancing quantum technologies and optoelectronics. Using scanning tunneling spectroscopy (STS) and luminescence (STML), we correlate the atomic structure and optical fingerprints of individual defects in monolayer MoS$_2$. A bilayer of hexagonal boron nitride (hBN) effec… ▽ More Understanding how atomic defects shape the nanoscale optical properties of two-dimensional (2D) semiconductors is essential for advancing quantum technologies and optoelectronics. Using scanning tunneling spectroscopy (STS) and luminescence (STML), we correlate the atomic structure and optical fingerprints of individual defects in monolayer MoS$_2$. A bilayer of hexagonal boron nitride (hBN) effectively decouples MoS$_2$ from the graphene substrate, increasing its band gap and extending the defect charge state lifetime. This enables the observation of sharp STML emission lines from MoS$_2$ excitons and trions exhibiting nanoscale sensitivity to local potential fluctuations. We identify the optical signatures of common point defects in MoS$_2$: sulfur vacancies (Vac$_\text{S}^-$), oxygen substitutions (O$_\text{S}$), and negatively charged carbon-hydrogen complexes (CH$_\text{S}^-$). While Vac$_\text{S}^-$ and O$_\text{S}$ only suppress pristine excitonic emission, CH$_\text{S}^-$ generate defect-bound exciton complexes ($A^-X$) about 200\,meV below the MoS$_2$ exciton. Sub-nanometer-resolved STML maps reveal large spectral shifts near charged defects, concurrent with the local band bending expected for band-to-defect optical transitions. These results establish an atomically precise correlation between structure, electronic states, and optical response, enabling deterministic engineering of quantum emitters in 2D materials. △ Less

Submitted 17 October, 2025; originally announced October 2025.

Realization of large magnetocaloric effect in the Kagome antiferromagnet Gd3BWO9 for Sub-Kelvin cryogenic refrigeration

Authors: Fangyuan Song, Xinyang Liu, Chao Dong, Jin Zhou, Xinlong Shi, Yuyan Han, Langsheng Ling, Huifen Ren, Songliu Yuan, Shun Wang, Junsen Xiang, Peijie Sun, Zhaoming Tian

Abstract: Rare-earth (RE) based frustrated magnets have attracted great attention as excellent candidates for magnetic refrigeration at sub-Kelvin temperatures, while the experimental identification on systems exhibiting both large volumetric cooling capacity and reduced working temperatures far below 1 K remain to be a challenge. Here, through the ultra-low temperature magnetism and thermodynamic character… ▽ More Rare-earth (RE) based frustrated magnets have attracted great attention as excellent candidates for magnetic refrigeration at sub-Kelvin temperatures, while the experimental identification on systems exhibiting both large volumetric cooling capacity and reduced working temperatures far below 1 K remain to be a challenge. Here, through the ultra-low temperature magnetism and thermodynamic characterizations, we unveil the large magnetocaloric effect (MCE) realized at sub-Kelvin temperatures in the frustrated Kagome antiferromagnet Gd3BWO9 with TN~1.0 K. The isothermal magnetization curves indicate the existence of field (B) induced anisotropic magnetic phase diagrams, where four distinct magnetic phases for B // c-axis and five magnetic phases for B // ab-plane are identified at T< TN. The analysis of magnetic entropy S(B, T) data and direct adiabatic demagnetization tests reveal a remarkable cooling performance at sub-Kelvin temperatures featured by a large volumetric entropy density 502.2 mJ/K/cm3 and a low attainable minimal temperature Tmin~168 mK from the initial cooling condition of 2 K and 6 T, surpassing most of Gd-based refrigerants previously documented in temperature ranges of 0.25-4 K. The realized Tmin~168 mK far below TN ~ 1.0 K in Gd3BWO9 is related to the combined effects of magnetic frustration and criticality-enhanced MCE, which together leave a substantial magnetic entropy at reduced temperatures by enhancing spin fluctuations. △ Less

Submitted 14 September, 2025; originally announced September 2025.

Layer-Dependent Interfacial Coupling and Exciton Pinning in WSe2/Graphene Heterostructures

Authors: Lan Huang, Laric Bobzien, Ángel Labordet Álvarez, Daniel E. Cintron Figueroa, Li-Syuan Lu, Chengye Dong, Michel Calame, Joshua A. Robinson, Bruno Schuler, Mirjana Dimitrievska

Abstract: Understanding interfacial interactions in two-dimensional heterostructures is crucial for their implementation in future optoelectronic and quantum technologies. Here, we investigate interactions between WSe2 and graphene by comparing 1-5 layer MOCVD-grown WSe2 on graphene/SiC with exfoliated WSe2 on SiO2/Si using Raman and photoluminescence spectroscopy combined with atomic force microscopy. Grow… ▽ More Understanding interfacial interactions in two-dimensional heterostructures is crucial for their implementation in future optoelectronic and quantum technologies. Here, we investigate interactions between WSe2 and graphene by comparing 1-5 layer MOCVD-grown WSe2 on graphene/SiC with exfoliated WSe2 on SiO2/Si using Raman and photoluminescence spectroscopy combined with atomic force microscopy. Growth on graphene induces persistent compressive strain of approximately 0.2% and reduces the interlayer WSe2 distance by 0.11 +/- 0.05 Angstrom. Interfacial disorder is strongest in the WSe2 layer directly contacting graphene, with an effective Urbach energy of approximately 20 meV, decreasing to approximately 16 meV upon addition of a second layer and remaining similar for thicker films. Increasing WSe2 thickness leads to progressive electron transfer from graphene to WSe2, resulting in p-type doping of graphene and n-type doping of WSe2, with the graphene hole density increasing from approximately 0.4 x 10^13 cm^-2 for 1L to 0.8 x 10^13 cm^-2 for 5L. The A- and B-exciton energies of WSe2 remain nearly pinned on graphene, in contrast to their pronounced thickness-dependent shifts on SiO2/Si. We show that this pinning arises primarily from electronic screening and compressive strain, with smaller contributions from charge transfer and modified interlayer coupling. These findings establish graphene as an active interface for controlling excitonic properties in scalable van der Waals heterostructures. △ Less

Submitted 25 August, 2026; v1 submitted 10 September, 2025; originally announced September 2025.

Orbital Hybridization-Induced Ising-Type Superconductivity in a Confined Gallium Layer

Authors: Hemian Yi, Yunzhe Liu, Chengye Dong, Yiheng Yang, Zi-Jie Yan, Zihao Wang, Lingjie Zhou, Dingsong Wu, Houke Chen, Stephen Paolini, Bing Xia, Bomin Zhang, Xiaoda Liu, Hongtao Rong, Annie G. Wang, Saswata Mandal, Kaijie Yang, Benjamin N. Katz, Lunhui Hu, Jieyi Liu, Tien-Lin Lee, Vincent H. Crespi, Yuanxi Wang, Yulin Chen, Joshua A. Robinson , et al. (2 additional authors not shown)

Abstract: In low-dimensional superconductors, the interplay between quantum confinement and interfacial hybridization effects can reshape Cooper pair wavefunctions and induce novel forms of unconventional superconductivity. In this work, we employ a plasma-free, carbon buffer layer-assisted confinement epitaxy method to synthesize trilayer gallium (Ga) sandwiched between a graphene layer and a 6H-SiC(0001)… ▽ More In low-dimensional superconductors, the interplay between quantum confinement and interfacial hybridization effects can reshape Cooper pair wavefunctions and induce novel forms of unconventional superconductivity. In this work, we employ a plasma-free, carbon buffer layer-assisted confinement epitaxy method to synthesize trilayer gallium (Ga) sandwiched between a graphene layer and a 6H-SiC(0001) substrate, forming an air-stable graphene/trilayer Ga/SiC heterostructure. In this confined light-element Ga layer, we demonstrate interfacial Ising-type superconductivity driven by atomic orbital hybridization between the Ga layer and the SiC substrate. Electrical transport measurements reveal that the in-plane upper critical magnetic field u0Hc2,|| reaches ~21.98T at T=400 mK, approximately 3.38 times the Pauli paramagnetic limit (~6.51T). Angle-resolved photoemission spectroscopy (ARPES) measurements combined with theoretical calculations confirm the presence of split Fermi surfaces with Ising-type spin textures at the K and K' valleys of the confined Ga layer strongly hybridized with SiC. Moreover, by incorporating finite relaxation time induced by impurity scattering into an Ising-type superconductivity model, we reproduce the entire temperature-dependent u0Hc2,|| phase diagram. This work establishes a new strategy to realize unconventional pairing wavefunctions by combining quantum confinement and interfacial hybridization effects in superconducting thin films. It also opens new avenues for designing scalable superconducting quantum electronic and spintronic devices through interfacial engineering. △ Less

Submitted 6 September, 2025; originally announced September 2025.

Comments: 40 pages, 4 figures and 10 extended data figures, comments are welcome

Journal ref: Nature Mater. (2026)

Asymmetric stress engineering of dense dislocations in brittle superconductors for strong vortex pinning

Authors: Meng Han, Chiheng Dong, Chao Yao, Zhihao Zhang, Qinghua Zhang, Yue Gong, He Huang, Dongliang Gong, Dongliang Wang, Xianping Zhang, Fang Liu, Yuping Sun, Zengwei Zhu, Jianqi Li, Junyi Luo, Satoshi Awaji, Xiaolin Wang, Jianxin Xie, Hideo Hosono, Yanwei Ma

Abstract: Large lossless currents in high-temperature superconductors (HTS) critically rely on dense defects with suitable size and dimensionality to pin vortices, with dislocations being particularly effective due to their one-dimensional geometry to interact extensively with vortex lines. However, in non-metallic compounds such as HTS with rigid lattices, conventional deformation methods typically lead to… ▽ More Large lossless currents in high-temperature superconductors (HTS) critically rely on dense defects with suitable size and dimensionality to pin vortices, with dislocations being particularly effective due to their one-dimensional geometry to interact extensively with vortex lines. However, in non-metallic compounds such as HTS with rigid lattices, conventional deformation methods typically lead to catastrophic fracture rather than dislocation-mediated plasticity, making it a persistent challenge to introduce dislocations at high density. Here, we propose an asymmetric stress field strategy using extrusion to directly nucleate a high-density of dislocations in HTS by activating shear-driven lattice slip and twisting under superimposed hydrostatic compression. As demonstrated in iron-based superconductors (IBS), atomic displacements of nearly one angstrom trigger the formation of tilted dislocation lines with a density approaching that of metals. With further structural refinement, these dislocations serve as strong pinning centers that lead to a fivefold enhancement in the current-carrying capacity of IBS at 33 T, along with low anisotropy and a large irreversibility field. This work not only establishes a scalable route to engineer pinning landscapes in HTS, but also offers a generalizable framework for manipulating dislocation structures in rigid crystalline systems. △ Less

Submitted 25 August, 2025; originally announced August 2025.

Comments: 27 pages, 5 figures

Journal ref: Adv. Mater. (2025): e13265

Unified Description of Spin-Lattice Coupling and Thermodynamics in the Pyrochlore Heisenberg Antiferromagnet

Authors: Masaki Gen, Hidemaro Suwa, Shusaku Imajo, Chao Dong, Hiroaki Ueda, Makoto Tachibana, Akihiko Ikeda, Koichi Kindo, Yoshimitsu Kohama

Abstract: We study an extended model to describe the spin-lattice coupling, incorporating individual vibrations of bonds and atomic sites alongside distance-dependent exchange interactions. The proposed spin Hamiltonian can be effectively considered as an interpolation between two well-established minimum models, the bond-phonon model and the site-phonon model. The extended model, which treats bond phonons… ▽ More We study an extended model to describe the spin-lattice coupling, incorporating individual vibrations of bonds and atomic sites alongside distance-dependent exchange interactions. The proposed spin Hamiltonian can be effectively considered as an interpolation between two well-established minimum models, the bond-phonon model and the site-phonon model. The extended model, which treats bond phonons and site phonons on comparable footing, well reproduces successive field-induced phase transitions as well as the thermodynamic properties of a three-up-one-down state in the pyrochlore-lattice Heisenberg antiferromagnet, including negative thermal expansion, an enhanced magnetocaloric effect, and a sharp specific-heat peak. The present approach is broadly applicable to various spin models, providing a framework for identifying the primary phonon modes responsible for spin-lattice coupling and for understanding complex magnetic phase diagrams. △ Less

Submitted 7 March, 2026; v1 submitted 19 August, 2025; originally announced August 2025.

Comments: 7 pages, 4 figures, SM: 8 pages, 8 figures. To be published in Physical Review Letters

Generalized Symmetries From Fusion Actions

Authors: Chongying Dong, Siu-Hung Ng, Li Ren, Feng Xu

Abstract: Let $A$ be a condensable algebra in a modular tensor category $\mathcal{C}$. We define an action of the fusion category $\mathcal{C}_A$ of $A$-modules in $\mathcal{C}$ on the morphism space $\mbox{Hom}_{\mathcal{C}}(x,A)$ for any $x$ in $\mathcal{C}$, whose characters are generalized Frobenius-Schur indicators. This fusion action can be considered on $A$, and we prove a categorical generalization… ▽ More Let $A$ be a condensable algebra in a modular tensor category $\mathcal{C}$. We define an action of the fusion category $\mathcal{C}_A$ of $A$-modules in $\mathcal{C}$ on the morphism space $\mbox{Hom}_{\mathcal{C}}(x,A)$ for any $x$ in $\mathcal{C}$, whose characters are generalized Frobenius-Schur indicators. This fusion action can be considered on $A$, and we prove a categorical generalization of the Schur-Weyl duality for this action. For any fusion subcategory $\mathcal{B}$ of $\mathcal{C}_A$ containing all the local $A$-modules, we prove the invariant subobject $B=A^\mathcal{B}$ is a condensable subalgebra of $A$. The assignment of $\mathcal{B}$ to $A^\mathcal{B}$ defines a Galois correspondence between this kind of fusion subcategories of $\mathcal{C}_A$ and the condensable subalgebras of $A$. In the context of VOAs, we prove for any nice VOAs $U \subset A$, $U=A^{\mathcal{C}_A}$ where $\mathcal{C}=\mathcal{M}_U$ is the category of $U$-modules. In particular, if $U = A^G$ for some finite automorphism group $G$ of $A,$ the fusion action of $\mathcal{C}_A$ on $A$ is equivalent to the $G$-action on $A.$ △ Less

Submitted 22 January, 2026; v1 submitted 18 August, 2025; originally announced August 2025.

Comments: minor revision of the previous version; Prop. 3.10 and some references are added; some typos are corrected; Latex 44 pages

Kondo-coupled van der Waals antiferromagnet with high-mobility quasiparticles

Authors: Hai Zeng, Yang Zhang, Bingke Ji, Jiaqiang Cai, Shuo Zou, Zhuo Wang, Chao Dong, Kangjian Luo, Yang Yuan, Kai Wang, Jinglei Zhang, Chuanyin Xi, Junfeng Wang, Liang Li, Yaomin Dai, Jing Li, Yongkang Luo

Abstract: Two-dimensional van der Waals (vdW) materials exhibit high carrier mobility and tunability, making them suitable for low-power, high-performance electronic and spintronic applications. Incorporating narrow-band electronic correlation effects could further promote tunability, though mass renormalization may impact carrier mobility. It is therefore challenging to identify a vdW material with both hi… ▽ More Two-dimensional van der Waals (vdW) materials exhibit high carrier mobility and tunability, making them suitable for low-power, high-performance electronic and spintronic applications. Incorporating narrow-band electronic correlation effects could further promote tunability, though mass renormalization may impact carrier mobility. It is therefore challenging to identify a vdW material with both high mobility and strong correlation. Herein, by a combination of optical spectroscopy and high-field quantum-oscillation measurements, we observe significant effective-mass enhancement in CeTe$_3$ at low temperature, arising from not only the band-structure modulation by antiferromagnetic ordering but also the narrow-band correlation effect. Despite the mass enhancement, the quantum mobility surprisingly \textit{increases} and reaches $\sim$2403 cm$^2$/Vs, likely benefiting from topological protection. Remarkably, these unique properties are maintained in atomically thin nanoflakes with quantum mobility enhanced to $\sim$3158 cm$^2$/Vs. Thus, CeTe$_3$ emerges as a promising Kondo-coupled vdW antiferromagnetic metal with high-mobility quasiparticles, potentially unlocking new device concepts. △ Less

Submitted 25 November, 2025; v1 submitted 30 June, 2025; originally announced June 2025.

Comments: 23+8 pages, 4+8 figures, 1 table

Journal ref: Newton 2, 100320 (2026)

Triplon Bose-Einstein condensation and proximate magnetism in dimerized antiferromagnets

Authors: Z. Y. Zhao, F. Y. Li, C. Dong, R. Chen, M. Y. Cui, Z. W. Ouyang, J. F. Wang, Y. Kohama, Z. Z. He, Gang v. Chen

Abstract: Dimerized quantum magnets provide a useful arena for novel quantum states and phases transitions with the singlet-triplet type of triplon excitations. Here we study the triplon physics and the Bose-Einstein condensation in two isostructural dimerized antiferromagnets $A$Cu(SeO$_3$)$_2$ ($A$ = Hg, Cd). With the systematic measurements, we demonstrate a dimer singlet ground state in HgCu(SeO$_3$)… ▽ More Dimerized quantum magnets provide a useful arena for novel quantum states and phases transitions with the singlet-triplet type of triplon excitations. Here we study the triplon physics and the Bose-Einstein condensation in two isostructural dimerized antiferromagnets $A$Cu(SeO$_3$)$_2$ ($A$ = Hg, Cd). With the systematic measurements, we demonstrate a dimer singlet ground state in HgCu(SeO$_3$)$_2$ with a triplon gap $\sim$ 7.9 K and a triplon Bose-Einstein condensation with an antiferromagnetic order in CdCu(SeO$_3$)$_2$ below 4.4 K. We further adopt the bond-operator technique and show that the elemental replacement preserves the Hamiltonian and allows the study in a unified theoretical framework with tunable interdimer and intradimer interactions on the opposite sides of the quantum critical point. With the peculiar Cu$_2$O$_8$ dimer configuration and effective ferromagnetic interdimer interaction, $A$Cu(SeO$_3$)$_2$ is distinguished from other $S$ = 1/2 dimerized antiferromagnets. Our results represent a global understanding of the magnetic ground states as well as the magnetic transitions in the dimerized magnets of this unusual crystal structure. △ Less

Submitted 26 May, 2025; originally announced May 2025.

Comments: 7 pages, 4 figures, with supplementary materials

TBA-enabled spin-coating of a percolatively connected GO nanosieve for thru-hole epitaxy: tuning GO flake stacking and coverage to control GaN nucleation

Authors: Gunhoon Beak, Changwook Dong, Minah Choi, Jieun Yang, Joonwon Lim, Chinkyo Kim

Abstract: We report a spin-coating-based approach for forming a percolatively connected graphene oxide (GO) nanosieve on SiO$_2$-patterned sapphire substrates, where the addition of tetrabutylammonium (TBA) to the GO solution significantly improves the uniformity of flake coverage and modulates GaN nucleation behavior. Upon thermal annealing of GO, the resulting reduced graphene oxide (rGO) films exhibit sp… ▽ More We report a spin-coating-based approach for forming a percolatively connected graphene oxide (GO) nanosieve on SiO$_2$-patterned sapphire substrates, where the addition of tetrabutylammonium (TBA) to the GO solution significantly improves the uniformity of flake coverage and modulates GaN nucleation behavior. Upon thermal annealing of GO, the resulting reduced graphene oxide (rGO) films exhibit spatially varying coverage, leading to three distinct GaN nucleation outcomes: (i) ELOG-like nucleation on exposed substrate regions, (ii) thru-hole epitaxy (THE)-like nucleation through appropriately thin areas, and (iii) complete nucleation suppression on thickly stacked zones. On spin-coated GO films without TBA, all three behaviors coexist, and undesired ELOG- and no-nucleation modes persist due to uneven coverage. Importantly, these issues cannot be resolved by simply adjusting GO flake concentration, as concentration tuning alone fails to eliminate the formation of locally bare and overly thick regions. In contrast, the addition of TBA results in a more uniform, moderately stacked rGO morphology that suppresses both ELOG- and no-nucleation modes while expanding THE-like nucleation regions. This reshaped nucleation landscape confines GaN growth to areas with engineered percolative transport. The approach offers a scalable, lithography-free route for controlling GaN epitaxy using solution-processable 2D material masks. △ Less

Submitted 7 May, 2025; originally announced May 2025.

Two-dimensional Indium Oxide at the Epitaxial Graphene/SiC Interface: Synthesis, Structure, Properties, and Devices

Authors: Furkan Turker, Bohan Xu, Chengye Dong, Michael Labella III, Nadire Nayir, Natalya Sheremetyeva, Zachary J. Trdinich, Duanchen Zhang, Gokay Adabasi, Bita Pourbahari, Wesley E. Auker, Ke Wang, Mehmet Z. Baykara, Vincent Meunier, Nabil Bassim, Adri C. T. van Duin, Vincent H. Crespi, Joshua A. Robinson

Abstract: High-quality two-dimensional (2D) dielectrics are crucial for fabricating 2D/3D hybrid vertical electronic devices such as metal-oxide-semiconductor (MOS) based Schottky diodes and hot electron transistors, the production of which is constrained by the scarcity of bulk layered wide bandgap semiconductors. In this research, we present the synthesis of a new 2D dielectric, monolayer InO2, which diff… ▽ More High-quality two-dimensional (2D) dielectrics are crucial for fabricating 2D/3D hybrid vertical electronic devices such as metal-oxide-semiconductor (MOS) based Schottky diodes and hot electron transistors, the production of which is constrained by the scarcity of bulk layered wide bandgap semiconductors. In this research, we present the synthesis of a new 2D dielectric, monolayer InO2, which differs in stoichiometry from its bulk form, over a large area (>300 um2) by intercalating at the epitaxial graphene (EG)/SiC interface. By adjusting the lateral size of graphene through optical lithography prior to the intercalation, we tune the thickness of InO2 where predominantly (~85%) monolayer InO2 is formed. The preference for monolayer formation of InO2 is explained using ReaxFF reactive molecular dynamics and density functional theory (DFT) calculations. Additionally, the band gap of InO2 is calculated to be 4.1 eV, differing from its bulk form (2.7 eV). Furthermore, MOS-based Schottky diode measurements on InO2 intercalated EG/n-SiC demonstrate that the EG/n-SiC junction transforms from ohmic to a Schottky junction upon intercalation, with a barrier height of 0.87 eV and a rectification ratio of ~10^5. These findings introduce a new addition to the 2D dielectric family, showing significant potential for monolayer InO2 to be used as a barrier in vertical electronic devices. △ Less

Submitted 10 November, 2025; v1 submitted 12 April, 2025; originally announced April 2025.

Journal ref: Adv. Mater. 2025, e16133

Atomic-scale imaging of graphene nanoribbons on graphene after polymer-free substrate transfer

Authors: Amogh Kinikar, Feifei Xiang, Lucia Palomino Ruiz, Li-Syuan Lu, Chengye Dong, Yanwei Gu, Rimah Darawish, Eve Ammerman, Oliver Groening, Klaus Muellen, Roman Fasel, Joshua A. Robinson, Pascal Ruffieux, Bruno Schuler, Gabriela Borin Barin

Abstract: On-surface synthesis enables the fabrication of atomically precise graphene nanoribbons (GNRs) with properties defined by their shape and edge topology. While this bottom-up approach provides unmatched control over electronic and structural characteristics, integrating GNRs into functional electronic devices requires their transfer from noble metal growth surfaces to technologically relevant subst… ▽ More On-surface synthesis enables the fabrication of atomically precise graphene nanoribbons (GNRs) with properties defined by their shape and edge topology. While this bottom-up approach provides unmatched control over electronic and structural characteristics, integrating GNRs into functional electronic devices requires their transfer from noble metal growth surfaces to technologically relevant substrates. However, such transfers often induce structural modifications, potentially degrading or eliminating GNRs' desired functionality - a process that remains poorly understood. In this study, we employ low-temperature scanning tunneling microscopy and spectroscopy (STM/STS) to characterize 9-atom-wide armchair GNRs (9-AGNRs) following polymer-free wet-transfer onto epitaxial graphene (EG) and quasi-freestanding epitaxial graphene (QFEG) substrates. Our results reveal that armchair GNRs maintain their structural integrity post-transfer, while GNRs with extended or modified edge topologies exhibit significant structural changes, including partial disintegration. Additionally, STS measurements reveal differences in the Fermi level alignment between GNRs and the graphene substrates, a key factor in optimizing carrier injection efficiency in electronic transport devices. This study establishes a framework for detecting post-processing structural modifications in GNRs, which are often hidden in optical ensemble measurements. By addressing the challenges of substrate transfer and providing new insights into GNR-substrate interactions, these findings pave the way for the reliable integration of atomically precise GNRs into next-generation nanoelectronic and optoelectronic devices. △ Less

Submitted 4 April, 2025; originally announced April 2025.

Hydrogel-to-Aerogel Transitions in Polymer-Particle Hydrogels Expand the Wildfire Defense Window

Authors: Changxin Dong, Samya Sen, Zhennan Ru, Athena Kolli, Paxton S. Appel, Jonathan Fan, Eric A. Appel

Abstract: The 2025 Los Angeles wildfires caused widespread urban destruction and displacement, and severe economic losses, highlighting the urgent need for better fire retardants. Current fire suppression strategies rely heavily on water, chemical fire retardants, and water-enhancing gels, which use superabsorbent polymers to retain water and adhere to substrates, offering extended fire protection compared… ▽ More The 2025 Los Angeles wildfires caused widespread urban destruction and displacement, and severe economic losses, highlighting the urgent need for better fire retardants. Current fire suppression strategies rely heavily on water, chemical fire retardants, and water-enhancing gels, which use superabsorbent polymers to retain water and adhere to substrates, offering extended fire protection compared to water alone. However, their effectiveness is limited by evaporation and degradation under extreme heat and wind conditions. This study investigates the thermal properties, evaporation dynamics, and fire retardancy mechanisms of a novel polymer-particle (PP) hydrogel with aerogel-forming capabilities. The boiling-induced water vapor expansion and bubble nucleation drive the transformation of the hydrogel into a highly porous, foam-like fire-retardant coating upon rapid heat desiccation, enhancing thermal insulation. By evaluating the retardancy window across different evaporation stages under high heat and wind conditions, this study aims to determine the duration, effectiveness, and governing physical mechanisms of this unique retardant system. These findings provide a framework for designing the next generation of fire retardants with optimized thermal stability and extended protection for wildfire mitigation. △ Less

Submitted 27 May, 2025; v1 submitted 19 March, 2025; originally announced March 2025.

Comments: 30 pages, 4 figures, last page TOC image

Evolving transport properties of dynamic hydrogels enable self-tuning of short- and long-term cargo delivery

Authors: Samya Sen, Changxin Dong, Carolyn K. Jons, Wencke Reineking, Alakesh Alakesh, Noah Eckman, Ye Eun Song, Alexander N. Prossnitz, Eric A. Appel

Abstract: Hydrogels are crosslinked polymer networks with high water content, widely employed in biomedical applications such as drug delivery, tissue engineering, and regenerative medicine. Injectable, depot-forming hydrogels enable sustained release of therapeutic agents by modulating macromolecular diffusion through dynamic polymer networks. However, achieving reliable control over release kinetics remai… ▽ More Hydrogels are crosslinked polymer networks with high water content, widely employed in biomedical applications such as drug delivery, tissue engineering, and regenerative medicine. Injectable, depot-forming hydrogels enable sustained release of therapeutic agents by modulating macromolecular diffusion through dynamic polymer networks. However, achieving reliable control over release kinetics remains a challenge, as the injection process induces shear-mediated disruption of transient crosslinks, leading to an initial burst release that can cause local toxicity and compromise therapeutic efficacy. Here, we present a hydrogel formulation strategy designed to restore network structure post-injection through rapid reformation of dynamic crosslinks, enabling time-dependent regulation of diffusion properties. By tuning viscoelastic parameters, including stress relaxation time and network recovery rate, we reduced the extent of burst release without compromising sustained delivery. Using model protein cargo, we demonstrate in both $in~vitro$ and $in~vivo$ settings that hydrogels with faster crosslink reformation kinetics exhibit significantly lower early-phase release while maintaining long-term delivery comparable to unmodified formulations. These results establish a mechanistic framework for decoupling short- and long-term release behavior, offering a broadly applicable strategy for precise drug delivery in soft tissue environments. △ Less

Submitted 15 September, 2025; v1 submitted 19 March, 2025; originally announced March 2025.

Comments: Manuscript: 24 pages, 5 figures; SI: 7 pages, 3 figures

Robust Super-Moiré in Large Angle Single-Twist Bilayers

Authors: Yanxing Li, Chuqiao Shi, Fan Zhang, Xiaohui Liu, Yuan Xue, Viet-Anh Ha, Qiang Gao, Chengye Dong, Yu-chuan Lin, Luke N Holtzman, Nicolas Morales-Durán, Hyunsue Kim, Yi Jiang, Madisen Holbrook, James Hone, Katayun Barmak, Joshua Robinson, Xiaoqin Li, Feliciano Giustino, Eslam Khalaf, Yimo Han, Chih-Kang Shih

Abstract: Forming long wavelength moiré superlattices (MSL) at small-angle twist van der Waals (vdW) bilayers has been a key approach to creating moiré flat bands. The small-angle twist, however, leads to strong lattice reconstruction, causing domain walls and moiré disorders, which pose considerable challenges in engineering such platforms. At large twist angles, the rigid lattices render a more robust, bu… ▽ More Forming long wavelength moiré superlattices (MSL) at small-angle twist van der Waals (vdW) bilayers has been a key approach to creating moiré flat bands. The small-angle twist, however, leads to strong lattice reconstruction, causing domain walls and moiré disorders, which pose considerable challenges in engineering such platforms. At large twist angles, the rigid lattices render a more robust, but shorter wavelength MSL, making it difficult to engineer flat bands. Here, we depict a novel approach to tailoring robust super-moiré (SM) structures that combines the advantages of both small-twist and large-twist transition metal dichalcogenides (TMDs) bilayers using only a single twist angle near a commensurate angle. Structurally, we unveil the spontaneous formation of a periodic arrangement of three inequivalent commensurate moiré (CM) stacking, where the angle deviation from the commensurate angle can tune the periodicity. Electronically, we reveal a large set of van Hove singularities (VHSs) that indicate strong band hybridization, leading to flat bands near the valence band maximum. Our study paves the way for a new platform of robust SM bilayers with structural rigidity and controllable wavelength, extending the investigation of the interplay among band topology, quantum geometry, and moiré superconductivity to the large twist angle regime. △ Less

Submitted 24 February, 2025; v1 submitted 17 February, 2025; originally announced February 2025.

Berezinskii-Kosterlitz-Thouless region and magnetization plateaus in easy-axis triangular weak-dimer antiferromagnet K$_2$Co$_2$(SeO$_3$)$_3$

Authors: Ying Fu, Han Ge, Jian Chen, Jie Xiao, Yi Tan, Le Wang, Junfeng Wang, Chao Dong, Zhe Qu, Miao He, Chuanying Xi, Langsheng Ling, Bin Xi, Jia-Wei Mei

Abstract: We investigate the magnetic phase diagram of the bilayer triangular antiferromagnet K$_2$Co$_2$(SeO$_3$)$_3$, revealing a rich interplay among geometric frustration, bilayer coupling, and symmetry-driven phenomena. High-field magnetization measurements show fractional magnetization plateaus at 1/3, 1/2, 2/3, and 5/6 of the saturation magnetization. To elucidate the experimental magnetic phase diag… ▽ More We investigate the magnetic phase diagram of the bilayer triangular antiferromagnet K$_2$Co$_2$(SeO$_3$)$_3$, revealing a rich interplay among geometric frustration, bilayer coupling, and symmetry-driven phenomena. High-field magnetization measurements show fractional magnetization plateaus at 1/3, 1/2, 2/3, and 5/6 of the saturation magnetization. To elucidate the experimental magnetic phase diagram at low fields, we propose that K$_2$Co$_2$(SeO$_3$)$_3$ can be described as an easy-axis triangular weak-dimer antiferromagnet. We emphasize the critical role of the emergent $U(1) \otimes S_3$ symmetry, where $S_3 = \mathbb{Z}_3 \otimes \mathbb{Z}_2^d$, in determining the magnetic phases at low fields. The remarkable agreement between the experimental and theoretical phase diagrams suggests that the phase transitions are governed by this symmetry. Notably, our combined experimental and theoretical results identify a Berezinskii-Kosterlitz-Thouless (BKT) phase region at finite fields. These findings provide new insights into the phase structure of frustrated magnets and establish K$_2$Co$_2$(SeO$_3$)$_3$ as a compelling platform for exploring unconventional quantum phenomena in $U(1) \otimes S_3$ systems. △ Less

Submitted 23 January, 2025; v1 submitted 16 January, 2025; originally announced January 2025.

Comments: 6 pages, 4 figures. Supplementary material is included in source file. Typos fixed

Charge to spin conversion in atomically thin bismuth

Authors: Wilson J. Yánez-Parreño, Alexander Vera, Sandra Santhosh, Chengye Dong, Jimmy C. Kotsakidis, Yongxi Ou, Saurav Islam, Adam L. Friedman, Maxwell Wetherington, Joshua Robinson, Nitin Samarth

Abstract: We report charge to spin conversion in a hybrid heterostructure comprised of atomically thin bismuth (Bi) confined between a silicon carbide (SiC) substrate and epitaxial graphene (EG). We confirm composition, dimensionality, and a 96.5 \% intercalation coverage using X-ray photolectron spectroscopy, scanning transmission microscopy, low energy electron diffraction, and Raman spectroscopy. Electri… ▽ More We report charge to spin conversion in a hybrid heterostructure comprised of atomically thin bismuth (Bi) confined between a silicon carbide (SiC) substrate and epitaxial graphene (EG). We confirm composition, dimensionality, and a 96.5 \% intercalation coverage using X-ray photolectron spectroscopy, scanning transmission microscopy, low energy electron diffraction, and Raman spectroscopy. Electrical transport measurements show signs of weak antilocalization in the heterostructure, consistent with spin-orbit coupling in this hybrid heterostructure. Spin torque ferromagnetic resonance measurements in permalloy/EG/2D-Bi heterostructures probe charge-to-spin conversion and revealing that an in plane polarization of the spin current, perpendicular to the charge current. The ratio of the in-plane to out-of-plane torque is 3.75 times higher than in hydrogenated graphene control samples. △ Less

Submitted 13 January, 2025; originally announced January 2025.

Journal ref: Phys. Rev. Applied 23, L061001 (2025)

Ultrafast Coulomb blockade in an atomic-scale quantum dot

Authors: Jonas Allerbeck, Laric Bobzien, Nils Krane, S. Eve Ammerman, Daniel E. Cintron Figueroa, Chengye Dong, Joshua A. Robinson, Bruno Schuler

Abstract: Controlling electron dynamics at optical clock rates is a fundamental challenge in lightwave-driven nanoelectronics. Here, we demonstrate ultrafast charge-state manipulation of individual selenium vacancies in monolayer and bilayer tungsten diselenide (WSe$_2$) using picosecond terahertz (THz) source pulses, focused onto the picocavity of a scanning tunneling microscope (STM). Using THz pump--THz… ▽ More Controlling electron dynamics at optical clock rates is a fundamental challenge in lightwave-driven nanoelectronics. Here, we demonstrate ultrafast charge-state manipulation of individual selenium vacancies in monolayer and bilayer tungsten diselenide (WSe$_2$) using picosecond terahertz (THz) source pulses, focused onto the picocavity of a scanning tunneling microscope (STM). Using THz pump--THz probe time-domain sampling of the defect charge population, we capture atomic-scale snapshots of the transient Coulomb blockade, a signature of charge transport via quantized defect states. We identify back tunneling of localized charges to the tip electrode as a key challenge for lightwave-driven STM when probing electronic states with charge-state lifetimes exceeding the pulse duration. However, we show that back tunneling can be mitigated by the Franck-Condon blockade, which limits accessible vibronic transitions and promotes unidirectional charge transport. Our rate equation model accurately reproduces the time-dependent tunneling process across the different coupling regimes. This work builds on recent progress in imaging coherent lattice and quasiparticle dynamics with lightwave-driven STM and opens new avenues for exploring ultrafast charge dynamics in low-dimensional materials, advancing the development of lightwave-driven nanoscale electronics. △ Less

Submitted 18 December, 2024; originally announced December 2024.

Giant and Tunable Bosonic Quantum Interference Induced by Two-Dimensional Metals

Authors: Kunyan Zhang, Rinu Abraham Maniyara, Yuanxi Wang, Arpit Jain, Maxwell T. Wetherington, Thuc T. Mai, Chengye Dong, Timothy Bowen, Ke Wang, Slava V. Rotkin, Angela R. Hight Walker, Vincent H. Crespi, Joshua Robinson, Shengxi Huang

Abstract: Harnessing quantum interference among bosons provides significant opportunities as bosons often carry longer coherence time than fermions. As an example of quantum interference, Fano resonance involving phonons or photons describes the coupling between discrete and continuous states, signified by an asymmetric spectral lineshape. Utilizing photon-based Fano resonance, molecule sensing with ultra-h… ▽ More Harnessing quantum interference among bosons provides significant opportunities as bosons often carry longer coherence time than fermions. As an example of quantum interference, Fano resonance involving phonons or photons describes the coupling between discrete and continuous states, signified by an asymmetric spectral lineshape. Utilizing photon-based Fano resonance, molecule sensing with ultra-high sensitivity and ultrafast optical switching has been realized. However, phonon-based Fano resonance, which would expand the application space to a vaster regime, has been less exploited because of the weak coupling between discrete phonons with continuous states such as electronic continuum. In this work, we report the discovery of giant phonon-based Fano resonance in a graphene/2D Ag/SiC heterostructure. The Fano asymmetry, being proportional to the coupling strength, exceeds prior reports by two orders of magnitude. This Fano asymmetry arises from simultaneous frequency and lifetime matching between discrete and continuous phonons of SiC. The introduction of 2D Ag layers restructures SiC at the interface and facilitates resonant scattering to further enhance the Fano asymmetry, which is not achievable with conventional Ag thin films. With these unique properties, we demonstrated that the phonon-based Fano resonance can be used for ultrasensitive molecule detection at the single-molecule level. Our work highlights strong Fano resonance in the phononic system, opening avenues for engineering quantum interference based on bosons. Further, our findings provide opportunities for advancing phonon-related applications, including biochemical sensing, quantum transduction, and superconductor-based quantum computing. △ Less

Submitted 30 September, 2024; originally announced October 2024.

Decoding the hidden dynamics of super-Arrhenius hydrogen diffusion in multi-principal element alloys via machine learning

Authors: Fei Shuang, Yucheng Ji, Zixiong Wei, Chaofang Dong, Wei Gao, Luca Laurenti, Poulumi Dey

Abstract: Understanding atomic hydrogen (H) diffusion in multi-principal element alloys (MPEAs) is essential for advancing clean energy technologies such as H transport, storage, and nuclear fusion applications. However, the vast compositional space and the intricate chemical environments inherent in MPEAs pose significant obstacles. In this work, we address this challenge by developing a multifaceted machi… ▽ More Understanding atomic hydrogen (H) diffusion in multi-principal element alloys (MPEAs) is essential for advancing clean energy technologies such as H transport, storage, and nuclear fusion applications. However, the vast compositional space and the intricate chemical environments inherent in MPEAs pose significant obstacles. In this work, we address this challenge by developing a multifaceted machine learning framework that integrates machine-learning force field, neural network-driven kinetic Monte Carlo, and machine-learning symbolic regression. This framework allows for accurate investigation of H diffusion across the entire compositional space of body-centered cubic (BCC) refractory MoNbTaW alloys, achieving density functional theory accuracy. For the first time, we discover that H diffusion in MPEAs exhibits super-Arrhenius behavior, described by the Vogel-Fulcher-Tammann model, where the Vogel temperature correlates with the 5th percentile of H solution energy spectrum. We also derive robust analytical expressions that can be used to predict H diffusivity in general BCC MPEAs. Our findings further elucidate that chemical short-range order (SRO) generally does not impact H diffusion, except it enhances diffusion when "H-favoring" elements (notably Nb and Ta) are present in low concentrations. These findings not only enhance our understanding of H diffusion dynamics in general MPEAs but also guide the development of advanced MPEAs in H-related applications by manipulating element type, composition and SRO. △ Less

Submitted 22 September, 2024; originally announced September 2024.

Optical pumping through the Liouvillian skin effect

Authors: De-Huan Cai, Wei Yi, Chen-Xiao Dong

Abstract: The Liouvillian skin effect describes the boundary affinity of Liouvillian eignemodes that originates from the intrinsic non-Hermiticity of the Liouvillian superoperators. Dynamically, it manifests as directional flow in the transient dynamics, and the accumulation of population near open boundaries at long times. Intriguingly, similar dynamic phenomena exist in the well-known process of optical p… ▽ More The Liouvillian skin effect describes the boundary affinity of Liouvillian eignemodes that originates from the intrinsic non-Hermiticity of the Liouvillian superoperators. Dynamically, it manifests as directional flow in the transient dynamics, and the accumulation of population near open boundaries at long times. Intriguingly, similar dynamic phenomena exist in the well-known process of optical pumping, where the system is driven into a desired state (or a dark-state subspace) through the interplay of dissipation and optical drive. In this work, we show that typical optical pumping processes can indeed be understood in terms of the Liouvillian skin effect. By studying the Liouvillian spectra under different boundary conditions, we reveal that the Liouvillian spectra of the driven-dissipative pumping process sensitively depend on the boundary conditions in the state space, a signature that lies at the origin of the Liouvillian skin effect. Such a connection provides insights and practical means for designing efficient optical-pumping schemes through engineering Liouvillian gaps under the open-boundary condition. Based on these understandings, we show that the efficiency of a typical side-band cooling scheme for trapped ions can be dramatically enhanced by introducing counterintuitive dissipative channels. Our results provide a useful perspective for optical pumping, with interesting implications for state preparation and cooling. △ Less

Submitted 8 April, 2025; v1 submitted 16 July, 2024; originally announced July 2024.

Journal ref: Phys.Rev.B 111, L060301 (2025)

Layer-Dependent Charge State Lifetime of Single Se Vacancies in WSe$_2$

Authors: Laric Bobzien, Jonas Allerbeck, Nils Krane, Andres Ortega-Guerrero, Zihao Wang, Daniel E. Cintron Figueroa, Chengye Dong, Carlo A. Pignedoli, Joshua A. Robinson, Bruno Schuler

Abstract: Defect engineering in two-dimensional semiconductors has been exploited to tune the optoelectronic properties and introduce new quantum states in the band gap. Chalcogen vacancies in transition metal dichalcogenides in particular have been found to strongly impact charge carrier concentration and mobility in 2D transistors as well as feature sub-gap emission and single-photon response. In this let… ▽ More Defect engineering in two-dimensional semiconductors has been exploited to tune the optoelectronic properties and introduce new quantum states in the band gap. Chalcogen vacancies in transition metal dichalcogenides in particular have been found to strongly impact charge carrier concentration and mobility in 2D transistors as well as feature sub-gap emission and single-photon response. In this letter, we investigate the layer-dependent charge state lifetime of Se vacancies in WSe$_2$. In one monolayer WSe$_2$, we observe ultrafast charge transfer from the lowest unoccupied orbital of the top Se vacancy to the graphene substrate within (1.0 $\pm$ 0.2) ps measured via the current saturation in scanning tunneling approach curves. For Se vacancies decoupled by TMD multilayers, we find a sub-exponential increase of the charge lifetime from (62 $\pm$ 14) ps in bilayer to few nanoseconds in four-layer WSe$_2$, alongside a reduction of the defect state binding energy. Additionally, we attribute the continuous suppression and energy shift of the dI/dV in-gap defect state resonances at very close tip--sample distances to a current saturation effect. Our results provide a key measure of the layer-dependent charge transfer rate of chalcogen vacancies in TMDs. △ Less

Submitted 5 July, 2024; originally announced July 2024.

Experimental signature of layer skyrmions and implications for band topology in twisted WSe2 bilayers

Authors: Fan Zhang, Nicolás Morales-Durán, Yanxing Li, Wang Yao, Jung-Jung Su, Yu-Chuan Lin, Chengye Dong, Xiaohui Liu, Fu-Xiang Rikudo Chen, Hyunsue Kim, Kenji Watanabe, Takashi Taniguchi, Xiaoqin Li, Joshua A. Robinson, Allan H. Macdonald, Chih-Kang Shih

Abstract: Transition metal dichalcogenide (TMD) twisted homobilayers have been established as an ideal platform for studying strong correlation phenomena, as exemplified by the recent discovery of fractional Chern insulator (FCI) states in twisted MoTe2 and Chern insulators (CI) and unconventional superconductivity in twisted WSe2 (tWSe2). In these systems, nontrivial topology in the strongly layer-hybridiz… ▽ More Transition metal dichalcogenide (TMD) twisted homobilayers have been established as an ideal platform for studying strong correlation phenomena, as exemplified by the recent discovery of fractional Chern insulator (FCI) states in twisted MoTe2 and Chern insulators (CI) and unconventional superconductivity in twisted WSe2 (tWSe2). In these systems, nontrivial topology in the strongly layer-hybridized regime can arise from a spatial patterning of interlayer tunneling amplitudes and layer-dependent potentials that yields a lattice of layer skyrmions. Here we report on experimental signatures of skyrmion textures in the layer degree of freedom of Rhombohedral-stacked (R-stacked) tWSe2 homobilayers. This observation is based on scanning tunneling spectroscopy that separately resolves the Gamma-valley and K-valley moiré electronic states. We show that Gamma-valley states are subjected to a moiré potential with an amplitude of ~ 120 meV. At ~150 meV above the Gamma-valley, the K-valley states are subjected to a weaker moiré potential of ~30 meV. Most significantly, we reveal opposite layer polarizations of the K-valley at the MX and XM sites within the moiré unit cell, confirming the theoretically predicted layer skyrmion texture. The dI/dV mappings allow the parameters that enter the continuum model of moiré bands in twisted TMD bilayers to be determined experimentally, further establishing a direct correlation between the shape of the LDOS profile in real space and the topology of topmost moiré band. △ Less

Submitted 4 February, 2025; v1 submitted 28 June, 2024; originally announced June 2024.

High-field magnetoelectric coupling and successive magnetic transitions in Mn-doped polar antiferromagnet Ni3TeO6

Authors: J. H. Zhang, L. Lin, C. Dong, Y. T. Chang, J. F. Wang, C. L. Lu, P. Z. Chen, W. J. Zhai, G. Z. Zhou, L. Huang, Y. S. Tang, S. H. Zheng, M. F. Liu, X. H. Zhou, Z. B. Yan, J. -M. Liu

Abstract: Among the 3d transition metal ions doped polar Ni3TeO6, Mn-doped Ni3TeO6 has stimulated great interest due to its high magnetic ordering temperature and complex magnetic phases, but the mechanism of magnetoelectric (ME) coupling is far from understood. Herein we report our systematic investigation of the chemical control of magnetism, metamagnetic transition, and ME properties of Ni3-xMnxTeO6 sing… ▽ More Among the 3d transition metal ions doped polar Ni3TeO6, Mn-doped Ni3TeO6 has stimulated great interest due to its high magnetic ordering temperature and complex magnetic phases, but the mechanism of magnetoelectric (ME) coupling is far from understood. Herein we report our systematic investigation of the chemical control of magnetism, metamagnetic transition, and ME properties of Ni3-xMnxTeO6 single crystals in high magnetic field (H) up to 52 T. We present a previously unreported weak ferromagnetic behavior appeared in the ab plane below 9.5 K in addition to the incommensurate helical and commensurate collinear antiferromagnetic states. In the low-field region, a spin-flop type metamagnetic transition without any hysteresis occurs at Hc1 for H // c, while another metamagnetic transition accompanied with a change in electric polarization is observed at Hc2 in the high-field region both for H // c and H // ab above 30 K, which can be attributed to the sudden rotation of magnetic moments at Ni2 sites. The ME measurements reveal that a first-order ME effect is observed in the low-T and low-H regions, while a second-order ME coupling term appears above 30 K in the magnetic field range of Hc1 < H < Hc2 for H // c and H < Hc2 for H // ab, both becoming significant with increasing temperature. Eventually, they are dominated by the second-order ME effect near the antiferromagnetic transition temperature. The present work demonstrates that Ni3-xMnxTeO6 is an exotic magnetoelectric material compared with Ni3TeO6 and its derivatives, thereby providing insights to better understand the magnetism and ME coupling in Ni3TeO6 and its derivatives. △ Less

Submitted 29 May, 2024; v1 submitted 24 May, 2024; originally announced May 2024.

Comments: 30 pages with 8 figures

Journal ref: Phys. Rev. B 109, 184112 (2024)

Water-enhancing gels exhibiting heat-activated formation of silica aerogels for protection of critical infrastructure during catastrophic wildfire

Authors: Changxin Dong, Andrea I. d'Aquino, Samya Sen, Ian A. Hall, Anthony C. Yu, Jesse D. Acosta, Eric A. Appel

Abstract: A promising strategy to address the pressing challenges with wildfire, particularly in the wildland-urban interface (WUI), involves developing new approaches for preventing and controlling wildfire within wildlands. Among sprayable fire-retardant materials, water-enhancing gels have emerged as exceptionally effective for protecting civil infrastructure. They possess favorable wetting and viscoelas… ▽ More A promising strategy to address the pressing challenges with wildfire, particularly in the wildland-urban interface (WUI), involves developing new approaches for preventing and controlling wildfire within wildlands. Among sprayable fire-retardant materials, water-enhancing gels have emerged as exceptionally effective for protecting civil infrastructure. They possess favorable wetting and viscoelastic properties that reduce the likelihood of ignition, maintaining strong adherence to a wide array of surfaces after application. Although current water-enhancing hydrogels effectively maintain surface wetness by creating a barricade, they rapidly desiccate and lose efficacy under high heat and wind typical of wildfire conditions. To address this limitation, we developed unique biomimetic hydrogel materials from sustainable cellulosic polymers crosslinked by colloidal silica particles that exhibit ideal viscoelastic properties and facile manufacturing. Under heat activation, the hydrogel transitions into a highly porous and thermally insulative silica aerogel coating in situ, providing a robust protective layer against ignition of substrates, even when the hydrogel fire suppressant becomes completely desiccated. By confirming the mechanical properties, substrate adherence, and enhanced substrate protection against fire, these heat-activatable biomimetic hydrogels emerge as promising candidates for next-generation water-enhancing fire suppressants. These advancements have the potential to dramatically improve our ability to protect homes and critical infrastructure during wildfire. △ Less

Submitted 23 May, 2024; v1 submitted 12 May, 2024; originally announced May 2024.

Comments: 21 pages, 4 figures

Thermodynamic origin of the phonon Hall effect in a honeycomb antiferromagnet

Authors: Qingkai Meng, Xiaokang Li, Jie Liu, Lingxiao Zhao, Chao Dong, Zengwei Zhu, Liang Li, Kamran Behnia

Abstract: The underlying mechanism of the thermal Hall effect (THE) generated by phonons in a variety of insulators is yet to be identified. Here, we report on a sizeable thermal Hall conductivity in NiPS$_3$, a van der Waals stack of honeycomb layers with a zigzag antiferromagnetic order below $T_N$ = 155 K. The longitudinal ($κ_{aa}$) and the transverse ($κ_{ab}$) thermal conductivities peak at the same t… ▽ More The underlying mechanism of the thermal Hall effect (THE) generated by phonons in a variety of insulators is yet to be identified. Here, we report on a sizeable thermal Hall conductivity in NiPS$_3$, a van der Waals stack of honeycomb layers with a zigzag antiferromagnetic order below $T_N$ = 155 K. The longitudinal ($κ_{aa}$) and the transverse ($κ_{ab}$) thermal conductivities peak at the same temperature and the thermal Hall angle, at this peak, respects a previously identified bound. The amplitude of $κ_{ab}$ is extremely sensitive to the amplitude of magnetization along the $b$-axis, in contrast to the phonon mean free path, which is not at all. We show that the magnon and acoustic phonon bands cross each other along the $b^\ast$ orientation in the momentum space. The relevance of a thermodynamic property, combined with the irrelevance of the mean free path, points to an intrinsic origin. △ Less

Submitted 1 October, 2024; v1 submitted 20 March, 2024; originally announced March 2024.

Comments: 7 pages, 4 figures, Supplemental Materials included

Corrosion-resistant aluminum alloy design through machine learning combined with high-throughput calculations

Authors: Yucheng Ji, Xiaoqian Fu, Feng Ding, Yongtao Xu, Yang He, Min Ao, Fulai Xiao, Dihao Chen, Poulumi Dey, Kui Xiao, Jingli Ren, Xiaogang Li, Chaofang Dong

Abstract: Efficiently designing lightweight alloys with combined high corrosion resistance and mechanical properties remains an enduring topic in materials engineering. To this end, machine learning (ML) coupled ab-initio calculations is proposed within this study. Due to the inadequate accuracy of conventional stress-strain ML models caused by corrosion factors, a novel reinforcement self-learning ML algor… ▽ More Efficiently designing lightweight alloys with combined high corrosion resistance and mechanical properties remains an enduring topic in materials engineering. To this end, machine learning (ML) coupled ab-initio calculations is proposed within this study. Due to the inadequate accuracy of conventional stress-strain ML models caused by corrosion factors, a novel reinforcement self-learning ML algorithm (accuracy R2 >0.92) is developed. Then, a strategy that integrates ML models, calculated energetics and mechanical moduli is implemented to optimize the Al alloys. Next, this Computation Designed Corrosion-Resistant Al alloy is fabricated that verified the simulation. The performance (elongation reaches ~30%) is attributed to the H-captured Al-Sc-Cu phases (-1.44 eV H-1) and Cu-modified η/η' precipitation inside the grain boundaries (GBs). The developed Al-Mg-Zn-Cu interatomic potential (energy accuracy 6.50 meV atom-1) proves the cracking resistance of the GB region enhanced by Cu-modification. Conceptually, our strategy is of practical importance for designing new alloys exhibiting corrosion resistance and mechanical properties. △ Less

Submitted 26 December, 2023; originally announced December 2023.

Biomimetic non-ergodic aging by dynamic-to-covalent transitions in physical hydrogels

Authors: Samya Sen, Anthony C. Yu, Changxin Dong, Andrea I. D'Aquino, Eric A. Appel

Abstract: Hydrogels are soft materials engineered to suit a multitude of applications that exploit their tunable mechanochemical properties. Dynamic hydrogels employing noncovalent, physically crosslinked networks dominated by either enthalpic or entropic interactions enable unique rheological and stimuli-responsive characteristics. In contrast to enthalpy-driven interactions that soften with increasing tem… ▽ More Hydrogels are soft materials engineered to suit a multitude of applications that exploit their tunable mechanochemical properties. Dynamic hydrogels employing noncovalent, physically crosslinked networks dominated by either enthalpic or entropic interactions enable unique rheological and stimuli-responsive characteristics. In contrast to enthalpy-driven interactions that soften with increasing temperature, entropic interactions result in largely temperature-independent mechanical properties. By engineering interfacial polymer-particle interactions, we can induce a dynamic-to-covalent transition in entropic hydrogels that leads to biomimetic non-ergodic aging in the microstructure without altering the network mesh size. This transition is tuned by varying temperature and formulation conditions such as $p$H, which allows for multivalent tunability in properties. These hydrogels can thus be designed to exhibit either temperature-independent metastable dynamic crosslinking or time-dependent stiffening based on formulation and storage conditions, all while maintaining strucutural features critical for controlling mass transport, akin to many biological tissues. Such robust materials with versatile and adaptable properties can be utilized in applications such as wildfire suppression, surgical adhesives, and depot-forming injectable drug delivery systems. △ Less

Submitted 25 November, 2023; originally announced November 2023.

Comments: 23 pages, 12 figures

Atomistic Control in Molecular Beam Epitaxy Growth of Intrinsic Magnetic Topological Insulator MnBi2Te4

Authors: Hyunsue Kim, Mengke Liu, Lisa Frammolino, Yanxing Li, Fan Zhang, Woojoo Lee, Chengye Dong, Yi-Fan Zhao, Guan-Yu Chen, Pin-Jui Hsu, Cui-Zu Chang, Joshua Robinson, Jiaqiang Yan, Xiaoqin Li, Allan H. MacDonald, Chih-Kang Shih

Abstract: Intrinsic magnetic topological insulators have emerged as a promising platform to study the interplay between topological surface states and ferromagnetism. This unique interplay can give rise to a variety of exotic quantum phenomena, including the quantum anomalous Hall effect and axion insulating states. Here, utilizing molecular beam epitaxy (MBE), we present a comprehensive study of the growth… ▽ More Intrinsic magnetic topological insulators have emerged as a promising platform to study the interplay between topological surface states and ferromagnetism. This unique interplay can give rise to a variety of exotic quantum phenomena, including the quantum anomalous Hall effect and axion insulating states. Here, utilizing molecular beam epitaxy (MBE), we present a comprehensive study of the growth of high-quality MnBi2Te4 thin films on Si (111), epitaxial graphene, and highly ordered pyrolytic graphite substrates. By combining a suite of in-situ characterization techniques, we obtain critical insights into the atomic-level control of MnBi2Te4 epitaxial growth. First, we extract the free energy landscape for the epitaxial relationship as a function of the in-plane angular distribution. Then, by employing an optimized layer-by-layer growth, we determine the chemical potential and Dirac point of the thin film at different thicknesses. Overall, these results establish a foundation for understanding the growth dynamics of MnBi2Te4 and pave the way for the future applications of MBE in emerging topological quantum materials. △ Less

Submitted 11 September, 2023; originally announced September 2023.

Comments: 20 pages, 4 figures

Orientation disparity in GaN/graphene/$m$-sapphire: control-based re-examination of thru-hole epitaxy

Authors: Su Young An, Hyunkyu Lee, Gunhoon Beak, Hyeonoh Jo, Jae Hun Kim, Jongwoo Ha, Jieun Yang, Changwook Dong, Jaewu Choi, Joonwon Lim, Chinkyo Kim

Abstract: The crystallographic orientation of films grown on 2D-masked substrates is often used to infer the pathway among remote, van der Waals, and thru-hole (pinhole-seeded) epitaxy. However, attribution of a specific growth mechanism based on orientation can be ambiguous unless mask continuity and substrate pre-treatment are evaluated within a single process window. We compare GaN grown under identical… ▽ More The crystallographic orientation of films grown on 2D-masked substrates is often used to infer the pathway among remote, van der Waals, and thru-hole (pinhole-seeded) epitaxy. However, attribution of a specific growth mechanism based on orientation can be ambiguous unless mask continuity and substrate pre-treatment are evaluated within a single process window. We compare GaN grown under identical conditions on four m-plane sapphire templates: (i) bare, (ii) "graphene-grown" (high-temperature Ar/H2 with CH4 on), (iii) "anneal-only" (high-temperature Ar/H2 with CH4 off), and (iv) graphene oxide spin-coated and reduced on pristine sapphire. GaN selects (103) on graphene-grown and anneal-only m-plane sapphire, selects (100) on bare m-plane sapphire, and is predominantly (100) with a minority (103) on graphene oxide spin-coated and reduced/pristine m-plane sapphire. High-resolution TEM shows that, on partly graphene-covered samples, nucleation occurs on exposed sapphire (thru-hole), not on graphene, providing mechanism evidence independent of orientation. Within this window, the substrate surface state set by high-temperature Ar/H2 pre-treatment (rather than mask continuity) primarily governs orientation, while open-area effects can play a secondary role. Thus, preferred orientation alone may not determine the growth mechanism; mask continuity and substrate pre-treatment must be explicitly controlled when using orientation as evidence for mechanism assignment. △ Less

Submitted 20 December, 2025; v1 submitted 30 August, 2023; originally announced August 2023.

Comments: 15 pages, 5 figures

Determining Quasi-Equilibrium Electron and Hole Distributions of Plasmonic Photocatalysts using Photomodulated X-ray Absorption Spectroscopy

Authors: Levi D. Palmer, Wonseok Lee, Chung Li Dong, Ru-Shi Liu, Nianqiang Wu, Scott K. Cushing

Abstract: Most photocatalytic and photovoltaic devices operate under broadband, constant illumination. Electron and hole dynamics in these devices, however, are usually measured using ultrafast pulsed lasers in a narrow wavelength range. In this work, we prove that steady-state, photomodulated X-ray spectra from a non-time-resolved synchrotron beamline can be used to estimate electron and hole distributions… ▽ More Most photocatalytic and photovoltaic devices operate under broadband, constant illumination. Electron and hole dynamics in these devices, however, are usually measured using ultrafast pulsed lasers in a narrow wavelength range. In this work, we prove that steady-state, photomodulated X-ray spectra from a non-time-resolved synchrotron beamline can be used to estimate electron and hole distributions. A set of plasmonic metal core-shell nanoparticles is designed to systematically isolate photothermal, hot electron, and thermalized electron-hole pairs in a TiO2 shell. Steady-state changes in the Ti L2,3 edge are measured with and without continuous-wave illumination of the nanoparticle's localized surface plasmon resonance. Ab initio excited-state X-ray theory developed for transient X-ray measurements is then applied to model the experimental spectra in an attempt to extract the resultant steady-state carrier distributions. The results suggest that, within error, the quasi-equilibrium carrier distribution can be determined even from relatively noisy data with mixed excited-state phenomena. △ Less

Submitted 24 January, 2024; v1 submitted 30 August, 2023; originally announced August 2023.

Comments: 41 pages, 18 figures

Journal ref: ACS Nano 2024, 18, 9344-9353

Charge State-Dependent Symmetry Breaking of Atomic Defects in Transition Metal Dichalcogenides

Authors: Feifei Xiang, Lysander Huberich, Preston A. Vargas, Riccardo Torsi, Jonas Allerbeck, Anne Marie Z. Tan, Chengye Dong, Pascal Ruffieux, Roman Fasel, Oliver Gröning, Yu-Chuan Lin, Richard G. Hennig, Joshua A. Robinson, Bruno Schuler

Abstract: The functionality of atomic quantum emitters is intrinsically linked to their host lattice coordination. Structural distortions that spontaneously break the lattice symmetry strongly impact their optical emission properties and spin-photon interface. Here we report on the direct imaging of charge state-dependent symmetry breaking of two prototypical atomic quantum emitters in mono- and bilayer MoS… ▽ More The functionality of atomic quantum emitters is intrinsically linked to their host lattice coordination. Structural distortions that spontaneously break the lattice symmetry strongly impact their optical emission properties and spin-photon interface. Here we report on the direct imaging of charge state-dependent symmetry breaking of two prototypical atomic quantum emitters in mono- and bilayer MoS$_2$ by scanning tunneling microscopy (STM) and non-contact atomic force microscopy (nc-AFM). By substrate chemical gating different charge states of sulfur vacancies (Vac$_\text{S}$) and substitutional rhenium dopants (Re$_\text{Mo}$) can be stabilized. Vac$_\text{S}^{-1}$ as well as Re$_\text{Mo}^{0}$ and Re$_\text{Mo}^{-1}$ exhibit local lattice distortions and symmetry-broken defect orbitals attributed to a Jahn-Teller effect (JTE) and pseudo-JTE, respectively. By mapping the electronic and geometric structure of single point defects, we disentangle the effects of spatial averaging, charge multistability, configurational dynamics, and external perturbations that often mask the presence of local symmetry breaking. △ Less

Submitted 4 August, 2023; originally announced August 2023.

Elucidating the Mechanism of Large Phosphate Molecule Intercalation Through Graphene Heterointerfaces

Authors: Jiayun Liang, Ke Ma, Xiao Zhao, Guanyu Lu, Jake V. Riffle, Carmen Andrei, Chengye Dong, Turker Furkan, Siavash Rajabpour, Rajiv Ramanujam Prabhakar, Joshua A. Robinson, Magdaleno R. Vasquez Jr., Quang Thang Trinh, Joel W. Ager, Miquel Salmeron, Shaul Aloni, Joshua D. Caldwell, Shawna M. Hollen, Hans A. Bechtel, Nabil Bassim, Matthew P. Sherburne, Zakaria Y. Al Balushi

Abstract: Intercalation is a process of inserting chemical species into the heterointerfaces of two-dimensional (2D) layered materials. While much research has focused on intercalating metals and small gas molecules into graphene, the intercalation of larger molecules through the basal plane of graphene remains highly unexplored. In this work, we present a new mechanism for intercalating large molecules thr… ▽ More Intercalation is a process of inserting chemical species into the heterointerfaces of two-dimensional (2D) layered materials. While much research has focused on intercalating metals and small gas molecules into graphene, the intercalation of larger molecules through the basal plane of graphene remains highly unexplored. In this work, we present a new mechanism for intercalating large molecules through monolayer graphene to form confined oxide materials at the graphene-substrate heterointerface. We investigate the intercalation of phosphorus pentoxide (P2O5) molecules directly from the vapor phase and confirm the formation of confined P2O5 at the graphene heterointerface using various techniques. Density functional theory (DFT) corroborate the experimental results and reveal the intercalation mechanism, whereby P2O5 dissociates into small fragments catalyzed by defects in the graphene that then permeates through lattice defects and reacts at the heterointerface to form P2O5. This process can also be used to form new confined metal phosphates (e.g., 2D InPO4). While the focus of this study is on P2O5 intercalation, the possibility of intercalation from pre-dissociated molecules catalyzed by defects in graphene may exist for other types of molecules as well. This study is a significant milestone in advancing our understanding of intercalation routes of large molecules via the basal plane of graphene, as well as heterointerface chemical reactions leading to the formation of distinctive confined complex oxide compounds. △ Less

Submitted 4 April, 2023; originally announced April 2023.

Simultaneous measurement of specific heat and thermal conductivity in pulsed magnetic fields

Authors: Tetsuya Nomoto, Chengchao Zhong, Hiroshi Kageyama, Yoko Suzuki, Marcelo Jaime, Yoshiaki Hashimoto, Shingo Katsumoto, Naofumi Matsuyama, Chao Dong, Akira Matsuo, Koichi Kindo, Koichi Izawa, Yoshimitsu Kohama

Abstract: We report an experimental setup for simultaneously measuring specific heat and thermal conductivity in feedback-controlled pulsed magnetic fields of 50 msec duration at cryogenic temperatures. A stabilized magnetic field pulse obtained by the feedback control, which dramatically improves the thermal stability of the setup and sample, is used in combination with the flash method to obtain absolute… ▽ More We report an experimental setup for simultaneously measuring specific heat and thermal conductivity in feedback-controlled pulsed magnetic fields of 50 msec duration at cryogenic temperatures. A stabilized magnetic field pulse obtained by the feedback control, which dramatically improves the thermal stability of the setup and sample, is used in combination with the flash method to obtain absolute values of thermal properties up to 37.2 T in the 2 K to 16 K temperature range. We describe the experimental setup and demonstrate the performance of the present method with measurements on single crystal samples of the geometrically frustrated quantum spin-dimer system SrCu$_2$(BO$_3$)$_2$. Our proof-of-principle results show excellent agreement with data taken using a standard steady-state method, confirming the validity and convenience of the present approach. △ Less

Submitted 3 February, 2023; originally announced February 2023.

Comments: 9 pages, 7 figures

In-situ electrical and thermal transport properties of FeySe1-xTex films with ionic liquid gating

Authors: Juan Xu, Mingyang Qin, Zefeng Lin, Xu Zhang, Ruozhou Zhang, Li Xu, Liping Zhang, Qiuyan Shi, Jie Yuan, Beiyi Zhu, Chao Dong, Rui Xiong, Qihong Chen, Yangmu Li, Jing Shi, Kui Jin

Abstract: We combine in-situ electrical transport and Seebeck coefficient measurements with the ionic liquid gating technique to investigate superconductivity and the normal state of FeySe1-xTex (FST) films. We find that the pristine FST films feature a non-Fermi liquid temperature dependence of the Seebeck coefficient, i.e., S/T ~ AS lnT, and AS is strongly correlated with the superconducting transition te… ▽ More We combine in-situ electrical transport and Seebeck coefficient measurements with the ionic liquid gating technique to investigate superconductivity and the normal state of FeySe1-xTex (FST) films. We find that the pristine FST films feature a non-Fermi liquid temperature dependence of the Seebeck coefficient, i.e., S/T ~ AS lnT, and AS is strongly correlated with the superconducting transition temperature (Tc). Ionic liquid gating significantly raises Tc of FST films, for which the Seebeck coefficient displays a novel scaling behavior and retains the logarithmic temperature dependence. Moreover, a quantitative relationship between the slope of T-linear resistivity (A\r{ho}) and Tc for gated films is observed, i.e., (A\r{ho})1/2 ~ Tc, consistent with previous reports on cuprates and FeSe. The scaling behaviors of AS and A\r{ho} point to a spin-fluctuation-associated transport mechanism in gated FeySe1-xTex superconductors. △ Less

Submitted 5 January, 2023; originally announced January 2023.

Comments: 12 pages,5 figures

Strengthened proximity effect at grain boundaries to enhance inter-grain supercurrent in Ba1-xKxFe2As2 superconductors

Authors: Zhe Cheng, Chiheng Dong, Huan Yang, Qinghua Zhang, Satoshi Awaji, Lin Gu, Hai-Hu Wen, Yanwei Ma

Abstract: Iron-based superconductors have great potential for high-power applications due to their prominent high-field properties. One of the central issues in enhancing the critical current density of iron-based superconducting wires is to reveal the roles and limitations of grain boundaries in supercurrent transport. Here, we finely tuned the electronic properties of grain boundaries by doping Ba1-xKxFe2… ▽ More Iron-based superconductors have great potential for high-power applications due to their prominent high-field properties. One of the central issues in enhancing the critical current density of iron-based superconducting wires is to reveal the roles and limitations of grain boundaries in supercurrent transport. Here, we finely tuned the electronic properties of grain boundaries by doping Ba1-xKxFe2As2 superconductors in a wide range (0.25<x<0.598). It is found that the intra-grain Jcintra peaks near x~0.287, while the inter-grain Jcinter has a maximum at about x~0.458. Remarkably, the grain boundary transparency parameter defined as Jcinter/Jcintra rises monotonically with doping. Through detailed microscopic analysis, we suggest that the FeAs segregation phase commonly existing at grain boundaries and the adjacent grains constitute superconductor-normal metal-superconductor (SNS) Josephson junctions which play a key role in transporting supercurrent. A sandwich model based on the proximity effect and the SNS junction is proposed to well interpret our data. It is found that overdoping in superconducting grains largely strengthens the proximity effect and consequently enhances the intergrain supercurrent. Our results will shed new insights and inspirations for improving the application parameters of iron-based superconductors by grain boundary engineering. △ Less

Submitted 3 October, 2022; originally announced October 2022.

Comments: 22 pages, 6 figures

Journal ref: Materials Today Physics 28 (2022) 100848

Strain Induced Indirect-to-Direct Bandgap Transition, Photoluminescence Enhancement, and Linewidth Reduction in Bilayer MoTe2

Authors: Yueyang Yu, Chuan-Ding Dong, Rolf Binder, Stefan Schumacher, Cun-Zheng Ning

Abstract: Two-dimensional (2D) layered materials provide an ideal platform for engineering electronic and optical properties through strain control because of their extremely high mechanical elasticity and sensitive dependence of material properties on mechanical strain. In this paper, a combined experimental and theoretical effort is made to investigate the effects of mechanical strain on various spectral… ▽ More Two-dimensional (2D) layered materials provide an ideal platform for engineering electronic and optical properties through strain control because of their extremely high mechanical elasticity and sensitive dependence of material properties on mechanical strain. In this paper, a combined experimental and theoretical effort is made to investigate the effects of mechanical strain on various spectral features of bilayer MoTe2 photoluminescence (PL). We found that bilayer MoTe2 can be converted from an indirect-to direct-bandgap material through strain engineering, resulting in a photoluminescence enhancement by a factor of 2.24. Over 90% of the PL comes from photons emitted by the direct excitons at the maximum strain applied. Importantly, we show that strain effects lead to a reduction of the overall linewidth of PL by as much as 36.6%. We attribute the dramatic decrease of linewidth to a strain-induced complex interplay among various excitonic varieties such as direct bright excitons, trions, and indirect excitons. Our experimental results on direct and indirect exciton emission features are explained by theoretical exciton energies that are based on first-principle electronic band structure calculations. The consistent theory-experimental trend shows that the enhancement of PL and the reduction of linewidth are the consequences of the increasing direct exciton contribution with the increase of strain. Our results demonstrate that strain engineering can lead to a PL quality of the bilayer MoTe2 comparable to that of the monolayer counterpart. The additional benefit of a longer emission wavelength makes the bilayer MoTe2 more suitable for Silicon-photonics integration due to the reduced Silicon absorption. △ Less

Submitted 23 September, 2022; originally announced September 2022.

Phase diagrams on composition-spread Fe$_y$Te$_{1-x}$Se$_x$ films

Authors: Zefeng Lin, Sijia Tu, Juan Xu, Yujun Shi, Beiyi Zhu, Chao Dong, Jie Yuan, Xiaoli Dong, Qihong Chen, Yangmu Li, Kui Jin, Zhongxian Zhao

Abstract: Fe$_y$Te$_{1-x}$Se$_x$, an archetypical iron-based high-temperature superconductor with a simple structure but rich physical properties, has attracted lots of attention because the two end compositions, Se content $x = 0$ and 1, exhibit antiferromagnetism and nematicity, respectively, making it an ideal candidate for studying their interactions with superconductivity. However, what is clearly lack… ▽ More Fe$_y$Te$_{1-x}$Se$_x$, an archetypical iron-based high-temperature superconductor with a simple structure but rich physical properties, has attracted lots of attention because the two end compositions, Se content $x = 0$ and 1, exhibit antiferromagnetism and nematicity, respectively, making it an ideal candidate for studying their interactions with superconductivity. However, what is clearly lacking to date is a complete phase diagram of Fe$_y$Te$_{1-x}$Se$_x$ as functions of its chemical compositions since phase separation usually occurs from $x\sim 0.6$ to 0.9 in bulk crystals. Moreover, fine control of its composition is experimentally challenging because both Te and Se are volatile elements. Here we establish a complete phase diagram of Fe$_y$Te$_{1-x}$Se$_x$, achieved by high-throughput film synthesis and characterization techniques. An advanced combinatorial synthesis process enables us to fabricate an epitaxial composition-spread Fe$_y$Te$_{1-x}$Se$_x$ film encompassing the entire Se content $x$ from 0 to 1 on a single piece of CaF$_2$ substrate. The micro-region composition analysis and X-ray diffraction show a successful continuous tuning of chemical compositions and lattice parameters, respectively. The micro-scale pattern technique allows the mapping of electrical transport properties as a function of relative Se content with an unprecedented resolution of 0.0074. Combining with the spin patterns in literature, we build a detailed phase diagram that can unify the electronic and magnetic properties of Fe$_y$Te$_{1-x}$Se$_x$. Our composition-spread Fe$_y$Te$_{1-x}$Se$_x$ films, overcoming the challenges of phase separation and precise control of chemical compositions, provide an ideal platform for studying the relationship between superconductivity and magnetism. △ Less

Submitted 2 August, 2022; originally announced August 2022.

Comments: 13 pages,5 figures and Supplementary Material 3 pages,3 figures

Journal ref: Sci. Bull. 67 (2022) 1443-1449