Showing 1–50 of 223 results for author: Fang, Y

Cross-Temperature Defect Identification in Atomistic Simulations via Multi-Level Domain Alignment

Authors: Yating Fang, Jungmin Kim, Qian Qian Zhao, Pallavi Biswas, Joshua M. Gonjon, Ryan B. Sills, Ahmed Aziz Ezzat

Abstract: Identifying atomic defects at elevated temperature is difficult because thermal fluctuations blur the local symmetry that both geometric heuristics and supervised classifiers rely on: trustworthy labels exist in low-temperature reference configurations, while the high-temperature regime where robust analysis matters most is effectively unlabeled. We cast this as a cross-temperature domain-shift pr… ▽ More Identifying atomic defects at elevated temperature is difficult because thermal fluctuations blur the local symmetry that both geometric heuristics and supervised classifiers rely on: trustworthy labels exist in low-temperature reference configurations, while the high-temperature regime where robust analysis matters most is effectively unlabeled. We cast this as a cross-temperature domain-shift problem and align the two domains at three levels: an equivariant denoiser at the input level, cross-temperature contrastive learning at the representation level, and a morphology-aware regularizer that steers predictions toward the compact geometry of physical defect structures. Because no atom-wise truth exists at temperature, we further introduce a label-free evaluation suite that scores predicted defect structures along five spatial and physics-based axes, enabling model assessment and selection without high-temperature labels. Near the melting point, the framework identifies vacancies and self-interstitial atoms across face-centered-cubic, body-centered-cubic, and hexagonal-close-packed iron systems with every interstitial localized and zero false detections in every vacancy system against Wigner-Seitz ground truth, with no high-temperature labels used in training. It sustains this fidelity on a million-atom, 2.5 ns trajectory, resolving single vacancy hops and complete Frenkel-pair recombination, and captures grain-boundary phase transformations in aluminum bicrystals, distinguishing two nucleation modes. Multi-level domain alignment thus offers a practical, label-efficient route to temperature-robust structural analysis of large-scale molecular dynamics. △ Less

Submitted 22 August, 2026; originally announced August 2026.

Comments: 46 pages, 8 figures

A novel strategy for achieving a low-field lightweight permanent MRI magnet system with good magnetic field homogeneity and low eddy current

Authors: Jingzhi Han, Jiangqian Guo, Peng Shen, Xiao Tong, Wenyun Yang, Ziheng Zhang, Jie Liu, Tianzhuo Yang, Yikun Fang, Shunquan Liu, Jie Zhang, Qing Xu, Jinbo Yang

Abstract: In low-field, lightweight, pole-pieceless permanent-magnet MRI systems built with sintered Nd-Fe-B or Sm-Co magnets, the rapid switching of gradient fields readily induces eddy currents in the sintered magnets, leading to image artifacts. To address this, we report for the first time a Sm-Fe-N permanent-magnet MRI system based on anisotropic Sm-Fe-N bonded magnets, whose high electrical resistivit… ▽ More In low-field, lightweight, pole-pieceless permanent-magnet MRI systems built with sintered Nd-Fe-B or Sm-Co magnets, the rapid switching of gradient fields readily induces eddy currents in the sintered magnets, leading to image artifacts. To address this, we report for the first time a Sm-Fe-N permanent-magnet MRI system based on anisotropic Sm-Fe-N bonded magnets, whose high electrical resistivity reduces the eddy currents in the X, Y and Z directions to 0.093%, 0.172% and 2.38%, respectively, while a magnetic field inhomogeneity below 150 ppm is achieved at the boundary of a 220 mm diameter of spherical volume (DSV). Compared with sintered Nd-Fe-B and Sm-Co magnets, using Sm-Fe-N bonded magnets as the source of the static magnetic field not only suppresses eddy currents but also makes a closely tiled, densely packed magnetic-circuit layout feasible, providing a more uniform static magnetic field for the MRI system. Imaging results free of obvious geometric distortion and banding artifacts further indicate that the Sm-Fe-N magnet system delivers low eddy currents and high static magnetic field homogeneity. △ Less

Submitted 22 August, 2026; originally announced August 2026.

Comments: 7 figures; supplementary material included

Quantum Fisher information of magnetic quantum phase transition on Kondo lattice

Authors: Yuan Fang, Lei Chen, Mounica Mahankali, Fang Xie, Yiming Wang, Shouvik Sur, Qimiao Si

Abstract: Strange metals exemplify highly collective quantum many-body systems that call for new means of characterization, and there is considerable potential for quantum information approaches contributing to the cause. We investigate multipartite entanglement across the quantum phase transition of a Kondo lattice model using the quantum Fisher information (QFI). We show that the QFI associated with the s… ▽ More Strange metals exemplify highly collective quantum many-body systems that call for new means of characterization, and there is considerable potential for quantum information approaches contributing to the cause. We investigate multipartite entanglement across the quantum phase transition of a Kondo lattice model using the quantum Fisher information (QFI). We show that the QFI associated with the spin components transverse to the order parameter characterizes the destruction of heavy quasiparticles in the Kondo-destroyed magnetic-ordered phase. The physical origin of this observation is elucidated through an analysis of the antiferromagnetic Heisenberg model. We propose to test the results in terms of both unpolarized and polarized inelastic neutron scattering measurements in the ordered part of the heavy fermion phase diagram. Our findings illustrate how different operators of a many-body system can be employed to not only witness multipartite entanglement in different sectors and but also elucidate the overall physics across different parts of the phase diagram. △ Less

Submitted 17 July, 2026; originally announced July 2026.

Comments: 7+8 pages, 3+5 figures

2.4 GHz Flip-flop Device within Nonequilibrium Superconducting Diode

Authors: Xiangyu Bi, Hongyi Li, Aoshen Yang, Yuqiang Fang, Ganyu Chen, Shichong Yang, Yicheng Shen, Qizheng Sun, Junwei Huang, Wei Jiang, Da Wang, Fuqiang Huang, Haijun Zhang, Qianghua Wang, Hongtao Yuan

Abstract: Superconducting diode effect exhibits asymmetric critical supercurrent and has profound implications for condensed matter physics. The technical appeals of such superconducting diodes are their ultrahigh on-off ratio and diode efficiency for superconducting electronics owing to the dissipationless supercurrent therein. However, realizing superconducting diode operation at high working frequency, w… ▽ More Superconducting diode effect exhibits asymmetric critical supercurrent and has profound implications for condensed matter physics. The technical appeals of such superconducting diodes are their ultrahigh on-off ratio and diode efficiency for superconducting electronics owing to the dissipationless supercurrent therein. However, realizing superconducting diode operation at high working frequency, which is a key requirement for practical applications, remains elusive and challenging. Here, we demonstrate a polarity-controllable superconducting diode with non-equilibrium Josephson junction and its edge-triggered flip-flop operation at a high frequency up to 2.4 GHz, within a van der Waals superconductor 2M-WS$_2$. By simply tuning the thickness of superconducting 2M-WS$_2$ nanoflakes to engineer inversion asymmetry in the junction, we achieve a high diode efficiency of 67% and an on-off ratio exceeding 10$^5$. Importantly, the pulse width and duty cycle of output pulse signals in such superconducting diode flip-flop devices can be controlled in a broadband frequency range crossing 12 orders of magnitude. Theoretical analysis reveals that the non-equilibrium dynamic nature of supercurrent in these Josephson junctions enables such a high diode operating frequency and the polarity control of supercurrent. The 2.4 GHz non-equilibrium Josephson diode developed here provides a promising platform for advanced superconducting logic circuits and broadband telecommunication applications. △ Less

Submitted 4 June, 2026; originally announced June 2026.

Comments: 33 pages, 4 figures

Electronic Origin of Ferromagnetic Excitations in the Candidate Spin-Triplet Superconductor CeSb2

Authors: Xiaoxiao Wang, Xiaoyang Chen, Suppanut Sangphet, Yifei Fang, Yilin Wang, Chihao Li, Minyinan Lei, Nan Guo, Yuanhe Song, Rui Peng, Haichao Xu, Donglai Feng

Abstract: The origin of quasi-one-dimensional (q1D) ferromagnetic (FM) excitations in the candidate spin-triplet superconductor CeSb$_2$ has remained unclear. Here we report an electronic mechanism for emergent q1D magnetism in the quasi-two-dimensional lattice of CeSb$_2$, revealed by angle-resolved photoemission spectroscopy (ARPES). High-resolution ARPES resolves no spin-density-wave gap on the dispersiv… ▽ More The origin of quasi-one-dimensional (q1D) ferromagnetic (FM) excitations in the candidate spin-triplet superconductor CeSb$_2$ has remained unclear. Here we report an electronic mechanism for emergent q1D magnetism in the quasi-two-dimensional lattice of CeSb$_2$, revealed by angle-resolved photoemission spectroscopy (ARPES). High-resolution ARPES resolves no spin-density-wave gap on the dispersive Fermi pockets, disfavoring a nesting-driven mechanism for the q1D FM excitations. Instead, resonant ARPES reveals a pronounced selective enhancement of Ce 4$f$ spectral weight on the $C_2$-distributed Fermi pockets aligned with the Ce ladder. This observation signifies band-selective Kondo coupling that generates strongly anisotropic magnetic exchange interactions, which can naturally account for both the q1D ferromagnetic excitations and the competing magnetic orders. Our results identify a band-selective Kondo coupling mechanism for emergent low-dimensional magnetism in correlated $f$-electron systems. △ Less

Submitted 28 May, 2026; originally announced May 2026.

Quantum geometry induced anomalous chiral transport and hidden symmetry breaking in centrosymmetric 2M-WS2

Authors: Hang Cui, Shao-Bo Liu, Erqing Wang, Mingxiang Pan, Yuqiang Fang, Ning Ma, Wenlong Liu, Di Chen, Yu Zhang, Yuanjun Song, Tingting Hao, Jiankun Li, Jian Cui, Ya Feng, Haiwen Liu, Fuqiang Huang, Huaqing Huang, X. -C. Xie, Jian-Hao Chen

Abstract: Chirality, a widely existing material property in nature involving the breaking of the left-right symmetry, has profound influences in various fields of natural sciences. Nonlinear response, such as electronic magnetochiral anisotropy (eMChA), has been recognized as a sensitive probe for the effects of symmetry breaking and nontrivial quantum geometries in solids. So far, observations of eMChA hav… ▽ More Chirality, a widely existing material property in nature involving the breaking of the left-right symmetry, has profound influences in various fields of natural sciences. Nonlinear response, such as electronic magnetochiral anisotropy (eMChA), has been recognized as a sensitive probe for the effects of symmetry breaking and nontrivial quantum geometries in solids. So far, observations of eMChA have primarily been limited to inversion-symmetry broken materials. Here, we report a remarkable chiral transport in centrosymmetric candidate topological superconductor 2M-WS2 flakes observed via second-harmonic generation under an out-of-plane magnetic field. More importantly, the eMChA becomes significant around the crossover temperature TFL ~ 25 K from the Fermi liquid (FL) to strange metal (SM) in the normal state, which interestingly echoes with the anomalously large Nernst response at the same temperature in bulk 2M-WS2. These observations reveal a direct correspondence between the nonlinear response, Nernst response, and FL-SM transition in 2M-WS2. Theoretical analysis indicates that nontrivial quantum geometry is behind the simultaneous response of eMChA and Nernst effects in 2M-WS2 and the contribution from the orbital magnetic moment at the Fermi surface becomes significant during the FL-SM transition. Based on first-principles calculations, a thick-layer-sliding mechanism with minimal energy gain in 2M-WS2 provides one possibility for the generation of such nontrivial quantum geometry. The intertwined physics of remarkable eMChA, Nernst response, and FL-SM transition make 2M-WS2 a rare quantum platform to study the chiral transport and unexplored phenomena in strange metals, which may shed light on the trans-century, unresolved scientific issue in unconventional high-temperature superconductivity. △ Less

Submitted 18 May, 2026; originally announced May 2026.

Comments: Accepted by Physical Review Letters

SemiConLens: Visual Analytics for 2D Semiconductor Discovery

Authors: Kavinda Athapaththu, Shiwei Chen, Yuan Fang, Sanchali Mitra, Yee Sin Ang, Yong Wang

Abstract: The past few years have witnessed vibrant efforts in discovering new two-dimensional (2D) semiconductor materials from both academia and the industry, due to their promising potential in resolving the severe performance deterioration of traditional semiconductors resulting from condensed silicon thickness. However, existing methods (e.g., Density Functional Theory (DFT) or machine-learning-based a… ▽ More The past few years have witnessed vibrant efforts in discovering new two-dimensional (2D) semiconductor materials from both academia and the industry, due to their promising potential in resolving the severe performance deterioration of traditional semiconductors resulting from condensed silicon thickness. However, existing methods (e.g., Density Functional Theory (DFT) or machine-learning-based approaches) suffer from various challenges such as small datasets, and reliability and trustworthiness issues. To bridge this gap, we propose SemiConLens, a visual analytics approach to combine human expertise with the power of ML to enable effective and reliable 2D semiconductor discovery. Specifically, we first develop a new Correlation Aware Multivariate Imputation (CAMI) method and use ML models like autoencoder, which can better learn from limited data and reveal uncertainty, to address the challenge of sparse data in semiconductivity prediction. Built upon this, our visualization module, consisting of three visualization views with linked interactions, allows material researchers to interactively filter, discover and compare 2D semiconductor candidates. A novel circular glyph design and a new cluster-aware layout optimization approach are proposed to effectively display all the user-configurable key attributes and possible prediction uncertainties of each semiconductor candidate, ensuring a reliable and trustable 2D semiconductor discovery. We assess SemiConLens through quantitative evaluations, expert interviews, and use cases. The results demonstrate SemiConLens's capability to help material researchers conduct effective discovery of desirable 2D semiconductors. △ Less

Submitted 11 April, 2026; originally announced May 2026.

Effect of Rashba spin-orbit coupling on Faraday rotation in an extended Haldane model

Authors: Yuan Fang, Yixiang Wang, Xiaopu Zhang

Abstract: Utilization of Faraday rotation (FR) properties of topological materials offers a promising route toward novel magneto-optical devices. We systematically investigated the effect of Rashba spin-orbit coupling (SOC) on FR spectra in an extended Haldane model, which incorporates Rashba SOC and exchange splitting into the original spinless Haldane framework. Using the Kubo formalism, we calculated the… ▽ More Utilization of Faraday rotation (FR) properties of topological materials offers a promising route toward novel magneto-optical devices. We systematically investigated the effect of Rashba spin-orbit coupling (SOC) on FR spectra in an extended Haldane model, which incorporates Rashba SOC and exchange splitting into the original spinless Haldane framework. Using the Kubo formalism, we calculated the FR spectra across the model's rich topological phase diagram. We found that in the Chern number C=2 region, in the absence of exchange splitting, the FR angle can exceed 4$^\circ$ and its peak position is tunable by the Rashba SOC. In contrast, with the inclusion of exchange splitting, a nearly flat FR profile emerges over a broad frequency range, and the FR peak values increase monotonically with the Rashba SOC strength. The Rashba SOC opens additional transition channels, whose net contribution constructively enhances the FR peak. Furthermore, we derived a low-energy effective Hamiltonian expanded up to quadratic terms, the results of which are in good agreement with tight-binding model calculations, thereby validating our numerical results. Our findings suggest that magneto-optical device characteristics can be designed and optimized through Rashba SOC engineering. △ Less

Submitted 7 July, 2026; v1 submitted 16 April, 2026; originally announced April 2026.

Comments: accepted by Chinese Physics B

Two-Dimensional Ferromagnetism in Monolayers of MnSi

Authors: Yuan Fang, Yang Liu, Dmitry V. Averyanov, Ivan S. Sokolov, Alexander N. Taldenkov, Oleg E. Parfenov, Oleg A. Kondratev, Andrey M. Tokmachev, Vyacheslav G. Storchak

Abstract: 2D ferromagnets offer valuable insights into the fundamentals of magnetism and stimulate the progress of ultracompact spintronics. The demand for seamless integration of the materials with the Si technology, particularly helpful to their applications in nanoelectronics, draws attention to 2D magnetic silicides. MnSi is a prominent silicide hosting magnetic phases with unconventional properties; ho… ▽ More 2D ferromagnets offer valuable insights into the fundamentals of magnetism and stimulate the progress of ultracompact spintronics. The demand for seamless integration of the materials with the Si technology, particularly helpful to their applications in nanoelectronics, draws attention to 2D magnetic silicides. MnSi is a prominent silicide hosting magnetic phases with unconventional properties; however, little is known about magnetic states of MnSi at the 2D limit. Here, we explore the magnetism of ultrathin films of MnSi on silicon, down to a single monolayer. Angle-resolved photoemission spectra suggest exchange splitting of MnSi bands. Magnetization measurements confirm that the ferromagnetic state in MnSi is rather robust with respect to the number of monolayers. Thick metallic films demonstrate the anomalous Hall effect and negative magnetoresistance; however, as the number of monolayers drops below 3, MnSi becomes an insulator. Most importantly, the ferromagnetism of ultrathin MnSi films acquires a 2D character, as its effective Curie temperature depends on weak magnetic fields. The present study establishes MnSi monolayers as 2D ferromagnets that can find potential applications in silicon-based spintronics. △ Less

Submitted 14 April, 2026; originally announced April 2026.

Comments: 29 pages, 16 figures

Robust topological BIC nanocavities for upconversion directional emission

Authors: Yongqi Chen, Ming Zhu, Qingfeng Bian, Xiumei Yin, Wenxin Wang, Bin Dong, Yurui Fang

Abstract: Photonic bound states in the continuum (BICs) provide a revolutionary paradigm for boosting light-matter interactions in integrated nanocavity systems. Nevertheless, precise manipulation of open cavity-emitter architectures still faces critical challenges, especially in realizing deterministic directional radiation and suppressing the perturbation of intrinsic cavity modes induced by emitters as l… ▽ More Photonic bound states in the continuum (BICs) provide a revolutionary paradigm for boosting light-matter interactions in integrated nanocavity systems. Nevertheless, precise manipulation of open cavity-emitter architectures still faces critical challenges, especially in realizing deterministic directional radiation and suppressing the perturbation of intrinsic cavity modes induced by emitters as local impurities. Conventional investigations on cavity-emitter coupling are predominantly based on ensemble measurements, which inevitably mask the intrinsic physics underlying individual light-matter interactions. Here, we propose a robust strategy to control the upconversion and emission of a single-particle emitter using a topological plasmonic cavity with broken σh mirror symmetry. This structured design enables the transition from symmetry-protected BICs to a multi-BIC regime with finite but ultrahigh confinement, where nontrivial phase evolution and hybridization of transverse electric and magnetic modes open a well-defined far-field radiation channel for directional emission. Leveraging this scheme, we experimentally demonstrate dramatically enhanced radiation intensity from a single point-like emitter, together with uniform and deterministic directional emission, while achieving excellent structural robustness against local perturbations. This work establishes a general framework for engineering coherent directional light emission at the nanoscale, which lays a solid foundation for high-performance chip-scale integrated nanophotonic applications. △ Less

Submitted 26 March, 2026; originally announced March 2026.

Comments: 39 pages including supporting information. 5 figures for main text and 14 figures for SI

MSC Class: 78-05

Small-Data Machine Learning Uncovers Decoupled Control Mechanisms of Crystallinity and Surface Morphology in $β$-Ga2O3 Epitaxy

Authors: Min Peng, Yuanjun Tang, Dianmeng Dong, Yang Zhang, Cheng Wang, Shulin Jiao, Xiaotong Ma, Shichao Zhang, Jingchen Wang, Huiying Wang, Yongxin Zhang, Huiping Zhu, Yue-Wen Fang, Fan Zhang, Zhenping Wu

Abstract: The ultrawide-bandgap semiconductor $β$-Ga2O3 holds exceptional promise for next-generation power electronics and deep-ultraviolet optoelectronics, yet its widespread application is hindered by the lack of cost-effective, high-quality heteroepitaxial thin films. Here, we demonstrate an interpretable machine learning framework that efficiently navigates the complex, multiparameter process space of… ▽ More The ultrawide-bandgap semiconductor $β$-Ga2O3 holds exceptional promise for next-generation power electronics and deep-ultraviolet optoelectronics, yet its widespread application is hindered by the lack of cost-effective, high-quality heteroepitaxial thin films. Here, we demonstrate an interpretable machine learning framework that efficiently navigates the complex, multiparameter process space of pulsed laser deposition (PLD) to achieve high-crystallinity $β$-Ga2O3 epitaxy on c-plane sapphire. By systematically benchmarking nine regression algorithms under limited experimental data conditions, we identify quadratic polynomial ridge regression as the optimal surrogate model, which combines predictive accuracy (R$^2$ $\approx$ 0.86) with full physical transparency through explicit analytical coefficients. Coupling this model with SHAP (SHapley Additive exPlanations) analysis and iterative experimental design, we construct a closed-loop optimization workflow that progressively refines the process-performance landscape over only three experimental rounds. This data-efficient strategy reduces the X-ray rocking curve (RC) full-width at half-maximum (FWHM) by 70$\%$ from > 3$^{\circ}$ to 0.92$^{\circ}$, which is the best reported value for PLD-grown $β$-Ga2O3 on sapphire. Intriguingly, concurrent modeling of surface roughness reveals that crystalline quality and surface morphology are governed by distinct dominant factors: temperature primarily controls bulk crystallinity, whereas oxygen pressure dictates surface kinetics. This decoupled mechanism, quantitatively captured for the first time via feature importance analysis, provides actionable physical insight for independent optimization of structural and morphological properties. Our work establishes a generalizable, resource-efficient paradigm for intelligent process development in oxide epitaxy and beyond. △ Less

Submitted 23 March, 2026; originally announced March 2026.

Comments: 31 pages, 5 figures

Journal ref: Applied Surface Science, 2026

Anharmonicity Driven by Vacancy Ordering Unlocks High-performance Thermoelectric Conversion in Defective Chalcopyrites II-III$_2$-VI$_4$

Authors: Hui Zhang, Jincheng Yue, Jiongzhi Zheng, Ning Wang, Wenling Ren, Shuyao Lin, Chen Shen, Hao Gao, Yanhui Liu, Yue-Wen Fang, Tian Cui

Abstract: Defective chalcopyrites have recently emerged as promising thermoelectric materials because their ordered intrinsic vacancies can profoundly reshape both lattice dynamics and electronic structure. Here, we present a comprehensive theoretical investigation of the lattice thermal and carrier transport properties of II-III$_2$-VI$_4$ defective chalcopyrites by combining first-principles calculations… ▽ More Defective chalcopyrites have recently emerged as promising thermoelectric materials because their ordered intrinsic vacancies can profoundly reshape both lattice dynamics and electronic structure. Here, we present a comprehensive theoretical investigation of the lattice thermal and carrier transport properties of II-III$_2$-VI$_4$ defective chalcopyrites by combining first-principles calculations with machine-learning interatomic potentials. We show that vacancy ordering enhances lattice distortion, leading to strong anharmonicity and metavalent bonding. The interplay of soft low-frequency phonons, strongly negative Grüneisen parameters, and a substantially enlarged four-phonon scattering phase space results in four-phonon-scattering-dominated heat transport, yielding ultralow lattice thermal conductivity. Meanwhile, systematic anion substitution at the VI-site provides an effective route to tune the electronic structure: reduced anion electronegativity weakens metal-anion hybridization, shifts anion $p$ states upward, narrows the band gap, and thereby improves electrical transport. Benefiting from this synergy between vacancy-induced phonon suppression and anion-regulated electronic optimization, CdGa$_2$Te$_4$ exhibits an ultralow lattice thermal conductivity of 0.19 W$\cdot$m$^{-1}$K$^{-1}$ and a high room-temperature $ZT$ of 0.957. This work not only predicts defective chalcopyrites as a promising platform for high-performance thermoelectrics but also provides a practical design strategy by integrating vacancy ordering, higher-order phonon scattering, and anion-dependent band engineering. △ Less

Submitted 23 March, 2026; v1 submitted 17 March, 2026; originally announced March 2026.

Dimensionality tuning of heavy-fermion states in ultrathin CeSi2 films

Authors: Yi Wu, Weifan Zhu, Teng Hua, Yuan Fang, Yanan Zhang, Jiawen Zhang, Yanen Huang, Hao Zheng, Shanyin Fu, Xinying Zheng, Zhengtai Liu, Mao Ye, Ye Chen, Tulai Sun, Michael Smidman, Johann Kroha, Chao Cao, Huiqiu Yuan, Frank Steglich, Hai-Qing Lin, Yang Liu

Abstract: Dimensionality tuning is an important method to modify the electronic states of quantum materials. However, the mechanism of such tuning in heavy fermion systems and its connection with transport properties remain largely unexplored. Here by combining molecular beam epitaxy (MBE), in-situ angle-resolved photoemission spectroscopy (ARPES) and transport measurements, we study the electronic states o… ▽ More Dimensionality tuning is an important method to modify the electronic states of quantum materials. However, the mechanism of such tuning in heavy fermion systems and its connection with transport properties remain largely unexplored. Here by combining molecular beam epitaxy (MBE), in-situ angle-resolved photoemission spectroscopy (ARPES) and transport measurements, we study the electronic states of the heavy-fermion compound CeSi2 as a function of film thickness. In three dimensional thick films, our measurements reveal a dispersive Kondo peak at the Fermi level (EF) and satellite peaks originating from crystal electric field (CEF) excitations, characteristic of heavy fermion systems. For two-dimensional ultrathin films, the CEF satellites are largely suppressed while the ground-state Kondo peak at EF remains strong, although it develops at lower temperatures. Simultaneously, the maximum temperature Tmax of the magnetic resistivity, \r{ho}m(T), changes from ~100 K in thick films to ~35 K in ultrathin films. This can be attributed to the dimensionality driven reduction of CEF excitations during the Kondo process, in good agreement with spectroscopic results. Our work provides direct insight to understand the quantum confinement effects on strongly correlated 4f-electron systems and opens up new opportunities to explore emergent phenomena in two-dimensional heavy-fermion materials. △ Less

Submitted 11 March, 2026; originally announced March 2026.

Journal ref: Phys. Rev. X 16, 011053(2026)

Pathway to lowest-energy structures and stress relaxation for the surface triple junction verified by machine learning

Authors: Yuan Fang, Ipen Demirel, Xiaopu Zhang, Yuchuan Shao, Jianda Shao, John J. Boland

Abstract: The behavior of surface triple junctions (STJ) at emergent grain boundaries on free surfaces is critical to the microstructure evolution, and therefore to the stability of the next generation interconnect. Yet,despite this significant importance, its lowest-energy structure and local stress have remained persistently unknown. Here, we fill this critical gap through high-resolution experimental map… ▽ More The behavior of surface triple junctions (STJ) at emergent grain boundaries on free surfaces is critical to the microstructure evolution, and therefore to the stability of the next generation interconnect. Yet,despite this significant importance, its lowest-energy structure and local stress have remained persistently unknown. Here, we fill this critical gap through high-resolution experimental mapping of the local surface deformation at STJ, the analysis of the local structure and stress relaxation, and ergodic searching metastable structures. We establish the zipped Y-shaped notch as the universal lowest-energy structures. This energetic preference was well explained by the distinctive local stress mechanism and was excellently verified with machine learning methods for a wide range of boundaries. By revealing the elusive thermodynamics of STJs, our findings advance the research field by redefining the energetic framework for capillary driven structure evolution and providing foundation for understanding kinetically diffusive deformation and for engineering thin-film interconnects and related materials. △ Less

Submitted 27 April, 2026; v1 submitted 2 March, 2026; originally announced March 2026.

Chiral Weyl-Kondo semimetals and hexagonal heavy fermion systems

Authors: Kuan-Sen Lin, Yuan Fang, Henrique Fabrelli, Runhan Li, Andrey Prokofiev, Fang Xie, Jennifer Cano, Maia G. Vergniory, Silke Paschen, Qimiao Si

Abstract: Strong correlation, in concert with symmetry and topology, engenders novel gapless phases of matter, though only a tip of the iceberg has been seen. An exemplary framework is provided by Weyl-Kondo semimetals, in which Weyl fermions develop through crystalline symmetry constraints on the emergent low-energy heavy-fermion excitations. This paradigm has opened up new opportunities to explore correla… ▽ More Strong correlation, in concert with symmetry and topology, engenders novel gapless phases of matter, though only a tip of the iceberg has been seen. An exemplary framework is provided by Weyl-Kondo semimetals, in which Weyl fermions develop through crystalline symmetry constraints on the emergent low-energy heavy-fermion excitations. This paradigm has opened up new opportunities to explore correlated topologies without a noninteracting counterpart, but fully realizing this potential requires a large base of candidate materials. Here we confront the challenge on both fronts by studying heavy fermion systems with hexagonal space groups. This family contains a large number of chiral nonsymmorphic crystal structures that promote Weyl degeneracies and, in addition, feature geometric frustration in the $f$-electron magnetism. Our calculations for the heavy fermion states identify Weyl-Kondo semimetals with chiral or achiral Weyl nodes in the respective structural classes. We also develop the first search strategy of any kind for the difficult case of strongly correlated materials, which is also suitable for automation, using a combination of materials database, symmetry classification and search for desired experimental properties, and propose as candidate topological heavy fermion systems the chiral CePt$_2$B and achiral Ce$_2$NiGe$_3$ and Ce$_6$Co$_{2-δ}$Si$_3$. Our findings raise the prospect for strongly correlated metallic topology in the unusual setting of exotic quantum magnetism and, moreover, point a way to go beyond serendipity in the search for novel strongly correlated quantum materials. △ Less

Submitted 9 March, 2026; v1 submitted 25 February, 2026; originally announced February 2026.

Comments: 24+58 pages, 3+30 figures

Uniaxial strain tuned magnetism of the altermagnet candidate h-FeS

Authors: Weiliang Yao, Feng Ye, Zachary J. Morgan, Douglas L. Abernathy, Ruixian Liu, Sijie Xu, Yuxiang Gao, Kevin Allen, Yuan Fang, Emilia Morosan, Qimiao Si, Pengcheng Dai

Abstract: Altermagnets are collinear magnetic materials with 'alter'nating local crystalline environments, characterized by joint spin and crystalline symmetries that enable ferromagnetic-like transport properties but with vanishing net magnetization. Hexagonal FeS (h-FeS) is a recently identified altermagnet candidate that shows a spontaneous anomalous Hall effect (AHE) accompanied by a tiny net magnetizat… ▽ More Altermagnets are collinear magnetic materials with 'alter'nating local crystalline environments, characterized by joint spin and crystalline symmetries that enable ferromagnetic-like transport properties but with vanishing net magnetization. Hexagonal FeS (h-FeS) is a recently identified altermagnet candidate that shows a spontaneous anomalous Hall effect (AHE) accompanied by a tiny net magnetization. Here, we show that both the spontaneous AHE and magnetization can be effectively suppressed by an in-plane compressive strain. Since neutron diffraction measurements show that the applied uniaxial strain only modifies the in-plane domain population but does not affect the in-plane magnetic structure, the major effect of the applied strain is to tune the small $c$-axis ferromagnetic moment. Our results demonstrate a strong correlation between the tiny net magnetization and the spontaneous AHE in h-FeS, and show that uniaxial strain provides an effective knob to tune both properties in this altermagnet candidate for spintronic applications. △ Less

Submitted 16 February, 2026; originally announced February 2026.

Journal ref: Advanced Materials (2026)

σh-Broken Induced Topological quasi-BIC

Authors: Yongqi Chen, Chaofeng Xie, Tongtong Zhu, Weiqiang Ding, Yurui Fang

Abstract: Transitions from bound states in the continuum (BICs) to quasi-BICs (qBICs) are typically realized by introducing in-plane asymmetry, including permittivity asymmetry (ε-qBICs) and geometry asymmetry (g-qBICs). Here, we demonstrate that when the in-plane symmetry is rigorously kept, the transition can also be occurred, provided the out-of-plane asymmetry is designed, which is called σh -qBICs in t… ▽ More Transitions from bound states in the continuum (BICs) to quasi-BICs (qBICs) are typically realized by introducing in-plane asymmetry, including permittivity asymmetry (ε-qBICs) and geometry asymmetry (g-qBICs). Here, we demonstrate that when the in-plane symmetry is rigorously kept, the transition can also be occurred, provided the out-of-plane asymmetry is designed, which is called σh -qBICs in this work. When the {σh symmetry is gradually broken, the system undergoes a topological phase transition characterized by a Zak phase inversion, leading to a band inversion between quadrupole and dipole modes. This process not only enables controlled radiation coupling of BICs but also introduces a defect-immune qBIC regime. Our findings establish a general mechanism for engineering high-Q resonances and topologically robust plasmonic cavities. △ Less

Submitted 21 January, 2026; originally announced January 2026.

Comments: 4 figures in article and 2 figures in SI. 22 pages including SI

MSC Class: 78-05

Iterative learning scheme for crystal structure prediction with anharmonic lattice dynamics

Authors: Hao Gao, Yue-Wen Fang, Ion Errea

Abstract: First-principles based crystal structure prediction (CSP) methods have revealed an essential tool for the discovery of new materials. However, in solids close to displacive phase transitions, which are common in ferroelectrics, thermoelectrics, charge-density wave systems, or superconducting hydrides, the ionic contribution to the free energy and lattice anharmonicity become essential, limiting th… ▽ More First-principles based crystal structure prediction (CSP) methods have revealed an essential tool for the discovery of new materials. However, in solids close to displacive phase transitions, which are common in ferroelectrics, thermoelectrics, charge-density wave systems, or superconducting hydrides, the ionic contribution to the free energy and lattice anharmonicity become essential, limiting the capacity of CSP techniques to determine the thermodynamical stability of competing phases. While variational methods like the stochastic self-consistent harmonic approximation (SSCHA) accurately account for anharmonic lattice dynamics \emph{ab initio}, their high computational cost makes them impractical for CSP. Machine-learning interatomic potentials offer accelerated sampling of the energy landscape compared to purely first-principles approaches, but their reliance on extensive training data and limited generalization restricts practical applications. Here, we propose an iterative learning framework combining evolutionary algorithms, atomic foundation models, and SSCHA to enable CSP with anharmonic lattice dynamics. Foundation models enable robust relaxations of random structures, drastically reducing required training data. Applied to the highly anharmonic H$_3$S system, our framework achieves good agreement with the benchmarks based on density functional theory, accurately predicting phase stability and vibrational properties from 50 to 200 GPa. Importantly, we find that the statistical averaging in the SSCHA reduces the error in the free energy evaluation, avoiding the need for extremely high accuracy of machine-learning potentials. This approach bridges the gap between data efficiency and predictive power, establishing a practical pathway for CSP with anharmonic lattice dynamics. △ Less

Submitted 23 December, 2025; originally announced December 2025.

Lattice-decoupled rotatable stripe-like charge order within the strange metal phase of 2M-WS2

Authors: Kebin Xiao, Yunkai Guo, Daran Fu, Yuqiang Fang, Yating Hu, Jingming Yan, Yucong Peng, Yuyang Wang, Yongkang Ju, Peizhe Tang, Xiangang Wan, Fuqiang Huang, Qi-Kun Xue, Wei Li

Abstract: In quantum materials, charge orders typically stabilize in specific crystallographic orientations, though their formation mechanisms may vary. Here, using low-temperature scanning tunneling microscopy (STM), we discover a lattice-decoupled rotatable stripe-like charge order coexisting with superconductivity in 2M-WS2. The charge order manifests five distinct orientations across different sample re… ▽ More In quantum materials, charge orders typically stabilize in specific crystallographic orientations, though their formation mechanisms may vary. Here, using low-temperature scanning tunneling microscopy (STM), we discover a lattice-decoupled rotatable stripe-like charge order coexisting with superconductivity in 2M-WS2. The charge order manifests five distinct orientations across different sample regions, yet maintains an identical wavelength. This directional decoupling from host lattice challenges existing paradigms. First-principles calculations of phonon spectra and nesting function fail to explain the ordering mechanism. Intriguingly, the transition temperature of the charge orders exhibits spatial variations (21-46 K), coinciding with the temperature range of the recently reported strange metal phase in this material. This correlation suggests that the interplay between strong electronic correlations and electron-phonon coupling must be critically evaluated to elucidate the emergence of this unconventional charge order. △ Less

Submitted 20 December, 2025; originally announced December 2025.

Comments: 12 pages, 5 figures. This article was published on PNAS (https://doi.org/10.1073/pnas.2513493122)

High-Tc superconductivity above 130 K in cubic MH4 compounds at ambient pressure

Authors: Xinxin Li, Weishuo Xu, Zengguang Zhou, Jingming Shi, Hanyu Liu, Yue-Wen Fang, Wenwen Cui, Yinwei Li, Miguel A. L. Marques

Abstract: Hydrides have long been considered promising candidates for achieving room-temperature superconductivity; however, the extremely high pressures typically required for high critical temperatures remain a major challenge in experiment. Here, we propose a class of high-Tc ambient-pressure superconductors with MH4 stoichiometry. These hydrogen-based compounds adopt the bcc PtHg4 structure type, in whi… ▽ More Hydrides have long been considered promising candidates for achieving room-temperature superconductivity; however, the extremely high pressures typically required for high critical temperatures remain a major challenge in experiment. Here, we propose a class of high-Tc ambient-pressure superconductors with MH4 stoichiometry. These hydrogen-based compounds adopt the bcc PtHg4 structure type, in which hydrogen atoms occupy the one-quarter body-diagonal sites of metal lattices, with the metal atoms acting as chemical templates for hydrogen assembly. Through comprehensive first-principles calculations, we identify three promising superconductors, PtH4, AuH4 and PdH4, with superconducting critical temperatures of 84 K, 89 K, and 133 K, respectively, all surpassing the liquid-nitrogen temperature threshold of 77 K. The remarkable superconducting properties originate from strong electron-phonon coupling associated with hydrogen vibrations, which in turn arise from phonon softening in the mid-frequency range. Our results provide crucial insights into the design of high-Tc superconductors suitable for future experiments and applications at ambient pressure. △ Less

Submitted 6 November, 2025; originally announced November 2025.

Comments: 9 pages, 5 figures

Direct Observation and Optical Manipulation of Exciton-polariton Parametric Scattering Lasing in Temporal

Authors: Junxing Dong, Si Shen, Jingzhuo Wang, Lisheng Wang, Yifan Zhang, Huashan Li, Xianghu Wang, Wei Gao, Yongzheng Fang, Hai Zhu

Abstract: The hybrid light-matter character of exciton-polaritons gives rise to distinct polariton parametric scattering (PPS) process, which holds promise for frontier applications in polaritonic quantum devices. However, the stable excitation and coherent optical manipulation of PPS remain challenging due to scattering bottlenecks and rapid dephasing effect in polariton many-body systems. In this study, w… ▽ More The hybrid light-matter character of exciton-polaritons gives rise to distinct polariton parametric scattering (PPS) process, which holds promise for frontier applications in polaritonic quantum devices. However, the stable excitation and coherent optical manipulation of PPS remain challenging due to scattering bottlenecks and rapid dephasing effect in polariton many-body systems. In this study, we first report the direct observation and optical amplification of non-degenerate intermode PPS lasing at room temperature (RT). The specific polariton branch of strong-coupled nanobelt planar microcavity is resonantly excited by a near-infrared (NIR) femtosecond laser via two-photon absorption (TPA) scheme, and the non-degenerate signal- and idler-states are stimulated. Angle-resolved dispersion patterns clearly reveal the evolution of the pump-, signal-, and idler-states under different excitation powers. Based on our self-constructed ultrafast femtosecond resonant optical trigger set-up, a selective enhancement and modulation of the signal-state is realized. Furthermore, the dynamic measurements of nonlinear signal-state enhancement process demonstrate a sub-picosecond response time (0.4ps), confirming its potential for ultrafast optical manipulation. Our work establishes a platform for exploring TPA-driven PPS laser and provides a novel optical modulation route for polariton-based optoelectronic devices. △ Less

Submitted 31 October, 2025; originally announced November 2025.

Spin-polarized chiral ZnIn2S4 for targeted solar-driven CO2 reduction to acetic acid

Authors: Yongping Cui, Yuanbo Li, Zhi-qiang Wang, Xueliang Zhang, Lu Han, Xueli Wang, Jinquan Chen, Aokun Liu, Lu Yu, Changlin Tian, Xue-qing Gong, Wanning Zhang, Yuxi Fang

Abstract: Acetic acid, an important industrial chemical, is a key target product for CO2 reduction due to its dual role in carbon utilization and chemical feedstock supply. Although photocatalytic CO2 reduction (PCCR) can generate acetic acid alongside other multicarbon products, its yield is typically low, limited by competing reactions and inefficient C-C coupling. Herein, we report a chiral mesostructure… ▽ More Acetic acid, an important industrial chemical, is a key target product for CO2 reduction due to its dual role in carbon utilization and chemical feedstock supply. Although photocatalytic CO2 reduction (PCCR) can generate acetic acid alongside other multicarbon products, its yield is typically low, limited by competing reactions and inefficient C-C coupling. Herein, we report a chiral mesostructured ZnIn2S4 (CMZI) photocatalyst that achieves a remarkable acetic acid yield of 962 {umol g-1 h-1 with a high selectivity of 97.3 %. This yield is ten times higher than the current highest reported value, while attaining state-of-the-art selectivity10. The remarkable productivity arises from synergistic effect between chiral structure and sulfur (S) sites of CMZI. Chirality-induced spin polarization in CMZI stabilizes the key triplet OCCO intermediate, significantly promoting C-C coupling efficiency. Theoretical calculations reveal that the S sites on {102} crystal facets of ZnIn2S4 exhibit thermodynamic and kinetic preferences for acetic acid formation. This work offers critical insights into catalytic strategies for CO2 reduction toward the efficient and scalable synthesis of various multicarbon products. △ Less

Submitted 5 October, 2025; v1 submitted 20 September, 2025; originally announced September 2025.

Comments: 9 pages, 4 figures

Interaction-driven quantum criticality in two-dimensional quadratic band crossing semimetals with time-reversal symmetry breaking

Authors: Yi-Kun Fang, Jing Wang

Abstract: We present a systematic investigation of all sixteen marginally relevant fermion-fermion interactions in two-dimensional time-reversal symmetry-breaking kagomé semimetals hosting a quadratic band crossing point. Employing a momentum-shell renormalization group approach that treats every interaction on equal footing, we derive energy-dependent flow equations that capture the hierarchical evolutions… ▽ More We present a systematic investigation of all sixteen marginally relevant fermion-fermion interactions in two-dimensional time-reversal symmetry-breaking kagomé semimetals hosting a quadratic band crossing point. Employing a momentum-shell renormalization group approach that treats every interaction on equal footing, we derive energy-dependent flow equations that capture the hierarchical evolutions of interaction parameters. Our analysis begins by tracking the energy-dependent flows of fermion-fermion interactions. The interaction couplings go towards divergence at a critical energy scale, signaling quantum critical behavior. Such behavior is characterized by a certain fixed point (FP) whose characteristics depends intimately on structural parameters $d_{0,1,2,3}$ that cluster the microscopic model into rotationally symmetric and asymmetric cases. Then, we identify two stable FPs in the rotationally symmetric and nine additional FPs in asymmetric case dubbed FP$_{1-10}$. Their boundary conditions are approximately demarcated and established by linear and plane fitting techniques in the structural parameter space. Furthermore, we examine distinct interaction-driven instabilities nearby these FPs by incorporating the relevant external source terms and computing their susceptibilities. It indicates that the charge density wave and superconductivity become dominant at FP$_{2,4,5,6,8}$ and FP$_{1,9,10}$, while the $x$-current and bond density prevail at FP$_3$ and FP$_7$, respectively. In addition to these leading states, several underlying subordinate instabilities are presented as well. These results would be helpful to further study the low-energy critical behavior in 2D kagomé QBCP and related materials. △ Less

Submitted 26 October, 2025; v1 submitted 5 September, 2025; originally announced September 2025.

Comments: 25 pages, 18 figures

Photonic restricted Boltzmann machine for content generation tasks

Authors: Li Luo, Yisheng Fang, Wanyi Zhang, Zhichao Ruan

Abstract: The restricted Boltzmann machine (RBM) is a neural network based on the Ising model, well known for its ability to learn probability distributions and stochastically generate new content. However, the high computational cost of Gibbs sampling in content generation tasks imposes significant bottlenecks on electronic implementations. Here, we propose a photonic restricted Boltzmann machine (PRBM) th… ▽ More The restricted Boltzmann machine (RBM) is a neural network based on the Ising model, well known for its ability to learn probability distributions and stochastically generate new content. However, the high computational cost of Gibbs sampling in content generation tasks imposes significant bottlenecks on electronic implementations. Here, we propose a photonic restricted Boltzmann machine (PRBM) that leverages photonic computing to accelerate Gibbs sampling, enabling efficient content generation. By introducing an efficient encoding method, the PRBM eliminates the need for computationally intensive matrix decomposition and reduces the computational complexity of Gibbs sampling from $O(N)$ to $O(1)$. Moreover, its non-Von Neumann photonic computing architecture circumvents the memory storage of interaction matrices, providing substantial advantages for large-scale RBMs. We experimentally validate the photonic-accelerated Gibbs sampling by simulating a two-dimensional Ising model, where the observed phase transition temperature closely matches the theoretical predictions. Beyond physics-inspired tasks, the PRBM demonstrates robust capabilities in generating and restoring diverse content, including images and temporal sequences, even in the presence of noise and aberrations. The scalability and reduced training cost of the PRBM framework underscore its potential as a promising pathway for advancing photonic computing in generative artificial intelligence. △ Less

Submitted 28 August, 2025; originally announced August 2025.

Comments: 9 pages, 5 figures

Journal ref: Physical Review X (2026)

Search for thermodynamically stable ambient-pressure superconducting hydrides in GNoME database

Authors: Antonio Sanna, Tiago F. T. Cerqueira, Ekin Dogus Cubuk, Ion Errea, Yue-Wen Fang

Abstract: Hydrides are considered to be one of the most promising families of compounds for achieving high temperature superconductivity. However, there are very few experimental reports of ambient-pressure hydride superconductivity, and the superconducting critical temperatures ($T_{\rm c}$) are typically less than 10 K. At the same time several hydrides have been predicted to exhibit superconductivity aro… ▽ More Hydrides are considered to be one of the most promising families of compounds for achieving high temperature superconductivity. However, there are very few experimental reports of ambient-pressure hydride superconductivity, and the superconducting critical temperatures ($T_{\rm c}$) are typically less than 10 K. At the same time several hydrides have been predicted to exhibit superconductivity around 100 K at ambient pressure but in thermodynamically unfavorable phases. In this work we aim at assessing the superconducting properties of thermodynamically stable hydride superconductors at room pressure by investigating the GNoME material database, which has been recently released and includes thousands of hydrides thermodynamically stable at 0K. To scan this large material space we have adopted a multi stage approach which combines machine learning for a fast initial evaluation and cutting edge ab initio methods to obtain a reliable estimation of ($T_{\rm c}$). Ultimately we have identified 25 cubic hydrides with ($T_{\rm c}$) above 4.2~K and reach a maximum ($T_{\rm c}$) of 17 K. While these critical temperatures are modest in comparison to some recent predictions, the systems where they are found, being stable, are likely to be experimentally accessible and of potential technological relevance. △ Less

Submitted 17 March, 2026; v1 submitted 27 August, 2025; originally announced August 2025.

Comments: 11 pages, 5 figures in main text

Journal ref: Commun Phys 9, 94 (2026)

Control of magnetic transition, metal-semiconductor transition, and magnetic anisotropy in noncentrosymmetric monolayer Cr$_2$Ge$_2$Se$_3$Te$_3$

Authors: Rui-Qi Wang, Tengfei Cao, Tian-Min Lei, Xie Zhang, Yue-Wen Fang

Abstract: Recent advances in two-dimensional materials have greatly expanded the family of ferromagnetic materials. The well-known 2D ferromagnets, such as CrI$_3$, Cr$_2$Ge$_2$Te$_6$, and Fe$_3$GeTe$_2$ monolayers, are characterized by centrosymmetric crystal structures. In contrast, ferromagnetic ordering in 2D noncentrosymmetric materials remains an underexplored area. Here we report a Janus ferromagnet,… ▽ More Recent advances in two-dimensional materials have greatly expanded the family of ferromagnetic materials. The well-known 2D ferromagnets, such as CrI$_3$, Cr$_2$Ge$_2$Te$_6$, and Fe$_3$GeTe$_2$ monolayers, are characterized by centrosymmetric crystal structures. In contrast, ferromagnetic ordering in 2D noncentrosymmetric materials remains an underexplored area. Here we report a Janus ferromagnet, Cr$_2$Ge$_2$Se$_3$Te$_3$ with inversion symmetry breaking, through first-principles calculations. This monolayer can undergo a ferromagnetic-antiferromagnetic transformation and a metal-semiconductor transition under different strains. Additionally, the strength of magnetocrystalline anisotropy energy (MAE) can be modulated by electric field or strain. In particular, the magnetization easy axis can be altered from in-plane to out-of-plane under strain. We find that Te$_3$ atoms play a key role in determining the MAE, where contributions are primarily from $p_z / p_y$ and $p_x / p_y$ orbitals. This study of Janus ferromagnetic materials has provided a promising platform for the research on the control of magnetism by strain or electric field. △ Less

Submitted 16 August, 2025; originally announced August 2025.

Comments: 11 pages, 5 figures in main text and 5 figures in supplementary

Journal ref: Appl. Phys. Lett. 127, 092402 (2025)

A Comprehensive Study on A$_2$PdH$_2$: From Ambient to High Pressure

Authors: Zahra Alizadeh, Yue-Wen Fang, Ion Errea, M. R. Mohammadizadeh

Abstract: We present a comprehensive first--principles study of the structural stability and superconducting behavior of Li$_2$PdH$_2$ under high pressure. Using random structure searching and phonon calculations, we identify a pressure--induced phase transition from a tetragonal I4/mmm structure, stable up to 5 GPa, to a monoclinic C2/m phase that remains thermodynamically stable up to 50 GPa. Superconduct… ▽ More We present a comprehensive first--principles study of the structural stability and superconducting behavior of Li$_2$PdH$_2$ under high pressure. Using random structure searching and phonon calculations, we identify a pressure--induced phase transition from a tetragonal I4/mmm structure, stable up to 5 GPa, to a monoclinic C2/m phase that remains thermodynamically stable up to 50 GPa. Superconductivity is absent in the tetragonal phase, even when anharmonic effects are considered, due to weak electron--phonon coupling and limited hydrogen involvement near the Fermi level. In contrast, the monoclinic phase exhibits a weak but pressure-enhanced superconducting transition, with Tc increasing from 0.6 K at 10 GPa to 4.7 K at 50 GPa, mainly driven by low--frequency Li and Pd-derived phonon modes. We further explore the isostructural A$_2$PdH$_2$ (A = Na, K, Rb, Cs) series to evaluate the impact of alkali-metal substitution on stability and superconductivity. Na, K, and Rb analogs retain dynamic stability at ambient pressure, with weak superconducting critical temperatures of 3.2 K, 2.1 K, and negligible Tc, respectively. Cs$_2$PdH$_2$, however, exhibits phonon instabilities, suggesting a need for external stabilization. These findings highlight the delicate balance between lattice dynamics, electronic structure, and atomic mass in tuning superconductivity in palladium-based hydrides. △ Less

Submitted 6 August, 2025; originally announced August 2025.

Unveiling quantum criticality of disordered Aubry-André-Harper models via typical fidelity susceptibility

Authors: Tian-Cheng Yi, Ying-Ying Fang, Wen Chen, Wen-Long You, Yunbo Zhang

Abstract: In this study, we investigate the localization transition and quantum criticality {in the ground state of the} disordered Aubry-André-Harper (AAH) model, where a quasiperiodic potential is hybridized with a disordered potential. In the clean limit, the AAH model undergoes a localization transition from an extended phase to a localized phase via an intermediate critical phase as the strength of the… ▽ More In this study, we investigate the localization transition and quantum criticality {in the ground state of the} disordered Aubry-André-Harper (AAH) model, where a quasiperiodic potential is hybridized with a disordered potential. In the clean limit, the AAH model undergoes a localization transition from an extended phase to a localized phase via an intermediate critical phase as the strength of the quasiperiodic potential is varied. While the staggered potential merely shifts the critical point to a lower value, Fibonacci and Thue-Morse potentials induce immediate localization. This contrast reveals the sensitivity of localization behavior to the structural complexity of the potential, with the onset of localization correlating with the sequence's complexity. More specifically, the system follows a hierarchy defined by the complexity measures of the applied potentials. In addition, the typical fidelity susceptibility exhibits a power-law scaling behavior at the localization transition, enabling reliable extraction of the critical exponent. We focus on the AAH model with the Fibonacci potential due to its minimal finite-size effects compared to other cases. For the disordered AAH model with the Fibonacci potential, we determine critical exponents that differ from those of the AAH model without disorder and the Anderson model. Moreover, despite differences in localization behavior, we find that the disordered AAH models with the staggered potential and the Fibonacci potential share the same correlation-length critical exponent. These findings provide a unified framework for understanding localization transitions in quasiperiodic systems and are amenable to experimental validation using emerging techniques. △ Less

Submitted 6 August, 2025; originally announced August 2025.

Comments: 8 pages, 7 figures

Journal ref: Phys. Rev. A 112, 023308 (2025)

Ultralow thermal conductivity via weak interactions in PbSe/PbTe monolayer heterostructure for thermoelectric design

Authors: Ruihao Tan, Kaiwang Zhang, Yue-Wen Fang

Abstract: In this study, we systematically investigate the thermal and electronic transport properties of two-dimensional PbSe/PbTe monolayer heterostructure by combining first-principles calculations, Boltzmann transport theory, and machine learning methods. The heterostructure exhibits a unique honeycomb-like corrugated and asymmetric configuration, which significantly enhances phonon scattering. Moreover… ▽ More In this study, we systematically investigate the thermal and electronic transport properties of two-dimensional PbSe/PbTe monolayer heterostructure by combining first-principles calculations, Boltzmann transport theory, and machine learning methods. The heterostructure exhibits a unique honeycomb-like corrugated and asymmetric configuration, which significantly enhances phonon scattering. Moreover, the relatively weak interatomic interactions in PbSe/PbTe lead to the formation of anti-bonding states, resulting in strong anharmonicity and ultimately yielding ultralow lattice thermal conductivity (${κ_{\rm L}}$). In the four-phonon scattering model, the ${κ_{\rm L}}$~values along the $x$ and $y$ directions are as low as 0.37 and 0.31 W/mK, respectively. Contrary to the conventional view that long mean free path acoustic phonons dominate heat transport, we find that optical phonons contribute approximately 59\% of the lattice thermal conductivity in this heterostructure. These optical phonons exhibit large Grüneisen parameters, strong anharmonic scattering, and relatively high group velocities, thereby playing a crucial role in the low ${κ_{\rm L}}$ regime. Further analysis of thermoelectric performance shows that at a high temperature of 800 K, the heterostructure achieves an exceptional dimensionless figure of merit ($ZT$) of 5.3 along the $y$ direction, indicating outstanding thermoelectric conversion efficiency. These findings not only provide theoretical insights into the transport mechanisms of PbSe/PbTe monolayer heterostructure but also offer a practical design strategy for developing high-performance two-dimensional layered thermoelectric materials. △ Less

Submitted 29 July, 2025; originally announced July 2025.

Comments: 46 pages, 22 figures (15 in main text, and other 7 ones in the appendix)

Journal ref: J. Mater. Inf. 2025, 5, 56

Superconductivity in RbH$_{12}$ at low pressures: an \emph{ab initio} study

Authors: Đorđe Dangić, Manex Alkorta, Yuewen Fang, Ion Errea

Abstract: High-pressure polyhydrides are leading contenders for room temperature superconductivity. The next frontier lies in stabilizing them at ambient pressure, which would allow their practical applications. In this first-principles computational study, we investigate the potential for record-low pressure stabilization of binary superhydrides within the RbH$_{12}$ system including lattice quantum anharm… ▽ More High-pressure polyhydrides are leading contenders for room temperature superconductivity. The next frontier lies in stabilizing them at ambient pressure, which would allow their practical applications. In this first-principles computational study, we investigate the potential for record-low pressure stabilization of binary superhydrides within the RbH$_{12}$ system including lattice quantum anharmonic effects in the calculations. We identify five competing phases for the pressure range between 0 and 100 GPa. Incorporating anharmonic and quantum effects on ion dynamics, we find the $Immm$ and $P6_3/mmc$ phases to be the most probable, potentially metastable even at pressures as low as 10 GPa. Notably, all phases exhibit metallic properties, with critical temperatures between 46 and 111 K within the pressure range they are dynamically stable. These findings have the potential to inspire future experimental exploration of high-temperature superconductivity at low pressures in Rb-H binary compounds. △ Less

Submitted 15 May, 2026; v1 submitted 16 July, 2025; originally announced July 2025.

Revealing THz optical signatures of Shiba-state-induced gapped and gapless superconductivity

Authors: F. Yang, R. Y. Fang, S. L. Zhang, L. Q. Chen

Abstract: We report a fully self-consistent calculation of the complex renormalization by exchange interactions and hence the complete phase diagram of conventional $s$-wave superconductors with magnetic impurities as well as the related physical properties including the optical response. We show that a small amount of magnetic disorder can drive the system into a gapless superconducting state, where the si… ▽ More We report a fully self-consistent calculation of the complex renormalization by exchange interactions and hence the complete phase diagram of conventional $s$-wave superconductors with magnetic impurities as well as the related physical properties including the optical response. We show that a small amount of magnetic disorder can drive the system into a gapless superconducting state, where the single-particle excitation gap vanishes whereas the superconducting order parameter $Δ_0$ remains finite. In this phase, the linear optical conductivity exhibits a finite absorption over the low-frequency regime, particularly for photon energies below the conventional threshold $2|Δ_0|$, even at low temperatures, in sharp contrast to the gapped state. The nonlinear response, however, remains coherent and is dominated by the Higgs-mode dynamics rather than gapless quasiparticle background. These findings reveal a fundamental distinction between dissipative single-particle excitations and coherent collective dynamics of the condensate, a feature likely general to other gapless superconductors, and introduces a fundamentally different detection scheme, using THz spectroscopy to probe the signatures of Shiba states. △ Less

Submitted 3 February, 2026; v1 submitted 7 July, 2025; originally announced July 2025.

Photomagnetic-Chiral Anisotropy mediated by Chirality-Driven Asymmetric Spin Splitting

Authors: Tianwei Ouyang, Hang Su, Wanning Zhang, Yingying Duan, Yuxi Fang, Shunai Che, Yizhou Liu

Abstract: Photo-magnetic effects (PMEs), intrinsic to transition metals, arises from the interaction between light-induced angu-lar momentum and electronic spin. These effects are suppressed in noble metals with high symmetry and electron density. Introducing chiral structures can induce photomagnetic-chiral anisotropy (PM-ChA) of metals by linking chirality and spin dynamics. However, a theoretical explain… ▽ More Photo-magnetic effects (PMEs), intrinsic to transition metals, arises from the interaction between light-induced angu-lar momentum and electronic spin. These effects are suppressed in noble metals with high symmetry and electron density. Introducing chiral structures can induce photomagnetic-chiral anisotropy (PM-ChA) of metals by linking chirality and spin dynamics. However, a theoretical explain remains elusive. Here, we investigated the mechanism of PM-ChA in tetrahelix-stacked chiral nanostructured gold chains (CNACs) using first-principles calculations. Non-equilibrium Green's function calculations reveal that chiral potentials enhance spin channel asymmetry by amplify-ing spin-orbit coupling (SOC)-induced spin splitting. Real-time time-dependent density functional theory simulations further identify SOC as the bridge connecting chiral spintronics to PME, where chirality-driven spin flips from asymmetric geometries generate opposing photomagnetic fields in materials of different handedness. These findings are consistent with experimental observations in chiral nanostructured gold films and provide a theoretical instruction for design metallic spintronic devices. △ Less

Submitted 16 June, 2025; originally announced June 2025.

Comments: 19 pages, 16 figures

Journal ref: Phys. Rev. Lett. 135, 166903 (2025)

Nonlinear thermal and thermoelectric transport from quantum geometry

Authors: Yuan Fang, Shouvik Sur, Yonglong Xie, Qimiao Si

Abstract: Quantum geometry may enable the development of quantum phases ranging from superconductivity to correlated topological states. One powerful probe of quantum geometry is the nonlinear Hall response which detects Berry curvature dipole in systems with time-reversal invariance and broken inversion symmetry. With broken time-reversal symmetry, this response is also associated with quantum metric dipol… ▽ More Quantum geometry may enable the development of quantum phases ranging from superconductivity to correlated topological states. One powerful probe of quantum geometry is the nonlinear Hall response which detects Berry curvature dipole in systems with time-reversal invariance and broken inversion symmetry. With broken time-reversal symmetry, this response is also associated with quantum metric dipole. Here we investigate nonlinear thermal and thermoelectric responses, which provide a wealth of new information about quantum geometry. In particular, we uncover a web of connections between these quantities that parallel the standard Wiedemann-Franz and Mott relations. Implications for the studies of a variety of topological systems, including Weyl-Kondo semimetals and Bernal bilayer graphene, are discussed. △ Less

Submitted 8 May, 2026; v1 submitted 22 May, 2025; originally announced May 2025.

Comments: 7+15 pages, 2+7 figures

Synthetic gauge field enabled realization of bulk- and edge-transported states in an aperiodic acoustic structure

Authors: Y. X. Fang, W. H. Zhu, Y. Cai, X. H. Li, M. Q. Zhang, J. Huang, Y. Li, S. Q. Wu

Abstract: Topologically protected edge states with immunity against various disorders have been implemented in a variety of topological insulators. In this Letter, we reveal that Landau levels in aperiodic acoustic structures can be achieved under different pseudomagnetic fields (PMFs). The produced zero order Landau modes (ZOLMs) could transmit along the channels at the interior or exterior of the inhomoge… ▽ More Topologically protected edge states with immunity against various disorders have been implemented in a variety of topological insulators. In this Letter, we reveal that Landau levels in aperiodic acoustic structures can be achieved under different pseudomagnetic fields (PMFs). The produced zero order Landau modes (ZOLMs) could transmit along the channels at the interior or exterior of the inhomogeneous array, which are separately termed as "bulk-transported states" (BTSs) and "edge-transported states" (ETSs). Distinct from conventional valley edge states, the ZOLMs show intriguing self-collimation feature. If a pseudoelectric field (PEF) is further included, the combination of a PMF and PEF can result in the formation of bulk or edge Landau rainbow, where Landau zero modes are distributed at various positions of the bulk or boundary of the sample at different frequencies. The synthetic-gauge-field-controlled topological states can enable fully control of robust transmission, and using the entire footprint of a topological lattice. Our findings not only profoundly advance the current understanding of topological phase matter but also offer new avenues for constructing topological acoustic devices. △ Less

Submitted 9 May, 2025; originally announced May 2025.

Comments: 19 pages, 7 figures

Emergent heavy-fermion physics in a new family of topological insulators RAsS (R = Y, La, and Sm)

Authors: Iñigo Robredo, Yuan Fang, Lei Chen, Nazar Zaremba, Yurii Prots, Mitja Krnel, Markus König, Thomas Doert, Jeroen van den Brink, Claudia Felser, Qimiao Si, Eteri Svanidze, Maia G. Vergniory

Abstract: Realizing topological phases in strongly correlated materials has become a major impetus in condensed matter physics. Although many compounds are now classified as topological insulators, $f$-electron systems (with their strong electron correlations) provide an especially fertile platform for emergent heavy-fermion phenomena driven by the interplay of topology and many-body effects. In this study,… ▽ More Realizing topological phases in strongly correlated materials has become a major impetus in condensed matter physics. Although many compounds are now classified as topological insulators, $f$-electron systems (with their strong electron correlations) provide an especially fertile platform for emergent heavy-fermion phenomena driven by the interplay of topology and many-body effects. In this study, we examine the crystalline topology of a new RAsS series (R = Y, La, Sm), revealing a structural variant from previous reports. We demonstrate that YAsS and SmAsS host hourglass fermions protected by glide symmetry. SmAsS notably exhibits a strong effective-mass enhancement, placing it alongside SmB${}_6$ and YbB${}_{12}$ as a material that couples topological surface states with emergent Kondo physics, yet distinguished by its crystalline symmetry constraints and $f$-$p$ orbital hybridization. To capture these features, we construct a minimal model incorporating $f$-electron degrees of freedom, which reproduces the observed topological properties and predicts that the surface states survive in the correlated regime, albeit shifted in energy. Our work thus introduces a new family of correlated topological materials and forecasts the robustness of their surface states under Kondo correlations. △ Less

Submitted 2 May, 2025; originally announced May 2025.

Comments: Main text: 11 pages, 5 figures. Supplementary material: 5 pages, 2 figures

Reshaping MOFs text mining with a dynamic multi-agents framework of large language model

Authors: Zuhong Lin, Daoyuan Ren, Kai Ran, Jing Sun, Songlin Yu, Xuefeng Bai, Xiaotian Huang, Haiyang He, Pengxu Pan, Ying Fang, Zhanglin Li, Haipu Li, Jingjing Yao

Abstract: Accurately identifying the synthesis conditions of metal-organic frameworks (MOFs) is essential for guiding experimental design, yet remains challenging because relevant information in the literature is often scattered, inconsistent, and difficult to interpret. We present MOFh6, a large language model driven system that reads raw articles or crystal codes and converts them into standardized synthe… ▽ More Accurately identifying the synthesis conditions of metal-organic frameworks (MOFs) is essential for guiding experimental design, yet remains challenging because relevant information in the literature is often scattered, inconsistent, and difficult to interpret. We present MOFh6, a large language model driven system that reads raw articles or crystal codes and converts them into standardized synthesis tables. It links related descriptions across paragraphs, unifies ligand abbreviations with full names, and outputs structured parameters ready for use. MOFh6 achieved 99% extraction accuracy, resolved 94.1% of abbreviation cases across five major publishers, and maintained a precision of 0.93 +/- 0.01. Processing a full text takes 9.6 s, locating synthesis descriptions 36 s, with 100 papers processed for USD 4.24. By replacing static database lookups with real-time extraction, MOFh6 reshapes MOF synthesis research, accelerating the conversion of literature knowledge into practical synthesis protocols and enabling scalable, data-driven materials discovery. △ Less

Submitted 20 February, 2026; v1 submitted 26 April, 2025; originally announced April 2025.

Comments: Accepted by TRAMAT 2 (2026) 100176

Journal ref: Transactions of Materials Research, 2026, 2(1), 100176

Interplay between trimer structure and magnetic ground state in Ba5Ru3O12 probed by Neutron and muSR techniques

Authors: E. Kushwaha, S. Ghosh, J. Sannigrahi, G. Roy, M. Kumar, S. Cottrell, M. B. Stone, Y. Fang, D. T. Adroja, X. Ke, T. Basu

Abstract: We report a detailed inelastic neutron scattering (INS) and muon spin relaxation (muSR) investigation of a trimer Ruthenate Ba5Ru3O12 system, which undergoes long-range antiferromagnetic ordering at TN = 60 K. The INS reveals two distinct spin wave excitations below TN: one at 5.6 meV and the other at 10-15 meV. By accompanying the INS spectra based on a linear spin wave theory using SpinW softwar… ▽ More We report a detailed inelastic neutron scattering (INS) and muon spin relaxation (muSR) investigation of a trimer Ruthenate Ba5Ru3O12 system, which undergoes long-range antiferromagnetic ordering at TN = 60 K. The INS reveals two distinct spin wave excitations below TN: one at 5.6 meV and the other at 10-15 meV. By accompanying the INS spectra based on a linear spin wave theory using SpinW software and machine learning force fields (MLFFs), we show that Ba5Ru3O12 exhibits spin frustration due to competing exchange interactions between neighboring and next-neighboring Ru-moments, exchange anisotropy, and strong spin-orbit coupling, which yields a non-collinear spin structure, in contrast to other ruthenate trimers in this series. Interestingly, these magnetic excitations do not completely vanish even at high temperatures above TN, evidencing short-range magnetic correlations in this trimer system. This is further supported by muSR spectroscopy, which exhibits a gradual drop in the initial asymmetry around the magnetic phase transition and is further verified through maximum entropy analysis. The results of muSR spectroscopy indicate a dynamic nature of magnetic order, attributed to local magnetic anisotropy within the trimer as a result of local structural distortion and different hybridization, consistent with canted spin-structure. We predict the ground state of Ru3O12-isolated trimer through theoretical calculations, which agree with the experimentally observed spin excitation △ Less

Submitted 14 August, 2025; v1 submitted 8 April, 2025; originally announced April 2025.

Journal ref: Physical Review B, 2025 (INS, muon-SR, spinW, AIML)

Correlated flat-band physics in a bilayer kagome metal based on compact molecular orbitals

Authors: Mounica Mahankali, Fang Xie, Yuan Fang, Lei Chen, Shouvik Sur, Silke Paschen, Jean C. Souza, Moshe Haim, Ambikesh Gupta, Nurit Avraham, Haim Beidenkopf, Hengxin Tan, Binghai Yan, Qimiao Si

Abstract: Flat bands, when located close to the Fermi energy, can considerably enhance the influence of electron correlations on the low energy physics in kagome and other frustrated-lattice metals. A major challenge in describing the interaction effects in such bulk materials is that the flat band is often intermixed with a large number of other bands. Here we show that the recently introduced notion of co… ▽ More Flat bands, when located close to the Fermi energy, can considerably enhance the influence of electron correlations on the low energy physics in kagome and other frustrated-lattice metals. A major challenge in describing the interaction effects in such bulk materials is that the flat band is often intermixed with a large number of other bands. Here we show that the recently introduced notion of compact molecular orbitals (CMOs) enable a path forward in describing the dominant effect of the Coulomb interactions in spite of the complexity of the bandstructure. Our materials-based analysis allows for the understanding of the scanning-tunneling-microscopy experiment [J. C. Souza et al., preprint (2024)] of the bilayer kagome metal Ni$_3$In in terms of the CMO notion. From the resulting CMO, an effective Anderson lattice model can be set up. This CMO-based approach enables the calculation of correlation effects that is difficult to do based on the atomic orbitals. Furthermore, it suggests an enriched phase diagram for the strange metal physics of the kagome metal, which can be tested by future experiments. We discuss the implications of our results for the general correlation physics of flat band systems and beyond. △ Less

Submitted 12 March, 2025; originally announced March 2025.

Comments: 6 + 5 pages, 4 + 5 figures

Resolving the Kagome Origin of the Strange Metallicity in Ni$_3$In

Authors: Jean C. Souza, Moshe Haim, Ambikesh Gupta, Mounica Mahankali, Fang Xie, Yuan Fang, Lei Chen, Shiang Fang, Hengxin Tan, Minyong Han, Caolan John, Jingxu Zheng, Yiwen Liu, Binghai Yan, Joseph G. Checkelsky, Qimiao Si, Nurit Avraham, Haim Beidenkopf

Abstract: Strong correlations promote singular properties such as strange metallicity, which shows considerable commonality across quantum materials platforms. Understanding the mechanism for such emerging universality is an outstanding challenge, given that the underlying degrees of freedom can be complex and varied. Progress may be made in flat band systems, especially kagome and other frustrated-lattice… ▽ More Strong correlations promote singular properties such as strange metallicity, which shows considerable commonality across quantum materials platforms. Understanding the mechanism for such emerging universality is an outstanding challenge, given that the underlying degrees of freedom can be complex and varied. Progress may be made in flat band systems, especially kagome and other frustrated-lattice metals with active flat bands. These systems show strange metal behavior that bears a striking resemblance to what happens in heavy-fermion metals. Here, in scanning tunneling spectroscopy of kagome metal Ni$_3$In, we find a zero-bias peak-dip structure whose variation with magnetic field and temperature tracks the evolution of the strange metal properties. We identify the origin of the peak as compact molecular orbitals formed by destructive interference over the kagome sites, resulting in emergent $f$-shell-like localized moments. Using quasi-particle interference, we visualize their interaction with the Dirac light bands. We thus unveil the essential microscopic ingredients of the $d$-electron-based kagome metals that, while distinct from the atomic orbitals of the $f$-electron-based heavy fermion materials, are responsible for a shared phenomenology between the two types of systems. Our findings provide a new window to uncover and interconnect the essential and yet diverse microscopic building blocks in disparate families of quantum materials that drive a convergence towards a universal understanding in the regime of amplified quantum fluctuations. △ Less

Submitted 12 March, 2025; originally announced March 2025.

Comments: 18 pages, 4 figures

The Maximum $T_c$ of Conventional Superconductors at Ambient Pressure

Authors: Kun Gao, Tiago F. T. Cerqueira, Antonio Sanna, Yue-Wen Fang, Đorđe Dangić, Ion Errea, Hai-Chen Wang, Silvana Botti, Miguel A. L. Marques

Abstract: The theoretical maximum critical temperature ($T_c$) for conventional superconductors at ambient pressure remains a fundamental question in condensed matter physics. Through analysis of electron-phonon calculations for over 20,000 metals, we critically examine this question. We find that while hydride metals can exhibit maximum phonon frequencies of more than 5000 K, the crucial logarithmic averag… ▽ More The theoretical maximum critical temperature ($T_c$) for conventional superconductors at ambient pressure remains a fundamental question in condensed matter physics. Through analysis of electron-phonon calculations for over 20,000 metals, we critically examine this question. We find that while hydride metals can exhibit maximum phonon frequencies of more than 5000 K, the crucial logarithmic average frequency $ω_\text{log}$ rarely exceeds 1800 K. Our data reveals an inherent trade-off between $ω_\text{log}$ and the electron-phonon coupling constant $λ$, suggesting that the optimal Eliashberg function that maximizes $T_c$ is unphysical. Based on our calculations, we identify Li$_2$AgH$_6$ and its sibling Li$_2$AuH$_6$ as theoretical materials that likely approach the practical limit for conventional superconductivity at ambient pressure. Analysis of thermodynamic stability indicates that compounds with higher predicted $T_c$ values are increasingly unstable, making their synthesis challenging. While fundamental physical laws do not strictly limit $T_c$ to low-temperatures, our analysis suggests that achieving room-temperature conventional superconductivity at ambient pressure is extremely unlikely. △ Less

Submitted 25 February, 2025; originally announced February 2025.

Journal ref: Nat Commun 16, 8253 (2025)

Local and Non-local Entanglement Witnesses of Fermi Liquid

Authors: Yiming Wang, Yuan Fang, Fang Xie, Qimiao Si

Abstract: There is a growing interest both in utilizing entanglement means to characterize many-body systems and in uncovering their entanglement depth. Motivated by recent findings that the spin quantum Fisher information witnesses amplified multipartite entanglement of strange metals and characterizes their loss of quasiparticles, we study the quantum Fisher information in various cases of Fermi liquid. W… ▽ More There is a growing interest both in utilizing entanglement means to characterize many-body systems and in uncovering their entanglement depth. Motivated by recent findings that the spin quantum Fisher information witnesses amplified multipartite entanglement of strange metals and characterizes their loss of quasiparticles, we study the quantum Fisher information in various cases of Fermi liquid. We show that local operators generically do not witness any multipartite entanglement in a Fermi liquid, but non-local many-body operators do. Our results point to novel experimental means to detect the entanglement depth of metallic fermionic systems and, in general, open a new avenue to the emerging exploration of entanglement in quantum materials. △ Less

Submitted 19 February, 2025; originally announced February 2025.

Comments: 6+8 pages, 4+1 figures

From superconductivity to non-superconductivity in LiPdH: a first principle approach

Authors: Zahra Alizadeh, Yue-Wen Fang, Ion Errea, M. R. Mohammadizadeh

Abstract: The layered structure of LiPdH was theoretically suggested to be a superconductor as a result of its larger electron-phonon coupling constant compared to that of PdH. However, the experimental results reported contrary findings, with no trace of superconductivity. We study the electronic, vibrational, and superconducting properties of the ambient pressure tetragonal phase of LiPdH ($P4/mmm$) withi… ▽ More The layered structure of LiPdH was theoretically suggested to be a superconductor as a result of its larger electron-phonon coupling constant compared to that of PdH. However, the experimental results reported contrary findings, with no trace of superconductivity. We study the electronic, vibrational, and superconducting properties of the ambient pressure tetragonal phase of LiPdH ($P4/mmm$) within first principles density functional theory methods, both in the harmonic and anharmonic approximations for the lattice dynamics, and conclude that it does not show any superconducting behavior. High-pressure crystal structure prediction calculations indicate that no structural transition is expected to occur under pressure up to 100 GPa in LiPdH. Our theoretical calculations demonstrate that increasing pressure reduces the density of states at the Fermi surface and consequently weakens electron-phonon interactions, leading to a further suppression of the superconducting critical temperature. △ Less

Submitted 4 February, 2025; originally announced February 2025.

Solid-state Synapse Based on Magnetoelectrically Coupled Memristor

Authors: Weichuan Huang, Yue-Wen Fang, Yuewei Yin, Bobo Tian, Wenbo Zhao, Chuangming Hou, Chao Ma, Qi Li, Evgeny Y. Tsymbal, Chun-Gang Duan, Xiaoguang Li

Abstract: Brain-inspired computing architectures attempt to emulate the computations performed in the neurons and the synapses in human brain. Memristors with continuously tunable resistances are ideal building blocks for artificial synapses. Through investigating the memristor behaviors in a La0.7Sr0.3MnO3/BaTiO3/La0.7Sr0.3MnO3 multiferroic tunnel junction, it was found that the ferroelectric domain dynami… ▽ More Brain-inspired computing architectures attempt to emulate the computations performed in the neurons and the synapses in human brain. Memristors with continuously tunable resistances are ideal building blocks for artificial synapses. Through investigating the memristor behaviors in a La0.7Sr0.3MnO3/BaTiO3/La0.7Sr0.3MnO3 multiferroic tunnel junction, it was found that the ferroelectric domain dynamics characteristics are influenced by the relative magnetization alignment of the electrodes, and the interfacial spin polarization is manipulated continuously by ferroelectric domain reversal, enriching our understanding of the magnetoelectric coupling fundamentally. This creates a functionality that not only the resistance of the memristor but also the synaptic plasticity form can be further manipulated, as demonstrated by the spike-timing-dependent plasticity investigations. Density functional theory calculations are carried out to describe the obtained magnetoelectric coupling, which is probably related to the Mn-Ti intermixing at the interfaces. The multiple and controllable plasticity characteristic in a single artificial synapse, to resemble the synaptic morphological alteration property in a biological synapse, will be conducive to the development of artificial intelligence. △ Less

Submitted 31 January, 2025; originally announced January 2025.

Comments: 5 figures, 20 pages

Journal ref: ACS Applied Materials & Interfaces 2018, 10, 6, 5649-5656

A Metal-Insulator Transition of the Buried MnO2 Monolayer in Complex Oxide Heterostructure

Authors: Heng-Jui Liu, Jheng-Cyuan Lin, Yue-Wen Fang, Jing-Ching Wang, Bo-Chao Huang, Xiang Gao, Rong Huang, Philip R. Dean, Peter D. Hatton, Yi-Ying Chin, Hong-Ji Lin, Chien-Te Chen, Yuichi Ikuhara, Ya-Ping Chiu, Chia-Seng Chang, Chun-Gang Duan, Qing He, Ying-Hao Chu

Abstract: Functionalities in crystalline materials are determined by 3-dimensional collective interactions of atoms. The confinement of dimensionality in condensed matter provides an exotic research direction to understand the interaction of atoms, thus can be used to tailor or create new functionalities in material systems. In this study, a 2-dimensional transition metal oxide monolayer is constructed insi… ▽ More Functionalities in crystalline materials are determined by 3-dimensional collective interactions of atoms. The confinement of dimensionality in condensed matter provides an exotic research direction to understand the interaction of atoms, thus can be used to tailor or create new functionalities in material systems. In this study, a 2-dimensional transition metal oxide monolayer is constructed inside complex oxide heterostructures based on the theoretical predictions. The electrostatic boundary conditions of oxide monolayer in the heterostructure is carefully designed to tune the chemical, electronic, and magnetic states of oxide monolayer. The challenge of characterizing such an oxide monolayer is overcome by a combination of transmission electron microscopy, x-ray absorption spectroscopy, cross-sectional scanning tunneling microscopy, and electrical transport measurements. An intriguing metal-insulator transition associated with a magnetic transition is discovered in the MnO2 monolayer. This study paves a new route to understand the confinement of dimensionality and explore new intriguing phenomena in condensed matters. △ Less

Submitted 31 January, 2025; originally announced January 2025.

Comments: 23 pages, 6 figures

Journal ref: Adv. Mater., 28: 9142-9151(2016)

Coupling Dichroism in Strong-Coupled Chiral Molecule-Plasmon Nanoparticle System

Authors: Nan Gao, Haoran Liu, Yurui Fang

Abstract: The interaction between intense light-matter not only promotes emerging applications in quantum and nonlinear optics but also facilitates changes in material properties. Plasmons can significantly enhance not only molecular chirality but also the coupling strength. In this study, we investigate the coupling dichroism in a strongly coupled chiral molecule-plasmonic nanoparticle system using RT-TDDF… ▽ More The interaction between intense light-matter not only promotes emerging applications in quantum and nonlinear optics but also facilitates changes in material properties. Plasmons can significantly enhance not only molecular chirality but also the coupling strength. In this study, we investigate the coupling dichroism in a strongly coupled chiral molecule-plasmonic nanoparticle system using RT-TDDFT. By simulating the interaction between L/D- Phenylglycinol molecules and chiral aluminum clusters (Na-doped Al197Na4), we examine the effects of molecular chirality, cluster chirality, and the coupled effect in the system. Our results demonstrate that the achiral/chiral clusters induce significant spectral shifts and enhance molecular CD signals due to strong plasmon-molecule coupling. The electric-field distribution and transition contribution maps (TCMs) reveal the formation of bonding and antibonding polaritonic modes, modulated by molecular proximity to the cluster. Both of the coupling factor and decay rate of the coupled system will be modulated by the chirality of the molecules and the cluster. Furthermore, we find that increasing the number of coupled molecules leads to a substantial increase in the intensity of lower polaritonic modes, highlighting the collective behavior in multi-molecule systems due to the modal crosstalk or resonance between cluster chirality and molecular chirality. These findings provide valuable insights into the fundamental mechanisms governing plasmon-enhanced chirality at the atomic scale, which have implications for the design of highly sensitive chiral sensors and optoelectronic devices. △ Less

Submitted 31 January, 2025; originally announced January 2025.

Comments: 36 pages, 18 figures including supporting information

MSC Class: 78-10

The Impact of Ionic Anharmonicity on Superconductivity in Metal-Stuffed B-C Clathrates

Authors: Wenbo Zhao, Ying Sun, Jiaxiang Li, Peng Yuan, Toshiaki Iitaka, Xin Zhong, Hefei Li, Yue-Wen Fang, Hanyu Liu, Ion Errea, Yu Xie

Abstract: Metal-stuffed B$-$C compounds with sodalite clathrate structure have captured increasing attention due to their predicted exceptional superconductivity above liquid nitrogen temperature at ambient pressure. However, by neglecting the quantum lattice anharmonicity, the existing studies may result in an incomplete understanding of such a lightweight system. Here, using state-of-the-art ab initio met… ▽ More Metal-stuffed B$-$C compounds with sodalite clathrate structure have captured increasing attention due to their predicted exceptional superconductivity above liquid nitrogen temperature at ambient pressure. However, by neglecting the quantum lattice anharmonicity, the existing studies may result in an incomplete understanding of such a lightweight system. Here, using state-of-the-art ab initio methods incorporating quantum effects and machine learning potentials, we revisit the properties of a series of $XY$$\text{B}_{6}\text{C}_{6}$ clathrates where $X$ and $Y$ are metals. Our findings show that ionic quantum and anharmonic effects can harden the $E_g$ and $E_u$ vibrational modes, enabling the dynamical stability of 15 materials previously considered unstable in the harmonic approximation, including materials with previously unreported ($XY$)$^{1+}$ state, which is demonstrated here to be crucial to reach high critical temperatures. Further calculations based on the anisotropic Migdal-Eliashberg equation demonstrate that the $T_\text{c}$ values for KRb$\text{B}_{6}\text{C}_{6}$ and Rb$\text{B}_{3}\text{C}_{3}$ among these stabilized compounds are 102 and 115 K at 0 and 15 GPa, respectively, both being higher than $T_\text{c}$ of 92 K of KPb$\text{B}_{6}\text{C}_{6}$ at the anharmonic level. These record-high $T_\text{c}$ values, surpassing liquid nitrogen temperatures, emphasize the importance of anharmonic effects in stabilizing B-C clathrates with large electron-phonon coupling strength and advancing the search for high-$T_\text{c}$ superconductivity at (near) ambient pressure. △ Less

Submitted 10 January, 2026; v1 submitted 21 January, 2025; originally announced January 2025.

Journal ref: npj Computational Materials volume 11, Article number: 347 (2025)

Influence of conjugated structure for tunable molecular plasmons in peropyrene and its derivatives

Authors: Haoran Liu, Nan Gao, Yurui Fang

Abstract: Advances in research have sparked an increasing curiosity in understanding the plasmonic excitation properties of molecular-scale systems. Polycyclic aromatic hydrocarbons, as the fundamental building blocks of graphene, have been documented to possess plasmonic properties through experimental observations, making them prime candidates for investigation. By doping different elements, the conjugate… ▽ More Advances in research have sparked an increasing curiosity in understanding the plasmonic excitation properties of molecular-scale systems. Polycyclic aromatic hydrocarbons, as the fundamental building blocks of graphene, have been documented to possess plasmonic properties through experimental observations, making them prime candidates for investigation. By doping different elements, the conjugated structure of the molecule can be altered. In this study, the plasmonic excitation properties influenced by conjugated structures in peropyrene and its derivatives are investigated through first-principles calculations that combine the plasmonicity index, generalized plasmonicity index and transition contribution maps. For molecular plasmonic excitation, the conjugated structure can influence the oscillation modes of valence electrons, which is pivotal in yielding distinct field enhancement characteristics. Furthermore, charge doping can lead to a certain degree of alteration in the conjugated structures, and the doping of elements will result in varying degrees of such alteration, thereby initiating different trends in the evolution of plasmonic resonance. This further enhances the tunability of molecular plasmonic resonance. The results provide novel insights into the development and utilization of molecular plasmonic devices in practical applications. △ Less

Submitted 20 January, 2025; originally announced January 2025.

Comments: 19 pages, 6 figures

MSC Class: 78-10

Mixed anion control of enhanced negative thermal expansion in the oxysulfide of PbTiO3

Authors: Zhao Pan, Zhengli Liang, Xiao Wang, Yue-Wen Fang, Xubin Ye, Zhehong Liu, Takumi Nishikubo, Yuki Sakai, Xi Shen, Qiumin Liu, Shogo Kawaguchi, Fei Zhan, Longlong Fan, Yong-Yang Wang, Chen-Yan Ma, Xingxing Jiang, Zheshuai Lin, Richeng Yu, Xianran Xing, Masaki Azuma, Youwen Long

Abstract: The rare physical property of negative thermal expansion (NTE) is intriguing because materials with large NTE over a wide temperature range can serve as high-performance thermal expansion compensators. However, applications of NTE are hindered by the fact that most of the available NTE materials show small magnitudes of NTE, and/or NTE occurs only in a narrow temperature range. Herein, for the fir… ▽ More The rare physical property of negative thermal expansion (NTE) is intriguing because materials with large NTE over a wide temperature range can serve as high-performance thermal expansion compensators. However, applications of NTE are hindered by the fact that most of the available NTE materials show small magnitudes of NTE, and/or NTE occurs only in a narrow temperature range. Herein, for the first time, we investigated the effect of anion substitution instead of general Pb/Ti-site substitutions on the thermal expansion properties of a typical ferroelectric NTE material, PbTiO3. Intriguingly, the substitution of S for O in PbTiO3 further increases the tetragonality of PbTiO3. Consequently, an unusually enhanced NTE with an average volumetric coefficient of thermal expansion $\barα_V$ = -2.50 $\times$ 10$^{-5}$/K was achieved over a wide temperature range (300 -- 790 K), which is contrasted to that of pristine PbTiO3 ($\barα_V$ = -1.99 $\times$ 10$^{-5}$/K RT -- 763 K). The intensified NTE is attributed to the enhanced hybridization between Pb/Ti and O/S atoms by the substitution of S, as evidenced by our theoretical investigations. We therefore demonstrate a new technique for introducing mixed anions to achieve large NTE over a wide temperature range in PbTiO3-based ferroelectrics. △ Less

Submitted 16 January, 2025; originally announced January 2025.

Comments: 14 pages, 4 figures

Journal ref: Materials Horizons, 11, 5394-5401, 2024

Ferroelectricity in layered bismuth oxide down to 1 nanometer

Authors: Qianqian Yang, Jingcong Hu, Yue-Wen Fang, Yueyang Jia, Rui Yang, Shiqing Deng, Yue Lu, Oswaldo Dieguez, Longlong Fan, Dongxing Zheng, Xixiang Zhang, Yongqi Dong, Zhenlin Luo, Zhen Wang, Huanhua Wang, Manling Sui, Xianran Xing, Jun Chen, Jianjun Tian, Linxing Zhang

Abstract: Atomic-scale ferroelectrics are of great interest for high-density electronics, particularly field-effect transistors, low-power logic, and nonvolatile memories. We devised a film with a layered structure of bismuth oxide that can stabilize the ferroelectric state down to 1 nanometer through samarium bondage. This film can be grown on a variety of substrates with a cost-effective chemical solution… ▽ More Atomic-scale ferroelectrics are of great interest for high-density electronics, particularly field-effect transistors, low-power logic, and nonvolatile memories. We devised a film with a layered structure of bismuth oxide that can stabilize the ferroelectric state down to 1 nanometer through samarium bondage. This film can be grown on a variety of substrates with a cost-effective chemical solution deposition. We observed a standard ferroelectric hysteresis loop down to a thickness of ~1 nanometer. The thin films with thicknesses that range from 1 to 4.56 nanometers possess a relatively large remanent polarization from 17 to 50 microcoulombs per square centimeter. We verified the structure with first-principles calculations, which also pointed to the material being a lone pair-driven ferroelectric material. The structure design of the ultrathin ferroelectric films has great potential for the manufacturing of atomic-scale electronic devices. △ Less

Submitted 16 January, 2025; originally announced January 2025.

Comments: preprint, 27 pages, 5 figures

Journal ref: Science 379(6638): 1218-1224 (2023)

Superconductivity in barium hydrides via incorporation of light elements

Authors: Yue-Wen Fang, Ion Errea

Abstract: Barium hydrides are of interest for their potential in both ionic conductivity and superconductivity. Recently, a superconducting hydride BaH$_{12}$ containing H$_2$ and H${_3}^{-1}$ molecular units was experimentally reported with a critical temperature $T_\text{c}$ of 20 K at 140 GPa [Nat Commun 12, 273 (2021)]. Herein, we combine ab initio methods with a rapid calculator of $T_\text{c}$ based o… ▽ More Barium hydrides are of interest for their potential in both ionic conductivity and superconductivity. Recently, a superconducting hydride BaH$_{12}$ containing H$_2$ and H${_3}^{-1}$ molecular units was experimentally reported with a critical temperature $T_\text{c}$ of 20 K at 140 GPa [Nat Commun 12, 273 (2021)]. Herein, we combine ab initio methods with a rapid calculator of $T_\text{c}$ based on the networking value model to predict that the introduction of light elements, such as Be, can effectively expand the structure diversity and structure space of barium hydrides. Although molecular hydrogen units are still widely present in thermodynamically stable and metastable crystal structures, we find that a metastable phase of BeBaH$_8$ shows a high $T_\text{c}$ of 49 K at 100 GPa, which is only 38 meV/atom above the thermodynamic stability energy. This BeBaH$_8$ remains dynamically stable at 15 GPa. Furthermore, our study shows that increasing pressure can further elevate $T_\text{c}$ beyond 100 K by enhancing the electron-phonon coupling constant. Our study proposes a feasible method for broadening the structural landscape in the exploration of superconducting phases of barium hydrides. △ Less

Submitted 5 September, 2025; v1 submitted 12 December, 2024; originally announced December 2024.

Comments: 9 pages and 5 figures in main text

Journal ref: Phys. Rev. B 112, 125204 (2025)