Showing 1–50 of 333 results for author: Cao, H

K$_2$Co$_2$(TeO$_{3}$)$_{3}$ $\cdot$ 2.5 H$_2$O : A mineral-inspired pseudo-honeycomb cobalt dimer antiferromagnet

Authors: Austin M. Ferrenti, Maxime A. Siegler, Yiqing Hao, Chris Lygouras, Tong Chen, Tiffany A. Soetojo, Megan R. Rutherford, Kenji M. Kojima, Huibo Cao, Natalia Drichko, Alannah M. Hallas, Tyrel M. McQueen

Abstract: In recent years, magnetically-frustrated triangular and honeycomb lattice cobaltates have seen extensive study in the pursuit of a quantum spin liquid (QSL) state in a real material. In this work, we describe the hydroflux synthesis of K$_2$Co$_2$(TeO$_{3}$)$_{3}$ $\cdot$ 2.5 H$_2$O (KCoTOH), a novel zemannite-type antiferromagnet (AFM) possessing structural elements of both triangular dimer and h… ▽ More In recent years, magnetically-frustrated triangular and honeycomb lattice cobaltates have seen extensive study in the pursuit of a quantum spin liquid (QSL) state in a real material. In this work, we describe the hydroflux synthesis of K$_2$Co$_2$(TeO$_{3}$)$_{3}$ $\cdot$ 2.5 H$_2$O (KCoTOH), a novel zemannite-type antiferromagnet (AFM) possessing structural elements of both triangular dimer and honeycomb structural motifs. Bulk magnetometry and specific heat data support the onset of long-range AFM order below $T_\text{N}$ = 7.6(1) K, with neutron diffraction and muon spin relaxation ($μ$SR) measurements placing the majority of the ordered moment within the pseudo-honeycomb plane. We resolve three unique oscillation frequencies from the zero-field $μ$SR spectra, additionally suggesting a remarkably low level of structural disorder in as-grown KCoTOH crystals. Whereas interactions between dimerized chains of Co$^{2+}$ cations are typically observed to be negligible or ferromagnetic in nature, the largely planar ordering motif observed in KCoTOH is instead stabilized by net antiferromagnetic interactions through bridging tellurite groups. This work highlights the potential of hydroflux synthesis methods in the stabilization of magnetic materials possessing novel and potentially more frustrated lattice geometries. △ Less

Submitted 7 April, 2026; originally announced April 2026.

Comments: Main text (21 pages, 5 figures, 1 table); Supplementary information (27 pages, 8 figures, 18 tables)

Grafted Low-Leakage Si/AlN p-n Diodes Enabled by Fluorinated AlN Interface

Authors: Yi Lu, Tsung-Han Tsai, Qingxiao Wang, Haicheng Cao, Jie Zhou, You Jin Koo, Chenyu Wang, Yang Liu, Yueyue Hao, Michael Eller, Connor Bailey, Stephanie Liu, Nicholas J. Tanen, Zhiyuan Liu, Mingtao Nong, Robert M. Jacobberger, Tien Khee Ng, Katherine Fountaine, Vincent Gambin, Boon S. Ooi, Xiaohang Li, Zhenqiang Ma

Abstract: Ultrawide-bandgap AlN is a promising material for next-generation power electronics; however, its practical implementation is hindered by unstable surface chemistry and the high activation energy of p-type dopants. In particular, high-temperature rapid thermal annealing (RTA), required for forming low-resistance contacts on n-type AlN, leads to the formation of thick and defective surface oxides t… ▽ More Ultrawide-bandgap AlN is a promising material for next-generation power electronics; however, its practical implementation is hindered by unstable surface chemistry and the high activation energy of p-type dopants. In particular, high-temperature rapid thermal annealing (RTA), required for forming low-resistance contacts on n-type AlN, leads to the formation of thick and defective surface oxides that degrade heterojunction performance. In this work, we present an interface engineering approach based on fluorination-induced AlFx formation combined with SiNx passivation to suppress defect-assisted leakage in p-Si/n-AlN heterojunction diodes fabricated via semiconductor grafting. A low-damage pseudo-atomic layer etching process is employed to remove RTA-induced oxides and restore a near-stoichiometric AlN surface. Subsequent XeF2 treatment forms an ultrathin AlFx layer, which is stabilized by an atomic-layer-deposited SiNx capping layer prior to p-Si nanomembrane integration. Electrical measurements show that the engineered AlFx/SiNx interface reduces reverse leakage current by several orders of magnitude compared to untreated or oxide-removed AlN surfaces, while preserving forward conduction characteristics. Temperature-dependent analysis indicates strong suppression of Poole-Frenkel emission and a shift of leakage onset to higher reverse bias, ultimately limited by bulk AlN crystal quality. X-ray photoelectron spectroscopy and transmission electron microscopy confirm the formation of Al-F bonds, reduced Al-O content, and the presence of a thin interfacial SiOx/SiON layer. These results establish AlFx/SiNx passivation as an effective strategy for stabilizing AlN interfaces and enabling low-leakage ultrawide-bandgap heterojunction devices. △ Less

Submitted 7 April, 2026; originally announced April 2026.

Comments: 12 pages

Enhanced synchronization with proportional coupling in Kuramoto oscillator networks

Authors: Amit Pando, Eran Bernstein, Tomer Hacohen, Nathan Vigne, Hui Cao, Oren Raz, Asher Friesem, Nir Davidson

Abstract: We introduce a novel coupling scheme for maximizing the synchronization of Kuramoto oscillator networks under a fixed coupling budget. We show that by scaling the interaction strength between oscillators according to their frequency detuning, synchronization is enhanced. The coupling scheme induces a change in criticality, driving the system from a continuous phase transition to an explosive trans… ▽ More We introduce a novel coupling scheme for maximizing the synchronization of Kuramoto oscillator networks under a fixed coupling budget. We show that by scaling the interaction strength between oscillators according to their frequency detuning, synchronization is enhanced. The coupling scheme induces a change in criticality, driving the system from a continuous phase transition to an explosive transition by changing a single parameter. Our work offers a general route to efficient synchronization in engineered networks and provides insight into the critical behavior of the Kuramoto model. △ Less

Submitted 31 March, 2026; originally announced March 2026.

Comments: Main: 5 pages, 6 figures. Supplemental: 8 pages, 3 figures

Kondo driven suppression of charge density wave in Van der Waals material UTe$_3$

Authors: Justin Shotton, Jiahui Zhu, David Martinez, Diana Golovanova, Dipanjan Chaudhuri, Xuefei Guo, Peter Abbamonte, Feng Ye, Yiqing Hao, Huibo Cao, Suk Hyun Sung, Carly Grossman, Ismail El Baggari, Gal Tuvia, Mengke Liu, Ruizhe Kang, Matt Boswell, Weiwei Xie, Debapratim Pal, Anil Kumar, Yun Suk Eo, Binghai Yan, Kai Sun, Jonathan Denlinger, Sheng Ran

Abstract: Competing electronic instabilities lie at the heart of emergent phenomena in quantum materials. In low-dimensional metals, Fermi-surface nesting can drive charge density wave (CDW) formation through a Peierls-like mechanism, while in strongly correlated systems, Kondo hybridization reconstructs the electronic structure by entangling localized moments with itinerant electrons. How these two fundame… ▽ More Competing electronic instabilities lie at the heart of emergent phenomena in quantum materials. In low-dimensional metals, Fermi-surface nesting can drive charge density wave (CDW) formation through a Peierls-like mechanism, while in strongly correlated systems, Kondo hybridization reconstructs the electronic structure by entangling localized moments with itinerant electrons. How these two fundamentally different instabilities interact$-$whether they coexist, compete, or mutually exclude each other$-$remains an open question. Here, we present suppression of charge density wave via the Kondo interaction in van der Waals material UTe$_3$. The angle-resolved photoemission spectroscopy (ARPES) data reveals Fermi surface nesting under similar conditions as seen in RETe$_3$ compounds. Despite that, no CDW is found in UTe$_3$ after an extensive search. We demonstrate that strong hybridization between U 5$f$ electrons and Te $p$ states reconstructs the low-energy electronic structure, removes the instability, and preempts CDW formation. Our results reveal a rare example where Kondo hybridization preempts density wave formation, offering a new route to controlling ordering phenomena in correlated 2D materials. △ Less

Submitted 3 March, 2026; originally announced March 2026.

Comments: 23 pages, 6 figures

Differentiable Maximum Likelihood Noise Estimation for Quantum Error Correction

Authors: Hanyan Cao, Dongyang Feng, Cheng Ye, Feng Pan

Abstract: Accurate noise estimation is essential for fault-tolerant quantum computing, as decoding performance depends critically on the fidelity of the circuit-level noise parameters. In this work, we introduce a differentiable Maximum Likelihood Estimation (dMLE) framework that enables exact, efficient, and fully differentiable computation of syndrome log-likelihoods, allowing circuit-level noise paramete… ▽ More Accurate noise estimation is essential for fault-tolerant quantum computing, as decoding performance depends critically on the fidelity of the circuit-level noise parameters. In this work, we introduce a differentiable Maximum Likelihood Estimation (dMLE) framework that enables exact, efficient, and fully differentiable computation of syndrome log-likelihoods, allowing circuit-level noise parameters to be optimized directly via gradient descent. Leveraging the exact Planar solver for repetition codes and a novel, simplified Tensor Network (TN) architecture combined with optimized contraction path finding for surface codes, our method achieves tractable and fully differentiable likelihood evaluation even for distance 5 surface codes with up to 25 rounds. Our method recovers the underlying error probabilities with near-exact precision in simulations and reduces logical error rates by up to 30.6(3)% for repetition codes and 8.1(2)% for surface codes on experimental data from Google's processor compared to previous state-of-the-art methods: correlation analysis and Reinforcement Learning (RL) methods. Our approach yields provably optimal, decoder-independent error priors by directly maximizing the syndrome likelihood, offering a powerful noise estimation and control tool for unlocking the full potential of current and future error-corrected quantum processors. △ Less

Submitted 23 February, 2026; originally announced February 2026.

Atomically-sharp magnetic soliton in the square-net lattice EuRhAl$_{4}$Si$_{2}$

Authors: Kevin Allen, Juba Bouaziz, Yichen Zhang, Kai Du, Sanu Mishra, Gustav Bihlmayer, Yiqing Hao, Victor Ukleev, Chen Luo, Florin Radu, Yuxiang Gao, Marta Zonno, Sergey Gorovikov, Christopher Lane, Jian-Xin Zhu, Huibo Cao, Sang-Wook Cheong, Ming Yi, Stefan Blügel, Emilia Morosan

Abstract: Topological spin textures are hallmark manifestations of competing interactions in magnetic matter. Their effective description by nonlinear field theories reflects an energetic frustration that destabilizes uniform order while selecting finite-size, topologically nontrivial configurations as stationary states. Among the most extreme realizations are atomically-sharp domain wall excitations, namel… ▽ More Topological spin textures are hallmark manifestations of competing interactions in magnetic matter. Their effective description by nonlinear field theories reflects an energetic frustration that destabilizes uniform order while selecting finite-size, topologically nontrivial configurations as stationary states. Among the most extreme realizations are atomically-sharp domain wall excitations, namely one-dimensional (1D) magnetic solitons, which represent the ultimate scaling limit of magnetic textures. Such solitons may emerge in magnetic systems where effective exchange interactions compete directly with uniaxial magnetic anisotropy. Here we show that the square-net rare earth compound EuRhAl$_{4}$Si$_{2}$ realizes a very susceptible regime where the magnetic anisotropy competes with highly frustrated exchange interactions stabilizing a rare ferrimagnetic $\uparrow\uparrow\downarrow$ state that, under applied magnetic field, supports the formation of atomically-sharp soliton defects. We confirm the bulk response of the 1D magnetic solitons via magnetization and electrical transport measurements. We establish both the zero- and in-field $\uparrow\uparrow\downarrow$ order via neutron diffraction, while magnetic force microscopy visualizes its real-space evolution into a stripe-like array. To elucidate the microscopic origin of the soliton, we relate the Ruderman-Kittel-Kasuya-Yosida (RKKY)-driven exchange interactions and the magnetic anisotropy through density functional theory, and we construct an effective 1D $J_{1}$-$J_{2}$-$K$ model whose atomistic spin dynamics simulations reproduce the observed soliton states as a function of external field. Our results demonstrate that EuRhAl$_{4}$Si$_{2}$ hosts atomically-sharp, field-driven 1D magnetic solitons, providing a new platform for studying 1D topological excitations at the atomic length scale. △ Less

Submitted 10 February, 2026; originally announced February 2026.

Frustrated Magnetism in FeGe$_3$O$_4$ with a Chiral Trillium Network

Authors: Matt Boswell, Mingyu Xu, Haozhe Wang, Mouyang Cheng, N. Li, X. F. Sun, Haidong Zhou, Huibo Cao, Mingda Li, Weiwei Xie

Abstract: The discovery of new magnetic ground states in geometrically frustrated lattices remains a central challenge in materials science. Here, we report the synthesis, structural characterization, and frustrated magnetic properties of FeGe$_3$O$_4$, a newly identified compound that crystallizes in the noncentrosymmetric cubic space group $P2_13$. In this structure, Fe atoms form an intricate double-tril… ▽ More The discovery of new magnetic ground states in geometrically frustrated lattices remains a central challenge in materials science. Here, we report the synthesis, structural characterization, and frustrated magnetic properties of FeGe$_3$O$_4$, a newly identified compound that crystallizes in the noncentrosymmetric cubic space group $P2_13$. In this structure, Fe atoms form an intricate double-trillium lattice with nearest-neighbor Fe--Fe distances of $\sim$4.2~Å, while Ge$^{2+}$ ions mediate magnetic interactions through Fe-Ge-Fe pathways. Field-dependent magnetization at 2~K shows a pronounced nonlinearity, reaching a maximum moment of 2.55(3)~$μ_\mathrm{B}$/Fe$^{2+}$ at 70~kOe without evidence of saturation. Magnetic susceptibility, heat capacity, and neutron scattering collectively reveal the onset of short-range magnetic interactions near 5~K, with no long-range ordering detected down to 0.06~K. Specific heat measurements demonstrate strong frustration: only $\sim$34\% of the expected magnetic entropy is recovered at 2.4~K. Taken together, these results establish FeGe$_3$O$_4$ as a rare example of a geometrically frustrated trillium-lattice magnet, offering a promising platform for exploring exotic quantum magnetic phenomena. △ Less

Submitted 13 January, 2026; originally announced January 2026.

Comments: 26 pages, 4+6 figures

Evidence for rare-region physics in the structural and electronic degrees of freedom of the nickelate La$_{2-x}$Sr$_x$NiO$_4$

Authors: R. J. Spieker, B. Krohnke, D. Zhai, A. Lopez Benet, M. Spaić, X. He, C. Y. Tan, Z. W. Anderson, F. Ye, H. Cao, M. J. Krogstad, R. Osborn, D. Pelc, M. Greven

Abstract: We present a diffuse neutron and x-ray scattering study of structural, spin- and charge-density-wave fluctuations in the electrical insulator La$_{2-x}$Sr$_x$NiO$_4$. This lamellar nickelate is an isostructural analogue of the high-temperature cuprate superconductor La$_{2-x}$Sr$_x$CuO$_4$, for which recent experiments uncovered evidence for unusual structural and superconducting fluctuations indi… ▽ More We present a diffuse neutron and x-ray scattering study of structural, spin- and charge-density-wave fluctuations in the electrical insulator La$_{2-x}$Sr$_x$NiO$_4$. This lamellar nickelate is an isostructural analogue of the high-temperature cuprate superconductor La$_{2-x}$Sr$_x$CuO$_4$, for which recent experiments uncovered evidence for unusual structural and superconducting fluctuations indicative of rare-region physics due to inherent inhomogeneity unrelated to common point disorder effects. We find closely analogous nanoscale orthorhombic fluctuation behavior in La$_{2-x}$Sr$_x$NiO$_4$, including exponential scaling of the diffuse scattering intensity and power-law scaling of the characteristic length with relative temperature. Moreover, our neutron and x-ray scattering data reveal similar behavior for short-range magnetic and charge fluctuations above the respective ordering temperatures. These observations indicate that rare-region effects are a generic feature of perovskite-related structures and lead to universal fluctuations of both structural and electronic degrees of freedom over extended temperature ranges. △ Less

Submitted 29 December, 2025; originally announced December 2025.

Comments: 20 pages, 10 figures, supplementary material included

Evidence of a two-dimensional nitrogen crystalline structure on silver surfaces

Authors: Xuegao Hu, Haijun Cao, Zhicheng Gao, Hui Zhou, Daiyu Geng, Dong Li, Jisong Gao, Qiaoxiao Zhao, Zhihao Cai, Peng Cheng, Lan Chen, Sheng Meng, Kehui Wu, Baojie Feng

Abstract: Nitrogen, the most abundant element in Earth's atmosphere, exists as a diatomic gas under standard temperature and pressure. In the two-dimensional (2D) limit, atomically thin nitrogen, termed nitrogene, has been theoretically predicted to form crystalline materials with various polymorphic configurations, exhibiting diverse chemical and physical properties. However, the synthesis of nitrogene has… ▽ More Nitrogen, the most abundant element in Earth's atmosphere, exists as a diatomic gas under standard temperature and pressure. In the two-dimensional (2D) limit, atomically thin nitrogen, termed nitrogene, has been theoretically predicted to form crystalline materials with various polymorphic configurations, exhibiting diverse chemical and physical properties. However, the synthesis of nitrogene has remained elusive due to the strong nitrogen-nitrogen triple bonds. Here, we report experimental evidence of the formation of nitrogen-based crystalline structures compatible with nitrogene on silver surfaces via ion-beam-assisted epitaxy. Through a combination of scanning tunneling microscopy, angle-resolved photoemission spectroscopy, and first-principles calculations, we demonstrate that the nitrogene-like structure adopts a puckered honeycomb lattice. Notably, our calculations predict a nitrogene band gap of up to 7.5 eV, positioning it as a promising candidate for ultraviolet optoelectronic devices and high-k dielectric applications. △ Less

Submitted 3 December, 2025; originally announced December 2025.

Comments: Nature Communications; In Press

Journal ref: Nat. Commun. 17, 846 (2026)

Light-engineered Multichannel Quantum Anomalous Hall Effect in High-order Topological Plumbene

Authors: Zhe Li, Fangyang Zhan, Haijun Cao, Jingjing Cao, Huisheng Zhang, Sheng Meng

Abstract: Floquet engineering severs as a forceful technique for uncovering high Chern numbers of quantum anomalous Hall (QAH) states with feasible tunability in high-order topologically insulating plumbene, which is readily accessible for experimental investigations. Under the irradiation of righthanded circularly polarized light, we predict a three-stage topological phase transition in plumbene, whether i… ▽ More Floquet engineering severs as a forceful technique for uncovering high Chern numbers of quantum anomalous Hall (QAH) states with feasible tunability in high-order topologically insulating plumbene, which is readily accessible for experimental investigations. Under the irradiation of righthanded circularly polarized light, we predict a three-stage topological phase transition in plumbene, whether it is in a free-standing form or grown on h-BN. Initially, a metallic state evolves into a K(K')-valley-based QAH state with a Chern number of -8, which then decreases to -6 after the valley gap closes. Finally, a band inversion occurs at the $Γ$ point, resulting in a multichannel QAH state with C = -3. The trigonal warping model accounts for both K(K')-valley-based and $Γ$-pointbased QAH states. Additionally, growing plumbene on a non-van-der-Waals substrate eliminates the K(K')-valley-based topology, leaving only the $Γ$-point-based QAH state with C = +3. Our findings propose the tunability of various high Chern numbers derived from high-order topological insulators, aiming to advance the next-generation dissipationless electronic devices. △ Less

Submitted 23 November, 2025; originally announced November 2025.

Floquet-engineered Valley Topology with Anisotropic Response in 1T'-WSe$_2$ and Janus WSeTe monolayers

Authors: Zhe Li, Haijun Cao, Lijuan Li, Huixia Fu, Mengxue Guan, Sheng Meng

Abstract: Valley topology has emerged as a key concept for realizing new classes of quantum states. Here, we investigate Floquet-engineered topological phase transitions in anisotropic 1T'-WSe$_2$ and its Janus derivative WSeTe monolayers, which exhibit valley-degenerate and valley-polarized characteristics, respectively. In 1T'-WSe$_2$, a single topological-phase-transition (TPT) occurs from the quantum-sp… ▽ More Valley topology has emerged as a key concept for realizing new classes of quantum states. Here, we investigate Floquet-engineered topological phase transitions in anisotropic 1T'-WSe$_2$ and its Janus derivative WSeTe monolayers, which exhibit valley-degenerate and valley-polarized characteristics, respectively. In 1T'-WSe$_2$, a single topological-phase-transition (TPT) occurs from the quantum-spin-Hall state (QSH) to the quantum anomalous Hall (QAH) state, involving one spin channel at both valleys simultaneously. In contrast, Janus WSeTe undergoes a two-stage Floquet-driven TPT that occurs within a single valley and sequentially involves two spin components. The intermediate phase manifests as a valley-polarized QAH (vp-QAH) state with a finite valley Chern number, while the final phase evolves into a high-Chern-number QAH state with distinct valley gaps. Furthermore, an in-plane anisotropic response of the TPTs is predicted under oblique light incidence, reflecting the intrinsic low-symmetry nature of the lattice. These findings provide a comprehensive understanding of Floquet-engineered valley-based topological properties and offer guidance for designing light-controllable valleytronic and topological devices. △ Less

Submitted 25 November, 2025; v1 submitted 20 November, 2025; originally announced November 2025.

Laser-engineered $Γ$-point Topology in Trigonal Bismuthene

Authors: Zhe Li, Haijun Cao, Sheng Meng

Abstract: The $Γ$-point topology represents a significant segment in the family of topological insulators. Here we provide a comprehensive prediction of light-induced $Γ$-point-based topological manipulation in trigonal bismuthene and its derivatives. Our findings unveil a two-stage process of topological phase transitions (TPT) as the laser intensity increases. Initially, a quantum-spin-Hall or metallic st… ▽ More The $Γ$-point topology represents a significant segment in the family of topological insulators. Here we provide a comprehensive prediction of light-induced $Γ$-point-based topological manipulation in trigonal bismuthene and its derivatives. Our findings unveil a two-stage process of topological phase transitions (TPT) as the laser intensity increases. Initially, a quantum-spin-Hall or metallic state transitions to a quantum-anomalous-Hall (QAH) state ($C$ = $\pm$3), followed by another TPT that yields a compensated Chern-insulating state ($C$ = 0). The trigonal warping model accounts for these states, describing the $C_{3z}$-rotational band-inversion process, which is determined by $\pm$1 orders of replica bands. Notably, this high Chern-number QAH state persists over a broad range of laser parameters, maintaining functionality beyond room temperature as evidenced by the large global gaps ($\geq$ 60 meV). Our work provides a comprehensive roadmap towards the designer $Γ$-point topology under laser excitation, facilitating applications of artificial topological materials. △ Less

Submitted 11 September, 2025; v1 submitted 9 September, 2025; originally announced September 2025.

Structural transition and possible pressure-induced superconductivity in a suboxide La$_5$Pb$_3$O

Authors: Jiaqiang Yan, David Singh, Bayram Saparov, Huibo Cao, Yejun Feng, Jinguang Cheng, Yoshia Uwatoko, David Mandrus

Abstract: Here we report a structural phase transition and its possible competition with superconductivity in the suboxide La$_5$Pb$_3$O. Upon cooling through $T_t$ = 225 K, La$_5$Pb$_3$O transforms from a high-temperature I4/mcm to a low-temperature P4/ncc structure in which La - Pb dimerization along the c-axis occurs. This transition is accompanied by anomalies in the temperature dependence of electrical… ▽ More Here we report a structural phase transition and its possible competition with superconductivity in the suboxide La$_5$Pb$_3$O. Upon cooling through $T_t$ = 225 K, La$_5$Pb$_3$O transforms from a high-temperature I4/mcm to a low-temperature P4/ncc structure in which La - Pb dimerization along the c-axis occurs. This transition is accompanied by anomalies in the temperature dependence of electrical resistivity and specific heat. High-pressure electrical transport measurements reveal that hydrostatic pressure suppresses the structural transition and possibly induces superconductivity with a maximum superconducting temperature of 10 K. Density functional theory calculations show minimal changes in the electronic density of states and no gap opening at $E_F$ across $T_t$, suggesting that the transition is driven by bonding effects rather than Fermi surface instability. These findings establish La$_5$Pb$_3$O as a promising platform for exploring the interplay between weak structural transitions and superconductivity. △ Less

Submitted 13 August, 2025; originally announced August 2025.

Comments: 9 figures, 9 pages

Journal ref: Phys. Rev. Materials 9, 124801 (2025)

Dichotomy of flat bands in the van der Waals ferromagnet Fe$_5$GeTe$_2$

Authors: Han Wu, Jianwei Huang, Chaowei Hu, Lei Chen, Yiqing Hao, Yue Shi, Paul Malinowski, Yucheng Guo, Bo Gyu Jang, Jian-Xin Zhu, Andrew F. May, Siqi Wang, Xiang Chen, Yaofeng Xie, Bin Gao, Yichen Zhang, Ziqin Yue, Zheng Ren, Makoto Hashimoto, Donghui Lu, Alexei Fedorov, Sung-Kwan Mo, Junichiro Kono, Yu He, Robert J. Birgeneau , et al. (6 additional authors not shown)

Abstract: Quantum materials with bands of narrow bandwidth near the Fermi level represent a promising platform for exploring a diverse range of fascinating physical phenomena, as the high density of states within the small energy window often enables the emergence of many-body physics. On one hand, flat bands can arise from strong Coulomb interactions that localize atomic orbitals. On the other hand, quantu… ▽ More Quantum materials with bands of narrow bandwidth near the Fermi level represent a promising platform for exploring a diverse range of fascinating physical phenomena, as the high density of states within the small energy window often enables the emergence of many-body physics. On one hand, flat bands can arise from strong Coulomb interactions that localize atomic orbitals. On the other hand, quantum destructive interference can quench the electronic kinetic energy. Although both have a narrow bandwidth, the two types of flat bands should exhibit very distinct spectral properties arising from their distinctive origins. So far, the two types of flat bands have only been realized in very different material settings and chemical environments, preventing a direct comparison. Here, we report the observation of the two types of flat bands within the same material system--an above-room-temperature van der Waals ferromagnet, Fe$_{5-x}$GeTe$_2$, distinguishable by a switchable iron site order. The contrasting nature of the flat bands is also identified by the remarkably distinctive temperature-evolution of the spectral features, indicating that one arises from electron correlations in the Fe(1) site-disordered phase, while the other geometrical frustration in the Fe(1) site-ordered phase. Our results therefore provide a direct juxtaposition of the distinct formation mechanism of flat bands in quantum materials, and an avenue for understanding the distinctive roles flat bands play in the presence of magnetism, topology, and lattice geometrical frustration, utilizing sublattice ordering as a key control parameter. △ Less

Submitted 6 August, 2025; v1 submitted 4 August, 2025; originally announced August 2025.

Comments: The manuscript was submitted on June 12 2024

Journal ref: Phys. Rev. B 113, 125120 (2026)

Harnessing coherent-wave control for sensing applications

Authors: Pablo Jara, Arthur Goetschy, Hui Cao, Alexey Yamilov

Abstract: Imaging techniques such as functional near-infrared spectroscopy (fNIRS) and diffuse optical tomography (DOT) achieve deep, non-invasive sensing in turbid media, but they are constrained by the photon budget. Wavefront shaping (WFS) can enhance signal strength via interference at specific locations within scattering media, enhancing light-matter interactions and potentially extending the penetrati… ▽ More Imaging techniques such as functional near-infrared spectroscopy (fNIRS) and diffuse optical tomography (DOT) achieve deep, non-invasive sensing in turbid media, but they are constrained by the photon budget. Wavefront shaping (WFS) can enhance signal strength via interference at specific locations within scattering media, enhancing light-matter interactions and potentially extending the penetration depth of these techniques. Interpreting the resulting measurements rests on the knowledge of optical sensitivity - a relationship between detected signal changes and perturbations at a specific location inside the medium. However, conventional diffusion-based sensitivity models rely on assumptions that become invalid under coherent illumination. In this work, we develop a microscopic theory for optical sensitivity that captures the inherent interference effects that diffusion theory necessarily neglects. We analytically show that under random illumination, the microscopic and diffusive treatments coincide. Using our microscopic approach, we explore WFS strategies for enhancing optical sensitivity beyond the diffusive result. We demonstrate that the input state obtained through phase conjugation at a given point inside the system leads to the largest enhancement of optical sensitivity but requires an input wavefront that depends on the target position. In sharp contrast, the maximum remission eigenchannel leads to a global enhancement of the sensitivity map with a fixed input wavefront. This global enhancement equals to remission enhancement and preserves the spatial distribution of the sensitivity, making it compatible with existing DOT reconstruction algorithms. Our results establish the theoretical foundation for integrating wavefront control with diffuse optical imaging, enabling deeper tissue penetration through improved signal strength in biomedical applications. △ Less

Submitted 19 October, 2025; v1 submitted 1 July, 2025; originally announced July 2025.

Comments: 26 pages, 11 figures

Robust superzone gap opening in incommensurate antiferromagnetic semimetal EuAg$_4$Sb$_2$ under in-plane magnetic field

Authors: J. Green, Arpit Arora, Madalynn Marshall, Wanfei Shan, Péter Udvarhelyi, Zachary Morgan, Prineha Narang, Huibo Cao, Ni Ni

Abstract: The interplay between magnetism and charge transport in semimetals has emerged as a fertile ground for discovering novel electronic phenomena. A notable example is the recent discovery of electronic commensuration arising from a spin moiré superlattice (SMS), realized as double-q spin modulation in the antiferromagnetic semimetal EuAg$_4$Sb$_2$. Here, we investigate the in-plane magnetic-field tun… ▽ More The interplay between magnetism and charge transport in semimetals has emerged as a fertile ground for discovering novel electronic phenomena. A notable example is the recent discovery of electronic commensuration arising from a spin moiré superlattice (SMS), realized as double-q spin modulation in the antiferromagnetic semimetal EuAg$_4$Sb$_2$. Here, we investigate the in-plane magnetic-field tunability of the SMS using neutron scattering, magnetic and transport measurements. We reveal an incommensurate noncollinear cycloidal magnetic ground state. Temperature-field phase diagrams constructed with field tilting uncover multiple spin-reoriented phases, suggesting the critical role of in-plane field components in driving magnetic transitions. Despite substantial spin reorientation of the double-q phase, we observe a persistent gap opening, evidenced by strong suppression in both Hall and longitudinal conductivities. Model calculations attribute this robustness to the stability of SMS under tilting fields. Our results establish EuAg$_4$Sb$_2$ as a tunable platform for exploring spin-texture-driven superzone gap opening in electronic states. △ Less

Submitted 17 May, 2025; originally announced May 2025.

Comments: 7 pages, 4 figures

Integrating Neural Networks and Tensor Networks for Computing Free Energy

Authors: Hanyan Cao, Yijia Wang, Feng Pan, Pan Zhang

Abstract: Computing free energy is a fundamental problem in statistical physics. Recently, two distinct methods have been developed and have demonstrated remarkable success: the tensor-network-based contraction method and the neural-network-based variational method. Tensor networks are accu?rate, but their application is often limited to low-dimensional systems due to the high computational complexity in hi… ▽ More Computing free energy is a fundamental problem in statistical physics. Recently, two distinct methods have been developed and have demonstrated remarkable success: the tensor-network-based contraction method and the neural-network-based variational method. Tensor networks are accu?rate, but their application is often limited to low-dimensional systems due to the high computational complexity in high-dimensional systems. The neural network method applies to systems with general topology. However, as a variational method, it is not as accurate as tensor networks. In this work, we propose an integrated approach, tensor-network-based variational autoregressive networks (TNVAN), that leverages the strengths of both tensor networks and neural networks: combining the variational autoregressive neural network's ability to compute an upper bound on free energy and perform unbiased sampling from the variational distribution with the tensor network's power to accurately compute the partition function for small sub-systems, resulting in a robust method for precisely estimating free energy. To evaluate the proposed approach, we conducted numerical experiments on spin glass systems with various topologies, including two-dimensional lattices, fully connected graphs, and random graphs. Our numerical results demonstrate the superior accuracy of our method compared to existing approaches. In particular, it effectively handles systems with long-range interactions and leverages GPU efficiency without requiring singular value decomposition, indicating great potential in tackling statistical mechanics problems and simulating high-dimensional complex systems through both tensor networks and neural networks. △ Less

Submitted 16 April, 2025; originally announced April 2025.

Journal ref: Communications in Theoretical Physics, 2025

Jeff = 1/2 Diamond Magnet CaCo2TeO6: A Pathway toward New Spin Physics and Quantum Functions

Authors: Xudong Huai, Luke Pritchard Cairns, Bridget Delles, Michal J. Winiarski, Maurice Sorolla II, Xinshu Zhang, Youzhe Chen, Stuart Calder, Tatenda Kanyowa, Anshul Kogar, Huibo Cao, Danielle Yahne, Robert Birgeneau, James Analytis, Thao T. Tran

Abstract: Diamond lattice magnets, formed by a framework of corner-sharing tetrahedra of magnetic cations, offer unique opportunities to realize novel states of matter for potential utility in information technology. However, research has mostly focused on AB2X4 spinels with Td magnetic ions. This hinders the atomically enabled tunability of competing interactions at different energy scales and the ability… ▽ More Diamond lattice magnets, formed by a framework of corner-sharing tetrahedra of magnetic cations, offer unique opportunities to realize novel states of matter for potential utility in information technology. However, research has mostly focused on AB2X4 spinels with Td magnetic ions. This hinders the atomically enabled tunability of competing interactions at different energy scales and the ability to harness many-body electronic states in quantum materials, making the discovery of quantum fluctuations and spin dynamics less accessible. We discover a new material CaCo2TeO6 featuring a diamond lattice of two distinct Oh-Co2+ sites. This material displays strong quantum fluctuations, increased competing magnetic exchange interactions, and field-induced tunability of magnetic structures. The results demonstrate how simple, fundamental refinements in ligand fields can profoundly influence the phase space of quantum matter. △ Less

Submitted 26 July, 2025; v1 submitted 22 March, 2025; originally announced March 2025.

Flat bands and temperature-driven phase transition in quasi-one-dimensional zigzag chains

Authors: Jisong Gao, Haijun Cao, Xuegao Hu, Hui Zhou, Zhihao Cai, Qiaoxiao Zhao, Dong Li, Zhicheng Gao, Shin-ichiro Ideta, Kenya Shimada, Peng Cheng, Lan Chen, Kehui Wu, Sheng Meng, Baojie Feng

Abstract: Flat-band materials have garnered extensive attention due to their captivating properties associated with strong correlation effects. While flat bands have been discovered in several types of 2D materials, their existence in 1D systems remains elusive. Here, we propose a 1D frustrated lattice, specifically the 1D zigzag lattice, as a platform for hosting flat bands. This lattice can be experimenta… ▽ More Flat-band materials have garnered extensive attention due to their captivating properties associated with strong correlation effects. While flat bands have been discovered in several types of 2D materials, their existence in 1D systems remains elusive. Here, we propose a 1D frustrated lattice, specifically the 1D zigzag lattice, as a platform for hosting flat bands. This lattice can be experimentally realized by growing CuTe chains on Cu(111). The presence of flat bands was confirmed by tight-binding model analysis, first-principles calculations, and angle-resolved photoemission spectroscopy measurements. In addition, we discovered a temperature-driven phase transition at approximately 250 K. Detailed analyses demonstrate that the system has a Tomonaga-Luttinger liquid behavior, accompanied by spin-charge separation effects. Our work unveils new prospects for investigating strongly correlated electron behaviors and topological properties in the 1D limit. △ Less

Submitted 3 March, 2025; originally announced March 2025.

Journal ref: Physical Review Letters 134, 086202 (2025)

Electromagnon signatures of a metastable multiferroic state

Authors: Blake S. Dastrup, Zhuquan Zhang, Peter R. Miedaner, Yu-Che Chien, Young Sun, Yan Wu, Huibo Cao, Edoardo Baldini, Keith A. Nelson

Abstract: Magnetoelectric multiferroic materials, particularly type-II multiferroics where ferroelectric polarizations arise from magnetic order, offer significant potential for the simultaneous control of magnetic and electric properties. However, it remains an open question as to how the multiferroic ground states are stabilized on the free-energy landscape in the presence of intricate competition between… ▽ More Magnetoelectric multiferroic materials, particularly type-II multiferroics where ferroelectric polarizations arise from magnetic order, offer significant potential for the simultaneous control of magnetic and electric properties. However, it remains an open question as to how the multiferroic ground states are stabilized on the free-energy landscape in the presence of intricate competition between the magnetoelectric coupling and thermal fluctuations. In this work, by using terahertz time-domain spectroscopy in combination with an applied magnetic field, photoexcitation, and single-shot detection, we reveal the spectroscopic signatures of a magnetic-field-induced metastable multiferroic state in a hexaferrite. This state remains robust until thermal influences cause the sample to revert to the original paraelectric state. Our findings shed light on the emergence of metastable multiferroicity and its interplay with thermal dynamics. △ Less

Submitted 14 February, 2025; originally announced February 2025.

Journal ref: Phys. Rev. Lett. 134, 086706 (2025)

Anomalous temperature-dependent magnetization in the nearly collinear antiferromagnet Y$_2$Co$_3$

Authors: Yunshu Shi, Huibo Cao, Hung-Cheng Wu, Li Yin, Neil Harrison, David S. Parker, Tushar Bhowmick, Tessa McNamee, Fatemeh Safari, Sergey L. Budko, James C. Fettinger, Susan M. Kauzlarich, Peter Klavins, Dmitry Popov, Ravhi Kumar, Russell J. Hemley, Shanti Deemyad, Taku J. Sato, Paul. C. Canfield, Valentin Taufour

Abstract: Y$_2$Co$_3$ is a newly discovered antiferromagnetic (AFM) compound with distorted kagome layers. Previous investigations via bulk magnetization measurements suggested a complex noncollinear magnetic behavior, with magnetic moments primarily anti-aligned along the $b$ axis and some canting towards the $ac$ plane. In this study, we report the magnetic structure of Y$_2$Co$_3$ to be an A-type AFM str… ▽ More Y$_2$Co$_3$ is a newly discovered antiferromagnetic (AFM) compound with distorted kagome layers. Previous investigations via bulk magnetization measurements suggested a complex noncollinear magnetic behavior, with magnetic moments primarily anti-aligned along the $b$ axis and some canting towards the $ac$ plane. In this study, we report the magnetic structure of Y$_2$Co$_3$ to be an A-type AFM structure with ferromagnetic (FM) interactions within the distorted kagome plane and an interplane antiferromagnetic interaction, as determined by single-crystal neutron diffraction. The magnetic moments align along the $b$ axis, with minimal canting towards the $c$ axis, at odds with the previous interpretation of bulk magnetization measurements. The magnetic moments on the two distinct Co sites are [0, -0.68(3), 0] $μ_B$ and [0, 1.25(4), 0.07(1)] $μ_B$. We attribute the previously reported "noncollinear" behavior to the considerable temperature dependence of itinerant AFM exchange interactions, induced by thermal contraction along the $b$ axis. Additionally, our examination of lattice constants through pressure studies reveals compensating effects on FM and AFM interactions, resulting in negligible pressure dependence of $T_\textrm{N}$. △ Less

Submitted 26 January, 2025; originally announced January 2025.

Journal ref: Physical Review B 110,235159 (2024)

Exact Decoding of Repetition Code under Circuit Level Noise

Authors: Hanyan Cao, Shoukuan Zhao, Dongyang Feng, Zisong Shen, Haisheng Yan, Tang Su, Weijie Sun, Huikai Xu, Feng Pan, Haifeng Yu, Pan Zhang

Abstract: Repetition code forms a fundamental basis for quantum error correction experiments. To date, it stands as the sole code that has achieved large distances and extremely low error rates. Its applications span the spectrum of evaluating hardware limitations, pinpointing hardware defects, and detecting rare events. However, current methods for decoding repetition codes under circuit level noise are su… ▽ More Repetition code forms a fundamental basis for quantum error correction experiments. To date, it stands as the sole code that has achieved large distances and extremely low error rates. Its applications span the spectrum of evaluating hardware limitations, pinpointing hardware defects, and detecting rare events. However, current methods for decoding repetition codes under circuit level noise are suboptimal, leading to inaccurate error correction thresholds and introducing additional errors in event detection. In this work, we establish that repetition code under circuit level noise has an exact solution, and we propose an optimal maximum likelihood decoding algorithm called planar. The algorithm is based on the exact solution of the spin glass partition function on planar graphs and has polynomial computational complexity. Through extensive numerical experiments, we demonstrate that our algorithm uncovers the exact threshold for depolarizing noise and realistic superconductor SI1000 noise. Furthermore, we apply our method to analyze data from recent quantum memory experiments conducted by Google Quantum AI, revealing that part of the error floor was attributed to the decoding algorithm used by Google. Finally, we implemented the repetition code quantum memory on superconducting systems with a 72-qubit quantum chip lacking reset gates, demonstrating that even with an unknown error model, the proposed algorithm achieves a significantly lower logical error rate than the matching-based algorithm. △ Less

Submitted 7 January, 2025; originally announced January 2025.

Coexistence of Commensurate and Incommensurate Antiferromagnetic Groundstates in Co$_x$NbSe$_2$ Single Crystal

Authors: H. Cein Mandujano, Peter Y. Zavalij, Alicia Manjón-Sanz, Huibo Cao, Efrain E. Rodriguez

Abstract: In Co$_x$NbSe$_2$, crystal symmetry, and cobalt site occupation drive the formation of two distinct magnetic phases. At $x = 1/4$, the centrosymmetric structure ($P$6$_3$/$mmc$) promotes Co-Co interactions leading to the formation of an $A$-type antiferromagnetic structure phase with a transition temperature of $T_N^A$ = 169 K. At $x = 1/3$, the non-centrosymmetric structure ($P$6$_3$22) induces a… ▽ More In Co$_x$NbSe$_2$, crystal symmetry, and cobalt site occupation drive the formation of two distinct magnetic phases. At $x = 1/4$, the centrosymmetric structure ($P$6$_3$/$mmc$) promotes Co-Co interactions leading to the formation of an $A$-type antiferromagnetic structure phase with a transition temperature of $T_N^A$ = 169 K. At $x = 1/3$, the non-centrosymmetric structure ($P$6$_3$22) induces a lower-temperature magnetic phase with $T_N^S$ = 28 K. We report the coexistence of both substructures within a superlattice, with a nuclear propagation vector of (1/3, 1/3, 0) relative to the host lattice. Single crystals of Co$_{0.28}$NbSe$_2$ exhibit both magnetic transitions, with $T_N^A$ corresponding to the $x \sim 1/4$ phase and $T_N^S$ corresponding to the $x \sim 1/3$ phase. Magnetic susceptibility and specific heat measurements confirm these transitions, although only the high-temperature $T_N^A$ phase significantly affects resistivity. We successfully isolate each phase in powder samples, while single crystals with an intercalation ratio of $x = 0.28$ display the coexistence of both phases in a single sample. Using single-crystal neutron diffraction, we solved the magnetic structure of the high-temperature centrosymmetric phase ($T_N^A$), and neutron powder diffraction revealed the double-$q$ magnetic structure of the low-temperature noncentrosymmetric phase ($T_N^S$) △ Less

Submitted 31 December, 2024; originally announced January 2025.

Magnetic excitations and interactions in the Weyl ferrimagnet NdAlSi

Authors: Chris J. Lygouras, Hung-Yu Yang, Xiaohan Yao, Jonathan Gaudet, Yiqing Hao, Huibo Cao, Jose A. Rodriguez-Rivera, Andrey Podlesnyak, Stefan Blügel, Predrag Nikolić, Fazel Tafti, Collin L. Broholm

Abstract: Weyl fermions can arise from time-reversal symmetry-breaking magnetism, but their impact on magnetic order is a source of ongoing research. Using high-precision neutron diffraction and spectroscopy, we present a comprehensive exploration of the magnetic structure and excitation spectrum of Weyl semimetal and helical magnet NdAlSi. We use Luttinger-Tisza, classical mean-field, and random-phase appr… ▽ More Weyl fermions can arise from time-reversal symmetry-breaking magnetism, but their impact on magnetic order is a source of ongoing research. Using high-precision neutron diffraction and spectroscopy, we present a comprehensive exploration of the magnetic structure and excitation spectrum of Weyl semimetal and helical magnet NdAlSi. We use Luttinger-Tisza, classical mean-field, and random-phase approximation techniques to model the dispersive crystal field excitons. We find extended-ranged and sign-changing interactions, suggesting a coupling between conduction electrons and the local moments. We demonstrate that low-symmetry anisotropic Dzyaloshinskii-Moriya interactions, in contrast with higher-symmetry interactions enabled by Weyl fermions, play an important role in stabilizing the complex spin spiral ground state of NdAlSi. Our work provides a first detailed view of microscopic interactions in a Weyl magnet, and constrains the role of Weyl electrons and their chirality on the spiral magnetism. △ Less

Submitted 30 December, 2024; originally announced December 2024.

Comments: 24 total pages, 6 main figures, supplementary information included

A Universal Method to Transform Aromatic Hydrocarbon Molecules into Confined Carbyne inside Single-Walled Carbon Nanotubes

Authors: Yingzhi Chen, Kunpeng Tang, Wendi Zhang, Huiju Cao, Hongwei Zhang, Yanghao Feng, Weili Cui, Yuan Hu, Lei Shi, Guowei Yang

Abstract: Carbyne, a sp1-hybridized allotrope of carbon, is a linear carbon chain with exceptional theoretically predicted properties that surpass those of sp2-hybridized graphene and carbon nanotubes (CNTs). However, the existence of carbyne has been debated due to its instability caused by Peierls distortion, which limits its practical development. The only successful synthesis of carbyne has been achieve… ▽ More Carbyne, a sp1-hybridized allotrope of carbon, is a linear carbon chain with exceptional theoretically predicted properties that surpass those of sp2-hybridized graphene and carbon nanotubes (CNTs). However, the existence of carbyne has been debated due to its instability caused by Peierls distortion, which limits its practical development. The only successful synthesis of carbyne has been achieved inside CNTs, resulting in a form known as confined carbyne (CC). However, CC can only be synthesized inside multi-walled CNTs, limiting its property-tuning capabilities to the inner tubes of the CNTs. Here, we present a universal method for synthesizing CC inside single-walled carbon nanotubes (SWCNTs) with diameter of 0.9-1.3 nm. Aromatic hydrocarbon molecules are filled inside SWCNTs and subsequently transformed into CC under low-temperature annealing. A variety of aromatic hydrocarbon molecules are confirmed as effective precursors for formation of CC, with Raman frequencies centered around 1861 cm-1. Enriched (6,5) and (7,6) SWCNTs with diameters less than 0.8 nm are less effective than the SWCNTs with diameter of 0.9-1.3 nm for CC formation. Furthermore, resonance Raman spectroscopy reveals that optical band gap of the CC at 1861 cm-1 is 2.353 eV, which is consistent with the result obtained using a linear relationship between the Raman signal and optical band gap. This newly developed approach provides a versatile route for synthesizing CC from various precursor molecules inside diverse templates, which is not limited to SWCNTs but could extend to any templates with appropriate size, including molecular sieves, zeolites, boron nitride nanotubes, and metal-organic frameworks. △ Less

Submitted 29 December, 2024; originally announced December 2024.

Comments: 31 pages, 5 figures

Quantum entanglement of XY-type spin dimers in Shastry-Sutherland lattice

Authors: Qianli Ma, Brianna R. Billingsley, Madalynn Marshall, David A. Dahlbom, Yiqing Hao, Daniel M. Pajerowski, Alexander I. Kolesnikov, Xiaojian Bai, Cristian D. Batista, Tai Kong, Huibo Cao

Abstract: We report a comprehensive study on the origin of the enigmatic disordered ground state within the Shastry-Sutherland lattice, BaCe$_2$ZnS$_5$, at low temperatures. The magnetization and heat capacity data show a lack of magnetic ordering down to 73 mK. We deploy a localized spin dimer model which can accurately reproduce the dynamic structure factor of the neutron data, magnetization and heat capa… ▽ More We report a comprehensive study on the origin of the enigmatic disordered ground state within the Shastry-Sutherland lattice, BaCe$_2$ZnS$_5$, at low temperatures. The magnetization and heat capacity data show a lack of magnetic ordering down to 73 mK. We deploy a localized spin dimer model which can accurately reproduce the dynamic structure factor of the neutron data, magnetization and heat capacity data. Remarkably, the intra-dimer exchange interaction shows strong XY-type anisotropy and the ground state of BaCe$_2$ZnS$_5$ is in an entangled state $(|\uparrow\uparrow> - |\downarrow\downarrow>)/\sqrt{2}$. This is in contrast to the singlet dimer state that is obtained for Heisenberg interactions. These results confirm that BaCe$_2$ZnS$_5$ is in a quantum paramagnet state consisting of entangled spin dimer states. △ Less

Submitted 23 December, 2024; originally announced December 2024.

Structural and magnetic properties of CoTeMoO$_6$ revisited

Authors: Yu Li, Jared Coles, Xin Gui, Hyowon Park, Yan Wu, Xinglong Chen, Jing-han Chen, Xiaoping Wang, Huibo Cao, Shane Stadler, Omar Chmaissem, David P. Young, Stephan Rosenkranz, John F. DiTusa

Abstract: We have conducted a comprehensive investigation into the magnetic properties of the chiral multiferroic material CoTeMoO$_6$. In contrast with the previous claim of canted antiferromagnetic order with ferromagnetic components, our investigation reveals an antiferromagnetic ground state with compensated moments, providing an interesting platform for exploring exotic material properties. Through car… ▽ More We have conducted a comprehensive investigation into the magnetic properties of the chiral multiferroic material CoTeMoO$_6$. In contrast with the previous claim of canted antiferromagnetic order with ferromagnetic components, our investigation reveals an antiferromagnetic ground state with compensated moments, providing an interesting platform for exploring exotic material properties. Through careful measurements of magnetization under a series of applied field, we demonstrate that there exist two sequential field-induced magnetic transitions in CoTeMoO$_6$, with one occurring at $H_{c1}$=460 Oe along the a-axis, and the other at $H_{c2}$=1.16 T with the field along the b-axis. The values of $H_{c1}$ and $H_{c2}$ exhibit strong angular dependence and diverge with different rates as the applied field is rotated 90 degrees within the ab plane. This reflects the distinct nature of these transitions, which is further supported by the different critical behavior of $H_{c1}$ and $H_{c2}$, characterized by the values of $γ$,in the function of $H_c=H_0\times(1-\frac{T}{T_c})^n$. Furthermore, we have demonstrated that there exist structural and magnetic twin domains in CoTeMoO$_6$ that strongly affect the experimental measurement of their macroscopic properties. Intriguingly, these twin domains can be related to the orthorhombicity/chirality of the crystal structure with the space group $P2_1 2_1 2$. We further explored the magnetic and structural domains with uniaxial pressure and polarized light microscopy. Our results suggest that CoTeMoO$_6$ could be used as a unique platform for investigating the intriguing physics involving intertwined degrees of freedom. The tunability of the underlying domain distribution and its strong anisotropy could also be useful for developing functional devices and applications. △ Less

Submitted 15 December, 2024; originally announced December 2024.

Comments: 11 figures 6 tables

Journal ref: Phys. Rev. B 111, 104434 (2025)

ASb3Mn9O19 (A = K or Rb): New Mn-Based Two-Dimensional Magnetoplumbites with Geometric and Magnetic Frustration

Authors: Jianyi Chen, Stuart Calder, Joseph A. M. Paddison, Gina Angelo, Liana Klivansky, Jian Zhang, Huibo Cao, Xin Gui

Abstract: Magnetoplumbites are one of the most broadly studied families of hexagonal ferrites, typically with high magnetic ordering temperatures, making them excellent candidates for permanent magnets. However, magnetic frustration was rarely observed in magnetoplumbites. Herein, we report the discovery, synthesis and characterization of the first Mn-based magnetoplumbite, as well as the first magnetoplumb… ▽ More Magnetoplumbites are one of the most broadly studied families of hexagonal ferrites, typically with high magnetic ordering temperatures, making them excellent candidates for permanent magnets. However, magnetic frustration was rarely observed in magnetoplumbites. Herein, we report the discovery, synthesis and characterization of the first Mn-based magnetoplumbite, as well as the first magnetoplumbite involving pnictogens (Sb), ASb3Mn9O19 (A = K or Rb). The Mn3+ (S = 2) cations, further confirmed by DC magnetic susceptibility and X-ray photoelectron spectroscopy, construct three geometrically frustrated sublattices, including Kagome, triangular and puckered honeycomb lattices. Magnetic properties measurements revealed strong antiferromagnetic spin-spin coupling as well as multiple low-temperature magnetic features. Heat capacity data did not show any prominent lambda-anomaly, suggesting minimal associated magnetic entropy. Moreover, neutron powder diffraction implied the absence of long-range magnetic ordering in KSb3Mn9O19 down to 3 K. However, several magnetic peaks were observed in RbSb3Mn9O19 at 3 K, corresponding to an incommensurate magnetic structure. Interestingly, strong diffuse scattering was seen in the neutron powder diffraction patterns of both compounds at low angles, and was analyzed by reverse Monte Carlo refinements, indicating short-range spin ordering related to frustrated magnetism as well as two-dimensional magnetic correlations in ASb3Mn9O19 (A = K or Rb). △ Less

Submitted 8 December, 2024; originally announced December 2024.

Comments: 39 pages, 14 figures, 8 tables

UOTe: Kondo-interacting topological antiferromagnet in a van der Waals lattice

Authors: Christopher Broyles, Sougata Mardanya, Mengke Liu, Junyeong Ahn, Thao Dinh, Gadeer Alqasseri, Jalen Garner, Zackary Rehfuss, Ken Guo, Jiahui Zhu, David Martinez, Du Li, Yiqing Hao, Huibo Cao, Matt Boswell, Weiwei Xie, Jeremy G. Philbrick, Tai Kong, Li Yang, Ashvin Vishwanath, Philip Kim, Su-Yang Xu, Jennifer E. Hoffman, Jonathan D. Denlinger, Sugata Chowdhury , et al. (1 additional authors not shown)

Abstract: Since the initial discovery of two-dimensional van der Waals (vdW) materials, significant effort has been made to incorporate the three properties of magnetism, band structure topology, and strong electron correlations $-$ to leverage emergent quantum phenomena and expand their potential applications. However, the discovery of a single vdW material that intrinsically hosts all three ingredients ha… ▽ More Since the initial discovery of two-dimensional van der Waals (vdW) materials, significant effort has been made to incorporate the three properties of magnetism, band structure topology, and strong electron correlations $-$ to leverage emergent quantum phenomena and expand their potential applications. However, the discovery of a single vdW material that intrinsically hosts all three ingredients has remained an outstanding challenge. Here we report the discovery of a Kondo-interacting topological antiferromagnet in the vdW 5$f$ electron system UOTe. It has a high antiferromagnetic (AFM) transition temperature of 150 K, with a unique AFM configuration that breaks the combined parity and time reversal ($PT$) symmetry in an even number of layers while maintaining zero net magnetic moment. Our angle-resolved photoemission spectroscopy (ARPES) measurements reveal Dirac bands near the Fermi level, which combined with our theoretical calculations demonstrate UOTe as an AFM Dirac semimetal. Within the AFM order, we observed the presence of the Kondo interaction, as evidenced by the emergence of a 5$f$ flat band near the Fermi level below 100 K and hybridization between the Kondo band and the Dirac band. Our density functional theory calculations in its bilayer form predict UOTe as a rare example of a fully-compensated AFM Chern insulator. △ Less

Submitted 15 November, 2024; v1 submitted 13 November, 2024; originally announced November 2024.

Comments: Accepted to Advanced Materials

Vacancy-induced suppression of CDW order and its impact on magnetic order in kagome antiferromagnet FeGe

Authors: Mason L. Klemm, Saif Siddique, Yuan-Chun Chang, Sijie Xu, Yaofeng Xie, Tanner Legvold, Mehrdad T. Kiani, Feng Ye, Huibo Cao, Yiqing Hao, Wei Tian, Hubertus Luetkens, Masaaki Matsuda, Douglas Natelson, Zurab Guguchia, Chien-Lung Huang, Ming Yi, Judy J. Cha, Pengcheng Dai

Abstract: Two-dimensional (2D) kagome lattice metals are interesting because they display flat electronic bands, Dirac points, Van Hove singularities, and can have interplay between charge density wave (CDW), magnetic order, and superconductivity. In kagome lattice antiferromagnet FeGe, a short-range CDW order was found deep within an antiferromagnetically ordered state, interacting with the magnetic order.… ▽ More Two-dimensional (2D) kagome lattice metals are interesting because they display flat electronic bands, Dirac points, Van Hove singularities, and can have interplay between charge density wave (CDW), magnetic order, and superconductivity. In kagome lattice antiferromagnet FeGe, a short-range CDW order was found deep within an antiferromagnetically ordered state, interacting with the magnetic order. Surprisingly, post-growth annealing of FeGe at 560$^{\circ}$C can suppress the CDW order while annealing at 320$^{\circ}$C induces a long-range CDW order, with the ability to cycle between the states repeatedly by annealing. Here we perform transport, neutron scattering, scanning transmission electron microscopy (STEM), and muon spin rotation ($μ$SR) experiments to unveil the microscopic mechanism of the annealing process and its impact on magneto-transport, CDW, and magnetic properties of FeGe. We find that 560$^{\circ}$C annealing creates germanium vacancies uniformly distributed throughout the FeGe kagome lattice, which prevent the formation of Ge-Ge dimers necessary for the CDW order. Upon annealing at 320$^{\circ}$C, the system segregates into stoichiometric FeGe regions with long-range CDW order and regions with stacking faults that act as nucleation sites for the CDW. The presence or absence of CDW order greatly affects the anomalous Hall effect, incommensurate magnetic order, and spin-lattice coupling in FeGe, thus placing FeGe as the only known kagome lattice material with a tunable CDW and magnetic order, potentially useful for sensing and information transmission. △ Less

Submitted 17 October, 2024; originally announced October 2024.

Altermagnetism in the layered intercalated transition metal dichalcogenide CoNb$_4$Se$_8$

Authors: Resham Babu Regmi, Hari Bhandari, Bishal Thapa, Yiqing Hao, Nileema Sharma, James McKenzie, Xinglong Chen, Abhijeet Nayak, Mohamed El Gazzah, Bence Gábor Márkus, László Forró, Xiaolong Liu, Huibo Cao, J. F. Mitchell, I. I. Mazin, Nirmal J. Ghimire

Abstract: Altermagnets (AMs) are a new class of magnetic materials that combine the beneficial spintronics properties of ferromagnets and antiferromagnets, garnering significant attention recently. Here, we have identified altermagnetism in a layered intercalated transition metal diselenide, CoNb$_4$Se$_8$, which crystallizes with an ordered sublattice of intercalated Co atoms between NbSe$_2$ layers. Singl… ▽ More Altermagnets (AMs) are a new class of magnetic materials that combine the beneficial spintronics properties of ferromagnets and antiferromagnets, garnering significant attention recently. Here, we have identified altermagnetism in a layered intercalated transition metal diselenide, CoNb$_4$Se$_8$, which crystallizes with an ordered sublattice of intercalated Co atoms between NbSe$_2$ layers. Single crystals are synthesized, and the structural characterizations are performed using single crystal diffraction and scanning tunneling microscopy. Magnetic measurements reveal easy-axis antiferromagnetism below 168 K. Density functional theory (DFT) calculations indicate that A-type antiferromagnetic ordering with easy-axis spin direction is the ground state, which is verified through single crystal neutron diffraction experiments. Electronic band structure calculations in this magnetic state display spin-split bands, confirming altermagnetism in this compound. The layered structure of CoNb$_4$Se$_8$ presents a promising platform for testing various predicted properties associated with altermagnetism. △ Less

Submitted 16 August, 2024; originally announced August 2024.

Anderson transition for light in three dimensions

Authors: Alexey Yamilov, Hui Cao, Sergey E. Skipetrov

Abstract: We study Anderson transition for light in three dimensions by performing large-scale ab-initio simulations of electromagnetic wave transport in disordered ensembles of conducting spheres. A mobility edge that separates diffusive transport and Anderson localization is identified, revealing a sharp transition from diffusion to localization for light. Critical behavior in the vicinity of the mobility… ▽ More We study Anderson transition for light in three dimensions by performing large-scale ab-initio simulations of electromagnetic wave transport in disordered ensembles of conducting spheres. A mobility edge that separates diffusive transport and Anderson localization is identified, revealing a sharp transition from diffusion to localization for light. Critical behavior in the vicinity of the mobility edge is well described by a single-parameter scaling law. The critical exponent is found to be consistent with the value known for the Anderson transition of the orthogonal universality class. Statistical distribution of total transmission at the mobility edge is described without any fit parameter by the diagrammatic perturbation theory originally developed for scalar wave diffusion, but notable deviation from the theory is found when Anderson localization sets in. △ Less

Submitted 9 August, 2024; originally announced August 2024.

Comments: 6 pages, 4 figures

Journal ref: Phys. Rev. Lett. 134, 046302 (2025)

Lattice and magnetic structure in the van der Waals antiferromagnet VBr3

Authors: Yimeng Gu, Yiqing Hao, Zeyu Kao, Yiqing Gu, Feiyang Liu, Shiyi Zheng, Huibo Cao, Lunhua He, Jun Zhao

Abstract: We report a comprehensive investigation of the lattice and magnetic structure in van der Waals antiferromagnet VBr3, characterized by a BiI3-type structure at room temperature. Neutron diffraction experiments were performed on both polycrystalline and single-crystalline VBr3 samples, revealing clear magnetic Bragg peaks emerging below the Néel temperature of TN = 26.5 K. These magnetic Bragg peaks… ▽ More We report a comprehensive investigation of the lattice and magnetic structure in van der Waals antiferromagnet VBr3, characterized by a BiI3-type structure at room temperature. Neutron diffraction experiments were performed on both polycrystalline and single-crystalline VBr3 samples, revealing clear magnetic Bragg peaks emerging below the Néel temperature of TN = 26.5 K. These magnetic Bragg peaks can be indexed by k = (0, 0.5, 1) in hexagonal notation. Our refinement analysis suggests that the antiferromagnetic order in VBr3 manifests as a zigzag structure. Moreover, we observed peak splitting for nuclear Bragg peaks in the HK-plane below the structure transition temperature of Ts = 94 K, indicating the breaking of 3-fold symmetry within the ab-plane. △ Less

Submitted 5 August, 2024; originally announced August 2024.

Comments: 13 pages, 4 figures

Journal ref: Phys. Rev. B 110, 064403 (2024)

Antiferroelectric Hafnia Down to the 2D Limit

Authors: Xin Li, Guodong Ren, Haidong Lu, Kartik Samanta, Amit Kumar Shah, Kai Huang, Pravan Omprakash, Yu Yun, Pratyush Buragohain, Huibo Cao, Yan Wu, Jordan A. Hachtel, Andrew R. Lupini, Miaofang Chi, Juan Carlos Idrobo, Evgeny Y. Tsymbal, Alexei Gruverman, Rohan Mishra, Xiaoshan Xu

Abstract: Antiferroelectricity is a material property characterized by alternating electric dipoles spontaneously ordered in antiparallel directions. Antiferroelectrics are promising for energy storage, solid-state cooling, and memory technologies; however, these materials are scarce, and their scalability remains largely unexplored. In this work, we demonstrate that single-crystalline hafnia, a lead-free C… ▽ More Antiferroelectricity is a material property characterized by alternating electric dipoles spontaneously ordered in antiparallel directions. Antiferroelectrics are promising for energy storage, solid-state cooling, and memory technologies; however, these materials are scarce, and their scalability remains largely unexplored. In this work, we demonstrate that single-crystalline hafnia, a lead-free CMOS-compatible material, exhibits antiferroelectricity under compressive-strain conditions. We observe antiparallel sublattice polarization and stable double-hysteresis in single-crystalline (111)-oriented epitaxial La-doped hafnia films grown on yttrium-stabilized zirconia and show that the antipolar orthorhombic phase of hafnia adheres to the Kittel model of antiferroelectricity. Notably, compressive strain strengthens the antiferroelectric order in thinner La-doped hafnia films, achieving an unprecedented 850 C ordering temperature in the two-dimensional limit, highlighting hafnia's potential for advanced antiferroelectric devices. △ Less

Submitted 2 August, 2025; v1 submitted 3 August, 2024; originally announced August 2024.

Evidence for Two-dimensional Weyl Fermions in Air-Stable Monolayer PtTe$_{1.75}$

Authors: Zhihao Cai, Haijun Cao, Haohao Sheng, Xuegao Hu, Zhenyu Sun, Qiaoxiao Zhao, Jisong Gao, Shin-ichiro Ideta, Kenya Shimada, Jiawei Huang, Peng Cheng, Lan Chen, Yugui Yao, Sheng Meng, Kehui Wu, Zhijun Wang, Baojie Feng

Abstract: The Weyl semimetals represent a distinct category of topological materials wherein the low-energy excitations appear as the long-sought Weyl fermions. Exotic transport and optical properties are expected because of the chiral anomaly and linear energy-momentum dispersion. While three-dimensional Weyl semimetals have been successfully realized, the quest for their two-dimensional (2D) counterparts… ▽ More The Weyl semimetals represent a distinct category of topological materials wherein the low-energy excitations appear as the long-sought Weyl fermions. Exotic transport and optical properties are expected because of the chiral anomaly and linear energy-momentum dispersion. While three-dimensional Weyl semimetals have been successfully realized, the quest for their two-dimensional (2D) counterparts is ongoing. Here, we report the realization of 2D Weyl fermions in monolayer PtTe$_{1.75}$, which has strong spin-orbit coupling and lacks inversion symmetry, by combined angle-resolved photoemission spectroscopy, scanning tunneling microscopy, second harmonic generation, X-ray photoelectron spectroscopy measurements, and first-principles calculations. The giant Rashba splitting and band inversion lead to the emergence of three pairs of critical Weyl cones. Moreover, monolayer PtTe$_{1.75}$ exhibits excellent chemical stability in ambient conditions, which is critical for future device applications. The discovery of 2D Weyl fermions in monolayer PtTe$_{1.75}$ opens up new possibilities for designing and fabricating novel spintronic devices. △ Less

Submitted 12 December, 2024; v1 submitted 30 July, 2024; originally announced July 2024.

Journal ref: Nano Lett. 24, 10237-10243 (2024)

Spin Excitations and Flat Electronic Bands in a Cr-based Kagome Superconductor

Authors: Zehao Wang, Yucheng Guo, Hsiao Yu Huang, Fang Xie, Yuefei Huang, Bin Gao, Ji Seop Oh, Han Wu, Jun Okamoto, Ganesha Channagowdra, Chien Te Chen, Feng Ye, Xingye Lu, Zhaoyu Liu, Zheng Ren, Yuan Fang, Yiming Wang, Ananya Biswas, Yichen Zhang, Ziqin Yue, Cheng Hu, Chris Jozwiak, Aaron Bostwick, Eli Rotenberg, Makoto Hashimoto , et al. (11 additional authors not shown)

Abstract: In the quest for topology- and correlation-driven quantum states, kagome lattice materials have garnered significant interest for their band structures, featuring flat bands (FBs) from the quantum destructive interference of the electronic wavefunction. Tuning an FB to the chemical potential could induce electronic instabilities and emergent orders. Despite extensive studies, direct evidence of FB… ▽ More In the quest for topology- and correlation-driven quantum states, kagome lattice materials have garnered significant interest for their band structures, featuring flat bands (FBs) from the quantum destructive interference of the electronic wavefunction. Tuning an FB to the chemical potential could induce electronic instabilities and emergent orders. Despite extensive studies, direct evidence of FBs tuned to the chemical potential and their role in emergent orders in bulk materials remains lacking. Using angle-resolved photoemission spectroscopy, resonant inelastic X-ray scattering, and density functional theory, we show that the low-energy structure of the Cr-based kagome metal superconductor {\Cr} is dominated by FBs at the Fermi level. We also observe low-energy magnetic excitations evolving across the low-temperature transition, largely consistent with the FB shift. Our results suggest that the low-temperature order contains a magnetic origin and that the kagome FBs may play a role in the emergence of this order. △ Less

Submitted 24 November, 2025; v1 submitted 7 June, 2024; originally announced June 2024.

Comments: Published in Nature Communications 16, 7573 (2025). 11 pages, 4 main figures, 13 supplementary figures

Journal ref: Nat Commun 16, 7573 (2025)

Stoichiometry-induced ferromagnetism in altermagnetic candidate MnTe

Authors: Michael Chilcote, Alessandro R. Mazza, Qiangsheng Lu, Isaiah Gray, Qi Tian, Qinwen Deng, Duncan Moseley, An-Hsi Chen, Jason Lapano, Jason S. Gardner, Gyula Eres, T. Zac Ward, Erxi Feng, Huibo Cao, Valeria Lauter, Michael A. McGuire, Raphael Hermann, David Parker, Myung-Geun Han, Asghar Kayani, Gaurab Rimal, Liang Wu, Timothy R. Charlton, Robert G. Moore, Matthew Brahlek

Abstract: The field of spintronics has seen a surge of interest in altermagnetism due to novel predictions and many possible applications. MnTe is a leading altermagnetic candidate that is of significant interest across spintronics due to its layered antiferromagnetic structure, high Neel temperature (TN ~ 310 K) and semiconducting properties. We present results on molecular beam epitaxy (MBE) grown MnTe/In… ▽ More The field of spintronics has seen a surge of interest in altermagnetism due to novel predictions and many possible applications. MnTe is a leading altermagnetic candidate that is of significant interest across spintronics due to its layered antiferromagnetic structure, high Neel temperature (TN ~ 310 K) and semiconducting properties. We present results on molecular beam epitaxy (MBE) grown MnTe/InP(111) films. Here, it is found that the electronic and magnetic properties are driven by the natural stoichiometry of MnTe. Electronic transport and in situ angle-resolved photoemission spectroscopy show the films are natively metallic with the Fermi level in the valence band and the band structure is in good agreement with first principles calculations for altermagnetic spin-splitting. Neutron diffraction confirms that the film is antiferromagnetic with planar anisotropy and polarized neutron reflectometry indicates weak ferromagnetism, which is linked to a slight Mn-richness that is intrinsic to the MBE grown samples. When combined with the anomalous Hall effect, this work shows that the electronic response is strongly affected by the ferromagnetic moment. Altogether, this highlights potential mechanisms for controlling altermagnetic ordering for diverse spintronic applications. △ Less

Submitted 6 June, 2024; originally announced June 2024.

Comments: Accepted in Advanced Functional Materials

Single crystal growth, chemical defects, magnetic and transport properties of antiferromagnetic topological insulators (Ge$_{1-δ-x}$Mn$_x$)$_2$Bi$_2$Te$_5$ ($x\leq 0.47$, $0.11 \leq δ\leq 0.20$)

Authors: Tiema Qian, Chaowei Hu, Jazmine C. Green, Erxi Feng, Huibo Cao, Ni Ni

Abstract: Magnetic topological insulators provide a platform for emergent phenomena arising from the interplay between magnetism and band topology. Here we report the single crystal growth, crystal structure, magnetic and transport properties, as well as the neutron scattering studies of topological insulator series (Ge$_{1-δ-x}$Mn$_x$)$_2$Bi$_2$Te$_5$ ($x\leq 0.47$, $0.11 \leq δ\leq 0.20$). Upon doping up… ▽ More Magnetic topological insulators provide a platform for emergent phenomena arising from the interplay between magnetism and band topology. Here we report the single crystal growth, crystal structure, magnetic and transport properties, as well as the neutron scattering studies of topological insulator series (Ge$_{1-δ-x}$Mn$_x$)$_2$Bi$_2$Te$_5$ ($x\leq 0.47$, $0.11 \leq δ\leq 0.20$). Upon doping up to $x = 0.47$, the lattice parameter $c$ decreases by 0.8\%, while the lattice parameter $a$ remains nearly unchanged. Significant Ge vacancies and Ge/Bi site mixing are revealed via elemental analysis as well as refinements of the neutron and X-ray diffraction data, resulting in holes dominating the charge transport. At $x = 0.47$, below 10.8 K, a bilayer A-type antiferromagnetic ordered state emerges, featuring an ordered moment of 3.0(3) $μ_{B}$/Mn at 5 K, with the $c$ axis as the easy axis. Magnetization data unveil a much stronger interlayer antiferromagnetic exchange interaction and a much smaller uniaxial anisotropy compared to MnBi$_{2}$Te$_{4}$. We attribute the former to the shorter superexchange path and the latter to the smaller ligand-field splitting in (Ge$_{1-δ-x}$Mn$_x$)$_2$Bi$_2$Te$_5$. Our study demonstrates that this series of materials holds promise for the investigation of the Layer Hall effect and quantum metric nonlinear Hall effect. △ Less

Submitted 26 April, 2024; originally announced April 2024.

Comments: 9 pages, 5 figures

Magnetic anisotropy in single-crystalline antiferromagnetic Mn$_2$Au

Authors: Mebatsion S. Gebre, Rebecca K. Banner, Kisung Kang, Kejian Qu, Huibo Cao, André Schleife, Daniel P. Shoemaker

Abstract: Multiple recent studies have identified the metallic antiferromagnet Mn$_2$Au to be a candidate for spintronic applications due to apparent in-plane anisotropy, preserved magnetic properties above room temperature, and current-induced Néel vector switching. Crystal growth is complicated by the fact that Mn$_2$Au melts incongruently. We present a bismuth flux method to grow millimeter-scale bulk si… ▽ More Multiple recent studies have identified the metallic antiferromagnet Mn$_2$Au to be a candidate for spintronic applications due to apparent in-plane anisotropy, preserved magnetic properties above room temperature, and current-induced Néel vector switching. Crystal growth is complicated by the fact that Mn$_2$Au melts incongruently. We present a bismuth flux method to grow millimeter-scale bulk single crystals of Mn$_2$Au in order to examine the intrinsic anisotropic electrical and magnetic properties. Flux quenching experiments reveal that the Mn$_2$Au crystals precipitate below 550°C, about 100°C below the decomposition temperature of Mn$_2$Au. Bulk Mn$_2$Au crystals have a room-temperature resistivity of 16-19 $μΩ$-cm and a residual resistivity ratio of 41. Mn$_2$Au crystals have a dimensionless susceptibility on the order of 10$^{-4}$, comparable to calculated and experimental reports on powder samples. Single-crystal neutron diffraction confirms the in-plane magnetic structure. The tetragonal symmetry of Mn$_2$Au constrains the $ab$-plane magnetic susceptibility to be constant, meaning that $χ_{100}=χ_{110}$ in the low-field limit, below any spin-flop transition. We find that three measured magnetic susceptibilities $χ_{100}$, $χ_{110}$, and $χ_{001}$ are the same order of magnitude and agree with the calculated prediction, meaning the low-field susceptibility of Mn$_2$Au is quite isotropic, despite clear differences in $ab$-plane and $ac$-plane magnetocrystalline anisotropy. Mn$_2$Au is calculated to have an extremely high in-plane spin-flop field above 30 T, which is much larger than that of another in-plane antiferromagnet Fe$_2$As (less than 1 T). The subtle anisotropy of intrinsic susceptibilities may lead to dominating effects from shape, crystalline texture, strain, and defects in devices that attempt spin readout in Mn$_2$Au. △ Less

Submitted 8 August, 2024; v1 submitted 23 April, 2024; originally announced April 2024.

Comments: 9 pages, 10 figures, 15 pages supplemental

Angle-Resolved Magneto-Chiral Anisotropy in a Non-Centrosymmetric Atomic Layer Superlattice

Authors: Long Cheng, Mingrui Bao, Jingxian Zhang, Xue Zhang, Qun Yang, Qiang Li, Hui Cao, Dawei Qiu, Jia Liu, Fei Ye, Qing Wang, Genhao Liang, Hui Li, Guanglei Cheng, Hua Zhou, Jian-Min Zuo, Xiaodong Zhou, Jian Shen, Zhifeng Zhu, Sai Mu, Wenbo Wang, Xiaofang Zhai

Abstract: Chirality in solid-state materials has sparked significant interest due to potential applications of topologically-protected chiral states in next-generation information technology. The electrical magneto-chiral effect (eMChE), arising from relativistic spin-orbit interactions, shows great promise for developing chiral materials and devices for electronic integration. Here we demonstrate an angle-… ▽ More Chirality in solid-state materials has sparked significant interest due to potential applications of topologically-protected chiral states in next-generation information technology. The electrical magneto-chiral effect (eMChE), arising from relativistic spin-orbit interactions, shows great promise for developing chiral materials and devices for electronic integration. Here we demonstrate an angle-resolved eMChE in an A-B-C-C type atomic-layer superlattice lacking time and space inversion symmetry. We observe non-superimposable enantiomers of left-handed and right-handed tilted uniaxial magnetic anisotropy as the sample rotates under static fields, with the tilting angle reaching a striking 45 degree. Magnetic force microscopy and atomistic simulations correlate the tilt to the emergence and evolution of chiral spin textures. The Dzyaloshinskii-Moriya interaction lock effect in competition with Zeeman effect is demonstrated to be responsible for the angle-resolved eMChE. Our findings open up a new horizon for engineering angle-resolved magneto-chiral anisotropy, shedding light on the development of novel angle-resolved sensing or writing techniques in chiral spintronics. △ Less

Submitted 20 April, 2024; originally announced April 2024.

Journal ref: Science Bulletin 2025;70(9)

Phase Diagram and Spectroscopic Signatures of a Supersolid in Quantum Ising Magnet K$_2$Co(SeO$_3$)$_2$

Authors: Tong Chen, Alireza Ghasemi, Junyi Zhang, Liyu Shi, Zhenisbek Tagay, Youzhe Chen, Lei Chen, Eun-Sang Choi, Marcelo Jaime, Minseong Lee, Yiqing Hao, Huibo Cao, Barry Winn, Andrey A. Podlesnyak, Daniel M. Pajerowski, Ruidan Zhong, Xianghan Xu, N. P. Armitage, Robert Cava, Collin Broholm

Abstract: A supersolid is a quantum-entangled state of matter exhibiting the dual characteristics of superfluidity and solidity. Theory predicts that hard-core bosons with repulsive interactions on a triangular lattice can form supersolid phases at half filling and near complete filling. Leveraging an exact mapping between bosons and spin-$\frac{1}{2}$ degrees of freedom, we investigate these phases in the… ▽ More A supersolid is a quantum-entangled state of matter exhibiting the dual characteristics of superfluidity and solidity. Theory predicts that hard-core bosons with repulsive interactions on a triangular lattice can form supersolid phases at half filling and near complete filling. Leveraging an exact mapping between bosons and spin-$\frac{1}{2}$ degrees of freedom, we investigate these phases in the spin-$\frac{1}{2}$ triangular-lattice antiferromagnet \K212 with exchange constants $J_z = 2.96(2)$~meV and $J_{\perp} = 0.21(3)$~meV. At zero field, neutron diffraction reveals the gradual development for $T<15$~K of quasi-two-dimensional $\sqrt{3}\times\sqrt{3}$ magnetic order with $Z_3$ translational symmetry breaking (solidity) albeit with 44(5)% reduced amplitude at $T=0.3$~K indicating strong quantum fluctuations. These are apparent in equidistant bands of continuum neutron scattering for $\hslashω_n\approx n\times J_z$, where $n=0,1,2,3$. The lowest energy ($n=0$) $\bf Q$-dependent continuum has a lower resonant edge and includes a quasi-elastic component at K $(\frac{1}{3}\frac{1}{3})$ consistent with broken $U(1)$ spin rotational symmetry (boson superfluidity). Competing instabilities are apparent in soft albeit finite-energy modes at M $(\frac{1}{2}0)$ and at $\frac{1}{2}$K $(\frac{1}{6}\frac{1}{6})$. For $\bf c$-axis-oriented magnetic fields $17~{\rm T} <μ_0 H< 21~{\rm T}$ that almost saturate the magnetization, corresponding to nearly filling the lattice with bosons, we find a new phase consistent with a second supersolid. These phases are separated by a pronounced 1/3 magnetization plateau that supports coherent spin waves, from which we determine the spin Hamiltonian. △ Less

Submitted 3 November, 2025; v1 submitted 24 February, 2024; originally announced February 2024.

Comments: 17 pages, 6 figures

Unsupervised learning of quantum many-body scars using intrinsic dimension

Authors: Harvey Cao, Dimitris G. Angelakis, Daniel Leykam

Abstract: Quantum many-body scarred systems contain both thermal and non-thermal scar eigenstates in their spectra. When these systems are quenched from special initial states which share high overlap with scar eigenstates, the system undergoes dynamics with atypically slow relaxation and periodic revival. This scarring phenomenon poses a potential avenue for circumventing decoherence in various quantum eng… ▽ More Quantum many-body scarred systems contain both thermal and non-thermal scar eigenstates in their spectra. When these systems are quenched from special initial states which share high overlap with scar eigenstates, the system undergoes dynamics with atypically slow relaxation and periodic revival. This scarring phenomenon poses a potential avenue for circumventing decoherence in various quantum engineering applications. Given access to an unknown scar system, current approaches for identification of special states leading to non-thermal dynamics rely on costly measures such as entanglement entropy. In this work, we show how two dimensionality reduction techniques, multidimensional scaling and intrinsic dimension estimation, can be used to learn structural properties of dynamics in the PXP model and distinguish between thermal and scar initial states. The latter method is shown to be robust against limited sample sizes and experimental measurement errors. △ Less

Submitted 31 January, 2024; v1 submitted 15 January, 2024; originally announced January 2024.

Comments: 16 pages, 5 figures; added references

Superconductivity in pressurized trilayer La$_4$Ni$_3$O$_{10-δ}$ single crystals

Authors: Yinghao Zhu, Di Peng, Enkang Zhang, Bingying Pan, Xu Chen, Lixing Chen, Huifen Ren, Feiyang Liu, Yiqing Hao, Nana Li, Zhenfang Xing, Fujun Lan, Jiyuan Han, Junjie Wang, Donghan Jia, Hongliang Wo, Yiqing Gu, Yimeng Gu, Li Ji, Wenbin Wang, Huiyang Gou, Yao Shen, Tianping Ying, Xiaolong Chen, Wenge Yang , et al. (5 additional authors not shown)

Abstract: The pursuit of discovering new high-temperature superconductors that diverge from the copper-based paradigm1-3 carries profound implications for elucidating mechanisms behind superconductivity and may also enable new applications4-8. Here, our investigation reveals that application of pressure effectively suppresses the spin and charge order in trilayer nickelate La4Ni3O10-δ single crystals, leadi… ▽ More The pursuit of discovering new high-temperature superconductors that diverge from the copper-based paradigm1-3 carries profound implications for elucidating mechanisms behind superconductivity and may also enable new applications4-8. Here, our investigation reveals that application of pressure effectively suppresses the spin and charge order in trilayer nickelate La4Ni3O10-δ single crystals, leading to the emergence of superconductivity with a maximum critical temperature (Tc) of around 30 K at 69.0 GPa. The DC susceptibility measurements confirm a substantial diamagnetic response below Tc, indicating the presence of bulk superconductivity with a volume fraction exceeding 80%. In the normal state, we observe a "strange metal" behavior, characterized by a linear temperature-dependent resistance extending up to 300 K. Furthermore, the layer-dependent superconductivity observed hints at a unique interlayer coupling mechanism specific to nickelates, setting them apart from cuprates in this regard. Our findings provide crucial insights into the fundamental mechanisms underpinning superconductivity, while also introducing a new material platform to explore the intricate interplay between the spin/charge order, flat band structures, interlayer coupling, strange metal behavior and high-temperature superconductivity. △ Less

Submitted 9 July, 2024; v1 submitted 13 November, 2023; originally announced November 2023.

Comments: Supplementary information included

Journal ref: Nature 631, 531-536 (2024)

Quantum to classical crossover in generalized spin systems -- the temperature-dependent spin dynamics of FeI$_2$

Authors: D. Dahlbom, D. Brooks, M. S. Wilson, S. Chi, A. I. Kolesnikov, M. B. Stone, H. Cao, Y. -W. Li, K. Barros, M. Mourigal, C. D. Batista, X. Bai

Abstract: Simulating quantum spin systems at finite temperatures is an open challenge in many-body physics. This work studies the temperature-dependent spin dynamics of a pivotal compound, FeI$_2$, to determine if universal quantum effects can be accounted for by a phenomenological renormalization of the dynamical spin structure factor $S(\mathbf{q}, ω)$ measured by inelastic neutron scattering. Renormaliza… ▽ More Simulating quantum spin systems at finite temperatures is an open challenge in many-body physics. This work studies the temperature-dependent spin dynamics of a pivotal compound, FeI$_2$, to determine if universal quantum effects can be accounted for by a phenomenological renormalization of the dynamical spin structure factor $S(\mathbf{q}, ω)$ measured by inelastic neutron scattering. Renormalization schemes based on the quantum-to-classical correspondence principle are commonly applied at low temperatures to the harmonic oscillators describing normal modes. However, it is not clear how to extend this renormalization to arbitrarily high temperatures. Here we introduce a temperature-dependent normalization of the classical moments, whose magnitude is determined by imposing the quantum sum rule, i.e. $\int dωd\mathbf{q} S(\mathbf{q}, ω) = N_S S (S+1)$ for $N_S$ dipolar magnetic moments. We show that this simple renormalization scheme significantly improves the agreement between the calculated and measured $S(\mathbf{q}, ω)$ for FeI$_{2}$ at all temperatures. Due to the coupled dynamics of dipolar and quadrupolar moments in that material, this renormalization procedure is extended to classical theories based on SU(3) coherent states, and by extension, to any SU(N) coherent state representation of local multipolar moments. △ Less

Submitted 30 October, 2023; originally announced October 2023.

Comments: Associated source code for reproducing calculations available at: https://github.com/SunnySuite/SunnyContributed

MgH2 nanoparticles confined in reduced graphene oxide pillared with organosilica: a novel type of hydrogen storage material

Authors: Feng Yan, Estela Moreton Alfonsín, Peter Ngene, Sytze de Graaf, Oreste De Luca, Huatang Cao, Konstantinos Spyrou, Liqiang Lu, Eleni Thomou, Yutao Pei, Bart J. Kooi, Dimitrios P. Gournis, Petra E. de Jongh, Petra Rudolf

Abstract: Hydrogen is a promising energy carrier that can push forward the energy transition because of its high energy density (142 MJ kg-1), variety of potential sources, low weight and low environmental impact, but its storage for automotive applications remains a formidable challenge. MgH2, with its high gravimetric and volumetric density, presents a compelling platform for hydrogen storage; however, it… ▽ More Hydrogen is a promising energy carrier that can push forward the energy transition because of its high energy density (142 MJ kg-1), variety of potential sources, low weight and low environmental impact, but its storage for automotive applications remains a formidable challenge. MgH2, with its high gravimetric and volumetric density, presents a compelling platform for hydrogen storage; however, its utilization is hindered by the sluggish kinetics of hydrogen uptake/release and high temperature operation. Herein we show that a novel layered heterostructure of reduced graphene oxide and organosilica with high specific surface area and narrow pore size distribution can serve as a scaffold to host MgH2 nanoparticles with a narrow diameter distribution around ~2.5 nm and superior hydrogen storage properties to bulk MgH2. Desorption studies showed that hydrogen release starts at 50 °C, with a maximum at 348 °C and kinetics dependent on particle size. Reversibility tests demonstrated that the dehydrogenation kinetics and re-hydrogenation capacity of the system remains stable at 1.62 wt.% over four cycles at 200 °C. Our results prove that MgH2 confinement in a nanoporous scaffold is an efficient way to constrain the size of the hydride particles, avoid aggregation and improve kinetics for hydrogen release and recharging. △ Less

Submitted 19 August, 2023; originally announced August 2023.

Disorder-induced excitation continuum in a spin-1/2 cobaltate on a triangular lattice

Authors: Bin Gao, Tong Chen, Chien-Lung Huang, Yiming Qiu, Guangyong Xu, Jesse Liebman, Lebing Chen, Matthew B. Stone, Erxi Feng, Huibo Cao, Xiaoping Wang, Xianghan Xu, Sang-Wook Cheong, Stephen M. Winter, Pengcheng Dai

Abstract: A spin-1/2 triangular-lattice antiferromagnet is a prototypical frustrated quantum magnet, which exhibits remarkable quantum many-body effects that arise from the synergy between geometric spin frustration and quantum fluctuations. It can host quantum frustrated magnetic topological phenomena like quantum spin liquid (QSL) states, highlighted by the presence of fractionalized quasiparticles within… ▽ More A spin-1/2 triangular-lattice antiferromagnet is a prototypical frustrated quantum magnet, which exhibits remarkable quantum many-body effects that arise from the synergy between geometric spin frustration and quantum fluctuations. It can host quantum frustrated magnetic topological phenomena like quantum spin liquid (QSL) states, highlighted by the presence of fractionalized quasiparticles within a continuum of magnetic excitations. In this work, we use neutron scattering to study CoZnMo$_3$O$_8$, which has a triangular lattice of Jeff = 1/2 Co2+ ions with octahedral coordination. We found a wave-vector-dependent excitation continuum at low energy that disappears with increasing temperature. Although these excitations are reminiscent of a spin excitation continuum in a QSL state, their presence in CoZnMo$_3$O$_8$ originates from magnetic intersite disorder-induced dynamic spin states with peculiar excitations. Our results, therefore, give direct experimental evidence for the presence of a disorder-induced spin excitation continuum. △ Less

Submitted 17 August, 2023; originally announced August 2023.

Journal ref: Phys. Rev. B 108, 024431 2023

qecGPT: decoding Quantum Error-correcting Codes with Generative Pre-trained Transformers

Authors: Hanyan Cao, Feng Pan, Yijia Wang, Pan Zhang

Abstract: We propose a general framework for decoding quantum error-correcting codes with generative modeling. The model utilizes autoregressive neural networks, specifically Transformers, to learn the joint probability of logical operators and syndromes. This training is in an unsupervised way, without the need for labeled training data, and is thus referred to as pre-training. After the pre-training, the… ▽ More We propose a general framework for decoding quantum error-correcting codes with generative modeling. The model utilizes autoregressive neural networks, specifically Transformers, to learn the joint probability of logical operators and syndromes. This training is in an unsupervised way, without the need for labeled training data, and is thus referred to as pre-training. After the pre-training, the model can efficiently compute the likelihood of logical operators for any given syndrome, using maximum likelihood decoding. It can directly generate the most-likely logical operators with computational complexity $\mathcal O(2k)$ in the number of logical qubits $k$, which is significantly better than the conventional maximum likelihood decoding algorithms that require $\mathcal O(4^k)$ computation. Based on the pre-trained model, we further propose refinement to achieve more accurately the likelihood of logical operators for a given syndrome by directly sampling the stabilizer operators. We perform numerical experiments on stabilizer codes with small code distances, using both depolarizing error models and error models with correlated noise. The results show that our approach provides significantly better decoding accuracy than the minimum weight perfect matching and belief-propagation-based algorithms. Our framework is general and can be applied to any error model and quantum codes with different topologies such as surface codes and quantum LDPC codes. Furthermore, it leverages the parallelization capabilities of GPUs, enabling simultaneous decoding of a large number of syndromes. Our approach sheds light on the efficient and accurate decoding of quantum error-correcting codes using generative artificial intelligence and modern computational power. △ Less

Submitted 18 July, 2023; originally announced July 2023.

Comments: Comments are welcome

Nonlinear optical encoding enabled by recurrent linear scattering

Authors: Fei Xia, Kyungduk Kim, Yaniv Eliezer, SeungYun Han, Liam Shaughnessy, Sylvain Gigan, Hui Cao

Abstract: Optical information processing and computing can potentially offer enhanced performance, scalability and energy efficiency. However, achieving nonlinearity-a critical component of computation-remains challenging in the optical domain. Here we introduce a design that leverages a multiple-scattering cavity to passively induce optical nonlinear random mapping with a continuous-wave laser at a low pow… ▽ More Optical information processing and computing can potentially offer enhanced performance, scalability and energy efficiency. However, achieving nonlinearity-a critical component of computation-remains challenging in the optical domain. Here we introduce a design that leverages a multiple-scattering cavity to passively induce optical nonlinear random mapping with a continuous-wave laser at a low power. Each scattering event effectively mixes information from different areas of a spatial light modulator, resulting in a highly nonlinear mapping between the input data and output pattern. We demonstrate that our design retains vital information even when the readout dimensionality is reduced, thereby enabling optical data compression. This capability allows our optical platforms to offer efficient optical information processing solutions across applications. We demonstrate our design's efficacy across tasks, including classification, image reconstruction, keypoint detection and object detection, all of which are achieved through optical data compression combined with a digital decoder. In particular, high performance at extreme compression ratios is observed in real-time pedestrian detection. Our findings open pathways for novel algorithms and unconventional architectural designs for optical computing. △ Less

Submitted 11 December, 2024; v1 submitted 17 July, 2023; originally announced July 2023.

Comments: 14 pages, 4 figures

Journal ref: Nature Photonics 18, no. 10 (2024): 1067-1075

Tiny Sc allows the chains to rattle: Impact of Lu and Y doping on the charge density wave in ScV$_6$Sn$_6$

Authors: William R. Meier, Richa Pokharel Madhogaria, Shirin Mozaffari, Madalynn Marshall, David E. Graf, Michael A. McGuire, Hasitha W. Suriya Arachchige, Caleb L. Allen, Jeremy Driver, Huibo Cao, David Mandrus

Abstract: The kagome metals display an intriguing variety of electronic and magnetic phases arising from the connectivity of atoms on a kagome lattice. A growing number of these materials with vanadium kagome nets host charge density waves (CDWs) at low temperatures including ScV$_6$Sn$_6$, CsV$_3$Sb$_5$, and V$_3$Sb$_2$. Curiously, only the Sc version of the $R$V$_6$Sn$_6$ HfFe$_6$Ge$_6$-type materials hos… ▽ More The kagome metals display an intriguing variety of electronic and magnetic phases arising from the connectivity of atoms on a kagome lattice. A growing number of these materials with vanadium kagome nets host charge density waves (CDWs) at low temperatures including ScV$_6$Sn$_6$, CsV$_3$Sb$_5$, and V$_3$Sb$_2$. Curiously, only the Sc version of the $R$V$_6$Sn$_6$ HfFe$_6$Ge$_6$-type materials hosts a CDW ($R = $Gd-Lu, Y, Sc). In this study we investigate the role of rare earth size in CDW formation in the $R$V$_6$Sn$_6$ compounds. Magnetization measurements on our single crystals of (Sc,Lu)V$_6$Sn$_6$ and (Sc,Y)V$_6$Sn$_6$ establish that the CDW is suppressed by substitution of Sc by larger Lu or Y. Single crystal x-ray diffraction reveals that compressible Sn-Sn bonds accommodate the larger rare earth atoms within loosely packed $R$-Sn-Sn chains without significantly expanding the lattice. We propose that Sc provides the extra room in these chains crucial to CDW formation in ScV$_6$Sn$_6$. Our rattling chain model explains why both physical pressure and substitution by larger rare earths hinder CDW formation despite opposite impacts on lattice size. We emphasize the cooperative effect of pressure and rare earth size by demonstrating that pressure further suppresses the CDW in a Lu-doped ScV$_6$Sn$_6$ crystal. Our model not only addresses why a CDW only forms in the $R$V$_6$Sn$_6$ materials with tiny Sc, it also advances to our understanding of why unusual CDWs form in the kagome metals. △ Less

Submitted 13 June, 2023; originally announced June 2023.

Comments: 28 pages, 9 figures, crystallographic information files for LuV6Sn6 and YV6Sn6 along with supplemental materials in ancillary files

Journal ref: J. Am. Chem. Soc. 2023, 145, 38, 20943

Static and dynamical properties of the spin-5/2 nearly ideal triangular lattice antiferromagnet Ba3MnSb2O9

Authors: Mingfang Shu, Weicen Dong, Jinlong Jiao, Jiangtao Wu, Gaoting lin, Tao Hong, Huibo Cao, Masaaki Matsuda, Wei Tian, Songxue Chi, Georg Ehlers, Zhongwen Ouyang, Hongwei Chen, Youming Zou, Zhe Qu, Qing Huang, Haidong Zhou, Yoshitomo Kamiya, Jie Ma

Abstract: We study the ground state and spin excitations in Ba3MnSb2O9, an easy-plane S = 5/2 triangular lattice antiferromagnet. By combining single-crystal neutron scattering, electric spin resonance (ESR), and spin wave calculations, we determine the frustrated quasi-two-dimensional spin Hamiltonian parameters describing the material. While the material has a slight monoclinic structural distortion, whic… ▽ More We study the ground state and spin excitations in Ba3MnSb2O9, an easy-plane S = 5/2 triangular lattice antiferromagnet. By combining single-crystal neutron scattering, electric spin resonance (ESR), and spin wave calculations, we determine the frustrated quasi-two-dimensional spin Hamiltonian parameters describing the material. While the material has a slight monoclinic structural distortion, which could allow for isosceles-triangular exchanges and biaxial anisotropy by symmetry, we observe no deviation from the behavior expected for spin waves in the in-plane 120o state. Even the easy-plane anisotropy is so small that it can only be detected by ESR in our study. In conjunction with the quasi-two-dimensionality, our study establishes that Ba3MnSb2O9 is a nearly ideal triangular lattice antiferromagnet with the quasi-classical spin S = 5/2, which suggests that it has the potential for an experimental study of Z- or Z2-vortex excitations. △ Less

Submitted 7 September, 2023; v1 submitted 9 June, 2023; originally announced June 2023.