Showing 1–50 of 222 results for author: Wei, Y

Observation of disorder-induced superfluidity

Authors: Nicole Ticea, Elias Portoles, Eliott Rosenberg, Alexander Schuckert, Aaron Szasz, Bryce Kobrin, Nicolas Pomata, Pranjal Praneel, Connie Miao, Shashwat Kumar, Ella Crane, Ilya Drozdov, Yuri Lensky, Sofia Gonzalez-Garcia, Thomas Kiely, Dmitry Abanin, Amira Abbas, Rajeev Acharya, Laleh Aghababaie Beni, Georg Aigeldinger, Ross Alcaraz, Sayra Alcaraz, Markus Ansmann, Frank Arute, Kunal Arya , et al. (277 additional authors not shown)

Abstract: The emergence of states with long-range correlations in a disordered landscape is rare, as disorder typically suppresses the particle mobility required for long-range coherence. But when more than two energy levels are available per site, disorder can induce resonances that locally enhance mobility. Here we explore phases arising from the interplay between disorder, kinetic energy, and interaction… ▽ More The emergence of states with long-range correlations in a disordered landscape is rare, as disorder typically suppresses the particle mobility required for long-range coherence. But when more than two energy levels are available per site, disorder can induce resonances that locally enhance mobility. Here we explore phases arising from the interplay between disorder, kinetic energy, and interactions on a superconducting processor with qutrit readout and control. Compressibility measurements distinguish an incompressible Mott insulator from surrounding compressible phases and reveal signatures of glassiness, reflected in non-ergodic behavior. Spatially-resolved two-point correlator measurements identify regions of the phase diagram with a non-vanishing condensate fraction. We also visualize the spectrum by measuring the dynamical structure factor. A linearly-dispersing phonon mode materializes in the superfluid, appearing even when disorder is introduced to the clean Mott insulator. Our results provide strong experimental evidence for disorder-induced superfluidity. △ Less

Submitted 24 December, 2025; originally announced December 2025.

Role of Phase Fluctuation in Dynamic Competition Between Charge Order and Superconductivity in Cuprates

Authors: Mingu Kang, Pavel E. Dolgirev, Chao C. Zhang, Hoyoung Jang, Byungjune Lee, Minseok Kim, Sang-Youn Park, Ronny Sutarto, Eugene Demler, Jae-Hoon Park, John Y. T. Wei, Riccardo Comin

Abstract: Phase fluctuations are a key factor distinguishing nonthermal (ultrafast) and thermal phase transitions. Charge order in cuprates is characterized by short-range coherence while competing with superconductivity, and as such, it provides a representative case to study the role of phase fluctuation in coupled order parameter dynamics. In this work, we investigated the intertwined evolution of charge… ▽ More Phase fluctuations are a key factor distinguishing nonthermal (ultrafast) and thermal phase transitions. Charge order in cuprates is characterized by short-range coherence while competing with superconductivity, and as such, it provides a representative case to study the role of phase fluctuation in coupled order parameter dynamics. In this work, we investigated the intertwined evolution of charge order and superconductivity in cuprate/manganite heterostructures using time-resolved resonant X-ray scattering. The resulting dynamics are analyzed within a space- and time-dependent nonperturbative model capturing both amplitude and phase dynamics. At low fluence, photo-induced suppression of superconductivity results in a nonthermal enhancement of charge order, underscoring the dynamic competition between charge order and superconductivity. With increasing fluence, the slowing down of melting and recovery dynamics is observed, indicating a critical role of phase fluctuations. At high fluence, both charge order and superconductivity remain suppressed for an extended time window due to decoupling between amplitude and phase dynamics and the delayed recovery of phase coherence. Our work underscores the importance of phase fluctuation for understanding the dynamic competition between order parameters in cuprates. △ Less

Submitted 30 October, 2025; originally announced October 2025.

Comments: 19 pages, 7 figures

Quantification of Electrolyte Degradation in Lithium-ion Batteries with Neutron Imaging Techniques

Authors: Yonggang Hu, Yiqing Liao, Lufeng Yang, Ke Zhang, Yufan Peng, Shijun Tang, Shengxiang Wang, Meifang Ding, Jiahao Wu, Jianrong Lin, Jinding Liang, Yimin Wei, Yanting Jin, Zhengliang Gong, Anatoliy Senyshyn, Jie Chen, Yong Yang

Abstract: Non-destructive characterization of lithium-ion batteries provides critical insights for optimizing performance and lifespan while preserving structural integrity. Optimizing electrolyte design in commercial LIBs requires consideration of composition, electrolyte-to-capacity ratio, spatial distribution, and associated degradation pathways. However, existing non-destructive methods for studying ele… ▽ More Non-destructive characterization of lithium-ion batteries provides critical insights for optimizing performance and lifespan while preserving structural integrity. Optimizing electrolyte design in commercial LIBs requires consideration of composition, electrolyte-to-capacity ratio, spatial distribution, and associated degradation pathways. However, existing non-destructive methods for studying electrolyte infiltration, distribution, and degradation in LIBs lack the spatiotemporal resolution required for precise observation and quantification of the electrolyte. In this study, we employ neutron imaging with sufficient spatial resolution ~150 um and large field of view 20x20 cm2 to quantitatively resolve the electrolyte inventory and distribution within LiFePO4/graphite pouch cells under high-temperature accelerated aging. Quantitative standard curves based on neutron transmission attenuation reveal a clear electrolyte dry-out threshold at 3.18 g Ah-1 and the two stages evolutions of EI during cell aging were quantified. By integrating non-destructive electrochemical diagnostics, accelerated graphite material loss and liquid phase Li+ diffusion degradation is observed during pore-drying. Further analysis, including operando cyclic aging, reveals that the neutron transmission below the saturation reference is due to the enrichment of hydrogen nuclei within the solid-electrolyte interphase. Assumed pore-drying does not occur, the SEI signal of the electrodes can be quantitatively decoupled during ageing. Combined analyses with NI, TOF-SIMS, and SEM reveal that high EI cells exhibit uniform SEI growth and reduced degradation, while low EI cells show uneven SEI formation, accelerating capacity loss. This study unveils a dynamic electrolyte infiltration-consumption-dry-out process in LIBs, offering non-destructive and quantitative insights to guide sustainable and durable battery development. △ Less

Submitted 13 October, 2025; originally announced October 2025.

Two-dimensional flat-bands in Moire-diamonds

Authors: Yalan Wei, Shifang Li, Yuke Song, Chaoyu He

Abstract: The discovery of flat-bands in magic-angle twisted bilayer graphene has underscored the potential of moire engineering for correlated states, but such phases are notoriously difficult to realize and highly fragile against perturbations. Here, we propose an alternative route to flat-bands by introducing sp3 hybridization in twisted graphite. Instead of relying on fine-tuned magic angles, our approa… ▽ More The discovery of flat-bands in magic-angle twisted bilayer graphene has underscored the potential of moire engineering for correlated states, but such phases are notoriously difficult to realize and highly fragile against perturbations. Here, we propose an alternative route to flat-bands by introducing sp3 hybridization in twisted graphite. Instead of relying on fine-tuned magic angles, our approach identifies flat-band states at relatively large twist angles with short moire periods. In this regime, sp3-induced reconstructions generate electronic states that, once formed, are locked by substantial energy barriers, rendering them robust against external perturbations. Using twisted graphite as a prototype, we uncover a series moire-diamond that host two-dimensional flat conduction of valence bands, where carriers are localized within specific momentum planes but remain dispersive along orthogonal directions. The emergence of dimensional flat-bands opens a new platform for flat-band-driven correlated physics and suggests opportunities for designing quantum materials with highly directional electronic functionalities. △ Less

Submitted 12 October, 2025; originally announced October 2025.

Comments: 12 pages, 3 figures

Defect-Charge-Driven 90° Switching in HfO2

Authors: Muting Xie, Hongyu Yu, Zhihao Dai, Yingfen Wei, Changsong Xu, Hongjun Xiang

Abstract: Hafnium dioxide (HfO2) is a CMOS-compatible ferroelectric showing both 180° and 90° switching, yet the microscopic nature of the 90° pathway remains unresolved. We show that the 90° rotation pathway, negligible in pristine HfO2, becomes dominant under E// [111] when induced by charged oxygen vacancies. This pathway is more fatigue-resistant than the 180° reversal pathway, while delivering the same… ▽ More Hafnium dioxide (HfO2) is a CMOS-compatible ferroelectric showing both 180° and 90° switching, yet the microscopic nature of the 90° pathway remains unresolved. We show that the 90° rotation pathway, negligible in pristine HfO2, becomes dominant under E// [111] when induced by charged oxygen vacancies. This pathway is more fatigue-resistant than the 180° reversal pathway, while delivering the same polarization change along [111] (2Pr=60 μC/cm^2 ). This charge-driven switching arises from two factors: the crystal geometry of HfO2 and the intrinsic nature of rotational pathways, the latter suggesting a possible general tendency for defect charge to bias rotation over reversal in ferroelectrics. Together these findings reveal a pathway-level origin of fatigue resistance and establish defect charge as a general control parameter for polarization dynamics. △ Less

Submitted 25 September, 2025; originally announced September 2025.

Impact of electronic correlations on the superconductivity of high-pressure CeH$_9$

Authors: Siyu Chen, Yao Wei, Bartomeu Monserrat, Jan M. Tomczak, Samuel Poncé

Abstract: Rare-earth superhydrides have attracted considerable attention because of their high critical superconducting temperature under extreme pressures. They are known to have localized valence electrons, implying strong electronic correlations. However, such many-body effects are rarely included in first-principles studies of rare-earth superhydrides because of the complexity of their high-pressure pha… ▽ More Rare-earth superhydrides have attracted considerable attention because of their high critical superconducting temperature under extreme pressures. They are known to have localized valence electrons, implying strong electronic correlations. However, such many-body effects are rarely included in first-principles studies of rare-earth superhydrides because of the complexity of their high-pressure phases. In this work, we use a combined density functional theory and dynamical mean-field theory approach to study both electrons and phonons in the prototypical rare-earth superhydride CeH$_9$, shedding light on the impact of electronic correlations on its critical temperature for phonon-mediated superconductivity. Our findings indicate that electronic correlations result in a larger electronic density at the Fermi level, a bigger superconducting gap, and softer vibrational modes associated with hydrogen atoms. Together, the inclusion of these correlation signatures increases the Migdal-Eliashberg superconducting critical temperature from 47 K to 96 K, close to the measured 95 K. Our results reconcile experimental observations and theoretical predictions for CeH$_9$ and herald a path towards the quantitative modeling of phonon-mediated superconductivity for interacting electron systems. △ Less

Submitted 21 November, 2025; v1 submitted 16 July, 2025; originally announced July 2025.

Comments: 11 pages, 4 figures

Nonlinear bulk photocurrent probe Z2 topological phase transition

Authors: Debasis Dutta, Raihan Ahammed, Yingdong Wei, Xiaokai Pan, Xiaoshuang Chen, Lin Wang, Amit Agarwal

Abstract: Detecting topological phase transitions in bulk is challenging due to the limitations of surface sensitive probes like ARPES. Here, we demonstrate that nonlinear bulk photocurrents, specifically shift and injection currents, serve as effective probes of Z_2 topological transitions. These photocurrents show a robust polarity reversal across the Z_2 phase transition, offering a direct optical signat… ▽ More Detecting topological phase transitions in bulk is challenging due to the limitations of surface sensitive probes like ARPES. Here, we demonstrate that nonlinear bulk photocurrents, specifically shift and injection currents, serve as effective probes of Z_2 topological transitions. These photocurrents show a robust polarity reversal across the Z_2 phase transition, offering a direct optical signature that distinguishes strong topological phases from weak or trivial ones. This effect originates from a reorganization of key band geometric quantities, the Berry curvature and shift vector, on time-reversal-invariant momentum planes. Using a low energy Dirac model, we trace this behaviour to a band inversion in the time-reversal-invariant momentum plane that drives the topological transition. We validate these findings through tight-binding model for Bi_2Te_3 and first-principles calculations for ZrTe_5 and BiTeI, where the topological phase can be tuned by pressure or temperature. Our results establish nonlinear photocurrent as a sensitive and broadly applicable probe of Z_2 topological phase transitions. △ Less

Submitted 16 June, 2025; originally announced June 2025.

Comments: 9 pages, 6 figures, 61 references. We will appreciate any comments of suggestions on this work

Journal ref: Materials Today Quantum, 100052 (2025)

Structure-Informed Learning of Flat Band 2D Materials

Authors: Xiangwen Wang, Yihao Wei, Anupam Bhattacharya, Qian Yang, Artem Mishchenko

Abstract: Flat electronic bands enhance electron-electron interactions and give rise to correlated states such as unconventional superconductivity or fractional topological phases. However, most current efforts towards flat-band materials discovery rely on density functional theory (DFT) calculations and manual band structures inspection, restraining their applicability to vast unexplored material spaces. W… ▽ More Flat electronic bands enhance electron-electron interactions and give rise to correlated states such as unconventional superconductivity or fractional topological phases. However, most current efforts towards flat-band materials discovery rely on density functional theory (DFT) calculations and manual band structures inspection, restraining their applicability to vast unexplored material spaces. While data-driven methods offer a scalable alternative, most existing models either depend on band structure inputs or focus on scalar properties like bandgap, which fail to capture flat-band characteristics. Here, we report a structure-informed framework for the discovery of previously unrecognized flat-band two-dimensional (2D) materials, which combines a data-driven flatness score capturing both band dispersion and density-of-states characteristics with multi-modal learning from atomic structure inputs. The framework successfully identified multiple flat-band candidates, with DFT validation of kagome-based systems confirming both band flatness and topological character. Our results show that the flatness score provides a physically meaningful signal for identifying flat bands from atomic geometry. The framework uncovers multiple new candidates with topologically nontrivial flat bands from unlabeled data, with consistent model performance across structurally diverse materials. By eliminating the need for precomputed electronic structures, our method enables large-scale screening of flat-band materials and expands the search space for discovering strongly correlated quantum materials. △ Less

Submitted 9 June, 2025; originally announced June 2025.

Atomic-scale mapping of interfacial phonon modes in epitaxial YBa2Cu3O7-δ / (La,Sr)(Al,Ta)O3 thin films: The role of surface phonons

Authors: Joaquin E. Reyes Gonzalez, Charles Zhang, Rainni K. Chen, John Y. T. Wei, Maureen J. Lagos

Abstract: We investigate the behavior of phonons at the epitaxial interface between YBa2Cu3O7-δ thin film and (La,Sr)(Al,Ta)O3 substrate using vibrational electron energy loss spectroscopy. Interfacial phonon modes with different degrees of scattering localization were identified. We find evidence that surface contributions from the surrounding environment can impose additional scattering modulation into lo… ▽ More We investigate the behavior of phonons at the epitaxial interface between YBa2Cu3O7-δ thin film and (La,Sr)(Al,Ta)O3 substrate using vibrational electron energy loss spectroscopy. Interfacial phonon modes with different degrees of scattering localization were identified. We find evidence that surface contributions from the surrounding environment can impose additional scattering modulation into local EELS measurements at the interface. A method to remove those contributions is then used to isolate the phonon information at the interface. This work unveils interfacial phonon modes in a high-Tc cuprate superconductor, that are not accessible with traditional phonon spectroscopy techniques, and provides a method for probing interfacial phonons in complex oxide heterostructures. △ Less

Submitted 2 June, 2025; originally announced June 2025.

Comments: 17 pages, 4 figures

Efficient Long-Range Machine Learning Force Fields for Liquid and Materials Properties

Authors: John L. Weber, Rishabh D. Guha, Garvit Agarwal, Yujing Wei, Aidan A. Fike, Xiaowei Xie, James Stevenson, Biswajit Santra, Richard A. Friesner, Karl Leswing, Mathew D. Halls, Robert Abel, Leif D. Jacobson

Abstract: Machine learning force fields (MLFFs) have emerged as a sophisticated tool for cost-efficient atomistic simulations approaching DFT accuracy, with recent message passing MLFFs able to cover the entire periodic table. We present an invariant message passing MLFF architecture (MPNICE) which iteratively predicts atomic partial charges, including long-range interactions, enabling the prediction of cha… ▽ More Machine learning force fields (MLFFs) have emerged as a sophisticated tool for cost-efficient atomistic simulations approaching DFT accuracy, with recent message passing MLFFs able to cover the entire periodic table. We present an invariant message passing MLFF architecture (MPNICE) which iteratively predicts atomic partial charges, including long-range interactions, enabling the prediction of charge-dependent properties while achieving 5-20x faster inference versus models with comparable accuracy. We train direct and delta-learned MPNICE models for organic systems, and benchmark against experimental properties of liquid and solid systems. We also benchmark the energetics of finite systems, contributing a new set of torsion scans with charged species and a new set of DLPNO-CCSD(T) references for the TorsionNet500 benchmark. We additionally train and benchmark MPNICE models for bulk inorganic crystals, focusing on structural ranking and mechanical properties. Finally, we explore multi-task models for both inorganic and organic systems, which exhibit slightly decreased performance on domain-specific tasks but surprising generalization, stably predicting the gas phase structure of $\simeq500$ Pt/Ir organometallic complexes despite never training to organometallic complexes of any kind. △ Less

Submitted 1 August, 2025; v1 submitted 9 May, 2025; originally announced May 2025.

Comments: 60 pages 10 figures

Stacking-orientation and twist-angle control on integer and fractional Chern insulators in moiré rhombohedral graphene

Authors: Chushan Li, Chuanqi Zheng, Kai Liu, Ke Huang, Zheng Sun, Lei Qiao, Yifan Wei, Chenyu Zhang, Fan Xu, Kenji Watanabe, Takashi Taniguchi, Hao Yang, Dandan Guan, Liang Liu, Shiyong Wang, Yaoyi Li, Hao Zheng, Canhua Liu, Bingbing Tong, Li Lu, Jinfeng Jia, Zhiwen Shi, Jianpeng Liu, Xiao Li, Guorui Chen , et al. (2 additional authors not shown)

Abstract: Rhombohedral-stacked multilayer graphene aligned with hexagonal boron nitride has emerged as an excellent platform for investigating exotic quantum phenomena arising from the interplay between electron correlations and nontrivial topology. However, the microscopic mechanism governing the emergence of both the integer and fractional Chern insulator states in this system remains an open question. In… ▽ More Rhombohedral-stacked multilayer graphene aligned with hexagonal boron nitride has emerged as an excellent platform for investigating exotic quantum phenomena arising from the interplay between electron correlations and nontrivial topology. However, the microscopic mechanism governing the emergence of both the integer and fractional Chern insulator states in this system remains an open question. In this work, we systematically investigate the electrical transport properties of RMG/hBN moiré devices with controlled alignment orientations and twist angles. We demonstrate that alignment orientation strongly modulates correlated phenomena in the moiré-proximal regime, while having negligible influence on the formation of integer and fractional Chern insulators in the moiré-distant regime. Instead, the moiré periodicity, tuned by the twist angle, serves as the key parameter controlling the stability of these correlated topological states in the moiré-distant regime. Furthermore, in the moiré-proximal regime of one specific alignment, we observe anomalous Hall effect and a variety of competing phases near ν = 1, including integer Chern insulator states, extended Chern insulator states, and trivial insulators, whose stability is highly sensitive to both the applied displacement electric field and magnetic field. Our results underscore the critical role of stacking-alignment and twist-angle engineering in exploring novel quantum states based on rhombohedral-stacked multilayer graphene moiré systems. △ Less

Submitted 11 November, 2025; v1 submitted 3 May, 2025; originally announced May 2025.

Machine learning enhanced atom probe tomography analysis: a snapshot review

Authors: Yue Li, Ye Wei, Alaukik Saxena, Markus Kühbach, Christoph Freysoldt, Baptiste Gault

Abstract: Atom probe tomography (APT) is a burgeoning characterization technique that provides compositional mapping of materials in three-dimensions at near-atomic scale. Since its significant expansion in the past 30 years, we estimate that one million APT datasets have been collected, each containing millions to billions of individual ions. Their analysis and the extraction of microstructural information… ▽ More Atom probe tomography (APT) is a burgeoning characterization technique that provides compositional mapping of materials in three-dimensions at near-atomic scale. Since its significant expansion in the past 30 years, we estimate that one million APT datasets have been collected, each containing millions to billions of individual ions. Their analysis and the extraction of microstructural information has largely relied upon individual users whose varied level of expertise causes clear and documented bias. Current practices hinder efficient data processing, and make challenging standardization and the deployment of data analysis workflows that would be compliant with FAIR data principles. Over the past decade, building upon the long-standing expertise of the APT community in the development of advanced data processing or data mining techniques, there has been a surge of novel machine learning (ML) approaches aiming for user-independence, and that are efficient, reproducible, and robust from a statistics perspective. Here, we provide a snapshot review of this rapidly evolving field. We begin with a brief introduction to APT and the nature of the APT data. This is followed by an overview of relevant ML algorithms and a comprehensive review of their applications to APT. We also discuss how ML can enable discoveries beyond human capability, offering new insights into the mechanisms within materials. Finally, we provide guidance for future directions in this domain. △ Less

Submitted 19 April, 2025; originally announced April 2025.

Observation of non-Hermitian bulk-boundary correspondence in non-chiral non-unitary quantum dynamics of single photons

Authors: Miao Zhang, Yue Zhang, Shuai Li, Rui Tian, Tianhao Wu, Yingchao Xu, Yi-an Li, Yuanbang Wei, Hong Gao, M. Suhail Zubairy, Fuli Li, Bo Liu

Abstract: The breakdown of conventional bulk-boundary correspondence, a cornerstone of topological physics, is one of counter-intuitive phenomena in non-Hermitian systems, that is deeply rooted in symmetry. In particular, preserved chiral symmetry is one of the key ingredients, which plays a pivotal role in determining non-Hermitian topology. Nevertheless, chiral symmetry breaking in non-Hermitian systems d… ▽ More The breakdown of conventional bulk-boundary correspondence, a cornerstone of topological physics, is one of counter-intuitive phenomena in non-Hermitian systems, that is deeply rooted in symmetry. In particular, preserved chiral symmetry is one of the key ingredients, which plays a pivotal role in determining non-Hermitian topology. Nevertheless, chiral symmetry breaking in non-Hermitian systems disrupts topological protection, modifies topological invariants, and substantially reshapes spectral and edge-state behavior. The corresponding fundamentally important bulk-boundary correspondence thus needs to be drastically reconstructed. However, it has so far eluded experimental efforts. Here, we theoretically predict and experimentally demonstrate the bulk-boundary correspondence of a one-dimensional (1D) non-Hermitian system with chiral symmetry breaking in discrete-time non-chiral non-unitary quantum walks of single photons. Through constructing a domain-wall configuration, we experimentally observe the photon localization at the interface of domain-wall structure, clearly indicating the presence of the topological edge mode. The appearance of that matches excellently with the prediction of our introduced non-chiral non-Bloch topological invariants pair. Our work thus unequivocally builds the non-Hermitian bulk-boundary correspondence as a general principle for studying topological physics in non-Hermitian systems with chiral symmetry breaking. △ Less

Submitted 7 April, 2025; originally announced April 2025.

Comments: 13 pages, 8 figures, including Supplementary Material

The fundamental localization phases in quasiperiodic systems: A unified framework and exact results

Authors: Xin-Chi Zhou, Bing-Chen Yao, Yongjian Wang, Yucheng Wang, Yudong Wei, Qi Zhou, Xiong-Jun Liu

Abstract: The disordered quantum systems host three types of quantum states, the extended, localized, and critical, which bring up seven distinct fundamental phases in nature: three pure phases and four coexisting ones with mobility edges, yet a unified theory with full characterization and realization of all these phases has not been developed. Here we propose a complete and unified framework based on a sp… ▽ More The disordered quantum systems host three types of quantum states, the extended, localized, and critical, which bring up seven distinct fundamental phases in nature: three pure phases and four coexisting ones with mobility edges, yet a unified theory with full characterization and realization of all these phases has not been developed. Here we propose a complete and unified framework based on a spinful quasiperiodic (QP) system which realizes all the fundamental localization phases, with the exact and universal results being obtained for their characterization. First, we show that the pure phases are obtained when the chiral symmetry preserves in the proposed spinful QP model, giving a criterion for the emergence of the pure phases and otherwise the coexisting ones. Further, we uncover a novel universal mechanism for the critical states that their emergence is protected by the generalized incommensurate matrix element zeros in the spinful QP model, which considerably broadens the rigorous realizations of the exotic critical states. We then show the criteria of exact solvability for the present spinful QP system, with which we construct various exactly solvable models for all distinct localization phases. In particular, we propose two novel models, dubbed spin-selective QP lattice model and QP optical Raman lattice model, to achieve all basic types of mobility edges and all the seven fundamental phases of Anderson localization physics, respectively. The experimental scheme is proposed and studied in detail to realize these models with high feasibility. This study establishes a complete and profound theoretical framework which enables an in-depth exploration of the broad classes of all fundamental localization phenomena in QP systems, and offers key insights for constructing their exactly solvable models with experimental feasibility. △ Less

Submitted 29 May, 2025; v1 submitted 31 March, 2025; originally announced March 2025.

Comments: 24 pages, 8 figures. The discussion has been significantly expanded, and a new appendix and an additional figure have been added

Quasiparticle Spectroscopy of Chiral Charge Order

Authors: Jiangchang Zheng, Caiyun Chen, Gaopei Pan, Xu Zhang, Chen Chen, Yuan Da Liao, Ganesh Pokharel, Andrea Capa Salinas, Yizhou Wei, Hoi Chun Po, Ding Pan, Stephen D. Wilson, Zi Yang Meng, Berthold Jäck

Abstract: Electronic interactions can give rise to novel charge density waves with unconventional ground states. Recent experiments report evidence for a chiral charge density wave (CDW) that breaks time-reversal symmetry in the kagome metals AV$_3$Sb$_5$ (A=K, Rb or Cs). Theoretical analyses propose a topologically nontrivial loop current phase that spontaneously breaks time-reversal symmetry as the favora… ▽ More Electronic interactions can give rise to novel charge density waves with unconventional ground states. Recent experiments report evidence for a chiral charge density wave (CDW) that breaks time-reversal symmetry in the kagome metals AV$_3$Sb$_5$ (A=K, Rb or Cs). Theoretical analyses propose a topologically nontrivial loop current phase that spontaneously breaks time-reversal symmetry as the favorable CDW ground state. However, spectroscopic insights into the quasiparticle excitations of chiral charge order in AV$_3$Sb$_5$ compounds are still missing and conflicting experimental results question the presence of a loop current phase. We employed individual magnetic atoms as local quantum sensors to examine the quasiparticle excitations of chiral charge order in CsV$_3$Sb$_5$ with the scanning tunneling microscope (STM). Our spectroscopic measurements show that the magnetic moment of Co induces a spatially-localized low-energy state in the CDW phase. The distinct spectral signatures of this state are consistent with theoretical expectations for the quasiparticle excitation of a loop current order parameter, while control experiment rule out alternative scenario. Our work provides unique insights into the ground state of chiral charge order in CsV$_3$Sb$_5$ and introduces a novel method to examine other topological states, such as the fractional Chern insulators, with the STM. △ Less

Submitted 24 March, 2025; originally announced March 2025.

Quantum Geometric Engineering of Dual Hall Effects in 2D Antiferromagnetic Bilayers via Interlayer Magnetic Coupling

Authors: Zhenning Sun, Tao Wang, Hao Jin, Xinru Li, Yadong Wei, Jian Wang

Abstract: The interplay between quantum geometry and magnetic order offers a novel strategy for designing next-generation nanodevices. Here, we demonstrate that interlayer magnetic coupling in two-dimensional (2D) CoPSe3 bilayers enables precise control over quantum geometric mechanisms, unlocking dual intrinsic Hall effects. Our first-principles calculations reveal that the altermagnetic (AM) phase exhibit… ▽ More The interplay between quantum geometry and magnetic order offers a novel strategy for designing next-generation nanodevices. Here, we demonstrate that interlayer magnetic coupling in two-dimensional (2D) CoPSe3 bilayers enables precise control over quantum geometric mechanisms, unlocking dual intrinsic Hall effects. Our first-principles calculations reveal that the altermagnetic (AM) phase exhibits a giant anisotropic anomalous Hall effect (AHE) ($σ_{xy}$ is approximately 46 S/cm) driven by Berry curvature localized at generic k-points, while the PT-symmetric antiferromagnetic (AFM) phase hosts an intrinsic second-order nonlinear anomalous Hall effect (NAHE) ($χ_{xyy}$ is approximately 160 $μ$S/V) originating from quantum metric accumulation at high-symmetry k-points. By tuning interlayer magnetic couplings, we achieve reversible switching between these phases, leveraging their distinct band structures and symmetry constraints. The Neel-vector-dependent AHE in the AM phase and the symmetry-protected NAHE in the AFM phase highlight quantum geometry as a versatile tool for manipulating transport properties. Our work establishes 2D antiferromagnets as a promising platform for multifunctional device architectures, bridging linear and nonlinear magnetoelectric responses through tailored quantum geometric engineering. △ Less

Submitted 4 March, 2025; originally announced March 2025.

A Radio-Frequency Emitter Design for the Low-Frequency Regime in Atomic Experiments

Authors: Yudong Wei, Zhongshu Hu, Yajing Guo, Zhentian Qian, Shengjie Jin, Xuzong Chen, Xiong-jun Liu

Abstract: Radio-frequency (RF) control is a key technique in cold atom experiments. We present a compact and efficient RF circuit based on a capacitive transformer network, where a low-frequency coil operating up to 30MHz serves as both an intrinsic inductor and a power-sharing element. The design enables high current delivery and flexible impedance matching across a wide frequency range. We integrate both… ▽ More Radio-frequency (RF) control is a key technique in cold atom experiments. We present a compact and efficient RF circuit based on a capacitive transformer network, where a low-frequency coil operating up to 30MHz serves as both an intrinsic inductor and a power-sharing element. The design enables high current delivery and flexible impedance matching across a wide frequency range. We integrate both broadband and narrowband RF networks into a unified configuration that overcomes the geometric constraints imposed by the metallic chamber. In evaporative cooling, the broadband network allows a reduction of the applied RF input power from 14.7dBW to -3.5dBW, owing to its non-zero coil current even at ultra-low frequencies. This feature enables the Bose-Fermi mixture to be cooled below 10μK. In a Landau-Zener protocol, the coil driven by the narrowband network transfers 80% of rubidium atoms from |F = 2,mF = 2> to |2,-2> in 1 millisecond, achieving a Rabi frequency of approximately 9 kHz at an input power of 0.1dBW. △ Less

Submitted 29 July, 2025; v1 submitted 17 February, 2025; originally announced February 2025.

Comments: 9 pages, 5 figures. Typos corrected

Spin correlations in La$_3$Ni$_2$O$_7$ superconducting thin films

Authors: Hengyang Zhong, Bo Hao, Zhijia Zhang, Anni Chen, Yuan Wei, Ruixian Liu, Xinru Huang, Chunyi Li, Wenting Zhang, Chang Liu, Xiao-Sheng Ni, Marli dos Reis Cantarino, Kurt Kummer, Nicholas Brookes, Kun Cao, Yuefeng Nie, Thorsten Schmitt, Xingye Lu

Abstract: The discovery of ambient-pressure superconductivity with $T_{c,\text{onset}} > 40$ K in {\LNO} (LNO) thin films grown on the SrLaAlO$_4$ (SLAO) substrate with compressive ($\varepsilon\approx-2\%$) epitaxial strain provides a unique platform for investigating the superconducting mechanisms in nickelate superconductors. Here, we use resonant inelastic X-ray scattering (RIXS) to unveil the dispersiv… ▽ More The discovery of ambient-pressure superconductivity with $T_{c,\text{onset}} > 40$ K in {\LNO} (LNO) thin films grown on the SrLaAlO$_4$ (SLAO) substrate with compressive ($\varepsilon\approx-2\%$) epitaxial strain provides a unique platform for investigating the superconducting mechanisms in nickelate superconductors. Here, we use resonant inelastic X-ray scattering (RIXS) to unveil the dispersive spin excitations in the LNO/SLAO superconducting thin film and establish the strain dependence of the electronic and spin excitations in LNO thin films with strain ranging from $\varepsilon\approx-2\%$ to $+1.9\%$. Compared with the bulk crystal, the LNO/SLAO thin film (with $\varepsilon\approx-2\%$) exhibits similar $dd$ excitations and spin dynamics with larger bandwidth. By contrast, tensile-strained LNO/SrTiO$_3$ ($\varepsilon \approx +1.9\%$) exhibits a marked suppression of both the spin excitations and the Ni 3{\dz}-derived $dd$ excitations. The strain dependence of the spin excitations reflects significant changes in the interlayer exchange coupling $J_z$, and the diminishing $dd$ excitations in tensile-strained samples indicate weaker Ni 3{\dz}-O 2$p_{z}$ hybridization. This strain evolution of the spin excitations and $J_z$ is attributed to the strain-tuned $c$-axis Ni-O-Ni bond angle $\varphi$, which controls the Ni 3{\dz}-O 2$p_{z}$ hybridization. Since superconductivity is observed only in films grown on SLAO, and spin correlations are enhanced along with the emergence of superconductivity, our results identify $\varphi$ as a key structural lever controlling $J_z$ and provide direct spectroscopic support for interlayer spin-fluctuation-mediated pairing scenarios in bilayer nickelates. △ Less

Submitted 16 November, 2025; v1 submitted 5 February, 2025; originally announced February 2025.

Comments: 7 pages, 4 figures. Supplementary is available upon reasonable request

Anomalous Magnetotransport in the Paramagnetic State of a Magnetic Kagome Metal EuTi$_3$Bi$_4$

Authors: Yun Shu, Xinrun Mi, Yuhao Wei, Sixue Tao, Aifeng Wang, Yisheng Chai, Dashuai Ma, Xiaolong Yang, Mingquan He

Abstract: We investigate the electrical transport properties of a magnetic kagome metal EuTi$_3$Bi$_4$, which undergoes magnetic ordering below $T_\mathrm{c}=10.5$ K. Unlike typical magnets showing anomalous magnetotransport in their ordered states, EuTi$_3$Bi$_4$ exhibits unusual magnetotransport behaviors in its paramagnetic phase. Specifically, the magnetoconductivity shows a linear dependence on magneti… ▽ More We investigate the electrical transport properties of a magnetic kagome metal EuTi$_3$Bi$_4$, which undergoes magnetic ordering below $T_\mathrm{c}=10.5$ K. Unlike typical magnets showing anomalous magnetotransport in their ordered states, EuTi$_3$Bi$_4$ exhibits unusual magnetotransport behaviors in its paramagnetic phase. Specifically, the magnetoconductivity shows a linear dependence on magnetic field at low fields below $\sim 1$ T, and the Hall conductivity undergoes a sign change below about 2 T. These behaviors resemble those observed in the charge density wave (CDW) phase of kagome metals $A$V$_3$Sb$_5$ ($A$ = K, Rb, Cs). The anomalous magnetotransport in $A$V$_3$Sb$_5$ has commonly been attributed to the possible emergence of a time-reversal symmetry breaking chiral CDW order. However, given the absence of CDW in EuTi$_3$Bi$_4$ and its manifestation exclusively in the paramagnetic state, the anomalous magnetotransport observed in EuTi$_3$Bi$_4$ is likely associated with multiband transport and/or the van Hove singularities near the Fermi level. △ Less

Submitted 6 January, 2025; v1 submitted 5 January, 2025; originally announced January 2025.

Comments: 9 pages, 5 figures

Journal ref: Phys. Rev. B 111, 155103 (2025)

Unusual topological polar texture in moiré ferroelectrics

Authors: Yuhao Li, Yuanhao Wei, Ruiping Guo, Yifei Wang, Hanhao Zhang, Takashi Taniguchi, Kenji Watanabe, Yan Shi, Yi Shi, Chong Wang, Zaiyao Fei

Abstract: Topological polar textures in ferroelectrics have attracted significant interest for their potential for energy-efficient and high-density data storage and processing. Among these, polar merons and antimerons are predicted in strained and twisted bilayers of inversion symmetry broken systems. However, experimental observation of these polar textures within twisted two-dimensional van der Waals (2D… ▽ More Topological polar textures in ferroelectrics have attracted significant interest for their potential for energy-efficient and high-density data storage and processing. Among these, polar merons and antimerons are predicted in strained and twisted bilayers of inversion symmetry broken systems. However, experimental observation of these polar textures within twisted two-dimensional van der Waals (2D vdW) materials remains challenging. Here, we utilize vector piezoresponse force microscopy (PFM) to reconstruct the polarization fields in R-type marginally twisted hexagonal boron nitride (hBN). We observe alternating out-of-plane (OOP) polarizations at domain regions and in-plane (IP) vortex-like polarization patterns along domain walls (DWs), indicative of a network of polar merons and antimerons. Notably, the OOP polarization exhibits three polarity reversals across a DW. Similar polar textures are identified in marginally twisted MoSe2 and WSe2 homobilayers. Our theoretical simulations attribute these unusual polarization reversals near the DWs to the competition between moiré ferroelectricity and piezoelectricity. These results provide experimental evidence of complex polar textures in moiré ferroelectrics, offering new insights into the electronic band topology in twisted transition metal dichalcogenides (TMDCs). △ Less

Submitted 24 December, 2024; originally announced December 2024.

Light-induced thermal noise \textit{anomaly} governed by quantum metric

Authors: Longjun Xiang, Lei Zhang, Jun Chen, Fuming Xu, Yadong Wei, Jian Wang

Abstract: Traditionally, thermal noise in electric currents, arising from thermal agitation, is expected to increase with temperature $T$ and disappear as $T$ approaches zero. Contrary to this expectation, we discover that the resonant DC thermal noise (DTN) in photocurrents not only persists at $T=0$ but also exhibits a divergence proportional to $1/T$. This thermal noise \textit{anomaly} arises from the u… ▽ More Traditionally, thermal noise in electric currents, arising from thermal agitation, is expected to increase with temperature $T$ and disappear as $T$ approaches zero. Contrary to this expectation, we discover that the resonant DC thermal noise (DTN) in photocurrents not only persists at $T=0$ but also exhibits a divergence proportional to $1/T$. This thermal noise \textit{anomaly} arises from the unique electron-photon interactions near the Fermi surface, manifesting as the interplay between the inherent Fermi-surface property and the resonant optical selection rules of DTN, and thereby represents an unexplored noise regime. Notably, we reveal that this \textit{anomalous} DTN, especially in time-reversal-invariant systems, is intrinsically linked to the quantum metric. We illustrate this \textit{anomalous} DTN in massless Dirac materials, including two-dimensional graphene, the surfaces of three-dimensional topological insulators, and three-dimensional Weyl semimetals, where the quantum metric plays a pivotal role. Finally, we find that the total noise spectrum at low temperatures, which includes both the DC shot noise and the \textit{anomalous} DTN, will universally peak at $ω_p=2|μ|$ with $ω_p$ the frequency of light and $μ$ the chemical potential of the bulk crystals. △ Less

Submitted 17 December, 2024; originally announced December 2024.

Origin of Increased Curie Temperature in Lithium-Substituted Ferroelectric Niobate Perovskite: Enhancement of the Soft Polar Mode

Authors: Hao-Cheng Thong, Fang-Zhou Yao, Xian-Xian Cai, Ze Xu, Mao-Hua Zhang, Huazhang Zhang, Ben Xu, Yan Wei, Shi-Dong Wang, Ke Wang

Abstract: The functionality of ferroelectrics is often constrained by their Curie temperature, above which depolarization occurs. Lithium (Li) is the only experimentally known substitute that can increase the Curie temperature in ferroelectric niobate-based perovskites, yet the mechanism remains unresolved. Here, the unique phenomenon in Li-substituted KNbO3 is investigated using first-principles density fu… ▽ More The functionality of ferroelectrics is often constrained by their Curie temperature, above which depolarization occurs. Lithium (Li) is the only experimentally known substitute that can increase the Curie temperature in ferroelectric niobate-based perovskites, yet the mechanism remains unresolved. Here, the unique phenomenon in Li-substituted KNbO3 is investigated using first-principles density functional theory. Theoretical calculations show that Li substitution at the A-site of perovskite introduces compressive chemical pressure, reducing Nb-O hybridization and associated ferroelectric instability. However, the large off-center displacement of the Li cation compensates for this reduction and further enhances the soft polar mode, thereby raising the Curie temperature. In addition, the stability of the tetragonal phase over the orthorhombic phase is predicted upon Li substitution, which reasonably explains the experimental observation of a decreased orthorhombic-to-tetragonal phase transition temperature. Finally, a metastable anti-phase polar state in which the Li cation displaces oppositely to the Nb cation is revealed, which could also contribute to the variation of phase transition temperatures. These findings provide critical insights into the atomic-scale mechanisms governing Curie temperature enhancement in ferroelectrics and pave the way for designing advanced ferroelectric materials with improved thermal stability and functional performance. △ Less

Submitted 6 December, 2024; originally announced December 2024.

PDMD: Potential-free Data-driven Molecular Dynamics for Variable-sized Water Clusters

Authors: Hongyu Yan, Qi Dai, Yong Wei, Minghan Chen, Hanning Chen

Abstract: Conventional molecular dynamics (MD) simulation approaches, such as ab initio MD and empirical force field MD, face significant trade-offs between physical accuracy and computational efficiency. This work presents a novel Potential-free Data-driven Molecular Dynamics (PDMD) framework for predicting system energy and atomic forces of variable-sized water clusters. Specifically, PDMD employs the smo… ▽ More Conventional molecular dynamics (MD) simulation approaches, such as ab initio MD and empirical force field MD, face significant trade-offs between physical accuracy and computational efficiency. This work presents a novel Potential-free Data-driven Molecular Dynamics (PDMD) framework for predicting system energy and atomic forces of variable-sized water clusters. Specifically, PDMD employs the smooth overlap of atomic positions descriptor to generate high-dimensional, equivariant features before leveraging ChemGNN, a graph neural network model that adaptively learns the atomic chemical environments without requiring a priori knowledge. Through an iterative self-consistent training approach, the converged PDMD achieves a mean absolute error of 7.1 meV/atom for energy and 59.8 meV/angstrom for forces, outperforming the state-of-the-art DeepMD by ~80% in energy accuracy and ~200% in force prediction. As a result, PDMD can reproduce the ab initio MD properties of water clusters at a tiny fraction of its computational cost. These results demonstrate that the proposed PDMD offers multiple-phase predictive power, enabling ultra-fast, general-purpose MD simulations while retaining ab initio accuracy. △ Less

Submitted 5 December, 2024; originally announced December 2024.

Dual-species Optical tweezer for Rb and K atoms

Authors: Yangbo Wei, Kedi Wei, Shangjin Li, Bo Yan

Abstract: The optical tweezer experiment with neutral atoms is a focal topic in cold atom physics due to its significant potential in quantum computing and simulation. Here, we present the realization of a dual-species optical tweezer for both Rb and K atoms, marking the first step towards creating a polar molecule optical tweezer array. Initially, Rb and K atoms are collected using a dual magneto-optical t… ▽ More The optical tweezer experiment with neutral atoms is a focal topic in cold atom physics due to its significant potential in quantum computing and simulation. Here, we present the realization of a dual-species optical tweezer for both Rb and K atoms, marking the first step towards creating a polar molecule optical tweezer array. Initially, Rb and K atoms are collected using a dual magneto-optical trap (MOT) and further cooled to 7 $μ$K for Rb and 10 $μ$K for K. By employing 850 nm tweezer beams, we demonstrate the ability to capture individual Rb or K atoms. The filling ratios of Rb and K can be finely adjusted by controlling the atomic densities of both species. Utilizing the post-selection technique, we can create a deterministic array of two-species atoms, paving the way for future polar molecule array formation. △ Less

Submitted 28 October, 2024; originally announced October 2024.

Comments: 6 pages, 4 figures

Journal ref: Phys. Rev. A 110 (4), 043118 (2024)

Characterization of Spin-Orbit Effects in Superconductors In$_5$Bi$_3$ and In$_5$Sb$_3$

Authors: Yao Wei, Siyu Chen, Bartomeu Monserrat

Abstract: We report a first principles computational analysis of two phonon-mediated superconductors, In$_{5}$Bi$_{3}$ and In$_{5}$Sb$_{3}$. We show that spin-orbit coupling leads to splitting of electron bands around the Fermi energy, resulting in a suppression of the electronic density of states in both compounds. In In$_{5}$Bi$_{3}$, the spin-orbit coupling is essential for the dynamical stability of the… ▽ More We report a first principles computational analysis of two phonon-mediated superconductors, In$_{5}$Bi$_{3}$ and In$_{5}$Sb$_{3}$. We show that spin-orbit coupling leads to splitting of electron bands around the Fermi energy, resulting in a suppression of the electronic density of states in both compounds. In In$_{5}$Bi$_{3}$, the spin-orbit coupling is essential for the dynamical stability of the experimentally observed phase, and the calculated superconducting critical temperature is in close agreement with measurements. In In$_{5}$Sb$_{3}$, the spin-orbit coupling significantly reduces the calculated superconducting critical temperature compared to calculations neglecting relativistic effects. Our work emphasises the subtle interplay between spin-orbit interactions and phonon-mediated superconductivity. △ Less

Submitted 27 October, 2024; originally announced October 2024.

Comments: 7 pages,6 figures

Exact Solutions Disentangle Higher-Order Topology in 2D Non-Hermitian Lattices

Authors: Lingfang Li, Yating Wei, Gangzhou Wu, Yang Ruan, Shihua Chen, Ching Hua Lee, Zhenhua Ni

Abstract: We report the exact closed-form solutions for higher-order topological states as well as explicit energy-spectrum relationships in two-dimensional (2D) non-Hermitian multi-orbital lattices with generalized boundary conditions. These analytical solutions unequivocally confirm that topological edge states in a 2D non-Hermitian system which feature point-gap topology must undergo the non-Hermitian sk… ▽ More We report the exact closed-form solutions for higher-order topological states as well as explicit energy-spectrum relationships in two-dimensional (2D) non-Hermitian multi-orbital lattices with generalized boundary conditions. These analytical solutions unequivocally confirm that topological edge states in a 2D non-Hermitian system which feature point-gap topology must undergo the non-Hermitian skin effect along the edge. Under double open boundary conditions, the occurrence of the non-Hermitian skin effect for either topological edge states or bulk states can be accurately predicted by our proposed winding numbers. We unveil that the zero-energy topological corner state only manifests itself on a corner where two nearby gapped edge states intersect, and thus can either disappear completely or strengthen drastically due to the non-Hermitian skin effect of gapped topological edge states. Our analytical results offer direct insight into the non-Bloch band topology in two or higher dimensions and trigger experimental investigations into related phenomena such as quadrupole topological insulators and topological lasing. △ Less

Submitted 21 October, 2024; originally announced October 2024.

Quantum Embedding of Non-local Quantum Many-body Interactions in Prototypal Anti-tumor Vaccine Metalloprotein on Near Term Quantum Computing Hardware

Authors: Elena Chachkarova, Terence Tse, Yordan Yordanov, Yao Wei, Cedric Weber

Abstract: The real world obeys quantum physics and quantum computing presents an alternative way to map physical problems to systems that follow the same laws. Such computation fundamentally constitutes a better way to understand the most challenging quantum problems. One such problem is the accurate simulation of highly correlated quantum systems. Due to the high dimensionality of the problem classical com… ▽ More The real world obeys quantum physics and quantum computing presents an alternative way to map physical problems to systems that follow the same laws. Such computation fundamentally constitutes a better way to understand the most challenging quantum problems. One such problem is the accurate simulation of highly correlated quantum systems. Due to the high dimensionality of the problem classical computers require considerable computer power to accurately predict material properties, especially when strong electron interactions are present. Still, modern day quantum hardware has many limitations and only allows for modeling of very simple systems. Here we present for the first time a quantum computer model simulation of a complex hemocyanin molecule, which is an important respiratory protein involved in various physiological processes such as oxygen transport and immune defence, and is also used as a key component in therapeutic vaccines for cancer. To better characterise the mechanism by which hemocyanin transports oxygen, variational quantum eigensolver (VQE) based on fermionic excitations and quantum embedding methods is used in the context of dynamic mean field theory to solve Anderson impurity model (AIM). Finally, it is concluded that the magnetic structure of hemocyanin is largely influenced by the many-body correction and that the computational effort for solving correlated electron systems could be substantially reduced with the introduction of quantum computing algorithms. We encourage the use of the Hamiltonian systems presented in this paper as a benchmark for testing quantum computing algorithms efficiency for chemistry applications. △ Less

Submitted 21 November, 2024; v1 submitted 16 October, 2024; originally announced October 2024.

Comments: 14 pages, 16 figures

A phase transition in sampling from Restricted Boltzmann Machines

Authors: Youngwoo Kwon, Qian Qin, Guanyang Wang, Yuchen Wei

Abstract: Restricted Boltzmann Machines are a class of undirected graphical models that play a key role in deep learning and unsupervised learning. In this study, we prove a phase transition phenomenon in the mixing time of the Gibbs sampler for a one-parameter Restricted Boltzmann Machine. Specifically, the mixing time varies logarithmically, polynomially, and exponentially with the number of vertices depe… ▽ More Restricted Boltzmann Machines are a class of undirected graphical models that play a key role in deep learning and unsupervised learning. In this study, we prove a phase transition phenomenon in the mixing time of the Gibbs sampler for a one-parameter Restricted Boltzmann Machine. Specifically, the mixing time varies logarithmically, polynomially, and exponentially with the number of vertices depending on whether the parameter $c$ is above, equal to, or below a critical value $c_\star\approx-5.87$. A key insight from our analysis is the link between the Gibbs sampler and a dynamical system, which we utilize to quantify the former based on the behavior of the latter. To study the critical case $c= c_\star$, we develop a new isoperimetric inequality for the sampler's stationary distribution by showing that the distribution is nearly log-concave. △ Less

Submitted 10 October, 2024; originally announced October 2024.

Comments: 43 pages, 4 figures

Persistent quantum vibronic dynamics in a $5d^1$ double perovskite oxide

Authors: Naoya Iwahara, Jian-Rui Soh, Daigorou Hirai, Ivica Živković, Yuan Wei, Wenliang Zhang, Carlos Galdino, Tianlun Yu, Kenji Ishii, Federico Pisani, Oleg Malanyuk, Thorsten Schmitt, Henrik M Rønnow

Abstract: Quantum entanglement between the spin, orbital, and lattice degrees of freedom in condensed matter systems can emerge due to an interplay between spin-orbit and vibronic interactions. Heavy transition metal ions decorated on a face-centered cubic lattice, for example, in $5d^1$ double perovskites, are particularly suited to support these quantum entangled states, but direct evidence has not yet be… ▽ More Quantum entanglement between the spin, orbital, and lattice degrees of freedom in condensed matter systems can emerge due to an interplay between spin-orbit and vibronic interactions. Heavy transition metal ions decorated on a face-centered cubic lattice, for example, in $5d^1$ double perovskites, are particularly suited to support these quantum entangled states, but direct evidence has not yet been presented. In this work, we report additional peaks in the low-energy spectra of a $5d^1$ double perovskite, Ba$_2$CaReO$_6$, which cannot be explained by adopting a purely classical description of lattice vibrations. Instead, our theoretical analysis demonstrates that these spectroscopic signatures are characteristic of orbital-lattice entangled states in Ba$_2$CaReO$_6$. Crucially, both theory and experiment demonstrate that these quantum-entangled states persist to low temperatures, despite the onset of multipolar order. △ Less

Submitted 15 August, 2025; v1 submitted 12 September, 2024; originally announced September 2024.

Comments: 7 pages, 4 figures

Journal ref: Phys. Rev. B 112, 104104 (2025)

Cascade of strongly correlated quantum states in a partially filled kagome flat band

Authors: Caiyun Chen, Jiangchang Zheng, Yuman He, Xuzhe Ying, Soumya Sankar, Luanjing Li, Yizhou Wei, Xi Dai, Hoi Chun Po, Berthold Jäck

Abstract: Coulomb interactions among charge carriers that occupy an electronic flat band have a profound impact on the macroscopic properties of materials. At sufficient strength, these interactions can give rise to captivating phenomena such as quantum criticality, Mott-Hubbard states, and unconventional superconductivity. The appearance of these characteristics sensitively depends on the number of electro… ▽ More Coulomb interactions among charge carriers that occupy an electronic flat band have a profound impact on the macroscopic properties of materials. At sufficient strength, these interactions can give rise to captivating phenomena such as quantum criticality, Mott-Hubbard states, and unconventional superconductivity. The appearance of these characteristics sensitively depends on the number of electrons occupying the flat band states. In this work, we present experimental evidence obtained from scanning tunneling microscopy measurements for a cascade of strongly correlated states appearing in the partially occupied kagome flat bands of Co$_{1-x}$Fe$_x$Sn whose filling can be controlled by the Fe-doping level $x$. At elevated temperatures ($T\geq16\,K$), we detect a nematic electronic state across a broad doping range $0.05<x<0.25$. The comparison with model calculations reveals that strong Coulomb interactions ($U>100\,$meV) blend the states of two $3d$-orbital derived flat bands and impart a nematic order parameter. This state serves as the parent phase of a strongly correlated phase diagram: At lower temperatures $T<16\,$K, we find spectroscopic evidence for an orbital-selective Mott state enabled by the $3d$-orbital degeneracy of the Co atom. This state can only be detected in samples with ideal Fe doping ($x=0.17$) and descends into pseudogap phases upon electron and hole doping. At $T<8\,$K, the pseudogap phase evolves into another nematic low temperature state. Our observations demonstrate that the electronic ground state of a kagome flat band depends on the complex interplay between strong Coulomb repulsion, $3d$-orbital degeneracy, and flat band filling fraction at different temperatures. △ Less

Submitted 10 September, 2024; originally announced September 2024.

Comments: 13 pages, 5 figures

Dynamic Jahn-Teller effect in the strong spin-orbit coupling regime

Authors: Ivica Zivkovic, Jian-Rui Soh, Oleg Malanyuk, Ravi Yadav, Federico Pisani, Aria M. Tehrani, Davor Tolj, Jana Pasztorova, Daigorou Hirai, Yuan Wei, Wenliang Zhang, Carlos Galdino, Tianlun Yu, Kenji Ishii, Albin Demuer, Oleg V. Yazyev, Thorsten Schmitt, Henrik M. Ronnow

Abstract: Exotic quantum phases, arising from a complex interplay of charge, spin, lattice and orbital degrees of freedom, are of immense interest to a wide research community. A well-known example of such an entangled behavior is the Jahn-Teller effect, where the lifting of orbital degeneracy proceeds through lattice distortions, often accompanied by ordering of spins and metal-insulator transitions. Stati… ▽ More Exotic quantum phases, arising from a complex interplay of charge, spin, lattice and orbital degrees of freedom, are of immense interest to a wide research community. A well-known example of such an entangled behavior is the Jahn-Teller effect, where the lifting of orbital degeneracy proceeds through lattice distortions, often accompanied by ordering of spins and metal-insulator transitions. Static distortions, including cooperative behavior, have been associated with colossal magneto-resistance, multiferroicity, high-$T_\mathrm{C}$ superconductivity and other correlated phenomena. Realizations of the dynamic Jahn-Teller effect, on the other hand, are scarce since the preservation of vibronic symmetries requires subtle tuning of the local environment. Here we demonstrate that a highly-symmetrical 5d$^1$ double perovskite Ba$_2$MgReO$_6$, comprising of a 3D array of isolated ReO$_6$ octahedra, fulfils these requirements, resulting in a unique case of a dynamic Jahn-Teller system with strong spin-orbit coupling. Thermodynamic and resonant inelastic x-ray scattering experiments undoubtedly show that the Jahn-Teller instability leads to a ground-state doublet, invoking a paradigm shift for this family of compounds. The restoration of vibronic degrees of freedom arises from a quantum-mechanical zero-point motion, as revealed by detailed quantum chemistry calculations. The dynamic state of ReO$_6$ octahedra persists down to the lowest temperatures, where a multipolar order sets in, allowing for investigations of the interplay between a dynamic JT effect and strongly correlated electron behavior. △ Less

Submitted 2 September, 2024; originally announced September 2024.

Journal ref: Nature Communications 15, 8587 (2024)

Non-Reciprocal Transport of Thermally-Generated Magnons

Authors: M. Cosset-Chéneau, S. H. Tirion, X. Y. Wei, J. Ben Youssef, B. J. van Wees

Abstract: We demonstrate the non-reciprocity of electrically and thermally-generated incoherent magnon transport using the magnetization direction of a Py wire placed on top of an ultrathin YIG film. We show that the transport properties of thermally-generated magnons under a Py wire depends on the relative orientation between the temperature gradient and the Py-magnetization direction. The symmetries of th… ▽ More We demonstrate the non-reciprocity of electrically and thermally-generated incoherent magnon transport using the magnetization direction of a Py wire placed on top of an ultrathin YIG film. We show that the transport properties of thermally-generated magnons under a Py wire depends on the relative orientation between the temperature gradient and the Py-magnetization direction. The symmetries of this non-reciprocal magnon transport match with those predicted by the remote dipolar interaction between YIG and Py magnons, controlled by the chirality of the YIG magnon dipolar stray fields. We also show that the directional magnon generation by the spin Seebeck effect from the Py wire displays the symmetries expected from the chiral spin Seebeck effect. △ Less

Submitted 28 August, 2024; originally announced August 2024.

First-principles investigation of elastic, vibrational, and thermodynamic properties of kagome metals CsM$_3$Te$_5$ (M = Ti, Zr, Hf)

Authors: Yifan Wei, Arjyama Bordoloi, Chaon-En, Chuang, Sobhit Singh

Abstract: Kagome metals are a unique class of quantum materials characterized by their distinct atomic lattice arrangement, featuring interlocking triangles and expansive hexagonal voids. These lattice structures impart exotic properties, including superconductivity, interaction-driven topological many-body phenomena, and magnetism, among others. The kagome metal CsM3Te5 (where M = Ti, Zr, or Hf) exhibits b… ▽ More Kagome metals are a unique class of quantum materials characterized by their distinct atomic lattice arrangement, featuring interlocking triangles and expansive hexagonal voids. These lattice structures impart exotic properties, including superconductivity, interaction-driven topological many-body phenomena, and magnetism, among others. The kagome metal CsM3Te5 (where M = Ti, Zr, or Hf) exhibits both superconductivity and nontrivial topological electronic properties, offering a promising platform for exploring topological superconductivity. This study employs first-principles density functional theory calculations to systematically analyze the elastic, mechanical, vibrational, thermodynamic, and electronic properties of CsM3Te5 (M = Ti, Zr, Hf). Our calculations reveal that the studied compounds - CsTi3Te5, CsZr3Te5, and CsHf3Te5 - are ductile metals with elastic properties akin to the hexagonal Bi and Sb, with average elastic constants, including a bulk modulus of 27 GPa, a shear modulus of 11 GPa, and Young's modulus of 29 GPa. We observe peculiar dispersionless, flat, phonon branches in the vibrational spectra of these metals. Additionally, we thoroughly analyze the symmetries of the zone-center phonon eigenvectors and predict vibrational fingerprints of the Raman- and infrared-active phonon modes. The analysis of thermodynamic properties reveals the Einstein temperature for CsTi3Te5, CsZr3Te5, and CsHf3Te5 to be 66, 54, and 53 K, respectively. Our orbital-decomposed electronic structure calculations reveal significant in-plane steric interactions and multiple Dirac band crossings near the Fermi level. We further investigate the role of spin-orbit coupling effect on the studied properties. This theoretical investigation sheds light on the intriguing quantum behaviour of kagome metals. △ Less

Submitted 20 November, 2024; v1 submitted 20 August, 2024; originally announced August 2024.

Comments: 10 pages, 8 figures

Layer-dependent electromechanical response in twisted graphene moiré superlattices

Authors: Hanhao Zhang, Yuanhao Wei, Yuhao Li, Shengsheng Lin, Jiarui Wang, Takashi Taniguchi, Kenji Watanabe, Jiangyu Li, Yi Shi, Xinran Wang, Yan Shi, Zaiyao Fei

Abstract: The coupling of mechanical deformation and electrical stimuli at the nanoscale has been a subject of intense investigation in the realm of materials science. Recently, twisted van der Waals (vdW) materials have emerged as a platform to explore exotic quantum states. These states are intimately tied to the formation of moiré superlattices, which can be visualized directly exploiting the electromech… ▽ More The coupling of mechanical deformation and electrical stimuli at the nanoscale has been a subject of intense investigation in the realm of materials science. Recently, twisted van der Waals (vdW) materials have emerged as a platform to explore exotic quantum states. These states are intimately tied to the formation of moiré superlattices, which can be visualized directly exploiting the electromechanical response. However, the origin of the response, even in twisted bilayer graphene (tBLG), remains unsettled. Here, employing lateral piezoresponse force microscopy (LPFM), we investigate the electromechanical responses of marginally twisted graphene moiré superlattices with different layer thicknesses. We observe distinct LPFM amplitudes and spatial profiles in tBLG and twisted monolayer-bilayer graphene (tMBG), exhibiting effective in-plane piezoelectric coefficients of 0.05 pm/V and 0.35 pm/V, respectively. Force tuning experiments further underscore a marked divergence in their responses. The contrasting behaviors suggest different electromechanical couplings in tBLG and tMBG. In tBLG, the response near the domain walls is attributed to the flexoelectric effect, while in tMBG, the behaviors can be comprehended within the context of piezoelectric effect. Our results not only provide insights to electromechanical and corporative effects in twisted vdW materials with different stacking symmetries, but may also show their potential for engineering them at the nanoscale. △ Less

Submitted 17 June, 2024; originally announced June 2024.

Rayleigh surface waves of extremal elastic materials

Authors: Yu Wei, Yi Chen, Wen Cheng, Xiaoning Liu, Gengkai Hu

Abstract: Extremal elastic materials here refer to a specific class of elastic materials whose elastic matrices exhibit one or more zero eigenvalues, resulting in soft deformation modes that, in principle, cost no energy. They can be approximated through artificially designed solid microstructures. Extremal elastic materials have exotic bulk wave properties unavailable with conventional solids due to the so… ▽ More Extremal elastic materials here refer to a specific class of elastic materials whose elastic matrices exhibit one or more zero eigenvalues, resulting in soft deformation modes that, in principle, cost no energy. They can be approximated through artificially designed solid microstructures. Extremal elastic materials have exotic bulk wave properties unavailable with conventional solids due to the soft modes, offering unprecedented opportunities for manipulating bulk waves, e.g., acting as phonon polarizers for elastic waves or invisibility cloaks for underwater acoustic waves. Despite their potential, Rayleigh surface waves, crucially linked to bulk wave behaviors of such extremal elastic materials, have largely remained unexplored so far. In this paper, we theoretically investigate the propagation of Rayleigh waves in extremal elastic materials based on continuum theory and verify our findings with designed microstructure metamaterials based on pantographic structures. Dispersion relations and polarizations of Rayleigh waves in extremal elastic materials are derived, and the impact of higher order gradient effects is also investigated by using strain gradient theory. This study provides a continuum model for exploring surface waves in extremal elastic materials and may stimulate applications of extremal elastic materials for controlling surface waves. △ Less

Submitted 11 June, 2024; originally announced June 2024.

Comments: 8 figures

Journal ref: J. Mech. Phys. Solids, 193(105842), 2024

Giant plateau-like topological Hall effect controlled by tailoring the magnetic exchange stiffness in a kagome magnet

Authors: Wei Xia, Aile Wang, Jian Yuan, Jiawei Luo, Yurui Wei, Haonan Wang, Wenjie Meng, Yubin Hou, Hong Du, Xiangqi Liu, Jiangteng Guo, Yixuan Luo, Ke Qu, Min Chen, Jinlong Jiao, Xia Wang, Xuerong Liu, Wenbo Wang, Yulin Chen, Jianpeng Liu, Xuewen Fu, Ruidan Zhong, Qingyou Lu, Shihao Zhang, Zhenzhong Yang , et al. (1 additional authors not shown)

Abstract: The ferrimagnet TbMn6Sn6 has attracted vast attention, because its pristine Mn kagome lattice with strong spin-orbit coupling and out-of-plane Tb-Mn exchange supports quantum-limit Chern topological magnetism which can be described by the simple spinless Haldane model. We unveil herein that engineering the kagome lattice through partial substitution of Mn with nonmagnetic Cr induces a striking str… ▽ More The ferrimagnet TbMn6Sn6 has attracted vast attention, because its pristine Mn kagome lattice with strong spin-orbit coupling and out-of-plane Tb-Mn exchange supports quantum-limit Chern topological magnetism which can be described by the simple spinless Haldane model. We unveil herein that engineering the kagome lattice through partial substitution of Mn with nonmagnetic Cr induces a striking structural reorganization-Cr preferentially concentrates within a single Mn layer per unit cell, reducing the crystal symmetry from the D6h point group to the C2. This tailored structure configuration gives rise to a plateau-like topological Hall effect (THE), achieving a record-breaking resistivity of 19.1 ohm cm among bulk systems. Complementary magnetic force microscopy measurements unveil a magnetic domain transition near 1 T at 180 K, aligning with the field-dependent phase diagram of the THE. Our direct visualization of the magnetic domain structure underscores the critical role of broken kagome lattice symmetry in generating distinct exchange stiffness between the two Mn layers. These findings establish a new paradigm for exploring exotic states in kagome topological magnets and provide a proof-of-principle strategy for unraveling the interplay between magnetism and emergent topological properties in kagome systems. △ Less

Submitted 25 July, 2025; v1 submitted 24 May, 2024; originally announced May 2024.

Spin-orbital excitations encoding the magnetic phase transition in the van der Waals antiferromagnet FePS$_{3}$

Authors: Yuan Wei, Yi Tseng, Hebatalla Elnaggar, Wenliang Zhang, Teguh Citra Asmara, Eugenio Paris, Gabriele Domaine, Vladimir N. Strocov, Luc Testa, Virgile Favre, Mario Di Luca, Mitali Banerjee, Andrew R. Wildes, Frank M. F. de Groot, Henrik M. Ronnow, Thorsten Schmitt

Abstract: In the rich phases of van der Waals (vdW) materials featuring intertwined electronic order and collective phenomena, characterizing elementary dynamics that entail the low-energy Hamiltonian and electronic degrees of freedom is of paramount importance. Here we performed resonant inelastic X-ray scattering (RIXS) to elaborate the spin-orbital ground and excited states of the vdW antiferromagnetic i… ▽ More In the rich phases of van der Waals (vdW) materials featuring intertwined electronic order and collective phenomena, characterizing elementary dynamics that entail the low-energy Hamiltonian and electronic degrees of freedom is of paramount importance. Here we performed resonant inelastic X-ray scattering (RIXS) to elaborate the spin-orbital ground and excited states of the vdW antiferromagnetic insulator FePS$_{3}$, as well as their relation to magnetism. We observed the spectral enhancement of spin-orbital multiplet transitions about $\sim$ 100 and $\sim$ 220 meV, as well as quasielastic response, when entering the zig-zag antiferromagnetic phase, where the spectral changes develop an order-parameter-like evolution with temperature. By comparing with ligand field theory calculations, we discovered the essential role of trigonal lattice distortion and negative metal-ligand charge-transfer to account for these emergent excitations. Such spectral profiles are further examined upon confinement by mechanical exfoliation. We reveal their spectral robustness down to the few atomic layer limit, in accordance with the persistent antiferromagnetic state previously reported in optical measurements. Our study demonstrates the versatile RIXS capability that resolves magneto-crystalline anisotropy and charge-transfer energetics. These provide the crucial insight to understand how the spontaneous magnetic symmetry-breaking stabilizes in the quasi-two-dimensional limit for the vdW magnet FePS$_{3}$. △ Less

Submitted 22 May, 2024; originally announced May 2024.

Direct visualization of the impurity occupancy roadmap in Ni-substituted van der Waals ferromagnet Fe3GaTe2

Authors: Jian Yuan, Haonan Wang, Xiaofei Hou, Binshuo Zhang, Yurui Wei, Jiangteng Guo, Lu Sun, Zhenhai Yu, Zhikai Li, Xiangqi Liu, Wei Xia, Xia Wang, Xuerong Liu, Yulin Chen, Shihao Zhang, Xuewen Fu, Ke Qu, Zhenzhong Yang, Yanfeng Guo

Abstract: Impurity substitution is a general strategy to study the intrinsic properties of a quantum material. However, when the target element has more than one Wyckoff position in the lattice, it is a big challenge but with extreme necessity to know the exact position and order of the occupancy of impurity atoms. Via comprehensive experimental and theoretical investigations, we establish herein the roadma… ▽ More Impurity substitution is a general strategy to study the intrinsic properties of a quantum material. However, when the target element has more than one Wyckoff position in the lattice, it is a big challenge but with extreme necessity to know the exact position and order of the occupancy of impurity atoms. Via comprehensive experimental and theoretical investigations, we establish herein the roadmap for Ni substitution in Fe3GaTe2, a van der Waals ferromagnet with the Curie temperature TC even reaching ~ 380 K. The results unambiguously reveal that in (Fe1-xNix)3GaTe2, Ni atoms initially form an van der Waals interlayer gap Ni3 sites when x < 0.1, and then gradually occupy the Fe2 sites. After replacing the Fe2 sites at x of ~ 0.75, they start to substitute for the Fe1 sites and eventually realize a full occupation at x = 1.0. Accordingly, TC and saturation magnetic moments of (Fe1-xNix)3GaTe2 both show nonlinear decrease, which is tightly tied to the Ni occupancy order as well as the different roles of Ni3, Fe1 and Fe2 sites in the spin Hamiltonian. The results not only yield fruitful insights into the essential roles of different Fe sites in producing the above room temperature high TC, but also set a paradigm for future impurity substitution study on other quantum materials. △ Less

Submitted 12 May, 2024; originally announced May 2024.

Comments: 24 pages,5 main figures+4 SI figures+2 SI tables

3D deep learning for enhanced atom probe tomography analysis of nanoscale microstructures

Authors: Jiwei Yu, Zhangwei Wang, Aparna Saksena, Shaolou Wei, Ye Wei, Timoteo Colnaghi, Andreas Marek, Markus Rampp, Min Song, Baptiste Gault, Yue Li

Abstract: Quantitative analysis of microstructural features on the nanoscale, including precipitates, local chemical orderings (LCOs) or structural defects (e.g. stacking faults) plays a pivotal role in understanding the mechanical and physical responses of engineering materials. Atom probe tomography (APT), known for its exceptional combination of chemical sensitivity and sub-nanometer resolution, primaril… ▽ More Quantitative analysis of microstructural features on the nanoscale, including precipitates, local chemical orderings (LCOs) or structural defects (e.g. stacking faults) plays a pivotal role in understanding the mechanical and physical responses of engineering materials. Atom probe tomography (APT), known for its exceptional combination of chemical sensitivity and sub-nanometer resolution, primarily identifies microstructures through compositional segregations. However, this fails when there is no significant segregation, as can be the case for LCOs and stacking faults. Here, we introduce a 3D deep learning approach, AtomNet, designed to process APT point cloud data at the single-atom level for nanoscale microstructure extraction, simultaneously considering compositional and structural information. AtomNet is showcased in segmenting L12-type nanoprecipitates from the matrix in an AlLiMg alloy, irrespective of crystallographic orientations, which outperforms previous methods. AtomNet also allows for 3D imaging of L10-type LCOs in an AuCu alloy, a challenging task for conventional analysis due to their small size and subtle compositional differences. Finally, we demonstrate the use of AtomNet for revealing 2D stacking faults in a Co-based superalloy, without any defected training data, expanding the capabilities of APT for automated exploration of hidden microstructures. AtomNet pushes the boundaries of APT analysis, and holds promise in establishing precise quantitative microstructure-property relationships across a diverse range of metallic materials. △ Less

Submitted 25 April, 2024; originally announced April 2024.

Quantum geometric tensor and the topological characterization of the extended Su-Schrieffer-Heeger model

Authors: Xiang-Long Zeng, Wen-Xi Lai, Yi-Wen Wei, Yu-Quan Ma

Abstract: We investigate the quantum metric and topological Euler number in a cyclically modulated Su-Schrieffer-Heeger (SSH) model with long-range hopping terms. By computing the quantum geometry tensor, we derive exactly expressions for the quantum metric and Berry curvature of the energy band electrons, and we obtain the phase diagram of the model marked by the first Chern number. Furthermore, we also ob… ▽ More We investigate the quantum metric and topological Euler number in a cyclically modulated Su-Schrieffer-Heeger (SSH) model with long-range hopping terms. By computing the quantum geometry tensor, we derive exactly expressions for the quantum metric and Berry curvature of the energy band electrons, and we obtain the phase diagram of the model marked by the first Chern number. Furthermore, we also obtain the topological Euler number of the energy band based on the Gauss-Bonnet theorem on the topological characterization of the closed Bloch states manifold in the first Brillouin zone. However, some regions where the Berry curvature is identically zero in the first Brillouin zone results in the degeneracy of the quantum metric, which leads to ill-defined non-integer topological Euler numbers. Nevertheless, the non-integer "Euler number" provides valuable insights and provide an upper bound for absolute values of the Chern numbers. △ Less

Submitted 11 April, 2024; originally announced April 2024.

Comments: 6 pages, 4 figures

Journal ref: Chin. Phys. B, 2024, 33 (3): 030310

Multipartite edge modes and tensor networks

Authors: Chris Akers, Ronak M. Soni, Annie Y. Wei

Abstract: Holographic tensor networks model AdS/CFT, but so far they have been limited by involving only systems that are very different from gravity. Unfortunately, we cannot straightforwardly discretize gravity to incorporate it, because that would break diffeomorphism invariance. In this note, we explore a resolution. In low dimensions gravity can be written as a topological gauge theory, which can be di… ▽ More Holographic tensor networks model AdS/CFT, but so far they have been limited by involving only systems that are very different from gravity. Unfortunately, we cannot straightforwardly discretize gravity to incorporate it, because that would break diffeomorphism invariance. In this note, we explore a resolution. In low dimensions gravity can be written as a topological gauge theory, which can be discretized without breaking gauge-invariance. However, new problems arise. Foremost, we now need a qualitatively new kind of "area operator," which has no relation to the number of links along the cut and is instead topological. Secondly, the inclusion of matter becomes trickier. We successfully construct a tensor network both including matter and with this new type of area. Notably, while this area is still related to the entanglement in "edge mode" degrees of freedom, the edge modes are no longer bipartite entangled pairs. Instead they are highly multipartite. Along the way, we calculate the entropy of novel subalgebras in a particular topological gauge theory. We also show that the multipartite nature of the edge modes gives rise to non-commuting area operators, a property that other tensor networks do not exhibit. △ Less

Submitted 19 June, 2024; v1 submitted 4 April, 2024; originally announced April 2024.

Comments: 49 pages, 78 pages with appendices, 19 figures

Journal ref: SciPost Phys. Core 7, 070 (2024)

A general formula of frequency and amplitude for shaking induced Mott insulator in atomtronic transistors

Authors: Wenxi Lai, Yu-Quan Ma, Yi-Wen Wei

Abstract: Mott insulator of atomic transport can be realized in driven optical lattices by choosing particular ratio of driving frequency and amplitude, which has been studied as Floquet engineering with time-independent effective Hamiltonian approach. Here, we give a general formula of frequency-amplitude radio for realization of the driving induced insulator-conductor transition in a double-well open syst… ▽ More Mott insulator of atomic transport can be realized in driven optical lattices by choosing particular ratio of driving frequency and amplitude, which has been studied as Floquet engineering with time-independent effective Hamiltonian approach. Here, we give a general formula of frequency-amplitude radio for realization of the driving induced insulator-conductor transition in a double-well open system, using numerical computation with instantaneous eigenstates approach. The result is owing to the fact that the instantaneous eigenstates approach is applicable in more wide parameter range compared with the time-independent effective Hamiltonian approach. Analysis from the results of quantum master equation shows that the insulator effect is originated from coherent localization of atom wave packets in optical wells. △ Less

Submitted 7 November, 2025; v1 submitted 17 March, 2024; originally announced March 2024.

Comments: 12 pages, 6 figures

Emergence of interfacial magnetism in strongly-correlated nickelate-titanate superlattices

Authors: Teguh Citra Asmara, Robert J. Green, Andreas Suter, Yuan Wei, Wenliang Zhang, Daniel Knez, Grant Harris, Yi Tseng, Tianlun Yu, Davide Betto, Mirian Garcia-Fernandez, Stefano Agrestini, Yannick Maximilian Klein, Neeraj Kumar, Carlos William Galdino, Zaher Salman, Thomas Prokscha, Marisa Medarde, Elisabeth Müller, Yona Soh, Nicholas B. Brookes, Ke-Jin Zhou, Milan Radovic, Thorsten Schmitt

Abstract: Strongly-correlated transition-metal oxides are widely known for their various exotic phenomena. This is exemplified by rare-earth nickelates such as LaNiO$_{3}$, which possess intimate interconnections between their electronic, spin, and lattice degrees of freedom. Their properties can be further enhanced by pairing them in hybrid heterostructures, which can lead to hidden phases and emergent phe… ▽ More Strongly-correlated transition-metal oxides are widely known for their various exotic phenomena. This is exemplified by rare-earth nickelates such as LaNiO$_{3}$, which possess intimate interconnections between their electronic, spin, and lattice degrees of freedom. Their properties can be further enhanced by pairing them in hybrid heterostructures, which can lead to hidden phases and emergent phenomena. An important example is the LaNiO$_{3}$/LaTiO$_{3}$ superlattice, where an interlayer electron transfer has been observed from LaTiO$_{3}$ into LaNiO$_{3}$ leading to a high-spin state. However, macroscopic emergence of magnetic order associated with this high-spin state has so far not been observed. Here, by using muon spin rotation, x-ray absorption, and resonant inelastic x-ray scattering, we present direct evidence of an emergent antiferromagnetic order with high magnon energy and exchange interactions at the LaNiO$_{3}$/LaTiO$_{3}$ interface. As the magnetism is purely interfacial, a single LaNiO$_{3}$/LaTiO$_{3}$ interface can essentially behave as an atomically thin strongly-correlated quasi-two-dimensional antiferromagnet, potentially allowing its technological utilisation in advanced spintronic devices. Furthermore, its strong quasi-two-dimensional magnetic correlations, orbitally-polarized planar ligand holes, and layered superlattice design make its electronic, magnetic, and lattice configurations resemble the precursor states of superconducting cuprates and nickelates, but with an $S \rightarrow 1$ spin state instead. △ Less

Submitted 5 November, 2024; v1 submitted 1 March, 2024; originally announced March 2024.

Comments: 41 pages, 14 figures

Journal ref: Advanced Materials 36, 2310668 (2024)

Roadmap on Data-Centric Materials Science

Authors: Stefan Bauer, Peter Benner, Tristan Bereau, Volker Blum, Mario Boley, Christian Carbogno, C. Richard A. Catlow, Gerhard Dehm, Sebastian Eibl, Ralph Ernstorfer, Ádám Fekete, Lucas Foppa, Peter Fratzl, Christoph Freysoldt, Baptiste Gault, Luca M. Ghiringhelli, Sajal K. Giri, Anton Gladyshev, Pawan Goyal, Jason Hattrick-Simpers, Lara Kabalan, Petr Karpov, Mohammad S. Khorrami, Christoph Koch, Sebastian Kokott , et al. (36 additional authors not shown)

Abstract: Science is and always has been based on data, but the terms "data-centric" and the "4th paradigm of" materials research indicate a radical change in how information is retrieved, handled and research is performed. It signifies a transformative shift towards managing vast data collections, digital repositories, and innovative data analytics methods. The integration of Artificial Intelligence (AI) a… ▽ More Science is and always has been based on data, but the terms "data-centric" and the "4th paradigm of" materials research indicate a radical change in how information is retrieved, handled and research is performed. It signifies a transformative shift towards managing vast data collections, digital repositories, and innovative data analytics methods. The integration of Artificial Intelligence (AI) and its subset Machine Learning (ML), has become pivotal in addressing all these challenges. This Roadmap on Data-Centric Materials Science explores fundamental concepts and methodologies, illustrating diverse applications in electronic-structure theory, soft matter theory, microstructure research, and experimental techniques like photoemission, atom probe tomography, and electron microscopy. While the roadmap delves into specific areas within the broad interdisciplinary field of materials science, the provided examples elucidate key concepts applicable to a wider range of topics. The discussed instances offer insights into addressing the multifaceted challenges encountered in contemporary materials research. △ Less

Submitted 1 May, 2024; v1 submitted 1 February, 2024; originally announced February 2024.

Comments: Review, outlook, roadmap, perspective

Global Optimization of Molybdenum Subnanoclusters on Graphene: a Consistent Approach Towards Catalytic Applications

Authors: Yao Wei, Alejandro Santana-Bonilla, Lev Kantorovich

Abstract: The development of novel sub-nanometer clusters (SNCs) catalysts with superior catalytic performance depends on the precise control of clusters' atomistic sizes, shapes, and accurate deposition onto surfaces. The intrinsic complexity of the adsorption process complicates the ability to achieve an atomistic understanding of the most relevant structure-reactivity relationships hampering the rational… ▽ More The development of novel sub-nanometer clusters (SNCs) catalysts with superior catalytic performance depends on the precise control of clusters' atomistic sizes, shapes, and accurate deposition onto surfaces. The intrinsic complexity of the adsorption process complicates the ability to achieve an atomistic understanding of the most relevant structure-reactivity relationships hampering the rational design of novel catalytic materials. In most cases, existing computational approaches rely on just a few structures to draw conclusions on clusters' reactivity thereby neglecting the complexity of the existing energy landscapes thus leading to insufficient sampling and, most likely, unreliable predictions. Moreover, modelling of the actual experimental procedure that is responsible for the deposition of SNCs on surfaces is often not done even though in some cases this procedure may enhance the significance of certain (e.g., metastable) adsorption geometries. This study proposes a novel systematic approach that utilizes global search techniques, specifically, the particle swarm optimization (PSO) method, in conjunction with \textit{ab-initio} calculations, to simulate {\it all stages} in the beam experiments, from predicting the most relevant SNCs structures in the beam and on a surface, to their reactivity. To illustrate the main steps of our approach, we consider the deposition of Molybdenum SNC of 6 Mo atoms on a free-standing graphene surface, as well as their catalytic properties with respect to the CO molecule dissociation reaction. Even though our calculations are not exhaustive and serve only to produce an illustration of the method, they are still able to provide insight into the complicated energy landscape of Mo SNCs on graphene demonstrating the catalytic activity of Mo SNCs and the importance of performing statistical sampling of available configurations... △ Less

Submitted 5 November, 2024; v1 submitted 9 February, 2024; originally announced February 2024.

Comments: 39 pages, 8 figures, due to the limitation "The abstract field cannot be longer than 1,920 characters", the abstract appearing here is slightly shorter than that in the PDF file

Aperiodic-quasiperiodic-periodic properties and topological transitions in twisted nested Moiré patterns

Authors: Peng Peng, Yuchen Peng, Aoqian Shi, Xiaogen Yi, Yizhou Wei, Jianjun Liu

Abstract: The Moiré patterns generated by altering the structural parameters in a two or more layers of periodic materials, including single-layer structure, interlayer stacking, and twisting parameters, exhibit prosperous topological physical properties. However, the intricate characteristics of twisted nested Moiré patterns and their relationship with topological transitions remain unclear. In this Letter… ▽ More The Moiré patterns generated by altering the structural parameters in a two or more layers of periodic materials, including single-layer structure, interlayer stacking, and twisting parameters, exhibit prosperous topological physical properties. However, the intricate characteristics of twisted nested Moiré patterns and their relationship with topological transitions remain unclear. In this Letter, based on the proposed twisted nested photonic crystal (TNPC), we derive its spatial geometric functions (SGFs), aperiodic-quasiperiodic-periodic properties in twisted nested Moiré patterns, and the SSHφ Hamiltonian. We reveal the intrinsic correlation between twisted nested Moiré patterns and topological transitions, obtaining higher-order topological states (HOTSs) with C2z symmetry. This work will provide theoretical references for the design and application of twisted topological PC and their devices. △ Less

Submitted 17 February, 2024; v1 submitted 28 January, 2024; originally announced January 2024.

Nematic charge-density-wave correlations in FeSe$_{1-x}$S$_{x}$

Authors: Ruixian Liu, Wenliang Zhang, Yuan Wei, Zhen Tao, Teguh C. Asmara, Vladimir N. Strocov, Thorsten Schmitt, Xingye Lu

Abstract: The occurrence of charge-density-wave (CDW) order is a common thread in the phase diagram of cuprate high-transition-temperature ($T_c$) superconductors. In iron-based superconductors (FeSCs), nematic order and fluctuations play a decisive role in driving other emergent orders. CDW order has been observed by scanning tunneling microscopy for various FeSCs such as FeSe thin films, uniaxially strain… ▽ More The occurrence of charge-density-wave (CDW) order is a common thread in the phase diagram of cuprate high-transition-temperature ($T_c$) superconductors. In iron-based superconductors (FeSCs), nematic order and fluctuations play a decisive role in driving other emergent orders. CDW order has been observed by scanning tunneling microscopy for various FeSCs such as FeSe thin films, uniaxially strained LiFeAs, and tetragonal FeSe$_{0.81}$S$_{0.19}$. However, it remains elusive if the CDW in these materials is a bulk phenomenon as well as if and how it intertwines with the electronic nematicity. Using energy-resolved resonant X-ray scattering at the Fe-L$_3$ edge, we report the discovery of a local-strain-induced incommensurate isotropic CDW order in FeSe$_{0.82}$S$_{0.18}$. A highly anisotropic CDW response under uniaxial strain unambiguously manifests that the CDW is directly coupled to the nematicity. Transforming part of Fe$^{2+}$ to Fe$^{3+}$ on the surface of FeSe$_{1-x}$S$_{x}$ reveals that the same isotropic CDW can be induced, enhanced, and stabilized in the whole nematic regime measured ($x=0-0.19$). As Fe$^{3+}$ can create local lattice distortions on the surface, the CDW could arise from the interaction between the local strain around Fe$^{3+}$ and the nematic electron correlations. Our experimental observation of a local-strain-induced CDW gives vital information for understanding the interplay between electron correlations and the electronic nematicity in FeSCs. △ Less

Submitted 21 December, 2023; v1 submitted 19 December, 2023; originally announced December 2023.

Comments: 7 pages, 4 figures

Tensor network renormalization: application to dynamic correlation functions and non-hermitian systems

Authors: Ying-Jie Wei, Zheng-Cheng Gu

Abstract: In recent years, tensor network renormalization (TNR) has emerged as an efficient and accurate method for studying (1+1)D quantum systems or 2D classical systems using real-space renormalization group (RG) techniques. One notable application of TNR is its ability to extract central charge and conformal scaling dimensions for critical systems. In this paper, we present the implementation of the Loo… ▽ More In recent years, tensor network renormalization (TNR) has emerged as an efficient and accurate method for studying (1+1)D quantum systems or 2D classical systems using real-space renormalization group (RG) techniques. One notable application of TNR is its ability to extract central charge and conformal scaling dimensions for critical systems. In this paper, we present the implementation of the Loop-TNR algorithm, which allows for the computation of dynamical correlation functions. Our algorithm goes beyond traditional approaches by not only calculating correlations in the spatial direction, where the separation is an integer, but also in the temporal direction, where the time difference can contain decimal values. Our algorithm is designed to handle both imaginary-time and real-time correlations, utilizing a tensor network representation constructed from a path-integral formalism. Additionally, we highlight that the Loop-TNR algorithm can also be applied to investigate critical properties of non-Hermitian systems, an area that was previously inaccessible using density matrix renormalization group(DMRG) and matrix product state(MPS) based algorithms. △ Less

Submitted 30 November, 2023; originally announced November 2023.

Comments: 18 pages, 28 figures

Spectral evidence for Dirac spinons in a kagome lattice antiferromagnet

Authors: Zhenyuan Zeng, Chengkang Zhou, Honglin Zhou, Lankun Han, Runze Chi, Kuo Li, Maiko Kofu, Kenji Nakajima, Yuan Wei, Wenliang Zhang, Daniel G. Mazzone, Zi Yang Meng, Shiliang Li

Abstract: Emergent quasiparticles with a Dirac dispersion in condensed matter systems can be described by the Dirac equation for relativistic electrons, in analogy with Dirac particles in high-energy physics. For example, electrons with a Dirac dispersion have been intensively studied in electronic systems such as graphene and topological insulators. However, charge is not a prerequisite for Dirac fermions,… ▽ More Emergent quasiparticles with a Dirac dispersion in condensed matter systems can be described by the Dirac equation for relativistic electrons, in analogy with Dirac particles in high-energy physics. For example, electrons with a Dirac dispersion have been intensively studied in electronic systems such as graphene and topological insulators. However, charge is not a prerequisite for Dirac fermions, and the emergence of Dirac fermions without charge degree of freedom has been theoretically predicted to be realized in Dirac quantum spin liquids. These quasiparticles carry a spin of 1/2 but are charge-neutral, and so are called spinons. Here we show that the spin excitations of a kagome antiferromagnet, YCu$_3$(OD)$_6$Br$_2$[Br$_{0.33}$(OD)$_{0.67}$], are conical with a spin continuum inside, which is consistent with the convolution of two Dirac spinons. The predictions of a Dirac spin liquid model with a spinon velocity obtained from the spectral measurements are in agreement with the low-temperature specific heat of the sample. Our results thus provide spectral evidence for the Dirac quantum spin liquid state emerging in this kagome lattice antiferromagnet. However, the locations of the conical spin excitations differ from those calculated by the nearest neighbor Heisenberg model, suggesting the Dirac spinons have an unexpected origin. △ Less

Submitted 21 May, 2024; v1 submitted 17 October, 2023; originally announced October 2023.

Comments: 6 pages, 4 figures

Journal ref: Nat. Phys. (2024)

A comprehensive exploration of structural and electronic properties of Molybdenum clusters

Authors: Yao Wei, Lev Kantorovich

Abstract: Molybdenum clusters, characterised by their unique structure and intriguing catalytic properties, have gained significant attention in recent years. In several existing studies density functional theory (DFT) methods have been used to find the lowest energy Mo clusters and explore their electronic and magnetic structure. In all cases, with the exception of a single recent study, where a genetic al… ▽ More Molybdenum clusters, characterised by their unique structure and intriguing catalytic properties, have gained significant attention in recent years. In several existing studies density functional theory (DFT) methods have been used to find the lowest energy Mo clusters and explore their electronic and magnetic structure. In all cases, with the exception of a single recent study, where a genetic algorithm was employed, initial geometries of the clusters, prior to geometry optimisation, were chosen using heuristic approaches based on symmetry considerations and known structures. DFT calculations were performed using different types of pseudopotentials, from hard to soft, and different types of basis sets. However, no comprehensive study has yet been done in which a DFT method with the best control on its precision would be complemented by a reliable global minimum search method to find the lowest energy Mo clusters. In this work, we employ a combination of a plane wave-based DFT method and \emph{ab initio} random structure searching (AIRSS) technique to find the lowest energy clusters of up to 10 Mo atoms. In each case, the search has been performed for clusters with different spin multiplicities, which enabled us to explore their magnetic structure. The results are compared for both hard and soft pseudopotentials stressing the importance of treating more electrons explicitly, in agreement with some of the previous studies. For most of the low-energy magnetic structures found, we investigate the distribution of their spin densities, and for all low energy clusters, we confirm their stability by calculating their phonon structure. Finally, free energies of the Mo clusters, within the quasi-harmonic approximation, are also calculated and discussed. △ Less

Submitted 2 October, 2023; originally announced October 2023.

Comments: 13 pages, 5 figures