Showing 1–50 of 189 results for author: ji, W

InvDesMobility: a reliability-gated first-principles feedback framework for closed-loop materials discovery

Authors: Wen-Kao Li, Ze-Feng Gao, Peng-Jie Guo, Wei Ji, Zhong-Yi Lu

Abstract: Inverse materials design starts from target functionality and searches for structures that can realize it. Its value in closed-loop discovery depends not only on prediction performance, but also on whether expensive first-principles results are independently validated, provenance-recorded, and admitted as feedback only when evidence is sufficient. This is especially important for composite propert… ▽ More Inverse materials design starts from target functionality and searches for structures that can realize it. Its value in closed-loop discovery depends not only on prediction performance, but also on whether expensive first-principles results are independently validated, provenance-recorded, and admitted as feedback only when evidence is sufficient. This is especially important for composite properties such as carrier mobility, where a final scalar value hides intermediate quantities, fit quality, convergence history, and workflow assumptions. Here we present InvDesMobility, a reliability-gated first-principles feedback framework that integrates multi-agent automated DFT, evidence stratification, generative structure proposal, acquisition ranking, and auditable release. Using 516 2DMatPedia-derived candidates, the workflow produced 280 QC-passed materials and 573 retained carrier-direction seed channels after channel-level reliability gating. These records were split into two feedback objects: relaxed structures updated the generative model, while retained mobility channels trained the acquisition model and set validation priority. Over multiple iterations, InvDesMobility screened 2.4 x 10^6 structures, submitted 102 candidates for DFT validation, and retained 86 reliability-gated generated channels across 41 formulas. Overall, the main contribution is not a fixed list of high-mobility materials, but a transferable feedback contract that makes closed-loop inverse design both useful and auditable when learning from expensive calculated properties. All source data, retained feedback records, and workflows are available at https://github.com/DreamLufei/invDesMobility, with an accompanying evidence website at https://dreamlufei.github.io/invDesMobility/. △ Less

Submitted 14 June, 2026; originally announced June 2026.

Comments: 33 pages, 4 main figures, 2 main tables; Supplementary Information included

Curvature-driven revival of charge density waves in non-Euclidean space

Authors: Zhipeng Song, Zeyu Liu, Junde Liu, Yi Biao, Anning Yang, Qian Fang, Mojun Pan, Chen Liu, Jiaou Wang, Tian Qian, Chenmin shen, Hongliang Lu, Wei Ji, Hong-Jun Gao, Xiao Lin

Abstract: Strongly correlated quantum states, such as charge density waves (CDWs), are exquisitely sensitive to Fermi surface topology and lattice symmetry, and are typically quenched by heavy carrier doping. In two-dimensional (2D) systems, however, macroscopic geometric curvature emerges as a novel structural degree of freedom to modulate microscopic quantum coherence. This raises a compelling physical qu… ▽ More Strongly correlated quantum states, such as charge density waves (CDWs), are exquisitely sensitive to Fermi surface topology and lattice symmetry, and are typically quenched by heavy carrier doping. In two-dimensional (2D) systems, however, macroscopic geometric curvature emerges as a novel structural degree of freedom to modulate microscopic quantum coherence. This raises a compelling physical question: can non-Euclidean geometric deformations compete with extreme electronic perturbations to reshape, or even revive, a quenched macroscopic quantum order? Here, by constructing monolayer TiSe$_2$-NbSe$_2$ heterostructure on a BLG/SiC substrate for the first time, we report the curvature-driven revival of a frustrated charge order in a non-Euclidean space. Low-temperature angle-resolved photoemission spectroscopy (ARPES) reveals a massive interfacial charge transfer, which destroys the global Fermi surface nesting and completely suppresses the long-range CDW order in Euclidean flat regions. Strikingly, high-resolution scanning tunneling microscopy (STM) reveals that a novel, non-linear CDW state miraculously survives, remaining strictly localized within morphologically distorted, non-Euclidean nanoscale curved regions. Atomistic simulations unravel the structural origin of this phenomenon, demonstrating that interfacial twist and lattice mismatch spontaneously generate a corrugated superlattice. △ Less

Submitted 3 June, 2026; originally announced June 2026.

Rongzai agent: A Large Language Model-Based Autonomous Assistant for Rietveld Refinement of Neutron Diffraction Data

Authors: Qingmeng Li, Hao Wang, Dongbo Xiong, Jiajun Zhong, Wenhai Ji, Hao Hu, Yiyu Zhang, Bolun Zhang, Hong Wang, Yongfeng Zhu, Rong Du, Zhengde Zhang, Fazhi Qi, Junrong Zhang

Abstract: Neutron diffraction (ND) is an indispensable technique for determining atomic positions (especially light elements) and thus serves as a critical probe for revealing microscopic structures in materials science. However, traditional Rietveld refinement of ND data relies heavily on manual operation of specialized software, which is time-consuming, labor-intensive, and highly dependent on user expert… ▽ More Neutron diffraction (ND) is an indispensable technique for determining atomic positions (especially light elements) and thus serves as a critical probe for revealing microscopic structures in materials science. However, traditional Rietveld refinement of ND data relies heavily on manual operation of specialized software, which is time-consuming, labor-intensive, and highly dependent on user expertise, severely hindering automated analysis. The automation of Rietveld refinement has long been a long-standing and challenging problem in crystallography. To address this challenge, this paper presents the Dr.Sai-Rongzai agent, an autonomous refinement assistant based on a large language model (LLM), a specialist knowledge base, and the GSAS-II refinement engine, achieving for the first time an intelligent refinement that integrates knowledge-driven decision-making. The agent accomplishes a fully automated workflow from natural language task parsing to autonomous decision-making, execution of refinement strategies, and report generation. Evaluation on five representative samples shows that the Rongzai agent achieves lower Rwp values than human specialists on three samples (2.88% vs. 4.42%, 5.06% vs. 5.40%, 7.60% vs. 9.00%), while on the other two samples its results are very close to those of the specialists. The agent is currently deployed at the China Spallation Neutron Source (CSNS) and is open for external user registration, providing an intelligent and user-friendly analytical tool for materials research. This work fully leverages the cutting-edge advantages of LLM, offers a new path to solve the long-standing problem of automated refinement, takes a key step toward intelligent and fully automated crystallographic analysis, and holds great potential to accelerate AI for Science discoveries in neutron-based materials characterization. △ Less

Submitted 13 May, 2026; originally announced May 2026.

G-type antiferromagnetic structure in Rb1-xV2Te2O

Authors: Wu Xie, Changchao Liu, Fayuan Zhang, Zhenhong Tan, Wenhai Ji, Nan Zhao, Lingxiang Bao, Dong Zhang, Feiran Shen, Lunhua He, Hao Wang, Rong Du, Guanghan Cao, Chaoyu Chen, Ping Miao

Abstract: Altermagnetism, known for its non-relativistic spin-split band structures with yet compensated moments, is being intensively investigated. Discovering new altermagnetic materials with characteristics suitable for practical use remains an important ongoing task. Recently a metallic room-temperature altermagnet candidate Rb1-xV2Te2O with a layered structure and d-wave spin symmetry has been reported… ▽ More Altermagnetism, known for its non-relativistic spin-split band structures with yet compensated moments, is being intensively investigated. Discovering new altermagnetic materials with characteristics suitable for practical use remains an important ongoing task. Recently a metallic room-temperature altermagnet candidate Rb1-xV2Te2O with a layered structure and d-wave spin symmetry has been reported based on experimental results from the spin-resolved photoemission spectroscopy and scanning tunnelling microscopy/spectroscopy (STM/STS) measurements. Here we report neutron powder diffraction (NPD) investigations on the magnetic structure of Rb1-xV2Te2O, which shows a G-type antiferromagnetic structure below the transition temperature of 337 K. The result is different from the original theoretical expectation, which might lead to new insights on the physics of this altermagnet candidate. △ Less

Submitted 22 April, 2026; v1 submitted 19 April, 2026; originally announced April 2026.

Comments: 6 pages, 4 figures

High-Mobility Indium Native Oxide Transistors via Liquid-Metal Printing in Air

Authors: Shi-Rui Zhang, Sanjoy Kumar Nandi, Felipe Kremer, Shimul Kanti Nath, Wenzhong Ji, Thomas Ratcliff, Li Li, Nicholas J. Ekins-Daukes, Teng Lu, Yun Liu, Robert Glen Elliman

Abstract: Oxide semiconductors have emerged as common channel materials in transistors and hold promise for next-generation electronics, yet achieving high mobility typically requires costly vacuum-based techniques. Here, ultrathin (5-nm) indium native oxide (InOx) prepared by ambient-air liquid-metal printing (LMP) at low temperature (250 °C), is applied as semiconducting channel in field-effect transistor… ▽ More Oxide semiconductors have emerged as common channel materials in transistors and hold promise for next-generation electronics, yet achieving high mobility typically requires costly vacuum-based techniques. Here, ultrathin (5-nm) indium native oxide (InOx) prepared by ambient-air liquid-metal printing (LMP) at low temperature (250 °C), is applied as semiconducting channel in field-effect transistor (FET). The resulting InOx is found to be polycrystalline with large lateral grains that extend vertically throughout the film thickness. InOx FETs in a transfer length method (TLM) configuration demonstrate a high conductivity mobility (uCON) of 125 cm2 V-1 s-1, with systematic analysis of contact resistance confirming potential for channel length scaling. Integration with atomic-layer-deposited (ALD) gate dielectrics further reveals excellent compatibility, for instance, InOx FET integrated with HfO2 exhibits a high field-effect mobility (uFE) of 107 cm2 V-1 s-1, an on/off current ratio (ION/IOFF) of >107, a subthreshold swing (SS) of 204 mV dec-1, a gate leakage of <10-6 A cm-2, while maintaining stable performance over 104 endurance cycles without degradation. Post-fabrication oxygen-plasma treatment is applied to achieve enhancement-mode operation and a depletion-load inverter is demonstrated, exhibiting a voltage gain of 69.8 V/V. These results demonstrate the great potential of LMP InOx as semiconducting channel in high-performance and power-efficient transistors for next-generation oxide electronics. △ Less

Submitted 8 April, 2026; originally announced April 2026.

Comments: ACS Applied Materials & Interfaces, Accepted

A Sc2C2@C88 cluster based ultra-compact multi-level probabilistic bit for matrix multiplication

Authors: Haoran Qi, Guohao Xi, Yuan-Biao Zhou, Xinrong Liu, Yifu Mao, Jian Yang, Jun Chen, Kuojuei Hu, Weiwei Gao, Shuai Zhang, Xiaoqin Gao, Jianguo Wan, Da-Wei Zhou, Junhong An, Xuefeng Wang, De-Chuan Zhan, Minhao Zhang, Cong Wang, Wei ji, Yuan-Zhi Tan, Su-Yuan Xie, Fengqi Song

Abstract: Information units are progressively approaching the fundamental physical limits of the integration density, including in terms of extremely small sizes, multistates and probabilistic traversal. However, simultaneously encompassing all of these characteristics in a unit remains elusive. Here, via real-time in situ electrical monitoring, we clearly observed stochastic alterations of multiple conduct… ▽ More Information units are progressively approaching the fundamental physical limits of the integration density, including in terms of extremely small sizes, multistates and probabilistic traversal. However, simultaneously encompassing all of these characteristics in a unit remains elusive. Here, via real-time in situ electrical monitoring, we clearly observed stochastic alterations of multiple conductance states in Sc2C2@C88. The true random bit sequence generated exhibited an autocorrelation function whose confidence interval fell within \pm 0.02, demonstrating high-quality randomness. The alterations of multiple conductance states are controllable, that is, whose probability distributions could traverse from 0 to 1, enabling us to factorize 551 into its prime factors. Furthermore, we proposed a matrix-chain multiplication scheme and experimentally verified the multiplication of two 4 \times 4 state-transition matrices with a small maximum error < 0.05. Combined with theoretical calculations, the stochastic but controllable multistates are probably attributed to the rich energy landscape, which could be stepwise changed by the electric field. Our findings reveal extremely small multi-level probabilistic bit for matrix multiplication, which pave the way for ultracompact intelligent electronic devices. △ Less

Submitted 27 March, 2026; originally announced March 2026.

Self-dual Higgs transitions: Toric code and beyond

Authors: Wenjie Ji, Ryan A. Lanzetta, Zheng Zhou, Chong Wang

Abstract: The toric code, when deformed in a way that preserves the self-duality $\mathbb{Z}_2$ symmetry exchanging the electric and magnetic excitations, admits a transition to a topologically trivial state that spontaneously breaks the $\mathbb{Z}_2$ symmetry. Numerically, this transition was found to be continuous, which makes it particularly enigmatic given the longstanding absence of a continuum field-… ▽ More The toric code, when deformed in a way that preserves the self-duality $\mathbb{Z}_2$ symmetry exchanging the electric and magnetic excitations, admits a transition to a topologically trivial state that spontaneously breaks the $\mathbb{Z}_2$ symmetry. Numerically, this transition was found to be continuous, which makes it particularly enigmatic given the longstanding absence of a continuum field-theoretic description. In this work we propose such a continuum field theory for the transition dubbed the $SO(4)_{2,-2}$ Chern-Simons-Higgs (CSH) theory. We show that our field theory provides a natural "mean-field" understanding of the phase diagram. Moreover, it can be generalized to an entire series of theories, namely the $SO(4)_{k,-k}$ CSH theories, labeled by an integer $k$. For each $k>2$, the theory describes an analogous transition involving different non-Abelian topological orders, such as the double Fibonacci order ($k=3$) and the $S_3$ quantum double ($k=4$). For $k=1$, we conjecture that the corresponding CSH transition is in fact infrared-dual to the $3d$ Ising transition, in close analogy with the particle-vortex duality of a complex scalar. △ Less

Submitted 28 January, 2026; originally announced January 2026.

Comments: 5+4 pages

Intertwined atomic-nanoscale-microscale structures via intralayer anisotropic Fe-chains in the layered ferromagnet FePd2Te2

Authors: Manyu Wang, Chang Li, Bingxian Shi, Shuo Mi, Xiaoxiao Pei, Shuming Meng, Yanyan Geng, Fei Pang, Rui Xu, Li Huang, Wei Ji, Hong-Jun Gao, Peng Cheng, Le Lei, Zhihai Cheng

Abstract: Controlling mesoscale and nanoscale material structures and properties through self-organized atomic behavior is essential for atomic-scale manufacturing. However, direct and visual studies on the cross-scale effects of such atomic self-organization on mesoscopic structures remain scarce. Here, we report the intertwined atomic-nanoscale-mesoscale structures via the intralayer Fe-chains in the sand… ▽ More Controlling mesoscale and nanoscale material structures and properties through self-organized atomic behavior is essential for atomic-scale manufacturing. However, direct and visual studies on the cross-scale effects of such atomic self-organization on mesoscopic structures remain scarce. Here, we report the intertwined atomic-nanoscale-mesoscale structures via the intralayer Fe-chains in the sandwich-like layered FePd2Te2 crystal by scanning tunneling microscopy (STM) and atomic force microscopy (AFM). The hierarchical orthogonal corrugated morphologies are directly revealed and attributed to its chain-orientation-determined twinning-domain effect. Both Fe-chains of middle-sublayer and two kinds of Te atoms of top-sublayer are further atomically resolved at the sub-Å level, indicating the critical effects of Pd-atoms/voids on the intra-layer anisotropic Fe-chains and the interlayer structural alignment. The thermal-induced and strain-related structural transitions of surface layer are further investigated and discussed based on the proposed filling model of Pd-voids by the intralayer Pd-atoms. Our work not only provides deep understanding of this exotic layered magnetic material, and will inspire more perspectives for tailoring its anisotropic atomic-to-mesoscale structures and properties. △ Less

Submitted 8 January, 2026; originally announced January 2026.

Comments: 19 pages,4 figures

Realization of polytype heterostructures via delicate structural transitions from a doped-Mott insulator

Authors: Yanyan Geng, Manyu Wang, Shumin Meng, Shuo Mi, Chang Li, Huiji Hu, Jianfeng Guo, Rui Xu, Fei Pang, Wei Ji, Weichang Zhou, Zhihai Cheng

Abstract: Transition metal dichalcogenides (TMDs) host multiple competing structural and electronic phases, making them an ideal platform for constructing polytype heterostructures with emergent quantum properties. However, controlling phase transitions to form diverse heterostructures inside a single crystal remains challenging. Here, we realize vertical/lateral polytype heterostructures in a hole-doped Mo… ▽ More Transition metal dichalcogenides (TMDs) host multiple competing structural and electronic phases, making them an ideal platform for constructing polytype heterostructures with emergent quantum properties. However, controlling phase transitions to form diverse heterostructures inside a single crystal remains challenging. Here, we realize vertical/lateral polytype heterostructures in a hole-doped Mott insulator via thermal-annealing-induced structural transitions. Raman spectroscopy, atomic force microscopy (AFM) and scanning Kelvin probe force microscopy (SKPM) confirm the coexistence of T-H polytype heterostructures. Atomic-scale scanning tunneling microscopy/spectroscopy (STM/STS) measurements reveal the transparent effect in 1H/1T vertical heterostructures, where the charge density wave (CDW) of the underlying 1T-layer superposes on the top 1H-layer under positive bias. By systematically comparing 1T/1H and 1T/1T interfaces, we demonstrate that the metallic 1H-layer imposes a Coulomb screening effect on the 1T-layer, suppressing the formation of CDW domain walls and forming more ordered electronic states. These results clarify the interfacial coupling between distinct quantum many-body phases and establish a controllable pathway for constructing two-dimensional polytype heterostructures with tunable electronic properties. △ Less

Submitted 2 December, 2025; originally announced December 2025.

Electric-Field-Tunable Luttinger compensated antiferromagnetism in double CrCl2 chains

Authors: Deping Guo, Weihan Zhang, Canbo Zong, Cong Wang, Wei Ji

Abstract: Luttinger compensated antiferromagnets (LcAFMs), combining spin polarization with vanishing net magnetization, offering distinct advantages for next-generation spintronic applications. Using first-principles calculations, we demonstrate that conventional antiferromagnetic CrCl2 double chains can be transformed into one-dimensional LcAFMs under an external electric field, exhibiting pronounced isot… ▽ More Luttinger compensated antiferromagnets (LcAFMs), combining spin polarization with vanishing net magnetization, offering distinct advantages for next-generation spintronic applications. Using first-principles calculations, we demonstrate that conventional antiferromagnetic CrCl2 double chains can be transformed into one-dimensional LcAFMs under an external electric field, exhibiting pronounced isotropic spin splitting. The magnitude of the splitting, as well as the band gap, can be effectively tuned by both in-plane and out-of-plane fields, thereby providing greater controllability than in two-dimensional counterparts. To further enhance the tunability, we design a nearly lattice-matched CrCl2/MoTe2 heterostructure and uncover that interfacial charge transfer generates a built-in electric field, inducing spin splitting comparable to that driven by external fields. These results establish interfacial engineering as a highly efficient route to realize and manipulate LcAFM states in low-dimensional magnets, expanding the design principles for spintronic functionalities at the nanoscale. △ Less

Submitted 25 October, 2025; originally announced October 2025.

BigBang-Proton Technical Report: Next-Word-Prediction is Scientific Multitask Learner

Authors: Hengkui Wu, Liujiang Liu, Jihua He, Qihao Wang, Keke Zhao, Shuyang Hu, Renle Fu, Dahao Liang, Lingyu Zeng, Bruce Liu, Yuan Liu, Jin Zhan, Jiaqiang Niu, Xinglong Jia, Yaqin Hu, Wenjun Ji, Panpan Chi, Ken Chen, Hengyuan Wu, Yingsi Xin, Yongfeng Zhu, Yuexin Wang, Manqi Ruan, Ningtao Bian, Xiaohua Wu , et al. (1 additional authors not shown)

Abstract: We introduce BigBang-Proton, a unified sequence-based architecture for auto-regressive language modeling pretrained on cross-scale, cross-structure, cross-discipline real-world scientific tasks to construct a scientific multi-task learner. BigBang-Proton incorporates three fundamental innovations compared to mainstream general-purpose LLMs: Theory-Experiment Learning paradigm aligns large-scale nu… ▽ More We introduce BigBang-Proton, a unified sequence-based architecture for auto-regressive language modeling pretrained on cross-scale, cross-structure, cross-discipline real-world scientific tasks to construct a scientific multi-task learner. BigBang-Proton incorporates three fundamental innovations compared to mainstream general-purpose LLMs: Theory-Experiment Learning paradigm aligns large-scale numerical experimental data with theoretical text corpora; Binary Patch Encoding replaces byte pair encoding(BPE) tokenization; Monte Carlo Attention substitutes traditional transformer architectures. Through next-word-prediction pretraining on cross-discipline scientific datasets of real-world problems mixed with general textual corpus, followed by fine-tuning and inference on downstream tasks, BigBang-Proton demonstrates 100\% accuracy in up to 50-digit arithmetic addition operations, performance on par with leading specialized models in particle physics jet tagging, matching MAE of specialized models in inter-atomic potential simulation, performance comparable to traditional spatiotemporal models in water quality prediction, and benchmark-exceeding performance in genome modeling. These results prove that language-guided scientific computing can match or exceed the performance of task-specific scientific models while maintaining multitask learning capabilities. We further hypothesize to scale the pretraining to the universe scale as a fundamental step toward developing material world foundational model. △ Less

Submitted 30 September, 2025; originally announced October 2025.

Comments: 93 pages, 39 figures

MSC Class: 68T05; 68T50; 00A69; 94A99 ACM Class: I.2.6; I.2.7; J.2; I.6.3; K.4.1

Understanding the atomically precise evolution of the miscibility of newly prepared face-centered cubic W-Cu nanoalloys and its asymmetry

Authors: Yongxin Zhang, Weihan Zhang, Luneng Zhao, Zixiang Zhao, Siqi Lu, Yangrui Liu, Dongsheng Song, Changzheng Wei, Zhentao Pang, Yifeng Ren, Junfeng Gao, Weiwei Gao, Di Wu, Jijun Zhao, Kuo-Juei Hu, Wei Ji, Yu Deng, Binghui Ge, Fengqi Song

Abstract: According to classical Miedema theory, reducing crystals to the order of nanometer sizes might greatly modulate the mixing enthalpy of elements, thus enabling the invention of a lot of new bulk-immiscible alloys. Although numerous alloys with higher mixing enthalpies remain unexplored, this strategy is approaching its limit, as reflected by the critical diameter of recent alloys of 1.8 nm, which c… ▽ More According to classical Miedema theory, reducing crystals to the order of nanometer sizes might greatly modulate the mixing enthalpy of elements, thus enabling the invention of a lot of new bulk-immiscible alloys. Although numerous alloys with higher mixing enthalpies remain unexplored, this strategy is approaching its limit, as reflected by the critical diameter of recent alloys of 1.8 nm, which corresponds to ~150 atoms and hardly provides a crystalline order. Future development requires not only even smaller atomic-scale control but also a new surface energy-saving mechanism. Here, we report the formation of W-Cu nanoalloys with a very large miscibility gap in the bulk via the use of an atomically size-selected cluster beam source as an example. The face-centered cubic (FCC) structure was demonstrated through electron diffraction, which indicated a lattice constant of 3.88Å for W0.85Cu0.15 nanoalloys (~2280 atoms). In this comprehensive study that covers a large parameter space of W/Cu compositions and numbers of atoms, an asymmetric miscibility nanophase diagram in which W-rich compositions favor mixing and the critical size is approximately 6000 atoms, which far exceeds the approximately tens of atoms predicted via classical theory, was obtained for the first time. Density functional theory (DFT) calculations revealed a mutual strain-induced mechanism that simultaneously lowers the surface energies while reducing the size to the atomic scale. This approach paves the way for the development of new high-performance nonequilibrium phase alloys. △ Less

Submitted 28 August, 2025; originally announced August 2025.

Robust Mottness and tunable interlayer magnetism in Nb3X8 (X = F, Cl, Br, I) bilayers

Authors: Zhongqin Zhang, Jiaqi Dai, Cong Wang, Zhihai Cheng, Wei Ji

Abstract: Kagome materials have attracted extensive attention due to their correlated properties. The breathing kagome material system Nb3X8 (X = F, Cl, Br, I) is regarded as a Mott insulator. However, studies on the influence of interlayer coupling on its magnetic and Mott properties are lacking. In this work, we investigated the effect of interlayer coupling on bilayer properties of each Nb3X8 (X = F, Cl,… ▽ More Kagome materials have attracted extensive attention due to their correlated properties. The breathing kagome material system Nb3X8 (X = F, Cl, Br, I) is regarded as a Mott insulator. However, studies on the influence of interlayer coupling on its magnetic and Mott properties are lacking. In this work, we investigated the effect of interlayer coupling on bilayer properties of each Nb3X8 (X = F, Cl, Br, I) compound via density functional theory (DFT) calculations, considering 24 stacking configurations per material. We found that each bilayer material is a Mott insulator. Due to the competition between interlayer Pauli repulsion and hopping, most interlayer magnetism is AFM, a small number of cases show AFM-FM degeneracy, and the magnetic ground state of 3 configurations is interlayer FM, i.e., tunable interlayer magnetism occurs. This robustness of Mott states coexisting with tunable interlayer magnetism provide novel and comprehensive analysis and insights for the research of breathing kagome Mott insulators. △ Less

Submitted 24 August, 2025; originally announced August 2025.

Anomaly-free symmetries with obstructions to gauging and onsiteability

Authors: Wilbur Shirley, Carolyn Zhang, Wenjie Ji, Michael Levin

Abstract: We present counterexamples to the lore that symmetries that cannot be gauged or made on-site are necessarily anomalous. Specifically, we construct unitary, internal symmetries of two-dimensional lattice models that cannot be consistently coupled to background or dynamical gauge fields or disentangled to a tensor product of on-site operators. These symmetries are nevertheless anomaly-free in the se… ▽ More We present counterexamples to the lore that symmetries that cannot be gauged or made on-site are necessarily anomalous. Specifically, we construct unitary, internal symmetries of two-dimensional lattice models that cannot be consistently coupled to background or dynamical gauge fields or disentangled to a tensor product of on-site operators. These symmetries are nevertheless anomaly-free in the sense that they admit symmetric, gapped Hamiltonians with unique, invertible ground states. We show that symmetries of this kind are characterized by an index $[ω]\in H^2(G,\mathbb{Q}_+)$, where $\mathbb{Q}_+$ is the multiplicative group of rational numbers labeling one-dimensional quantum cellular automata. △ Less

Submitted 28 July, 2025; originally announced July 2025.

Comments: 6+20 pages, 12 figures

Mechanically and electrically switchable triferroic altermagnet in a pentagonal FeO2 monolayer

Authors: Deping Guo, Jiaqi Dai, Renhong Wang, Cong Wang, Wei Ji

Abstract: Two-dimensional multiferroics promise low-power, multifunctional devices, yet the intrinsic coexistence and mutual control of three coupled ferroic orders in a single layer remains elusive. Here, we identify pentagonal monolayer FeO$_2$ as an intrinsic triferroic altermagnet where ferroelectric (FE), ferroelastic (FA), and altermagnetic (AM) orders coexist and are tightly coupled, accompanied by a… ▽ More Two-dimensional multiferroics promise low-power, multifunctional devices, yet the intrinsic coexistence and mutual control of three coupled ferroic orders in a single layer remains elusive. Here, we identify pentagonal monolayer FeO$_2$ as an intrinsic triferroic altermagnet where ferroelectric (FE), ferroelastic (FA), and altermagnetic (AM) orders coexist and are tightly coupled, accompanied by a competing antiferroelectric (AFE) phase using first-principles calculations. The sole presence of glide mirror $M_x$ symmetry in a FeO$_2$ sublayer, with the breaking of four-fold rotation $C_{4z}$ symmetry, induces in-plane vector ferroelectricity and twin-related ferroelastic strains. Both FE and AFE phases break combined parity - time symmetry and display sizable altermagnetic spin splitting with Néel temperatures over 200~K. Electric-field-induced rotation of the FE polarization reverses the sign of the spin splitting, while in-plane uniaxial strain triggers ferroelastic switching that simultaneously rotates the FE polarization vector by $90^\circ$ and reverses the AM state. These electric-field- and strain-mediated pathways interlink six distinct polarization states that can be selected purely by electric fields and/or mechanical strain. This work extends intrinsic triferroicity to pentagonal monolayers and outlines a symmetry-based route toward mechanically and electrically configurable altermagnetic spintronics. △ Less

Submitted 25 November, 2025; v1 submitted 23 July, 2025; originally announced July 2025.

Anomalous charge density wave in altermagnetism

Authors: Zi-Hao Ding, Lei Wang, Zhen-Feng Ouyang, Jingsi Qiao, Ze-Feng Gao, Wei Ji, Kai Liu, Peng-Jie Guo, Zhong-Yi Lu

Abstract: Exploring the intricate interplay between magnetism and charge density waves has long been a fundamental pursuit at the forefront of condensed matter research. In this letter, based on symmetry analysis and first-principles calculations, we propose for the first time that anomalous charge density wave can be realized in two-dimensional altermagnetic WO. The anomalous charge density wave is charact… ▽ More Exploring the intricate interplay between magnetism and charge density waves has long been a fundamental pursuit at the forefront of condensed matter research. In this letter, based on symmetry analysis and first-principles calculations, we propose for the first time that anomalous charge density wave can be realized in two-dimensional altermagnetic WO. The anomalous charge density wave is characterized by three key features: (i) Unlike conventional charge density wave, whose stabilization is driven by the opening of a gap near the Fermi level, the anomalous charge density wave is stabilized by the occupied states with energies shifting lower far away from the Fermi level; (ii) the anomalous charge density wave increases the density of states near the Fermi level and then enhances-rather than diminishes-the metallicity of materials; (iii) altermagnetism plays a crucial role in stabilizing anomalous charge density wave. Thus, our work offers a pathway for exploring both the realization and the underlying mechanisms of anomalous charge density waves in magnetic systems. △ Less

Submitted 5 August, 2025; v1 submitted 21 July, 2025; originally announced July 2025.

Comments: 6 pages, 4 figures

Kinetically accessible 1D magnetic chains of transition-metal chalcogenides and halides on van der Waals surfaces

Authors: Canbo Zong, Deping Guo, Renhong Wang, Weihan Zhang, Jiaqi Dai, Zhongqin Zhang, Cong Wang, Xianghua Kong, Fei Pang, Zhihai Cheng, Zhong-Yi Lu, Wei Ji

Abstract: One-dimensional (1D) chains offer unique opportunities for nanoelectronics and spintronics, yet their experimental realization remains challenging because 1D motifs are often thermodynamically disfavored relative to higher-dimensional phases. Here we present a high-throughput first-principles exploration of 1D single-atomic transition-metal chalcogenide and halide chains, screening 6,832 candidate… ▽ More One-dimensional (1D) chains offer unique opportunities for nanoelectronics and spintronics, yet their experimental realization remains challenging because 1D motifs are often thermodynamically disfavored relative to higher-dimensional phases. Here we present a high-throughput first-principles exploration of 1D single-atomic transition-metal chalcogenide and halide chains, screening 6,832 candidates constructed from binary combinations of 28 metals and 8 non-metals. To assess kinetic accessibility, we compare the formation energetics of 1D chains with competing two-dimensional polymorphs at the nucleation stage across relevant chemical-potential windows, using nucleation-stage thermodynamic selectivity as a proxy. This workflow identifies 183 kinetically accessible 1D chains. Interpretable machine-learning analysis reveals two simple stability descriptors as key drivers of 1D stabilization. The accessible chains exhibit diverse magnetic configurations with different magnetic characters. We further uncover their pronounced magnetoelastic couplings, exemplified by CrTe with giant magnetostriction reaching 5.93%. Finally, we show that selected metallic ferromagnetic chains retain robust edge magnetism on superconducting substrates, laying the groundwork for proximity-induced topological superconductivity and Majorana zero modes. △ Less

Submitted 29 December, 2025; v1 submitted 14 July, 2025; originally announced July 2025.

Comments: 22 pages, 4 figures, Supplementary Information supplied

Real-space titration and manipulation of particle-like correlated electrons in doped Mott insulator

Authors: Yanyan Geng, Haoyu Dong, Renhong Wang, Zilu Wang, Jianfeng Guo, Shuo Mi, Yan Li, Fei Pang, Rui Xu, Li Huang, Hong-Jun Gao, Wei Ji, Shancai Wang, Weichang Zhou, Zhihai Cheng

Abstract: The localized (particle-like) correlated electrons deserve particular attention as they govern various exotic quantum phenomena, such as quantum spin liquids, Wigner crystals, and Mott insulators in correlated systems. However, direct observation and manipulation of these particle-like electrons at the atomic or single-electron scale remain highly challenging. Here, we successfully realize and dir… ▽ More The localized (particle-like) correlated electrons deserve particular attention as they govern various exotic quantum phenomena, such as quantum spin liquids, Wigner crystals, and Mott insulators in correlated systems. However, direct observation and manipulation of these particle-like electrons at the atomic or single-electron scale remain highly challenging. Here, we successfully realize and directly visualize particle-like correlated electrons in 1T-TaS2 through hole doping. The potential-dependent local electronic structure of single particle-like electron is revealed by angle-resolved photoemission spectroscopy (ARPES), scanning tunneling spectroscopy (STS) combined with theoretical calculations. The complex correlated interactions including nearest-neighbor attractive interactions and many-body repulsive interactions are further demonstrated and discussed based on the spatial distribution of particle-like electrons. Furthermore, the tentative manipulation of the particle-like electrons is successfully achieved by the energy-excitation mechanism. Our results not only provide profound insights into particle-like electrons in correlated systems, but also establish a versatile platform for designing and controlling quantum states at the atomic scale. △ Less

Submitted 8 July, 2025; originally announced July 2025.

Comments: 20 pages, 4 figures

Bulk Excitations of Invertible Phases

Authors: Wenjie Ji, David T. Stephen, Michael Levin, Xie Chen

Abstract: Recent developments in the study of topological defects highlight the importance of understanding the multi-dimensional structure of bulk excitations inside a quantum system. When the bulk ground state is trivial, i.e. a product state, excitations on top of it are decoupled from each other and correspond to lower-dimensional phases and their defects within. In this paper, we expand the discussion… ▽ More Recent developments in the study of topological defects highlight the importance of understanding the multi-dimensional structure of bulk excitations inside a quantum system. When the bulk ground state is trivial, i.e. a product state, excitations on top of it are decoupled from each other and correspond to lower-dimensional phases and their defects within. In this paper, we expand the discussion to invertible phases and study the bulk excitations in, for example, SPT phases, Majorana chains, p + ip superconductors etc. We find that there is a one-to-one correspondence between bulk excitations inside a nontrivial invertible phase and those in a product state. For SPT phases, this can be shown using the symmetric Quantum Cellular Automaton that maps from the product state to the SPT state. More generally, for invertible phases realizable using the Topological Holography construction, we demonstrate the correspondence using the fact that certain gapped boundary conditions of a topological bulk state have only relative distinctions but no absolute ones. △ Less

Submitted 12 June, 2025; originally announced June 2025.

Comments: 41 pages, 27 figures

Atomic to mesoscale hierarchical structures and magnetic states in an anisotropic layered ferromagnet FePd2Te2

Authors: Shuo Mi, Manyu Wang, Bingxian Shi, Songyang Li, Xiaoxiao Pei, Yanyan Geng, Shumin Meng, Rui Xu, Li Huang, Wei Ji, Fei Pang, Peng Cheng, Jianfeng Guo, Zhihai Cheng

Abstract: Two-dimensional (2D) magnetic materials have predominantly exhibited easy-axis or easy-plane anisotropy and display a high sensitivity to the underlying crystal structure and lattice symmetry. Recently, an in-plane anisotropic 2D ferromagnet of FePd2Te2 has been discovered with intriguing structure and quasi-one-dimensional spin system. Here, we report a real-space investigation of its twinning st… ▽ More Two-dimensional (2D) magnetic materials have predominantly exhibited easy-axis or easy-plane anisotropy and display a high sensitivity to the underlying crystal structure and lattice symmetry. Recently, an in-plane anisotropic 2D ferromagnet of FePd2Te2 has been discovered with intriguing structure and quasi-one-dimensional spin system. Here, we report a real-space investigation of its twinning structure and magnetic states using atomic/magnetic force microscopy (AFM/MFM) combined with scanning tunneling microscopy (STM). The atomic to mesoscale hierarchical structures with the orthogonal and corrugated compressive /tensile(C/T) regions are directly observed due to the intrinsic twinning-domain characteristic. The structure-related intact ferromagnetic (FM), field-induced polarized-FM states and their transitions are comparatively discussed at the mesoscale with the corresponding macroscopic magnetic measurements. Temperature- and field-dependent evolution of magnetic phase are further investigated at the FM and PM states, and summarized to obtain a unique H-T phase diagram of FePd2Te2. Our work provides key results for understanding the complicated magnetic properties of FePd2Te2, and suggests new directions for manipulating magnetic states through the atomic and mesoscale structure engineering. △ Less

Submitted 10 June, 2025; originally announced June 2025.

Disentangling hierarchical relaxations in glass formers via dynamic eigenmodes

Authors: Wensi Sun, Yanshuang Chen, Wencheng Ji, Yi Zhou, Hua Tong, Ke Chen, Xiaosong Chen, Hajime Tanaka, Peng Tan

Abstract: Hierarchical dynamics in glass-forming systems span multiple timescales, from fast vibrations to slow structural rearrangements, appearing in both supercooled fluids and glassy states. Understanding how these diverse processes interact across timescales remains a central challenge. Here, by combining direct particle-level observations with a dynamic eigenmode approach that decomposes intermediate-… ▽ More Hierarchical dynamics in glass-forming systems span multiple timescales, from fast vibrations to slow structural rearrangements, appearing in both supercooled fluids and glassy states. Understanding how these diverse processes interact across timescales remains a central challenge. Here, by combining direct particle-level observations with a dynamic eigenmode approach that decomposes intermediate-timescale responses into distinct modes, we reveal the microscopic organisation of relaxation dynamics in two-dimensional colloidal systems. We identify five classes of modes characterizing hierarchical dynamics: (i) quasi-elastic modes, (ii) slow-reversible string modes contributing to dynamic heterogeneity, (iii) slow-irreversible string modes leading to flow, (iv) fast-$β$ modes with fast-reversible strings, and (v) random noise modes. The emergence of quasi-elastic modes marks the onset of glassy dynamics, while reversible string modes dominate dynamic heterogeneity throughout both supercooled and glassy regimes. Our findings offer a unified microscopic framework for understanding how distinct relaxation processes interconnect across timescales, illuminating the mechanisms driving glass formation. △ Less

Submitted 26 May, 2025; v1 submitted 26 May, 2025; originally announced May 2025.

Comments: 37 pages, 3 figures, 8 extended data figures

Semiregular tessellation of electronic lattices in untwisted bilayer graphene under anisotropic strain gradients

Authors: Zeyu Liu, Xianghua Kong, Zhidan Li, Zewen Wu, Linwei Zhou, Cong Wang, Wei Ji

Abstract: Two-dimensional (2D) moiré superlattices have emerged as a versatile platform for uncovering exotic quantum phases, many of which arise in bilayer systems exhibiting Archimedean tessellation patterns such as triangular, hexagonal, and kagome lattices. Here, we propose a strategy to engineer semiregular tessellation patterns in untwisted bilayer graphene by applying anisotropic epitaxial tensile st… ▽ More Two-dimensional (2D) moiré superlattices have emerged as a versatile platform for uncovering exotic quantum phases, many of which arise in bilayer systems exhibiting Archimedean tessellation patterns such as triangular, hexagonal, and kagome lattices. Here, we propose a strategy to engineer semiregular tessellation patterns in untwisted bilayer graphene by applying anisotropic epitaxial tensile strain (AETS) along crystallographic directions. Through force-field and first-principles calculations, we demonstrate that AETS can induce a rich variety of semiregular tessellation geometries, including truncated hextille, prismatic pentagon, and brick-phase arrangements. The characteristic electronic bands (Dirac and flat bands) of the lattice models associated with these semiregular tessellations are observed near the Fermi level, arising from interlayer interactions generated by the redistribution of specific stacking registries (AB, BA, and SP). Furthermore, the electronic kagome, distorted Lieb, brick-like, and one-dimensional stripe lattices captured in real-space confirm the tunable nature of the semiregular tessellation lattices enabled by AETS. Our study identifies AETS as a promising new degree of freedom in moiré engineering, offering a reproducible and scalable platform for exploring exotic electronic lattices in moiré systems. △ Less

Submitted 20 May, 2025; originally announced May 2025.

Tailoring composite skyrmionic spin textures in an above-room-temperature ferromagnet Fe3-xGaTe2

Authors: Songyang Li, Jianfeng Guo, Zizhao Gong, Guojing Hu, Shuo Mi, Chang Li, Yanyan Geng, Manyu Wang, Shumin Meng, Shiyu Zhu, Fei Pang, Wei Ji, Rui Xu, Haitao Yang, Zhihai Cheng

Abstract: Realizing room-temperature tunable skyrmionic objects in van der Waals ferromagnet offers unparalleled prospects for future spintronics. Here, we report an experimental investigation on the emergence and evolution of skyrmionic spin textures in the non-stoichiometric Fe3-xGaTe2 using magnetic force microscopy. The iron-deficiency-specific magnetic states of stripe, striped skyrmionium and striped… ▽ More Realizing room-temperature tunable skyrmionic objects in van der Waals ferromagnet offers unparalleled prospects for future spintronics. Here, we report an experimental investigation on the emergence and evolution of skyrmionic spin textures in the non-stoichiometric Fe3-xGaTe2 using magnetic force microscopy. The iron-deficiency-specific magnetic states of stripe, striped skyrmionium and striped skyrmion sack are observed. Through zero-field-cooling and field-cooling measurements, we observed distinct topological transitions and trivial transitions (distinguished by changes in topological charge) emerging during the stepwise evolution of topological spin textures, which enabled us to develop an evolution pathway model. Leveraging this model, the room-temperature stable composite topological spin textures of skyrmionium, skyrmion bag and sack states are further controllably realized via the exclusive topological-transition path (regulated by magnetic field and DMI intensity). Our work provides valuable insights into the room-temperature realization of topological spin textures in Fe3-xGaTe2, and inspires further exploration of their potential applications in heterostructure spintronics. △ Less

Submitted 8 May, 2025; originally announced May 2025.

Comments: 26 pages, 5 figures

Charge-polarized superconducting state emerging in a superatomic antipolar metal

Authors: Shuya Xing, Zhongxu Wei, Xu Chen, Junming Zhang, Zhenyu Yuan, Jiali Zhao, Feng Jin, Tao Sun, Huifen Ren, Minjie Cui, Hong Chang, Tianping Ying, Jiangang Guo, Hechang Lei, Shifeng Zhao, Wenping Zhou, Xinqi Li, Tian Qian, Wei Ji, Zhihai Cheng

Abstract: The simultaneous presence of polarity and metallicity or superconductivity in a material signifies the exotic polar metallic or superconducting (SC) state, while such materials are extremely rare due to their exclusive nature. Recently, the interweaved CDW and antipolar charge orders have been discovered in a metallic superatomic crystal of Au6Te12Se8 (ATS), while their interplay and competition w… ▽ More The simultaneous presence of polarity and metallicity or superconductivity in a material signifies the exotic polar metallic or superconducting (SC) state, while such materials are extremely rare due to their exclusive nature. Recently, the interweaved CDW and antipolar charge orders have been discovered in a metallic superatomic crystal of Au6Te12Se8 (ATS), while their interplay and competition with the following emergent SC state remains elusive. Here, we report a further experimental investigation of the SC state emerged from the preformed CDW and antipolar order states using scanning tunneling microscopy/spectroscopy in combination with transport and Raman measurements. The temperature-dependent pre-formation and condensation of Cooper pairs are experimentally identified. The pre-existent CDW is gradually suppressed by the preformed Cooper pairs, and then the antipolar charge order is spatially suppressed into a ferrielectric-like polar order by the condensed Cooper pairs of SC state. The exotic charge-polarized superconducting state is discovered in the polar metal of ATS, suggesting a valuable platform for the exploration of intriguing polar superconducting properties. △ Less

Submitted 30 July, 2025; v1 submitted 12 March, 2025; originally announced March 2025.

Comments: 17 pages, 4 figures

Spatially anisotropic Kondo resonance coupled with the superconducting gap in a kagome metal

Authors: Zichen Huang, Hui Chen, Zhongqin Zhang, Hao Zhang, Zhen Zhao, Ruwen Wang, Haitao Yang, Wei Ji, Ziqiang Wang, Hong-Jun Gao

Abstract: The chromium-based kagome metal CsCr3Sb5 has garnered significant interest due to its strong electron correlations, intertwined orders and potential for unconventional superconductivity under high pressure. The evolution of magnetic and superconducting interactions as the more frequently studied CsV3Sb5 is doped to CsCr3Sb5 remains poorly understood. Here, we demonstrate the emergence of a spatial… ▽ More The chromium-based kagome metal CsCr3Sb5 has garnered significant interest due to its strong electron correlations, intertwined orders and potential for unconventional superconductivity under high pressure. The evolution of magnetic and superconducting interactions as the more frequently studied CsV3Sb5 is doped to CsCr3Sb5 remains poorly understood. Here, we demonstrate the emergence of a spatially anisotropic Kondo resonance intertwined with the superconducting gap, enabled by introducing magnetic Cr impurities into the kagome superconductor CsV3Sb5. The addition of dilute Cr impurities not only weakens long range charge density wave order but also produces local magnetic moments that leads to Kondo resonances. We show that the Kondo resonance forms anisotropic, ripple like spatial patterns around individual Cr atoms, breaking all local mirror symmetries. We further reveal that with the emergence of Kondo screening, the coherence peak and depth of superconducting gap with finite zero-energy conductance are enhanced. This suggests that non superconducting carriers at the Fermi surface in the parent compound participate in the Kondo effect, simultaneously screening Cr magnetic moments and increasing the superfluid density. Our findings offer an opportunity to study the interplay between superconductivity and local magnetism in kagome materials. △ Less

Submitted 29 April, 2026; v1 submitted 28 February, 2025; originally announced February 2025.

Luttinger compensated bipolarized magnetic semiconductor

Authors: Peng-Jie Guo, Xiao-Yao Hou, Ze-Feng Gao, Huan-Cheng Yang, Wei Ji, Zhong-Yi Lu

Abstract: Altermagnetic materials, with real-space antiferromagnetic arrangement and reciprocal-space anisotropic spin splitting, have attracted much attention. However, the spin splitting is small in most altermagnetic materials, which is a disadvantage to their application in electronic devices. In this study, based on symmetry analysis and the first-principles electronic structure calculations, we predic… ▽ More Altermagnetic materials, with real-space antiferromagnetic arrangement and reciprocal-space anisotropic spin splitting, have attracted much attention. However, the spin splitting is small in most altermagnetic materials, which is a disadvantage to their application in electronic devices. In this study, based on symmetry analysis and the first-principles electronic structure calculations, we predict for the first time two Luttinger compensated bipolarized magnetic semiconductors Mn(CN)2 and Co(CN)2 with isotropic spin splitting as in the ferromagnetic materials. Our further analysis shows that the Luttinger compensated magnetism here depends not only on spin group symmetry, but also on the crystal field splitting and the number of d-orbital electrons. In addition, the polarized charge density indicates that both Mn(CN)2 and Co(CN)2 have the quasi-symmetry Tτ , resulting from the crystal field splitting and the number of d-orbital electrons. The Luttinger compensated magnetism not only has the zero total magnetic moment as the antiferromagnetism, but also has the isotropic spin splitting as the ferromagnetism, thus our work not only provides theoretical guidance for searching Luttinger compensated magnetic materials with distinctive properties, but also provides a material basis for the application in spintronic devices. △ Less

Submitted 25 February, 2025; originally announced February 2025.

Artificially creating emergent interfacial antiferromagnetism and its manipulation in a magnetic van-der-Waals heterostructure

Authors: Xiangqi Wang, Cong Wang, Yupeng Wang, Chunhui Ye, Azizur Rahman, Min Zhang, Suhan Son, Jun Tan, Zengming Zhang, Wei Ji, Je-Geun Park, Kai-Xuan Zhang

Abstract: Van der Waals (vdW) magnets, with their two-dimensional (2D) atomic structures, provide a unique platform for exploring magnetism at the nanoscale. Although there have been numerous reports on their diverse quantum properties, the emergent interfacial magnetism--artificially created at the interface between two layered magnets--remains largely unexplored. This work presents observations of such em… ▽ More Van der Waals (vdW) magnets, with their two-dimensional (2D) atomic structures, provide a unique platform for exploring magnetism at the nanoscale. Although there have been numerous reports on their diverse quantum properties, the emergent interfacial magnetism--artificially created at the interface between two layered magnets--remains largely unexplored. This work presents observations of such emergent interfacial magnetism at the ferromagnet/antiferromagnet interface in a vdW heterostructure. We report the discovery of an intermediate Hall resistance plateau in the anomalous Hall loop, indicative of emergent interfacial antiferromagnetism fostered by the heterointerface. This plateau can be stabilized and further manipulated under varying pressures but collapses under high pressures over 10 GPa. Our theoretical calculations reveal that charge transfer at the interface is pivotal in establishing the interlayer antiferromagnetic spin-exchange interaction. This work illuminates the previously unexplored emergent interfacial magnetism at a vdW interface comprised of a ferromagnetic metal and an antiferromagnetic insulator, and highlights its gradual evolution under increasing pressure. These findings enrich the portfolio of emergent interfacial magnetism and support further investigations on vdW magnetic interfaces and the development of next-generation spintronic devices. △ Less

Submitted 18 February, 2025; originally announced February 2025.

Comments: Accepted by ACS Nano; 42 pages, 5 main figures, 8 supporting figures

Journal ref: ACS Nano 19, 8108 (2025)

Tunable altermagnetism via inter-chain engineering in parallelassembled atomic chains

Authors: Deping Guo, Canbo Zong, Weihan Zhang, Cong Wang, Junwei Liu, Wei Ji

Abstract: Altermagnetism has recently drawn considerable attention in three- and twodimensional materials. Here, we extend this concept to quasi-one-dimensional (Q1D) monolayers assembled from single-atomic magnetic chains. Through systematically examining nine types of structures, two stacking orders, and intra-/inter-chain magnetic couplings, we identify four out of thirty promising structural prototypes… ▽ More Altermagnetism has recently drawn considerable attention in three- and twodimensional materials. Here, we extend this concept to quasi-one-dimensional (Q1D) monolayers assembled from single-atomic magnetic chains. Through systematically examining nine types of structures, two stacking orders, and intra-/inter-chain magnetic couplings, we identify four out of thirty promising structural prototypes for hosting altermagnetism, which yields 192 potential monolayer materials. We further confirm eight thermodynamically stable Q1D monolayers via high-throughput calculations. Using symmetry analysis and first-principles calculations, we find that the existence of altermagnetism is determined by the type of inter-chain magnetic coupling and predict three intrinsic altermagnets,\(CrBr_3\),\(VBr_3\),\(MnBr_3\),due to their ferromagnetic inter-chain couplings and five extrinsic ones,\(CrF_3\),\(CrCl_3\),\(CrI_3\),\(FeCl_3\)and \(CoTe_3\), ascribed to their neglectable or antiferromagnetic inter-chain couplings. Moreover, the inter-chain magnetic coupling here is highly tunable by manipulating the inter-chain spacing, leading to experimentally feasible transitions between altermagnetic and nodal-line semiconducting states. In addition, applying external electric fields can further modulate the spin splitting. Our findings establish a highly tunable family of Q1D altermagnets, offering fundamental insights into the intricate relationship between geometry, electronic structure, and magnetism.These discoveries hold significant promises for experimental realization and future spintronic applications. △ Less

Submitted 3 July, 2025; v1 submitted 9 February, 2025; originally announced February 2025.

Layered semiconducting electrides in p-block metal oxides

Authors: Jiaqi Dai, Feng Yang, Cong Wang, Fei Pang, Zhihai Cheng, Wei Ji

Abstract: In conventional electrides, excess electrons are localized in crystal voids to serve as anions. Most of these electrides are metallic and the metal cations are primarily from the s-block, d-block, or rare-earth elements. Here, we report a class of p-block metal-based electrides found in bilayer SnO and PbO, which are semiconducting and feature electride states in both the valence band (VB) and con… ▽ More In conventional electrides, excess electrons are localized in crystal voids to serve as anions. Most of these electrides are metallic and the metal cations are primarily from the s-block, d-block, or rare-earth elements. Here, we report a class of p-block metal-based electrides found in bilayer SnO and PbO, which are semiconducting and feature electride states in both the valence band (VB) and conduction band (CB), as referred to 2D "bipolar" electrides. These bilayers are hybrid electrides where excess electrons are localized in the interlayer region and hybridize with the orbitals of Sn atoms in the VB, exhibiting strong covalent-like interactions with neighboring metal atoms. Compared to previously studied hybrid electrides, the higher electronegativity of Sn and Pb enhances these covalent-like interactions, leading to largely enhanced semiconducting bandgap of up to 2.5 eV. Moreover, the CBM primarily arises from the overlap between metal states and interstitial charges, denoting a potential electride and forming a free-electron-like (FEL) state with small effective mass. This state offers high carrier mobilities for both electron and hole in bilayer SnO, suggesting its potential as a promising p-type semiconductor material. △ Less

Submitted 18 November, 2024; originally announced November 2024.

High-Throughput Discovery of Kagome Materials in Transition Metal Oxide Monolayers

Authors: Renhong Wang, Cong Wang, Ruixuan Li, Deping Guo, Jiaqi Dai, Canbo Zong, Weihan Zhang, Wei Ji

Abstract: Kagome materials are known for hosting exotic quantum states, including quantum spin liquids, charge density waves, and unconventional superconductivity. The search for kagome monolayers is driven by their ability to exhibit neat and well-defined kagome bands near the Fermi level, which are more easily realized in the absence of interlayer interactions. However, this absence also destabilizes the… ▽ More Kagome materials are known for hosting exotic quantum states, including quantum spin liquids, charge density waves, and unconventional superconductivity. The search for kagome monolayers is driven by their ability to exhibit neat and well-defined kagome bands near the Fermi level, which are more easily realized in the absence of interlayer interactions. However, this absence also destabilizes the monolayer forms of many bulk kagome materials, posing significant challenges to their discovery. In this work, we propose a strategy to address this challenge by utilizing oxygen vacancies in transition metal oxides within a "1+3" design framework. Through high-throughput computational screening of 349 candidate materials, we identified 12 thermodynamically stable kagome monolayers with diverse electronic and magnetic properties. These materials were classified into three categories based on their lattice geometry, symmetry, band gaps, and magnetic configurations. Detailed analysis of three representative monolayers revealed kagome band features near their Fermi levels, with orbital contributions varying between oxygen 2p and transition metal d states. This study demonstrates the feasibility of the "1+3" strategy, offering a promising approach to uncovering low-dimensional kagome materials and advancing the exploration of their quantum phenomena. △ Less

Submitted 27 January, 2025; v1 submitted 10 October, 2024; originally announced October 2024.

Journal ref: Chinese Physics B (2025)

Two-dimensional Kagome Materials: Theoretical Insights, Experimental Realizations, and Electronic Structures

Authors: Zhongqin Zhang, Jiaqi Dai, Cong Wang, Hua Zhu, Fei Pang, Zhihai Cheng, Wei Ji

Abstract: In recent years, kagome materials have attracted significant attention due to their rich emergent phenomena arising from the quantum interplay of geometry, topology, spin, and correlations. However, in the search for kagome materials, it has been found that bulk compounds with electronic properties related to the kagome lattice are relatively scarce, primarily due to the hybridization of kagome la… ▽ More In recent years, kagome materials have attracted significant attention due to their rich emergent phenomena arising from the quantum interplay of geometry, topology, spin, and correlations. However, in the search for kagome materials, it has been found that bulk compounds with electronic properties related to the kagome lattice are relatively scarce, primarily due to the hybridization of kagome layers with adjacent layers. Therefore, researchers have shown increasing interest in the discovery and construction of two-dimensional (2D) kagome materials, aiming to achieve clean kagome bands near the Fermi level in monolayer or few-layer systems. Substantial advancements have already been made in this area. In this review, we summarize the current progress in the construction and development of 2D kagome materials. We begin by introducing the geometric and electronic structures of the kagome lattice model and its variants, followed by discussions on the experimental realizations and electronic structure characterizations of 2D kagome materials. Finally, we provide an outlook on the future developments of 2D kagome materials. △ Less

Submitted 15 January, 2025; v1 submitted 4 September, 2024; originally announced September 2024.

Comments: 56 pages, 12 figures

Interlayer coupling rotatable magnetic easy-axis in MnSe2 mono- and bi-layers

Authors: Zhongqin Zhang, Cong Wang, PengJie Guo, Linwei Zhou, Yuhao Pan, Zhixin Hu, Wei Ji

Abstract: Interlayer coupling plays a critical role in tuning the electronic structures and magnetic ground states of two-dimensional materials, influenced by the number of layers, interlayer distances, and stacking order. However, its effect on the orientation of the magnetic easy axis remains underexplored. In this study, we demonstrate that interlayer coupling can significantly alter the magnetic easy-ax… ▽ More Interlayer coupling plays a critical role in tuning the electronic structures and magnetic ground states of two-dimensional materials, influenced by the number of layers, interlayer distances, and stacking order. However, its effect on the orientation of the magnetic easy axis remains underexplored. In this study, we demonstrate that interlayer coupling can significantly alter the magnetic easy-axis orientation, as shown by the magnetic easy-axis of monolayer 1T-MnSe2 tilting 67° from the z-axis, while aligning with the z-axis in the bilayer. This change results from variations in orbital occupations near the Fermi level, particularly involving nonmetallic Se atoms. Contrary to the traditional focus on magnetic metal atoms, our findings reveal that Se orbitals play a key role in influencing the easy-axis orientation and topological Chern numbers. Furthermore, we validated our conclusions by changing stacking orders, introducing charge doping, applying in-plane biaxial strains, and substituting non-metallic atoms. Our results highlight the pivotal role of interlayer coupling in tuning the magnetic properties of layered materials, with important implications for spintronic applications. △ Less

Submitted 16 December, 2024; v1 submitted 4 September, 2024; originally announced September 2024.

Kagome bands and magnetism in MoTe$_{2-x}$ kagome monolayers

Authors: Jiaqi Dai, Zhongqin Zhang, Zemin Pan, Cong Wang, Chendong Zhang, Zhihai Cheng, Wei Ji

Abstract: Kagome lattices facilitate various quantum phases, yet in bulk materials, their kagome flat-bands often interact with bulk bands, suppressing kagome electronic characteristics for hosting these phases. Here, we use density-functional-theory calculations to predict the geometric and electronic structures, as well as the topological and magnetic properties, of a series of MoTe$_{2-x}$ kagome monolay… ▽ More Kagome lattices facilitate various quantum phases, yet in bulk materials, their kagome flat-bands often interact with bulk bands, suppressing kagome electronic characteristics for hosting these phases. Here, we use density-functional-theory calculations to predict the geometric and electronic structures, as well as the topological and magnetic properties, of a series of MoTe$_{2-x}$ kagome monolayers formed by mirror-twin-boundary (MTB) loops. We analyze ten MTB-loop configurations of varying sizes and arrangements to assess their impact on various properties. Within the intrinsic bandgap of MoTe$_{2}$, we identify two sets of kagome bands, primarily originating from in-plane and out-of-plane Mo d-orbitals at MTB-loop edges and -vertices, respectively. Three configurations exhibit superior stability, while three others show comparable stability. Among these, four display bandgaps and potentially non-zero Z$_{2}$ topological invariants, suggesting possible topological phases, while the remaining two are metallic and feature Stoner magnetization. These findings guide the design of kagome-based two-dimensional materials with tunable electronic, topological, and magnetic properties. △ Less

Submitted 28 August, 2024; v1 submitted 26 August, 2024; originally announced August 2024.

Comments: 18 pages, 5 figures

Real-space topology-engineering of skyrmionic spin textures in a van der Waals ferromagnet Fe3GaTe2

Authors: Shuo Mi, Jianfeng Guo, Guojing Hu, Guangcheng Wang, Songyang Li, Zizhao Gong, Shuaizhao Jin, Rui Xu, Fei Pang, Wei Ji, Weiqiang Yu, Xiaolei Wang, Xueyun Wang, Haitao Yang, Zhihai Cheng

Abstract: Realizing magnetic skyrmions in two-dimensional (2D) van der Waals (vdW) ferromagnets offers unparalleled prospects for future spintronic applications. The room-temperature ferromagnet Fe3GaTe2 provides an ideal platform for tailoring these magnetic solitons. Here, skyrmions of distinct topological charges are artificially introduced and spatially engineered using magnetic force microscopy (MFM).… ▽ More Realizing magnetic skyrmions in two-dimensional (2D) van der Waals (vdW) ferromagnets offers unparalleled prospects for future spintronic applications. The room-temperature ferromagnet Fe3GaTe2 provides an ideal platform for tailoring these magnetic solitons. Here, skyrmions of distinct topological charges are artificially introduced and spatially engineered using magnetic force microscopy (MFM). The skyrmion lattice is realized by specific field-cooling process, and can be further controllably erased and painted via delicate manipulation of tip stray field. The skyrmion lattice with opposite topological charges (S = +1 or -1) can be tailored at the target regions to form topological skyrmion junctions (TSJs) with specific configurations. The delicate interplay of TSJs and spin-polarized device current were finally investigated via the in-situ transport measurements, alongside the topological stability of TSJs. Our results demonstrate that Fe3GaTe2 not only serves as a potential building block for room-temperature skyrmion-based spintronic devices, but also presents promising prospects for Fe3GaTe2-based heterostructures with the engineered topological spin textures. △ Less

Submitted 23 July, 2024; originally announced July 2024.

Regulated magnetic anisotropy and charge density wave in uniformly fabricated Janus CrTeSe monolayer

Authors: Jin-Hua Nie, Cong Wang, Mao-Peng Miao, Kang-Di Niu, Tao Xie, Ting-Fei Guo, Wen-Hao Zhang, Chao-Fei Liu, Rui-Jing Sun, Jian-Wang Zhou, Jun-Hao Lin, Wei Ji, Ying-Shuang Fu

Abstract: Two-dimensional materials with Janus structure host novel physical properties due to their inversional symmetry breaking. However, it remains elusive to synthesize Janus monolayer crystals with tailored long-range magnetic orders. Here, we have developed a general method to fabricate uniform Janus CrTeSe monolayers by selective selenization of preformed CrTe2 monolayers with molecular beam epitaxy… ▽ More Two-dimensional materials with Janus structure host novel physical properties due to their inversional symmetry breaking. However, it remains elusive to synthesize Janus monolayer crystals with tailored long-range magnetic orders. Here, we have developed a general method to fabricate uniform Janus CrTeSe monolayers by selective selenization of preformed CrTe2 monolayers with molecular beam epitaxy. The uniform Janus structure of CrTeSe with high crystal quality is confirmed by high-resolution scanning transmission electron microscopy. Spin-polarized scanning tunneling microscopy/spectroscopy measurements unveil that the Janus CrTeSe undergoes a charge density wave (CDW) transition and a robust antiferromagnetic order. The magnetic anisotropy of CrTeSe is drastically altered compared to monolayer CrTe2 by the breaking symmetries induced from the Janus structure and the CDW transition, as is substantiated with first principles calculations. Our research achieves the construction of large-area Janus structures, and artificially tailors the electronic and magnetic properties of Janus systems at the two-dimensional limit. △ Less

Submitted 23 July, 2024; originally announced July 2024.

Comments: 19 pages, 4 figures

Topological defects of 2+1D systems from line excitations in 3+1D bulk

Authors: Wenjie Ji, Xie Chen

Abstract: The bulk-boundary correspondence of topological phases suggests strong connections between the topological features in a d+1-dimensional bulk and the potentially gapless theory on the (d-1)+1-dimensional boundary. In 2+1D topological phases, a direct correspondence can exist between anyonic excitations in the bulk and the topological point defects/primary fields in the boundary 1+1D conformal fiel… ▽ More The bulk-boundary correspondence of topological phases suggests strong connections between the topological features in a d+1-dimensional bulk and the potentially gapless theory on the (d-1)+1-dimensional boundary. In 2+1D topological phases, a direct correspondence can exist between anyonic excitations in the bulk and the topological point defects/primary fields in the boundary 1+1D conformal field theory. In this paper, we study how line excitations in 3+1D topological phases become line defects in the boundary 2+1D theory using the Topological Holography/Symmetry Topological Field Theory framework. We emphasize the importance of "descendent" line excitations and demonstrate in particular the effect of the Majorana chain defect: it leads to a distinct loop condensed gapped boundary state of the 3+1D fermionic Z2 topological order, and leaves signatures in the 2+1D Majorana-cone critical theory that describes the transition between the two types of loop condensed boundaries. Effects of non-invertible line excitations, such as Cheshire strings, are also discussed in bosonic 3+1D topological phases and the corresponding 2+1D critical points. △ Less

Submitted 2 July, 2024; originally announced July 2024.

Comments: 19 pages, 13 figures. Comments are welcome

Unusual charge density wave introduced by Janus structure in monolayer vanadium dichalcogenides

Authors: Ziqiang Xu, Yan Shao, Chun Huang, Genyu Hu, Shihao Hu, Zhi-Lin Li, Xiaoyu Hao, Yanhui Hou, Teng Zhang, Jin-An Shi, Chen Liu, Jia-Ou Wang, Wu Zhou, Jiadong Zhou, Wei Ji, Jingsi Qiao, Xu Wu, Hong-Jun Gao, Yeliang Wang

Abstract: As a fundamental structural feature, the symmetry of materials determines the exotic quantum properties in transition metal dichalcogenides (TMDs) with charge density wave (CDW). Breaking the inversion symmetry, the Janus structure, an artificially constructed lattice, provides an opportunity to tune the CDW states and the related properties. However, limited by the difficulties in atomic-level fa… ▽ More As a fundamental structural feature, the symmetry of materials determines the exotic quantum properties in transition metal dichalcogenides (TMDs) with charge density wave (CDW). Breaking the inversion symmetry, the Janus structure, an artificially constructed lattice, provides an opportunity to tune the CDW states and the related properties. However, limited by the difficulties in atomic-level fabrication and material stability, the experimental visualization of the CDW states in 2D TMDs with Janus structure is still rare. Here, using surface selenization of VTe2, we fabricated monolayer Janus VTeSe. With scanning tunneling microscopy, an unusual root13-root13 CDW state with threefold rotational symmetry breaking was observed and characterized. Combined with theoretical calculations, we find this CDW state can be attributed to the charge modulation in the Janus VTeSe, beyond the conventional electron-phonon coupling. Our findings provide a promising platform for studying the CDW states and artificially tuning the electronic properties toward the applications. △ Less

Submitted 17 June, 2024; originally announced June 2024.

Correlated electrons of the flat band in charge density wave state of 4Hb-TaSexS2-x

Authors: Yanyan Geng, Jianfeng Guo, Fanyu Meng, Manyu Wang, Shuo Mi, Li Huang, Rui Xu, Fei Pang, Kai Liu, Shancai Wang, Hong-Jun Gao, Weichang Zhou, Wei Ji, Hechang Lei, Zhihai Cheng

Abstract: Many intriguing quantum states of matter, such as unconventional superconductivity, magnetic phases and fractional quantum Hall physics, emergent from the spatially-correlated localized electrons in the flat band of solid materials. By using scanning tunneling microscopy and spectroscopy (STM/STS), we report the real-space investigation of correlated electrons in the flat band of superlattice 4Hb-… ▽ More Many intriguing quantum states of matter, such as unconventional superconductivity, magnetic phases and fractional quantum Hall physics, emergent from the spatially-correlated localized electrons in the flat band of solid materials. By using scanning tunneling microscopy and spectroscopy (STM/STS), we report the real-space investigation of correlated electrons in the flat band of superlattice 4Hb-TaSexS2-x. In contrast with the pristine 4Hb-TaS2, the selenium (Se) substitutions significantly affect the interfacial transfer of correlated electrons between the CDW states of 1T- and 1H-TaS2 layers, and contribute a real-space fractional electron-filling configurations with the distributed electron-filled and -void SoD clusters of 1T-layer. The site-specific STS spectra directly reveal their respective prominent spectra weight above EF and symmetric Mott-like spectra. In addition, the spatial distributions of these electron-filled SoDs in the 1T-layer of 4Hb-TaSe0.7S1.3 demonstrate different local short-range patterning, clearly indicating the complex neighboring interactions among the localized electrons in the flat band of 1T-layer. Our results not only provide an in-depth insight of correlated electrons in the flat CDW band, and provide a simple platform to manipulate the electron-correlation-related quantum states. △ Less

Submitted 10 June, 2024; originally announced June 2024.

Comments: 18 pages, 4 figures

Controlled fabrication of freestanding monolayer SiC by electron irradiation

Authors: Yunli Da, Ruichun Luo, Bao Lei, Wei Ji, Wu Zhou

Abstract: The design and preparation of novel quantum materials with atomic precision are crucial for exploring new physics and for device applications. Electron irradiation has demonstrated as an effective method for preparing novel quantum materials and quantum structures that could be challenging to obtain otherwise. It features the advantages of precise control over the patterning of such new materials… ▽ More The design and preparation of novel quantum materials with atomic precision are crucial for exploring new physics and for device applications. Electron irradiation has demonstrated as an effective method for preparing novel quantum materials and quantum structures that could be challenging to obtain otherwise. It features the advantages of precise control over the patterning of such new materials and their integration with other materials with different functionalities. Here, we present a new strategy for fabricating freestanding monolayer SiC within nanopores of a graphene membrane. By regulating the energy of the incident electron beam and the in-situ heating temperature in a scanning transmission electron microscope (STEM), we can effectively control the patterning of nanopores and subsequent growth of monolayer SiC within the graphene lattice. The resultant SiC monolayers seamlessly connect with the graphene lattice, forming a planar structure distinct by a wide direct bandgap. Our in-situ STEM observations further uncover that the growth of monolayer SiC within the graphene nanopore is driven by a combination of bond rotation and atom extrusion, providing new insights into the atom-by-atom self-assembly of freestanding two-dimensional (2D) monolayers. △ Less

Submitted 5 June, 2024; originally announced June 2024.

Alkaline earth metal mediated inter-molecular magnetism in perfluorocubane dimers and chains

Authors: Zhuohang Li, Cong Wang, Linwei Zhou, Yurou Guan, Linlu Wu, Jiaqi Dai, Wei Ji

Abstract: Perfluorocubane ($C_8F_8$) was successfully synthesized and found to accept and store electrons in its internal cubic cavity to form magnetic moments. However their inter-molecule spin-exchange coupling mechanism is yet to be revealed. In this study, we found the inter-molecule magnetic groundstates of $C_8F_8$ dimer and one-dimensional (1D) chain are tunable from antiferromagnetic (AFM) to ferrom… ▽ More Perfluorocubane ($C_8F_8$) was successfully synthesized and found to accept and store electrons in its internal cubic cavity to form magnetic moments. However their inter-molecule spin-exchange coupling mechanism is yet to be revealed. In this study, we found the inter-molecule magnetic groundstates of $C_8F_8$ dimer and one-dimensional (1D) chain are tunable from antiferromagnetic (AFM) to ferromagnetic (FM) by stacking orders and alkaline earth metals intercalation using first-principle calculations. The inter-molecule couplings are dominated by noncovalent halogen $C-F...C_4$ interactions. Stacking orders of dimers can regulate the relative position of the lone pairs and $σ-holes$ at the molecular interface and thus the magnetic groundstates. Alkaline earth metals M (M = Na, Mg) intercalations could form $C_4-M-C_4$ bonds and lead to FM direct exchange at the inter-molecule region. An unpaired electron donated by the intercalated atoms or electron doping can result in a local magnetic moment in dimers, exhibiting an on-off switching by the odd-even number of electron filling. Novel electronic properties such as spin gapless semiconductor and charge density wave (CDW) states emerge when $C_8F_8$ molecules self-assemble with intercalated atoms to form 1D chains. These findings manifest the roles of stacking and intercalation in modifying intermolecular magnetism and the revealed halogen bond-dominated exchange mechanisms are paramount additions to those previously established non-covalent couplings. △ Less

Submitted 20 May, 2024; originally announced May 2024.

Comments: 5 figures, 3 supplementary tables and 8 supplementary figures

Magnetic Properties of NH$_4$H$_2$PO$_4$ and KH$_2$PO$_4$: Emergence of Multiferroic Salts

Authors: Lei Meng, Chen He, Wei Ji, Fei Yen

Abstract: We observe sharp step-down discontinuities in the magnetic susceptibility of NH$_4$H$_2$PO$_4$ and NH$_4$H$_2$PO$_4$-$d$$_{60}$ (60% deuterated) along the $a$ and $c$-axes occurring exactly at their antiferroelectric transition temperatures. For the case of KH$_2$PO$_4$, less pronounced discontinuities occur at the ferroelectric transition temperature. To explain this, we treat the acid protons as… ▽ More We observe sharp step-down discontinuities in the magnetic susceptibility of NH$_4$H$_2$PO$_4$ and NH$_4$H$_2$PO$_4$-$d$$_{60}$ (60% deuterated) along the $a$ and $c$-axes occurring exactly at their antiferroelectric transition temperatures. For the case of KH$_2$PO$_4$, less pronounced discontinuities occur at the ferroelectric transition temperature. To explain this, we treat the acid protons as individual oscillators that generate current elements which translate to magnetic forces in near resonance with each other. With decreasing temperature, the resonant forces become more commensurate which amplifies a disproportionate drop off of two types of magnetic forces to eventually trigger the structural phase transitions. For the case of NH$_4$H$_2$PO$_4$, the associated internal magnetic field appears to aid the NH$_4$$^+$ to order at higher temperature. At 49 K, a shoulder-like anomaly in both NH$_4$H$_2$PO$_4$ and KH$_2$PO$_4$ is attributed to a possible onset of macroscopic quantum tunneling of protons. Our findings bring forth a new category of intrinsic multiferroic systems. △ Less

Submitted 14 May, 2024; originally announced May 2024.

Comments: 14 pages with 5 figures

Journal ref: J. Phys. Chem. Lett. 11, 8297-8301 (2020)

The Role of Excitations in Supercooled Liquids: Density, Geometry, and Relaxation Dynamics

Authors: Wencheng Ji, Massimo Pica Ciamarra, Matthieu Wyart

Abstract: Low-energy excitations play a key role in all condensed-matter systems, yet there is limited understanding of their nature in glasses, where they correspond to local rearrangements of groups of particles. Here we introduce an algorithm to systematically uncover these excitations up to the activation energy scale relevant to structural relaxation. We use it in a model system to measure the density… ▽ More Low-energy excitations play a key role in all condensed-matter systems, yet there is limited understanding of their nature in glasses, where they correspond to local rearrangements of groups of particles. Here we introduce an algorithm to systematically uncover these excitations up to the activation energy scale relevant to structural relaxation. We use it in a model system to measure the density of states on a scale never achieved before, confirming that this quantity shifts to higher energy under cooling, precisely as the activation energy does. Secondly, we show that the excitations' energetic and spatial features allow one to predict with great accuracy the dynamic propensity, i.e. the location of future relaxation dynamics. Finally, we find that excitations have a core whose properties, including the displacement of the most mobile particle, scale as a power-law of their activation energy and are independent of temperature. Additionally, they exhibit an outer deformation field that depends on the material's stability and, therefore, on temperature. We build a scaling description of these findings. Overall, our analysis supports that excitations play a crucial role in regulating relaxation dynamics near the glass transition, effectively suppressing the transition to dynamical arrest predicted by mean-field theories while also being strongly influenced by it. △ Less

Submitted 26 August, 2024; v1 submitted 1 May, 2024; originally announced May 2024.

Evidence of Ferroelectricity in an Antiferromagnetic Vanadium Trichloride Monolayer

Authors: Jinghao Deng, Deping Guo, Yao Wen, Shuangzan Lu, Hui Zhang, Zhengbo Cheng, Zemin Pan, Tao Jian, Dongyu Li, Hao Wang, Yusong Bai, Zhilin Li, Wei Ji, Jun He, Chendong Zhang

Abstract: A reduced dimensionality of multiferroic materials is highly desired for device miniaturization, but the coexistence of ferroelectricity and magnetism at the two-dimensional limit is yet to be conclusively demonstrated. Here, we used a NbSe2 substrate to break both the C3 rotational and inversion symmetries in monolayer VCl3 and thus introduced exceptional in-plane ferroelectricity into a two-dime… ▽ More A reduced dimensionality of multiferroic materials is highly desired for device miniaturization, but the coexistence of ferroelectricity and magnetism at the two-dimensional limit is yet to be conclusively demonstrated. Here, we used a NbSe2 substrate to break both the C3 rotational and inversion symmetries in monolayer VCl3 and thus introduced exceptional in-plane ferroelectricity into a two-dimensional magnet. Scanning tunneling spectroscopy directly visualized ferroelectric domains and manipulated their domain boundaries in monolayer VCl3, where coexisting antiferromagnetic order with canted magnetic moments was verified by vibrating sample magnetometer measurements. Our density functional theory calculations highlight the crucial role that highly directional interfacial Cl-Se interactions play in breaking the symmetries and thus in introducing in-plane ferroelectricity, which was further verified by examining an ML-VCl3/graphene sample. Our work demonstrates an approach to manipulate the ferroelectric states in monolayered magnets through van der Waals interfacial interactions. △ Less

Submitted 11 June, 2025; v1 submitted 20 April, 2024; originally announced April 2024.

Journal ref: Sci. Adv.11,eado6538(2025)

Site-ordering/disordering-induced magnetic textures in a vdW ferromagnet by competing global and broken inversion-symmetry

Authors: Haoyan Zhang, Jianfeng Guo, Cong Wang, Le Lei, Shuo Mi, Songyang Li, Congkuan Tian, Shaohua Yan, Hanxiang Wu, Shiyu Zhu, Rui Xu, Xueyun Wang, Hechang Lei, Peng Cheng, Fei Pang, Wei Ji, Zhihai Cheng

Abstract: Fe5GeTe2 single crystals can be divided into nonquenched (NQ) and quench-cooled (QC) phases with different magnetic properties. A comprehensive understanding of the magnetic property variations in the NQ and QC phases is imperative for guiding Fe5GeTe2 towards spintronics applications; however, it remains elusive. Here, we report a real-space study on the structural and magnetic properties of thes… ▽ More Fe5GeTe2 single crystals can be divided into nonquenched (NQ) and quench-cooled (QC) phases with different magnetic properties. A comprehensive understanding of the magnetic property variations in the NQ and QC phases is imperative for guiding Fe5GeTe2 towards spintronics applications; however, it remains elusive. Here, we report a real-space study on the structural and magnetic properties of these two magnetic phases using cryogenic magnetic force microscopy and scanning tunneling microscopy. The thermal history introduces disorder and order to the Fe(1) sites, resulting in the NQ and QC phases exhibiting global and broken inversion symmetry, respectively. The observed magnetic domain transitions (branching to labyrinthine) in the spin reorientation process and the distinct 3D spin textures stabilized by magnetic dipolar interaction observed in field-dependent studies allow the NQ phase to exhibit a more resilient global magnetic state. In contrast, the QC phase exhibits enhanced magnetic anisotropy, resulting in a higher TC. Meanwhile, the Dzyaloshinskii-Moriya interaction (DMI) introduced by the broken inversion symmetry causes the QC phase to exhibit a localized magnetic state: no domain transformation occurs during spin reorientation, and irregular domain states are observed in field-related studies. Our work provides an important reference for understanding the complex magnetic properties in Fe5GeTe2. △ Less

Submitted 7 April, 2024; originally announced April 2024.

Comments: 18 pages,4 figures

Convert laser light into single photons via interference

Authors: Yanfeng Li, Manman Wang, Guoqi Huang, Li Liu, Wenyan Wang, Weijie Ji, Hanqing Liu, Xiangbin Su, Shulun Li, Deyan Dai, Xiangjun Shang, Haiqiao Ni, Zhichuan Niu, Chengyong Hu

Abstract: Laser light possesses perfect coherence, but cannot be attenuated to single photons via linear optics. An elegant route to convert laser light into single photons is based on photon blockade in a cavity with a single atom in the strong coupling regime. However, the single-photon purity achieved by this method remains relatively low. Here we propose an interference-based approach where laser light… ▽ More Laser light possesses perfect coherence, but cannot be attenuated to single photons via linear optics. An elegant route to convert laser light into single photons is based on photon blockade in a cavity with a single atom in the strong coupling regime. However, the single-photon purity achieved by this method remains relatively low. Here we propose an interference-based approach where laser light can be transformed into single photons by destructively interfering with a weak but super-bunched incoherent field emitted from a cavity coupling to a single quantum emitter. We demonstrate this idea by measuring the reflected light of a laser field which drives a double-sided optical microcavity containing a single artificial atom-quantum dot (QD) in the Purcell regime. The reflected light consists of a superposition of the driving field with the cavity output field. We achieve the second-order autocorrelation g2(0)=0.030+-0.002 and the two-photon interference visibility 94.3%+-0.2. By separating the coherent and incoherent fields in the reflected light, we observe that the incoherent field from the cavity exhibits super-bunching with g2(0)=41+-2 while the coherent field remains Poissonian statistics. By controlling the relative amplitude of coherent and incoherent fields, we verify that photon statistics of reflected light is tuneable from perfect anti-bunching to super-bunching in agreement with our predictions. Our results demonstrate photon statistics of light as a quantum interference phenomenon that a single QD can scatter two photons simultaneously at low driving fields in contrast to the common picture that a single two-level quantum emitter can only scatter (or absorb and emit) single photons. This work opens the door to tailoring photon statistics of laser light via cavity or waveguide quantum electrodynamics and interference. △ Less

Submitted 25 March, 2024; originally announced March 2024.

Comments: Comments are welcome

Journal ref: Optica 12, 1838-1844(2025)

Correlated sensing with a solid-state quantum multi-sensor system for atomic-scale structural analysis

Authors: Wentao Ji, Zhaoxin Liu, Yuhang Guo, Zhihao Hu, Jingyang Zhou, Siheng Dai, Yu Chen, Pei Yu, Mengqi Wang, Kangwei Xia, Fazhan Shi, Ya Wang, Jiangfeng Du

Abstract: Developing superior quantum sensing strategies ranging from ultra-high precision measurement to complex structural analysis is at the heart of quantum technologies. While strategies using quantum resources, such as entanglement among sensors, to enhance the sensing precision have been abundantly demonstrated, the signal correlation among quantum sensors is rarely exploited. Here we develop a novel… ▽ More Developing superior quantum sensing strategies ranging from ultra-high precision measurement to complex structural analysis is at the heart of quantum technologies. While strategies using quantum resources, such as entanglement among sensors, to enhance the sensing precision have been abundantly demonstrated, the signal correlation among quantum sensors is rarely exploited. Here we develop a novel sensing paradigm exploiting the signal correlation among multiple quantum sensors to resolve overlapping signals from multiple targets that individual sensors can't resolve and complex structural construction struggles with. With three nitrogen-vacancy centers as a quantum electrometer system, we demonstrate this multi-sensor paradigm by resolving individual defects' fluctuating electric fields from ensemble signals. We image the three-dimensional distribution of 16 dark electronic point-defects in diamond with accuracy approaching 1.7 nm via a GPS-like localization method. Furthermore, we obtain the real-time charge dynamics of individual point defects and visualize how the dynamics induce the well-known optical spectral diffusion. The multi-sensor paradigm extends the quantum sensing toolbox and offers new possibilities for structural analysis. △ Less

Submitted 4 January, 2024; originally announced January 2024.

Filling-dependent intertwined electronic and atomic orders in the flat-band state of 1T-TaS2

Authors: Yanyan Geng, Haoyu Dong, Renhong Wang, Jianfeng Guo, Shuo Mi, Le Lei, Yan Li, Li Huang, Fei Pang, Rui Xu, Weiqiang Yu, Wei Ji, Hong-Jun Gao, Weichang Zhou, Zhihai Cheng

Abstract: The delicate interplay among the complex intra-/inter-layer electron-electron and electron-lattice interactions is the fundamental prerequisite of these exotic quantum states, such as superconductivity, nematic order, and checkerboard charge order. Here we explore the filling-dependent multiple stable intertwined electronic and atomic orders of flat-band state of 1T-TaS2 encompassing hole order, p… ▽ More The delicate interplay among the complex intra-/inter-layer electron-electron and electron-lattice interactions is the fundamental prerequisite of these exotic quantum states, such as superconductivity, nematic order, and checkerboard charge order. Here we explore the filling-dependent multiple stable intertwined electronic and atomic orders of flat-band state of 1T-TaS2 encompassing hole order, phase orders, coexisting left- and right-chiral orders and mixed phase/chiral orders via scanning tunneling microscopy (STM). Combining first-principles calculations, the emergent electronic/atomic orders can be attributed to the weakening of electron-electron correlations and stacking-dependent interlayer interactions. Moreover, achiral intermediate ring-like clusters and nematic charge density wave (CDW) states are successfully realized in intralayer chiral domain wall and interlayer heterochiral stacking regions through chiral overlap configurations. Our study not only deepens the understanding of filling-dependent electronic/atomic orders in flat-band systems, but also offers perspectives for exploring exotic quantum states in correlated electronic systems. △ Less

Submitted 8 February, 2025; v1 submitted 2 January, 2024; originally announced January 2024.

Coherence in resonance fluorescence

Authors: Xu-Jie Wang, Guoqi Huang, Ming-Yang Li, Yuan-Zhuo Wang, Li Liu, Bang Wu, Hanqing Liu, Haiqiao Ni, Zhichuan Niu, Weijie Ji, Rongzhen Jiao, Hua-Lei Yin, Zhiliang Yuan

Abstract: Resonance fluorescence of a two-level emitter displays persistently anti-bunching irrespective of the excitation intensity, but inherits the driving laser's linewidth under weak monochromatic excitation. These properties are commonly explained in terms of two disjoined pictures, i.e., the emitter's single photon saturation or passively scattering light. Here, we propose a unified model that treats… ▽ More Resonance fluorescence of a two-level emitter displays persistently anti-bunching irrespective of the excitation intensity, but inherits the driving laser's linewidth under weak monochromatic excitation. These properties are commonly explained in terms of two disjoined pictures, i.e., the emitter's single photon saturation or passively scattering light. Here, we propose a unified model that treats all fluorescence photons as spontaneous emission, one at a time, and can explain simultaneously both the spectral and correlation properties of the emission. We theoretically derive the excitation power dependencies, measurable at the single-photon incidence level, of the first-order coherence of the whole resonance fluorescence and super-bunching of the spectrally filtered, followed by experimental confirmation on a semiconductor quantum dot micro-pillar device. Furthermore, our model explains peculiar coincidence bunching observed in phase-dependent two-photon interference experiments. Our work provides an intuitive understanding of coherent light-matter interaction and may stimulate new applications. △ Less

Submitted 28 January, 2025; v1 submitted 21 December, 2023; originally announced December 2023.

Comments: Theoretical derivation of Eq. (1) is included

Journal ref: Nature Communications 16, 6453 (2025)

Kagome electronic states in gradient-strained untwisted graphene bilayers

Authors: Zeyu Liu, Xianghua Kong, Zewen Wu, Linwei Zhou, Jingsi Qiao, Wei Ji

Abstract: Moiré superlattices in twisted homo-bilayers have revealed exotic electronic states, including unconventional superconductivity and correlated insulating phases. However, their fabrication process often introduces moiré disorders, hindering reproducibility and experimental control. Here, we propose an alternative approach using gradient strain to construct moiré superlattices in untwisted bilayer… ▽ More Moiré superlattices in twisted homo-bilayers have revealed exotic electronic states, including unconventional superconductivity and correlated insulating phases. However, their fabrication process often introduces moiré disorders, hindering reproducibility and experimental control. Here, we propose an alternative approach using gradient strain to construct moiré superlattices in untwisted bilayer graphene (gs-BLG). Through force-field and first-principles calculations, we show that gs-BLG exhibits kagome-like interlayer-spacing distributions and strain-tunable kagome electronic bands. The competition between interlayer coupling and in-plane strain relaxation leads to distinct structural deformations, giving rise to three forms of diatomic kagome lattices: subtle, pronounced, and distorted. Kagome electronic bands are identified near the Fermi level in their band structures. Modulating strain gradients enables tailoring bandwidths and signs of hopping parameters of these kagome bands, providing a versatile platform for studying exotic electronic phases. Our findings establish gradient strain as an alternative to twist engineering, opening an avenue for exploring emergent electronic phases in graphene-based systems. △ Less

Submitted 11 February, 2025; v1 submitted 29 November, 2023; originally announced November 2023.

Comments: 15 pages, 4 figures

Observation of unconventional van der Waals multiferroics near room temperature

Authors: Yangliu Wu, Haipeng Lu, Xiaocang Han, Chendi Yang, Nanshu Liu, Xiaoxu Zhao, Liang Qiao, Wei Ji, Renchao Che, Longjiang Deng, Bo Peng

Abstract: The search for two-dimensional (2D) van der Waals (vdW) multiferroics is an exciting yet challenging endeavor. Room-temperature 2D vdW few-layer multiferroic is a much bigger insurmountable obstacle. Here we report the discovery of an unconventional 2D vdW multiferroic with out-of-plane ferroelectric polarization and long-range magnetic orders in trilayer NiI2 device from 10 K to 295 K. The evolut… ▽ More The search for two-dimensional (2D) van der Waals (vdW) multiferroics is an exciting yet challenging endeavor. Room-temperature 2D vdW few-layer multiferroic is a much bigger insurmountable obstacle. Here we report the discovery of an unconventional 2D vdW multiferroic with out-of-plane ferroelectric polarization and long-range magnetic orders in trilayer NiI2 device from 10 K to 295 K. The evolutions of magnetic domains with magnetic field, and the evolutions between ferroelectric and antiferroelectric phase have been unambiguously observed. More significantly, we realize a robust mutual control of magnetism and ferroelectricity at room temperature. The magnetic domains are manipulated by a small voltage ranging from 1 V to 6 V at 0 T and 295 K. This work opens opportunities for exploring multiferroic physics at the limit of few atomic layers. △ Less

Submitted 23 February, 2024; v1 submitted 24 November, 2023; originally announced November 2023.

Comments: 4 figures

MSC Class: 14J60 ACM Class: F.2.2; I.2.7