Showing 1–50 of 147 results for author: Zhong, R

Distinguishing Majorana zero modes from trivial defect states in an iron-based superconductor

Authors: Dongfei Wang, Jon Ortuzar, Freek Massee, Ruidan Zhong, Genda Gu, Wende Xiao, Yugui Yao, Roland Wiesendanger

Abstract: Majorana zero modes, which obey non-Abelian exchange statistics, are promising candidates for topological quantum computation due to their robustness against environmental perturbations. The iron-based superconductor Fe(Te,Se) has been identified as an intrinsic topological superconductor, possibly hosting Majorana zero modes. In this paper, we report the observation of near-zero-energy localized… ▽ More Majorana zero modes, which obey non-Abelian exchange statistics, are promising candidates for topological quantum computation due to their robustness against environmental perturbations. The iron-based superconductor Fe(Te,Se) has been identified as an intrinsic topological superconductor, possibly hosting Majorana zero modes. In this paper, we report the observation of near-zero-energy localized states at multiple structural defects on the Fe(Te,Se) surface, which could be misidentified as Majorana zero modes without additional verification. By using spin-polarized scanning tunneling spectroscopy, we demonstrate that the near-zero-energy localized states on step edges and line defects originate from topologically trivial Yu-Shiba-Rusinov states. In addition, zero-energy bound states are also observed for regions without surface defects. A combined spatial and magnetic field dependent analysis of the spin-resolved tunneling spectra in these regions reveals that this type of zero-energy states cannot be attributed to the presence of Majorana bound states. These findings emphasize the importance of spin-dependent studies of low-energy states for pursuing Majorana zero modes. △ Less

Submitted 9 August, 2026; v1 submitted 16 June, 2026; originally announced June 2026.

Comments: 41 pages, 17 figures

Field-Induced Up-Up-Down State and Frustrated Magnetism in a Non-Kramers Triangular Antiferromagnet

Authors: Zhaoyi Li, Qinchen Duan, Bo Wen, Ruidan Zhong, Shu Guo

Abstract: A previously unreported triangular lattice (TL) antiferromagnet, TmZnGaO4, was synthesized as single crystals, and its crystal structure, magnetic susceptibilities, and specific heat were reported. Its crystal structure is isomorphic to that of the transverse-field Ising antiferromagnet TmMgGaO4, with Tm3+ ions located in the TLs, separated by a nonmagnetic bilayer composed mainly of Ga3+ and Zn2+… ▽ More A previously unreported triangular lattice (TL) antiferromagnet, TmZnGaO4, was synthesized as single crystals, and its crystal structure, magnetic susceptibilities, and specific heat were reported. Its crystal structure is isomorphic to that of the transverse-field Ising antiferromagnet TmMgGaO4, with Tm3+ ions located in the TLs, separated by a nonmagnetic bilayer composed mainly of Ga3+ and Zn2+ ions. The magnetic susceptibilities indicate the dominating antiferromagnetic interactions. The magnetization curves (M-H) exhibit strong easy-c-axis anisotropy, with a clear one-third magnetic plateau emerging, consistent with a field-induced up-up-down spin configuration. Instead of forming a conventional long-range magnetic order, the system exhibits two broad anomalies at 0.11 K and 2.81 K in zero-field specific heat measurements, highlighting the persistence of strong spin fluctuations and the potential for exotic quantum spin states. The above results reveal its future interest in exploring exotic quantum spin states in TmZnGaO4. △ Less

Submitted 9 June, 2026; originally announced June 2026.

Symplectic connection third-order Hall effect in a room-temperature ferromagnet

Authors: Yu Cao, Xukun Feng, Yiming Guo, Huiying Liu, Qia Shen, Hongliang Chen, Wanxi Gong, Yu Yang, Dandan Guan, Yaoyi Li, Shiyong Wang, Hao Zheng, Canhua Liu, Xiaoxue Liu, Yumeng Yang, Xuepeng Qiu, Ruidan Zhong, Jinfeng Jia, Shengyuan A. Yang, Cong Xiao, Liang Liu

Abstract: Third-order nonlinear Hall effects (THE) have recently attracted considerable experimental interest as powerful probes for quantum geometric properties in emergent quantum materials, encompassing quadrupole moments of quantum metric and Berry curvature. Here, we report a fundamentally new THE in room-temperature van der Waals ferromagnet Fe3GaTe2 from second-order Berry connection polarizability,… ▽ More Third-order nonlinear Hall effects (THE) have recently attracted considerable experimental interest as powerful probes for quantum geometric properties in emergent quantum materials, encompassing quadrupole moments of quantum metric and Berry curvature. Here, we report a fundamentally new THE in room-temperature van der Waals ferromagnet Fe3GaTe2 from second-order Berry connection polarizability, which manifests a higher-order characterization of band geometry called symplectic connection. Our observations show that the third-order transverse response in Fe3GaTe2 is odd to magnetization, vanishes above the Curie temperature and remains independent of driving current directions. Scaling law analysis combined with first-principles calculations establishes this response as the symplectic-connection-induced THE. This discovery opens the door to probing high-order quantum geometric properties beyond Berry curvature and quantum metric through nonlinear transport, unveiling the potential of exploring nonlinear Hall phenomena in broad classes of magnets without breaking inversion symmetry. Moreover, the room-temperature manipulation of THE holds promises for device applications based on harnessing the quantum-geometric connection structure. △ Less

Submitted 22 April, 2026; originally announced April 2026.

Comments: The submitted version for review on April 30, 2025. 22 pages, 5 figures

Direct observation of quadruple spin-texture locking in a 2D d-wave altermagnet

Authors: Dan Mu, Bei Jiang, Qingchen Duan, Zulin Xu, Xingkai Cheng, Yusen Xiao, Xinru Han, Xinyu Liang, Zhaokun Luo, Ryan L. Kong, Qiheng Wang, Junwei Liu, Jianxin Zhong, Ruidan Zhong, Qiangqiang Gu, Baiqing Lv, Hong Ding

Abstract: Altermagnets combine vanishing net magnetization with nonrelativistic, momentum-dependent spin splitting, offering a new paradigm for spintronics. Spin-crystal symmetry coupling, namely spin-lattice locking, is the defining mechanism of altermagnetism, enforcing opposite spin sublattices in real space and spin-momentum-locked electronic structure in reciprocal space. Direct atomic-scale visualizat… ▽ More Altermagnets combine vanishing net magnetization with nonrelativistic, momentum-dependent spin splitting, offering a new paradigm for spintronics. Spin-crystal symmetry coupling, namely spin-lattice locking, is the defining mechanism of altermagnetism, enforcing opposite spin sublattices in real space and spin-momentum-locked electronic structure in reciprocal space. Direct atomic-scale visualization of spin-lattice locking therefore constitutes a decisive benchmark of the altermagnetic state, yet such evidence has remained elusive despite extensive efforts. Here we show that the electronic states in RbV2Se2O exhibit a d-wave-like spin texture at the sublattice level, providing the first atomic-scale evidence of spin-lattice locking with a predominantly c-axis spin orientation. By employing an in-situ, field-switchable spin-polarized Cr tip, we realize spin-contrast mapping of quasiparticle interference at identical energies, overcoming a long-standing experimental barrier in altermagnets. The resulting interference patterns exhibit pronounced spin-dependent modulations, establishing spin scattering locking and spin momentum locking as the real and reciprocal space manifestations. Unexpectedly, we uncover that the spin-selective scattering response is organized by a long-period stripe modulation, giving rise to a previously unidentified form of spin-texture locking, spin-stripe locking. We attribute this behavior to the emergence of a spin-density-wave moiré pattern. Together, these results establish a unified picture of quadruple spin-texture locking phenomena in a d-wave altermagnet, and position altermagnets as a versatile platform for exploring many-body interactions among intertwined degrees of freedom, including spin, lattice, momentum, moiré potential and valley. △ Less

Submitted 20 April, 2026; originally announced April 2026.

Comments: Under Review

Symmetry-guided and AI-accelerated design of intercalated transition metal dichalcogenides for antiferromagnetic spintronics

Authors: Yu Pang, Yue Gu, Runsheng Zhong, Liyang Zou, Xiaobin Chen, Xiaolong Zou, Wenhui Duan

Abstract: The advancement of antiferromagnetic spintronics depends on quantum materials with target symmetry-dictated functionalities, however, their systematic discovery is hindered by the immense configurational complexity of the available material space. Here, we introduce a symmetry-guided, AI-accelerated framework incorporating graph neural networks with high generalization ability to overcome this bot… ▽ More The advancement of antiferromagnetic spintronics depends on quantum materials with target symmetry-dictated functionalities, however, their systematic discovery is hindered by the immense configurational complexity of the available material space. Here, we introduce a symmetry-guided, AI-accelerated framework incorporating graph neural networks with high generalization ability to overcome this bottleneck. Based on fully intercalated transition metal dichalcogenides (iTMDs) and using only 200 relaxed partially intercalated structures for transfer learning, our model effectively explores more than 100,000 partially intercalated configurations and identifies 35 altermagnetic and 20 $Tτ$-antiferromagnetic ground-state candidates. Interestingly, we show that tuning spin-group symmetry through intercalant arrangement or magnetic ordering realizes a series of d-wave altermagnets in these hexagonal systems with high spin-charge conversion efficiency. Furthermore, we reveal plentiful $Tτ$-antiferromagnets enabling efficient Néel spin-orbit torque switching, driven by giant $T$-odd spin Edelstein susceptibilities. These results establish iTMDs as a versatile platform for spintronics and provide a general strategy for the accelerated design of symmetry-enforced quantum materials. △ Less

Submitted 8 April, 2026; originally announced April 2026.

Comments: 29 pages, 4 figures, 2 tables

Neutralization of the impact of belt speed on screen printed copper metallization by LECO on PERC homogeneous emitter

Authors: Abasifreke Ebong, Donald Intal, Sandra Huneycutt, Ajeet Rohatgi, Vijay Upadhyaya, Sagnik Dasgupta, Ruohan Zhong, Thad Druffel, Ruvini Dharmadasa

Abstract: Copper fire-through metallization is a cost-effective alternative to Ag counterpart for industrial high efficiency solar cells. The fire through dielectric metallization relies on belt speed, which dictates the ramp up and ramp down rates for effective contact formation. In this paper three belt speeds (325oC, 360oC, 390oC) at constant peak firing temperature, were used to process PERC (homogeneou… ▽ More Copper fire-through metallization is a cost-effective alternative to Ag counterpart for industrial high efficiency solar cells. The fire through dielectric metallization relies on belt speed, which dictates the ramp up and ramp down rates for effective contact formation. In this paper three belt speeds (325oC, 360oC, 390oC) at constant peak firing temperature, were used to process PERC (homogeneous emitter) cells. After the contact firing the electrical parameters were dependent on belt speed, but after LECO treatment, they were identical. The SEM/EDS cross sectional analyses showed increased elemental Cu with belt speed, and the series resistance was lowest for the middle belt speed before LECO. However, after the LECO treatment, the series resistance dropped, respectively, to 0.503 ohm-cm-2, 0.428 ohm-cm-2 and 0.500 ohm-cm-2 leading to efficiency of 20.8% on homogeneous PERC emitter. △ Less

Submitted 24 March, 2026; v1 submitted 20 March, 2026; originally announced March 2026.

Critical look at the atmospheric Cu fire-through dielectric metallization for cost-effective and high efficiency silicon solar cells

Authors: Donald Intal, Sandra Huneycutt, Abasifreke Ebong, Ajeet Rohatgi, Vijay Upadhyaya, Sagnik Dasgupta, Ruohan Zhong, Thad Druffel, Ruvini Dharmadasa

Abstract: The formation of stable copper-silicide (Cu3Si) interfaces is crucial for cost-effective, high-efficiency solar cells. However, copper's diffusivity and electromigration issues pose challenges for contact stability. This study employs Laser-Enhanced Contact Optimization (LECO) to induce localized nano-scale Joule heating at the Cu-Si interface in phosphorus-doped p-PERC solar cells. High-resolutio… ▽ More The formation of stable copper-silicide (Cu3Si) interfaces is crucial for cost-effective, high-efficiency solar cells. However, copper's diffusivity and electromigration issues pose challenges for contact stability. This study employs Laser-Enhanced Contact Optimization (LECO) to induce localized nano-scale Joule heating at the Cu-Si interface in phosphorus-doped p-PERC solar cells. High-resolution STEM and bright field analyses confirm stable Cu3Si formation in LECO-treated samples, with significantly reduced material segregation compared to nonLECO samples. SEM and post-etch EDS mapping demonstrate improved chemical resistance and interface cleanliness. Electrically, LECO treatmenet reduces series resistance by a factor 3, enhancing fill factor and efficiency while preserving diode quality. These results highlight LECO as a scalable method for reliable, silver-free solar cell metallization. △ Less

Submitted 20 March, 2026; originally announced March 2026.

Optimized growth of large-size, high quality $\text{ZrTe}_5$ single crystals enabling clear quantum oscillations in electrical transport

Authors: Hong Du, Yu Cao, Jiahao Chen, Tian Liang, Liang Liu, Ruidan Zhong

Abstract: Quantum oscillation with nontrivial Berry phase is one of the characteristics of topological materials. As a Dirac semimetal candidate, zirconium pentatelluride ($\text{ZrTe}_5$) stands out as an intriguing material for investigating topological phase transitions and Dirac fermion physics; however, the extreme sensitivity of its electronic properties to stoichiometric variations and crystalline de… ▽ More Quantum oscillation with nontrivial Berry phase is one of the characteristics of topological materials. As a Dirac semimetal candidate, zirconium pentatelluride ($\text{ZrTe}_5$) stands out as an intriguing material for investigating topological phase transitions and Dirac fermion physics; however, the extreme sensitivity of its electronic properties to stoichiometric variations and crystalline defects has hindered consistent experimental observation. Here, we report an optimized Te-flux synthesis method designed to produce centimeter-scale, high-quality single crystals meanwhile minimizing extrinsic carrier contamination. Comprehensive morphology, structural and chemical characterizations, including scanning electron microscopy, Laue backscattering and Rietveld refinement, confirm a high-purity $Cmcm$ phase with excellent crystallinity. Furthermore, magnetotransport measurements reveal a remarkably low Shubnikov-de Haas oscillation onset field ($B_{int} \approx 0.38$ T) with an ultra-high mobility of $5.58\times10^5$cm$^2$V$^{-1}$s$^{-1}$ and access to the the quantum limit at $B \approx 1.3$ T, attesting to the superior crystalline quality and the efficacy of this growth optimization. These results demonstrate that growth control is crucial for stabilizing intrinsic electronic behavior in $\text{ZrTe}_5$, establishing a robust platform for exploring topological phase transitions and exotic quantum phenomena in topological semimetals. △ Less

Submitted 20 March, 2026; v1 submitted 13 March, 2026; originally announced March 2026.

Heavy-Fermion Behavior and a Tunable Density Wave in a Novel Vanadium-based Mosaic Lattice

Authors: Yusen Xiao, Zhibin Qiu, Qingchen Duan, Zhaoyi Li, Hengxin Tan, Shu Guo, Ruidan Zhong

Abstract: The pursuit of geometrically frustrated lattices beyond conventional paradigms remains a central challenge in the design of quantum materials. Herein, we report the discovery of Cs3V9Te13 (CVT), a novel intermetallic compound that hosts a unique two-dimensional vanadium mosaic lattice, composed of an ordered tessellation of triangles, squares, and pentagons, bearing profound structural kinship wit… ▽ More The pursuit of geometrically frustrated lattices beyond conventional paradigms remains a central challenge in the design of quantum materials. Herein, we report the discovery of Cs3V9Te13 (CVT), a novel intermetallic compound that hosts a unique two-dimensional vanadium mosaic lattice, composed of an ordered tessellation of triangles, squares, and pentagons, bearing profound structural kinship with the celebrated kagome lattice. Remarkably, CVT exhibits behavior analogous to heavy fermion systems, characterized by a large Sommerfeld coefficient(γ = 425 mJ mol-1 K-2) and a coherent density-wave-like (DW-like) transition at T* = 47 K. This establishes CVT as a rare and intriguing example of a strongly correlated system. Inspired by pressure-tuning in related compounds, we demonstrate that this ground state is exquisitely tunable via chemical pressure. Systematic substitution of Cs with smaller Rb ions suppresses the DW-like order while strongly weakening the heavy-electron response, ultimately driving the system into a distinct non-magnetic, semiconducting, quantum-disordered state above 60 mK. This work unveils a new arena for exploring the interplay between heavy-fermion physics, density waves, and quantum disorder. The mosaic lattice in Cs3V9Te13 provides an unprecedented, chemically controllable platform for navigating the phase space between distinct correlated electronic states. △ Less

Submitted 1 April, 2026; v1 submitted 9 March, 2026; originally announced March 2026.

Comments: This is the first complete work on the A3V9Te13 (A = Rb, Cs) family. Two follow-up works on Cs3V9Te13 appeared after this preprint: arXiv:2603.16625 and arXiv:2603.27682

Hydrostatic Pressure-enhanced correlated magnetism and Chern insulator in moir'e WSe2

Authors: Pengfei Jiao, Chenghao Qian, Ning Mao, Xumin Chang, Jiayong Xiao, Feng Liu, Shaozheng Wang, Xiaokai Wu, Di Peng, Cheng Xu, Hongliang Dong, Yuchen Zheng, Juncai Wu, Tong Zheng, Kenji Watanabe, Takashi Taniguchi, Jinfeng Jia, Xiaoxue Liu, Zhiwen Shi, Shiyong Wang, Guorui Chen, Tingxin Li, Ruidan Zhong, Yang Zhang, Dong Qian , et al. (2 additional authors not shown)

Abstract: Moiré semiconductors offer flat bands where Coulomb interactions and band topology intertwine, while interlayer coupling plays a central role in forming the moiré potential. However, limited interlayer coupling strength and the lack of efficient tuning methods hinder further exploration of correlated phenomena in moiré semiconductors. Here we introduce a cryogenic dual-gated diamond-anvil platform… ▽ More Moiré semiconductors offer flat bands where Coulomb interactions and band topology intertwine, while interlayer coupling plays a central role in forming the moiré potential. However, limited interlayer coupling strength and the lack of efficient tuning methods hinder further exploration of correlated phenomena in moiré semiconductors. Here we introduce a cryogenic dual-gated diamond-anvil platform using helium as a pressure medium, enabling reversible hydrostatic tuning together with magneto-optical spectroscopy in twisted bilayer WSe2. Pressure enhances the moiré potential, redshifts excitons, and stabilizes Stoner ferromagnetism otherwise absent at a 3.1-degree twist. Simultaneously, the half-filled C = 1 Chern insulating state strengthens, exhibiting a reduced saturation field. Moreover, we observe a topological phase transition from a Chern insulator to a Mott insulator at around 2 GPa. First-principles calculations reveal that a Gamma-to-K valence-band-maximum switching drives this transition by converting an Ising-like topological K-valley miniband into a spin-degenerate trivial Gamma miniband. Our findings demonstrate hydrostatic pressure as a powerful, continuous control axis for correlated magnetism and topological band engineering in moiré materials. △ Less

Submitted 17 February, 2026; originally announced February 2026.

Thermodynamics of the Heisenberg XXX chain with negative spin

Authors: Rong Zhong, Yang-Yang Chen, Kun Hao, Wen-li Yang, Vladimir Korepin

Abstract: We study the thermodynamics of the isotropic Heisenberg XXX spin chain with negative spin, focusing on the case $s=-1$. The model is equivalent to the quantum lattice nonlinear Schrödinger (NLS) model and appears as an effective theory in deep inelastic scattering in high-energy quantum chromodynamics. Owing to its integrability, it admits a consistent Bethe Ansatz description and a well-defined t… ▽ More We study the thermodynamics of the isotropic Heisenberg XXX spin chain with negative spin, focusing on the case $s=-1$. The model is equivalent to the quantum lattice nonlinear Schrödinger (NLS) model and appears as an effective theory in deep inelastic scattering in high-energy quantum chromodynamics. Owing to its integrability, it admits a consistent Bethe Ansatz description and a well-defined thermodynamic limit. Using the thermodynamic Bethe Ansatz, we analyze the ground state, elementary excitations, and finite-temperature properties. In contrast to the conventional positive spin XXX chain, the negative spin model exhibits a distinct vacuum structure and excitation spectrum, leading to modified TBA equations and unconventional low-temperature behavior. Although the integral equations resemble those of the Lieb-Liniger Bose gas, the thermodynamics and scaling properties are qualitatively different and cannot be continuously connected. We derive the free energy, entropy, and specific heat, and identify a quantum phase transition separating different thermodynamic regimes. At zero temperature, the excitation spectrum becomes linear in the continuum limit and can be described by a conformal field theory. The low-temperature regime realizes a Luttinger-liquid like phase with features unique to the negative spin XXX chain. △ Less

Submitted 13 August, 2026; v1 submitted 3 February, 2026; originally announced February 2026.

Comments: 41 pages, 15 figures

Journal ref: JHEP 08 (2026) 101

Superconductivity in non-centrosymmetric rhombohedral NbSe2

Authors: Zhengxian Li, Xiaoyu Shen, Kai Liu, Yating Sha, Tianyang Wang, Feng Liu, Qingchen Duan, Kenji Watanabe, Takashi Taniguchi, Peng Chen, Shiyong Wang, Ruidan Zhong, Dong Qian, Shengwei Jiang, Yufan Li, Noah F. Q. Yuan, Guorui Chen

Abstract: Crystal stacking offers a powerful yet underexplored route to engineer symmetry in layered superconductors. Here we report superconductivity in rhombohedral-stacked NbSe2 (3R-NbSe2), a non-centrosymmetric polytype in which global inversion symmetry is removed by stacking alone. Using comprehensive structural, transport, magnetic, and thermodynamic measurements, we establish superconductivity as a… ▽ More Crystal stacking offers a powerful yet underexplored route to engineer symmetry in layered superconductors. Here we report superconductivity in rhombohedral-stacked NbSe2 (3R-NbSe2), a non-centrosymmetric polytype in which global inversion symmetry is removed by stacking alone. Using comprehensive structural, transport, magnetic, and thermodynamic measurements, we establish superconductivity as a bulk property of the 3R phase and find that the in-plane upper critical field exceeds the Pauli paramagnetic limit, indicating the persistence of strong Ising-type spin-orbit coupling. Unlike the thickness-dependent superconductivity in centrosymmetric 2H-NbSe2, the superconducting transition temperature in 3R-NbSe2 shows little dependence on layer number but exhibits an unusually strong sensitivity to disorder. We further observe strongly enhanced nonlinear optical and electrical responses near the superconducting transition, consistent with stacking-induced inversion-symmetry breaking. Our results identify 3R-NbSe2 as a single-phase platform in which stacking engineering reshapes superconductivity and enables nonlinear transport phenomena in layered materials. △ Less

Submitted 23 January, 2026; originally announced January 2026.

Coexistence of stripe order and superconductivity in NaAlSi

Authors: Ruixia Zhong, Qi Wang, Zhongzheng Yang, Fanbang Zheng, Wenhui Li, Yanpeng Qi, Shichao Yan

Abstract: Here, we report a scanning tunneling microscopy study on an s-wave superconductor NaAlSi, revealing the coexistence of stripe order and superconductivity. This stripe order manifests as a unidirectional spatial charge modulation with a commensurate period of four times the lattice constant. This modulation undergoes a phase shift in the differential conductance maps under opposite bias voltages, w… ▽ More Here, we report a scanning tunneling microscopy study on an s-wave superconductor NaAlSi, revealing the coexistence of stripe order and superconductivity. This stripe order manifests as a unidirectional spatial charge modulation with a commensurate period of four times the lattice constant. This modulation undergoes a phase shift in the differential conductance maps under opposite bias voltages, while its period remains approximately constant over an energy range of $\pm$50 meV. These features suggest that this stripe is likely a static charge order. Furthermore, we find that the stripe order imposes a periodic modulation on the intensity of the superconducting coherence peaks. This work provides new perspectives on the intricate interplay between stripe order and s-wave superconductivity. △ Less

Submitted 19 January, 2026; originally announced January 2026.

Comments: 12 pages, 4 figures

Journal ref: Physical Review B 113, 104507 (2026)

Observation of spin-valley locked nodal lines in a quasi-2D altermagnet

Authors: Quanxin Hu, Xingkai Cheng, Qingchen Duan, Yudong Hu, Bei Jiang, Yusen Xiao, Yaqi Li, Mojun Pan, Liwei Deng, Changchao Liu, Guanghan Cao, Zhengtai Liu, Mao Ye, Shan Qiao, Zhanfeng Liu, Zhe Sun, Anyuan Gao, Yaobo Huang, Ruidan Zhong, Junwei Liu, Baiqing Lv, Hong Ding

Abstract: The interplay among quantum degrees of freedom-spin, orbital and momentum-has emerged as a fertile ground for realizing magnetic quantum states with transformative potential for electronic and spintronic technologies. Prominent examples include ferromagnetic Weyl semimetals and antiferromagnetic axion insulators. Recently, altermagnets(AMs) have been identified as a distinct spin-splitting class o… ▽ More The interplay among quantum degrees of freedom-spin, orbital and momentum-has emerged as a fertile ground for realizing magnetic quantum states with transformative potential for electronic and spintronic technologies. Prominent examples include ferromagnetic Weyl semimetals and antiferromagnetic axion insulators. Recently, altermagnets(AMs) have been identified as a distinct spin-splitting class of collinear antiferromagnets(AFMs), characterized by crystal symmetry that connects magnetic sublattices in real space and enforces C-paired spin-momentum locking in reciprocal space. These materials combine the advantages of nonrelativistic spin-polarization akin to FMs and vanished net-magnetization as AFMs, making them highly promising for spintronic applications. Furthermore, they introduce nontrivial spin-momentum locking spin texture as an additional degree of freedom for realizing novel quantum phases. In this work, we report the discovery of a new type of spin-valley-locked nodal line phase in the layered AM Rb-intercalated V{_2}Te{_2}O. By combining high-resolution spin and angle-resolved photoemission spectroscopy with first-principles calculations, we observe the coexistence of both spinless and spinful nodal lines near the Fermi level. Remarkably, the spinful nodal lines exhibit uniform spin polarization within each valley, while displaying opposite spin polarizations across symmetry-paired valleys-a unique feature we term spin-valley-locked nodal lines, which is exclusive to AMs. Direct measurements of out-of-plane band dispersion using a side-cleaving technique reveal the two-dimensional nature of these nodal lines. Our findings not only unveil a previously unexplored topological phase in AMs where valley-locked spin as an additional quantum character but also establish RbV{_2}Te{_2}O as a promising platform for spintronics, valleytronics, and moire-engineered quantum devices. △ Less

Submitted 6 January, 2026; originally announced January 2026.

Comments: 26 pages, 13 figures

Magnetism and Correlated Electrons in LaCr$_2$Ge$_2$N

Authors: Jiao-Jiao Meng, Yu-Sen Xiao, Gen Li, Shao-Hua Liu, Bai-Zhuo Li, Hao Jiang, Zhen Yu, Yi-Qiang Lin, Xin-Yu Zhao, Qing-Chen Duan, Wu-Zhang Yang, Chong-Yao Zhao, Zhi Ren, Yu-Xue Mei, Yong-Liang Chen, Rui-Dan Zhong, Qing-Xin Dong, Peng-Tao Yang, Shu-Gang Tan, Bo-Sen Wang, Huiqian Luo, Jin-Guang Cheng, Xue Ming, Cao Wang, Guang-Han Cao

Abstract: We report the synthesis, structure and physical properties of a new quaternary nitride LaCr$_2$Ge$_2$N. The compound crystallizes in the CeCr$_2$Si$_2$C-type structure (P4/mmm), featuring distinctive Cr$_2$N square sheets within Cr$_2$Ge$_2$N block layers. Physical characterizations reveal enhanced electron correlations evidenced by a Sommerfeld coefficient substantially larger than band calculati… ▽ More We report the synthesis, structure and physical properties of a new quaternary nitride LaCr$_2$Ge$_2$N. The compound crystallizes in the CeCr$_2$Si$_2$C-type structure (P4/mmm), featuring distinctive Cr$_2$N square sheets within Cr$_2$Ge$_2$N block layers. Physical characterizations reveal enhanced electron correlations evidenced by a Sommerfeld coefficient substantially larger than band calculations and pressure-induced deviation from Fermi-liquid behavior. Magnetic measurements show short-range antiferromagnetic correlations developing around 460 K, followed by long-range magnetic ordering at 14 K. Additionally, subtle anomalies at 378 K suggest possible electronic ordering. First-principles calculations reveal nearly-flat Cr-3d bands near the Fermi level and predict a striped antiferromagnetic ground state. This work demonstrates how electron count variation in the CeCr$_2$Si$_2$C-type structure family leads to magnetic ordering in LaCr$_2$Ge$_2$N, contrasting with the paramagnetic behavior of LnCr$_2$Si$_2$C compounds. △ Less

Submitted 23 December, 2025; originally announced December 2025.

Comments: 8 pages, 5 figures, 3 tables. Accepted for publication in Physical Review B

Journal ref: Phys. Rev. B 112, 235164 (2025)

Stoichiometry-Controlled Structural Order and Tunable Antiferromagnetism in $\mathrm{Fe}_{x}\mathrm{NbSe_2}$ ($0.05 \le x \le 0.38$)

Authors: Xiaotong Xu, Bei Jiang, Runze Wang, Zhibin Qiu, Shu Guo, Baiqing Lv, Ruidan Zhong

Abstract: Transition metal dichalcogenides (TMDs) enable magnetic property engineering via intercalation, but stoichiometry-structure-magnetism correlations remain poorly defined for Fe-intercalated $\mathrm{NbSe_2}$. Here, we report a systematic study of $\mathrm{Fe}_{x}\mathrm{NbSe_2}$ across an extended composition range $0.05 \le x \le 0.38$, synthesized via chemical vapor transport and verified by rigo… ▽ More Transition metal dichalcogenides (TMDs) enable magnetic property engineering via intercalation, but stoichiometry-structure-magnetism correlations remain poorly defined for Fe-intercalated $\mathrm{NbSe_2}$. Here, we report a systematic study of $\mathrm{Fe}_{x}\mathrm{NbSe_2}$ across an extended composition range $0.05 \le x \le 0.38$, synthesized via chemical vapor transport and verified by rigorous energy-dispersive x-ray spectroscopy (EDS) microanalysis. X-ray diffraction, magnetic, and transport measurements reveal an intrinsic correlation between Fe content, structural ordering, and magnetic ground states. With increasing $x$, the system undergoes a successive transition from paramagnetism to a spin-glass state, then to long-range antiferromagnetism (AFM), and ultimately to a reentrant spin-glass phase, with the transition temperatures exhibiting a nonmonotonic dependence on Fe content. The maximum Néel temperature ($T_{\mathrm{N}}$ = $\mathrm{175K}$) and strongest AFM coupling occur at $x=0.25$, where Fe atoms form a well-ordered $2a_0 \times 2a_0 $ superlattice within van der Waals gaps. Beyond $x = 0.25$, the superlattice transforms or disorders, weakening Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions and significantly reducing $T_{\mathrm{N}}$. Electrical transport exhibits distinct anomalies at magnetic transition temperatures, corroborating the magnetic state evolution. Our work extends the compositional boundary of Fe-intercalated $\mathrm{NbSe_2}$, establishes precise stoichiometry-structure-magnetism correlations, and identifies structural ordering as a key tuning parameter for AFM. These findings provide a quantitative framework for engineering altermagnetic or switchable antiferromagnetic states in van der Waals materials. △ Less

Submitted 14 April, 2026; v1 submitted 21 December, 2025; originally announced December 2025.

From fractional Chern insulators to topological electronic crystals in moiré MoTe2: quantum geometry tuning via remote layer

Authors: Feng Liu, Fan Xu, Cheng Xu, Jiayi Li, Zheng Sun, Jiayong Xiao, Ning Mao, Xumin Chang, Xinglin Tao, Kenji Watanabe, Takashi Taniguchi, Jinfeng Jia, Ruidan Zhong, Zhiwen Shi, Shiyong Wang, Guorui Chen, Xiaoxue Liu, Dong Qian, Yang Zhang, Tingxin Li, Shengwei Jiang

Abstract: The quantum geometry of Bloch wavefunctions,encoded in the Berry curvature and quantum metric, is believed to be a decisive ingredient in stabilizing fractional quantum anomalous Hall (FQAH) effect(i.e., fractional Chern insulator, FCI, at zero magnetic field), against competing symmetry-breaking phases.A direct experimental demonstration of quantum geometry-driven switching between distinct corre… ▽ More The quantum geometry of Bloch wavefunctions,encoded in the Berry curvature and quantum metric, is believed to be a decisive ingredient in stabilizing fractional quantum anomalous Hall (FQAH) effect(i.e., fractional Chern insulator, FCI, at zero magnetic field), against competing symmetry-breaking phases.A direct experimental demonstration of quantum geometry-driven switching between distinct correlated topological phases, however, has been lacking. Here, we report experimental evidence of such a switch in a high-quality 3.7 twisted MoTe2 (tMoTe2) device consisting of both A-A bilayer and A-AB trilayer regions. While composite Fermi liquid CFL/FQAH phases are established in A-A tMoTe2,the A-AB region-effectively an A-A moire bilayer proximitized by a remote B layer-develops a series of topological electronic crystal (TEC, also referred to as generalized QAH crystal, QAHC) states with integer quantized Hall conductance at commensurate fractional fillings v=1/2, 2/3, and an incommensurate filling factor v=0.53.The electrostatic phase diagram is mapped out by combined transport and optical measurements, showing that these TEC states emerge within the first moir'e valence band prior to any charge transfer to the B layer. Exact diagonalization (ED) incorporating the remote-layer-induced intralayer potential demonstrates a transition from a CFL-like manifold in the A-A limit to a Chern number C=1 ground-state consistent with a TEC at v=1/2 , accompanied by the further breakdown of ideal band geometry. Our results provide experimental evidence of quantum geometry-tuned competition between FQAH/CFL and TEC phases in a moiré Chern band and pave the way for further exploring correlation-driven topological phenomena by tuning quantum geometry. △ Less

Submitted 3 December, 2025; originally announced December 2025.

Light-induced Asymmetric Pseudogap below T$_\text{c}$ in cuprates

Authors: D. Armanno, O. Gingras, F. Goto, J. -M. Parent, A. Longa, A. Jabed, B. Frimpong, R. D. Zhong, J. Schneeloch, G. D. Gu, G. Jargot, H. Ibrahim, F. Legare, B. J. Siwick, N. Gauthier, A. Georges, A. J. Millis, F. Boschini

Abstract: To this day, high-temperature cuprate superconductors remain an unparalleled platform for studying the competition and coexistence of emergent, static and dynamic, quantum phases of matter exhibiting high transition temperature non-s-wave superconductivity, non-Fermi liquid transport and a still enigmatic pseudogap regime. However, how superconductivity emerges alongside and competes with the pseu… ▽ More To this day, high-temperature cuprate superconductors remain an unparalleled platform for studying the competition and coexistence of emergent, static and dynamic, quantum phases of matter exhibiting high transition temperature non-s-wave superconductivity, non-Fermi liquid transport and a still enigmatic pseudogap regime. However, how superconductivity emerges alongside and competes with the pseudogap regime remains an open question. Here, we present a high-resolution, time- and angle-resolved photoemission study of the near-antinodal region of optimally-doped Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$. For a sufficiently high excitation fluence, we disrupt superconductivity and drive a transient change from a symmetric superconducting-like to an asymmetric pseudogap-like density of states, for electronic temperatures well below the equilibrium superconducting critical temperature. Conversely, when the superconductivity is fully restored, the pseudogap is suppressed, as signaled by a fully particle-hole symmetric density of states. A unique aspect of our experiments is that the pseudogap coexists with superconducting features at intermediate times or at intermediate fluence. Our findings challenge the paradigm that superconductivity emerges by establishing phase coherence in the pseudogap. Instead, our experimental results, supported by phenomenological theory, demonstrate that the two states compete, and that the low-temperature ground state of the cuprates originates from a competition between superconducting and pseudogap states. △ Less

Submitted 25 November, 2025; originally announced November 2025.

Coexistence of unconventional spin-orbit torque and in-plane Hall effect in a single ferromagnetic layer

Authors: Jiaxin Chen, Hongsheng Zheng, Hongliang Chen, Qia Shen, Chang Pan, Zhenyi Zheng, Hemian Yi, Dandan Guan, Xiaoxue Liu, Yaoyi Li, Shiyong Wang, Hao Zheng, Canhua Liu, Jinfeng Jia, Jingsheng Chen, Ruidan Zhong, Lei Wang, Xuepeng Qiu, Yumeng Yang, Aurélien Manchon, Liang Liu

Abstract: The symmetry of a material fundamentally governs its spin transport properties. While unconventional spin transport phenomena have been predominantly explored in low-symmetry systems (e.g., $C_{1v}$ symmetry), high-symmetry crystals--which constitute the majority of industry-compatible materials--are generally expected to exhibit only conventional spin-transport behavior. Here, we report the coexi… ▽ More The symmetry of a material fundamentally governs its spin transport properties. While unconventional spin transport phenomena have been predominantly explored in low-symmetry systems (e.g., $C_{1v}$ symmetry), high-symmetry crystals--which constitute the majority of industry-compatible materials--are generally expected to exhibit only conventional spin-transport behavior. Here, we report the coexistence of two unconventional spin transport effects, the crystal spin-orbit torque (CSOT) and the crystal in-plane Hall effect (CIHE), in a CoPt single ferromagnetic layer with $C_{3v}$ symmetry. Leveraging the CSOT, we achieve nearly 100% field-free perpendicular magnetization switching in a 6 nm CoPt layer at room temperature. Simultaneously, the CIHE observed in this material exhibits nearly identical dependencies on both current angle and growth temperature as the CSOT. Symmetry analysis confirms that both effects share a common physical origin. Our work not only establishes CoPt as a high-performance spin-orbit material, but also demonstrates that unconventional spin transport can be realized in high-symmetry systems, thereby opening a broad pathway for their application in practical spintronics. △ Less

Submitted 21 November, 2025; originally announced November 2025.

Investigating the relationship between the Weyl semimetal phase and the three-dimensional quantum Hall phase in ZrTe$_5$

Authors: Jiahao Chen, Yu Cao, Hong Du, Yuanze Li, Ruidan Zhong, Tian Liang

Abstract: The material ZrTe$_5$ exhibits distinct topological phases, including a Weyl semimetal phase, characterized by a chiral anomaly and in-plane Hall effect, and a three-dimensional quantum Hall phase. The relationship between these phases remains poorly understood. This work systematically explores their connection in ZrTe$_5$ through rotatable, pressure-dependent measurements. At ambient pressure, b… ▽ More The material ZrTe$_5$ exhibits distinct topological phases, including a Weyl semimetal phase, characterized by a chiral anomaly and in-plane Hall effect, and a three-dimensional quantum Hall phase. The relationship between these phases remains poorly understood. This work systematically explores their connection in ZrTe$_5$ through rotatable, pressure-dependent measurements. At ambient pressure, both phases are observed; the WSM phase requires strong electronic polarization, while the 3D QH phase appears when the characteristic resistivity peak temperature $T_p$ is approximately 90 K. Under applied pressure, the polarization diminishes, weakening the WSM phase and its associated nontrivial Hall signals. Concurrently, $T_p$ rises dramatically from 2 K at ambient pressure to 70 K at 2.2 GPa, approaching the expected regime for the 3D QH phase. These findings clarify the conditions underlying the WSM and 3D QH phases and suggest that exploring the 3D QH phase at even higher pressures is a promising direction for future research. △ Less

Submitted 14 October, 2025; originally announced October 2025.

Comments: 13 pages, 4 figures

Disorder-induced spin excitation continuum and spin-glass ground state in the inverse spinel CuGa$_2$O$_4$

Authors: Zhentao Huang, Zhijun Xu, Shuaiwei Li, Qingchen Duan, Junbo Liao, Song Bao, Yanyan Shangguan, Bo Zhang, Hao Xu, Shufan Cheng, Zihang Song, Shuai Dong, Maofeng Wu, M. B. Stone, Yiming Qiu, Ruidan Zhong, Guangyong Xu, Zhen Ma, G. D. Gu, J. M. Tranquada, Jinsheng Wen

Abstract: Spinel-structured compounds serve as prototypical examples of highly frustrated systems, and are promising candidates for realizing the long-sought quantum spin liquid (QSL) state. However, structural disorder is inevitable in many real QSL candidates and its impact remains a topic of intense debate. In this work, we conduct comprehensive investigations on CuGa$_2$O$_4$, a spinel compound with sig… ▽ More Spinel-structured compounds serve as prototypical examples of highly frustrated systems, and are promising candidates for realizing the long-sought quantum spin liquid (QSL) state. However, structural disorder is inevitable in many real QSL candidates and its impact remains a topic of intense debate. In this work, we conduct comprehensive investigations on CuGa$_2$O$_4$, a spinel compound with significant structural disorder, focusing on its thermodynamic properties and spectroscopic behaviors. No long-range magnetic order is observed down to $\sim$80 mK, as evidenced by magnetic susceptibility, specific heat and elastic neutron scattering measurements. More intriguingly, inelastic neutron scattering experiments reveal a broad gapless continuum of magnetic excitations around the Brillouin zone boundary, resembling the magnetic excitation spectra expected for a QSL. Nevertheless, a spin-freezing transition at $T_{\rm{f}} \approx $ 0.88 K is identified from the cusp in the dc susceptibility curves, where a bifurcation between zero-field-cooling and field-cooling curves occurs. Furthermore, ac susceptibility measurements show a peak close to $T_{\rm{f}}$ at low frequency, which shifts to higher temperature with increasing frequency. These results are evident that CuGa$_2$O$_4$ has spin-glass ground state, consistent with the establishment of short-range order inferred from the specific heat measurements. Collectively, these results illustrate the crucial role of disorder in defining the excitation spectrum out of the disordered ground state. Our findings shed light onto the broader class of AB$_2$O$_4$ spinels and advance our understanding of the spin dynamics in magnetically disordered systems. △ Less

Submitted 17 July, 2025; originally announced July 2025.

Comments: Published in PRB, 11 pages, 5 figures

Journal ref: Phys. Rev. B 112, 035128 (2025)

Direct evidence of light-induced phase-fluctuations in cuprates via time-resolved ARPES

Authors: D. Armanno, F. Goto, J. -M. Parent, S. Lapointe, A. Longa, R. D. Zhong, J. Schneeloch, G. D. Gu, G. Jargot, H. Ibrahim, F. Legare, B. J. Siwick, N. Gauthier, F. Boschini

Abstract: Phase fluctuations are widely accepted to play a primary role in the quench of the long-range superconducting order in cuprates. However, an experimental probe capable of unambiguously assessing their impact on the superconducting order parameter with momentum and time resolutions is still lacking. Here, we performed a high-resolution time- and angle-resolved photoemission study of optimally-doped… ▽ More Phase fluctuations are widely accepted to play a primary role in the quench of the long-range superconducting order in cuprates. However, an experimental probe capable of unambiguously assessing their impact on the superconducting order parameter with momentum and time resolutions is still lacking. Here, we performed a high-resolution time- and angle-resolved photoemission study of optimally-doped Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ and demonstrated a new experimental strategy to directly probe light-induced changes in the order parameter's phase with momentum resolution. To do this, we tracked the ultrafast response of a phase-sensitive hybridization gap that appears at the crossing between two bands with opposite superconducting gap signs. Supported by theoretical modeling, we established phase fluctuations as the dominant factor defining the non-thermal response of the unconventional superconducting phase in cuprates. △ Less

Submitted 6 May, 2025; originally announced May 2025.

Magnetically disordered ground state in the triangular-lattice antiferromagnets Rb$_3$Yb(VO$_4$)$_2$ and Cs$_3$Yb(VO$_4$)$_2$

Authors: Zhen Ma, Yingqi Chen, Zhongtuo Fu, Shuaiwei Li, Xin-An Tong, Hong Du, Jan Peter Embs, Shuhan Zheng, Yongjun Zhang, Meifeng Liu, Ruidan Zhong, Jun-Ming Liu, Jinsheng Wen

Abstract: Quantum spin liquids~(QSLs) represent a unique quantum disordered state of matter that hosts long-range quantum entanglement and fractional excitations. However, structural disorder resulting from site mixing between different types of ions usually arises in real QSL candidates, which is considered as an obstacle to gain the insight into the intrinsic physics. Here, we have synthesized two new rar… ▽ More Quantum spin liquids~(QSLs) represent a unique quantum disordered state of matter that hosts long-range quantum entanglement and fractional excitations. However, structural disorder resulting from site mixing between different types of ions usually arises in real QSL candidates, which is considered as an obstacle to gain the insight into the intrinsic physics. Here, we have synthesized two new rare-earth compounds Rb$_3$Yb(VO$_4$)$_2$ and Cs$_3$Yb(VO$_4$)$_2$. X-ray diffractions reveal a perfect triangular-lattice structure with no detectable disorder. Magnetic susceptibility measurements do not capture any phase transition or spin freezing down to 1.8~K. A fit to low-temperature data indicates dominant antiferromagnetic interactions with the Curie-Weiss temperature of -1.40~K and -0.43~K for Rb$_3$Yb(VO$_4$)$_2$ and Cs$_3$Yb(VO$_4$)$_2$, respectively. Specific heat results show no sign of long-range magnetic order down to $\sim$0.1~K either, but only a Schottky anomaly that is continuously mediated by the external magnetic fields. Additionally, inelastic neutron scattering is employed to detect low-energy spin excitations in Rb$_3$Yb(VO$_4$)$_2$. The absence of magnetic excitation signals as well as static magnetic order down to 97~mK aligns with the results from magnetic susceptibility and specific heat. Collectively, these findings point to a quantum disordered ground state with persistent spin dynamics, reminiscent of QSL behaviors. Our work provides a promising platform for further exploration of quantum magnetism in this new disorder-free system. △ Less

Submitted 24 April, 2025; originally announced April 2025.

Comments: 11 pages, 5 figures

Journal ref: Phys. Rev. B 111, 155141 (2025)

Superconductivity and Electron Correlations in Kagome Metal LuOs3B2

Authors: Yusen Xiao, Qingchen Duan, Tao Jia, Yajing Cui, Shaohua Liu, Zhiwei Wen, Liangwen Ji, Ruidan Zhong, Yongliang Chen, Yong Zhao

Abstract: We report a comprehensive investigation of the physical properties of LuOs3B2, characterized by an ideal Os-based kagome lattice. Resistivity and magnetization measurements confirm the emergence of type-II bulk superconductivity with a critical temperature Tc=4.63 K. The specific heat jump and the calculated electron-phonon coupling parameter support a moderately coupled superconducting state. Ele… ▽ More We report a comprehensive investigation of the physical properties of LuOs3B2, characterized by an ideal Os-based kagome lattice. Resistivity and magnetization measurements confirm the emergence of type-II bulk superconductivity with a critical temperature Tc=4.63 K. The specific heat jump and the calculated electron-phonon coupling parameter support a moderately coupled superconducting state. Electron correlation effects are supported by the enhanced Wilson ratios. First-principles calculations reveal hallmark features of kagome band structure, including Dirac points, van Hove singularities, and quasi-flat bands, primarily derived from the Os d orbitals. The inclusion of spin-orbit coupling opens a gap at the Dirac points, significantly altering the electronic properties. Furthermore, the superconductivity and electronic properties of isomorphic compounds are discussed. This work provides a thorough exploration of the superconducting and normal states of LuOs3B2, deepening the understanding of kagome superconductors. △ Less

Submitted 31 March, 2026; v1 submitted 23 April, 2025; originally announced April 2025.

Comments: DOI: https://doi.org/10.1103/PhysRevB.111.195132

Report number: Phys. Rev. B 111, 195132

Journal ref: Physical Review B 2025

Evidence of competing ground states between fractional Chern insulator and antiferromagnetism in moiré MoTe2

Authors: Xumin Chang, Feng Liu, Fan Xu, Cheng Xu, Jiayong Xiao, Zheng Sun, Pengfei Jiao, Yixin Zhang, Shaozheng Wang, Bohan Shen, Renjie He, Kenji Watanabe, Takashi Taniguchi, Ruidan Zhong, Jinfeng Jia, Zhiwen Shi, Xiaoxue Liu, Yang Zhang, Dong Qian, Tingxin Li, Shengwei Jiang

Abstract: Two-dimensional moire materials present unprecedented opportunities to explore quantum phases of matter arising from the interplay of band topology and strong correlations.One of the most striking examples is the recent observation of fractional quantum anomalous Hall (FQAH) effect in twisted bilayer MoTe$_2$ (tMoTe2) with relatively large twist angles(~3.7deg-3.9deg). The electronic ground states… ▽ More Two-dimensional moire materials present unprecedented opportunities to explore quantum phases of matter arising from the interplay of band topology and strong correlations.One of the most striking examples is the recent observation of fractional quantum anomalous Hall (FQAH) effect in twisted bilayer MoTe$_2$ (tMoTe2) with relatively large twist angles(~3.7deg-3.9deg). The electronic ground states are usually expected to be sensitive to the twist angle, as the twist angle determines the electron bandwidth and correlation strength in the moire system. Here, we report the observation of unexpected competing magnetic ground states in tMoTe2 moire superlattice, on which balance can be tipped by both twist angle and electric field (E). Specifically, we observed anomalous antiferromagnetic (AFM) ground states with zero Hall resistance at both v_h=1 and 2/3, at intermediate twist angles ~3deg. The AFM orders are suppressed by applying vertical E, and emergent ferromagnetism accompanied by integer Chern insulator (ICI) or fractional Chern insulator (FCI) states are observed near the critical E (E_c) of moire superlattice symmetry transition. Our results demonstrate tMoTe2 as a fascinating platform for exploring unexpected correlated phases with nontrivial topology and fractional excitations and point to electric-field-controlled ultralow-power spin-valleytronic devices. △ Less

Submitted 15 May, 2025; v1 submitted 17 March, 2025; originally announced March 2025.

Zeeman split Kramers doublets in spin-supersolid candidate Na$_{2}$BaCo(PO$_{4}$)$_{2}$

Authors: T. I. Popescu, N. Gora, F. Demmel, Z. Xu, R. Zhong, T. J. Williams, R. J. Cava, G. Xu, C. Stock

Abstract: Na$_{2}$BaCo(PO$_{4}$)$_{2}$ is a triangular antiferromagnet that displays highly efficient adiabatic demagnetization cooling (J. Xiang $\textit{et al.}$ Nature ${\bf{625}}$, 270 (2024)) near a quantum critical point at $μ_{0}H_{c}\sim 1.6$ T, separating a low-field magnetically disordered from a high-field fully polarized ferromagnetic phase. We apply high resolution backscattering neutron spectr… ▽ More Na$_{2}$BaCo(PO$_{4}$)$_{2}$ is a triangular antiferromagnet that displays highly efficient adiabatic demagnetization cooling (J. Xiang $\textit{et al.}$ Nature ${\bf{625}}$, 270 (2024)) near a quantum critical point at $μ_{0}H_{c}\sim 1.6$ T, separating a low-field magnetically disordered from a high-field fully polarized ferromagnetic phase. We apply high resolution backscattering neutron spectroscopy in an applied field to study the magnetic excitations near $μ_{0}H_{c}$. At large fields we observe ferromagnetic fluctuations that gradually transition to being overdamped in energy below $μ_{0}H_{c}$ where the magnetism is spatially disordered. We parameterize the excitations in the high field polarized phase in terms of coupled Zeeman split Kramers doublets originating from the presence of spin-orbit coupling. On reducing the field, the splitting between the Kramers doublets is reduced and if done adiabatically, provides a mechanism for reducing temperature. On lowering the applied field through the $μ_{0}H_{c}$ the excitations characterize a textured phase that we suggest is inefficient for cooling. Low temperature disordered frustrated magnets built on Kramers doublets with nearby quantum critical points provide a route for efficient magnetocalorics. △ Less

Submitted 1 March, 2025; originally announced March 2025.

Comments: (main text - 5 pages, 4 figures; supplementary information - 7 pages, 7 figures, to be published in Physical Review Letters)

Journal ref: Phys. Rev. Lett. 134, 136703 (2025)

Kagome Metal GdNb$_6$Sn$_6$: A 4d Playground for Topological Magnetism and Electron Correlations

Authors: Yusen Xiao, Qingchen Duan, Zhaoyi Li, Shu Guo, Hengxin Tan, Ruidan Zhong

Abstract: Magnetic kagome metals have garnered considerable attention as an ideal platform for investigating intrinsic topological structures, frustrated magnetism, and electron correlation effects. In this work, we present the synthesis and detailed characterization of GdNb$_6$Sn$_6$, a metal that features a niobium-based kagome lattice and a frustrated triangular gadolinium network. The compound adopts th… ▽ More Magnetic kagome metals have garnered considerable attention as an ideal platform for investigating intrinsic topological structures, frustrated magnetism, and electron correlation effects. In this work, we present the synthesis and detailed characterization of GdNb$_6$Sn$_6$, a metal that features a niobium-based kagome lattice and a frustrated triangular gadolinium network. The compound adopts the HfFe$_6$Ge$_6$-type crystal structure, with lattice parameters of a = b = 5.765(4) Å and c = 9.536(8) Å. Magnetic susceptibility and specific heat measurements reveal a magnetic transition near 2.3 K. Electrical transport data confirm metallic behavior, unsaturated positive magnetoresistance, and a hole-dominated multiband Hall effect. Furthermore, first-principles calculations indicate that Nb-4d orbitals predominantly contribute to the electronic states near the Fermi energy, with the band structure showing multiple topologically nontrivial crossings around the Fermi surface. This study also compares GdNb$_6$Sn$_6$ with GdV$_6$Sn$_6$, highlighting their similarities and differences. Our findings pave the way for exploring RNb$_6$Sn$_6$ (R = rare earth) with customized substitutions of R sites to fine-tune their properties. △ Less

Submitted 1 January, 2025; originally announced January 2025.

Comments: 7 pages, 7 figures

Topological surface state dominated nonlinear transverse response and microwave rectification at room temperature

Authors: Qia Shen, Jiaxin Chen, Bin Rong, Yaqi Rong, Hongliang Chen, Tieyang Zhao, Xianfa Duan, Dandan Guan, Shiyong Wang, Yaoyi Li, Hao Zheng, Xiaoxue Liu, Xuepeng Qiu, Jingsheng Chen, Longqing Cong, Tingxin Li, Ruidan Zhong, Canhua Liu, Yumeng Yang, Liang Liu, Jinfeng Jia

Abstract: Nonlinear Hall effect (NLHE) offers a novel means of uncovering symmetry and topological properties in quantum materials, holding promise for exotic (opto)electronic applications such as microwave rectification and THz detection. The BCD-independent NLHE could exhibit a robust response even at room temperature, which is highly desirable for practical applications. However, in materials with bulk i… ▽ More Nonlinear Hall effect (NLHE) offers a novel means of uncovering symmetry and topological properties in quantum materials, holding promise for exotic (opto)electronic applications such as microwave rectification and THz detection. The BCD-independent NLHE could exhibit a robust response even at room temperature, which is highly desirable for practical applications. However, in materials with bulk inversion symmetry, the coexistence of bulk and surface conducting channels often leads to a suppressed NLHE and complex thickness-dependent behavior. Here, we report the observation of room-temperature nonlinear transverse response in 3D topological insulator Bi2Te3 thin films, whose electrical transport properties are dominated by topological surface state (TSS). By varying the thickness of Bi2Te3 epitaxial films from 7 nm to 50 nm, we found that the nonlinear transverse response increases with thickness from 7 nm to 25 nm and remains almost constant above 25 nm. This is consistent with the thickness-dependent basic transport properties, including conductance, carrier density, and mobility, indicating a pure and robust TSS-dominated linear and nonlinear transport in thick (>25 nm) Bi2Te3 films. The weaker nonlinear transverse response in Bi2Te3 below 25 nm was attributed to Te deficiency and poorer crystallinity. By utilizing the TSS-dominated electrical second harmonic generation, we successfully achieved the microwave rectification from 0.01 to 16.6 GHz in 30 nm and bulk Bi2Te3. Our work demonstrated the room temperature nonlinear transverse response in a paradigm topological insulator, addressing the tunability of the topological second harmonic response by thickness engineering. △ Less

Submitted 29 October, 2024; originally announced October 2024.

Magnetization dependent anisotropic topological properties in EuCuP

Authors: Jian Yuan, Xianbiao Shi, Hong Du, Xia Wang, Jinguang Cheng, Baotian Wang, Ruidan Zhong, Shihao Zhang, Yanfeng Guo

Abstract: The correlation between magnetism and nontrivial topological band structure serves as a unique venue for discovering exotic topological properties. Combining magnetotransport measurements and first-principles calculations, we unveil herein that the hexagonal EuCuP holds topologically trivial state in the paramagnetic structure, while strong magnetization dependent anisotropic topological states in… ▽ More The correlation between magnetism and nontrivial topological band structure serves as a unique venue for discovering exotic topological properties. Combining magnetotransport measurements and first-principles calculations, we unveil herein that the hexagonal EuCuP holds topologically trivial state in the paramagnetic structure, while strong magnetization dependent anisotropic topological states in the spin-polarization structures. Specifically, it hosts a trivial topological state in the in-plane spin-polarization structure, while a Weyl semimetal state in the out-of-plane spin-polarization structure. Our scaling analysis suggests that the intrinsic Berry curvature in the spin-polarization structures can account for the observed large anisotropic anomalous Hall effect. First-principles calculations show that the magnetization and the spin-orbit coupling simultaneously play essential roles for the appearance of the four pairs of Weyl points in the out-of-plane spin-polarization structure. Our work therefore establishes in EuCuP the intimate relation between magnetism and the nontrivial topological states, which would be instructive for future study on this key issue of topological physics. △ Less

Submitted 16 September, 2024; originally announced September 2024.

Comments: 15 papes, 5 figures and 2 tables

Journal ref: Physical Review Materials, 2024

Scaling behavior and giant field-enhancement of the thermal conductivity in the honeycomb antiferromagnet BaCo2(AsO4)2

Authors: Jiayi Hu, Ruidan Zhong, Peter Czajka, Tong Gao, R. J Cava, N. P. Ong

Abstract: The layered honeycomb material BaCo$_2$(AsO$_4$)$_2$ (BCAO) is of topical interest because its magnetic state is related to that of the Kitaev magnet $α$-RuCl$_3$. Using thermal transport to probe how magnetic excitations interact with phonons in the magnetically disordered regime, we have uncovered an unusually large enhancement of the thermal conductivity $κ_{xx}$ in an in-plane magnetic field… ▽ More The layered honeycomb material BaCo$_2$(AsO$_4$)$_2$ (BCAO) is of topical interest because its magnetic state is related to that of the Kitaev magnet $α$-RuCl$_3$. Using thermal transport to probe how magnetic excitations interact with phonons in the magnetically disordered regime, we have uncovered an unusually large enhancement of the thermal conductivity $κ_{xx}$ in an in-plane magnetic field ${\bf H}$. Just above the Néel temperature $T_{\rm N}$, a field of 13 T increases $κ_{xx}$ by a factor $\sim 211$, much larger than reported previously in any magnetic insulator. Interestingly, $κ_{xx}(H,T)$ exhibits a scaling behavior in the entire magnetically disordered region that surrounds the ordered zigzag state. The ratio $Δκ_{xx}(H,T)/κ_{xx}(13,T)$, measured throughout the disordered region, collapses to a one-parameter scaling function ${\rm exp}(-1/gx)$ (where $x = μ_{\rm B}B/k_{\rm B}T$ and $g$ is a constant). △ Less

Submitted 24 October, 2024; v1 submitted 1 August, 2024; originally announced August 2024.

Comments: 8 pages, 4 figures

Journal ref: Physical Review Materials, 9 (2025) L061401

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

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

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

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

Spinons in a new Shastry-Sutherland lattice magnet Pr$_2$Ga$_2$BeO$_7$

Authors: N. Li, A. Brassington, M. F. Shu, Y. Y. Wang, H. Liang, Q. J. Li, X. Zhao, P. J. Baker, H. Kikuchi, T. Masuda, G. Duan, C. Liu, H. Wang, W. Xie, R. Zhong, J. Ma, R. Yu, H. D. Zhou, X. F. Sun

Abstract: Identifying the elusive spinon excitations in quantum spin liquid (QSL) materials is what scientists have long sought for. Recently, thermal conductivity ($κ$) has emerged to be a decisive probe because the fermionic nature of spinons leads to a characteristic nonzero linear $κ_0/T$ term while approaching zero Kelvin. So far, only a few systems have been reported to exhibit such term. Here, we rep… ▽ More Identifying the elusive spinon excitations in quantum spin liquid (QSL) materials is what scientists have long sought for. Recently, thermal conductivity ($κ$) has emerged to be a decisive probe because the fermionic nature of spinons leads to a characteristic nonzero linear $κ_0/T$ term while approaching zero Kelvin. So far, only a few systems have been reported to exhibit such term. Here, we report a $κ_0/T \approx$ 0.01 WK$^{-2}$m$^{-1}$, the largest $κ_0/T$ value ever observed in magnetic oxide QSL candidates, in a new quantum magnet Pr$_2$Ga$_2$BeO$_7$ with a Shastry-Sutherland lattice (SSL). Its QSL nature is further supported by the power-law temperature dependence of the specific heat, a plateau of muon spin relaxation rate, and gapless inelastic neutron spectra. Our theoretical analysis reveals that the introduction of XY spin anisotropy is the key for Pr$_2$Ga$_2$BeO$_7$ to be the first QSL realized on the SSL, after more than four decades of extensive studies on this celebrated magnetically frustrated lattice. △ Less

Submitted 22 May, 2024; originally announced May 2024.

Comments: 20 pages, 6 figures, with Supplementary Information

Possible gapless quantum spin liquid behavior in the triangular-lattice Ising antiferromagnet PrMgAl$_{11}$O$_{19}$

Authors: Zhen Ma, Shuhan Zheng, Yingqi Chen, Ruokai Xu, Zhao-Yang Dong, Jinghui Wang, Hong Du, Jan Peter Embs, Shuaiwei Li, Yao Li, Yongjun Zhang, Meifeng Liu, Ruidan Zhong, Jun-Ming Liu, Jinsheng Wen

Abstract: Quantum spin liquids (QSLs) represent a novel state where spins are highly entangled but do not order even at zero temperature due to strong quantum fluctuations. Such a state is mostly studied in Heisenberg models defined on geometrically frustrated lattices. Here, we turn to a new triangular-lattice antiferromagnet PrMgAl$_{11}$O$_{19}$, in which the interactions are believed to be of Ising type… ▽ More Quantum spin liquids (QSLs) represent a novel state where spins are highly entangled but do not order even at zero temperature due to strong quantum fluctuations. Such a state is mostly studied in Heisenberg models defined on geometrically frustrated lattices. Here, we turn to a new triangular-lattice antiferromagnet PrMgAl$_{11}$O$_{19}$, in which the interactions are believed to be of Ising type. Magnetic susceptibility measured with an external field along the $c$ axis is two orders of magnitude larger than that with a field in the $ab$ plane, displaying an ideal easy-axis behavior. Meanwhile, there is no magnetic phase transition or spin freezing observed down to 1.8 K. Ultralow-temperature specific heat measured down to 50 mK does not capture any phase transition either, but a hump at 4.5 K, below which the magnetic specific heat exhibits a quasi-quadratic temperature dependence that is consistent with a Dirac QSL state. Inelastic neutron scattering technique is also employed to elucidate the nature of its ground state. In the magnetic excitation spectra, there is a gapless broad continuum at the base temperature 55~mK, in favor of the realization of a gapless QSL. Our results provide a scarce example for the QSL behaviors observed in an Ising-type magnet, which can serve as a promising platform for future research on QSL physics based on an Ising model. △ Less

Submitted 24 April, 2024; originally announced April 2024.

Comments: 11 pages, 5 figures

Journal ref: Phys. Rev. B 109, 165143 (2024)

Comparative Raman Scattering Study of Crystal Field Excitations in Co-based Quantum Magnets

Authors: Banasree S. Mou, Xinshu Zhang, Li Xiang, Yuanyuan Xu, Ruidan Zhong, Robert J. Cava, Haidong Zhou, Zhigang Jiang, Dmitry Smirnov, Natalia Drichko, Stephen M. Winter

Abstract: Co-based materials have recently been explored due to potential to realise complex bond-dependent anisotropic magnetism. Prominent examples include Na$_2$Co$_2$TeO$_6$, BaCo$_2$(AsO$_4$)$_2$, Na$_2$BaCo(PO$_4$)$_2$, and CoX$_2$ (X = Cl, Br, I). In order to provide insight into the magnetic interactions in these compounds, we make a comparative analysis of their local crystal electric field excitat… ▽ More Co-based materials have recently been explored due to potential to realise complex bond-dependent anisotropic magnetism. Prominent examples include Na$_2$Co$_2$TeO$_6$, BaCo$_2$(AsO$_4$)$_2$, Na$_2$BaCo(PO$_4$)$_2$, and CoX$_2$ (X = Cl, Br, I). In order to provide insight into the magnetic interactions in these compounds, we make a comparative analysis of their local crystal electric field excitations spectra via Raman scattering measurements. Combining these measurements with theoretical analysis confirms the validity of $j_{\rm eff} = 1/2$ single-ion ground states for all compounds, and provides accurate experimental estimates of the local crystal distortions, which play a prominent role in the magnetic couplings between spin-orbital coupled Co moments. △ Less

Submitted 18 March, 2024; originally announced March 2024.

Comments: 11 pages, 7 figures

Crystal structure, properties and pressure-induced insulator-metal transition in layered kagome chalcogenides

Authors: Hong Du, Yu Zheng, Cuiying Pei, Chi-Ming Yim, Yanpeng Qi, Ruidan Zhong

Abstract: Layered materials with kagome lattice have attracted a lot of attention due to the presence of nontrivial topological bands and correlated electronic states with tunability. In this work, we investigate a unique van der Waals (vdW) material system, $A_{2}M_{3}X_{4}$ ($A$ = K, Rb, Cs; $M$ = Ni, Pd; $X$ = S, Se), where transition metal kagome lattices, chalcogen honeycomb lattices and alkali metal t… ▽ More Layered materials with kagome lattice have attracted a lot of attention due to the presence of nontrivial topological bands and correlated electronic states with tunability. In this work, we investigate a unique van der Waals (vdW) material system, $A_{2}M_{3}X_{4}$ ($A$ = K, Rb, Cs; $M$ = Ni, Pd; $X$ = S, Se), where transition metal kagome lattices, chalcogen honeycomb lattices and alkali metal triangular lattices coexist simultaneously. A notable feature of this material is that each Ni/Pd atom is positioned in the center of four chalcogen atoms, forming a local square-planar environment. This crystal field environment results in a low spin state $S$ = 0 of Ni$^{2+}$/Pd$^{2+}$. A systematic study of the crystal growth, crystal structure, magnetic and transport properties of two representative compounds, Rb$_{2}$Ni$_{3}$S$_{4}$ and Cs$_{2}$Ni$_{3}$Se$_{4}$, has been carried out on powder and single crystal samples. Both compounds exhibit nonmagnetic $p$-type semiconducting behavior, closely related to the particular chemical environment of Ni$^{2+}$ ions and the alkali metal intercalated vdW structure. Additionally, Cs$_{2}$Ni$_{3}$Se$_{4}$ undergoes an insulator-metal transition (IMT) in transport measurements under pressure up to 87.10 GPa without any structural phase transition, while Rb$_{2}$Ni$_{3}$S$_{4}$ persists in its semiconducting behavior. △ Less

Submitted 10 June, 2024; v1 submitted 7 March, 2024; originally announced March 2024.

Comments: 9 pages, 6 figures

Journal ref: J. Phys. Condens. Matter 36, 365702 (2024)

Spatially Dependent in-Gap States Induced by Andreev Tunneling through a Single Electronic State

Authors: Ruixia Zhong, Zhongzheng Yang, Qi Wang, Fanbang Zheng, Wenhui Li, Juefei Wu, Chenhaoping Wen, Xi Chen, Yanpeng Qi, Shichao Yan

Abstract: By using low-temperature scanning tunneling microscopy and spectroscopy (STM/STS), we observe in-gap states induced by Andreev tunneling through a single impurity state in a low carrier density superconductor (NaAlSi). The energy-symmetric in-gap states appear when the impurity state is located within the superconducting gap. In-gap states can cross the Fermi level, and they show X-shaped spatial… ▽ More By using low-temperature scanning tunneling microscopy and spectroscopy (STM/STS), we observe in-gap states induced by Andreev tunneling through a single impurity state in a low carrier density superconductor (NaAlSi). The energy-symmetric in-gap states appear when the impurity state is located within the superconducting gap. In-gap states can cross the Fermi level, and they show X-shaped spatial variation. We interpret the in-gap states as a consequence of the Andreev tunneling through the impurity state, which involves the formation or breakup of a Cooper pair. Due to the low carrier density in NaAlSi, the in-gap state is tunable by controlling the STM tip-sample distance. Under strong external magnetic fields, the impurity state shows Zeeman splitting when it is located near the Fermi level. Our findings not only demonstrate the Andreev tunneling involving single electronic state, but also provide new insights for understanding the spatially-dependent in-gap states in low carrier density superconductors. △ Less

Submitted 3 July, 2024; v1 submitted 4 March, 2024; originally announced March 2024.

Comments: 12 pages, 4 figures

Journal ref: Nano Letters 24, 8580 (2024)

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

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

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

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

Comments: 17 pages, 6 figures

Kink in cuprates: the role of the low-energy density of states

Authors: E. Razzoli, F. Boschini, M. Zonno, M. X. Na, M. Michiardi, M. Schneider, E. H. da Silva Neto, S. Gorovikov, R. D. Zhong, J. Schneeloch, G. D. Gu, S. Zhdanovich, A. K. Mills, G. Levy, D. J. Jones, C. Giannetti, A. Damascelli

Abstract: The 40-70 meV band-structure renormalization (so-called kink) in high-temperature cuprate superconductors - which has been mainly interpreted in terms of electron-boson coupling - is observed to be strongly suppressed both above the superconducting transition temperature and under optical excitation. We employ equilibrium and time- and angle-resolved photoemission spectroscopy, in combination with… ▽ More The 40-70 meV band-structure renormalization (so-called kink) in high-temperature cuprate superconductors - which has been mainly interpreted in terms of electron-boson coupling - is observed to be strongly suppressed both above the superconducting transition temperature and under optical excitation. We employ equilibrium and time- and angle-resolved photoemission spectroscopy, in combination with Migdal-Eliashberg simulations, to investigate the suppression of the near-nodal kink in Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$. We show that the $\sim$30$\%$ decrease of the kink strength across the superconducting-to-normal-state phase transition can be entirely accounted for by the filling of the superconducting gap, without additional consideration of temperature-dependent electron-boson coupling. Our findings demonstrate that consideration of changes in the density of states is essential to quantitatively account for the band structure renormalization effects in cuprates. △ Less

Submitted 8 December, 2023; originally announced December 2023.

Superconductivity and Charge-density-wave-like Transition in Th2Cu4As5

Authors: Qing-Chen Duan, Shao-Hua Liu, Bai-Zhuo Li, Jiao-Jiao Meng, Wu-Zhang Yang, Yi Liu, Yi-Qiang Lin, Si-Qi Wu, Jia-Yi Lu, Jin-Ke Bao, Yu-Sen Xiao, Xin-Yu Zhao, Yu-Xue Mei, Yu-Ping Sun, Dan Yu, Shu-Gang Tan, Qiang Jing, Rui-Dan Zhong, Yong-Liang Chen, Yong Zhao, Zhi Ren, Cao Wang, Guang-Han Cao

Abstract: We report the synthesis, crystal structure, and physical properties of a novel ternary compound, Th$_2$Cu$_4$As$_5$. The material crystallizes in a tetragonal structure with lattice parameters $a=4.0716(1)$ Å and $c=24.8131(4)$ Å. Its structure can be described as an alternating stacking of fluorite-type Th$_2$As$_2$ layers with antifluorite-type double-layered Cu$_4$As$_3$ slabs. The measurement… ▽ More We report the synthesis, crystal structure, and physical properties of a novel ternary compound, Th$_2$Cu$_4$As$_5$. The material crystallizes in a tetragonal structure with lattice parameters $a=4.0716(1)$ Å and $c=24.8131(4)$ Å. Its structure can be described as an alternating stacking of fluorite-type Th$_2$As$_2$ layers with antifluorite-type double-layered Cu$_4$As$_3$ slabs. The measurement of electrical resistivity, magnetic susceptibility and specific heat reveals that Th$_2$Cu$_4$As$_5$ undergoes bulk superconducting transition at 4.2 K. Moreover, all these physical quantities exhibit anomalies at 48 K, where the Hall coefficient change the sign. These findings suggest a charge-density-wave-like (CDW) transition, making Th$_2$Cu$_4$As$_5$ a rare example for studying the interplay between CDW and superconductivity. △ Less

Submitted 22 November, 2023; originally announced November 2023.

Comments: 11 pages, 6 figures, and 1 table

Observation of Chern insulator in crystalline ABCA-tetralayer graphene with spin-orbit coupling

Authors: Yating Sha, Jian Zheng, Kai Liu, Hong Du, Kenji Watanabe, Takashi Taniguchi, Jinfeng Jia, Zhiwen Shi, Ruidan Zhong, Guorui Chen

Abstract: Degeneracies in multilayer graphene, including spin, valley, and layer degrees of freedom, are susceptible to Coulomb interactions and can result into rich broken-symmetry states. In this work, we report a ferromagnetic state in charge neutral ABCA-tetralayer graphene driven by proximity-induced spin-orbit coupling from adjacent WSe2. The ferromagnetic state is further identified as a Chern insula… ▽ More Degeneracies in multilayer graphene, including spin, valley, and layer degrees of freedom, are susceptible to Coulomb interactions and can result into rich broken-symmetry states. In this work, we report a ferromagnetic state in charge neutral ABCA-tetralayer graphene driven by proximity-induced spin-orbit coupling from adjacent WSe2. The ferromagnetic state is further identified as a Chern insulator with Chern number of 4, and its Hall resistance reaches 78% and 100% quantization of h/4e2 at zero and 0.4 tesla, respectively. Three broken-symmetry insulating states, layer-antiferromagnet, Chern insulator and layer-polarized insulator and their transitions can be continuously tuned by the vertical displacement field. Remarkably, the magnetic order of the Chern insulator can be switched by three knobs, including magnetic field, electrical doping, and vertical displacement field. △ Less

Submitted 27 October, 2023; originally announced October 2023.

Detection of a two-phonon mode in a cuprate superconductor via polarimetric RIXS

Authors: Kirsty Scott, Elliot Kisiel, Flora Yakhou, Stefano Agrestini, Mirian Garcia-Fernandez, Kurt Kummer, Jaewon Choi, Ruidan Zhong, John A. Schneeloch, Genda D. Gu, Ke-Jin Zhou, Nicholas B. Brookes, Alexander F. Kemper, Matteo Minola, Fabio Boschini, Alex Frano, Adrian Gozar, Eduardo H. da Silva Neto

Abstract: Recent improvements in the energy resolution of resonant inelastic x-ray scattering experiments (RIXS) at the Cu-L$_3$ edge have enabled the study of lattice, spin, and charge excitations. Here, we report on the detection of a low intensity signal at 140meV, twice the energy of the bond-stretching (BS) phonon mode, in the cuprate superconductor… ▽ More Recent improvements in the energy resolution of resonant inelastic x-ray scattering experiments (RIXS) at the Cu-L$_3$ edge have enabled the study of lattice, spin, and charge excitations. Here, we report on the detection of a low intensity signal at 140meV, twice the energy of the bond-stretching (BS) phonon mode, in the cuprate superconductor $\textrm{Bi}_2\textrm{Sr}_2\textrm{Ca}\textrm{Cu}_2\textrm{O}_{8+x}$ (Bi-2212). Ultra-high resolution polarimetric RIXS measurements allow us to resolve the outgoing polarization of the signal and identify this feature as a two-phonon excitation. Further, we study the connection between the two-phonon mode and the BS one-phonon mode by constructing a joint density of states toy model that reproduces the key features of the data. △ Less

Submitted 27 September, 2023; originally announced September 2023.

Superconductivity in the cobalt-doped V3Si A15 intermetallic compound

Authors: Lingyong Zeng, Huawei Zhou, Hong Du, Ruidan Zhong, Ruixin Guo, Shu Guo, Wanzhen Su, Kuan Li, Chao Zhang, Peifeng Yu, Huixia Luo

Abstract: The A15 structure of superconductors is a prototypical type-II superconductor that has generated considerable interest since the early history of superconducting materials. This paper discusses the superconducting properties of previously unreported V3-xCoxSi alloys. It is found that the lattice parameter decreases with increasing cobalt-doped content and leads to an increased residual resistivity… ▽ More The A15 structure of superconductors is a prototypical type-II superconductor that has generated considerable interest since the early history of superconducting materials. This paper discusses the superconducting properties of previously unreported V3-xCoxSi alloys. It is found that the lattice parameter decreases with increasing cobalt-doped content and leads to an increased residual resistivity ratio (RRR) value of the V3-xCoxSi system. Meanwhile, the superconducting transition temperature (Tc) cobalt-doped content. Furthermore, the fitted data show that the increase of cobalt-doped content also reduces the lower/upper critical fields of the V3-xCoxSi system. Type-II superconductivity is demonstrated on all V3-xCoxSi samples. With higher Co-doped content, V3-xCoxSi alloys may have superconducting and structural phase transitions at low-temperature regions. As the electron/atom (e/a) ratio increases, the Tc variation trend of V3Si is as pronounced as in crystalline alloys and monotonically follows the trend observed for amorphous superconductors. △ Less

Submitted 20 September, 2023; originally announced September 2023.

Comments: 20 pages, 7 figures

Journal ref: Supercond. Sci. Technol.2023,36,035003

Superconductivity in the medium-entropy alloy TiVNbTa with a body-centered cubic structure

Authors: Kuan Li, Xunwu Hu, Ruixin Guo, Wenrui Jiang, Lingyong Zeng, Longfu Li, Peifeng Yu, Kangwang Wang, Chao Zhang, Shu Guo, Ruidan Zhong, Tao Xie, DaoXin Yao, Huixia Luo

Abstract: Here we report the TiVNbTa medium-entropy alloy (MEA) superconductor with the mixed 3d - 5d elements synthesized by an arc-melting method. The TiVNbTa material has a body-centered cubic structure. The superconducting properties of TiVNbTa were studied by resistivity, magnetic susceptibility, and specific heat measurements. The experimental results show that the bulk superconducting phase transitio… ▽ More Here we report the TiVNbTa medium-entropy alloy (MEA) superconductor with the mixed 3d - 5d elements synthesized by an arc-melting method. The TiVNbTa material has a body-centered cubic structure. The superconducting properties of TiVNbTa were studied by resistivity, magnetic susceptibility, and specific heat measurements. The experimental results show that the bulk superconducting phase transition temperature of TiVNbTa is about 4.65 K, and the upper and lower critical fields are 49.3(4) mT and 5.9(5) T, respectively, which indicates TiVNbTa is a type-II superconductor. First-principles calculations show that the d electrons of Ti, V, Nb, and Ta atoms play a significant role near the Fermi level. The results show TiVNbTa is a traditional s-wave superconductor. △ Less

Submitted 30 August, 2023; originally announced August 2023.

Comments: 20 pages, 7 figures

Journal ref: J.Phys.Chem.C 2023,127,16211-16218

Signatures of a gapless quantum spin liquid in the Kitaev material Na$_3$Co$_{2-x}$Zn$_x$SbO$_6$

Authors: Zhongtuo Fu, Ruokai Xu, Yingqi Chen, Song Bao, Hong Du, Jiahua Min, Shuhan Zheng, Yongjun Zhang, Meifeng Liu, Xiuzhang Wang, Hong Li, Ruidan Zhong, Huiqian Luo, Jun-Ming Liu, Zhen Ma, Jinsheng Wen

Abstract: The honeycomb-lattice cobaltate Na$_3$Co$_2$SbO$_6$ has recently been proposed to be a proximate Kitaev quantum spin liquid~(QSL) candidate. However, non-Kitaev terms in the Hamiltonian lead to a zigzag-type antiferromagnetic~(AFM) order at low temperatures. Here, we partially substitute magnetic Co$^{2+}$ with nonmagnetic Zn$^{2+}$ and investigate the chemical doping effect in tuning the magnetic… ▽ More The honeycomb-lattice cobaltate Na$_3$Co$_2$SbO$_6$ has recently been proposed to be a proximate Kitaev quantum spin liquid~(QSL) candidate. However, non-Kitaev terms in the Hamiltonian lead to a zigzag-type antiferromagnetic~(AFM) order at low temperatures. Here, we partially substitute magnetic Co$^{2+}$ with nonmagnetic Zn$^{2+}$ and investigate the chemical doping effect in tuning the magnetic ground states of Na$_3$Co$_{2-x}$Zn$_x$SbO$_6$. X-ray diffraction characterizations reveal no structural transition but quite tiny changes on the lattice parameters over our substitution range $0\leq x\leq0.4$. Magnetic susceptibility and specific heat results both show that AFM transition temperature is continuously suppressed with increasing Zn content $x$ and neither long-range magnetic order nor spin freezing is observed when $x\geq0.2$. More importantly, a linear term of the specific heat representing fermionic excitations is captured below 5~K in the magnetically disordered regime, as opposed to the $C_{\rm m}\propto T^3$ behavior expected for bosonic excitations in the AFM state. Based on the data above, we establish a magnetic phase diagram of Na$_3$Co$_{2-x}$Zn$_x$SbO$_6$. Our results indicate the presence of gapless fractional excitations in the samples with no magnetic order, evidencing a potential QSL state induced by doping in a Kitaev system. △ Less

Submitted 26 April, 2023; originally announced April 2023.

Comments: 10 pages, 5 figures

Journal ref: Phys. Rev. B 107, 165143 (2023)

Fe$_{1+y}$Te$_{x}$Se$_{1-x}$: a delicate and tunable Majorana material

Authors: Fazhi Yang, Giao Ngoc Phan, Renjie Zhang, Jin Zhao, Jiajun Li, Zouyouwei Lu, John Schneeloch, Ruidan Zhong, Mingwei Ma, Genda Gu, Xiaoli Dong, Tian Qian, Hong Ding

Abstract: We report the observation for the p$_{z}$ electron band and the band inversion in Fe$_{1+y}$Te$_{x}$Se$_{1-x}$ with angle-resolved photoemission spectroscopy. Furthermore, we found that excess Fe (y>0) inhibits the topological band inversion in Fe$_{1+y}$Te$_{x}$Se$_{1-x}$, which explains the absence of Majorana zero modes in previous reports for Fe$_{1+y}$Te$_{x}$Se$_{1-x}$ with excess Fe. Based… ▽ More We report the observation for the p$_{z}$ electron band and the band inversion in Fe$_{1+y}$Te$_{x}$Se$_{1-x}$ with angle-resolved photoemission spectroscopy. Furthermore, we found that excess Fe (y>0) inhibits the topological band inversion in Fe$_{1+y}$Te$_{x}$Se$_{1-x}$, which explains the absence of Majorana zero modes in previous reports for Fe$_{1+y}$Te$_{x}$Se$_{1-x}$ with excess Fe. Based on our analysis of different amounts of Te doping and excess Fe, we propose a delicate topological phase in this material. Thanks to this delicate phase, one may be able to tune the topological transition via applying lattice strain or carrier doping. △ Less

Submitted 20 February, 2023; originally announced February 2023.

Journal ref: Chinese Physics Letters 40 (1), 017401 (2023)

Low-energy quasi-circular electron correlations with charge order wavelength in $\textrm{Bi}_2\textrm{Sr}_2\textrm{Ca}\textrm{Cu}_2\textrm{O}_{8+δ}$

Authors: K. Scott, E. Kisiel, T. J. Boyle, R. Basak, G. Jargot, S. Das, S. Agrestini, M. Garcia-Fernandez, J. Choi, J. Pelliciari, J. Li, Y. D. Chuang, R. D. Zhong, J. A. Schneeloch, G. D. Gu, F. Légaré, A. F. Kemper, Ke-Jin Zhou, V. Bisogni, S. Blanco-Canosa, A. Frano, F. Boschini, E. H. da Silva Neto

Abstract: In the study of dynamic charge order correlations in the cuprates, most high energy-resolution resonant inelastic x-ray scattering (RIXS) measurements have focused on momenta along the high-symmetry directions of the copper oxide plane. However, electron scattering along other in-plane directions should not be neglected as they may contain information relevant, for example, to the origin of charge… ▽ More In the study of dynamic charge order correlations in the cuprates, most high energy-resolution resonant inelastic x-ray scattering (RIXS) measurements have focused on momenta along the high-symmetry directions of the copper oxide plane. However, electron scattering along other in-plane directions should not be neglected as they may contain information relevant, for example, to the origin of charge order correlations or to our understanding of the isotropic scattering responsible for strange metal behavior in cuprates. We report high-resolution resonant inelastic x-ray scattering (RIXS) experiments that reveal the presence of dynamic electron correlations over the $q_x$-$q_y$ scattering plane in underdoped $\textrm{Bi}_2\textrm{Sr}_2\textrm{Ca}\textrm{Cu}_2\textrm{O}_{8+δ}$ with $T_c=54$ K. We use the softening of the RIXS-measured bond stretching phonon line as a marker for the presence of charge-order-related dynamic electron correlations. The experiments show that these dynamic correlations exist at energies below approximately $70$ meV and are centered around a quasi-circular manifold in the $q_x$-$q_y$ scattering plane with radius equal to the magnitude of the charge order wave vector, $q_{CO}$. We also demonstrate how this phonon-tracking procedure provides the necessary experimental precision to rule out fluctuations of short-range directional charge order (i.e. centered around $[q_x=\pm q_{CO}, q_y=0]$ and $[q_x=0, q_y=\pm q_{CO}]$) as the origin of the observed correlations. △ Less

Submitted 19 January, 2023; originally announced January 2023.

Comments: Submitted and under review

Journal ref: Science Advances 9, eadg3710 (2023)

Real-space Observation of Unidirectional Charge Density Wave and Complex Structural Modulation in the Pnictide Superconductor Ba$_{1-x}$Sr$_x$Ni$_2$As$_2$

Authors: Tian Qin, Ruixia Zhong, Weizheng Cao, Shiwei Shen, Chenhaoping Wen, Yanpeng Qi, Shichao Yan

Abstract: Here we use low-temperature and variable-temperature scanning tunneling microscopy to study the pnictide superconductor, Ba$_{1-x}$Sr$_x$Ni$_2$As$_2$. In the low-temperature phase (triclinic phase) of BaNi$_2$As$_2$, we observe the unidirectional charge density wave (CDW) with $Q$ = 1/3 on both the Ba and NiAs surfaces. On the NiAs surface of the triclinic BaNi$_2$As$_2$, there are structural-modu… ▽ More Here we use low-temperature and variable-temperature scanning tunneling microscopy to study the pnictide superconductor, Ba$_{1-x}$Sr$_x$Ni$_2$As$_2$. In the low-temperature phase (triclinic phase) of BaNi$_2$As$_2$, we observe the unidirectional charge density wave (CDW) with $Q$ = 1/3 on both the Ba and NiAs surfaces. On the NiAs surface of the triclinic BaNi$_2$As$_2$, there are structural-modulation-induced chain-like superstructures with distinct periodicities. In the high-temperature phase (tetragonal phase) of BaNi$_2$As$_2$, the NiAs surface appears as the periodic 1 by 2 superstructure. Interestingly, in the triclinic phase of Ba$_{0.5}$Sr$_{0.5}$Ni$_2$As$_2$, the unidirectional CDW is suppressed on both the Ba/Sr and NiAs surfaces, and the Sr substitution stabilizes the periodic 1 by 2 superstructure on the NiAs surface, which enhance the superconductivity in Ba$_{0.5}$Sr$_{0.5}$Ni$_2$As$_2$. Our results provide important microscopic insights for the interplay among the unidirectional CDW, structural modulation, and superconductivity in this class of pnictide superconductors. △ Less

Submitted 30 March, 2023; v1 submitted 14 October, 2022; originally announced October 2022.

Comments: 15 pages, 4 figures

Journal ref: Nano Letters 23, 2958-2963 (2023)

Multimodal synchrotron X-ray diffraction across the superconducting transition of Sr$_{0.1}$Bi$_2$Se$_3$

Authors: M. P. Smylie, Z. Islam, G. D. Gu, J. Schneeloch, R. D. Zhong, S. Rosenkranz, W. -K. Kwok, U. Welp

Abstract: In the doped topological insulator Sr$_x$Bi$_2$Se$_3$, a pronounced in-plane two-fold symmetry is observed in electronic properties below the superconducting transition temperature $T_c \sim$ 3 K, despite the three-fold symmetry of the observed $R\bar{3}m$ space group. The axis of two-fold symmetry is nominally pinned to one of three rotational equivalent directions and crystallographic strain has… ▽ More In the doped topological insulator Sr$_x$Bi$_2$Se$_3$, a pronounced in-plane two-fold symmetry is observed in electronic properties below the superconducting transition temperature $T_c \sim$ 3 K, despite the three-fold symmetry of the observed $R\bar{3}m$ space group. The axis of two-fold symmetry is nominally pinned to one of three rotational equivalent directions and crystallographic strain has been proposed to be the origin of this pinning. We carried out multimodal synchrotron diffraction and resistivity measurements down to $\sim$0.68 K and in magnetic fields up to 45 kG on a single crystal of Sr$_{0.1}$Bi$_2$Se$_3$ to probe the effect of superconductivity on the crystallographic distortion. Our results indicate that there is no in-plane crystallographic distortion at the level of $1x10^{-5}$ associated with the superconducting transition. These results further support the model that the large two-fold in-plane anisotropy of superconducting properties of Sr$_x$Bi$_2$Sr$_3$ is not structural in origin but electronic, namely it is caused by a nematic superconducting order parameter of Eu symmetry. △ Less

Submitted 26 July, 2022; originally announced July 2022.

Comments: 7 pages, 6 figures

Enhanced low-energy magnetic excitations evidencing the Cu-induced localization in an Fe-based superconductor Fe$_{0.98}$Te$_{0.5}$Se$_{0.5}$

Authors: Jinghui Wang, Song Bao, Yanyan Shangguan, Zhengwei Cai, Yuan Gan, Shichao Li, Kejing Ran, Zhen Ma, B. L. Winn, A. D. Christianson, Ruidan Zhong, Jun Li, Genda Gu, Jinsheng Wen

Abstract: We have performed inelastic neutron scattering measurements on optimally-doped Fe$_{0.98}$Te$_{0.5}$Se$_{0.5}$ and 10% Cu-doped Fe$_{0.88}$Cu$_{0.1}$Te$_{0.5}$Se$_{0.5}$ to investigate the substitution effects on the spin excitations in the whole energy range up to 300 meV. It is found that substitution of Cu for Fe enhances the low-energy spin excitations ($\le$ 100 meV), especially around the (0… ▽ More We have performed inelastic neutron scattering measurements on optimally-doped Fe$_{0.98}$Te$_{0.5}$Se$_{0.5}$ and 10% Cu-doped Fe$_{0.88}$Cu$_{0.1}$Te$_{0.5}$Se$_{0.5}$ to investigate the substitution effects on the spin excitations in the whole energy range up to 300 meV. It is found that substitution of Cu for Fe enhances the low-energy spin excitations ($\le$ 100 meV), especially around the (0.5, 0.5) point, and leaves the high-energy magnetic excitations intact. In contrast to the expectation that Cu with spin 1/2 will dilute the magnetic moments contributed by Fe with a larger spin, we find that the 10% Cu doping enlarges the effective fluctuating moment from 2.85 to 3.13 $μ_{\rm B}$/Fe, although there is no long- or short-range magnetic order around (0.5, 0.5) and (0.5, 0). The presence of enhanced magnetic excitations in the 10% Cu doped sample which is in the insulating state indicates that the magnetic excitations must have some contributions from the local moments, reflecting the dual nature of the magnetism in iron-based superconductors. We attribute the substitution effects to the localization of the itinerant electrons induced by Cu dopants. These results also indicate that the Cu doping does not act as electron donor as in a rigid-band shift model, but more as scattering centers that localize the system. △ Less

Submitted 24 June, 2022; originally announced June 2022.

Comments: Published in PRB, 8 pages, 3 figures

Journal ref: Phys. Rev. B 105, 245129 (2022)

Geometrical frustration versus Kitaev interactions in BaCo$_2$(AsO$_4$)$_2$

Authors: Thomas Halloran, Félix Desrochers, Emily Z. Zhang, Tong Chen, Li Ern Chern, Zhijun Xu, Barry Winn, M. K. Graves-Brook, M. B. Stone, Alexander I. Kolesnikov, Yiming Qui, Ruidan Zhong, Robert Cava, Yong Baek Kim, Collin Broholm

Abstract: Recently, Co-based honeycomb magnets have been proposed as promising candidate materials to host the Kitaev spin liquid state. One of the front-runners is BaCo$_2$(AsO$_4$)$_2$ (BCAO), where it was suggested that the exchange processes between Co$^{2+}$ ions via the surrounding edge-sharing oxygen octahedra could give rise to bond-dependent Kitaev interactions. In this work, we present and analyze… ▽ More Recently, Co-based honeycomb magnets have been proposed as promising candidate materials to host the Kitaev spin liquid state. One of the front-runners is BaCo$_2$(AsO$_4$)$_2$ (BCAO), where it was suggested that the exchange processes between Co$^{2+}$ ions via the surrounding edge-sharing oxygen octahedra could give rise to bond-dependent Kitaev interactions. In this work, we present and analyze comprehensive inelastic neutron scattering studies of BCAO with fields in the honeycomb plane. Combining the constraints from the magnon excitations in the high-field polarized state and the inelastic spin structure factor measured in zero magnetic field, we examine two leading theoretical models: the Kitaev-type \JKG model and the \XXZ model. We show that the existing experimental data can be consistently accounted for by the \XXZ model but not by the \JKG model, and we discuss the implications of these results for the realization of a spin liquid phase in BCAO and more generally for the realization of the Kitaev model in cobaltates. △ Less

Submitted 30 May, 2022; originally announced May 2022.

Comments: 15 pages, 10 figures