Showing 1–50 of 219 results for author: Lue, C

Field-controlled breaking and restoration of parity-time symmetry in Josephson interference

Authors: Yi-Chen Tsai, Yung-Yeh Chang, Tao-Yi Hsu, Thomas Kuo, Chia-Nung Kuo, Chin-Shan Lue, Kuei-Lin Chiu, Chen-Hsuan Hsu, Chung-Ting Ke

Abstract: Symmetry plays a fundamental role in determining the phases and physical properties of quantum matter. Controlling symmetry in mesoscopic superconducting devices provides a route to reconfigure their phase-coherent transport. Here we demonstrate symmetry-selective Josephson interferometry in lateral NbTi/PtTe2/NbTi junctions by controlling the relative orientations of the current and magnetic fiel… ▽ More Symmetry plays a fundamental role in determining the phases and physical properties of quantum matter. Controlling symmetry in mesoscopic superconducting devices provides a route to reconfigure their phase-coherent transport. Here we demonstrate symmetry-selective Josephson interferometry in lateral NbTi/PtTe2/NbTi junctions by controlling the relative orientations of the current and magnetic field. From the supercurrent interference patterns, we construct a field-current symmetry map that identifies configurations exhibiting or violating the device-level parity (\mathcal{P}), time-reversal (\mathcal{T}) and their combined \mathcal{P}\mathcal{T} symmetry. In the absence of an in-plane field, the junction exhibits a symmetric Fraunhofer pattern. An in-plane field parallel to the current produces a pronounced side-lobe asymmetry, whereas reversing both the current and the complete magnetic-field configuration restores a generalized \mathcal{T} relation. Remarkably, orienting the in-plane field perpendicular to the current restores the \mathcal{P}\mathcal{T}-symmetric Fraunhofer response even at substantial field strengths. A microscopic model attributes this behavior to the interplay between disorder-induced potential variations and flux dipoles generated by in-plane-field Meissner focusing near the superconducting electrodes. Our results establish a reconfigurable Josephson interferometer in which the field-current geometry selects the symmetry operation being probed and switches the device between symmetry-broken and symmetry-restored interference states. △ Less

Submitted 17 August, 2026; originally announced August 2026.

Comments: Main text: 12 pages, 4 figures. Supplementary Information: 23 pages, 18 figures

Analytical Charge Density Profile of Vortex Core in Weak-Coupling Superconductor

Authors: Chi-Ken Lu

Abstract: Self-consistent Bogoliubov-de Gennes calculations have long shown that solving the Poisson equation inside a superconducting vortex turns a one-signed charge depletion into a modulation that alternates in sign with period $π/k_F$. We give an elementary account of that result. Taking the Caroli-de Gennes-Matricon bound states in a step-like gap, we show that the normalization of the bound-state spi… ▽ More Self-consistent Bogoliubov-de Gennes calculations have long shown that solving the Poisson equation inside a superconducting vortex turns a one-signed charge depletion into a modulation that alternates in sign with period $π/k_F$. We give an elementary account of that result. Taking the Caroli-de Gennes-Matricon bound states in a step-like gap, we show that the normalization of the bound-state spinor is nearly independent of angular momentum, which collapses the mode sum into closed form. Inside the core the vortex winding removes one Bessel channel from a completeness sum, so the density vanishes on the vortex line and carries Friedel-like oscillations of wavevector $2k_F$; outside it the sum gives a $1/r$ envelope decaying over a coherence length, with a residual ripple. The bound-state charge does not integrate to zero, so neutrality obliges the extended states to compensate it exactly. That compensation is complete at long wavelength but fails at the diameter of the Fermi circle, and what survives is a sign-alternating $2k_F$ modulation reduced only by $4k_F^2/(4k_F^2+k_{TF}^2)$, a factor lying between one-half and three-quarters for any metal. The oscillation is therefore not a delicate effect but a consequence of neutrality and the inefficiency of screening at large momentum transfer: in the screened total the smooth terms cancel and only the ripple is left. △ Less

Submitted 31 July, 2026; originally announced August 2026.

Orbital-Selective Diagonal-Gap Test of Pairing in La$_3$Ni$_2$O$_7$

Authors: Yu-Bo Liu, Zhi-Yan Shao, Zhiming Pan, Chen Lu, Fan Yang

Abstract: Recent angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy (STM) measurements on bilayer nickelate La$_3$Ni$_2$O$_7$ reveal a nearly isotropic, nodeless superconducting gap. We show that these single-particle spectra provide a symmetry-enforced test of the pairing nature. Mirror symmetry forces the hybridization between $d_{z^2}$ and $d_{x^2-y^2}$ orbitals to vanish… ▽ More Recent angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy (STM) measurements on bilayer nickelate La$_3$Ni$_2$O$_7$ reveal a nearly isotropic, nodeless superconducting gap. We show that these single-particle spectra provide a symmetry-enforced test of the pairing nature. Mirror symmetry forces the hybridization between $d_{z^2}$ and $d_{x^2-y^2}$ orbitals to vanish along the Brillouin-zone (BZ) diagonal. Consequently, the gaps on the diagonal portions of the $α/β$ and $γ$ Fermi pockets separately probe the intrinsic pairing strengths of the $d_{x^2-y^2}$ and $d_{z^2}$ sectors. A pairing state with pure or dominant intrinsic $d_{z^2}$-orbital pairing component produces nodes or near-nodes on the BZ diagonal of the $α/β$ pockets and is thus challenged by ARPES and STM, whereas the pairing state with dominant intrinsic $d_{x^2-y^2}$-orbital pairing component has a nearly isotropic, nodeless gap on all pockets which well fits ARPES and STM data. The dominant $d_{x^2-y^2}$-orbital pairing is compatible with Hund's-rule-driven pairing mechanisms. △ Less

Submitted 5 August, 2026; v1 submitted 28 June, 2026; originally announced June 2026.

Comments: 4.1 pages, 4 figures, with Appendix

Many-Body Non-Hermitian Physics in the Generalized Brillouin Zone

Authors: Chaoze Lu, Chuanshu Xu, Zhenghao Yang, Xiancong Lu

Abstract: The breakdown of conventional bulk-boundary correspondence (BBC) in non-Hermitian system can be resolved by the generalized Brillouin zone (GBZ) theory. However, extending the GBZ theory to interacting many-body systems remains an open problem. Here, we consider an interacting non-Hermitian model characterized by a circular GBZ. We show that, based on a GBZ transformation, a quasi-recipr… ▽ More The breakdown of conventional bulk-boundary correspondence (BBC) in non-Hermitian system can be resolved by the generalized Brillouin zone (GBZ) theory. However, extending the GBZ theory to interacting many-body systems remains an open problem. Here, we consider an interacting non-Hermitian model characterized by a circular GBZ. We show that, based on a GBZ transformation, a quasi-reciprocal many-body Hamiltonian can be constructed which, under periodic boundary conditions (PBC), captures the physics of the original non-Hermitian model under open boundary conditions (OBC). Using exact diagonalization (ED), we determine the phase diagram for the quasi-reciprocal many-body Hamiltonian by computing the Zak phase and the structure factor of the charge-density-wave (CDW) phase. We further investigate the entanglement properties and find that the degeneracy of the low-lying entanglement spectrum characterizes each phase in the phase diagram. These findings demonstrate that the topological properties in interacting non-Hermitian system is encoded in the entanglement spectrum of the quasi-reciprocal model. Our work establishes a route to studying many-body non-Hermitian physics within the GBZ formalism. △ Less

Submitted 2 June, 2026; originally announced June 2026.

Comments: 5 pages, 4 figures

Theory and Experiment of Chirality-induced Magnetic Nonreciprocity Manifested by Coupling Phase

Authors: Jiguang Yao, Ying Yang, Chenyang Lu, Lihua Zhong, Xiaolong Fan, Desheng Xue, C. -M. Hu

Abstract: Magnetic interactions have long served as the most robust and widely used approach for realizing nonreciprocity, with an externally applied magnetic field breaking time-reversal symmetry (TRS) and chiral photon-magnon interactions introducing spatial asymmetry. In this work, we investigate the chirality mechanisms essential for magnetic nonreciprocity from a unified experimental and theoretical pe… ▽ More Magnetic interactions have long served as the most robust and widely used approach for realizing nonreciprocity, with an externally applied magnetic field breaking time-reversal symmetry (TRS) and chiral photon-magnon interactions introducing spatial asymmetry. In this work, we investigate the chirality mechanisms essential for magnetic nonreciprocity from a unified experimental and theoretical perspective. We begin by examining conventional chiral interactions that generate chiral electromagnetic fields through specially designed structures, and then place particular emphasis on synthetic chirality enabled by nontrivial phase accumulation in traveling-wave-mediated coupling systems. We establish a microscopic theoretical framework that maps field polarization onto the phase of a complex coupling strength and validate it with systematic experiments, thereby providing a consistent formalism that describes both conventional and synthetic chirality. Notably, we highlight the symmetry properties and the unique features of synthetic chirality that distinguish it from conventional nonreciprocal mechanisms. △ Less

Submitted 9 May, 2026; originally announced May 2026.

Comments: 27 pages, 18 figures, under review at Physical Review B

Journal ref: Phys. Rev. B 114, 024408 (2026)

Superconductivity in bilayer La$_3$Ni$_2$O$_7$: A review focusing on the strong-coupling Hund's rule assisted pairing mechanism

Authors: Zhiming Pan, Chen Lu, Fan Yang, Congjun Wu

Abstract: Discovery of high-$T_c$ superconductivity (SC) in the bilayer nickelate series La$_3$Ni$_2$O$_7$ have attracted substantial interest, providing a new platform for exploring unconventional SC. Certain experimental evidence has pointed to a correlated electronic nature, which is the driving force responsible for its high critical temperature ($T_c$). This work reviews the SC in La$_3$Ni$_2$O$_7$, wi… ▽ More Discovery of high-$T_c$ superconductivity (SC) in the bilayer nickelate series La$_3$Ni$_2$O$_7$ have attracted substantial interest, providing a new platform for exploring unconventional SC. Certain experimental evidence has pointed to a correlated electronic nature, which is the driving force responsible for its high critical temperature ($T_c$). This work reviews the SC in La$_3$Ni$_2$O$_7$, with a particular focus on theoretical understanding of its pairing mechanism driven by this strong-coupling, Hund-assisted scenario. The electronic landscape is governed by two $E_g$-orbitals within the bilayer structure of NiO$_2$ planes. The $3d_{z^2}$ orbital is nearly half-filled and exhibits a stronger localized character, while the $3d_{x^2-y^2}$ is approximately quarter-filled and remains highly itinerant. The localized $3d_{z^2}$ orbitals experience robust interlayer hybridization, mediated by the $2p_z$ orbitals of the inner apical oxygen atoms. This hybridization generates a strong interlayer antiferromagnetic (AFM) exchange. In the strong coupling regime, Hund's rule coupling aligns the spins of the two $E_g$ orbitals on the same nickel site. The strong interlayer AFM exchange is effectively transferred to the itinerant $3d_{x^2-y^2}$ orbital, generating an effective coupling $J_{\perp}$ within this orbital. This mechanism is captured by a minimal strong-coupling bilayer $t$-$J$-$J_{\perp}$ model for the $3d_{x^2-y^2}$ band. Driven by $J_{\perp}$, $3d_{x^2-y^2}$ electrons can form interlayer Cooper pairs, leading to an extended $s$-wave pairing SC with high $T_c$. Meanwhile, the strongly localized $3d_{z^2}$ electrons tend to form interlayer rung singlets. Due to a lack of phase coherence, these singlets do not directly participate in the SC condensate, but instead give rise to a pseudogap phase. △ Less

Submitted 22 April, 2026; originally announced April 2026.

Comments: 21 pages, 14 figures

Non-Hermitian reshaping of high-order Landau modes

Authors: Zhihao Wang, Jie Jiang, Yanji Zheng, Wen Zhao, Chenyang Wang, Zhiwei Guo, Yong-Chun Liu, Shuang Zhang, Cuicui Lu

Abstract: When charged particles are subjected to strong magnetic fields, they form discrete energy levels known as Landau levels. The Landau levels consist of a series of degenerate states of Landau modes, making them a promising platform for large-capacity information processing. However, to date, exploiting the high-order Landau modes and control their spatial distributions has remained elusive. Here, we… ▽ More When charged particles are subjected to strong magnetic fields, they form discrete energy levels known as Landau levels. The Landau levels consist of a series of degenerate states of Landau modes, making them a promising platform for large-capacity information processing. However, to date, exploiting the high-order Landau modes and control their spatial distributions has remained elusive. Here, we propose to construct magnetic fields, electric fields, and imaginary momentum simultaneously to reshape high-order Landau modes in non-Hermitian systems. By building a non-Hermitian electric circuit platform, we experimentally realize pseudomagnetic fields via inhomogeneous coupling and pseudoelectric fields via a gradient on-site potential, while simultaneously introducing an imaginary momentum via non-reciprocal coupling. We directly observe multi-frequency single-peak localization of high-order Landau modes. Our work provides a universal method for manipulating high-order Landau modes and exploring applications in nonHermitian systems, such as frequency multiplexing and wave packet reshaping. △ Less

Submitted 15 April, 2026; originally announced April 2026.

Charge-4e/6e superconductivity and chiral metal from 3D chiral superconductor

Authors: Chu-Tian Gao, Chen Lu, Yu-Bo Liu, Zhiming Pan, Fan Yang

Abstract: Unconventional superconductivity (SC) characterized by multi-fermion orderings has attracted substantial attention. However, previous studies have largely focused on 2D systems or 3D systems with effective 2D symmetries. Here, we investigate the vestigial phases arising from thermal fluctuations of chiral SC in 3D systems governed by the cubic $O_h$ point group. By constructing low-energy effectiv… ▽ More Unconventional superconductivity (SC) characterized by multi-fermion orderings has attracted substantial attention. However, previous studies have largely focused on 2D systems or 3D systems with effective 2D symmetries. Here, we investigate the vestigial phases arising from thermal fluctuations of chiral SC in 3D systems governed by the cubic $O_h$ point group. By constructing low-energy effective Hamiltonians via Ginzburg-Landau analysis and conducting Monte Carlo simulations, we systematically investigate the phase fluctuations of chiral orders within the $E_g$ and $T_{2g}/T_{1u}$ irreducible representations (IRRPs). We identify a phase diagram topology different from 2D counterparts, where the multi-phase intersection manifests as a tetracritical point rather than the triple point typically found in 2D systems. We elucidate the evolution of these phases under thermal fluctuations. Our findings reveal that for both $E_g$ and $T_{2g}/T_{1u}$ IRRPs, the primary chiral orders could melt into a chiral metallic phase across specific parameter regimes. Moreover, for the $E_g$ IRRP, phase fluctuation could also induce a charge-$4e$ phase under certain regime, while for the $T_{2g}$ and $T_{1u}$ IRRPs, it leads to a higher-order charge-$6e$ SC state. Our work paves the way for exploring exotic vestigial orders driven by non-trivial 3D crystalline symmetries. △ Less

Submitted 14 April, 2026; originally announced April 2026.

Comments: 17 pages, 13 figures

Nonlocal Linear Instability Drives the Initiation of Motion of Rational and Irrational Twin Interfaces

Authors: Chang-Tsan Lu, Anthony Rollett, Kaushik Dayal

Abstract: Twin boundaries play a central role in the functional behavior of martensitic materials, yet the mechanisms governing the initiation of their motion remain poorly understood for twins lying along irrational crystallographic directions. Here we present an atomistic investigation of the onset of motion of both rational and irrational twin interfaces in a two-dimensional model lattice with rectangula… ▽ More Twin boundaries play a central role in the functional behavior of martensitic materials, yet the mechanisms governing the initiation of their motion remain poorly understood for twins lying along irrational crystallographic directions. Here we present an atomistic investigation of the onset of motion of both rational and irrational twin interfaces in a two-dimensional model lattice with rectangular unit cells. Using quasistatic shear loading and full linear stability analysis, we show that the initiation of twin boundary motion is signaled by a nonlocal linear instability, marked by the vanishing of the lowest eigenvalue of the Hessian; the corresponding eigenmode predicts the atomic displacements that initiate motion. We find that irrational twin boundaries have significantly lower critical shear stress to initiate motion compared to rational twin boundaries. Further, we find that they display unusual mechanisms to initiate motion such as the formation of microtwins in directions orthogonal to the overall twin boundary. Finally, we compare various local measures against the nonlocal stability analysis, and find that the former do not capture that irrational twin boundaries initiate their motion at lower stresses compared to rational boundaries. △ Less

Submitted 6 April, 2026; originally announced April 2026.

Comments: To appear in Journal of Applied Mechanics

Coherent perfect absorption of anti-modes in an indirect coupled magnon-polariton system

Authors: Chenyang Lu, Jiguang Yao, Jiongjie Wang, Jiang Xiao, Can-Ming Hu

Abstract: In this work, we report coherent perfect absorption (CPA) of anti-modes in an indirectly coupled magnon--polariton system. By examining both single and indirectly coupled cases, we experimentally distinguish the modal decay rate $γ$ from the effective decay rate $γ_{\rm{eff}}$. At CPA, $γ_{\rm{eff}} = 0$, leading to a vanishing output and a visually narrow spectrum in the dB-scale, while the intri… ▽ More In this work, we report coherent perfect absorption (CPA) of anti-modes in an indirectly coupled magnon--polariton system. By examining both single and indirectly coupled cases, we experimentally distinguish the modal decay rate $γ$ from the effective decay rate $γ_{\rm{eff}}$. At CPA, $γ_{\rm{eff}} = 0$, leading to a vanishing output and a visually narrow spectrum in the dB-scale, while the intrinsic linewidth set by $2γ$ remains unchanged, demonstrating that the effective decay rate dictates the spectral amplitude rather than the physical loss. Furthermore, in the indirectly coupled system, CPA persists over a broad, magnetically tunable detuning range, in contrast to the single-detuning CPA observed in the directly coupled case, thereby enabling magnetically reconfigurable and frequency-selective microwave absorbers. △ Less

Submitted 12 March, 2026; originally announced March 2026.

Giant Magnetocrystalline Anisotropy in Honeycomb Iridate NiIrO3 with Large Coercive Field Exceeding 17 T

Authors: Chuanhui Zhu, Pengfei Tan, Xiao-Sheng Ni, Jingchun Gao, Yuting Chang, Mei-Huan Zhao, Zheng Deng, Shuang Zhao, Tao Xia, Jinjin Yang, Changqing Jin, Junfeng Wang, Chengliang Lu, Yisheng Chai, Dao-Xin Yao, Man-Rong Li

Abstract: The realization of unconventional quantum phases in frustrated and spin-orbit coupled materials remains at the forefront of quantum materials research. Here we report the synthesis and discovery of NiIrO3, the first honeycomb iridate with coupled 3d-5d magnetic sublattices, through a soft topotactic reaction. Structural analysis reveals an ilmenite-type stacking of edge-sharing NiO6 and IrO6 octah… ▽ More The realization of unconventional quantum phases in frustrated and spin-orbit coupled materials remains at the forefront of quantum materials research. Here we report the synthesis and discovery of NiIrO3, the first honeycomb iridate with coupled 3d-5d magnetic sublattices, through a soft topotactic reaction. Structural analysis reveals an ilmenite-type stacking of edge-sharing NiO6 and IrO6 octahedral honeycomb sublattices in a Kitaev geometry. Comprehensive magnetic and electrical transport measurements unveil its long-range ferrimagnetic order below 213 K, which is in sharp contrast to the predominantly antiferromagnetic order in the known honeycomb iridates. Notably, the titled compound displays an exceptionally large magnetocrystalline anisotropy energy of 32.2 meV/f.u. and a giant coercivity with coercive field exceeding 17.3 T below 4.2 K, both ranking among the highest observed in iridates to date. Combined experimental and theoretical investigations indicate that the exceptional anisotropy and coercivity originate from the synergistic effect between strong lattice frustration in the coupled 3d-5d honeycomb lattice network and the robust spin-orbit coupling of the Ir4+ (Jeff = 1/2) state. This work positions NiIrO3 as a promising platform to investigate low-dimensional and frustrated quantum spin systems, and highlights its potential for spintronic applications through the targeted engineering of 3d-5d interactions. △ Less

Submitted 4 March, 2026; originally announced March 2026.

One-Dimensional Metallic Polymeric Nitrogen

Authors: Kewei Ding, Junyi Miao, Ying Liu, Anxin Yu, Cheng Lu, Wenrui Zhang, Yanchun Li, Haipeng Su, Zhongxue Ge, Xianlong Wang

Abstract: The pressure-induced metallic states of light elements attract significant attention, because of potential applications as high-temperature superconductor and high-energy-density material, especially for hydrogen and nitrogen1-10. Several semiconducting polymeric nitrogen phases with three- or two-dimensional sp3-bonded networks were synthesized6-10, but its metallic form remains unobserved. Here,… ▽ More The pressure-induced metallic states of light elements attract significant attention, because of potential applications as high-temperature superconductor and high-energy-density material, especially for hydrogen and nitrogen1-10. Several semiconducting polymeric nitrogen phases with three- or two-dimensional sp3-bonded networks were synthesized6-10, but its metallic form remains unobserved. Here, we report the synthesis of a metallic polymeric nitrogen with one-dimensional feature (1D-PN) at 130-140 GPa and above 3000 K. Synchrotron XRD and Raman spectroscopy, supported by DFT calculations, reveal that it adopts an infinite arm-chair like chain with sp2-hybridized pi-bonds. Simulations predict a superconducting transition at 21.19 K under 113 GPa, higher than that reported in high-pressure experiments for non-metallic elements. At ambient pressure, this phase acquiring an energy density of as high as 8.78 kJ/g is not only kinetically stable but also thermodynamically more stable than cubic gauche nitrogen. This multifunctional property profile positions 1D-PN as a disruptive candidate for both electronic and energetic applications. △ Less

Submitted 3 March, 2026; originally announced March 2026.

Comments: 22 pages, 3 figures

Anisotropic magnetoresistance and magnetic field-tunable Weyl nodes in Weyl metal SrRuO$_{3}$ thin films

Authors: Uddipta Kar, Akhilesh Kr. Singh, Elisha Cho-Hao Lu, P. V. Sreenivasa Reddy, Fu-En Cheng, Wazid Ahmed, Song Yang, Chun-Yen Lin, Chia-Hung Hsu, Guang-Yu Guo, Wei-Li Lee

Abstract: Weyl semimetals are a unique class of topological materials, possessing Fermi-arc surface states and exhibiting the chiral anomaly effect. The chiral anomaly refers to non-equilibrium charge transfer within a Weyl-node pair of opposite chirality under the condition of aligned electric and magnetic fields ($\bf{E} \parallel \bf{B}$), leading to non-conserved chiral charges and thus enhanced electri… ▽ More Weyl semimetals are a unique class of topological materials, possessing Fermi-arc surface states and exhibiting the chiral anomaly effect. The chiral anomaly refers to non-equilibrium charge transfer within a Weyl-node pair of opposite chirality under the condition of aligned electric and magnetic fields ($\bf{E} \parallel \bf{B}$), leading to non-conserved chiral charges and thus enhanced electrical conductivity. In experiments, such an enhanced conductivity due to the chiral anomaly manifests as a negative longitudinal magnetoresistance (MR) when the external field $\bf{H}$ is applied along the bias current direction $\bf{I}$. In this work, we present rigorous $φ$- and $α$-dependent magnetotransport measurements to investigate such a negative longitudinal MR due to the chiral anomaly in a sunbeam-shaped device fabricated from an untwinned Weyl metal SrRuO$_{3}$ (SRO) thin film. Here, $φ$($α$) represents the angle between $\bf{I}$ and the in-plane $\bf{H}$(SRO monoclinic [001]$_{\rm o}$). Unusual $φ$ dependences of in-plane MR and Hall effects were uncovered at low temperatures, accompanied by the emergence of the fourfold-symmetric component in the in-plane MR. These results indicate that the chiral anomaly and resistivity anisotropy in SRO play important roles. In particular, the dramatic variation of Weyl nodes near the Fermi level through magnetic field manipulation of the magnetization orientation, as revealed by band structure calculations, is consistent with the observed in-plane MR and Hall effect. △ Less

Submitted 22 February, 2026; originally announced February 2026.

Comments: 12 pages, 5 figures

Inverse orbital Hall effect induced terahertz emission enabled by a ferromagnet with quenched orbital moment in Fe/Pt/W trilayers

Authors: Chao Zhou, Lei Hao, Shaohua Zhang, Yaxuan Jin, Xianguo Jiang, Ning Yang, Li Zheng, Hao Meng, Chao Lu, Wendeng Huang, Yizheng Wu, Yan Zhou, Jia Xu

Abstract: The inverse orbital Hall effect (IOHE) has recently attracted considerable attention as an emerging mechanism for terahertz (THz) emission based on ultrafast angular-momentum-to-charge conversion. Most experimental studies have focused on materials with strong spin-orbit coupling or pronounced orbital character, where sizable orbital Hall responses are expected. Elemental ferromagnets such as Fe a… ▽ More The inverse orbital Hall effect (IOHE) has recently attracted considerable attention as an emerging mechanism for terahertz (THz) emission based on ultrafast angular-momentum-to-charge conversion. Most experimental studies have focused on materials with strong spin-orbit coupling or pronounced orbital character, where sizable orbital Hall responses are expected. Elemental ferromagnets such as Fe are generally regarded as quenched orbital sources and are not expected to exhibit orbital-dominated THz emission. Here, we report a pronounced enhancement of THz emission in Fe/Pt/W trilayer heterostructures, despite the absence of detectable orbital contributions in the corresponding Fe/Pt and Fe/W bilayers. Thickness-dependent measurements reveal long-distance signal persistence, systematic delay accumulation, and pronounced pulse broadening with increasing W thickness. These features are inconsistent with diffusive spin transport and indicate that orbital angular momentum transport in the W layer, converted into charge current via the IOHE, becomes a dominant channel for THz emission in the trilayer configuration. Our results demonstrate that strong IOHE can emerge in heterostructures incorporating a quenched orbital ferromagnet, providing an effective route to enhance spintronic THz emitters through orbital Hall physics. △ Less

Submitted 9 February, 2026; originally announced February 2026.

Comments: 19 pages, 4 figures

Van Hove singularity-induced multiple magnetic transitions in multi-orbital systems

Authors: Chen Lu, Lun-Hui Hu

Abstract: Van Hove singularities (VHSs) amplify electronic correlations, providing a crucial platform for discovering novel quantum phase transitions. Here, we show that VHSs in multi-orbital systems can stabilize a variety of competing $\bm{Q}=0$ magnetic orders, including intrinsic altermagnetism emerging from spontaneous orbital antiferromagnetism. This intrinsic phase, in which antiparallel spins reside… ▽ More Van Hove singularities (VHSs) amplify electronic correlations, providing a crucial platform for discovering novel quantum phase transitions. Here, we show that VHSs in multi-orbital systems can stabilize a variety of competing $\bm{Q}=0$ magnetic orders, including intrinsic altermagnetism emerging from spontaneous orbital antiferromagnetism. This intrinsic phase, in which antiparallel spins reside on distinct orbitals, is realized across all four 2D Bravais lattices. It is driven by orbital-resolved spin fluctuations enhanced by inter-orbital hopping and favors suppressed Hund's coupling $J_H$, strong inter-orbital hybridization, and filling near a VHS from quadratic band touching. Through Hubbard-$U$-$J_H$ phase diagrams we map several magnetic phase transitions: (i) ferrimagnet to $d$-wave extrinsic altermagnet, (ii) $d$-wave intrinsic altermagnet to ferromagnet, and (iii) $g$-wave extrinsic altermagnet to either $d$-wave extrinsic altermagnet or ferromagnet. Our work identifies VHSs as a generic route to altermagnetism in correlated materials. △ Less

Submitted 31 January, 2026; originally announced February 2026.

Unexpected type-II multiferroic phase in GdMnO3 under high magnetic fields

Authors: Ming Yang, Jun Chen, Junfeng Wang, Chao Dong, Chengliang Lu, Gang Xu, Jinguang Cheng, Jianshi Zhou, Shuai Dong

Abstract: Perovskite manganites with small A-site ions, as the first and canonical branch of type-II multiferroics, are ideal systems to exhibit magnetism-induced ferroelectricity. Despite their established magnetoelectric phase diagrams under low magnetic fields, here an unidentified phase with a large magnetism-induced polarization (up to 1500 μC/m2) is revealed in GdMnO3 under high magnetic fields up to… ▽ More Perovskite manganites with small A-site ions, as the first and canonical branch of type-II multiferroics, are ideal systems to exhibit magnetism-induced ferroelectricity. Despite their established magnetoelectric phase diagrams under low magnetic fields, here an unidentified phase with a large magnetism-induced polarization (up to 1500 μC/m2) is revealed in GdMnO3 under high magnetic fields up to 60 T. Based on multiprobe experiments, a complete phase diagram is constructed with successive polar-nonpolar-polar-nonpolar transitions. Such a nonmonotonic evolution is well mimicked by model simulation, while the spin-lattice coupling is the key ingredient for the reentrant ferroelectric phase. △ Less

Submitted 13 January, 2026; originally announced January 2026.

Observation of flat-band skin effect

Authors: Xulong Wang, Dongyi Wang, Congwei Lu, Ruo-Yang Zhang, Ching Hua Lee, Kun Ding, Guancong Ma

Abstract: Symmetry-protected ideal flat bands in one-dimensional (1D) Hermitian lattices are populated by compact localized states (CLS) - a special class of localization with wavefunctions confined within a small region. In this work, we discover that the non-Hermitian skin effect (NHSE) can appear in a flat band. Unlike conventional NHSEs for dispersive bands that are protected by nontrivial point-gap top… ▽ More Symmetry-protected ideal flat bands in one-dimensional (1D) Hermitian lattices are populated by compact localized states (CLS) - a special class of localization with wavefunctions confined within a small region. In this work, we discover that the non-Hermitian skin effect (NHSE) can appear in a flat band. Unlike conventional NHSEs for dispersive bands that are protected by nontrivial point-gap topology, the flat band remains a point on the complex-energy plane and is therefore always topologically trivial. We found that, intriguingly, the flat-band skin effect (FBSE) is associated with the non-trivial spectral topology of the dispersive bands enclosing the flat band on the complex-energy plane, so it only emerges within a finite range of non-Hermitian parameters and can counterintuitively disappear at large non-Hermiticity. Moreover, the gaps between the flat and the dispersive bands can close at higher-order exceptional points under both periodic and open boundary conditions. The flat-band wavefunctions are discontinuous in quantum distance across these exceptional points, signifying that the gap-closing is singular. The FBSE was experimentally observed in a non-Hermitian mechanical lattice. Our work reveals flat-band phenomena unique to non-Hermitian systems and highlights new possibilities in quantum geometry and localization control. △ Less

Submitted 14 August, 2026; v1 submitted 18 December, 2025; originally announced December 2025.

Comments: This paper supercedes arXiv:2412.19034, which contains erraneous analyses and was posted prematurely. We apologize for any confusion and inconvenience

Journal ref: Phys. Rev. Lett. 137, 076601 (2026)

The nexus between negative charge-transfer and reduced on-site Coulomb energy in a correlated topological metal CoTe$_2$

Authors: A. R. Shelke, C. -W. Chuang, S. Hamamoto, M. Oura, M. Yoshimura, N. Hiraoka, C. -N. Kuo, C. -S. Lue, A. Fujimori, A. Chainani

Abstract: The layered $3d$ transition metal dichalcogenide (TMD) CoTe$_2$ is a topological Dirac Type-II metal. However, the Co $3d$-bands in CoTe$_2$ do not exhibit the expected correlation-induced band narrowing seen in CoO. We address this conundrum by studying the electronic structure of CoTe$_2$ using hard x-ray photoemission spectroscopy (HAXPES), x-ray absorption spectroscopy (XAS) and Resonant-PES.… ▽ More The layered $3d$ transition metal dichalcogenide (TMD) CoTe$_2$ is a topological Dirac Type-II metal. However, the Co $3d$-bands in CoTe$_2$ do not exhibit the expected correlation-induced band narrowing seen in CoO. We address this conundrum by studying the electronic structure of CoTe$_2$ using hard x-ray photoemission spectroscopy (HAXPES), x-ray absorption spectroscopy (XAS) and Resonant-PES. We quantify the on-site Coulomb energy $U_{dd}$ via single-particle partial density of states and the two-hole correlation satellite using valence band Resonant-PES), and obtain $U_{dd}$ = 3.0 eV for CoTe$_2$. Charge-transfer (CT) cluster model simulations of the measured core-level Co $2p$ PES and $L$-edge XAS spectra of CoTe\textsubscript{2} and CoO validate their contrasting electronic parameters:$U_{dd}$ and CT energy $Δ$ are (3.0 eV, -2.0 eV) for CoTe\textsubscript{2}, and (5.0 eV, 4.0 eV) for CoO, respectively. The $d$-$p$ hybridization strength $T_{eg}$ for CoTe$_2$$<$CoO, and indicates that the reduced $U_{dd}$ in CoTe\textsubscript{2} is not due to $T_{eg}$. The increase in $d^n$-count$\sim$1 by CT from ligand to Co site in CoTe$_2$ is due to a negative-$Δ$ and reduced $U_{dd}$. Yet, only because $U_{dd}$$>$$\big|Δ\big|$, CoTe$_{2}$ becomes a topological metal with $p$$\rightarrow$$p$ type lowest energy excitations. The study reveals the nexus between negative-$Δ$ and reduced $U_{dd}$ required for setting up the electronic structure framework for achieving topological behavior via band inversion in the correlated metal CoTe$_2$. △ Less

Submitted 25 February, 2026; v1 submitted 5 November, 2025; originally announced November 2025.

Comments: 14 pages + 12 figures(main) and 3 pages + 2 figures (SM) (revised manuscript submitted to PRB);typos corrected

Role of on-site Coulomb energy and negative-charge transfer in a Dirac semi-metal NiTe$_2$

Authors: A. R. Shelke, C. -W. Chuang, S. Hamamoto, M. Oura, M. Yoshimura, N. Hiraoka, C. -N. Kuo, C. -S. Lue, A. Fujimori, A. Chainani

Abstract: Angle-resolved photoemission spectroscopy (ARPES) combined with band structure calculations have shown that the layered transition metal dichalcogenide(TMD) NiTe$_2$ is a type-II Dirac semimetal. However, conflicting conclusions were reported regarding the role of electron correlations in NiTe$_2$. We study core-levels and valence band electronic structure of single crystal NiTe$_2$ using soft and… ▽ More Angle-resolved photoemission spectroscopy (ARPES) combined with band structure calculations have shown that the layered transition metal dichalcogenide(TMD) NiTe$_2$ is a type-II Dirac semimetal. However, conflicting conclusions were reported regarding the role of electron correlations in NiTe$_2$. We study core-levels and valence band electronic structure of single crystal NiTe$_2$ using soft and hard x-ray photoemission spectroscopy(SXPES, HAXPES), X-ray absorption spectroscopy(XAS) and Ni $2p-3d$ Resonant-PES to quantify electronic parameters in NiTe$_2$. The Ni $3d$ on-site Coulomb energy ($U_{dd}$) is quantified from measurements of the Ni $3d$ single particle density of states(DOS) and the two-hole correlation satellite. The Ni $2p$ core level and $L$-edge XAS spectra are analyzed by charge-transfer (CT) cluster model calculations using the experimental $U_{dd}$, and it shows that NiTe$_2$ exhibits a negative CT energy $Δ$. A comparative analysis of NiO $L$-edge XAS confirms its well-known strongly correlated CT insulator character, with a larger $U_{dd}$ and positive $Δ$. The $d$-$p$ hybridization strength $T_{eg}$ for NiTe$_2$$<$NiO, and shows that $T_{eg}$ is not responsible for reducing $U_{dd}$ in NiTe\textsubscript{2} compared to NiO. The negative-$Δ$ and a reduced $U_{dd}$ leads to the increase in $d^n$ count on the Ni site in NiTe$_{2}$ by nearly one electron. However, importantly, since $U_{dd}$$>$$|Δ|$, a finite repulsive $U_{dd}$ results in pushing $d$-states away from Fermi level and this is required to make NiTe$_{2}$ a moderately correlated Dirac semi-metal with band inversion in the $p$-$p$ type lowest energy excitations. △ Less

Submitted 25 February, 2026; v1 submitted 3 November, 2025; originally announced November 2025.

Comments: 13 pages, 13 figures (Revised version submitted to Physical Review B);typos corrected

Inter-orbital spin-triplet superconductivity from altermagnetic fluctuations

Authors: Chen Lu, Chuang Li, Chao Cao, Huiqiu Yuan, Fu-Chun Zhang, Lun-Hui Hu

Abstract: Altermagnetic (AM) fluctuations are a new class of collinear spin fluctuations whose role in mediating superconductivity faces a fundamental tension: their $Γ$-point peak favors intra-orbital spin-triplet pairing, while their spin compensation favors inter-orbital singlets. Here, we demonstrate that inversion-symmetry-broken AM fluctuations generically resolve this competition in favor of spin-tri… ▽ More Altermagnetic (AM) fluctuations are a new class of collinear spin fluctuations whose role in mediating superconductivity faces a fundamental tension: their $Γ$-point peak favors intra-orbital spin-triplet pairing, while their spin compensation favors inter-orbital singlets. Here, we demonstrate that inversion-symmetry-broken AM fluctuations generically resolve this competition in favor of spin-triplet pairing. As a proof of concept, we study a minimal two-orbital model with two van Hove singularities. The broken inversion symmetry induces momentum-orbital locking: the same orbital dominates at opposite momenta, enhancing the triplet channel. Crucially, a subdominant fluctuation channel arising from inter-van-Hove nesting provides an internal Josephson coupling that locks the phase difference between triplet pairs on different orbitals. We find this coupling changes sign ($+$ to $-$) upon a crossover from AM-dominant to ferromagnetic-dominant fluctuations. The resulting $π$-phase difference manifests as a $τ_z$-type order parameter, $c_{k,1\uparrow}c_{-k,1\uparrow} - c_{k,2\uparrow}c_{-k,2\uparrow}$. Although intra-orbital in the original basis, its orbital-nontrivial character, as manifested by its equivalence to inter-orbital pairing under rotation, defines a general \textit{inter-orbital spin-triplet superconductivity}. This state is distinct from the $τ_0$-triplet pairing mediated by ferromagnetic fluctuations, as evidenced by the canceled intra-orbital supercurrent in a Josephson junction between them. △ Less

Submitted 21 October, 2025; originally announced October 2025.

Comments: 5 pages, 5 figures. Comments are welcome

Breakdown of Stoner Ferromagnetism by Intrinsic Altermagnetism

Authors: Chen Lu, Chao Cao, Huiqiu Yuan, Piers Coleman, Lun-Hui Hu

Abstract: The Stoner criterion for ferromagnetism arises from interaction-driven asymmetric filling of spin bands, requiring that the spin susceptibility: (i) peaks dominantly at $\mathbf{Q}=\bm{0}$; and (ii) diverges at a critical interaction strength. Here, we demonstrate that this Stoner mechanism breaks down due to competition with altermagnetic orders, even when both conditions are met. Altermagnetism… ▽ More The Stoner criterion for ferromagnetism arises from interaction-driven asymmetric filling of spin bands, requiring that the spin susceptibility: (i) peaks dominantly at $\mathbf{Q}=\bm{0}$; and (ii) diverges at a critical interaction strength. Here, we demonstrate that this Stoner mechanism breaks down due to competition with altermagnetic orders, even when both conditions are met. Altermagnetism in solids is characterized by collinear antiparallel spin alignment that preserves translational symmetry, and inherently fulfills these requirements. As a proof of concept, we study a two-orbital Hubbard model with electron filling near Van Hove singularities at high-symmetry momenta. Our results reveal that orbital-resolved spin fluctuations, amplified by strong inter-orbital hopping, stabilize intrinsic altermagnetic order. A quantum phase transition from altermagnetism to ferromagnetism occurs at critical Hund's coupling $J_H$. We further propose directional spin conductivity anisotropy as a detectable signature of this transition via non-local spin transport. This work establishes the pivotal role of altermagnetism in correlated systems. △ Less

Submitted 1 October, 2025; originally announced October 2025.

Comments: 5 pages, 4 figures. Supplementary material is available upon request

Classification of Magnetism and Altermagnetism in Quasicrystals

Authors: Zhi-Yan Shao, Chen Lu, Zhiming Pan, Yu-Bo Liu, Fan Yang

Abstract: Altermagnetism (AM), an unconventional magnetic phase characterized by zero net magnetism protected by symmetry(s) other than parity-time ($\mathcal{P}\mathcal{T}$) and a resulting spin-split band, has been studied exclusively in crystalline materials. Here, we extend the framework of AM to quasicrystals (QCs). We start from a comparison between the Néel state on the square lattice and that on a… ▽ More Altermagnetism (AM), an unconventional magnetic phase characterized by zero net magnetism protected by symmetry(s) other than parity-time ($\mathcal{P}\mathcal{T}$) and a resulting spin-split band, has been studied exclusively in crystalline materials. Here, we extend the framework of AM to quasicrystals (QCs). We start from a comparison between the Néel state on the square lattice and that on a $D_4$-symmetric Thue-Morse QC, with both belonging to the same $d$-wave irreducible representation (IRRP) of the $D_4$ point group. Consequently, while the former is antiferromagnetism (AFM) protected by the combined $\mathcal{P}\mathcal{T}$ and translational symmetry, the lack of translational symmetry in the latter breaks the $\mathcal{P}\mathcal{T}$ symmetry, and the additional mirror or rotation symmetry protects AM. This example suggests that AM is more common in QCs than in crystals and can be easily explored through a point-group symmetry-based classification. Therefore, we classify magnetic phases in 2D $D_n$-symmetric QCs without spin-orbit coupling, by using IRRPs of $D_n$. Consequently, the identity IRRP represents ferromagnetism, the inversion-odd 1D IRRPs for twice-of-odd $n$ represent AFM, and all the remaining 1D IRRPs represent AM, protected by either mirror or rotation symmetry. We further take the Hubbard model to verify this result in various QCs with different symmetries. Our work highlights the QC as a natural platform where AM is common among magnetic phases. △ Less

Submitted 22 September, 2025; v1 submitted 21 August, 2025; originally announced August 2025.

Comments: 4.2pages, with Appendix

Reproducibility of high-throughput density-functional-theory calculations

Authors: Chenxi Lu, Musen Li, Jeffrey R. Reimers

Abstract: While standard computational protocols for density functional theory (DFT) have universal applicability, differences exist in code implementations. Specific applications require manual parameter optimization, whereas high-throughput calculations employ predefined workflows. This paper uses the bandgap as a key property to reveal the impact of computational workflow differences on the reproducibili… ▽ More While standard computational protocols for density functional theory (DFT) have universal applicability, differences exist in code implementations. Specific applications require manual parameter optimization, whereas high-throughput calculations employ predefined workflows. This paper uses the bandgap as a key property to reveal the impact of computational workflow differences on the reproducibility of high-throughput calculation results. The study proposes basic requirements for ensuring reproducibility: using structures optimised using the same procedure as used to calculate properties and ensuring Brillouin zone (k-point) integration grid accuracy. This research establishes a foundation for the reproducibility of DFT calculations and reliable application of results, which is of great significance for method development and artificial intelligence model training. △ Less

Submitted 10 August, 2025; originally announced August 2025.

Pairing without $γ$-Pocket in the La$_3$Ni$_2$O$_7$ Thin Film

Authors: Zhi-Yan Shao, Chen Lu, Min Liu, Yu-Bo Liu, Zhiming Pan, Congjun Wu, Fan Yang

Abstract: The recent discovery of high-temperature superconductivity (HTSC) in the La$_3$Ni$_2$O$_7$ ultrathin film at ambient pressure has aroused great research interest. The $γ$-pocket formed by the bonding $d_{z^2}$ band, which was previously proposed to be crucial in the pairing mechanism of pressurized bulk La$_3$Ni$_2$O$_7$, is reported to be either present or absent here by different experimental gr… ▽ More The recent discovery of high-temperature superconductivity (HTSC) in the La$_3$Ni$_2$O$_7$ ultrathin film at ambient pressure has aroused great research interest. The $γ$-pocket formed by the bonding $d_{z^2}$ band, which was previously proposed to be crucial in the pairing mechanism of pressurized bulk La$_3$Ni$_2$O$_7$, is reported to be either present or absent here by different experimental groups, giving rise to the problem: what is the pairing mechanism and pairing nature without the $γ$-pocket? Here, we start from a band structure obtained via density-functional-theoretical calculation, which exhibits no $γ$-pocket. Then, equipped with electron interactions, we study the pairing nature via combined weak- and strong- coupling approaches, which provide consistent results. In the weak-coupling study, the nesting between the $α$- and $β$- pockets leads to an $s^\pm$-wave pairing in which the gap signs on the two pockets are opposite, as provided by our random-phase-approximation based calculations. In real-space, the pairing pattern is dominated by the interlayer pairing of the $d_{x^2-y^2}$ orbital. In the strong-coupling study, as the $d_{z^2}$ orbitals are nearly half-filled and hence localized, the $d_{x^2-y^2}$ orbitals carry the HTSC. Driven by the interlayer superexchange transferred from the $d_{z^2}$ orbital through the Hund's rule coupling, the $d_{x^2-y^2}$ orbital electrons form interlayer $s$-wave pairing, as suggested by our slave-boson-mean-field study on the related two-orbital $t$-$J$ model. Projected onto the Fermi surface, this pairing just gives the $s^\pm$-wave pattern consistent with that obtained in the weak-coupling study. Our result is consistent with that obtained in recent scanning tunneling microscopy experiment. △ Less

Submitted 27 July, 2025; originally announced July 2025.

Incipient ionic conductors: Ion-constrained lattices achieving superionic-like thermal conductivity by extreme anharmonicity

Authors: Yongheng Li, Chunqiu Lu, Bin Wei, Cong Lu, Xingang Jiang, Daisuke Ishikawa, Taishun Manjo, Caofeng Pan, Alfred Q. R. Baron, Jiawang Hong

Abstract: Phonon liquid-like thermal conduction in the solid state enables superionic conductors to serve as efficient thermoelectric device candidates. While liquid-like motion of ions effectively suppresses thermal conductivity (κ), their high mobility concurrently triggers material degradation due to undesirable ion migration and consequent metal deposition, making it still a challenge to balancing low κ… ▽ More Phonon liquid-like thermal conduction in the solid state enables superionic conductors to serve as efficient thermoelectric device candidates. While liquid-like motion of ions effectively suppresses thermal conductivity (κ), their high mobility concurrently triggers material degradation due to undesirable ion migration and consequent metal deposition, making it still a challenge to balancing low κand high stability. Here, we report a superionic-like thermal transport alongside restricted long-range ion migration in CsCu_2I_3 with incipient ionic conduction, using synchrotron X-ray diffraction, inelastic X-ray scattering, and machine-learning potential-based simulations. We reveal that the Cu ions exhibit confined migration between CuI_4 tetrahedra at high temperatures, displaying extreme anharmonicity of dominated phonons beyond conventional rattling and comparable to that in superionic conductorsl. Consequently, a glass-like κ(~0.3 W m^{-1} K^{-1} at 300 K) following the relationship of κ~ T^{0.17}, was achieved along the x-direction, where Cu ion migration is three oders of magnitude lower than in superionic conductors. These results highlight the advantage of incipient ionic conductors in simultaneously maintaining both low κand high stability, elucidate the thermal transport mechanism via ion migration constraints, and pave an effective pathway toward ultralow thermal conductivity in ionic conductors. △ Less

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

Comments: 24 pages, 5 figures

Anomalous Charge Density Wave and Fermi Surface Reconstruction in Pressurized BaFe2Al9

Authors: Govindaraj Lingannan, M. Sundaramoorthy, Nabeel M. Jasim, I. K. Abbas, C. S. Lue, Leon F. Carstens, A. Bertrand, M. Mito, B. Joseph, Rüdiger Klingeler, S. Arumugam, Mahmoud Abdel-Hafiez

Abstract: The intermetallic compound BaFe2Al9 exhibits unusual physical properties associated with a charge density wave (CDW) transition. Unlike conventional CDW materials, which typically display subtle structural distortions or lattice modulations, BaFe2Al9 undergoes a first-order phase transition in which lattice strain plays a crucial role in the formation of the CDW state. To further explore this uniq… ▽ More The intermetallic compound BaFe2Al9 exhibits unusual physical properties associated with a charge density wave (CDW) transition. Unlike conventional CDW materials, which typically display subtle structural distortions or lattice modulations, BaFe2Al9 undergoes a first-order phase transition in which lattice strain plays a crucial role in the formation of the CDW state. To further explore this unique behavior, we conducted high-pressure studies, examining the electrical transport, magnetic, and structural properties to gain deeper insight into the underlying CDW mechanism. At ambient pressure, electrical resistivity and magnetization measurements confirm the presence of a CDW transition. Upon applying pressure, the CDW transition temperature (TCDW) shifts to higher values, reaching approximately 300 K near 3.2 GPa, and the electrical resistivity increases, suggesting that pressure modulates the charge carrier concentration. Furthermore, the initially sharp first-order transition becomes more gradual, and analysis of the temperature derivative of resistivity indicates a crossover from first-order to second-order like behavior under pressure. High-pressure magnetization measurements are consistent with the electrical transport data, showing an enhancement of TCDW with increasing pressure. The residual resistivity increases with pressure, while the Fermi liquid coefficient A decreases above 2 GPa, pointing to a possible Fermi surface reconstruction. High-pressure synchrotron powder X-ray diffraction (XRD) measurements at room temperature reveal a lattice anomaly near 3.8 GPa, marked by a distinct trend change in macrostrain, further supporting the existence of a pressure induced structural response. These findings provide valuable insight into the nature of CDW formation in BaFe2Al9 and highlight the critical role of lattice strain and external pressure in tuning its electronic ground state. △ Less

Submitted 4 July, 2025; originally announced July 2025.

Comments: 19 pages with SI materials

Observation of universal topological magnetoelectric switching in multiferroic GdMn2O5

Authors: Haowen Wang, Fan Wang, Ming Yang, Yuting Chang, Mengyi Shi, Liang Li, Jun-Ming Liu, Junfeng Wang, Shuai Dong, Chengliang Lu

Abstract: Topological magnetoelectricity was recently revealed as an emergent topic, which opens a unique route to precisely control magnetoelectric functionality. Here we report the synchronous magnetic-electric-cycle operation of topological magnetoelectric switching in GdMn2O5. Compared with pure magnetic-cycle operation, this topological winding can be accessed in a much broader parameter space, i.e. or… ▽ More Topological magnetoelectricity was recently revealed as an emergent topic, which opens a unique route to precisely control magnetoelectric functionality. Here we report the synchronous magnetic-electric-cycle operation of topological magnetoelectric switching in GdMn2O5. Compared with pure magnetic-cycle operation, this topological winding can be accessed in a much broader parameter space, i.e. orientation of magnetic field is not limited to the magic angle and the effect can persist up to the Curie temperature. The fine tuning of free energy landscape is responsible to this topological behavior. △ Less

Submitted 1 June, 2025; originally announced June 2025.

Journal ref: Phys. Rev. Lett. 134, 016708 (2025)

Cryogenic scanning photocurrent spectroscopy for materials responses to structured optical fields

Authors: Duxing Hao, Chun-I Lu, Ziqi Sun, Yu-Chen Chang, Wen-Hao Chang, Ye-Ru Chen, Akiyoshi Park, Beining Rao, Siyuan Qiu, Yann-Wen Lan, Ting-Hua Lu, Nai-Chang Yeh

Abstract: Circular dichroism spectroscopy is known to provide important insights into the interplay of different degrees of freedom in quantum materials, and yet spectroscopic study of the optoelectronic responses of quantum materials to structured optical fields, such as light with finite spin and orbital angular momentum, has not yet been widely explored, particularly at cryogenic temperature. Here we dem… ▽ More Circular dichroism spectroscopy is known to provide important insights into the interplay of different degrees of freedom in quantum materials, and yet spectroscopic study of the optoelectronic responses of quantum materials to structured optical fields, such as light with finite spin and orbital angular momentum, has not yet been widely explored, particularly at cryogenic temperature. Here we demonstrate the design and application of a novel instrument that integrates scanning spectroscopic photocurrent measurements with structured light of controlled spin and orbital angular momentum. For structured photons with wavelengths between 500 nm to 700 nm, this instrument can perform spatially resolved photocurrent measurements of two-dimensional materials or thin crystals under magnetic fields up to $\pm$ 14 Tesla, at temperatures from 300 K down to 3 K, with either spin angular momentum $\pm \hbar$ ororbital angular momentum $\pm \ell \hbar$ (where $\ell$=1,2,3... is the topological charge), and over a (35 $\times$ 25) $μm^2$ area with ~ 1 $μm$ spatial resolution. These capabilities of the instrument are exemplified by magneto-photocurrent spectroscopic measurements of monolayer 2H-$MoS_2$ field-effect transistors, which not only reveal the excitonic spectra but also demonstrate monotonically increasing photocurrents with increasing |$\ell $| as well as excitonic Zeeman splitting and an enhanced Landé g-factor due to the enhanced formation of intervalley dark excitons under magnetic field. These studies thus demonstrate the versatility of the scanning photocurrent spectrometry for investigating excitonic physics, optical selection rules, and optoelectronic responses of novel quantum materials and engineered quantum devices to structured light. △ Less

Submitted 30 May, 2025; originally announced May 2025.

General First-Principles Approach to Crystals in Finite Magnetic Fields

Authors: Chengye Lü, Yingwei Chen, Yuzhi Wang, Zhihao Dai, Zhong Fang, Xin-Gao Gong, Quansheng Wu, Hongjun Xiang

Abstract: We introduce a general first-principles methodology for computing electronic structure in a finite uniform magnetic field which allows for an arbitrary rational magnetic flux and nonlocal pseudopotentials, at a comparable time complexity of conventional plane-wave pseudopotential approaches in zero-field conditions. The versatility of this method is demonstrated through comprehensive applications… ▽ More We introduce a general first-principles methodology for computing electronic structure in a finite uniform magnetic field which allows for an arbitrary rational magnetic flux and nonlocal pseudopotentials, at a comparable time complexity of conventional plane-wave pseudopotential approaches in zero-field conditions. The versatility of this method is demonstrated through comprehensive applications to both molecular and crystalline systems, including calculations of magnetizabilities, magnetically induced currents, and magnetic energy bands. Furthermore, we provide rigorous proofs of two properties for crystals in uniform magnetic fields: the "strong translational symmetry" and "magnetic bands shift" phenomena. △ Less

Submitted 6 October, 2025; v1 submitted 10 May, 2025; originally announced May 2025.

Tensor-monopole-induced topological boundary effects in four-dimensional acoustic metamaterials

Authors: Qingyang Mo, Shanjun Liang, Cuicui Lu, Jie Zhu, Shuang Zhang

Abstract: Gauge field theory provides the mathematical and conceptual framework to describe and understand topological singularities such as Weyl points and magnetic monopoles. While singularities associated with vector electromagnetic gauge fields have been well-studied, those of higher-form tensor gauge fields, like the four-dimensional (4D) tensor monopoles predicted by string theory, have remained large… ▽ More Gauge field theory provides the mathematical and conceptual framework to describe and understand topological singularities such as Weyl points and magnetic monopoles. While singularities associated with vector electromagnetic gauge fields have been well-studied, those of higher-form tensor gauge fields, like the four-dimensional (4D) tensor monopoles predicted by string theory, have remained largely theoretical or limited to experimental demonstration in pure synthetic dimensions, thereby not allowing investigations of the associated boundary effects. Here, we present a 4D system with tensor monopoles using engineered acoustic metamaterials. Our momentum space combines three real momentum dimensions and a geometric parameter as the fourth. By varying this fourth momentum, we experimentally reveal two distinct topological surface states in 3D subsystems: Fermi-arc surface states in a gapless subsystem and Dirac-cone surface states in a gapped subsystem. Our work introduces a novel platform for exploring new topological structures associated with tensor gauge field and topological phenomena in higher dimensions. △ Less

Submitted 17 April, 2025; originally announced April 2025.

Strong-coupling study of the pairing mechanism in pressurized La$_3$Ni$_2$O$_7$

Authors: Jia-Heng Ji, Chen Lu, Zhi-Yan Shao, Zhiming Pan, Fan Yang, Congjun Wu

Abstract: Recently, the bilayer perovskite nickelate La$_3$Ni$_2$O$_7$ has been reported to exhibit high-temperature superconductivity near $80$ K under a moderate pressure of about $14$GPa. To investigate the underlying pairing mechanism and symmetry in this complex system, we propose and analyze a mixed spin-$1$ and spin-$\frac{1}{2}$ bilayer $t$-$J$ model in the strong coupling regime. This model explici… ▽ More Recently, the bilayer perovskite nickelate La$_3$Ni$_2$O$_7$ has been reported to exhibit high-temperature superconductivity near $80$ K under a moderate pressure of about $14$GPa. To investigate the underlying pairing mechanism and symmetry in this complex system, we propose and analyze a mixed spin-$1$ and spin-$\frac{1}{2}$ bilayer $t$-$J$ model in the strong coupling regime. This model explicitly incorporates the crucial role of strong Hund's coupling, which favors the formation of local spin-triplet states from the two onsite $E_g$ orbital electrons at half-filling. We further investigate the model using both slave-particle mean-field theory and the density matrix renormalization group method. Our simulation results reveal that the dominate pairing channel is the interlayer one in the $3d_{x^2-y^2}$ orbital. The Hund's coupling is shown to enhance superconductivity within a reasonable physical range. Moreover, electron doping strengthens superconductivity by increasing carrier density; in contrast, hole doping weakens superconductivity. These findings offer critical insights into the unconventional superconductivity of pressurized La$_3$Ni$_2$O$_7$ and underline the important role of orbital-selective behavior and Hund's rule. △ Less

Submitted 5 January, 2026; v1 submitted 16 April, 2025; originally announced April 2025.

Comments: 18 pages, 16 figures

Journal ref: Phys. Rev. B 112, 214515 (2025)

Magnetotransport evidence of a potential low-lying Dirac node in NbAl$_3$

Authors: Ying Kit Tsui, Chia-Nung Kuo, Makoto Shimizu, Yajian Hu, Youichi Yanase, Chin Shan Lue, Wei Zhang, Swee K. Goh

Abstract: NbAl$_3$ is a novel semimetal with a type-II Dirac node ~230 meV above the Fermi energy. We have performed both out-of-plane ($B\parallel c$) and in-plane magnetotransport measurements ($B\perp c$) on single-crystalline NbAl$_3$. In our out-of-plane data, we observe an interesting linear component in the transverse magnetoresistance, and the mobility spectrum analysis of the out-of-plane data reve… ▽ More NbAl$_3$ is a novel semimetal with a type-II Dirac node ~230 meV above the Fermi energy. We have performed both out-of-plane ($B\parallel c$) and in-plane magnetotransport measurements ($B\perp c$) on single-crystalline NbAl$_3$. In our out-of-plane data, we observe an interesting linear component in the transverse magnetoresistance, and the mobility spectrum analysis of the out-of-plane data reveals an emergence of high-mobility electrons at low temperatures. Near $B\parallel c$, Shubnikov-de Haas oscillations are discerned in the magnetoresistance. The oscillation frequencies agree with the density functional theory calculation, the same theory that shows that the Dirac node is far above the Fermi energy. Therefore, the out-of-plane results cannot be attributed to the type-II Dirac node but suggest NbAl$_3$ has additional Dirac or Weyl nodes close to the Fermi energy. To support this, we examine the in-plane data obtained with the magnetic field perpendicular to the tilting direction of the type-II Dirac cone. Such field direction excludes the possibility of chiral anomaly from the predicted type-II Dirac node. Remarkably, we observe the planar Hall effect, anisotropic magnetoresistance, and negative longitudinal magnetoresistance. These in-plane results are a strong indication of chiral anomaly unrelated to the previously established type-II Dirac node, pointing to the presence of additional Dirac or Weyl nodes near the Fermi energy. Our new density functional theory calculation reveals a type-I Dirac node ~50 meV below the Fermi energy that has previously been overlooked. We argue that the exotic transport phenomena observed in NbAl$_3$ can be attributed to the newly identified type-I Dirac node. △ Less

Submitted 13 March, 2025; originally announced March 2025.

Comments: 4 figures. Accepted for publication as a Letter in Phys. Rev. B

Journal ref: Phys. Rev. B 111, L121111 (2025)

Impact of Pressure and Apical Oxygen Vacancies on Superconductivity in La$_3$Ni$_2$O$_7$

Authors: Chen Lu, Ming Zhang, Zhiming Pan, Congjun Wu, Fan Yang

Abstract: The bilayer nickelate La$_3$Ni$_2$O$_7$ under pressure has recently emerged as a promising system for high-$T_c$ superconductivity. In this work, we investigate the fate of the superconducting properties in La$_3$Ni$_2$O$_{7}$ under pressure, focusing on the effects of structural deformation and apical oxygen vacancies. Employing a low-energy effective $t$-$J_{\parallel}$-$J_{\perp}$ model for the… ▽ More The bilayer nickelate La$_3$Ni$_2$O$_7$ under pressure has recently emerged as a promising system for high-$T_c$ superconductivity. In this work, we investigate the fate of the superconducting properties in La$_3$Ni$_2$O$_{7}$ under pressure, focusing on the effects of structural deformation and apical oxygen vacancies. Employing a low-energy effective $t$-$J_{\parallel}$-$J_{\perp}$ model for the $3d_{x^2-y^2}$ orbitals within the slave-boson mean-field approach, we demonstrate that the pairing strength is significantly enhanced in the high-pressure tetragonal $I4/mmm$ phase compared to the ambient pressure orthorhombic $Amam$ phase. Furthermore, by simulating random configurations of apical oxygen vacancies, we show that oxygen vacancies suppress both pairing strength and superfluid density. These results underscore the critical role of pressure and oxygen stoichiometry in tuning the SC of La$_3$Ni$_2$O$_7$, providing key insights into optimizing its high-$T_c$ behavior. △ Less

Submitted 5 January, 2026; v1 submitted 20 February, 2025; originally announced February 2025.

Comments: 8 pages, 8 figures

Journal ref: Communications Physics 8, 354 (2025)

Nonreciprocal Control of the Speed of Light Using Cavity Magnonics

Authors: Jiguang Yao, Chenyang Lu, Xiaolong Fan, Desheng Xue, Greg E. Bridges, C. -M. Hu

Abstract: We demonstrate nonreciprocal control of the speed of light by sending a microwave pulse through a cavity magnonics device. In contrast to reciprocal group velocity controlled by conventional electromagnetically induced transparency (EIT) effect, incorporating dissipative magnon-photon coupling establishes a non-reciprocal EIT effect, allowing slow and fast light propagation in opposite directions… ▽ More We demonstrate nonreciprocal control of the speed of light by sending a microwave pulse through a cavity magnonics device. In contrast to reciprocal group velocity controlled by conventional electromagnetically induced transparency (EIT) effect, incorporating dissipative magnon-photon coupling establishes a non-reciprocal EIT effect, allowing slow and fast light propagation in opposite directions at the same frequency with comparable amplitude. Remarkably, reversing the magnetic field enables a directional switch between non-reciprocal fast and slow light. This discovery may offer new possibilities for pulse time regulation in microwave signal communications, neuromorphic computing, and quantum signal processing. △ Less

Submitted 14 February, 2025; originally announced February 2025.

Comments: 7 pages, 4 figures

Reliable Density Functional Theory Predictions of Bandgaps for Materials

Authors: Chenxi Lu, Musen Li, Michael J. Ford, Rika Kobayashi, Roger Amos, Jeffrey R. Reimers

Abstract: We consider methods for optimizing the bandgap calculation of 3D materials, considering 340 sample materials. Examined are the effects of the choice of the pseudopotential to describe core electrons, the plane-wave basis set cutoff energy, and the Brillouin zone integration. Cost-saving calculations in which the structure is optimized using reduced-quality Brillouin zone integrations and cutoff en… ▽ More We consider methods for optimizing the bandgap calculation of 3D materials, considering 340 sample materials. Examined are the effects of the choice of the pseudopotential to describe core electrons, the plane-wave basis set cutoff energy, and the Brillouin zone integration. Cost-saving calculations in which the structure is optimized using reduced-quality Brillouin zone integrations and cutoff energies were found to lead to experimentally significant errors exceeding 0.1 eV in 18% of cases using the PBE functional and 21% of cases using PBE0. Such cost-savings approaches are therefore not recommended for general applications. Also, the current practice of using unoptimized grids to perform the Brillouin-zone integrations in bandgap calculations is found to be unreliable for 16% of materials using PBE and for 23% using PBE0. A k-space optimization scheme is introduced that interpolates extensive PBE results to determine a generally useful approach that when used in PBE0 calculations is found to be inadequate for only 1.6% of the materials studied. △ Less

Submitted 27 January, 2025; originally announced January 2025.

Journal ref: Computational Condensed Matter 45 2025 e01122

Octupolar Weyl Superconductivity from Electron-electron Interaction

Authors: Zhiming Pan, Chen Lu, Fan Yang, Congjun Wu

Abstract: Unconventional superconductivity arising from electron-electron interaction can manifest exotic symmetry and topological properties. We investigate the superconducting pairing symmetry problem based on the 3D cubic $O_h$ symmetry with both weak- and strong-coupling approaches. The dominant pairing symmetries belong to the two-dimensional $E_g$ representation at low and intermediate doping levels,… ▽ More Unconventional superconductivity arising from electron-electron interaction can manifest exotic symmetry and topological properties. We investigate the superconducting pairing symmetry problem based on the 3D cubic $O_h$ symmetry with both weak- and strong-coupling approaches. The dominant pairing symmetries belong to the two-dimensional $E_g$ representation at low and intermediate doping levels, and the complex mixing gap function of the $d_{3z^2-r^2}+id_{x^2-y^2}$-type is energetically favored in the ground state. Cooper pairs with such a symmetry do not possess orbital angular momentum (OAM) moments, which is different from other time-reversal symmetry breaking pairings such as $p_x+ip_y$ (e.g $^3$He-A) and $d_{x^2-y^2}+id_{xy}$ under the planar hexagonal symmetry. Instead, they develop the octupolar $O_{xyz}$ component of OAM, which results in 8 nodal points along the body diagonal directions exhibiting an alternating distribution of monopole charges $\pm 1$. This leads to an intriguing 3D Weyl topological SC, which accommodates nontrivial surface states of Majorana arcs. Our results appeal for material realizations and experimental tests in optical lattices. △ Less

Submitted 18 June, 2025; v1 submitted 11 November, 2024; originally announced November 2024.

Comments: 7+9 pages, 3+3 figures

Magnetic Field-Induced Polar Order in Monolayer Molybdenum Disulfide Transistors

Authors: Duxing Hao, Wen-Hao Chang, Yu-Chen Chang, Wei-Tung Liu, Sheng-Zhu Ho, Chen-Hsuan Lu, Tilo H. Yang, Naoya Kawakami, Yi-Chun Chen, Ming-Hao Liu, Chun-Liang Lin, Ting-Hua Lu, Yann-Wen Lan, Nai-Chang Yeh

Abstract: In semiconducting monolayer transition metal dichalcogenides (ML-TMDs), broken inversion symmetry and strong spin-orbit coupling result in spin-valley lock-in effects so that the valley degeneracy may be lifted by external magnetic fields, potentially leading to real-space structural transformation. Here, we report magnetic field (B)-induced giant electric hysteretic responses to back-gate voltage… ▽ More In semiconducting monolayer transition metal dichalcogenides (ML-TMDs), broken inversion symmetry and strong spin-orbit coupling result in spin-valley lock-in effects so that the valley degeneracy may be lifted by external magnetic fields, potentially leading to real-space structural transformation. Here, we report magnetic field (B)-induced giant electric hysteretic responses to back-gate voltages in ML-MoS2 field-effect transistors (FETs) on SiO2/Si at temperatures < 20 K. The observed hysteresis increases with |B| up to 12 T and is tunable by varying the temperature. Raman spectroscopic and scanning tunneling microscopic studies reveal significant lattice expansion with increasing |B| at 4.2 K, and this lattice expansion becomes asymmetric in ML-MoS2 FETs on rigid SiO2/Si substrates, leading to out-of-plane mirror symmetry breaking and the emergence of a tunable out-of-plane ferroelectric-like polar order. This broken symmetry-induced polarization in ML-MoS2 shows typical ferroelectric butterfly hysteresis in piezo-response force microscopy, adding ML-MoS2 to the single-layer material family that exhibit out-of-plane polar order-induced ferroelectricity, which is promising for such technological applications as cryo-temperature ultracompact non-volatile memories, memtransistors, and ultrasensitive magnetic field sensors. Moreover, the polar effect induced by asymmetric lattice expansion may be further generalized to other ML-TMDs and achieved by nanoscale strain engineering of the substrate without magnetic fields. △ Less

Submitted 27 October, 2024; originally announced October 2024.

Journal ref: Adv. Mater. 36 (2024) 2411393

Finite-temperature topological invariant for higher-order topological insulators

Authors: Congwei Lu, Lixiong Wu, Qing Ai

Abstract: We investigate the effects of temperature on the higher-order topological insulators (HOTIs). The finite-temperature topological invariants for the HOTIs can be constructed by generalizing the Resta's polarization for the ground state to the ensemble geometric phase (EGP) for the mixed states, [C.-E. Bardyn, L. Wawer, A. Altland, M. Fleischhauer, and S. Diehl, PhysRevX.8.011035}{Phys. Rev. X 8, 01… ▽ More We investigate the effects of temperature on the higher-order topological insulators (HOTIs). The finite-temperature topological invariants for the HOTIs can be constructed by generalizing the Resta's polarization for the ground state to the ensemble geometric phase (EGP) for the mixed states, [C.-E. Bardyn, L. Wawer, A. Altland, M. Fleischhauer, and S. Diehl, PhysRevX.8.011035}{Phys. Rev. X 8, 011035 (2018)}]. The EGP is consistent with the Resta's polarization both at zero temperature and at finite temperatures in the thermodynamic limit. {We find that the temperature can change the critical point and thus induces a phase transition from a topologically-trivial phase to a nontrivial phase in a finite-size system, manifesting changes in the winding of the EGP. △ Less

Submitted 28 July, 2024; originally announced July 2024.

Journal ref: Phys. Rev. B 111, L201101 (2025)

Entangelment Entropy on Generalized Brillouin Zone

Authors: Zhenghao Yang, Chaoze Lu, Xiancong Lu

Abstract: We investigate the entanglement properties of non-Hermitian Su-Schrieffer-Heeger (SSH) model from the perspective of the Generalized Brillouin Zone (GBZ). The non-Bloch entanglement entropy is defined on a quasi-reciprocal lattice, obtained by performing an ordinary Fourier transformation on the non-Bloch Hamiltonian. We demonstrate that the broken bulk-boundary correspondence is recovered in term… ▽ More We investigate the entanglement properties of non-Hermitian Su-Schrieffer-Heeger (SSH) model from the perspective of the Generalized Brillouin Zone (GBZ). The non-Bloch entanglement entropy is defined on a quasi-reciprocal lattice, obtained by performing an ordinary Fourier transformation on the non-Bloch Hamiltonian. We demonstrate that the broken bulk-boundary correspondence is recovered in terms of the non-Bloch entanglement entropy. When the GBZ is circular, we show that the non-Bloch entanglement entropy is well-defined (real and positive-definite) in large parameter regions, except close to the exceptional points (EPs). In the critical region, we found that each Fermi point contributes precisely 1 to the central charge $c$ of the logarithmic scaling. At the EP, the central charge becomes negative due to the presence of the exceptional bound state. For the case of non-circular GBZ, long-range hopping emerges in the quasi-reciprocal lattice, and the von Neumann entropy on the GBZ is no longer real. However, the non-Bloch edge entanglement entropy remains real, which serves as a reliable topological indicator and respects the bulk-boundary correspondence. We compute the topological phase diagram, and reveal the critical behavior along the exceptional phase boundaries. △ Less

Submitted 12 January, 2025; v1 submitted 21 June, 2024; originally announced June 2024.

Comments: 9 pages, 7 figures

Journal ref: Phys. Rev. B 110, 235127 (2024) (EDITORS' SUGGESTION)

High-field magnetoelectric coupling and successive magnetic transitions in Mn-doped polar antiferromagnet Ni3TeO6

Authors: J. H. Zhang, L. Lin, C. Dong, Y. T. Chang, J. F. Wang, C. L. Lu, P. Z. Chen, W. J. Zhai, G. Z. Zhou, L. Huang, Y. S. Tang, S. H. Zheng, M. F. Liu, X. H. Zhou, Z. B. Yan, J. -M. Liu

Abstract: Among the 3d transition metal ions doped polar Ni3TeO6, Mn-doped Ni3TeO6 has stimulated great interest due to its high magnetic ordering temperature and complex magnetic phases, but the mechanism of magnetoelectric (ME) coupling is far from understood. Herein we report our systematic investigation of the chemical control of magnetism, metamagnetic transition, and ME properties of Ni3-xMnxTeO6 sing… ▽ More Among the 3d transition metal ions doped polar Ni3TeO6, Mn-doped Ni3TeO6 has stimulated great interest due to its high magnetic ordering temperature and complex magnetic phases, but the mechanism of magnetoelectric (ME) coupling is far from understood. Herein we report our systematic investigation of the chemical control of magnetism, metamagnetic transition, and ME properties of Ni3-xMnxTeO6 single crystals in high magnetic field (H) up to 52 T. We present a previously unreported weak ferromagnetic behavior appeared in the ab plane below 9.5 K in addition to the incommensurate helical and commensurate collinear antiferromagnetic states. In the low-field region, a spin-flop type metamagnetic transition without any hysteresis occurs at Hc1 for H // c, while another metamagnetic transition accompanied with a change in electric polarization is observed at Hc2 in the high-field region both for H // c and H // ab above 30 K, which can be attributed to the sudden rotation of magnetic moments at Ni2 sites. The ME measurements reveal that a first-order ME effect is observed in the low-T and low-H regions, while a second-order ME coupling term appears above 30 K in the magnetic field range of Hc1 < H < Hc2 for H // c and H < Hc2 for H // ab, both becoming significant with increasing temperature. Eventually, they are dominated by the second-order ME effect near the antiferromagnetic transition temperature. The present work demonstrates that Ni3-xMnxTeO6 is an exotic magnetoelectric material compared with Ni3TeO6 and its derivatives, thereby providing insights to better understand the magnetism and ME coupling in Ni3TeO6 and its derivatives. △ Less

Submitted 29 May, 2024; v1 submitted 24 May, 2024; originally announced May 2024.

Comments: 30 pages with 8 figures

Journal ref: Phys. Rev. B 109, 184112 (2024)

Observation of oriented Landau levels in Berry dipole semimetals

Authors: Qingyang Mo, Riyi Zheng, Cuicui Lu, Xueqin Huang, Zhengyou Liu, Shuang Zhang

Abstract: Band crossing points, such as Weyl and Dirac points, play a crucial role in the topological classification of materials and guide the exploration of exotic topological phases. The Berry dipole, a three-dimensional band crossing point beyond the Chern class, hosts a dipolar Berry curvature field and gives rise to numerous nontrivial quantum geometric effects. It has been proposed that the Berry dip… ▽ More Band crossing points, such as Weyl and Dirac points, play a crucial role in the topological classification of materials and guide the exploration of exotic topological phases. The Berry dipole, a three-dimensional band crossing point beyond the Chern class, hosts a dipolar Berry curvature field and gives rise to numerous nontrivial quantum geometric effects. It has been proposed that the Berry dipole exhibits oriented Landau levels, whose spectrum critically relies on the orientation of the applied magnetic field. However, experimental demonstration of this phenomenon has remained elusive. Here we experimentally demonstrate oriented Landau levels by carefully engineering an inhomogeneous acoustic lattice. We observe distinct Landau level spectra and different propagation properties when the orientation of the pseudomagnetic field is reversed. Notably, we discover a new type of helical zero modes whose existence critically depends on the magnetic field's orientation. Our work paves the way for studying band crossings beyond Chern-class crossing points, including Berry multipoles and even-dimensional monopoles. Furthermore, it offers new insight for exploring topological devices. △ Less

Submitted 13 May, 2024; originally announced May 2024.

Physical properties and electronic structure of the two-gap superconductor V$_{2}$Ga$_{5}$

Authors: P. -Y. Cheng, Mohamed Oudah, T. -L. Hung, C. -E. Hsu, C. -C. Chang, J. -Y. Haung, T. -C. Liu, C. -M. Cheng, M. -N. Ou, W. -T. Chen, L. Z. Deng, C. -C. Lee, Y. -Y. Chen, C. -N. Kuo, C. -S. Lue, Janna Machts, Kenji M. Kojima, Alannah M. Hallas, C. -L. Huang

Abstract: We present a thorough investigation of the physical properties and superconductivity of the binary intermetallic V2Ga5. Electrical resistivity and specific heat measurements show that V2Ga5 enters its superconducting state below Tsc = 3.5 K, with a critical field of Hc2,perp c(Hc2,para c) = 6.5(4.1) kOe. With H perp c, the peak effect was observed in resistivity measurements, indicating the ultrah… ▽ More We present a thorough investigation of the physical properties and superconductivity of the binary intermetallic V2Ga5. Electrical resistivity and specific heat measurements show that V2Ga5 enters its superconducting state below Tsc = 3.5 K, with a critical field of Hc2,perp c(Hc2,para c) = 6.5(4.1) kOe. With H perp c, the peak effect was observed in resistivity measurements, indicating the ultrahigh quality of the single crystal studied. The resistivity measurements under high pressure reveal that the Tsc is suppressed linearly with pressure and reaches absolute zero around 20 GPa. Specific heat and muon spin relaxation measurements both indicate that the two-gap s-wave model best describes the superconductivity of V2Ga5. The spectra obtained from angle-resolved photoemission spectroscopy measurements suggest that two superconducting gaps open at the Fermi surface around the Z and Γ points. These results are verified by first-principles band structure calculations. We therefore conclude that V2Ga5 is a phonon-mediated two-gap s-wave superconductor △ Less

Submitted 6 May, 2024; originally announced May 2024.

Comments: Some images experience distortion during the conversion process to EPS format

Journal ref: Phys. Rev. Research 6 6, 033253 (2024)

Significantly Enhanced Vacancy Diffusion in Mn-containing Alloys

Authors: Huaqing Guan, Hanwen Cui, Ning Ding, Kuo Yang, Siqi Jiang, Yanfei Sui, Yuanyuan Wang, Fuyang Tian, Zhe Li, Shuai Wang, Pengfei Zheng, Chenyang Lu, Qiu Xu, Levente Vitos, Shaosong Huang

Abstract: Manipulating point defects for tailored macroscopic properties remains a formidable challenge in materials science. This study demonstrates a proof-of-principle for a universal law involving element Mn, significantly enhancing vacancy diffusion through an unprecedented anomalous Friedel Oscillations phenomenon, across most metals in the periodic table. The correlation between Mn-induced point-defe… ▽ More Manipulating point defects for tailored macroscopic properties remains a formidable challenge in materials science. This study demonstrates a proof-of-principle for a universal law involving element Mn, significantly enhancing vacancy diffusion through an unprecedented anomalous Friedel Oscillations phenomenon, across most metals in the periodic table. The correlation between Mn-induced point-defect dynamic changes and intrinsic macro-properties is robustly validated through the first-principles theory and well-designed experiments. The physical origin stems from Mn's exceptionally large effective intra-elemental 3d electron interactions, surpassing the Coulomb attraction induced by vacancy and disrupting the electron screening effect. Given the ubiquitous nature of vacancies and their recognition as the most crucial defects influencing nearly all physical and mechanical properties of crystalline materials, this outcome may drive advances in a broad domain. △ Less

Submitted 4 April, 2024; originally announced April 2024.

Boson sampling enhanced quantum chemistry

Authors: Zhong-Xia Shang, Han-Sen Zhong, Yu-Kun Zhang, Cheng-Cheng Yu, Xiao Yuan, Chao-Yang Lu, Jian-Wei Pan, Ming-Cheng Chen

Abstract: In this work, we give a hybrid quantum-classical algorithm for solving electronic structure problems of molecules using only linear quantum optical systems. The variational ansatz we proposed is a hybrid of non-interacting Boson dynamics and classical computational chemistry methods, specifically, the Hartree-Fock method and the Configuration Interaction method. The Boson part is built by a linear… ▽ More In this work, we give a hybrid quantum-classical algorithm for solving electronic structure problems of molecules using only linear quantum optical systems. The variational ansatz we proposed is a hybrid of non-interacting Boson dynamics and classical computational chemistry methods, specifically, the Hartree-Fock method and the Configuration Interaction method. The Boson part is built by a linear optical interferometer which is easier to realize compared with the well-known Unitary Coupled Cluster (UCC) ansatz composed of quantum gates in conventional VQE and the classical part is merely classical processing acting on the Hamiltonian. We called such ansatzes Boson Sampling-Classic (BS-C). The appearance of permanents in the Boson part has its physical intuition to provide different kinds of resources from commonly used single-, double-, and higher-excitations in classical methods and the UCC ansatz to exploring chemical quantum states. Such resources can help enhance the accuracy of methods used in the classical parts. We give a scalable hybrid homodyne and photon number measurement procedure for evaluating the energy value which has intrinsic abilities to mitigate photon loss errors and discuss the extra measurement cost induced by the no Pauli exclusion principle for Bosons with its solutions. To demonstrate our proposal, we run numerical experiments on several molecules and obtain their potential energy curves reaching chemical accuracy. △ Less

Submitted 18 April, 2024; v1 submitted 25 March, 2024; originally announced March 2024.

Comments: 15 pages, 5 figures

Journal ref: PRX Quantum 2025

Phonon and defect mediated quantum anomalous Hall insulator to metal transition in magnetically doped topological insulators

Authors: Akiyoshi Park, Adrian Llanos, Chun-I Lu, Yinan Chen, Sebastien N. Abadi, Chien- Chang Chen, Marcus L. Teague, Lixuan Tai, Peng Zhang, Kang L. Wang, Nai-Chang Yeh

Abstract: Quantum Anomalous Hall (QAH) state in six quintuple layer Cr$_{0.1}$(Bi$_{0.2}$Sb$_{0.8}$)$_{1.9}$Te$_3$ thin films were studied through scanning tunneling spectroscopy (STS) and electrical transport measurements. While the surface state is gapless above the Curie temperature ($T_\mathrm{C} \approx 30$ K), scanning tunneling spectroscopy (STS) of the sample reveals a topologically non-trivial gap… ▽ More Quantum Anomalous Hall (QAH) state in six quintuple layer Cr$_{0.1}$(Bi$_{0.2}$Sb$_{0.8}$)$_{1.9}$Te$_3$ thin films were studied through scanning tunneling spectroscopy (STS) and electrical transport measurements. While the surface state is gapless above the Curie temperature ($T_\mathrm{C} \approx 30$ K), scanning tunneling spectroscopy (STS) of the sample reveals a topologically non-trivial gap with an average value of $\approx 13.5$ meV at 4.2 K below the ferromagnetic transition. Nonetheless, areal STS scans of the magnetic topological insulator exhibit energy modulations on the order of several meV's in the surface bands which result in the valence band maximum in some regions becoming higher than the energy of the conduction band minimum of some other regions that are spatially separated by no more than 3 nm. First principle calculations demonstrate that the origin of the observed inhomogeneous energy band alignment is an outcome of many-body interactions, namely electron-defect interactions and electron-phonon interactions. Defects play the role of locally modifying the energy landscape of surface bands while electron-phonon interactions renormalize the surface bands such that the surface gap becomes reduced by more than 1 meV as temperature is raised from 0 to 4.2 K. These many-body interactions at a finite temperature result in substantial increase of electron tunneling across the spatially separated conduction band pockets even for finite temperatures well below $T_\mathrm{C}$ , thus driving the magnetic topological insulator out of its QAH insulating phase into a metallic phase at a relatively low temperature. △ Less

Submitted 12 February, 2024; originally announced February 2024.

Comments: 15 pages, 15 figures

Journal ref: Phys. Rev. B 109, 075125 (2024)

Superconductivity in La$_4$Ni$_3$O$_{10}$ Under Pressure

Authors: Chen Lu, Zhiming Pan, Fan Yang, Congjun Wu

Abstract: The discovery of superconductivity (SC) in the trilayer nickelate compound La$_{4}$Ni$_3$O$_{10}$ under pressure has generated significant interest. In this work, we propose a trilayer two $E_g$-orbital $t$-$J_{\parallel}$-$J_{\perp}$ model to investigate the microscopic origin of SC in this system. In the strong-coupling regime, each layer is governed by a $t$-$J_{\parallel}$ model with intra-lay… ▽ More The discovery of superconductivity (SC) in the trilayer nickelate compound La$_{4}$Ni$_3$O$_{10}$ under pressure has generated significant interest. In this work, we propose a trilayer two $E_g$-orbital $t$-$J_{\parallel}$-$J_{\perp}$ model to investigate the microscopic origin of SC in this system. In the strong-coupling regime, each layer is governed by a $t$-$J_{\parallel}$ model with intra-layer antiferromagnetic exchange $J_{\parallel}$, while electrons are allowed to hop between layers, interacting via inter-layer exchange $J_{\perp}$. The inner-layer $3d_{z^2}$-orbital electrons tends to form bonding states with those in the neighboring layers, leading to redistribution of the electron densities. The numerical simulation results indicate that SC is predominantly mediated by the $3d_{z^2}$ orbital, characterized by an intra-layer extended $s$-wave pairing in the outer layers, accompanied by an inter-layer pairing with opposite sign. Furthermore, we find that electron doping enhances SC, while hole doping tends to suppress it. These findings provide new insights into the SC mechanisms of La$_{4}$Ni$_3$O$_{10}$ and its sensitivity to charge doping. △ Less

Submitted 22 April, 2025; v1 submitted 9 February, 2024; originally announced February 2024.

Comments: 8 pages, 6 figures

Journal ref: Phys. Rev. B 111, 134515 (2025)

Many-body phase transitions in a non-Hermitian Ising chain

Authors: Chao-Ze Lu, Xiaolong Deng, Su-Peng Kou, Gaoyong Sun

Abstract: We study many-body phase transitions in a one-dimensional ferromagnetic transversed field Ising model with an imaginary field and show that the system exhibits three phase transitions: one second-order phase transition and two $\mathcal{PT}$ phase transitions. The second-order phase transition occurring in the ground state is investigated via biorthogonal and self-normal entanglement entropy, for… ▽ More We study many-body phase transitions in a one-dimensional ferromagnetic transversed field Ising model with an imaginary field and show that the system exhibits three phase transitions: one second-order phase transition and two $\mathcal{PT}$ phase transitions. The second-order phase transition occurring in the ground state is investigated via biorthogonal and self-normal entanglement entropy, for which we develop an approach to perform finite-size scaling theory to extract the central charge for small systems. Compared with the second-order phase transition, the first $\mathcal{PT}$ transition is characterized by the appearance of an exceptional point in the full energy spectrum, while the second $\mathcal{PT}$ transition only occurs in specific excited states. Furthermore, we interestingly show that both of exceptional points are second-order in terms of scalings of imaginary parts of the energy. This work provides an exact solution for many-body phase transitions in non-Hermitian systems. △ Less

Submitted 8 August, 2024; v1 submitted 19 November, 2023; originally announced November 2023.

Comments: 7 pages, 5 figures

Journal ref: Phys. Rev. B 110, 014441 (2024)

Hydrogen Doping Induced $p_x\pm ip_y$ Triplet Superconductivity in Quasi-One-Dimensional K$_2$Cr$_3$As$_3$

Authors: Ming Zhang, Chen Lu, Yajiang Chen, Yunbo Zhang, Fan Yang

Abstract: Quasi-one-dimensional (Q1D) Cr-based pnictide K$_2$Cr$_3$As$_3$ has aroused great research interest due to its possible triplet superconducting pairing symmetry. Recent experiments have shown that incorporating hydrogen atoms into K$_2$Cr$_3$As$_3$ would significantly change its electronic and magnetic properties. Hence, it's necessary to investigate the impact of hydrogen doping in superconductin… ▽ More Quasi-one-dimensional (Q1D) Cr-based pnictide K$_2$Cr$_3$As$_3$ has aroused great research interest due to its possible triplet superconducting pairing symmetry. Recent experiments have shown that incorporating hydrogen atoms into K$_2$Cr$_3$As$_3$ would significantly change its electronic and magnetic properties. Hence, it's necessary to investigate the impact of hydrogen doping in superconducting pairing symmetry of this material. Employing the hydrogen as an non-trivial electron-doping, our calculates show that, different from the $p_z$-wave obtained without hydrogen, the system exhibits $p_x\pm ip_y$ pairing superconductivity under specific hydrogen doping. Specifically, we adopt the random-phase-approximation approach based on a six-band tight-binding model equipped with multi-orbital Hubbard interactions to study the hydrogen-doping dependence of the pairing symmetry and superconducting $T_c$. Under the rigid-band approximation, our pairing phase diagram shows the spin-triplet pairing states is dominated through out the hydrogen-doping regime $x\in (0,0.7)$. Particularly, the $T_c\sim x$ curve shows a peak at the 3D-quasi-1D Lifshitz transition point, and the pairing symmetry around this doping level is $p_x\pm ip_y$. The physical origin of this pairing symmetry is that the density of states is mainly concentrated at $k_x(k_y)$ with large momentum. Due to the three-dimensional character of the real material, this $p_x\pm ip_y$-wave superconducting state possesses point gap nodes. We further provide experiment prediction to identify this triplet $p_x\pm ip_y$-wave superconductivity. △ Less

Submitted 24 December, 2023; v1 submitted 17 November, 2023; originally announced November 2023.

Comments: 9 pages,9 figures. arXiv admin note: substantial text overlap with arXiv:2111.14367

Report number: Phys. Rev. B 110, 094519

Journal ref: Phys. Rev. B 2024

Theory of $d + id$ Second-Order Topological Superconductors

Authors: Zi-Ming Wang, Meng Zeng, Chen Lu, Da-Shuai Ma, Rui-Xing Zhang, Lun-Hui Hu, Dong-Hui Xu

Abstract: Topological superconductors are a class of unconventional superconducting materials featuring sub-gap zero-energy Majorana bound modes that hold promise as a building block for topological quantum computing. In this work, we study the realization of second-order topology that defines anomalous gapless boundary modes in a two-orbital superconductor with spin-orbital couplings. We reveal a time-reve… ▽ More Topological superconductors are a class of unconventional superconducting materials featuring sub-gap zero-energy Majorana bound modes that hold promise as a building block for topological quantum computing. In this work, we study the realization of second-order topology that defines anomalous gapless boundary modes in a two-orbital superconductor with spin-orbital couplings. We reveal a time-reversal symmetry-breaking second-order topological superconducting phase with $d+id$-wave orbital-dependent paring without the need for the external magnetic field. Remarkably, this orbital-active $d$-wave paring gives rise to anomalous zero-energy Majorana corner modes, which is in contrast to conventional chiral $d$-wave pairing, accommodating one-dimensional Majorana edge modes. Our work not only reveals a unique mechanism of time-reversal symmetry breaking second-order topological superconductors but also bridges the gap between second-order topology and orbital-dependent pairings. △ Less

Submitted 27 October, 2023; originally announced October 2023.

Comments: 5+ pages, 5 figures

Berry Curvature and Bulk-Boundary Correspondence from Transport Measurement for Photonic Chern Bands

Authors: Chao Chen, Run-Ze Liu, Jizhou Wu, Zu-En Su, Xing Ding, Jian Qin, Lin Wang, Wei-Wei Zhang, Yu He, Xi-Lin Wang, Chao-Yang Lu, Li Li, Barry C. Sanders, Xiong-Jun Liu, Jian-Wei Pan

Abstract: Berry curvature is a fundamental element to characterize topological quantum physics, while a full measurement of Berry curvature in momentum space was not reported for topological states. Here we achieve two-dimensional Berry curvature reconstruction in a photonic quantum anomalous Hall system via Hall transport measurement of a momentum-resolved wave packet. Integrating measured Berry curvature… ▽ More Berry curvature is a fundamental element to characterize topological quantum physics, while a full measurement of Berry curvature in momentum space was not reported for topological states. Here we achieve two-dimensional Berry curvature reconstruction in a photonic quantum anomalous Hall system via Hall transport measurement of a momentum-resolved wave packet. Integrating measured Berry curvature over the two-dimensional Brillouin zone, we obtain Chern numbers corresponding to -1 and 0. Further, we identify bulk-boundary correspondence by measuring topology-linked chiral edge states at the boundary. The full topological characterization of photonic Chern bands from Berry curvature, Chern number, and edge transport measurements enables our photonic system to serve as a versatile platform for further in-depth study of novel topological physics. △ Less

Submitted 16 October, 2023; originally announced October 2023.

Journal ref: Phys. Rev. Lett. 131, 133601 (25 September 2023)