Showing 1–50 of 623 results for author: Wu, C

Second-Chern Bounds in Non-Abelian Quantum Geometry

Authors: Junwen Zhao, Zhiming Pan, Kang Yang, Congjun Wu

Abstract: We study the quantum geometry of doubly degenerate energy levels in a four-dimensional parameter space. For degenerate pairs with $SU(2)$ gauge structures, the quantum geometry obeys $\big(\textrm{tr } g\big)^2/16\geq\sqrt{\det g}\geq |\textrm{Tr}(F\wedge F)|/12$. The first inequality characterizes the anisotropy in the metric. The second determinant inequality measures the self-duality of the cur… ▽ More We study the quantum geometry of doubly degenerate energy levels in a four-dimensional parameter space. For degenerate pairs with $SU(2)$ gauge structures, the quantum geometry obeys $\big(\textrm{tr } g\big)^2/16\geq\sqrt{\det g}\geq |\textrm{Tr}(F\wedge F)|/12$. The first inequality characterizes the anisotropy in the metric. The second determinant inequality measures the self-duality of the curvature under Hodge star operation and the inter-level processes that do not close under the three $SU(2)$ rotations of the doubly degenerate levels. The saturation of the determinant bound induces a quaternion Kähler structure on the four-dimensional parameter space, analogous to the complex structure induced by the ideal-band condition in two-dimensional Chern insulators. As examples, four-band Dirac Hamiltonians automatically saturate the determinant bound and possess a topological zero in $\textrm{Tr}(F\wedge F)$. We discuss the comparison to degenerate pairs with $U(2)$ gauge structures. △ Less

Submitted 12 August, 2026; originally announced August 2026.

Comments: 6 pages

Annular Majorana mode in a superconducting topological insulator

Authors: Shengshan Qin, Chi Wu, Lun-hui Hu, Tiantian Zhang, Jiangping Hu

Abstract: When the surface states of a topological insulator becomes superconducting, topological superconductivity can be obtained, and each vortex on the surface can host one single Majorana zero-energy mode which is usually a wave packet decaying exponentially off the vortex core. Here, we predict stable Majorana zero-energy mode whose wave function is ring-shape, dubbed as annular Majorana mode, in the… ▽ More When the surface states of a topological insulator becomes superconducting, topological superconductivity can be obtained, and each vortex on the surface can host one single Majorana zero-energy mode which is usually a wave packet decaying exponentially off the vortex core. Here, we predict stable Majorana zero-energy mode whose wave function is ring-shape, dubbed as annular Majorana mode, in the superconducting vortex in topological insulators respecting $3$-fold or $6$-fold rotational symmetry. Such topological insulators are featured with a single nonlinear Dirac cone located at $\barΓ$ or three linear Dirac cones at $\bar{\text{M}}$ in the surface Brillouin zone. The annular Majorana mode originates from the effective chiral $f$-wave superconductivity on the nonlinear Dirac cone in the former case and the interference of the effective chiral $p$-wave superconductivity on the three linear Dirac cones in the latter. In both cases, the annular Majorana mode is stabilized by the rotational symmetry and the winding number $3$ carried by the surface states. Candidate materials supporting the annular Majorana mode are predicted. Our work provides new insights into the topological superconductivity in superconducting topological insulators. △ Less

Submitted 6 August, 2026; originally announced August 2026.

Emergent Interfacial Magnetism in Epitaxial RuO$_2$

Authors: Yudi Yang, Zhuang Qian, Shi Liu, Congjun Wu

Abstract: The magnetic ground state of the altermagnet candidate RuO$_2$ remains controversial, with magnetic signatures observed mainly in epitaxial films. Here we show, using first-principles calculations, that magnetism in epitaxial RuO$_2$ can emerge as an interfacial boundary phase at TiO$_2$/RuO$_2$ interfaces. While TiO$_2$-induced epitaxial strain alone does not make (001)-oriented RuO$_2$ magnetic,… ▽ More The magnetic ground state of the altermagnet candidate RuO$_2$ remains controversial, with magnetic signatures observed mainly in epitaxial films. Here we show, using first-principles calculations, that magnetism in epitaxial RuO$_2$ can emerge as an interfacial boundary phase at TiO$_2$/RuO$_2$ interfaces. While TiO$_2$-induced epitaxial strain alone does not make (001)-oriented RuO$_2$ magnetic, explicit TiO$_2$/RuO$_2$ interfaces stabilize sizable Ru moments confined to the first few Ru layers. Charge-density and orbital-resolved analyses reveal interfacial electronic reconstruction, and substrate doping provides a route to tune the induced moments. In symmetric TiO$_2$/RuO$_2$/TiO$_2$ heterostructures, the two magnetic interfaces couple through the metallic RuO$_2$ spacer, producing a thickness-dependent alternation between weak-ferromagnetic and compensated altermagnetic states. Our results identify interface engineering as a practical route to stabilize and control fragile magnetism in RuO$_2$. △ Less

Submitted 17 July, 2026; originally announced July 2026.

Phase-Field Simulation of Dendrite Evolution in All-Solid-State Sodium Batteries during Cycling

Authors: Chengyin Wu, Wolfgang Windl, Jung-Hyun Kim, Yanzhou Ji

Abstract: Dendrite growth during cycling remains a critical challenge for all-solid-state batteries (SSBs), limiting the full realization of their inherent safety and high energy density. In particular, the mechanisms of continuous dendrite penetration during charge-discharge cycling remain poorly understood and are difficult to characterize experimentally. This study applies a phase-field model, informed b… ▽ More Dendrite growth during cycling remains a critical challenge for all-solid-state batteries (SSBs), limiting the full realization of their inherent safety and high energy density. In particular, the mechanisms of continuous dendrite penetration during charge-discharge cycling remain poorly understood and are difficult to characterize experimentally. This study applies a phase-field model, informed by density functional theory calculations, to rationalize and visualize the dendrite penetration behaviors during cycling in sodium (Na) SSBs with pure Na or Na-Sb alloy anodes and polycrystalline Na$_3$SbS$_4$ electrolyte. We show that dendrite stripping is intrinsically asymmetric with respect to plating due to grain boundary geometry, leading to the formation of isolated Na metal that persists between cycles. This residual Na metal becomes kinetically stabilized at grain-boundary junctions and is readily reactivated during subsequent plating, thereby accelerating and amplifying dendrite penetration. We further investigate the effects of applied voltage, solid-electrolyte microstructure, and anode chemistry on this phenomenon. These findings establish isolated Na metal as a key contributor for continued dendrite propagation in Na SSBs and provide design principles for stabilizing anode/electrolyte interfaces in Na SSBs. △ Less

Submitted 19 August, 2026; v1 submitted 16 July, 2026; originally announced July 2026.

Dynamical Generation of Rectified Electric Current

Authors: Jin-Xin Hu, Congjun Wu

Abstract: Rectification is a fundamental nonlinear transport process that converts an alternating drive into a direct current. In this work, we propose a general theoretical framework for electric current rectification triggered by a dynamical external drive that couples to an arbitrary well-defined operator of a periodic system, and which in the static limit forbids any steady current. In the dynamical reg… ▽ More Rectification is a fundamental nonlinear transport process that converts an alternating drive into a direct current. In this work, we propose a general theoretical framework for electric current rectification triggered by a dynamical external drive that couples to an arbitrary well-defined operator of a periodic system, and which in the static limit forbids any steady current. In the dynamical regime, the finite frequency $Ω$ of the time-varying drive breaks time-translation invariance and injects energy into the system, enabling a second-order {\it nonlinear rectified} current that has no static counterpart. This rectification process has two distinct origins: (i) an impurity-scattering-modified distribution function at finite frequency, and (ii) a time-domain anomalous velocity stemming from a dynamical mixed Berry curvature. Both contributions persist when the driving frequency lies well below the optical transition gap. Applying our general theory to a buckled magnetic system subject to an out-of-plane oscillating electric field, we characterize the generated current as a {\it nonlinear magnetoelectric gyrotropic effect} and predict that the induced rectified current is sensitive to the magnetic order, thereby offering a feasible electrical probe of Néel order in non-coplanar antiferromagnets. △ Less

Submitted 14 July, 2026; originally announced July 2026.

Comments: 7 pages, 3 figures

Quantum Dot Moiré from Crossed MoS2 Nanoribbons

Authors: Xinting Shuai, Hao Zhang, Wenjing Wu, Chongning Wu, Maryam Amiri, T. A. M. Ragib Shahriar, Dian Pan, Zhi Kai Ng, Tymofii Pieshkov, Leeza Dutta, Yijun Zhou, Rohith Narra, Luke Van Leeuwen, Jishnu Murukeshan, Luyao Shi, Jiawei Lai, Atin Pramanik, Bipin Kumar Gupta, Edwin Hang Tong Teo, Robert Vajtai, Xiang Zhang, Hanyu Zhu, Shengxi Huang, Aditya D. Mohite, Pulickel M. Ajayan

Abstract: Twisted atomically thin layers have attracted much attention for Moiré potential and correlated quantum phenomena. However, existing Moiré superlattices have largely been limited to extensive wavefunction without lateral confinement. Here we introduce a new platform where 1D nanoribbons of 2D MoS2 grown by vapor deposition can be easily superposed at various angles from stacking and transferring,… ▽ More Twisted atomically thin layers have attracted much attention for Moiré potential and correlated quantum phenomena. However, existing Moiré superlattices have largely been limited to extensive wavefunction without lateral confinement. Here we introduce a new platform where 1D nanoribbons of 2D MoS2 grown by vapor deposition can be easily superposed at various angles from stacking and transferring, to form Moiré quantum dots at their intersections with unique exciton physics. Angle-dependent Moiré intersections show enhanced exciton emission at commensurate angle 22 deg, which demonstrates faster relaxation at the cryogenic temperature. A size-dependent study further exhibits a reduced exciton energy and soften out-of-plane interlayer coupling for smaller Moiré areas. Our results reveal exciton physics turnability via precise overlapping of 1D nanoribbons. △ Less

Submitted 8 July, 2026; originally announced July 2026.

Comments: 20 pages, 4 figures

Universal scaling of many-body effects in quantum tunneling

Authors: Hongmian Shui, Chi-Kin Lai, Chengyang Wu, Lorenzo Pizzino, Chi Zhang, Guohao Shen, Thierry Giamarchi, Hepeng Yao, Xiaoji Zhou

Abstract: Quantum tunneling is fundamental to diverse phenomena and underpins a wide range of modern technologies. In the study of superconducting quantum computation and high-temperature superconducting materials, tunneling on multi-particle scale is central. Recently, several cold atom experiments successfully simulated the tunneling process in a many-particle ensemble. However, the many-body nature remai… ▽ More Quantum tunneling is fundamental to diverse phenomena and underpins a wide range of modern technologies. In the study of superconducting quantum computation and high-temperature superconducting materials, tunneling on multi-particle scale is central. Recently, several cold atom experiments successfully simulated the tunneling process in a many-particle ensemble. However, the many-body nature remains largely unexplored. Here, we observe the universal scaling of many-body effects in quantum tunneling process, using a hexagonal-triangular quantum simulator with independent control of barrier, temperature and interaction. In the weak-interaction regime, the critical tunneling coefficient scales parabolically with temperature under various conditions, in contrast to the linear scaling of single-particle tunneling. By further increasing the interactions beyond the mean-field regime, the scaling exponent decreases, consistent with quantum field theory predictions. Our results address the fundamental question of how many-body effects renormalize quantum tunneling, with direct implications for correlated quantum matter and devices. △ Less

Submitted 30 June, 2026; originally announced June 2026.

Comments: 12 pages, 8 figures

Sliding ferroelectricity tunable conventional and anomalous spin Hall effects in bilayer 1T'-WTe2

Authors: Chao Wu, Pengqiang Dong, Kai Wei, Hanbo Sun, Ping Li

Abstract: The spin Hall effect, recognized for its high-speed, low-power, and highly controllable characteristics, is a key enabler for next-generation memory and logic devices. However, a primary challenge lies in achieving 180$^{\circ}$ magnetization switching without an external magnetic field in spin-orbit torque devices. Here, we propose a method to tune the conventional and anomalous spin Hall effects… ▽ More The spin Hall effect, recognized for its high-speed, low-power, and highly controllable characteristics, is a key enabler for next-generation memory and logic devices. However, a primary challenge lies in achieving 180$^{\circ}$ magnetization switching without an external magnetic field in spin-orbit torque devices. Here, we propose a method to tune the conventional and anomalous spin Hall effects by the intrinsic sliding ferroelectricity. Importantly, the anomalous spin Hall effect can enable the field-free switching of perpendicular magnetization. We find a substantial anomalous spin Hall conductivity of $σ_{xy}^{y}$ = 45.62 ($\hbar$/e)S/cm and $σ_{yx}^{y}$ = 56.84 ($\hbar$/e)S/cm in monolayer 1T'-WTe$_2$. These values are significantly enhanced to $σ_{xy}^{y}$ = -96.77 ($\hbar$/e)S/cm and $σ_{yx}^{y}$ = 104.03 ($\hbar$/e)S/cm in the bilayer 1T'-WTe$_2$. More interestingly, the sliding ferroelectricity enables reversible switching of the signs and magnitudes for both the conventional and anomalous spin Hall conductivities. This originates from the fact that the sliding ferroelectric markedly shifts the relative spin Berry curvature contributions from the valence and conduction bands around the $Γ$-X path. Our findings not only reveal a strong coupling between sliding ferroelectricity and spin transport, but also propose a strategy for the nonvolatile electrical control of spintronic devices. △ Less

Submitted 20 June, 2026; originally announced June 2026.

Comments: 9 pages, 5 figures, Accepted Applied Physics Letters

Steering Selective Formation and 2D Crystallization of [4]Radialenes on Au(111) via [1+1+1+1] Cycloaddition of Isocyanides and Enantioselective Molecular Recognition

Authors: Jian-Wei Liu, Ying Wang, Cui-Ping Wu, Jia-Xin Li, Li-Xia Kang, Jian-Hui Fu, Wen-Wen Gong, Pei-Nian Liu, Deng-Yuan Li

Abstract: Conjugated carbon rings are fundamental skeletons of organic functional materials, and their selective formation is of paramount importance in molecular materials engineering. However, steering the formation and 2D crystallization of conjugated carbon rings on the surface with high chemo- and stereoselectivities remains a great challenge. Here, we report a highly chemoselective [1+1+1+1] cycloaddi… ▽ More Conjugated carbon rings are fundamental skeletons of organic functional materials, and their selective formation is of paramount importance in molecular materials engineering. However, steering the formation and 2D crystallization of conjugated carbon rings on the surface with high chemo- and stereoselectivities remains a great challenge. Here, we report a highly chemoselective [1+1+1+1] cycloaddition of isocyanides on the Au(111) surface, which affords the stereospecific tetraaza[4]radialene products and further enables their long-range-ordered 2D crystallization via enantioselective molecular recognition. Using the progressive annealing method, we found that at room temperature, isocyanides undergo a coordination reaction with Au adatoms to form two-fold symmetric isocyanide-Au-isocyanide complexes. In contrast, gradually increasing the annealing temperature induces the transformation of these complexes and subsequent covalent polymerization, leading to the selective generation of tetraaza[4]radialenes with homotactic configurations. The tetraaza[4]radialenes further assemble into 2D homochiral molecular crystals through enantioselective molecular recognition driven by multiple C-H -- Cl hydrogen-bonding interactions. By combining scanning tunneling microscopy/spectroscopy and non-contact atomic force microscopy, we determined the atomic structure and molecular orbitals of tetraaza[4]radialene, confirming that its four-membered ring adopts a planar geometry with a localized lowest unoccupied molecular orbital. Density functional theory calculations suggest that the [1+1+1+1] cycloaddition process involves stepwise formation of C-C bonds and its high selectivity arises from the spatial steric hindrance. Our findings provide new insights into the selective formation of conjugated rings on surfaces and have implications for engineering 2D homochiral molecular crystallization. △ Less

Submitted 6 June, 2026; originally announced June 2026.

Layer-Resolved Nonlinear Optics in Finite-Thickness Two-Dimensional Systems

Authors: Liangting Ye, Chengzhi Wu, Zeyu Jiang, Bing Huang

Abstract: Nonlinear optical (NLO) responses in two-dimensional quantum-confined systems are typically described within bulk-based frameworks as macroscopic spatial averages. In finite-thickness van der Waals multilayers directly relevant to nanoscale devices, this picture substantially breaks down. Here, we establish a general symmetry-based framework for classifying second-order NLO responses in multilayer… ▽ More Nonlinear optical (NLO) responses in two-dimensional quantum-confined systems are typically described within bulk-based frameworks as macroscopic spatial averages. In finite-thickness van der Waals multilayers directly relevant to nanoscale devices, this picture substantially breaks down. Here, we establish a general symmetry-based framework for classifying second-order NLO responses in multilayers. We reveal a layer-resolved organization into skin, weak-skin, and hidden effects governed by local symmetry and stacking order. First-principles calculations for both nonmagnetic and spin-polarized systems confirm our predictions, demonstrating that stacking alone suffices to dramatically reshape both the spatial pattern and magnitude of the NLO response, a phenomenon not explainable within standard bulk theory. Our results establish stacking geometry as an effective knob for engineering surface-selective NLO responses in layered materials. △ Less

Submitted 1 June, 2026; originally announced June 2026.

Comments: 9 pages, 5 figures

Effective Theory of Fermion Quartet Condensation

Authors: Qiao-Ru Xu, Congjun Wu

Abstract: We develop a theory of superconductivity (or superfluidity) based on condensed fermion quartets focusing on the dilute spin-$\frac{1}{2}$ systems at zero temperature. In the spirit of the Bardeen--Cooper--Schrieffer ansatz, a variational wavefunction is constructed such that, within the so-called ``dilute quartet approximation", it is the ground state of an effective quartic Hamiltonian. For a giv… ▽ More We develop a theory of superconductivity (or superfluidity) based on condensed fermion quartets focusing on the dilute spin-$\frac{1}{2}$ systems at zero temperature. In the spirit of the Bardeen--Cooper--Schrieffer ansatz, a variational wavefunction is constructed such that, within the so-called ``dilute quartet approximation", it is the ground state of an effective quartic Hamiltonian. For a given two-body interaction in favor of quartetting, the gap parameter is suitably defined and the gap equation is also derived. As to the excited states, an intuitive physical picture based on a sixteen-dimensional ``occupation space" is depicted and the associated eigen-energies are obtained. This theory is applied to compute the superfluid fraction, which is found to be the same as in conventional superconductors, despite the interacting nature of the quartet problem. △ Less

Submitted 28 May, 2026; originally announced May 2026.

Comments: 4 pages, 1 figure, 1 table

The wave nature of a Mott insulator

Authors: Xudong Yu, Chengyang Wu, Wenhan Chen, Igor Zhuravlev, Zekui Wang, Yi Zeng, Sudipta Dhar, Milena Horvath, Thierry Giamarchi, Manuele Landini, Hanns-Christoph Nägerl, Hepeng Yao, Yanliang Guo

Abstract: Quantum phases of matter are routinely identified by coherence features, with interference patterns being one of the most directly observable quantities. In lattices, the superfluid-to-Mott-insulator (SF-MI) transition is commonly viewed as a change from wave-like coherence to particle-like localization: interference peaks are taken as a hallmark of superfluidity, whereas their disappearance is us… ▽ More Quantum phases of matter are routinely identified by coherence features, with interference patterns being one of the most directly observable quantities. In lattices, the superfluid-to-Mott-insulator (SF-MI) transition is commonly viewed as a change from wave-like coherence to particle-like localization: interference peaks are taken as a hallmark of superfluidity, whereas their disappearance is used to diagnose insulating behavior. Here, we challenge this picture for one-dimensional (1D) strongly interacting gases subject to a lattice potential. We realize a gapped Mott insulator through pinning in a shallow lattice and find that pronounced interference peaks persist deep in the insulating regime. Strikingly, the interference becomes stronger as the Mott fraction increases, demonstrating that a certain degree of coherence still exists in the insulator state. Measurements of the one-body correlation function reveal an oscillatory, exponentially decaying coherence pattern across several lattice sites, in quantitative agreement with quantum Monte Carlo (QMC) simulations. Our work shows that interference does not uniquely diagnose superfluidity and it exposes the unexpected wave nature of a 1D Mott insulator. △ Less

Submitted 12 May, 2026; originally announced May 2026.

Comments: 9 pages, 4 figures

Spin Quadrupolar orders in $d$-wave Unconventional Magnetism

Authors: Jian-Keng Yuan, Zhiming Pan, Congjun Wu

Abstract: Unconventional magnetism represents a class of metallic states whose Fermi surfaces exhibit spin-dependent splittings under the non-trivial representations of the rotation group. The $d$-wave $α$-phase unconventional magnetic state, commonly known as altermagnet, recently, has attracted significant attention. While these systems exhibit distinct anisotropic $d$-wave characteristics in momentum spa… ▽ More Unconventional magnetism represents a class of metallic states whose Fermi surfaces exhibit spin-dependent splittings under the non-trivial representations of the rotation group. The $d$-wave $α$-phase unconventional magnetic state, commonly known as altermagnet, recently, has attracted significant attention. While these systems exhibit distinct anisotropic $d$-wave characteristics in momentum space, how this microscopic topology translates into the spin distributions in real space remains a question. In this work, we bridge the intrinsic spin quadrupolar ordering in momentum space to the real-space staggered magnetic distribution. By introducing a weak, non-magnetic periodic crystal potential into a $d$-wave unconventional magnetic state, the spin-charge cross susceptibility is calculated by using the linear response theory. We reveal that the interplay between the crystal potential and the intrinsic $d$-wave spin-splitting naturally induces a spatial spin quadrupole distribution without enlarging the unit cell. Our study thus provides a physical connection between momentum-space multipoles in the even partial wave channel and real-space spin multipole orders. △ Less

Submitted 10 May, 2026; originally announced May 2026.

Comments: 7 pages, 3 figures

Gapped 1/9 Magnetization Plateau in the Anisotropic Kagome Antiferromagnet Y-kapellasite

Authors: Dipranjan Chatterjee, Paul A. Goddard, Ewan R. P. Thomas, Katharina M. Zoch, Hank C. H. Wu, Benjamin M. Huddart, Cornelius Krellner, Edwin Kermarrec, Mladen Horvatić, Steffen Krämer, Pascal Puphal, John Singleton, Stephen J. Blundell, Fabrice Bert

Abstract: Fractional magnetization plateaus provide a sensitive probe of many-body spin states in frustrated quantum magnets, yet their microscopic origin in kagome antiferromagnets remains unresolved. This is particularly true of the mysterious $1/9$ plateau, which is predicted by theory but infrequently observed in experiment. Here, we investigate this problem in the $S = 1/2$ anisotropic kagome antiferro… ▽ More Fractional magnetization plateaus provide a sensitive probe of many-body spin states in frustrated quantum magnets, yet their microscopic origin in kagome antiferromagnets remains unresolved. This is particularly true of the mysterious $1/9$ plateau, which is predicted by theory but infrequently observed in experiment. Here, we investigate this problem in the $S = 1/2$ anisotropic kagome antiferromagnet Y-kapellasite, Y$_3$Cu$_9$(OH)$_{19}$Cl$_8$, using pulsed-field magnetization measurements on single crystals and high-field $^{35}$Cl NMR. We identify a hierarchy of field-induced fractional features, including $1/3$ and $1/9$ plateaus, as well as a weaker low-field feature. Analysis of the NMR spectra and the magnetic susceptibility across the $1/9$ plateau demonstrate that it is accompanied by an ordered local spin configuration, a strong suppression of low-energy spin fluctuations and activated behavior, consistent with a gapped fractional state. These features differ from those in the only other material YCu$_3$(OH)$_6$Br$_2$[Br$_{1-y}$(OH)$_y$] in which this plateau is observed, implying a surprising robustness of the $1/9$ state to the details of the underlying magnetism. △ Less

Submitted 8 May, 2026; originally announced May 2026.

Comments: 7 pages, 4 figures

Response tensor for the superconducting (Josephson) diode effect

Authors: Qiong Qin, Jie Wu, Congjun Wu

Abstract: We propose a response tensor $\mathbf{\hat χ}$ to characterize the non-reciprocal critical current response of the superconducting (Josephson) diode effect. It describes the coupling between the dipole component of the angular distribution of the critical current and the applied magnetic field -- an analogue to the Hall response in the normal state. In quasi-2D systems with Rashba spin-orbit coupl… ▽ More We propose a response tensor $\mathbf{\hat χ}$ to characterize the non-reciprocal critical current response of the superconducting (Josephson) diode effect. It describes the coupling between the dipole component of the angular distribution of the critical current and the applied magnetic field -- an analogue to the Hall response in the normal state. In quasi-2D systems with Rashba spin-orbit coupling and point group symmetries $C_{3v}$, $C_{4v}$ or $C_{6v}$, this tensor takes a fully antisymmetric form. When nematicity is present, a symmetric contribution emerges, providing an indicator of the nematic order in the superconducting state. In contrast, for systems exhibiting Dresselhaus spin-orbit coupling with the $D_{2d}$ symmetry, the tensor becomes diagonal traceless, and nematicity brings in a trace part. Our analysis not only accounts for the superconducting diode effect under external applied or intrinsic effective magnetic fields, but also predicts the symmetry conditions for realizing the diode effect when the magnetic field is aligned with the current. Beyond this, the proposed tensor provides a promising tool for detecting nematicity and potential nematic transitions deep within the superconducting phase. It may also encode additional information about the underlying electronic structure and symmetry-breaking orders, warranting further experimental investigation. △ Less

Submitted 6 May, 2026; originally announced May 2026.

Contrasting Effects of Functionalization in Binary and Medium-Entropy MXene Coatings for Corrosion Protection

Authors: Aqsa Fayyaz, Ulises Martin Diaz, Jianyu Dai, Homero Castaneda, Chenglin Wu

Abstract: Developing scalable and environmentally benign anticorrosion coatings is critical for protecting steel infrastructure in chloride-rich environments. Here, a nacre-inspired multilayer epoxy coating reinforced with four MXene systems is investigated. This architecture forms a dense lamellar network that increases diffusion tortuosity and introduces electroactive surfaces for ion interactions. Electr… ▽ More Developing scalable and environmentally benign anticorrosion coatings is critical for protecting steel infrastructure in chloride-rich environments. Here, a nacre-inspired multilayer epoxy coating reinforced with four MXene systems is investigated. This architecture forms a dense lamellar network that increases diffusion tortuosity and introduces electroactive surfaces for ion interactions. Electrochemical impedance spectroscopy (EIS) confirms that the multilayer design increases coating resistance from ~103 to ~108 Ohm/cm2. A clear performance hierarchy was observed: P-(TiVCrMo)C3 > O-Ti3C2Tx > O-(TiVCrMo)C3 > P-Ti3C2Tx. Density functional theory (DFT) calculations reveal that P-Ti3C2 strongly adsorbs O2, indicating higher surface reactivity, while oxygen termination stabilizes the surface by partially passivating Ti sites. In contrast, P-(TiVCrMo)C3 exhibits strong adsorption of oxygen-containing species due to its multi-metal electronic structure, promoting the formation of protective oxides. These results highlight the delicate balance of surface chemistry, electronic structure, and compositional entropy in designing next-generation MXene-based anticorrosion coatings for marine and industrial environments. △ Less

Submitted 29 April, 2026; originally announced April 2026.

Large magnetoresistance and weak-antilocalization in the nodal-line semimetal VP2

Authors: Chunxiang Wu, Shuijin Chen, Tingyu Zhou, Le Liu, Xin Peng, Jianjian Jia, Xinyu Yu, Hangdong Wang, Jinhu Yang, Jianhua Du, Minghu Fang

Abstract: After growing successfully high quality VP$_2$ single crystals, we studied systematically their longitudinal $ρ_{xx}(T)$ and Hall resistivity $ρ_{yx}(T)$ at various magnetic fields, combining the electronic band and Fermi surface (FS) calculations. Band calculations reveal that VP$_2$ is a type-II nodal-line semimetal, evidenced by the Hall resistivity measurements. It is found that the magnetores… ▽ More After growing successfully high quality VP$_2$ single crystals, we studied systematically their longitudinal $ρ_{xx}(T)$ and Hall resistivity $ρ_{yx}(T)$ at various magnetic fields, combining the electronic band and Fermi surface (FS) calculations. Band calculations reveal that VP$_2$ is a type-II nodal-line semimetal, evidenced by the Hall resistivity measurements. It is found that the magnetoresistance (MR) at higher magnetic fields exhibits a linear behavior and does not show any sign of saturation, reaching 170\% at 40 K up to 9 T, which is determined by the intrinsic electronic structure and dominated by the Lorenz force, demonstrated by the resistivity anisotropy measurements and the numerical simulations. We also found that the existence of small amount magnetic impurities (V$^{4+}$, $S=1/2$, 2.24\%) results in Kondo effect emerging in $ρ_{xx}(T)$, the conductivity at lower magnetic fields exhibits a typical weak anti-localization (WAL) behavior. These results illustrate that VP$_2$ is a platform to study the electronic transport properties of a topological material containing magnetic impurities. △ Less

Submitted 29 April, 2026; originally announced April 2026.

Comments: 8 pages, 4 figures,

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

Topological multicomponent superconductivity with sizable $s$-wave admixture in twisted bilayer cuprates

Authors: Yu-Hang Li, Congjun Wu, Wang Yang

Abstract: We investigate multicomponent superconductivity in twisted bilayer cuprates with order parameter $s+d_1 e^{iφ_1}+d_2 e^{iφ_2}$, where $s=s_1+s_2$ is the symmetric layer-resolved $s$-wave component and $d_i$ denotes the $d$-wave pairing in layer $i$. When $φ_1-φ_2\neq 0,π$, this three-component state breaks time-reversal and $C_4$ rotational symmetries and is topologically nontrivial. Combining Gin… ▽ More We investigate multicomponent superconductivity in twisted bilayer cuprates with order parameter $s+d_1 e^{iφ_1}+d_2 e^{iφ_2}$, where $s=s_1+s_2$ is the symmetric layer-resolved $s$-wave component and $d_i$ denotes the $d$-wave pairing in layer $i$. When $φ_1-φ_2\neq 0,π$, this three-component state breaks time-reversal and $C_4$ rotational symmetries and is topologically nontrivial. Combining Ginzburg--Landau analysis with self-consistent microscopic mean-field calculations, we show that this topological state is stabilized over a broad parameter regime. We further identify nematic Kerr anisotropy as a smoking-gun signature distinguishing it from $s+id$ and $d_1+e^{iφ}d_2$ states. Our results show that a sizable $s$-wave component does not preclude chiral topological superconductivity, pointing to twisted cuprates as a more robust platform than previously appreciated. △ Less

Submitted 28 May, 2026; v1 submitted 9 April, 2026; originally announced April 2026.

Comments: 7 pages, 5 figures

Two-Dimensional Space-Time Groups: Classification and Applications

Authors: Chenhang Ke, Congjun Wu

Abstract: The concept of space group has long served as the fundamental framework to describe the physical properties of crystalline materials, from electronic bands to photonic dispersions. The recent progress of spatiotemporal control, such as laser-driven lattices, dynamic photonic and phononic crystals, and dynamic optical lattices, necessitates the study of a new framework, space-time group, beyond tha… ▽ More The concept of space group has long served as the fundamental framework to describe the physical properties of crystalline materials, from electronic bands to photonic dispersions. The recent progress of spatiotemporal control, such as laser-driven lattices, dynamic photonic and phononic crystals, and dynamic optical lattices, necessitates the study of a new framework, space-time group, beyond that based on the Floquet theorem. Space-time group includes novel intertwined non-symmorphic spatial-temporal symmetries such as time-glide reflection and time-screw rotation. Here, we perform a complete classification of the 2+1D space-time groups based on the method of group cohomology, leading to the identification of all 275 space-time crystals, including 203 non-symmorphic ones. Under this formalism, unique physical phenomena are uncovered: A chirality-selective response rule with specific space-time symmetry is fully investigated and a novel ``horizontal cone" structure is predicted in space-time metamaterials as a direct consequence of non-symmorphic space-time symmetry. This work serves as a starting point for predicting and engineering a wide range of novel spatiotemporal phenomena across condensed matter and metamaterials. △ Less

Submitted 7 April, 2026; originally announced April 2026.

Comments: 9 pages, 2 figures

Compositional Complexity-Induced Ultralow Friction in Medium-Entropy MXenes

Authors: Jiaoli Li, Yuwei Zhang, Congjie Wei, Yanxiao Li, Shuo He, Risheng Wang, Brian Wyatt, Reza Namakian, Babak Anasori, Kelvin Xie, Tobin Filleter, Ali Erdemir, Wei Gao, Chenglin Wu

Abstract: Two-dimensional MXenes are promising solid lubricants, but the roles of compositional complexity and surface chemistry in governing interfacial friction remain unclear. Here, we systematically investigate the adhesion and friction behaviors of medium-entropy (ME) MXenes, TiVNbMoC3 and TiVCrMoC3, and compare them with conventional titanium carbide MXenes, Ti2C and Ti3C2, using a SiO2 colloidal atom… ▽ More Two-dimensional MXenes are promising solid lubricants, but the roles of compositional complexity and surface chemistry in governing interfacial friction remain unclear. Here, we systematically investigate the adhesion and friction behaviors of medium-entropy (ME) MXenes, TiVNbMoC3 and TiVCrMoC3, and compare them with conventional titanium carbide MXenes, Ti2C and Ti3C2, using a SiO2 colloidal atomic force microscopy probe. Thermal annealing at 200 C converts OH surface terminations to O terminations, leading to pronounced reductions in adhesion energy and friction force across all MXenes studied. ME MXenes exhibit larger adhesion reductions because of their higher initial OH contents and more extensive OH-to-O conversion. In addition, their intrinsically higher out-of-plane bending stiffness suppresses energy dissipation during sliding, enabling ultralow friction. Notably, superlubricity is achieved in ME MXenes, with annealed TiVCrMoC3 exhibiting a coefficient of friction as low as 0.0022, outperforming graphene, MoSe2, and other MXenes evaluated using the same experimental approach. These findings identify compositional complexity as a powerful strategy for engineering MXenes with exceptional tribological performance and establish ME MXenes as a new class of solid lubricants. △ Less

Submitted 26 March, 2026; originally announced March 2026.

Interfacial Polytype Engineering of Polymer-Derived SiC via Compositionally Complex MXene Templating

Authors: Yuxiang Gan, Jianyu Dai, Laxmi Sai Viswanadha, Congjie Wei, Kelvin Y. Xie, Jeremy Watts, Mohammad Naraghi, Chenglin Wu

Abstract: Controlling polytype selection in polymer-derived silicon carbide (SiC) remains challenging since stacking sequences are determined locally at the nucleation front. Here, we demonstrate an interface-driven strategy to bias SiC polytype evolution by introducing compositionally complex TiVCrMoC3 MXene nanosheets at the preceramic stage. Under spark plasma sintering (1900 C, 70 MPa), which typically… ▽ More Controlling polytype selection in polymer-derived silicon carbide (SiC) remains challenging since stacking sequences are determined locally at the nucleation front. Here, we demonstrate an interface-driven strategy to bias SiC polytype evolution by introducing compositionally complex TiVCrMoC3 MXene nanosheets at the preceramic stage. Under spark plasma sintering (1900 C, 70 MPa), which typically stabilizes cubic beta-SiC, the MXene partially transforms into multicomponent carbide structures and generates two distinct heterogeneous interfacial states: reconstructed carbide/SiC interfaces that locally disrupt stacking sequences and promote hexagonal ordering, driving the emergence of alpha-SiC; and coherent MXene/SiC interfaces that preserve cubic stacking. Mechanical testing further reveals peak performance at an optimal MXene loading where interfacial reconstruction is most pronounced, with an around 82% increase in Young's modulus and 42% improvement in fracture toughness. These findings highlight interfacial polytype engineering via two-dimensional carbide templates as a promising route for directing crystal structure evolution in polymer-derived ceramics. △ Less

Submitted 26 March, 2026; originally announced March 2026.

Orbital-specific Itinerancy and Localization in a Kagome Magnet

Authors: S. V. Streltsov, H. Y. Huang, A. Ushakov, C. I. Wu, A. Singh, J. Su, J. Okamoto, C. T. Chen, K. Wang, A. I. Poteryaev, S-W. Cheong, A. Fujimori, D. J. Huang

Abstract: The kagome lattice naturally hosts flat bands, Dirac fermions, and van Hove singularities, yet whether its geometry can stabilize orbital-selective phases - a hallmark of Hund's physics in multi-orbital correlated systems - has remained an open question. Here, we combine resonant inelastic X-ray scattering with density functional theory and dynamical mean-field theory to demonstrate that YMn$_6$Sn… ▽ More The kagome lattice naturally hosts flat bands, Dirac fermions, and van Hove singularities, yet whether its geometry can stabilize orbital-selective phases - a hallmark of Hund's physics in multi-orbital correlated systems - has remained an open question. Here, we combine resonant inelastic X-ray scattering with density functional theory and dynamical mean-field theory to demonstrate that YMn$_6$Sn$_6$ exhibits a spontaneous orbital differentiation into coexisting itinerant and localized electrons within the same Mn $3d$ manifold. Orbitals directed along Mn-Mn bonds provide coherent quasiparticles and metallic bands, while those pointing toward ligands become strongly correlated and display non-Fermi-liquid behavior. Hund's intra-atomic exchange suppresses orbital fluctuations, stabilizing this dichotomy and providing a natural double-exchange-like mechanism for the observed ferromagnetic bilayer coupling. Our work establishes YMn$_6$Sn$_6$ as a kagome platform where orbital selectivity, flat-band topology, and Hund's metallicity converge - revealing that geometric frustration and correlation-driven orbital differentiation can cooperatively design exotic quantum phases beyond the canonical paradigms of Mott physics or band topology alone. △ Less

Submitted 22 March, 2026; originally announced March 2026.

Efficient method for calculation of low-temperature phase boundaries

Authors: Lucas Svensson, Babak Sadigh, Christine Wu, Paul Erhart

Abstract: Understanding phase stability and phase transformations is central to predicting material behavior under varying thermodynamic conditions. One of the earliest and most influential applications of density functional theory in materials science has been the prediction of pressure-induced phase transitions at 0 K. Extending these calculations to finite temperatures, however, requires accounting for t… ▽ More Understanding phase stability and phase transformations is central to predicting material behavior under varying thermodynamic conditions. One of the earliest and most influential applications of density functional theory in materials science has been the prediction of pressure-induced phase transitions at 0 K. Extending these calculations to finite temperatures, however, requires accounting for thermal, quantum, and anharmonic contributions to the free energy, often at significant computational cost. In this work, we present a general and efficient framework for calculating low-temperature phase boundaries by combining the Clausius-Clapeyron equation with the quasi-harmonic approximation. This methodology requires a minimal number of calculations, while naturally incorporating internal degrees of freedom as well as quantum and low-order anharmonic effects. We illustrate the accuracy and efficiency of the approach by constructing the phase diagram of silica in the pressure range from -2 to 12 GPa and temperatures up to 1750 K. To this end, we employ a machine-learned interatomic potential trained on density functional theory reference data, enabling well-converged free energy estimates via efficient thermodynamic sampling and a rigorous comparison between the proposed framework and free energy integration. △ Less

Submitted 7 May, 2026; v1 submitted 10 March, 2026; originally announced March 2026.

Comments: 8 pages, 3 figures

General linear correction method for DFT+X energy: application to U-M (M=Al, Ga, In) alloys under high pressure

Authors: X. L. Pan, H. X. Song, Y. Sun, F. C. Wu, H. Wang, Y. F. Wang, Y. Chen, X. R. Chen, Hua Y. Geng

Abstract: DFT+X methods, such as DFT+U and DFT+DMFT, are important supplements to standard density functional theory when strong on-site Coulomb interactions are present. However, the involvement of external parameters in the underlying model Hamiltonian introduces intrinsic ambiguity when comparing the total energies obtained with different model parameters. This renders DFT+X approaches semi-empirical and… ▽ More DFT+X methods, such as DFT+U and DFT+DMFT, are important supplements to standard density functional theory when strong on-site Coulomb interactions are present. However, the involvement of external parameters in the underlying model Hamiltonian introduces intrinsic ambiguity when comparing the total energies obtained with different model parameters. This renders DFT+X approaches semi-empirical and severely hinders their capability to describe phase ordering and phase stability, especially when reliable experimental benchmarks are unavailable, such as under high pressure. In this work, we resolve this longstanding problem by proposing a general linear correction method that eliminates the ambiguous energy contributions introduced by the model Hamiltonian in DFT+X approaches, thereby enabling direct comparison of their energies calculated with different interaction parameters. The method is demonstrated and validated within the framework of DFT+U, an important member of the DFT+X family. It is then applied to important nuclear materials of uranium-based binaries U-M (M=Al, Ga, In) alloys. With this approach, we resolve the long-standing discrepancy between theoretical predictions and experimental observations of phase stability with unprecedented accuracy, and predict several previously unknown stable intermetallic compounds under high pressure. The broad applicability of the method is further confirmed by accurate predictions of formation enthalpies for diverse systems, including Np-Al, U-Si, and Cu-O binaries, the ternary MnSnAu compound, and oxygen adsorption on the Cu(111) surface. This work establishes linear-corrected DFT+U as a fully first-principles approach and validates the linear correction method as a robust and general scheme that can be readily extended to other DFT+X methods. △ Less

Submitted 28 February, 2026; originally announced March 2026.

Comments: 45 pages, 5 figures, with Supplementary Material

Journal ref: Acta Materialia 306, 121935 (2026)

Sliding Ferroelectricity Induced and Switched Altermagnetism in GaSe-VPSe3-GaSe Sandwiched Heterostructure with Strong Magnetoelectric Effect

Authors: Pengqiang Dong, Hanbo Sun, Chao Wu, Ping Li

Abstract: Magnetoelectric coupling is vital for exploring fundamental science and driving the development of high-density memory and energy-efficient spintronic devices. Altermagnets, which merge the benefits of ferromagnets and antiferromagnets, pave the way for unprecedented magnetoelectric coupling effects. However, the spin splitting in altermagnets is robustly protected by spin space group symmetry, po… ▽ More Magnetoelectric coupling is vital for exploring fundamental science and driving the development of high-density memory and energy-efficient spintronic devices. Altermagnets, which merge the benefits of ferromagnets and antiferromagnets, pave the way for unprecedented magnetoelectric coupling effects. However, the spin splitting in altermagnets is robustly protected by spin space group symmetry, posing a significant challenge for external manipulation. Here, we propose to utilize the coupling between the layer degree of freedom and the altermagnet to achieve an altermagnetic multiferroic with strong magnetoelectric coupling. In the GaSe-VPSe3-GaSe sandwiched structure, the magnetic order can be switched between altermagnetic and conventional antiferromagnetic by controllably breaking and restoring the combined spatial inversion and time-reversal symmetry using sliding ferroelectricity. Moreover, our systematic investigation of all pathways revealed that the transition from a ferroelectric CB stacking, through an antiferroelectric CC stacking, to a ferroelectric BC stacking is the most favorable, with an energy barrier of only 50.13 meV/f.u.. More importantly, we reveal that the microscopic mechanism of the magnetic phase transition stems from the interlayer covalent bonding of Se-Se or Se-P atomic pairs at the interface. Our findings unveil a new form of magnetoelectric coupling and lay the groundwork for designing miniature information processing and multiferroic memory devices based on altermagnetism. △ Less

Submitted 28 February, 2026; originally announced March 2026.

Comments: 12 pages, 6 figures, Accepted Acta Materialia

Journal ref: Acta Materialia (2026)

Near-single-domain superconducting aluminum films on GaAs(111)A with exceptional crystalline quality for scalable quantum circuits

Authors: Hsien-Wen Wan, Yi-Ting Cheng, Chao-Kai Cheng, Jui-Min Chia, Chien-Ting Wu, Sheng-Shiuan Yeh, Chia-Hung Hsu, Jueinai Kwo, Minghwei Hong

Abstract: We have reproducibly grown near-single-domain superconducting aluminum (Al) films on GaAs(111)A wafers using molecular beam epitaxy. Synchrotron X-ray diffraction revealed twin-domain ratios of 0.00005 and 0.0003 for 19.4-nm- and 9.6-nm-thick films, respectively-the lowest reported for Al on any substrate and long considered unattainable for practical device platforms. Azimuthal scans across off-n… ▽ More We have reproducibly grown near-single-domain superconducting aluminum (Al) films on GaAs(111)A wafers using molecular beam epitaxy. Synchrotron X-ray diffraction revealed twin-domain ratios of 0.00005 and 0.0003 for 19.4-nm- and 9.6-nm-thick films, respectively-the lowest reported for Al on any substrate and long considered unattainable for practical device platforms. Azimuthal scans across off-normal Al{$11\bar{1}$} reflections exhibit narrow full width at half maximum (FWHM) values down to $0.55^\circ$, unmatched by epi-Al grown by any other method. Normal scans showed a well-defined (111) orientation with pronounced Pendellösung fringes, and $θ$-rocking-curve FWHM values down to $0.018^\circ$; the former indicates abrupt film-substrate and oxide-film interfaces. Electron backscatter diffraction mapping confirms macroscopic in-plane uniformity and the absence of $Σ$3 twin domains. Atomic force microscopy and scanning transmission electron microscopy confirmed atomically smooth surfaces and abrupt heterointerfaces. The films exhibit critical temperatures approaching bulk values, establishing a materials platform for scalable, high-coherence superconducting qubits. △ Less

Submitted 19 February, 2026; originally announced February 2026.

Comments: 19 pages, 4 figures, 1 table

Nonvolatile electric switching of critical current in cross-bar superconducting junctions

Authors: Jiajun Ma, Jingyi He, Qiong Qin, Tian Le, Zhiwei Wang, Jie Wu, Congjun Wu, Xiao Lin

Abstract: Superconducting (SC) diodes are key passive building blocks for future SC electronics. However, realizing their active counterparts is essential for functional logic. Here, we demonstrate deterministic nonvolatile electrical switching of the critical current ($I_\text{c}$) in overlap crossbar SC junctions. By applying a minimal perpendicular magnetic field ($H_\text{z}$), $I_\text{c}$ is modulated… ▽ More Superconducting (SC) diodes are key passive building blocks for future SC electronics. However, realizing their active counterparts is essential for functional logic. Here, we demonstrate deterministic nonvolatile electrical switching of the critical current ($I_\text{c}$) in overlap crossbar SC junctions. By applying a minimal perpendicular magnetic field ($H_\text{z}$), $I_\text{c}$ is modulated by a factor of four with a large switching efficiency of 60\%, achieved at a significantly reduced excitation current density of $5\times10^5$~A/cm$^2$. We also uncover anomalous behaviors: an electrically switchable critical temperature and a non-monotonic $I_\text{c}$-$H_\textit{z}$ response. These observations are interpreted in terms of unique asymmetry involving isolated vortex injection, configuration and repulsion inherent to the junction geometry. Our device provides a scalable, low-power alternative to complex SQUID-based architectures, paving the way for high-density SC integrated circuits. △ Less

Submitted 23 January, 2026; originally announced January 2026.

Comments: 7 pages, 4 figures

Direct probing the quantum geometric tensor for bosonic collective excitations

Authors: Chi Wu, Takashi Oka, Shuichi Murakami, Tiantian Zhang

Abstract: The quantum geometric tensor (QGT), whose real and imaginary parts define the quantum metric and Berry curvature, encodes the intrinsic geometry of quantum states. While electronic QGT has recently become experimentally accessible and linked to diverse physical phenomena, its bosonic counterpart remains largely unexplored. Here we show that the dynamical structure factor encodes the momentum-space… ▽ More The quantum geometric tensor (QGT), whose real and imaginary parts define the quantum metric and Berry curvature, encodes the intrinsic geometry of quantum states. While electronic QGT has recently become experimentally accessible and linked to diverse physical phenomena, its bosonic counterpart remains largely unexplored. Here we show that the dynamical structure factor encodes the momentum-space structure of bosonic wave functions and thereby provides direct access to the full bosonic QGT throughout the Brillouin zone. Applying this framework, we uncover clear geometric signatures in the twofold quadrupole-Weyl phonon of BaPtGe and the nodal-line magnon in Gd, and further generalize the formalism to multiband systems. Our results establish a general route to measuring (non-)Abelian quantum geometry in bosonic systems, a crucial step toward elucidating its impact on condensed matter phenomena. △ Less

Submitted 4 June, 2026; v1 submitted 20 January, 2026; originally announced January 2026.

Comments: 8 pages, 4 figures

Two-dimensional Intrinsic Janus Structures: Design Principle and Anomalous Nonlinear Optics

Authors: Yang Li, Chengzhi Wu, Xuelian Sun, Liangting Ye, Yirui Lu, Hai-Qing Lin, Wenhui Duan, Bing Huang

Abstract: Two-dimensional Janus structures have garnered rapidly growing attention across multidisciplinary fields. However, despite extensive theoretical and experimental efforts, a principle for designing intrinsic Janus materials remains elusive. Here, we propose a first-principles alloy theory based on cluster expansion, incorporating a strong repulsive interaction of a cation-mediated anion-pair cluste… ▽ More Two-dimensional Janus structures have garnered rapidly growing attention across multidisciplinary fields. However, despite extensive theoretical and experimental efforts, a principle for designing intrinsic Janus materials remains elusive. Here, we propose a first-principles alloy theory based on cluster expansion, incorporating a strong repulsive interaction of a cation-mediated anion-pair cluster and refined short-range cluster-cluster competitions, to unravel the formation mechanism of intrinsic Janus structures with a distorted 1T phase among numerous competing phases. Our theory not only explains why intrinsic Janus structures are accidentally observed in RhSeCl and BiTeI which are composed of alloyed elements from different groups, but also accurately predicts a wide range of 1T-like intrinsic Janus materials that are ready for synthesis. Intriguingly, as demonstrated in the case of RhSeCl, we reveal that intrinsic Janus materials can exhibit anomalous second-harmonic generation (SHG) with a distinct quantum geometric effect, originating from strong lattice and chemical-potential mirror asymmetry. Furthermore, a novel skin effect unexpectedly emerges in finite-thickness RhSeCl, accompanied by a hidden SHG effect within the bulk region. Our theory paves the way for the ab initio design of intrinsic Janus materials, significantly accelerating progress in Janus science. △ Less

Submitted 16 January, 2026; originally announced January 2026.

Comments: 23 pages, 4 figures

Journal ref: Newton, 2, 100368 (2026)

A monolithic fabrication platform for intrinsically stretchable polymer transistors and complementary circuits

Authors: Yujia Yuan, Chuanzhen Zhao, Margherita Ronchini, Yuya Nishio, Donglai Zhong, Can Wu, Hyukmin Kweon, Zehao Sun, Rachael K. Mow, Yuran Shi, Lukas Michalek, Haotian Wu, Qianhe Liu, Weichen Wang, Yating Yao, Zelong Yin, Junyi Zhao, Zihan He, Ke Chen, Ruiheng Wu, Jiuyun Shi, Jian Pei, Zhenan Bao

Abstract: Soft, stretchable organic field-effect transistors (OFETs) can provide powerful on-skin signal conditioning, but current fabrication methods are often material-specific: each new polymer semiconductor (PSC) requires a tailored process. The challenge is even greater for complementary OFET circuits, where two PSCs must be patterned sequentially, which often leads to device degradation. Here, we intr… ▽ More Soft, stretchable organic field-effect transistors (OFETs) can provide powerful on-skin signal conditioning, but current fabrication methods are often material-specific: each new polymer semiconductor (PSC) requires a tailored process. The challenge is even greater for complementary OFET circuits, where two PSCs must be patterned sequentially, which often leads to device degradation. Here, we introduce a universal, monolithic photolithography process that enables high-yield, high-resolution stretchable complementary OFETs and circuits. This approach is enabled by a process-design framework that includes (i) a direct, photopatternable, solvent-resistant, crosslinked dielectric/semiconductor interface, (ii) broadly applicable crosslinked PSC blends that preserve high mobility, and (iii) a patterning strategy that provides simultaneous etch masking and encapsulation. Using this platform, we achieve record integration density for stretchable OTFTs (55,000 cm^-2), channel lengths down to 2 um, and low-voltage operation at 5 V. We demonstrate photopatterning across multiple PSC types and realize complementary circuits, including 3 kHz stretchable ring oscillators, the first to exceed 1 kHz and representing more than a 60-fold increase in stage switching speed over the state of the art. Finally, we demonstrate the first stretchable complementary OTFT neuron circuit, where the output frequency is modulated by the input current to mimic neuronal signal processing. This scalable approach can be readily extended to diverse high-performance stretchable materials, accelerating the development and manufacturing of skin-like electronics. △ Less

Submitted 15 January, 2026; originally announced January 2026.

Comments: Submitted to Nature Electronics by December 2025

Revealing altermagnetic Fermi surfaces with two Kondo impurities

Authors: Qiong Qin, Toshihiro Sato, Marcin Raczkowski, Jeroen van den Brink, Congjun Wu, Fakher F. Assaad

Abstract: Motivated by recent advances in the study of altermagnetism, or unconventional magnetism, and in the realization and manipulation of two-impurity Kondo physics in real materials, we propose a phase-sensitive method to explore unconventional magnetic symmetries. Our method can be implemented with spin-resolved scanning tunneling microscopy to study two-impurity Kondo phenomena on altermagnetic meta… ▽ More Motivated by recent advances in the study of altermagnetism, or unconventional magnetism, and in the realization and manipulation of two-impurity Kondo physics in real materials, we propose a phase-sensitive method to explore unconventional magnetic symmetries. Our method can be implemented with spin-resolved scanning tunneling microscopy to study two-impurity Kondo phenomena on altermagnetic metals by varying the distance and orientation between magnetic impurities. Using quantum Monte Carlo simulations, we analyze the spin splitting of the Kondo resonance, whose spatial distribution sensitively captures the symmetry of the underlying altermagnetic order. Furthermore, the impurity spin correlations reflects the anisotropy of the RKKY interaction due to the altermagnetic Fermi surface splitting. This work provides a framework for studying the competition between the Kondo effect, the RKKY interaction and altermagnetism, in the simplest possible system. △ Less

Submitted 11 January, 2026; originally announced January 2026.

Electrical Regulation of Transverse Spin Currents in Unconventional Magnetic Ferroeletrics

Authors: Yudi Yang, Zhuang Qian, Ruichun Xiao, Yuanyuan Xu, Hua Wang, Shi Liu, Congjun Wu

Abstract: We identify hexagonal YMnO$_3$ as a material realization of the elusive $β$-phase of unconventional magnetism, a noncollinear, noncoplanar antiferromagnetic state defined by intrinsic spin-momentum locking and a topological spin texture. First-principle calculations reveal that this unique electronic structure enables a perpendicular electric field to generate a transverse pure spin current, a res… ▽ More We identify hexagonal YMnO$_3$ as a material realization of the elusive $β$-phase of unconventional magnetism, a noncollinear, noncoplanar antiferromagnetic state defined by intrinsic spin-momentum locking and a topological spin texture. First-principle calculations reveal that this unique electronic structure enables a perpendicular electric field to generate a transverse pure spin current, a response that occurs without requiring relativistic spin-orbit coupling. Symmetry analysis demonstrates that this spin current is intimately related to the material's ferroelectric polarization that breaks the inversion symmetry and is rigorously forbidden at domain walls where electrical polarization vanishes. This provides a blueprint for a non-volatile transistor where a gate voltage switches the spin current conductivity by controlling domain wall density, enabling all-electrical control for energy-efficient antiferromagnetic spintronics. △ Less

Submitted 4 January, 2026; originally announced January 2026.

Orbital homology of p and t2g orbitals in models and materials

Authors: Gang v. Chen, Congjun Wu

Abstract: The nominal divide between $p$- and $d$-electron systems often obscures a deep underlying unity in condensed matter physics. This review elucidates the orbital homology between the $p$ and $t_{2g}$ orbital manifolds, establishing the correspondence that extends from minimal model Hamiltonians to the complex behaviors of real quantum materials. We demonstrate that despite their distinct atomic orig… ▽ More The nominal divide between $p$- and $d$-electron systems often obscures a deep underlying unity in condensed matter physics. This review elucidates the orbital homology between the $p$ and $t_{2g}$ orbital manifolds, establishing the correspondence that extends from minimal model Hamiltonians to the complex behaviors of real quantum materials. We demonstrate that despite their distinct atomic origins, these orbitals host nearly identical hopping physics and spin-orbit coupling, formalized through an effective ${l=1}$ angular momentum algebra for the $t_{2g}$ case. This equivalence allows one to transpose physical intuition and theoretical models developed for $p$-orbital systems directly onto the more complex $t_{2g}$ materials, and vice versa. We showcase how this paradigm provides a unified understanding of emergent phenomena, including non-trivial band topology, itinerant ferromagnetism, and unconventional superconductivity, across a wide range of platforms, from transition metal compounds, two-dimensional oxide heterostructures, and iron-based superconductors, to $p$-orbital ultracold gases. Ultimately, this $p$-$t_{2g}$ homology serves not only as a tool for interpretation but also as a robust design principle for engineering novel quantum states. △ Less

Submitted 8 August, 2026; v1 submitted 27 December, 2025; originally announced December 2025.

Comments: 15 pages, 8 figures. To appear in Physics Reports

Journal ref: Physics Reports, 1202, 1-16 (2027)

Topological Charge-2ne Superconductors

Authors: Zhi-Qiang Gao, Yan-Qi Wang, Hui Yang, Congjun Wu

Abstract: Charge-$4e$ superconductors are phases where quartets of electrons condense in the absence of Cooper pairing condensation. They exhibit distinctive signatures including fractional flux quantization and anomalous Josephson effects, and are actively being explored in strongly correlated systems, such as moiré materials. In this work we develop a general framework for topological charge-$2ne$ superco… ▽ More Charge-$4e$ superconductors are phases where quartets of electrons condense in the absence of Cooper pairing condensation. They exhibit distinctive signatures including fractional flux quantization and anomalous Josephson effects, and are actively being explored in strongly correlated systems, such as moiré materials. In this work we develop a general framework for topological charge-$2ne$ superconductors based on both wavefunction and field theory approaches. In particular, we generate topological charge-$2ne$ superconductors from charge-$2e$ ingredients, and by breaking the charge $U(1)$ symmetry in certain classes of quantum Hall states, in both spinless and spinful systems. Via bulk-edge correspondence, we further construct the corresponding edge conformal field theory and bulk topological quantum field theory for topological charge-$2ne$ superconductors that suggests fermionic nonabelian topological orders. Our results provide a unified low-energy description of the topological charge-$2ne$ superconductivity, offer a concrete platform for studying symmetry breaking and enrichment in interacting topological phases of matter, and have direct implications for experimental probes such as quasiparticle interferometry. △ Less

Submitted 10 June, 2026; v1 submitted 24 December, 2025; originally announced December 2025.

Comments: 4.5+6 pages, 1+0 figures

A Cartesian-3j Framework for Machine Learning Interatomic Potentials

Authors: Zemin Xu, Chenyu Wu, Wenbo Xie, P. Hu

Abstract: Machine learning interatomic potentials (MLIPs) have brought substantial gains in the extrapolation capability in computational chemistry. However, most equivariant models are typically built with spherical tensors (STs), while Cartesian tensor formulations remain less developed despite their natural alignment with atomic coordinates and tensorial targets. In this work, we develop a Cartesian fram… ▽ More Machine learning interatomic potentials (MLIPs) have brought substantial gains in the extrapolation capability in computational chemistry. However, most equivariant models are typically built with spherical tensors (STs), while Cartesian tensor formulations remain less developed despite their natural alignment with atomic coordinates and tensorial targets. In this work, we develop a Cartesian framework for irreducible Cartesian tensors (ICTs) by introduce the \texttt{Cartesian-3j} symbol and Cartesian Generalized Clebsch-Gordan Coefficients, which serve as direct analogues of the \texttt{Wigner-3j} symbol and Generalized Clebsch-Gordan coefficients defined for ST coupling. We extend the \texttt{e3nn} library to support ICT product, and use this framework to build Cartesian counterparts of \texttt{MACE}, \texttt{NequIP}, and \texttt{Allegro}, allowing the first controlled comparison where architectures are held fixed and only the tensor basis is changed. Our experiments show that irreducible Cartesian models can achieve accuracy comparable to spherical counterparts, but direct Cartesianization incurs unfavorable compute and memory scaling, motivating dedicated Cartesian architectural choices. Leveraging ICTs and our framework, we introduce \texttt{TACE-v1-OAM-M} and demonstrate that it achieves competitive performance on Matbench Discovery compared to state-of-the-art ST models. △ Less

Submitted 1 June, 2026; v1 submitted 18 December, 2025; originally announced December 2025.

Self-consistent renormalized spin-wave theory of magnetic and topological transitions in two-dimensional honeycomb ferromagnets

Authors: Jian-Lin Li, Chien-Te Wu

Abstract: We investigate finite-temperature magnetic and topological phase transitions in two-dimensional honeycomb ferromagnets using an extended self-consistent renormalized spin-wave theory (SRSWT) that incorporates higher-order corrections from the Holstein--Primakoff expansion. Focusing on the combined effects of single-ion anisotropy, Zeeman field, next-nearest-neighbor (NNN) exchange, and Dzyaloshins… ▽ More We investigate finite-temperature magnetic and topological phase transitions in two-dimensional honeycomb ferromagnets using an extended self-consistent renormalized spin-wave theory (SRSWT) that incorporates higher-order corrections from the Holstein--Primakoff expansion. Focusing on the combined effects of single-ion anisotropy, Zeeman field, next-nearest-neighbor (NNN) exchange, and Dzyaloshinskii--Moriya interaction, we analyze how these parameters influence the magnetization curves and magnon spectra. This work serves two main goals. First, we critically examine the limitations of SRSWT, showing that in the absence of external or interaction tuning, the theory tends to overestimate magnon self-energy corrections, often predicting first-order magnetic transitions with multivalued magnetization and metastable solution branches (i.e., self-consistent but thermodynamically unstable states). Second, we demonstrate that topological transitions -- signaled by magnon gap closings at the Dirac points -- can be tuned to occur below the magnetic transition temperature and within the thermodynamically stable regime. In particular, we identify two practical tuning strategies: applying an external Zeeman field of appropriate sign depending on the anisotropy strength, and introducing a small antiferromagnetic NNN exchange coupling. These findings not only clarify the predictive scope and limitations of SRSWT but also provide experimentally relevant guidance for realizing thermally driven topological transitions in two-dimensional honeycomb magnetic insulators. △ Less

Submitted 13 February, 2026; v1 submitted 12 December, 2025; originally announced December 2025.

Journal ref: Phys. Rev. B 113, 075129 (2026)

New insights into hydrogen-assisted intergranular cracking in nickel

Authors: S. Quan, A. Zafra, E. Martínez-Pañeda, C. Wu, Z. D. Harris, L. Cupertino-Malheiros

Abstract: We characterize the grain boundary (GB) susceptibility to hydrogen-assisted intergranular cracking in pure nickel as a function of coincident site lattice value ($Σ$-n), over a wide range of hydrogen concentrations (4 to 14 wppm). Cracks on the surface and within the bulk material were identified across the entire gauge region of the specimens. The susceptibility of GBs to crack initiation and pro… ▽ More We characterize the grain boundary (GB) susceptibility to hydrogen-assisted intergranular cracking in pure nickel as a function of coincident site lattice value ($Σ$-n), over a wide range of hydrogen concentrations (4 to 14 wppm). Cracks on the surface and within the bulk material were identified across the entire gauge region of the specimens. The susceptibility of GBs to crack initiation and propagation was evaluated by separating cracks containing single GB or multiple GBs. A larger loss in fracture strain, a smaller reduction in area, and an increase in the percentage of intergranular fracture indicated a higher degree of embrittlement at elevated hydrogen concentrations. The number of cracks was significantly higher on the surface than in the bulk for the most severe hydrogen charging conditions ($\geq$ 8 wppm), while a similar number was observed for lower concentrations. The propensity for hydrogen-assisted intergranular cracking at different types of GBs on the surface and in the bulk material was consistent, indicating that while cathodic charging can promote surface cracks, it does not significantly impact the GBs relative susceptibility. The $Σ$-3 boundaries were the most resistant to cracking, as evidenced by the considerably lower fraction of these GBs exhibiting intergranular cracking at all hydrogen concentrations considered. This contrasts literature findings for Ni alloys and can be explained by the segregation energies and reductions in the cohesive strength with hydrogen, with less favorable trapping at the $Σ$-3 boundaries. No evidence of plasticity-mediated cracking initiation was observed. △ Less

Submitted 2 December, 2025; originally announced December 2025.

Quasi-steady electron-excitonic complexes coupling in a two-dimensional semiconductor

Authors: Shangkun Mo, Hao Zhong, Keming Zhao, Yunfei Bai, Dingkun Qin, Chunlong Wu, Qiang Wan, Renzhe Li, Cao Peng, Xingzhe Wang, Enting Li, Sheng Meng, Nan Xu

Abstract: Excitons and their complexes govern optical-related behaviors in semiconductors. Here, using angle-resolved photoemission spectroscopy (ARPES), we have elucidated the light-matter interaction mediated by quasi-steady excitonic complexes within a monolayer of the prototypical two-dimensional (2D) semiconductor WSe2. Under continuous incident light, we have observed the generation of quasi-steady ex… ▽ More Excitons and their complexes govern optical-related behaviors in semiconductors. Here, using angle-resolved photoemission spectroscopy (ARPES), we have elucidated the light-matter interaction mediated by quasi-steady excitonic complexes within a monolayer of the prototypical two-dimensional (2D) semiconductor WSe2. Under continuous incident light, we have observed the generation of quasi-steady excitons and their complexes, encompassing ground and excited state excitons, trions, as well as their intricate interplay. We further show spectral evidence of electronic excitation states within the background of quasi-steady excitonic complexes, characterized by valence band (VB) effective mass renormalization, the enhanced spin-orbit coupling (SOC), the formation of an excitonic gap near the Fermi level (EF ) of the conduction band (CB), and intervalley excitonic band folding. Our findings not only unveil a quasi-steady excitonic complex background for the creation of diverse electronic excitations in 2D semiconductors but also offer new insights into the role of excitons in the charge density wave (CDW) formation mechanism and facilitate the advancement of correlated electronic state engineering based on the coupling between electrons and excitonic complexes in a quasi-equilibrium state. △ Less

Submitted 2 December, 2025; originally announced December 2025.

Comments: 6 pages, 4 figures

Evaluation of carbon incorporation in sulfide thin films grown by hybrid pulsed laser deposition

Authors: Claire Wu, Mythili Surendran, Shin Muramoto, Alexander Grutter, Jayakanth Ravichandran

Abstract: Vapor-pressure-mismatched materials, such as transition metal chalcogenides, have emerged as key electronic, photonic, and quantum materials. Hybrid pulsed laser deposition (hPLD) has become a preferred method for epitaxial or textured growth of these materials; however, unintentional carbon (C) incorporation remains a persistent concern, particularly when using organic chalcogen precursors as saf… ▽ More Vapor-pressure-mismatched materials, such as transition metal chalcogenides, have emerged as key electronic, photonic, and quantum materials. Hybrid pulsed laser deposition (hPLD) has become a preferred method for epitaxial or textured growth of these materials; however, unintentional carbon (C) incorporation remains a persistent concern, particularly when using organic chalcogen precursors as safer alternatives to toxic hydrides. The mechanisms governing C incorporation and its impact on film growth and properties in hPLD remain poorly understood. Here, we investigate the influence of C-containing side products generated from organosulfur precursor pyrolysis on ZnS, BaTiS$_3$, and TiS$_2$ thin films grown by hPLD using tert-butyl disulfide (TBDS). Structural characterization via X-ray diffraction and atomic force microscopy, combined with secondary ion mass spectrometry, is used to systematically examine the effects of growth temperature and TBDS partial pressure on film morphology, crystallinity, and C incorporation. Optimal growth temperatures of 400°C, 500°C, and 700°C are identified for ZnS, TiS$_2$, and BaTiS$_3$, respectively. Growth above or below these temperatures leads to increased C incorporation at both the interface and within the film, correlating with degraded texture. In contrast, highly textured films exhibit minimal C content, comparable to films grown without TBDS. For TiS$_2$, C incorporation depends strongly on TBDS pressure, with 10$^{-1}$ Pa identified as the optimal pressure for minimizing contamination. At higher pressures, loss of preferential texture is observed, likely due to C graphitization poisoning the interface and bulk. These results provide new insight into process-induced C impurities in hPLD-grown chalcogenide thin films and have important implications for sulfide-based thin film technologies. △ Less

Submitted 1 December, 2025; originally announced December 2025.

Multiphase transport and compositional mixing mechanisms in twin-wire laser directed energy deposition: toward process stability and graded material fabrication

Authors: Yi Li, Yuhui Li, Jianzhao Wu, Luxuan Zhang, Maoyuan Li, Chaochao Wu, Zhenzhong Wang

Abstract: Twin-wire laser directed energy deposition (TW-LDED) provides a promising route for alloying and fabrication of compositionally graded structures. However, inherent multiparameter coupling in twin-wire systems critically exacerbates both process instabilities and compositional inhomogeneity. This unresolved issue escalates into a fundamental technological bottleneck, as the underlying physical mec… ▽ More Twin-wire laser directed energy deposition (TW-LDED) provides a promising route for alloying and fabrication of compositionally graded structures. However, inherent multiparameter coupling in twin-wire systems critically exacerbates both process instabilities and compositional inhomogeneity. This unresolved issue escalates into a fundamental technological bottleneck, as the underlying physical mechanisms remain poorly understood. This study developed a high-fidelity multi-physics and multiphase simulation framework coupled with experimental validation to reveal thermal-fluid behavior and heat-mass transfer mechanisms in TW-LDED using Inconel 718 and SS316L fine wires. Three distinct transition modes were identified: twin-wire melt droplet, twin-wire liquid bridge, and droplet-bridge mixed transitions, with the twin-wire liquid bridge regime delivering optimal stability and uniform mixing. Parametric analysis demonstrates that increasing wire feeding speed or decreasing wire initial height promotes stable liquid bridge formation, while small laser spots at low feeding speeds induce excessive volumetric energy density and bridge instability. Simulation and single-track experiments confirm that liquid bridge transitions reduce dimensional fluctuations by 85% while enhancing compositional homogeneity. Conversely, the melt droplet-bridge transition mode creates periodic flow switching and compositional discontinuities along the scan direction. Finally, a 60 mm functionally graded ring was successfully fabricated using optimized parameters, achieving uniform elemental distribution in the transition zone without significant segregation, validating the feasibility of TW-LDED for functionally graded components. △ Less

Submitted 19 January, 2026; v1 submitted 17 November, 2025; originally announced November 2025.

Comments: There are multiple labeling errors in the preprint version, such as those related to substrate materials, and the version has been withdrawn for revision

Many-body wave function and edge magnetization of an open $p+is$ superconducting chain

Authors: Jiarui Jiao, Chao Xu, Congjun Wu, Wang Yang

Abstract: Although BCS wave functions for superconductors under periodic boundary conditions are well established, obtaining an explicit form of the many-body BCS wave function under open boundary condition is usually a nontrivial problem. In this work, we construct the exact BCS ground-state wave function of a one-dimensional spin-$\frac12$ superconductor with $p+is$ pairing symmetry under open boundary co… ▽ More Although BCS wave functions for superconductors under periodic boundary conditions are well established, obtaining an explicit form of the many-body BCS wave function under open boundary condition is usually a nontrivial problem. In this work, we construct the exact BCS ground-state wave function of a one-dimensional spin-$\frac12$ superconductor with $p+is$ pairing symmetry under open boundary conditions for special sets of parameters. The spin magnetization on the edges is calculated explicitly using the obtained wave function. Our work is useful for obtaining deeper understandings of open $p+ is$ superconducting chains on a wave-function level. △ Less

Submitted 17 July, 2026; v1 submitted 7 November, 2025; originally announced November 2025.

Comments: 21 pages, 9 figures

Journal ref: Phys. Rev. B 113, 224525 (2026)

Time-reversal symmetry breaking superconductivity in the presence of loop-current fluctuations

Authors: Zenghui Fan, Runyu Ma, Stefano Chesi, Congjun Wu, Tianxing Ma

Abstract: Loop currents have been proposed in various superconductors and recently confirmed in kagome materials, raising a fundamental question regarding their intrinsic connection to superconductivity. Here, we study a sign-problem-free bilayer $t-J_{\perp}-V$ model hosting a spontaneous interlayer loop-current parent state, and explore the interplay between loop-current fluctuations and superconductivity… ▽ More Loop currents have been proposed in various superconductors and recently confirmed in kagome materials, raising a fundamental question regarding their intrinsic connection to superconductivity. Here, we study a sign-problem-free bilayer $t-J_{\perp}-V$ model hosting a spontaneous interlayer loop-current parent state, and explore the interplay between loop-current fluctuations and superconductivity using unbiased projector quantum Monte Carlo simulations. Near half-filling, unbiased interlayer interactions induce spontaneous loop currents that break time-reversal symmetry. Upon hole doping, the loop-current order is suppressed, and interlayer $s$-wave superconductivity emerges where loop-current fluctuations become dominant. We establish a phase diagram revealing a transition from the loop-current parent to a superconducting state, reminiscent of the evolution from an antiferromagnetic parent to superconductivity in cuprates. Strikingly, a coexisting regime emerges near the phase boundary, yielding time-reversal-symmetry-breaking superconductivity. Our study reveals an intrinsic connection between loop currents and superconductivity, and identifies a promising mechanism for time-reversal symmetry breaking in superconductors. Furthermore, our results offer insights into unconventional superconductivity in loop-current systems and establish a minimal theoretical framework for understanding time-reversal symmetry breaking in bilayer correlated electron systems. △ Less

Submitted 24 April, 2026; v1 submitted 22 October, 2025; originally announced October 2025.

Comments: MAIN TEXT: 8 pages, 5 figures; SUPPLEMENTARY MATERIALS(attached in the end): 4 pages, 5 figures

Vector spin polarization evolution determined in an entangled muon-fluorine system under pulsed excitation

Authors: Dipranjan Chatterjee, Benjamin M. Huddart, Hank C. H. Wu, Dharmalingam Prabhakaran, Alex Louat, Stephen P. Cottrell, Stephen J. Blundell

Abstract: A spin-polarized muon implanted into a fluoride forms a coupled F--$μ$--F complex in which the muon spin and neighbouring fluorine nuclear spins become entangled. Here we apply radio-frequency (RF) excitation to this coupled system and use the three-dimensional distribution of emitted positrons to reconstruct the time-dependent evolution of the muon spin polarization. This three-dimensional readou… ▽ More A spin-polarized muon implanted into a fluoride forms a coupled F--$μ$--F complex in which the muon spin and neighbouring fluorine nuclear spins become entangled. Here we apply radio-frequency (RF) excitation to this coupled system and use the three-dimensional distribution of emitted positrons to reconstruct the time-dependent evolution of the muon spin polarization. This three-dimensional readout, using single spin detection, is not possible in a single NMR experiment and demonstrates significant advantages that are achieved by using RF muon techniques. We demonstrate the application of this vector-readout method to the experimental observation of a muon spin echo signal that is controlled by the dipolar coupling to fluorine, as well as to a double resonance experiment, in which we use pulses tuned to separate frequencies to address both the muon and fluorine spins. This targeted approach, in which selective RF pulses can control the muon spin and other spins to which it is coupled, provides a novel route for probing systems of entangled spins. △ Less

Submitted 21 October, 2025; originally announced October 2025.

AtomWorld: A Benchmark for Evaluating Spatial Reasoning in Large Language Models on Crystalline Materials

Authors: Taoyuze Lv, Alexander Chen, Fengyu Xie, Chu Wu, Jeffrey Meng, Dongzhan Zhou, Yingheng Wang, Bram Hoex, Zhicheng Zhong, Tong Xie

Abstract: Large language models (LLMs) have shown promising potential in scientific research, enabling tasks ranging from knowledge retrieval to property prediction. Existing science benchmarks mainly focus on perceptual or knowledge-based tasks, largely ignoring the modelling tasks, a fundamental starting point for any real scientific research. For materials science, constructing and manipulating atomic st… ▽ More Large language models (LLMs) have shown promising potential in scientific research, enabling tasks ranging from knowledge retrieval to property prediction. Existing science benchmarks mainly focus on perceptual or knowledge-based tasks, largely ignoring the modelling tasks, a fundamental starting point for any real scientific research. For materials science, constructing and manipulating atomic structures is one of the most creative and least automated steps. In this work, we introduce AtomWorld, a benchmark designed to evaluate the abilities of LLMs on structure modifications. The benchmark includes ten fundamental actions under four widely used modelling categories, enabling verifiable evaluation metrics. We find that Claude Opus 4.6 generally performs the best. While the success rate decreases markedly with increasing modelling complexity, with particularly low success rates (below 12\% for rotation) for operations involving complex spatial relations. Our results suggest that contemporary LLMs are better suited as copilots for materials structure modelling rather than fully unsupervised autonomous scientific agents. Beyond evaluation, AtomWorld also serves as a testbed and playground for developing future structure-aware models, including reinforcement learning and agentic approaches. △ Less

Submitted 28 May, 2026; v1 submitted 6 October, 2025; originally announced October 2025.

Topological nontrivial berry phase in altermagnet CrSb

Authors: Jianhua Du, Xin Peng, Yuzhi Wang, Shengnan Zhang, Yuran Sun, Chunxiang Wu, Tingyu Zhou, Le Liu, Hangdong Wang, Jinhu Yang, Bin Chen, Chuanying Xi, Zhiwei Jiao, Quansheng Wu, Minghu Fang

Abstract: The study of topological properties in magnetic materials has long been one of the forefront research areas in condensed matter physics. CrSb, as a prototypical candidate material for altermagnetism, has attracted significant attention due to its unique magnetic properties. This system provides a novel platform for exploring the intrinsic relationship between altermagnetic order and exotic topolog… ▽ More The study of topological properties in magnetic materials has long been one of the forefront research areas in condensed matter physics. CrSb, as a prototypical candidate material for altermagnetism, has attracted significant attention due to its unique magnetic properties. This system provides a novel platform for exploring the intrinsic relationship between altermagnetic order and exotic topological states. In this study, we combine systematic electrical transport experiments with first-principles calculations to investigate the possible realization mechanisms of topological semimetal states in CrSb and their manifestations in quantum transport phenomena. Our high field magneto-transport measurements reveal that the magnetoresistance of CrSb exhibits no sign of saturation up to 35 T, following a distinct power-law dependence with an exponent of 1.48. The nonlinear Hall resistivity further indicates a multiband charge transport mechanism. Under high magnetic fields, we observe pronounced Shubnikov-de Haas (SdH) quantum oscillations and discernible Zeeman-effect-induced band splitting at 1.6 K. Systematic Fermi surface and band calculations combined with Berry phase analysis confirm the nontrivial topological character of this material (with a Berry phase approaching π). These findings not only provide crucial experimental evidence for understanding the electronic structure of CrSb, but also establish an important foundation for investigating topological quantum states in altermagnets. △ Less

Submitted 25 September, 2025; originally announced September 2025.

Comments: 10 pages, 5 figures

Report number: published on Sci. China Phys. Mech. Astron. 69, 267512 (2026)

Incommensurate magnetic order drives singular angular magnetoresistance in a Weyl semimetal

Authors: X. Yao, P. Chen, R. Verma, X. Zhao, H. -Y. Yang, L. DeBeer-Schmitt, A. A. Aczel, C. -M. Wu, D. Alba Venero, T. Ohhara, K. Munakata, M. Takahashi, Y. Noda, A. Bansil, B. Singh, P. Nikolić, F. Tafti, J. Gaudet

Abstract: We demonstrate that a multi-$\mathbf{k}$ incommensurate magnetic state in the Weyl semimetal CeAlGe gives rise to singular angular magnetoresistance (SAMR), an electrical-transport signature that detects the magnetic-field direction with exceptional precision. In contrast, the sister compound CeAlSi shows neither multi-$\mathbf{k}$ order nor SAMR. Both phenomena emerge upon $\sim57\%$ Ge substitut… ▽ More We demonstrate that a multi-$\mathbf{k}$ incommensurate magnetic state in the Weyl semimetal CeAlGe gives rise to singular angular magnetoresistance (SAMR), an electrical-transport signature that detects the magnetic-field direction with exceptional precision. In contrast, the sister compound CeAlSi shows neither multi-$\mathbf{k}$ order nor SAMR. Both phenomena emerge upon $\sim57\%$ Ge substitution in CeAlSi$_{1-x}$Ge$_x$ and coincide with electronic-structure changes that soften the single-ion in-plane anisotropy and enhance Weyl-mediated magnetic interactions. These results reveal a direct connection between band topology, electronic transport, and collective magnetism in Weyl semimetals. △ Less

Submitted 22 September, 2025; originally announced September 2025.

Comments: 6 pages, 4 figures. Submitted to Phys. Rev. Lett

3D microwave imaging of a van der Waals heterostructure

Authors: Leonard W. Cao, Chen Wu, Lingyuan Lyu, Liam Cohen, Noah Samuelson, Ziying Yan, Sneh Pancholi, Kenji Watanabe, Takashi Taniguchi, Daniel E. Parker, Andrea F. Young, Monica T. Allen

Abstract: Van der Waals (vdW) heterostructures offer a tunable platform for the realization of emergent phenomena in layered electron systems. While scanning probe microscopy techniques have proven useful for the characterization of surface states and 2D crystals, the subsurface imaging of quantum phenomena in multi-layer systems presents a significant challenge. In 3D heterostructures, states that occupy d… ▽ More Van der Waals (vdW) heterostructures offer a tunable platform for the realization of emergent phenomena in layered electron systems. While scanning probe microscopy techniques have proven useful for the characterization of surface states and 2D crystals, the subsurface imaging of quantum phenomena in multi-layer systems presents a significant challenge. In 3D heterostructures, states that occupy different planes can simultaneously contribute to the signal detected by the microscope probe, which complicates image analysis and interpretation. Here we present a quantum imaging technique that offers a glimpse into the third dimension by resolving states out of plane: it extracts the charge density landscape of individual atomic planes inside a vdW heterostructure, layer by layer. As a proof-of-concept, we perform layer-resolved imaging of quantum Hall states and charge disorder in double-layer graphene using milliKelvin microwave impedance microscopy. Here the discrete energy spectrum of the top layer enables transmission of microwaves through gapped states, thus opening direct access to quantum phases in the subsurface layer. Resolving how charge is distributed out-of-plane offers a direct probe of interlayer screening, revealing signatures of negative quantum capacitance driven by many-body correlations. At the same time, we extract key features of the band structure and thermodynamics, including gap sizes. Notably, by imaging the charge distribution on different atomic planes beneath the surface, we shed light on the roles of surface impurities and screening on the stability of fractional quantum Hall states. We also show that the uppermost graphene layer can serve as a top gate: This unlocks access to a wide range of phenomena that require displacement field control, from fractional Chern insulators in Moiré superlattices to correlated states in multilayer graphene. △ Less

Submitted 25 August, 2025; originally announced August 2025.

Incompressible quantum liquid on the four-dimensional sphere

Authors: Junwen Zhao, Xue Meng, Wei Zhu, Congjun Wu

Abstract: The study of quantum Hall effect (QHE) is a foundation of topological physics, inspiring extensive explorations of its high-dimensional generalizations. Notably, the four dimensional (4D) QHE has been experimentally realized in synthetic quantum systems, including cold atoms, photonic lattices, and metamaterials. However, the many-body effect in the 4D QHE system remains poorly understood. In this… ▽ More The study of quantum Hall effect (QHE) is a foundation of topological physics, inspiring extensive explorations of its high-dimensional generalizations. Notably, the four dimensional (4D) QHE has been experimentally realized in synthetic quantum systems, including cold atoms, photonic lattices, and metamaterials. However, the many-body effect in the 4D QHE system remains poorly understood. In this study, we explore this problem by formulating the microscopic wavefunctions inspired by Laughlin's seminal work. Employing a generalized pseudo-potential framework, we derive an exact microscopic Hamiltonian consisting of two-body projectors that annihilate the microscopic wavefunctions. Diagonalizations on a small size system show that the quasi-hole states remain zero energy while the quasi-particle states exhibit a finite gap, in consistency with an incompressible state. Furthermore, the pairing distribution is calculated to substantiate the liquid-like nature of the wavefunction. Our work provides a preliminary understanding to the fractional topological states in high dimension. △ Less

Submitted 10 February, 2026; v1 submitted 25 August, 2025; originally announced August 2025.

Comments: 7 pages,3 figures

Spin-Orbit Driven Topological Phases in Kagome Materials

Authors: Chi Wu, Tiantian Zhang

Abstract: Kagome materials have garnered substantial attention owing to their diverse physical phenomena, yet canonical systems such as the AV$_3$Sb$_5$ family exhibit poor $Z_{2}$-type topological properties, spurring an urgent quest for kagome platforms hosting ideal topological states. Recently, Zhou et al. proposed the kagome-type IAMX family, which exhibits distinctive ideal topological states; however… ▽ More Kagome materials have garnered substantial attention owing to their diverse physical phenomena, yet canonical systems such as the AV$_3$Sb$_5$ family exhibit poor $Z_{2}$-type topological properties, spurring an urgent quest for kagome platforms hosting ideal topological states. Recently, Zhou et al. proposed the kagome-type IAMX family, which exhibits distinctive ideal topological states; however, their analysis is primarily restricted to the spinless approximation. In this work, we model relativistic effects in the IAMX family, demonstrating that tuning the spin-orbit coupling (SOC) strength drives topological phase transitions and induces novel topological states, resulting in a rich phase diagram. The configuration of topological surface states evolves continuously as the SOC strength is modulated, consistent with the evolution of the topological phase transition. This suggests a viable route toward designing multi-functional topological devices. First-principles calculations performed on three specific IAMX compounds confirm that SOC governs their topological phases, in complete accord with our model analysis. △ Less

Submitted 15 March, 2026; v1 submitted 24 August, 2025; originally announced August 2025.

Comments: 10 pages, 5 figures