Showing 1–50 of 545 results for author: Liu, K

Layer-Number-Controlled Symmetry Breaking and Surface-State Transport in Rhombohedral Graphene Multilayers

Authors: Bosai Lyu, Jian Zheng, Kai Liu, Yulu Ren, Size Wu, Yating Sha, Shuhan Liu, Youngju Park, Kenji Watanabe, Takashi Taniguchi, Jinfeng Jia, Zhiwen Shi, Jeil Jung, Weidong Luo, Guorui Chen

Abstract: Rhombohedral multilayer graphene hosts layer-polarized flat bands, providing an intriguing platform for correlated and topological electronic states; however, the role of layer number in governing symmetry breaking and surface screening remains elusive. Here we prepare rhombohedral graphene multilayers and systematically conduct electrical transport measurements. We uncover an unconventional layer… ▽ More Rhombohedral multilayer graphene hosts layer-polarized flat bands, providing an intriguing platform for correlated and topological electronic states; however, the role of layer number in governing symmetry breaking and surface screening remains elusive. Here we prepare rhombohedral graphene multilayers and systematically conduct electrical transport measurements. We uncover an unconventional layer dependence of phase transitions: the critical displacement field (D$_{c}$) for the layer-antiferromagnetic (LAF)-to-semimetal transitions remains constant across tetralayer to hexalayer graphene, whereas the D$_{c}$ for semimetal-to-layer-polarized-insulator (LPI) transition increases with layer number, defying unscreened Coulomb interaction models. In hexalayer graphene, surface-state-dominated transport emerges, with Landau levels (LLs) and resistive peaks selectively controlled by adjacent gates, a signature of strong interlayer screening absent in thinner stacks. High magnetic fields reveal valley-layer-locked LLs and dissipative states possibly from interlayer backscattering, highlighting the presence of decoupled surface states. Our findings establish layer number as a key tuning knob for engineering correlated and topological phases in rhombohedral graphene multilayers. △ Less

Submitted 11 August, 2026; originally announced August 2026.

Screening phonon-mediated superconductors from static orbital Hamiltonians

Authors: Jian-Feng Zhang, Ze-Feng Gao, Xiao-Qi Han, Dingshun Lv, Miao Gao, Kai Liu, Xinguo Ren, Zhong-Yi Lu, Tao Xiang

Abstract: The first-principles search for superconductors is severely limited by the high cost of electron-phonon coupling (EPC) calculations. Here we develop a low-cost, physically transparent framework that identifies strong-EPC materials directly from static orbital-based Hamiltonians without explicit phonon perturbation calculations. Verification using density functional perturbation theory (DFPT) for r… ▽ More The first-principles search for superconductors is severely limited by the high cost of electron-phonon coupling (EPC) calculations. Here we develop a low-cost, physically transparent framework that identifies strong-EPC materials directly from static orbital-based Hamiltonians without explicit phonon perturbation calculations. Verification using density functional perturbation theory (DFPT) for representative superconductors shows that the framework captures semi-quantitatively the EPC scale at substantially lower computational cost. Applied to more than 36,000 compounds in the MattKeyBond database, it identifies 34 dynamically stable superconducting candidates with calculated $T_c > 10$ K after DFPT verification. These candidates reveal two distinct routes to relatively high-$T_c$ superconductivity: a metallized covalent $σ$-bond route that is more favorable for achieving high-$T_c$ superconductors, and a Fermi-level density-of-states accumulation route that can enhance $T_c$ but usually to a more limited extent. △ Less

Submitted 3 August, 2026; originally announced August 2026.

Comments: 12 pages, 5 figures, 2 tables

Decoding the Micromagnetic Hamiltonian from Magnetic Fingerprints

Authors: Bradley J. Fugetta, Anqi Liu, Kai Liu, Amy Y. Liu, Gen Yin

Abstract: Extracting intrinsic magnetic Hamiltonians directly from magnetometry is challenging due to the high dimensionality of the parameter space and the degeneracy induced by ensemble averaging. Here, we introduce a collection of deep convolutional neural networks (CNNs) to extract the full phenomenological micromagnetic Hamiltonian directly from the magnetic fingerprints encoded within First-Order Reve… ▽ More Extracting intrinsic magnetic Hamiltonians directly from magnetometry is challenging due to the high dimensionality of the parameter space and the degeneracy induced by ensemble averaging. Here, we introduce a collection of deep convolutional neural networks (CNNs) to extract the full phenomenological micromagnetic Hamiltonian directly from the magnetic fingerprints encoded within First-Order Reversal Curves (FORCs). We validate this approach via closed-loop verification, re-creating the input magnetometry for both simulated and experimental FORCs. To mitigate false positives, we deploy an `Alice--Bob' parallel network that quantifies prediction uncertainty based on solely the information in FORCs without any additional ground-truth knowledge. This framework provides a robust, machine-learning-assisted approach to unravel the underlying spin behaviors in complex magnetic systems △ Less

Submitted 29 July, 2026; originally announced July 2026.

Direct Measurement of Exciton Dispersion in the Long-Wavelength Limit

Authors: Peiyi He, Jiade Li, Jiakai Wang, Jiangxu Li, Jiahao Wang, Weiyu Sun, Yiwen Song, Xiaoyue Gao, Quanlin Guo, Bo Han, Ruochen Shi, Niklas Dellby, Tracy Lovejoy, Xing-Qiu Chen, Kaihui Liu, Yu Ye, Hailin Peng, Peng Gao

Abstract: Exciton dispersion, which governs the propagation, scattering and radiative decay of electron-hole pairs, is essential to optoelectronics and quantum materials. In two-dimensional systems, weakened dielectric screening and long-range electron-hole exchange are predicted to induce nonanalytic exciton dispersion in the long-wavelength limit. However, direct quantitative characterization of its dimen… ▽ More Exciton dispersion, which governs the propagation, scattering and radiative decay of electron-hole pairs, is essential to optoelectronics and quantum materials. In two-dimensional systems, weakened dielectric screening and long-range electron-hole exchange are predicted to induce nonanalytic exciton dispersion in the long-wavelength limit. However, direct quantitative characterization of its dimensional evolution remains lacking, especially in the ultralow-q regime (q < 0.02 $Å^{-1}$). Here we employ defocus-engineered momentum-resolved electron energy-loss spectroscopy in scanning transmission electron microscopy, achieving an ultrahigh momentum resolution of 0.0002 $Å^{-1}$. Using freestanding hBN as a prototypical platform, we resolve layer-dependent exciton dispersion and quantify its characteristic crossover momentum and group velocity in the long-wavelength limit. With increasing thickness, the nonanalytic linear-dispersion regime is progressively compressed, manifested by a reduction in characteristic crossover momentum q_c from $1.82 \times 10^{-1} Å^{-1}$ in the monolayer to $3.0 \times 10^{-1} Å^{-1}$ in 25 layers. Meanwhile, the low-q group velocity increases from $2.0 \times 10^{-3} c$ to $2.9 \times 10^{-2} c$, before the dispersion ultimately approaches the bulk-like parabolic limit. We further examine how the exciton band structure of monolayer hBN responds to its surrounding environment, including temperature, adjacent graphene layers, and interlayer twist in BN/graphene heterostructures. These findings uncover the fundamental physics of low-dimensional excitons, deliver valuable guidance for modulating exciton transport, diffusion and quasiparticle coupling in layered quantum materials, and establish a powerful experimental route to explore low-dimensional exciton physics. △ Less

Submitted 23 July, 2026; originally announced July 2026.

Emergent d-wave altermagnetism in chlorine-adsorbed FeSe monolayer

Authors: Zi-Hao Ding, Ze-Feng Gao, Kai Liu, Peng-Jie Guo, Zhong-Yi Lu

Abstract: The recent emergence of altermagnetism has opened new frontiers in condensed matter physics, yet material platforms capable of hosting both intrinsic altermagnetic order and superconductivity remain exceedingly rare. Here, based on symmetry analysis and first-principles calculations, we propose a realistic route to engineer robust altermagnetism in monolayer FeSe, a prototypical iron-based superco… ▽ More The recent emergence of altermagnetism has opened new frontiers in condensed matter physics, yet material platforms capable of hosting both intrinsic altermagnetic order and superconductivity remain exceedingly rare. Here, based on symmetry analysis and first-principles calculations, we propose a realistic route to engineer robust altermagnetism in monolayer FeSe, a prototypical iron-based superconductor. By designing a stoichiometric Fe2Se2Cl structure through single-side Cl adsorption and introducing gate-tunable hole doping, we achieve a highly stable altermagnetic ground state. Our calculations reveal a synergistic mechanism: hole doping firmly stabilizes the checkerboard magnetic order, while the asymmetric ligand environment intrinsically breaks the outof-plane spatial inversion symmetry. Consequently, this interplay induces a giant altermagnetic spin splitting of up to 620 meV. Crucially, we demonstrate that this altermagnetic state and its giant spin splitting are highly resilient, persisting even in a 10-layer slab model that accurately simulates the bulk limit. By introducing altermagnetism into the well-established FeSe-based superconducting family, our findings identify Fe2Se2Cl as a promising platform for spintronic applications and motivate future studies of the possible interplay between altermagnetism and superconductivity. △ Less

Submitted 16 July, 2026; originally announced July 2026.

A real-space exceptional ring mediates an eigenframe-charge transition in a non-Hermitian skyrmion

Authors: Kejun Liu

Abstract: The integer topological charge of a skyrmion is the standard example of topological protection. We ask what happens to that protection when the local generator is made non-Hermitian by polarization-selective gain or loss. The texture charge of a smoothly evolving state remains homotopy-protected under the usual fixed-boundary condition: after projective normalization, the gain/loss contribution ha… ▽ More The integer topological charge of a skyrmion is the standard example of topological protection. We ask what happens to that protection when the local generator is made non-Hermitian by polarization-selective gain or loss. The texture charge of a smoothly evolving state remains homotopy-protected under the usual fixed-boundary condition: after projective normalization, the gain/loss contribution has the Gilbert relaxation form on the target sphere. The spectral charges of the local generator behave differently. Its biorthogonal eigenframe charge is quantized while the texture avoids exceptional points. At linewidth matching, the skyrmion equator becomes a real-space exceptional ring on which the biorthogonal Bloch field diverges, and the eigenframe class jumps from +1 to 0 in a parameter-driven spectral transition. The closed contour relies on constant splitting along the equator, or an equivalent design constraint; a partial or amplitude-anisotropic realization instead leaves isolated real-space exceptional points. We use an operational Jones parametrization of an isolated polarization doublet and give a Stokes-tomography reconstruction of the left-right frame. The result identifies a spatially resolved exceptional contour that mediates an integer transition of a real-space eigenframe charge. △ Less

Submitted 21 July, 2026; v1 submitted 26 June, 2026; originally announced June 2026.

Comments: 14 pages, 3 figures. v5: reorganized as a full article

MSC Class: 47A10 81Q12 55M25

Selective stabilization of antiferromagnetic orders in FeTe films via local strain engineering

Authors: Hao Xu, Jing Jiang, Xuesong Gai, Haicheng Lin, Kai Liu, Zhong-Yi Lu, Kai Chang, Chong Liu

Abstract: The parent compound FeTe hosts a complex magnetic landscape that is highly susceptible to lattice distortions. Although theoretical models have predicted a bicollinear to dimer antiferromagnetic (AFM) phase transition under tensile strain, its experimental realization and deterministic control has remained elusive owing to severe magnetic frustration. Here, combining high-resolution scanning tunne… ▽ More The parent compound FeTe hosts a complex magnetic landscape that is highly susceptible to lattice distortions. Although theoretical models have predicted a bicollinear to dimer antiferromagnetic (AFM) phase transition under tensile strain, its experimental realization and deterministic control has remained elusive owing to severe magnetic frustration. Here, combining high-resolution scanning tunneling microscopy (STM) and density functional theory (DFT) calculations, we demonstrate the selective stabilization of bicollinear and dimer AFM orders in few-layer FeTe films via local uniaxial strain engineering. By mapping the strain fields near dislocation areas in FeTe films and FeTe/FeSe heterostructures, we establish a direct correspondence between specific strain components and the resulting magnetic ground states. We find that uniaxial compression along the Fe-Fe next-nearest-neighbor direction stabilizes the bicollinear AFM order, with the stripe orientation aligning parallel to the compression axis. Crucially, we report the experimental realization of the long-range dimer AFM order, which emerges under anisotropic strain along the Fe-Fe nearest-neighbor direction. This phase manifests as a distinct $\sqrt{2} \times \sqrt{2}$ electronic reconstruction and shares a common Neel temperature with the bicollinear phase. Our findings reveal that anisotropic strain effectively lifts the magnetic degeneracy among competing states. This work provides a robust strategy for the manipulation of elusive magnetic orders and offers insights into the interplay between lattice, spin, and electronic degrees of freedom in iron-based superconductors. △ Less

Submitted 11 June, 2026; originally announced June 2026.

High-Density Horizontal Arrays of Single-Chirality Carbon Nanotubes

Authors: Yanzhao Liu, Zilong Qiu, Yuguang Chen, Nie Zhang, Bing Han, Huimin Yin, Bojun Liu, Min Lyu, Zhihong Li, Yiran Ma, Jian Sheng, Jiahui Shao, Zeyao Zhang, Li Ding, Hao Hong, Chuanhong Jin, Sheng Wang, Kaihui Liu, Xiaowei He, Lian-Mao Peng, Yan Li

Abstract: Highly ordered high-density arrays of single-chirality single-walled carbon nanotubes (SWCNTs) are greatly desired for exploring the intrinsic anisotropic properties and collective performance of such 1-dimensional (1D) nanomaterials. Here we present a Marangoni flow-induced self-assembly (MISA) strategy to fabricate monolayered SWCNT arrays achieving a packing density of ~200 ${μm}^{-1}$ and a 2-… ▽ More Highly ordered high-density arrays of single-chirality single-walled carbon nanotubes (SWCNTs) are greatly desired for exploring the intrinsic anisotropic properties and collective performance of such 1-dimensional (1D) nanomaterials. Here we present a Marangoni flow-induced self-assembly (MISA) strategy to fabricate monolayered SWCNT arrays achieving a packing density of ~200 ${μm}^{-1}$ and a 2-dimensional order parameter ($S_{2\mathrm{D}}$) of ~0.95. Relying on its general compatibility with both organic and aqueous dispersions, we prepare single-chirality and enantiomer-pure SWCNT arrays from organic and aqueous dispersions resulting from the sorting processes. The anisotropic optical and electrical properties of the arrays are demonstrated by the polarization-dependent Rabi splitting as well as polarized near-infrared light emission and detection. With the great tolerance to solutions, substrates, and materials, as well as the feasibility and controllability, MISA shows great potential in the assembly of 1D nanomaterials. △ Less

Submitted 18 May, 2026; originally announced May 2026.

Field-induced asymmetric band flattening and ideal quantum geometry in rhombohedral graphene

Authors: Hongyun Zhang, Jinxi Lu, Size Wu, Yijie Wang, Kai Liu, Fei Wang, Wanying Chen, Lingzhi Wen, Jinling Zhou, Kenji Watanabe, Takashi Taniguchi, Jose Avila, Pavel Dudin, Matthew D. Watson, Takafumi Sato, Pu Yu, Wenhui Duan, Zhida Song, Guorui Chen, Shuyun Zhou

Abstract: Rhombohedral graphene exhibits an exceptionally diverse array of correlated phases that depend sensitively on the displacement field. Compiling reported phases into a unified phase diagram reveals a pronounced field-dependent electron-hole asymmetry: correlated states on the hole-doped side emerge at small displacement fields, whereas the fractional quantum anomalous Hall effect (FQAHE) is observe… ▽ More Rhombohedral graphene exhibits an exceptionally diverse array of correlated phases that depend sensitively on the displacement field. Compiling reported phases into a unified phase diagram reveals a pronounced field-dependent electron-hole asymmetry: correlated states on the hole-doped side emerge at small displacement fields, whereas the fractional quantum anomalous Hall effect (FQAHE) is observed exclusively on the electron-doped side under large displacement fields. This stark asymmetry highlights the need to understand how flat bands evolve with displacement fields. Here, we directly visualize the field-induced electron-hole asymmetric band flattening in rhombohedral pentalayer graphene (R5G) using nanospot angle-resolved photoemission spectroscopy with electrostatic gating. Beyond gap opening and spectral weight redistribution indicative of layer polarization, the gating field drives a strongly asymmetric modification of the flat bands: the flat valence band (FVB) evolves into an M-shaped dispersion at high field, whereas the flat conduction band (FCB) progressively flattens with increasing field. Comparison with calculations identifies critical parameters governing the band curvature of R5G, from which the resulting finite Berry curvature and near-ideal quantum geometry support the emergence of topological phases under electron doping at large fields. These results establish a direct link between the asymmetric phase diagram, band structure evolution, and quantum geometry, providing a microscopic framework for understanding correlated and topological phases in rhombohedral graphene. △ Less

Submitted 6 May, 2026; originally announced May 2026.

Comments: 17 pages, 5 figures

Finite-frequency fluctuation-response bounds for open quantum systems

Authors: Jie Gu, Kangqiao Liu

Abstract: We derive a finite-frequency fluctuation-response inequality for Markovian open quantum systems in an input-output setting. For any downstream measurement of the emitted field, the measured lock-in response-to-noise matrix is bounded by the output-field quantum Fisher information rate. For dissipative amplitude modulation with vacuum inputs, this information rate is further bounded by a frequency-… ▽ More We derive a finite-frequency fluctuation-response inequality for Markovian open quantum systems in an input-output setting. For any downstream measurement of the emitted field, the measured lock-in response-to-noise matrix is bounded by the output-field quantum Fisher information rate. For dissipative amplitude modulation with vacuum inputs, this information rate is further bounded by a frequency-independent signal-channel activity, which reduces for kinetic modulation to the stationary channel fluxes. The result is detector-facing but unraveling-independent: it applies after choosing a measurement record, while the information ceiling is set by the quantum field before any detection scheme or trajectory representation is selected. We formulate the bound for multiple signal channels and real finite-frequency quadratures, and illustrate it with a single-sided cavity, resonance fluorescence, and a truncated Kerr-parametric cat resonator. △ Less

Submitted 5 May, 2026; originally announced May 2026.

Comments: 21 pages, 2 figures

Operator-Valued Hardy Spaces and Kramers--Kronig Relations for Non-Markovian Quantum Memory Kernels

Authors: Kejun Liu

Abstract: Retarded support, upper-half-plane holomorphy, and Hardy boundary control are distinct properties of a memory kernel. We give sufficient conditions linking them for the Nakajima--Zwanzig kernel of an open system with finite-dimensional system Liouville space. If the projected kernel has an absolutely continuous real-axis representation with density w in L1 intersect Lp0, no singular part, and p0 >… ▽ More Retarded support, upper-half-plane holomorphy, and Hardy boundary control are distinct properties of a memory kernel. We give sufficient conditions linking them for the Nakajima--Zwanzig kernel of an open system with finite-dimensional system Liouville space. If the projected kernel has an absolutely continuous real-axis representation with density w in L1 intersect Lp0, no singular part, and p0 > 1, its transform lies in the operator-valued Hardy class Hp(B) for 1 < p <= p0. A finite-dimensional componentwise argument yields the corresponding principal-value and once-subtracted Kramers--Kronig (KK) boundary formulas; the H1 endpoint is separate. Microscopic unitary evolution gives holomorphy and a trace-norm bound for reduced-state transforms for arbitrary trace-class initial states, without that spectral hypothesis. On a common analytic domain, a perturbative force-fit equation has a first-order quotient pole at a simple baseline state-transform zero zeta only when the first-order inhomogeneous numerator I_tilde^(1)(zeta) is nonzero; at finite perturbation the actual zero and numerator must be checked, while matrix reconstructions additionally require adjugate non-cancellation. For rational reconstructions, the printed local or global clearing and no-cancellation hypotheses convert a rational kernel pole into a genuine upper-half-plane propagator pole. Such a pole is incompatible with a uniformly bounded CPTP family when the transforms agree on an open set, with Vieta's formula giving the imaginary-part budget. We formalize these paper-specific implications in Lean 4 from named classical inputs. A finite Jaynes--Cummings calculation provides a shifted, distributional KK check with a 0.024 percent fixed-truncation residual. △ Less

Submitted 7 August, 2026; v1 submitted 18 April, 2026; originally announced April 2026.

Comments: 35 pages, 2 figures, Springer Nature sn-jnl math-physics format.The Lean 4 development checks paper-specific deductions from explicitly named classical inputs

MSC Class: 81S22; 30H10; 47A56; 44A15

Topological surface states revealed by the Zeeman effect in superconducting UTe2

Authors: Zhen Zhu, Hans Christiansen, Yudi Huang, Kaiming Liu, Zheyu Wu, Shanta R. Saha, Johnpierre Paglione, Alexander G. Eaton, Andrej Cabala, Michal Vališka, Rafael M. Fernandes, Andreas Kreisel, Brian M. Andersen, Vidya Madhavan

Abstract: Intrinsic topological superconductors with protected boundary modes obeying non-Abelian statistics constitute a vanishingly small class of quantum materials. A defining spectroscopic signature of such phases is the presence of in-gap topological surface states (TSS). However, despite extensive theoretical proposals, their unambiguous experimental identification has remained elusive. Here we use ve… ▽ More Intrinsic topological superconductors with protected boundary modes obeying non-Abelian statistics constitute a vanishingly small class of quantum materials. A defining spectroscopic signature of such phases is the presence of in-gap topological surface states (TSS). However, despite extensive theoretical proposals, their unambiguous experimental identification has remained elusive. Here we use vector magnetic-field scanning tunnelling microscopy to obtain direct spectroscopic evidence of TSS in the spin-triplet superconductor UTe2. Atomic-scale spectroscopy reveals striking site-dependent superconductivity: Te sites host a large in-gap density of states that nearly fills the superconducting gap, whereas neighboring atomic sites remain gapped. Upon application of a magnetic field, the in-gap states on the Te sites are selectively suppressed, yielding a spatially homogeneous superconducting state with a markedly deeper gap relative to zero field. This site-selective gap evolution is in quantitative agreement with theoretical predictions for TSS in UTe2 that possess dominant Te-orbital character. Spectral-function calculations incorporating the Zeeman coupling reproduce the observed magnetic-field response. Our results provide a spectroscopic fingerprint of the long-sought TSS in superconductors and establish UTe2 as a compelling system for exploring intrinsic topological superconductivity. △ Less

Submitted 6 April, 2026; originally announced April 2026.

Comments: Main text: 17 pages, 5 figures; Supplementary Information: 12 pages, 9 figures

Benchmarking Chemically Scalable Machine-Learning Interatomic Potentials for Large-Scale Simulations of Multicomponent Alloys

Authors: Fei Shuang, Penghua Ying, Kai Liu, Zixiong Wei, Fengxian Liu, Zheyong Fan, Minqiang Jiang, Poulumi Dey

Abstract: Machine learning interatomic potentials (MLIPs) with broad chemical flexibility are essential for atomistic simulations of compositionally complex alloys, but their deployment in large-scale molecular dynamics requires a balance among accuracy, efficiency, stability, transferability, and uncertainty quantification. Here, we benchmark two chemically scalable MLIP frameworks, neuroevolution potentia… ▽ More Machine learning interatomic potentials (MLIPs) with broad chemical flexibility are essential for atomistic simulations of compositionally complex alloys, but their deployment in large-scale molecular dynamics requires a balance among accuracy, efficiency, stability, transferability, and uncertainty quantification. Here, we benchmark two chemically scalable MLIP frameworks, neuroevolution potential (NEP) and graph atomic cluster expansion (GRACE), for 16 elemental metals and their multicomponent alloys. GRACE-FS shows higher training efficiency and generally better average accuracy, chemical transferability, and finite-temperature robustness, whereas UNEP-v1 provides substantially higher inference speed and remains competitive in selected stress and large-error metrics. We further show that chemical transferability is closely linked to high-temperature MD stability in highly multicomponent environments and that ensemble-based uncertainty provides a more reliable error indicator than D-optimality for the heterogeneous systems considered here. Finally, three-million-atom shock simulations demonstrate that UNEP-v1, combined with ensemble uncertainty, enables uncertainty-aware simulations under extreme dynamic conditions, yielding robust global spall-strength predictions while revealing model sensitivity in local damage pathways. These results provide practical guidelines for selecting and deploying MLIPs in large-scale simulations of multicomponent alloys. △ Less

Submitted 19 June, 2026; v1 submitted 2 April, 2026; originally announced April 2026.

Journal ref: Physical Review Materials 10, 073802 (2026)

Chemical Medium-Range Order Enables Stoichiometric Rigidity

Authors: Kejun Liu

Abstract: Maxwell counting predicts an isostatic threshold at $\langle r\rangle = 2.4$ for covalent network glasses, but which structural correlations actually produce rigidity near this point is still unclear. In this work, we test four candidates: enthalpic stress, chemical defects, geometric interlocking, and medium-range order (MRO). We use a locally tree-like configuration model as a zero-MRO baseline… ▽ More Maxwell counting predicts an isostatic threshold at $\langle r\rangle = 2.4$ for covalent network glasses, but which structural correlations actually produce rigidity near this point is still unclear. In this work, we test four candidates: enthalpic stress, chemical defects, geometric interlocking, and medium-range order (MRO). We use a locally tree-like configuration model as a zero-MRO baseline and apply perturbations to test each candidate. We find that (i) enthalpic stress delays rigidity rather than enabling it; (ii) chemical defects require fractions ($\sim$40%) far above experimental values ($\sim$16% in GeSe$_2$); (iii) geometric linking density does not govern the threshold location, which is instead set by loop-induced redundancy; and (iv) only phenomenological MRO proxies recover rigidity at experimentally accessible strengths. Consequently, chalcogenide intermediate-phase data and amorphous SiO$_2$ ring statistics positively implicate chemical MRO, while DNA spatial networks independently rule out pure geometric entanglement. We conclude that rigidity near the Maxwell threshold requires chemistry-specific correlations beyond pure connectivity. △ Less

Submitted 24 April, 2026; v1 submitted 28 March, 2026; originally announced March 2026.

Comments: 4 pages + 7 pages Supplemental Material, 2 main-text figures + 5 SM figures

MSC Class: 82B43; 82D30

Strain-released epitaxy of GaN enabled by compliant single-crystalline metal foils

Authors: Yaqing Ma, Junwei Cao, Huaze Zhu, Yijian Song, Huicong Chen, Menglin He, Jun Yang, Ping Jiang, Tong Jiang, Han Chen, Xiang Xu, Yuqiao Zheng, Hao Wang, Muhong Wu, Yu Zou, Xiaochuan Chen, Tongbo Wei, Kaihui Liu, Wei Kong

Abstract: Heteroepitaxy conventionally relies on rigid crystalline substrates, implicitly assuming that lattice and thermal mismatch must be accommodated within the epitaxial layer, leading to residual strain and defects that worsen with increasing substrate size. Here we demonstrate a substrate-mediated strain-partitioning regime in which lattice and thermal mismatch are preferentially partitioned into the… ▽ More Heteroepitaxy conventionally relies on rigid crystalline substrates, implicitly assuming that lattice and thermal mismatch must be accommodated within the epitaxial layer, leading to residual strain and defects that worsen with increasing substrate size. Here we demonstrate a substrate-mediated strain-partitioning regime in which lattice and thermal mismatch are preferentially partitioned into the substrate rather than stored in the epitaxial layer. We report the epitaxial growth of single-crystalline GaN on mechanically compliant yet crystallographically ordered single-crystalline copper foils. Atomic-resolution microscopy, geometric phase analysis and density functional theory reveal that mismatch-induced stress is primarily screened by elastic deformation of the Cu lattice, accompanied by localized interfacial slip confined to a few atomic layers, leaving the AlN and GaN epilayers nearly strain-free despite large nominal mismatch. Leveraging this strain-released epitaxial platform, we further demonstrate dense GaN micro-light-emitting diode arrays that benefit from efficient vertical electrical conduction and thermal dissipation enabled by the metallic substrate. By establishing compliant single-crystal metal foils as a new substrate class, this work identifies mechanical contrast as an underexplored governing parameter in heteroepitaxial design, with implications extending beyond GaN. △ Less

Submitted 27 March, 2026; originally announced March 2026.

Invariant ionic conductance in an atomically thin polar nanopore

Authors: Shengping Zhang, Haiou Zeng, Ningran Wu, Guodong Xue, Xiao Li, Anshul Saxena, Junhe Tong, Nianjie Liang, Zeyu Zhuang, Jing Yang, Narayana R. Aluru, Kaihui Liu, Bai Song, Luda Wang

Abstract: Ion channels regulate many essential properties of biological cells, especially the membrane potential. Despite decades of efforts on artificial channels, it remains a great challenge to mimic the dipole potential-an indispensable constituent of the membrane potential, due to its angstrom-scale characteristic length. Here, we explore nanopores in monolayer molybdenum sulfide selenide (MoSSe) consi… ▽ More Ion channels regulate many essential properties of biological cells, especially the membrane potential. Despite decades of efforts on artificial channels, it remains a great challenge to mimic the dipole potential-an indispensable constituent of the membrane potential, due to its angstrom-scale characteristic length. Here, we explore nanopores in monolayer molybdenum sulfide selenide (MoSSe) considering its intrinsic dipole and atomic thickness. Remarkably, an invariant ionic conductance was observed over salt concentrations spanning six orders of magnitude, distinct from all known conductance-concentration scaling laws and reminiscent of the current saturation in cell membranes at high concentrations. Molecular dynamics simulations revealed the fundamental role of the dipole-modulated dielectric properties of nanoconfined water. Our findings highlight an exotic conductance scaling law and open up a novel avenue for controlling ion transport in unprecedented ways. △ Less

Submitted 12 May, 2026; v1 submitted 23 March, 2026; originally announced March 2026.

Bridging Crystal Structure and Material Properties via Bond-Centric Descriptors

Authors: Jian-Feng Zhang, Ze-Feng Gao, Xiao-Qi Han, Bo Zhan, Dingshun Lv, Miao Gao, Kai Liu, Xinguo Ren, Zhong-Yi Lu, Tao Xiang

Abstract: Although chemical bonding is the fundamental mechanistic bridge connecting atomic structure to macroscopic material properties, current data-driven materials science largely treats it as an implicit "black box". Existing machine learning (ML) models rely predominantly on geometric coordinates, forcing them to implicitly relearn complex quantum mechanics from scratch. This lack of intermediate phys… ▽ More Although chemical bonding is the fundamental mechanistic bridge connecting atomic structure to macroscopic material properties, current data-driven materials science largely treats it as an implicit "black box". Existing machine learning (ML) models rely predominantly on geometric coordinates, forcing them to implicitly relearn complex quantum mechanics from scratch. This lack of intermediate physical features limits model interpretability and generalizability, particularly when training data is scarce. To solve this problem, we introduce MattKeyBond, a bond-centric materials database that explicitly maps the local electronic landscape and bonding interactions of materials. Building on this, we propose Bonding Attractivity (BA), a novel element-specific descriptor that quantifies the intrinsic capability of atoms to form covalent networks. By providing pre-calculated, energy-dimensional bonding descriptors, MattKeyBond transforms the implicit "black box" into physically interpretable features. This strategy relieves ML models from the burden of deducing physical laws from pure geometry, enabling accurate predictions even with limited data and seamlessly integrating electronic structure theory into modern AI workflows. △ Less

Submitted 27 July, 2026; v1 submitted 19 March, 2026; originally announced March 2026.

Comments: 17 pages, 10 figures

Interfacial exchange and magnetostatic coupling in a CoFeB/Thulium Iron Garnet heterostructure

Authors: Walid Al Misba, Jenae E. Shoup, Miela J. Gross, Dhritiman Bhattacharya, Kai Liu, Caroline A. Ross, Daniel B. Gopman, Jayasimha Atulasimha

Abstract: We investigate the exchange coupling between a ferrimagnetic insulator (FI) thulium iron garnet (TmIG) deposited on a gadolinium gallium garnet (GGG) substrate, which shows perpendicular magnetic anisotropy and a ferromagnetic metal (FMM) stack with oxide capping that consists of CoFeB(x)/W(0.4 nm)/CoFeB(0.8 nm)/MgO(1 nm)/W(5 nm). Vibrating sample magnetometry, magneto-optical Kerr microscopy and… ▽ More We investigate the exchange coupling between a ferrimagnetic insulator (FI) thulium iron garnet (TmIG) deposited on a gadolinium gallium garnet (GGG) substrate, which shows perpendicular magnetic anisotropy and a ferromagnetic metal (FMM) stack with oxide capping that consists of CoFeB(x)/W(0.4 nm)/CoFeB(0.8 nm)/MgO(1 nm)/W(5 nm). Vibrating sample magnetometry, magneto-optical Kerr microscopy and first-order reversal curve studies coupled with micromagnetic simulations are used to analyze the coupling between these layers. Strong interlayer exchange coupling and magnetostatic coupling are observed in the samples where the relative strength between these interactions can be controlled by varying the thickness of the CoFeB layer. Films with CoFeB thickness x <=1 nm are strongly exchange coupled, whereas the magnetostatic coupling dominates when the thickness is increased to 3 nm or above. These findings have important implications towards realizing fast and energy efficient spintronic devices using a FI, as its coupling to the FMM layer can be used for effective electrical read out of the magnetic state of the FI. △ Less

Submitted 15 March, 2026; originally announced March 2026.

Evidence of intertwined pair density and charge density wave orders in UTe2

Authors: Zhen Zhu, Yudi Huang, Julian May-Mann, Kaiming Liu, Zheyu Wu, Shanta R. Saha, Johnpierre Paglione, Alexander G. Eaton, Andrej Cabala, Michal Vališka, Eduardo Fradkin, Vidya Madhavan

Abstract: The strongly correlated spin-triplet superconductor UTe2 hosts an unusual landscape of magnetic-field-sensitive charge density wave (CDW) phases, positioning it as a compelling system for studying intertwined electronic orders. A central challenge is determining whether the observed charge modulations arise from a triplet pair density wave (PDW) order and, if so, how the anisotropic magnetic field… ▽ More The strongly correlated spin-triplet superconductor UTe2 hosts an unusual landscape of magnetic-field-sensitive charge density wave (CDW) phases, positioning it as a compelling system for studying intertwined electronic orders. A central challenge is determining whether the observed charge modulations arise from a triplet pair density wave (PDW) order and, if so, how the anisotropic magnetic field response of triplet superconductivity is manifested in the CDW response. Here, using a scanning tunneling microscope equipped with a vector magnetic field, we systematically investigate the evolution and interrelation of distinct CDW orders. Complementing the previously identified incommensurate CDW peaks (qi=1,2,3), we resolve an additional set of nondispersive modulations (pi=1,2,3 and h1,2) with distinct temperature and magnetic field dependencies. The pi CDW peaks vanish near Tc, while the qi peaks survive well above Tc but are progressively suppressed by magnetic field in an anisotropic manner. The critical fields of the qi peaks mirror the directional hierarchy of Hc2, which suggests a PDW is present above the bulk Tc. This is consistent with a Landau free-energy picture where PDWs with wavevectors pi form above the bulk Tc, leading to composite CDW orders with wavevector qi. Below Tc, the coupling of PDWs and uniform superconductivity leads to the pi CDWs. Together, these findings establish UTe2 as a rare platform where both the parent PDW and descendant orders are directly resolved, enabling access to both the fundamental and emergent manifestations of PDW physics. △ Less

Submitted 25 June, 2026; v1 submitted 9 March, 2026; originally announced March 2026.

Comments: Accepted for publication in PNAS

Journal ref: PNAS 123 (29) e2602117123 (2026)

Reversible tuning of magnetic order and intrinsic superconductivity in strained FeTe films via stoichiometry control

Authors: Hao Xu, Jing Jiang, Xuesong Gai, Rui-Qi Cao, Kaiwei Chen, Xiao-Xiao Man, Haicheng Lin, Peng Deng, Ke He, Kai Liu, Dapeng Zhao, Zhong-Yi Lu, Kai Chang, Chong Liu

Abstract: FeTe is a prototypical parent compound of iron-based superconductors. While bulk FeTe is non-superconducting with a long-range bicollinear antiferromagnetic order, superconductivity has been achieved in thin films. However, the approaches usually involve complex oxygen incorporation or interfacial effects, the microscopic mechanisms of which remain elusive. Here, we prepare high-purity, bare FeTe… ▽ More FeTe is a prototypical parent compound of iron-based superconductors. While bulk FeTe is non-superconducting with a long-range bicollinear antiferromagnetic order, superconductivity has been achieved in thin films. However, the approaches usually involve complex oxygen incorporation or interfacial effects, the microscopic mechanisms of which remain elusive. Here, we prepare high-purity, bare FeTe thin films on SrTiO3 and investigate their magnetic and superconducting states combining both microscopic and macroscopic characterizations. By reducing the interstitial Fe impurities, we successfully suppress the long-range antiferromagnetic order, enhance the quasiparticle coherence and induce superconductivity at ~10 K. Moreover, this process is readily reversible by tuning the Fe concentration. Our findings reveal that precise stoichiometric control is sufficient to induce intrinsic superconductivity in strained FeTe thin films. This work provides insights into the competition between magnetism and superconductivity in iron chalcogenides, and supplies methods for developing stable, high-purity superconducting FeTe films. △ Less

Submitted 22 May, 2026; v1 submitted 15 February, 2026; originally announced February 2026.

Comments: 5 figures,1 table

Journal ref: ACS Nano (2026)

Exotic vortex states at high magnetic fields in a quasi-two-dimensional FeSe-based superconductor

Authors: Xuyang Li, Jian Li, Kai Liu, Jiaqiang Cai, Shunjiao Li, Baolei Kang, Mengzhu Shi, Dan Zhao, Chuanying Xi, Jinglei Zhang, Tao Wu, Xianhui Chen

Abstract: Owing to strong electronic correlations, high-temperature superconductivity always exhibits intricate intertwinement with various competing electronic orders in phase diagrams, such as spin/charge density waves (S/CDWs). In cuprate superconductors,the intertwinement of superconductivity and CDW order could strongly affect the fundamental properties of superconductivity, such as the critical temper… ▽ More Owing to strong electronic correlations, high-temperature superconductivity always exhibits intricate intertwinement with various competing electronic orders in phase diagrams, such as spin/charge density waves (S/CDWs). In cuprate superconductors,the intertwinement of superconductivity and CDW order could strongly affect the fundamental properties of superconductivity, such as the critical temperature(Tc) and critical magnetic field(Hc). Recent high-field transport measurements indicate that when quantum fluctuations become important at low temperatures and high magnetic fields, the CDW order also reshapes the vortex states, which leads to fragile superconductivity with extremely low critical current(Jc). Here, by performing comprehensive high-field transport measurements, the H-T phase diagram of vortex states is mapped to H = 33 T in a quasi-two-dimensional FeSe-based superconductor (TBA+)xFeSe with a zero-resistivity transition temperature above 40 K. Our results indicate that (TBA+)xFeSe is an extremely type II superconductor with significant thermal fluctuations.At low temperatures, high magnetic fields cause the vortex solid state to exhibit similar current-dependent zero-resistance behavior as the fragile superconductivity in cuprate superconductors with CDW order. When the vortex solid state is melted with increasing temperature, a superconducting regime with vortex-like phase fluctuations emerges as an intermediate state, which features finite longitudinal resistance and vanishing Hall resistance. At higher temperatures, a vortex liquid state with finite Hall resistance eventually appears due to thermal fluctuations. All these observations suggest exotic vortex states beyond the classical paradigm of vortex matter. △ Less

Submitted 26 January, 2026; originally announced January 2026.

Comments: 33 pages, 13 figures, 1 table

Superconductivity in non-centrosymmetric rhombohedral NbSe2

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

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

Submitted 23 January, 2026; originally announced January 2026.

Topological Semimetal Transport Modulated by Interstitial Fe in Ba(Fe$_{1-x}$Co$_x$)$_{2+δ}As$_2$ Superconductors

Authors: Ze-Xian Deng, Qiang-Jun Cheng, Jing Jiang, Yong-Wei Wang, Xi Zhou, Ming-Qiang Ren, Cong Cong Lou, Xiao-Xiang Chen, Bin-Jie Wu, Zeng-Wei Zhu, Qing-Hua Zhang, Lin Gu, Ding Zhang, Kai Liu, Xu-Cun Ma, Qi-Kun Xue, Can-Li Song

Abstract: Topological semimetals are renowned for exhibiting large, unsaturated magnetoresistance arising from ultrahigh carrier mobility and electron-hole compensation. However, such behaviors remain poorly understood in iron-based superconductors that have been recently recognized to harbor rich nontrivial topology. Here, we combine angle-resolved magneto-transport measurements with first principles calcu… ▽ More Topological semimetals are renowned for exhibiting large, unsaturated magnetoresistance arising from ultrahigh carrier mobility and electron-hole compensation. However, such behaviors remain poorly understood in iron-based superconductors that have been recently recognized to harbor rich nontrivial topology. Here, we combine angle-resolved magneto-transport measurements with first principles calculations to reveal the emergence and tunability of topological semimetals in ferropnictide Ba(Fe$_{1-x}$Co$_x$)$_{2+δ}As$_2$ epitaxial films, modulated by interstitial Fe. These states exhibit ultralow residual resistivity, coexisting high-mobility electron and hole carriers, and linear positive magnetoresistance below 110 K. Remarkably, the magnetoresistance becomes more pronounced when the magnetic field is applied parallel to the film plane, reaching an unsaturated 1206% at 56 T. Furthermore, superconductivity persists in these ferropnictide films, establishing them as a tunable platform for investigating the interplay among electron correlation, topology, and superconductivity. △ Less

Submitted 22 January, 2026; originally announced January 2026.

Comments: 18 pages, 4 figures, Supplemental Material

Single-Atom Tuning of Structural and Optoelectronic Properties in Halogenated Anthracene-Based Covalent Organic Frameworks

Authors: Klaudija Paliušytė, Laura Fuchs, Zehua Xu, Kuangjie Liu, Kornel Roztocki, Shuo Sun, Hendrik Zipse, Achim Hartschuh, Frank Ortmann, Jenny Schneider

Abstract: Strategies for tuning structural and (opto-)electronic properties are fundamental to the rational design of functional materials. Here, we present a molecular design approach for precisely modulating the optoelectronic properties of covalent organic frameworks (COFs) through single-atom halogen substitution on $π$-extended anthracene linkers. Using a Wurster-type tetratopic amine (W-NH$_2$) and a… ▽ More Strategies for tuning structural and (opto-)electronic properties are fundamental to the rational design of functional materials. Here, we present a molecular design approach for precisely modulating the optoelectronic properties of covalent organic frameworks (COFs) through single-atom halogen substitution on $π$-extended anthracene linkers. Using a Wurster-type tetratopic amine (W-NH$_2$) and a series of anthracene-based dialdehydes bearing H, Cl, Br, or I at the 2-position, a family of imine-linked COFs, W-A-X (X = H, Cl, Br, I), was synthesized, all displaying well-ordered porous structures. The halogen substituent strongly influences framework formation, with brominated COFs forming substantially larger crystalline domains than their chloro- and iodo-functionalized analogues. UV-vis absorption and photoluminescence measurements reveal a systematic redshift across the series $(\mathrm{H < Cl < Br < I})$, demonstrating that a single-atom modification effectively tunes the optical response. Time-dependent density functional theory calculations on both isolated fragments and extended COF models attribute these trends to halogen-induced changes in the COF band structure and provide a mechanistic understanding of how single-atom substitution influences the optoelectronic properties of the extended $π$-framework. Overall, this study establishes single-atom halogen substitution as a powerful and modular strategy for tailoring the structural and optical properties of anthracene-based COFs. △ Less

Submitted 17 January, 2026; originally announced January 2026.

Comments: main text and supporting information

Thermally Configurable Multi-Order Polar Skyrmions in Multiferroic Oxide Superlattices

Authors: Kefan Liu, Yuhui Huang, Xiangwei Guo, Yongjun Wu, Juan Li, Zijian Hong

Abstract: Polar topological textures in low-dimensional ferroelectrics have emerged as a versatile platform for high-density information storage and neuromorphic computing. While low-order topological states, such as vortices and skyrmions, have been extensively studied, high-order polar topological families remain largely unexplored due to their higher energy requirements and limited stabilization methods.… ▽ More Polar topological textures in low-dimensional ferroelectrics have emerged as a versatile platform for high-density information storage and neuromorphic computing. While low-order topological states, such as vortices and skyrmions, have been extensively studied, high-order polar topological families remain largely unexplored due to their higher energy requirements and limited stabilization methods. Here, using a BiFeO3 (BFO)-based multiferroic superlattice as a model system, we demonstrate a thermal-modulation strategy that stabilizes multi-order polar skyrmions and enables reversible tuning of their topological order through phase-field simulations. It was found that temperature modulation drives the system from polar solitons through 1π-, 2π-, 3π-, and 4π-skyrmion states, with closed heating-cooling path analyses revealing the widest thermal stability window for 2π-skyrmions (up to 600 K). Leveraging this robustness, 2% Sm doping in BFO lowers the transition temperatures, enabling room-temperature stabilization of 2π-skyrmions. These findings enrich the fundamental understanding of multi-order polar topologies and establish a tunable strategy for realizing variable-order topological configurations in practical memory devices. △ Less

Submitted 9 January, 2026; originally announced January 2026.

Comments: 5 figures, 19 pages

Symmetry-engineered and electrically tunable in-plane anomalous Hall effect in oxide heterostructures

Authors: Kunjie Dai, Zhen Wang, Wenfeng Wu, Feng Jin, Enda Hua, Nan Liu, Jingdi Lu, Jinfeng Zhang, Yuyue Zhao, Linda Yang, Kai Liu, Huan Ye, Qiming Lv, Zhengguo Liang, Ao Wang, Dazhi Hou, Yang Gao, Shengchun Shen, Jing Tao, Liang Si, Wenbin Wu, Lingfei Wang

Abstract: The family of Hall effects has long served as a premier probe of how symmetry, magnetic order, and topology intertwine in solids. Recently, the in-plane anomalous Hall effect (IP-AHE), a transverse Hall response driven by in-plane magnetization, has emerged as a distinct member of this family, offering innovative spintronic functionalities and illuminating intricate interplay between mirror-symmet… ▽ More The family of Hall effects has long served as a premier probe of how symmetry, magnetic order, and topology intertwine in solids. Recently, the in-plane anomalous Hall effect (IP-AHE), a transverse Hall response driven by in-plane magnetization, has emerged as a distinct member of this family, offering innovative spintronic functionalities and illuminating intricate interplay between mirror-symmetry breaking and in-plane magnetic order. However, practical routes to deterministically and reversibly control IP-AHE remain limited. Here, we establish a symmetry-engineered IP-AHE platform, CaRuO3/La2/3Ca1/3MnO3/CaRuO3 heterostructure on NdGaO3(110), that turns strict mirror-symmetry breaking constraints into effective tuning knobs. IP-AHE in these epitaxial trilayers unambiguously couples to the CaRuO3-buffer-induced mirror-symmetry breaking and faithfully reproduces the ferromagnetic hysteresis. Ionic liquid gating further enables reversible reconfigurations of the symmetry breaking, thereby achieving electrical modulation and ON/OFF switching of IP-AHE. This highly tunable IP-AHE platform opens pathways for exploring nontrivial magnetic order and developing programmable Hall functionalities in planar geometries. △ Less

Submitted 8 January, 2026; originally announced January 2026.

Roadmap for Condensates in Cell Biology

Authors: Dilimulati Aierken, Sebastian Aland, Stefano Bo, Steven Boeynaems, Danfeng Cai, Serena Carra, Lindsay B. Case, Hue Sun Chan, Jorge R. Espinosa, Trevor K. GrandPre, Alexander Y. Grosberg, Ivar S. Haugerud, William M. Jacobs, Jerelle A. Joseph, Frank Jülicher, Kurt Kremer, Guido Kusters, Liedewij Laan, Keren Lasker, Katrin S. Laxhuber, Hyun O. Lee, Kathy F. Liu, Dimple Notani, Yicheng Qiang, Paul Robustelli , et al. (16 additional authors not shown)

Abstract: Biomolecular condensates govern essential cellular processes yet elude description by traditional equilibrium models. This roadmap, distilled from structured discussions at a workshop and reflecting the consensus of its participants, clarifies key concepts for researchers, funding bodies, and journals. After unifying terminology that often separates disciplines, we outline the core physics of cond… ▽ More Biomolecular condensates govern essential cellular processes yet elude description by traditional equilibrium models. This roadmap, distilled from structured discussions at a workshop and reflecting the consensus of its participants, clarifies key concepts for researchers, funding bodies, and journals. After unifying terminology that often separates disciplines, we outline the core physics of condensate formation, review their biological roles, and identify outstanding challenges in nonequilibrium theory, multiscale simulation, and quantitative in-cell measurements. We close with a forward-looking outlook to guide coordinated efforts toward predictive, experimentally anchored understanding and control of biomolecular condensates. △ Less

Submitted 7 January, 2026; originally announced January 2026.

Comments: 14 pages, 5 figures

Error Resilience of Fracton Codes and Near Saturation of Code-Capacity Threshold in Three Dimensions

Authors: Giovanni Canossa, Lode Pollet, Miguel A. Martin-Delgado, Hao Song, Ke Liu

Abstract: Fracton codes have been intensively studied as novel topological states of matter, yet their fault-tolerant properties remain largely unexplored. Here, we investigate the optimal thresholds of self-dual fracton codes, in particular the checkerboard code, against stochastic Pauli noise. By utilizing a statistical-mechanical mapping combined with large-scale parallel tempering Monte Carlo simulation… ▽ More Fracton codes have been intensively studied as novel topological states of matter, yet their fault-tolerant properties remain largely unexplored. Here, we investigate the optimal thresholds of self-dual fracton codes, in particular the checkerboard code, against stochastic Pauli noise. By utilizing a statistical-mechanical mapping combined with large-scale parallel tempering Monte Carlo simulations, we calculate the optimal code capacity of the checkerboard code to be $p_{th} \simeq 0.107(3)$. This value is the highest among known three-dimensional codes and nearly saturates the theoretical limit for topological codes. Our results further validate the generalized entropy relation for two mutually dual models, $H(p_{th}) + H(\tilde{p}_{th}) \approx 1$, and extend its applicability beyond standard topological codes. This verification indicates the Haah's code also possesses a code capacity near the theoretical limit $p_{th} \approx 0.11$. These findings highlight fracton codes as highly resilient quantum memory and demonstrate the utility of duality techniques in analyzing intricate quantum error-correcting codes. △ Less

Submitted 3 March, 2026; v1 submitted 28 December, 2025; originally announced December 2025.

Comments: 12 pages, 5 figures, 2 tables

Journal ref: Phys. Rev. B 113, 104204 (2026)

Fractional High-Chern Insulator in Twisted Rhombohedral Graphene

Authors: Zexu Li, Wenxuan Wang, Fajie Wang, Zaizhe Zhang, Qiu Yang, Kenji Watanabe, Takashi Taniguchi, X. C. Xie, Jie Wang, Kaihui Liu, Zhida Song, Xiaobo Lu

Abstract: The realization of fractional Chern insulators opens up the possibility of exploring fractionally charged excitations and anyonic statistics in the absence of a magnetic field. A central question is whether lattice-based systems can give rise to radically new states, distinct from those observed in traditional fractional quantum Hall systems. In this work, we investigate a new type of moiré flat b… ▽ More The realization of fractional Chern insulators opens up the possibility of exploring fractionally charged excitations and anyonic statistics in the absence of a magnetic field. A central question is whether lattice-based systems can give rise to radically new states, distinct from those observed in traditional fractional quantum Hall systems. In this work, we investigate a new type of moiré flat band system composed of Bernal bilayer graphene and rhombohedral tetralayer graphene. We discover an unprecedented richness of quantum anomalous Hall insulators with Chern numbers from C = 1 to C = 7 at v = 1 and around v = 3. Remarkably, we observe an exotic fractional Chern insulator with C = 7/3 around v = 2/3 which is beyond all known fractional Chern insulators described by either the Jain sequence or current high Chern theory. Our work expands the understanding of fractionally charged excitations beyond the Landau level basis and offers a new moire platform for exploring anyons. △ Less

Submitted 2 June, 2026; v1 submitted 25 December, 2025; originally announced December 2025.

Coexistence of near-EF van Hove singularity and in-gap topological Dirac surface states in superconducting electrides

Authors: Yin Yang, Peihan Sun, Ye Shen, Zhijun Tu, Pengcheng Ma, Hongrun Zhen, Tianqi Wang, Longli Tian, Tian Cui, Hechang Lei, Kai Liu, Zhonghao Liu

Abstract: Superconducting electrides have attracted growing attention for their potential to achieve high superconducting transition temperatures (TC) under pressure. However, many known electrides are chemically reactive and unstable, making high-quality single-crystal growth, characterization, and measurements difficult, and most do not exhibit superconductivity at ambient pressure. In contrast, La3In sta… ▽ More Superconducting electrides have attracted growing attention for their potential to achieve high superconducting transition temperatures (TC) under pressure. However, many known electrides are chemically reactive and unstable, making high-quality single-crystal growth, characterization, and measurements difficult, and most do not exhibit superconductivity at ambient pressure. In contrast, La3In stands out for its ambient-pressure superconductivity (TC ~ 9.4 K) and the availability of high-quality single crystals. Here, we investigate its low-energy electronic structure using angle-resolved photoemission spectroscopy and first-principles calculations. The bands near the Fermi energy are mainly derived from La 5d and In 5p orbitals. A saddle point is directly observed at the Brillouin zone (BZ) boundary, while a three-dimensional van Hove singularity crosses EF at the BZ corner. First-principles calculations further reveal topological Dirac surface states within the bulk energy gap above EF. The coexistence of a high density of states and in-gap topological surface states near EF suggests that La3In offers a promising platform for tuning superconductivity and exploring possible topological superconducting phases through doping or external pressure. △ Less

Submitted 28 November, 2025; originally announced November 2025.

Comments: See also our related works on the formation mechanisms of electrides and their connection to SC and unconventional metallic behavior: "Evidence for Anion-Electron Duality and Enhanced Superconducting Role of Interstitial Anionic Electrons in Electrides" and "Interstitial Anionic Electrons-Involved Superconductivity and T-Linear Resistivity Behavior in Electride"

Electron-phonon coupling of one-dimensional (3,0) carbon nanotube

Authors: Zhenfeng Ouyang, Jing Jiang, Jian-Feng Zhang, Miao Gao, Kai Liu, Zhong-Yi Lu

Abstract: A very recent report claims that ambient-pressure high-temperature ($T_c$) superconductivity was found in boron-doped three-dimensional networks of carbon nanotubes (CNTs). Here, we systematically study the electron-phonon coupling (EPC) of one-dimensional (1D) (3,0) CNT under ambient pressure. Our results show that the EPC constant $λ$ of the undoped 1D (3,0) CNT is 0.70, and reduces to 0.44 afte… ▽ More A very recent report claims that ambient-pressure high-temperature ($T_c$) superconductivity was found in boron-doped three-dimensional networks of carbon nanotubes (CNTs). Here, we systematically study the electron-phonon coupling (EPC) of one-dimensional (1D) (3,0) CNT under ambient pressure. Our results show that the EPC constant $λ$ of the undoped 1D (3,0) CNT is 0.70, and reduces to 0.44 after 1.3 holes/cell doping. Further calculations show that the undoped (3,0) CNT is a two-gap superconductor with a superconducting $T_c$ $\sim$ 33 K under ambient pressure. Additionally, we identify three characteristic phonon modes with strong EPC, establishing that the pristine (3,0) CNT is a high-$T_c$ superconducting unit, and further suggest that searching for those superconducting units with strong EPC phonon mode would be an effective way to discover high-$T_c$ phonon-mediated superconductors. Our study not only provide a crucial and timely theoretical reference for the recent report regarding superconducting CNTs, but also uncover that the pristine (3,0) CNT hosts the highest record of superconducting $T_c$ among the elemental superconductors under ambient pressure. △ Less

Submitted 5 November, 2025; originally announced November 2025.

Comments: 6 pages, 5 figures, 1 table

Ultrafast magnetic moment transfer and bandgap renormalization in monolayer FeCl$_2$

Authors: Yu-Hui Song, Huan-Cheng Yang, Kai Liu, Zhong-Yi Lu

Abstract: The microscopic origin of laser-induced ultrafast demagnetization remains an open question, to which the non-thermal electronic distribution plays a vital role at the initial stage. Herein, we investigate the connection between the non-thermal electronic distribution and the ultrafast spin dynamics as well as the electronic structure evolution in ferromagnetic FeCl$_2$ monolayer using real-time ti… ▽ More The microscopic origin of laser-induced ultrafast demagnetization remains an open question, to which the non-thermal electronic distribution plays a vital role at the initial stage. Herein, we investigate the connection between the non-thermal electronic distribution and the ultrafast spin dynamics as well as the electronic structure evolution in ferromagnetic FeCl$_2$ monolayer using real-time time-dependent density functional theory (rt-TDDFT) with self-consistent Hubbard $U$ correction. Our simulations reveal that femtosecond laser pulses induce ultrafast magnetic moment transfer from Fe to Cl atoms. More importantly, through a comprehensive analysis of orbital-resolved electronic structure, we elucidate the microscopic origin of this transfer, attributing it to specific intra-atomic and inter-atomic charge transfer pathways driven by non-thermal excitations. The extent of demagnetization of Fe atoms exhibits a non-monotonic dependence on the laser photon energy, reaching a maximum at the resonant excitation. In addition, the dynamical evolution of the band structure was studied based on the eigenstates of the instantaneous Hamiltonian. Under resonant excitation, the bandgap reduction reaches up to $41\%$ within tens of fs. These findings provide fundamental insights into ultrafast spin control and suggest a strategy to optically engineer the magnetism in two-dimensional magnetic materials. △ Less

Submitted 4 November, 2025; v1 submitted 4 November, 2025; originally announced November 2025.

Comments: 8 pages, 8 figures

Journal ref: Phy Rev B 112, 214449 (2025)

Phenomenological Noise Models and Optimal Thresholds of the 3D Toric Code

Authors: Ji-Ze Xu, Yin Zhong, Miguel A. Martin-Delgado, Hao Song, Ke Liu

Abstract: Three-dimensional (3D) topological codes offer the advantage of supporting fault-tolerant implementations of non-Clifford gates, yet their performance against realistic noise remains largely unexplored. In this work, we focus on the paradigmatic 3D toric code and investigate its fault-tolerance thresholds in the presence of both Pauli and measurement errors. Two randomly coupled lattice gauge mode… ▽ More Three-dimensional (3D) topological codes offer the advantage of supporting fault-tolerant implementations of non-Clifford gates, yet their performance against realistic noise remains largely unexplored. In this work, we focus on the paradigmatic 3D toric code and investigate its fault-tolerance thresholds in the presence of both Pauli and measurement errors. Two randomly coupled lattice gauge models that describe the code's correctability are derived, including a random 2-form $\mathbb{Z}_2$ gauge theory. By exploiting a generalized duality technique, we show that the 3D toric code exhibits optimal thresholds of $p^{X,M}_{th} \approx 11\%$ and $p^{Z,M}_{th} \approx 2\%$ against bit-flip and phase-flip errors, respectively. These threshold values show modest reductions compared to the case of perfect measurements, establishing the robustness of the 3D toric code against measurement errors. Our results constitute a substantial advance towards assessing the practical performance of 3D topological codes. This contribution is timely and in high demand, as rapid hardware advancements are bringing complex codes into experimental reach. Moreover, our work highlights the interdisciplinary nature of fault-tolerant quantum computation and holds significant interest for quantum information science, high-energy physics, and condensed matter physics. △ Less

Submitted 30 June, 2026; v1 submitted 23 October, 2025; originally announced October 2025.

Comments: 14+7 pages, 6+2 figures

Journal ref: Quantum Sci. Technol. 11, 035022 (2026)

Does Moire Matter? Critical Moire Dependence with Quantum Fluctuations in Graphene Based Integer and Fractional Chern Insulators

Authors: Zihao Huo, Wenxuan Wang, Jian Xie, Yves H. Kwan, Jonah Herzog-Arbeitman, Zaizhe Zhang, Qiu Yang, Min Wu, Kenji Watanabe, Takashi Taniguchi, Kaihui Liu, Nicolas Regnault, B. Andrei Bernevig, Xiaobo Lu

Abstract: Rhombohedral multilayer graphene has emerged as a powerful platform for investigating flat-band-driven correlated phenomena, yet most aspects remain not understood. In this work, we systematically study the moire-dependent band topology in rhombohedral hexalayer graphene. For the first time we demonstrate that the moire twist angle plays a crucial role in the formation of the moire Chern insulator… ▽ More Rhombohedral multilayer graphene has emerged as a powerful platform for investigating flat-band-driven correlated phenomena, yet most aspects remain not understood. In this work, we systematically study the moire-dependent band topology in rhombohedral hexalayer graphene. For the first time we demonstrate that the moire twist angle plays a crucial role in the formation of the moire Chern insulators in rhombohedral hexalayer graphene/hexagonal boron nitride (RHG/hBN) moire superlattices. In the moire-distant regime at filling factor v = 1, only systems with a twist angle θ < 1.1° exhibit an integer moire Chern insulator, while the fractional Chern insulator at v = 2/3 requires smaller twist angle to be stabilized. Our theoretical modelling, which includes quantum fluctuations and exact diagonalization results, suggests that mean-field theory, which has been widely adopted, does not explain the twist-angle dependence of the v = 1 phase diagram, and that correlation effects are crucial. Moreover, we realize two distinct stacking configurations ( /Xi=0 and /Xi=1) between graphene and hBN, and find that both cases can yield a Chern insulator at v = 1. Our experimental work upends the current mean-field paradigm, illuminates how quantum fluctuations and moiré effects shape the RHG/hBN phase diagram, and paves the way for future understanding and engineering of topological correlated states in rhombohedral graphene moire systems. △ Less

Submitted 17 October, 2025; originally announced October 2025.

Two-Dimensional Altermagnetism in Epitaxial CrSb Ultrathin Films

Authors: Keren Li, Yuzhong Hu, Yue Li, Ruohang Xu, Shaozhong Ma, Heping Li, Kun Liu, Chen Liu, Lu Cao, Jincheng Zhuang, Yee Sin Ang, Jiaou Wang, Haifeng Feng, Weichang Hao, Yi Du

Abstract: Altermagnets constitute an emerging class of collinear magnets that exhibit zero net magnetization yet host spin-split electronic bands arising from non-relativistic spin-space-group symmetries. Realization of altermagnetism in the two-dimensional (2D) limit remains an outstanding challenge because dimensional reduction suppresses kZ dispersion and destabilizes the symmetry operations essential fo… ▽ More Altermagnets constitute an emerging class of collinear magnets that exhibit zero net magnetization yet host spin-split electronic bands arising from non-relativistic spin-space-group symmetries. Realization of altermagnetism in the two-dimensional (2D) limit remains an outstanding challenge because dimensional reduction suppresses kZ dispersion and destabilizes the symmetry operations essential for spin compensation. Here, we investigate ultrathin CrSb films grown epitaxially on Bi2Te3 substrate and uncover the evolution of altermagnetism in the 2D limit. Scanning tunneling microscopy (STM), quasiparticle interference (QPI), angle-resolved photoemission spectroscopy (ARPES), and density functional theory (DFT) calculations show that interfacial symmetry breaking in the one-unit-cell (1 UC) limit gives rise to localized electronic states and uncompensated magnetic moments. These interfacial effects become weakened from 7/4 UC, accompanied by the recovery of a bulk-like coordination environment and the emergence of altermagnetic electronic characteristics. Our results show that the essential altermagnetic electronic structure of CrSb survives at a thickness of only ~1.05 nm, demonstrating the robustness of altermagnetism in the 2D limit and opening opportunities for integrating stray-field-free spin order into low dimensional spintronic architectures. △ Less

Submitted 3 July, 2026; v1 submitted 14 October, 2025; originally announced October 2025.

Comments: 18 pages, 4 figures

Projected Holstein-Primakoff boson representation of quantum spins for spin wave theory

Authors: Ke Liu, Fangyu Xiong, Fa Wang

Abstract: The Holstein-Primakoff boson representation of quantum spins and associated large-$S$ expansion have been the standard framework for describing the spin wave excitations in magnetically order phases of quantum spin systems. However, we will show that the omission of projection operators and normal-ordering in this representation can produce incorrect magnon hamiltonians for finite $S$. We will pre… ▽ More The Holstein-Primakoff boson representation of quantum spins and associated large-$S$ expansion have been the standard framework for describing the spin wave excitations in magnetically order phases of quantum spin systems. However, we will show that the omission of projection operators and normal-ordering in this representation can produce incorrect magnon hamiltonians for finite $S$. We will present the exact normal-ordered forms of the finite-$S$ projection operators and projected Holstein-Primakoff boson representations of spin and quadrupole operators, which can produce exact two-magnon interaction terms under ferromagnetic or fully polarized states. We will also discuss the difficulties of applying this projected representation to antiferromagnetic spin wave theory. △ Less

Submitted 22 March, 2026; v1 submitted 30 September, 2025; originally announced September 2025.

Comments: 13 pages, 2 figures, 1 table

Journal ref: Phys. Rev. B 113, 024413 (2026)

Superconductivity in cubic La3Al with interstitial anionic electrons

Authors: Zhijun Tu, Peihan Sun, Donghan Jia, Huiyang Gou, Kai Liu, Hechang Lei

Abstract: We report the observation of superconductivity in cubic La3Al single crystal. It shows a metallic behavior at a normal state without observable structural transition and enters the superconducting state below Tc ~ 6.32 K. Detailed characterizations and analysis indicate that cubic La3Al is a bulk type-II BCS superconductor. Moreover, theoretical calculations show that it can host interstitial anio… ▽ More We report the observation of superconductivity in cubic La3Al single crystal. It shows a metallic behavior at a normal state without observable structural transition and enters the superconducting state below Tc ~ 6.32 K. Detailed characterizations and analysis indicate that cubic La3Al is a bulk type-II BCS superconductor. Moreover, theoretical calculations show that it can host interstitial anionic electrons, which are located at the body center of cubic unit cell, and confirm the electron-phonon coupling as the superconducting mechamism. Thus, cubic La3Al can be regarded as an novel electride superconductor. △ Less

Submitted 26 September, 2025; originally announced September 2025.

Comments: 7 page, 4 figure, 1 table

Journal ref: Chin. Phys. Lett. 42, 027302 (2025)

How to Identify Suitable Gate Dielectrics for Transistors based on Two-Dimensional Semiconductors

Authors: Theresia Knobloch, Quentin Smets, Anton E. O. Persson, Pedram Khakbaz, Christoph Wilhelmer, Dennis Lin, Zherui Han, Yunyan Chung, Kevin P. OBrien, Chelsey Dorow, Cormac OCoileain, Mario Lanza, Dominic Waldhoer, Alexander Karl, Kailang Liu, Tianyou Zhai, Hailin Peng, Congwei Tan, Xiao Renshaw Wang, Georg S. Duesberg, John Robertson, Uygar Avci, Iuliana Radu, Eric Pop, Cesar J. Lockhart de la Rosa , et al. (1 additional authors not shown)

Abstract: The recent progress in nanosheet transistors has established two-dimensional (2D) semiconductors as viable candidates for future ultra-scaled electronic devices. Next to reducing contact resistance, identifying good gate dielectrics is a fundamental challenge, as the dielectric/channel interface dramatically impacts virtually all performance parameters. While several promising gate dielectrics hav… ▽ More The recent progress in nanosheet transistors has established two-dimensional (2D) semiconductors as viable candidates for future ultra-scaled electronic devices. Next to reducing contact resistance, identifying good gate dielectrics is a fundamental challenge, as the dielectric/channel interface dramatically impacts virtually all performance parameters. While several promising gate dielectrics have recently been reported, the evaluation of their quality and suitability is often fragmentary and focused on selected important performance metrics of the gate stack, such as the capacitive gate control, leakage currents, reliability, and ease of fabrication and integration. However, identifying a suitable gate stack is a complex problem that has not yet been approached systematically. In this perspective, we aim to formulate general criteria for good gate dielectrics. △ Less

Submitted 24 September, 2025; originally announced September 2025.

Comments: 21 pages, 4 figures, perspective article

Superconductivity in W3Re2C with chiral structure

Authors: Lei Yang, Jing Jiang, Hui-Hui He, Ying Ma, Kai Liu, Xiao Zhang, Hechang Lei

Abstract: We discover superconductivity in cubic W3Re2C with chiral structure and the superconducting transition temperature Tc is about 6.2 K. Detailed characterizations and analysis indicate that W3Re2C is a bulk type-II BCS superconductor with full isotropic gap. Moreover, first-principles calculations indicate that the electron-phonon coupling primarily arises from interactions between W/Re 5d electroni… ▽ More We discover superconductivity in cubic W3Re2C with chiral structure and the superconducting transition temperature Tc is about 6.2 K. Detailed characterizations and analysis indicate that W3Re2C is a bulk type-II BCS superconductor with full isotropic gap. Moreover, first-principles calculations indicate that the electron-phonon coupling primarily arises from interactions between W/Re 5d electronic states and their low-frequency phonons. Furthermore, the breaking of inversion symmetry in W3Re2C facilitates the emergence of Weyl points in the electronic structure. Therefore, W3Re2C can serve as a promising platform for investigating the influences of chiral structure on both superconductivity and band topology. △ Less

Submitted 21 January, 2026; v1 submitted 18 September, 2025; originally announced September 2025.

Comments: 23 pages, 5 figures

Journal ref: J. Am. Chem. Soc. 148, 2429-2436 (2026)

Dichotomy in Low- and High-energy Band Renormalizations in Trilayer Nickelate $La_{4}Ni_{3}O_{10}$: a Comparison with Cuprates

Authors: X. Du, Y. L. Wang, Y. D. Li, Y. T. Cao, M. X. Zhang, C. Y. Pei, J. M. Yang, W. X. Zhao, K. Y. Zhai, Z. K. Liu, Z. W. Li, J. K. Zhao, Z. T. Liu, D. W. Shen, Z. Li, Y. He, Y. L. Chen, Y. P. Qi, H. J. Guo, L. X. Yang

Abstract: Band renormalizations comprise crucial insights for understanding the intricate roles of electron-boson coupling and electron correlation in emergent phenomena such as superconductivity. In this study, by combining high-resolution angle-resolved photoemission spectroscopy and theoretical calculations, we systematically investigate the electronic structure of the trilayer nickelate superconductor… ▽ More Band renormalizations comprise crucial insights for understanding the intricate roles of electron-boson coupling and electron correlation in emergent phenomena such as superconductivity. In this study, by combining high-resolution angle-resolved photoemission spectroscopy and theoretical calculations, we systematically investigate the electronic structure of the trilayer nickelate superconductor $La_{4}Ni_{3}O_{10}$ at ambient pressure. We reveal a dichotomy in the electronic band renormalizations of $La_{4}Ni_{3}O_{10}$ in comparison to cuprate superconductors. At a high energy scale of hundreds of meV, its band structure is strongly renormalized by electron correlation effect enhanced by Hund coupling. The resultant waterfall-like dispersions resemble the high-energy kinks in cuprate superconductors. However, at low energy scales of tens of meV, the dispersive bands are nearly featureless and devoid of any resolvable electron-boson interactions, in drastic contrast to the low-energy kinks observed in cuprates and other correlated 3d transition-metal compounds. The dichotomic band renormalizations highlight the disparity between nickelate and cuprate superconductors and emphasize the importance of strong electron-correlation in the superconductivity of Ruddlesden-Popper phase nickelates. △ Less

Submitted 10 September, 2025; originally announced September 2025.

Comments: accepted by Physical Review Letters

Journal ref: Phys. Rev. Lett. 135, 146506 (2025)

Observation of tunable chiral spin textures with nonlinear optics

Authors: Youqiang Huang, Tiago V. C. Antao, Adolfo O. Fumega, Mikko Turunen, Yi Zhang, Hanlin Fang, Nianze Shang, Juan C. Arias-Munoz, Fedor Nigmatulin, Hao Hong, Andrew S. Kim, Faisal Ahmed, Hyunyong Choi, Sanshui Xiao, Kaihui Liu, Jose L. Lado, Zhipei Sun

Abstract: Chiral spin textures, such as spin spirals and skyrmions, are key to advancing spintronics by enabling ultrathin, energy-efficient memory, and high-density data storage and processing. However, their realization remains hindered by the scarcity of suitable host materials and the formidable experimental challenges associated with the characterization of these intricate chiral magnetic states. Here,… ▽ More Chiral spin textures, such as spin spirals and skyrmions, are key to advancing spintronics by enabling ultrathin, energy-efficient memory, and high-density data storage and processing. However, their realization remains hindered by the scarcity of suitable host materials and the formidable experimental challenges associated with the characterization of these intricate chiral magnetic states. Here, we report the observation of tunable chiral magnetic textures in van der Waals magnet CrPS$_4$ with nonlinear optics. These tunable textures exhibit strong chiral third-order nonlinear optical responses, driven by interlayer and intralayer spin couplings under varying magnetic fields and temperatures. These pronounced chiral nonlinear optical responses highlight the potency and high sensitivity of the nonlinear optical readout for probing non-collinear magnetic orders. Moreover, our findings position van der Waals magnets and their heterostructures as an exceptional platform for reconfigurable spin-photonics and spintronics, unifying optical, electrical, and magnetic properties through unique intralayer and interlayer spin coupling properties and effective spin interaction between photons and electrons. △ Less

Submitted 10 September, 2025; originally announced September 2025.

Model Accuracy and Data Heterogeneity Shape Uncertainty Quantification in Machine Learning Interatomic Potentials

Authors: Fei Shuang, Zixiong Wei, Kai Liu, Wei Gao, Poulumi Dey

Abstract: Machine learning interatomic potentials (MLIPs) enable accurate atomistic modelling, but reliable uncertainty quantification (UQ) remains elusive. In this study, we investigate two UQ strategies, ensemble learning and D-optimality, within the atomic cluster expansion framework. It is revealed that higher model accuracy strengthens the correlation between predicted uncertainties and actual errors a… ▽ More Machine learning interatomic potentials (MLIPs) enable accurate atomistic modelling, but reliable uncertainty quantification (UQ) remains elusive. In this study, we investigate two UQ strategies, ensemble learning and D-optimality, within the atomic cluster expansion framework. It is revealed that higher model accuracy strengthens the correlation between predicted uncertainties and actual errors and improves novelty detection, with D-optimality yielding more conservative estimates. Both methods deliver well calibrated uncertainties on homogeneous training sets, yet they underpredict errors and exhibit reduced novelty sensitivity on heterogeneous datasets. To address this limitation, we introduce clustering-enhanced local D-optimality, which partitions configuration space into clusters during training and applies D-optimality within each cluster. This approach substantially improves the detection of novel atomic environments in heterogeneous datasets. Our findings clarify the roles of model fidelity and data heterogeneity in UQ performance and provide a practical route to robust active learning and adaptive sampling strategies for MLIP development. △ Less

Submitted 5 August, 2025; originally announced August 2025.

Sliding two-dimensional superconductivity and charge-density-wave state in a bulk crystal

Authors: Xiangqi Liu, Chen Xu, Jing Jiang, Haonan Wang, Shaobo Liu, Gan Liu, Ziyi Zhu, Jian Yuan, Wei Xia, Lianbing Wen, Jiawei Luo, Yixuan Luo, Xia Wang, Na Yu, Peihong Cheng, Leiming Chen, Rui Zhou, Jun Li, Yulin Chen, Shiwei Wu, Ke Qu, Wei Li, Guangming Zhang, Chungang Duan, Jianhao Chen , et al. (4 additional authors not shown)

Abstract: Superconductivity in the two-dimensional (2D) limit is a fertile ground for exotic quantum phenomena-many of which remain elusive in their 3D counterparts. While studies of 2D superconductivity have predominantly focused on mono- or few-layer systems, we demonstrate an alternative route-interlayer sliding in bulk crystals. Through a precisely controlled growth strategy, we engineer interlayer slid… ▽ More Superconductivity in the two-dimensional (2D) limit is a fertile ground for exotic quantum phenomena-many of which remain elusive in their 3D counterparts. While studies of 2D superconductivity have predominantly focused on mono- or few-layer systems, we demonstrate an alternative route-interlayer sliding in bulk crystals. Through a precisely controlled growth strategy, we engineer interlayer sliding in bulk 3R-NbSe2, deliberately disrupting [001] mirror symmetry and drastically suppressing interlayer coupling. Remarkably, this structural manipulation stabilizes Ising-type superconductivity coexisting with an unconventional charge-density-wave (CDW) state akin to that of monolayer 2H-NbSe2. The sliding phase exhibits a pronounced suppression of the upper critical field at low temperatures, revealing a delicate competition between Ising and Rashba spin-orbit coupling (SOC) in the globally noncentrosymmetric lattice. Intriguingly, the superconducting state displays two-fold symmetry, a signature that may arise from asymmetric SOC or a multi-component pairing order parameter. Our work establishes interlayer sliding as a symmetry-breaking tool to promote 2D superconductivity in bulk materials-without resorting to extrinsic intercalation or doping. More broadly, this approach sets a paradigm for unlocking hidden quantum states in layered materials, offering a new dimension in design of quantum matter. △ Less

Submitted 2 August, 2025; originally announced August 2025.

Comments: Main Text 36 Pages + 3 figures; SI 38 pages + 30 figures + 8 tables

Heterogeneous Ensemble Enables a Universal Uncertainty Metric for Atomistic Foundation Models

Authors: Kai Liu, Zixiong Wei, Wei Gao, Poulumi Dey, Marcel H. F. Sluiter, Fei Shuang

Abstract: Universal machine learning interatomic potentials (uMLIPs) are reshaping atomistic simulation as foundation models, delivering near \textit{ab initio} accuracy at a fraction of the cost. Yet the lack of reliable, general uncertainty quantification limits their safe, wide-scale use. Here we introduce a unified, scalable uncertainty metric \(U\) based on a heterogeneous model ensemble with reuse of… ▽ More Universal machine learning interatomic potentials (uMLIPs) are reshaping atomistic simulation as foundation models, delivering near \textit{ab initio} accuracy at a fraction of the cost. Yet the lack of reliable, general uncertainty quantification limits their safe, wide-scale use. Here we introduce a unified, scalable uncertainty metric \(U\) based on a heterogeneous model ensemble with reuse of pretrained uMLIPs. Across chemically and structurally diverse datasets, \(U\) shows a strong correlation with the true prediction errors and provides a robust ranking of configuration-level risk. Leveraging this metric, we propose an uncertainty-aware model distillation framework to produce system-specific potentials: for W, an accuracy comparable to full-DFT training is achieved using only \(4\%\) of the DFT labels; for MoNbTaW, no additional DFT calculations are required. Notably, by filtering numerical label noise, the distilled models can, in some cases, surpass the accuracy of the DFT reference labels. The uncertainty-aware approach offers a practical monitor of uMLIP reliability in deployment, and guides data selection and fine-tuning strategies, thereby advancing the construction and safe use of foundation models and enabling cost-efficient development of accurate, system-specific potentials. △ Less

Submitted 28 July, 2025; originally announced July 2025.

Cascade of Even-Denominator Fractional Quantum Hall States in Mixed-Stacked Multilayer Graphene

Authors: Yating Sha, Kai Liu, Chenxin Jiang, Dan Ye, Shuhan Liu, Zhongxun Guo, Jingjing Gao, Ming Tian, Neng Wan, Kenji Watanabe, Takashi Taniguchi, Bingbing Tong, Guangtong Liu, Li Lu, Yuanbo Zhang, Zhiwen Shi, Zixiang Hu, Guorui Chen

Abstract: The fractional quantum Hall effect (FQHE), particularly at half-filling of Landau levels, provides a unique window into topological phases hosting non-Abelian excitations. However, experimental platforms simultaneously offering large energy gaps, delicate tunability, and robust non-Abelian signatures remain scarce. Here, we report the observation of a cascade of even-denominator FQH states at fill… ▽ More The fractional quantum Hall effect (FQHE), particularly at half-filling of Landau levels, provides a unique window into topological phases hosting non-Abelian excitations. However, experimental platforms simultaneously offering large energy gaps, delicate tunability, and robust non-Abelian signatures remain scarce. Here, we report the observation of a cascade of even-denominator FQH states at filling factors $ν$ = ${-5/2}$, ${-7/2}$, ${-9/2}$, ${-11/2}$, and ${-13/2}$, alongside numerous odd-denominator states in mixed-stacked pentalayer graphene, a previously unexplored system characterized by intertwined quadratic and cubic band dispersions. These even-denominator states, representing the highest filling half-filled states reported so far in the zeroth Landau level (ZLL), emerge from two distinct intra-ZLL and exhibit unprecedented displacement field tunability driven by LL crossings in the hybridized multiband structure. At half fillings, continuous quasiparticle phase transitions between paired FQH states, magnetic Bloch states, and composite Fermi liquids are clearly identified upon tuning external fields. Numerical calculations, revealing characteristic sixfold ground-state degeneracy and chiral graviton spectral analysis, suggest the observed even-denominator FQH states belong to the non-Abelian Moore-Read type. These results establish mixed-stacked multilayer graphene as a rich and versatile crystalline platform for exploring tunable correlated topological phases. △ Less

Submitted 28 July, 2025; originally announced July 2025.

On zeros and algorithms for disordered systems: mean-field spin glasses

Authors: Ferenc Bencs, Brice Huang, Daniel Z. Lee, Kuikui Liu, Guus Regts

Abstract: Spin glasses are fundamental probability distributions at the core of statistical physics, the theory of average-case computational complexity, and modern high-dimensional statistical inference. In the mean-field setting, we design deterministic quasipolynomial-time algorithms for estimating the partition function to arbitrarily high accuracy for all inverse temperatures in the second moment regim… ▽ More Spin glasses are fundamental probability distributions at the core of statistical physics, the theory of average-case computational complexity, and modern high-dimensional statistical inference. In the mean-field setting, we design deterministic quasipolynomial-time algorithms for estimating the partition function to arbitrarily high accuracy for all inverse temperatures in the second moment regime. In particular, for the Sherrington--Kirkpatrick model, our algorithms succeed for the entire replica-symmetric phase. To achieve this, we study the locations of the zeros of the partition function. Notably, our methods are conceptually simple, and apply equally well to the spherical case and the case of Ising spins. △ Less

Submitted 6 November, 2025; v1 submitted 21 July, 2025; originally announced July 2025.

Comments: Compared to the previous version, we establish an improved zero-free result for the second moment regime

Anomalous charge density wave in altermagnetism

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

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

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

Comments: 6 pages, 4 figures

Programmable Quantum Anomalous Hall Insulator in Twisted Crystalline Flatbands

Authors: Wenxuan Wang, Yijie Wang, Zaizhe Zhang, Zihao Huo, Gengdong Zhou, Kenji Watanabe, Takashi Taniguchi, X. C. Xie, Kaihui Liu, Zhida Song, Xiaobo Lu

Abstract: The isospin flavors in condensed matters can be continuously broken, forming various symmetry-broken quantum states. In moiré crystals, the competition between different isospin configurations can be effectively tuned by the twist angles and staciking orders. Here we report twisted double rhombohedral-trilayer-gaphene as a new twisted crystalline flatbands system showing rich moiré dependent topol… ▽ More The isospin flavors in condensed matters can be continuously broken, forming various symmetry-broken quantum states. In moiré crystals, the competition between different isospin configurations can be effectively tuned by the twist angles and staciking orders. Here we report twisted double rhombohedral-trilayer-gaphene as a new twisted crystalline flatbands system showing rich moiré dependent topological phenomena. In devices with small twist angles, programmable Chern insulators with Chern number C = 3 at integer moiré filling v = 1 have been observed. We have further revealed an exotic hidden order which can quench the Chern insulator as well as multiple first-order transitions between different symmetry-broken phases. Interestly, in the device with a slightly larger twist angle, multiple Chern insulators with C = 1 at fractional moiré fillings including v = 1/4, 1/3 and 1/2 have been observed, whereas the Chern insulator at v = 1 is abscent. Our study demonstrated the twisted flatbands form rhombohedral-multilayer-graphene as a new platform to study tunable high Chern insulators as well as new devices for quantum storage and computation. △ Less

Submitted 6 January, 2026; v1 submitted 14 July, 2025; originally announced July 2025.

Origin of insulating-like behavior of Bi$_2$Sr$_2$CaCu$_2$O$_{8+x}$ under pressure: A first-principles study

Authors: Xin Du, Jian-Feng Zhang, Zhong-Yi Lu, Kai Liu

Abstract: Recent experimental study on Bi$_2$Sr$_2$CaCu$_2$O$_{8+x}$ superconductors has revealed an unexpected quantum phase transition from superconducting state to insulatinglike state under pressure [Zhou et al., Nat. Phys. 18, 406 (2022)]. To better understand the physical origin of this pressure-induced phenomenon, here we have studied the structural, electronic, and magnetic properties of undoped and… ▽ More Recent experimental study on Bi$_2$Sr$_2$CaCu$_2$O$_{8+x}$ superconductors has revealed an unexpected quantum phase transition from superconducting state to insulatinglike state under pressure [Zhou et al., Nat. Phys. 18, 406 (2022)]. To better understand the physical origin of this pressure-induced phenomenon, here we have studied the structural, electronic, and magnetic properties of undoped and O-doped Bi$_2$Sr$_2$CaCu$_2$O$_{8+x}$ (Bi2212) under pressures based on density-functional theory calculations. We first identified the crystal structure of undoped Bi2212 with the armchair distortions in the BiO layers and reproduced the insulating feature of the parent compound. Then we added an extra O atom to the parent compound to simulate the hole-doping effect and found that the structure with O dopant located in the van der Waals (vdW) gap is energetically the most stable. Further calculations on O-doped (0.125 holes/Cu) Bi2212 revealed that the pressure can induce charge redistributions between CuO$_2$ planes and BiO layers; specifically, Cu-$d_{x^2-y^2}$ orbitals gain electrons and Cu atoms rather than O atoms dominate around the Fermi level under high pressure. Along with the increasing pressure, the density of states at the Fermi level first reaches the maximum at $\sim$ 10 GPa and then shows a valley near the Fermi level above 20 GPa, which may be responsible for the insulatinglike state observed in recent experiments. We suggest that the competition among several factors, such as the increase of electrons in the CuO$_2$ plane, the variation of in-plane hopping due to the shortened Cu-O distance, and the enhanced Coulomb repulsion among the Cu-3$d$ electrons, could lead to the exotic transition under pressure. Our work provides an explanation of the high-pressure behaviors of Bi2212, which may facilitate a comprehensive understanding of cuprate superconductors. △ Less

Submitted 9 July, 2025; originally announced July 2025.

Comments: 9 pages, 7 figures, 1 table

Journal ref: Phys. Rev. B 112, 045113 (2025)

Full-Gap Superconductivity in BaAs/Ferropnictide Heterostructures

Authors: Ming-Qiang Ren, Qiang-Jun Cheng, Hui-Hui He, Ze-Xian Deng, Fang-Jun Cheng, Yong-Wei Wang, Cong-Cong Lou, Qinghua Zhang, Lin Gu, Kai Liu, Xu-Cun Ma, Qi-Kun Xue, Can-Li Song

Abstract: Interfacial interactions often promote the emergence of unusual phenomena in two-dimensional systems, including high-temperature superconductivity. Here, we report the observation of full-gap superconductivity with a maximal spectroscopic temperature up to 26 K in a BaAs monolayer grown on ferropnictide Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ (abbreviated as BFCA) epitaxial films. The superconducting gap r… ▽ More Interfacial interactions often promote the emergence of unusual phenomena in two-dimensional systems, including high-temperature superconductivity. Here, we report the observation of full-gap superconductivity with a maximal spectroscopic temperature up to 26 K in a BaAs monolayer grown on ferropnictide Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ (abbreviated as BFCA) epitaxial films. The superconducting gap remains robust even when the thickness of underlying BFCA is reduced to the monolayer limit, in contrast to the rapid suppression of $T_\textrm{c}$ in standalone BFCA thin films. We reveal that the exceptional crystallinity of the BaAs/BFCA heterostructures, featured by their remarkable electronic and geometric uniformities, is crucial for the emergent full-gap superconductivity with mean-field temperature dependence and pronounced bound states within magnetic vortices. Our findings open up new avenues to unravel the mysteries of unconventional superconductivity in ferropnictides and advance the development of FeAs-based heterostructures. △ Less

Submitted 19 June, 2025; originally announced June 2025.

Comments: 6 pages, 4 figures

Journal ref: Phys. Rev. Lett. 134, 246203 (2025)