Showing 1–50 of 499 results for author: Guo, Y

Dynamical Spectral Function of the Kagome Quantum Spin Liquid

Authors: Jiahang Hu, Runze Chi, Yibin Guo, B. Normand, Hai-Jun Liao, T. Xiang

Abstract: Quantum spin liquids (QSLs) host exotic fractionalized magnetic and gauge-field excitations whose microscopic origins and experimental verification remain frustratingly elusive. In the absence of static magnetic order, the spin excitation spectrum constitutes the crucial probe of QSL behavior, but its theoretical computation remains a serious challenge. Here we employ state-of-the-art tensor-netwo… ▽ More Quantum spin liquids (QSLs) host exotic fractionalized magnetic and gauge-field excitations whose microscopic origins and experimental verification remain frustratingly elusive. In the absence of static magnetic order, the spin excitation spectrum constitutes the crucial probe of QSL behavior, but its theoretical computation remains a serious challenge. Here we employ state-of-the-art tensor-network methods to obtain the full dynamical spectral function of the $J_1$-$J_2$ kagome Heisenberg model and benchmark our results by tracking their evolution across the magnetically ordered and QSL phases. Reducing $|J_2|/J_1$ causes increasingly strong spin-wave renormalization, flattening these modes then merging them into a continuum characteristic of deconfined spinons at all finite energies in the QSL. The low-energy continuum and the occurrence of gap closure at multiple high-symmetry points identify this gapless QSL as the U(1) Dirac spin liquid. These results establish a unified understanding of spin excitations in highly frustrated quantum magnets and provide clear spectral fingerprints for experimental detection in candidate kagome QSL materials. △ Less

Submitted 21 December, 2025; originally announced December 2025.

Comments: 16 pages, 13 figures

Lattice-decoupled rotatable stripe-like charge order within the strange metal phase of 2M-WS2

Authors: Kebin Xiao, Yunkai Guo, Daran Fu, Yuqiang Fang, Yating Hu, Jingming Yan, Yucong Peng, Yuyang Wang, Yongkang Ju, Peizhe Tang, Xiangang Wan, Fuqiang Huang, Qi-Kun Xue, Wei Li

Abstract: In quantum materials, charge orders typically stabilize in specific crystallographic orientations, though their formation mechanisms may vary. Here, using low-temperature scanning tunneling microscopy (STM), we discover a lattice-decoupled rotatable stripe-like charge order coexisting with superconductivity in 2M-WS2. The charge order manifests five distinct orientations across different sample re… ▽ More In quantum materials, charge orders typically stabilize in specific crystallographic orientations, though their formation mechanisms may vary. Here, using low-temperature scanning tunneling microscopy (STM), we discover a lattice-decoupled rotatable stripe-like charge order coexisting with superconductivity in 2M-WS2. The charge order manifests five distinct orientations across different sample regions, yet maintains an identical wavelength. This directional decoupling from host lattice challenges existing paradigms. First-principles calculations of phonon spectra and nesting function fail to explain the ordering mechanism. Intriguingly, the transition temperature of the charge orders exhibits spatial variations (21-46 K), coinciding with the temperature range of the recently reported strange metal phase in this material. This correlation suggests that the interplay between strong electronic correlations and electron-phonon coupling must be critically evaluated to elucidate the emergence of this unconventional charge order. △ Less

Submitted 20 December, 2025; originally announced December 2025.

Comments: 12 pages, 5 figures. This article was published on PNAS (https://doi.org/10.1073/pnas.2513493122)

Topological cluster synchronization via Dirac spectral programming on directed hypergraphs

Authors: Yupeng Guo, Ahmed A. A. Zaid, Xueming Liu, Ginestra Bianconi

Abstract: Collective synchronization in complex systems arises from the interplay between topology and dynamics, yet how to design and control such patterns in higher-order networks remains unclear. Here we show that a Dirac spectral programming framework enables programmable topological cluster synchronization on directed hypergraphs. By encoding tail-head hyperedges into a topological Dirac operator and i… ▽ More Collective synchronization in complex systems arises from the interplay between topology and dynamics, yet how to design and control such patterns in higher-order networks remains unclear. Here we show that a Dirac spectral programming framework enables programmable topological cluster synchronization on directed hypergraphs. By encoding tail-head hyperedges into a topological Dirac operator and introducing a tunable mass term, we obtain a spectrum whose isolated eigenvalues correspond to distinct synchronization clusters defined jointly on nodes and hyperedges. Selecting a target eigenvalue allows the system to self-organize toward the associated cluster state without modifying the underlying hypergraph structure. Simulations on directed-hypergraph block models and empirical systems--including higher-order contact networks and the ABIDE functional brain network--confirm that spectral selection alone determines the accessible synchronization patterns. Our results establish a general and interpretable route for controlling collective dynamics in directed higher-order systems. △ Less

Submitted 9 December, 2025; originally announced December 2025.

Isotropic Dirac fermion and anomalous oscillator strength of zeroth Landau level transition

Authors: Zeping Shi, Wenbin Wu, Guangyi Wang, Mykhaylo Ozerov, Jian Yuan, Wei Xia, Yuhan Du, Xianghao Meng, Xiangyu Jiang, Mingsen Zhou, Yuxi Chen, Hao Shen, Yanfeng Guo, Junhao Chu, Xiang Yuan

Abstract: Dirac fermions, characterized by their linear dispersion and relativistic nature, have emerged as a prominent class of quasiparticles in condensed matter physics. While the Dirac equation, initially developed in the context of high-energy physics, provides a remarkable framework for describing the electronic properties of these materials, the inherent symmetry constraints of condensed matter often… ▽ More Dirac fermions, characterized by their linear dispersion and relativistic nature, have emerged as a prominent class of quasiparticles in condensed matter physics. While the Dirac equation, initially developed in the context of high-energy physics, provides a remarkable framework for describing the electronic properties of these materials, the inherent symmetry constraints of condensed matter often lead to deviations from the idealized paradigm. In particular, three-dimensional Dirac fermions in solids often exhibit anisotropic behavior, challenging the notion of perfect symmetry inherent in the Dirac equation. Here, we report the observation of isotropic massive Dirac fermions in LaAlSi through Landau level spectroscopy. The presence of three-dimensional massive Dirac fermions across the Fermi energy is demonstrated by quantized and semiclassical analyses of the magnetic field evolution of Landau level transitions. The isotropic topological nature, Fermi velocity, and Dirac mass are evidenced by the identical magneto-infrared response among the Faraday and three Voigt geometries. Furthermore, we observe an unusually large oscillator strength in the zeroth Landau level transition of the Dirac fermion, compared to transitions with higher indices. This phenomenon, supported by model calculations, can be attributed to the combined effects of the partial excitation of Dirac fermion and the resonant dielectric coupling with the Weyl plasma. Our work provides a strategy for realizing ideal quasiparticle excitations and their coupling effects in condensed matter systems, offering a platform for exploring relativistic physics. △ Less

Submitted 16 December, 2025; originally announced December 2025.

Journal ref: Communications Physics, 8, 376. (2025) Communications Physics, 8, 376. (2025) Communications Physics, 8, 376. (2025) Communications Physics, 8, 376. (2025)

Gate tuning of coupled electronic and structural phase transition in atomically thin Ta$_2$NiSe$_5$

Authors: Keyu Wei, Yixuan Luo, Kenji Watanabe, Takashi Taniguchi, Yanfeng Guo, Xiaoxiang Xi

Abstract: Realizing an excitonic insulator phase from narrow-gap semiconductors remains challenging, as unambiguous experimental signatures are difficult to establish. Ta$_2$NiSe$_5$ has been widely regarded as a leading candidate, yet the nature of its phase transition and insulating state remains controversial. Here, we report a systematic Raman spectroscopy study of Ta$_2$NiSe$_5$ as a function of thickn… ▽ More Realizing an excitonic insulator phase from narrow-gap semiconductors remains challenging, as unambiguous experimental signatures are difficult to establish. Ta$_2$NiSe$_5$ has been widely regarded as a leading candidate, yet the nature of its phase transition and insulating state remains controversial. Here, we report a systematic Raman spectroscopy study of Ta$_2$NiSe$_5$ as a function of thickness and field-effect doping, complemented by electrical transport measurements. The phase transition persists down to the monolayer limit, with the critical temperature increasing as thickness decreases. In bilayer samples, both electron and hole doping suppress the insulating state, with electron doping lowering and hole doping raising the transition temperature. Importantly, the quasi-elastic scattering, previously attributed to excitonic fluctuations, evolves monotonically across the entire doping range, inconsistent with the expected suppression of excitonic correlations by Coulomb screening. These findings rule out a dominant excitonic mechanism and instead point to a coupled electronic and structural phase transition, whose stability is tunable by carrier doping. Our doping-based approach offers a general strategy for evaluating the role of excitonic effects in candidate excitonic insulators. △ Less

Submitted 10 December, 2025; originally announced December 2025.

Journal ref: Nature Communications 16, 10999 (2025)

Angle evolution of the superconducting phase diagram in twisted bilayer WSe2

Authors: Yinjie Guo, John Cenker, Ammon Fischer, Daniel Muñoz-Segovia, Jordan Pack, Luke Holtzman, Lennart Klebl, Kenji Watanabe, Takashi Taniguchi, Katayun Barmak, James Hone, Angel Rubio, Dante M. Kennes, Andrew J. Millis, Abhay Pasupathy, Cory R. Dean

Abstract: Recent observations of superconductivity in twisted bilayer WSe$_2$ have extended the family of moiré superconductors beyond twisted graphene. In WSe$_2$ two different twist angles were studied, 3.65° and 5.0°, and two seemingly distinct superconducting phase diagrams were reported, raising the question of whether the superconducting phases in the two devices share a similar origin. Here we addres… ▽ More Recent observations of superconductivity in twisted bilayer WSe$_2$ have extended the family of moiré superconductors beyond twisted graphene. In WSe$_2$ two different twist angles were studied, 3.65° and 5.0°, and two seemingly distinct superconducting phase diagrams were reported, raising the question of whether the superconducting phases in the two devices share a similar origin. Here we address the question by experimentally mapping the evolution of the phase diagram across devices with twist angles spanning the range defined by the initial reports, and comparing the results to twist angle-dependent theory. We find that the superconducting state evolves smoothly with twist angle and at all twist angles is proximal to a Fermi surface reconstruction with, presumably, antiferromagnetic ordering, but is neither necessarily tied to the Van Hove singularity, nor to the half band insulator. Our results connect the previously distinct phase diagrams at 3.65° and 5°, and offer new insight into the origin of the superconductivity in this system and its evolution as the correlation strength increases. More broadly, the smooth phase diagram evolution, repeatability between different devices, and dynamic gate tunability within each device, establish twisted transition metal dichalcogenides as a unique platform for the study of correlated phases as the ratio of interaction strength to bandwidth is varied. △ Less

Submitted 5 December, 2025; originally announced December 2025.

Flat band surface state superconductivity in thick rhombohedral graphene

Authors: Yi Guo, Owen I. Sheekey, Trevor Arp, Kryštof Kolář, Thibault Charpentier, Ludwig Holleis, Ben Foutty, Aidan Keough, Maya Kang-Chou, Martin E. Huber, Takashi Taniguchi, Kenji Watanabe, Cyprian Lewandowski, Andrea F. Young

Abstract: Rhombohedral multilayer graphene has recently emerged as a rich platform for studying correlation driven magnetic, topological and superconducting states. While most experimental efforts have focused on devices with N$\leq 9$ layers, the electronic structure of thick rhombohedral graphene features flat-band surface states even in the infinite layer limit. Here, we use layer resolved capacitance me… ▽ More Rhombohedral multilayer graphene has recently emerged as a rich platform for studying correlation driven magnetic, topological and superconducting states. While most experimental efforts have focused on devices with N$\leq 9$ layers, the electronic structure of thick rhombohedral graphene features flat-band surface states even in the infinite layer limit. Here, we use layer resolved capacitance measurements to directly detect these surface states for $N\approx 13$ layer rhombohedral graphene devices. Using electronic transport and local magnetometry, we find that the surface states host a variety of ferromagnetic phases, including both valley imbalanced quarter metals and broad regimes of density in which the system spontaneously spin polarizes. We observe several superconducting states localized to a single surface state. These superconductors appear on the unpolarized side of the density-tuned spin transitions, and show strong violations of the Pauli limit consistent with a dominant attractive interaction in the spin-triplet, valley-singlet pairing channel. In contrast to previous studies of rhombohedral multilayers, however, we find that superconductivity can persist to zero displacement field where the system is inversion symmetric. Energetic considerations suggest that superconductivity in this regime is described by the existence of two independent surface superconductors coupled via tunneling through the insulating single crystal graphite bulk. △ Less

Submitted 21 November, 2025; originally announced November 2025.

Mass-imbalance effect on the cluster formation in a one-dimensional Fermi gas with coexistent $s$- and $p$-wave interactions

Authors: Yixin Guo

Abstract: We consider the mass-imbalance effect on the clustering in a one-dimensional two-component Fermi gas with coexistent even- and odd-wave interactions resulting in different configurations of clustering phases. We obtain the solutions of both stable two- and three-body cluster states with different mass ratios and configurations by solving the corresponding variational equations. We feature out phas… ▽ More We consider the mass-imbalance effect on the clustering in a one-dimensional two-component Fermi gas with coexistent even- and odd-wave interactions resulting in different configurations of clustering phases. We obtain the solutions of both stable two- and three-body cluster states with different mass ratios and configurations by solving the corresponding variational equations. We feature out phase diagrams consisting of the $s$- and $p$-wave pairing phases, and tripling phase with different configurations, in a plane of $s$- and $p$-wave pairing strengths. As for the in-vacuum case, the three-body clustering is always the lowest-lying phase. While for the in-medium case, the Cooper tripling phase dominates over the pairing phases when both $s$- and $p$-wave interactions are moderately strong. There is also a competition between different clustering configurations of three-body clustering. △ Less

Submitted 18 November, 2025; originally announced November 2025.

Comments: 8 pages, 6 figures

Swarming Lattice in Frustrated Vicsek-Kuramoto Systems

Authors: Yichen Lu, Yingshan Guo, Yiyi Zhang, Tong Zhu, Zhigang Zheng

Abstract: We introduce a frustration parameter $α$ into the Vicsek-Kuramoto systems of self-propelled particles. While the system exhibits conventional synchronized states, such as global phase synchronization and swarming, for low frustration ($α< π/2$), beyond the critical point $α= π/2$, a Hopf-Turing bifurcation drives a transition to a resting hexagonal lattice, accompanied by spatiotemporal patterns s… ▽ More We introduce a frustration parameter $α$ into the Vicsek-Kuramoto systems of self-propelled particles. While the system exhibits conventional synchronized states, such as global phase synchronization and swarming, for low frustration ($α< π/2$), beyond the critical point $α= π/2$, a Hopf-Turing bifurcation drives a transition to a resting hexagonal lattice, accompanied by spatiotemporal patterns such as vortex lattices and dual-cluster lattices with oscillatory unit-cell motions. Lattice dominance is governed by coupling strength and interaction radius, with a clear parametric boundary balancing pattern periodicity and particle dynamics. Our results demonstrate that purely orientational interactions are sufficient to form symmetric lattices, challenging the necessity of spatial forces and illuminating the mechanisms driving lattice formation in active matter systems. △ Less

Submitted 21 December, 2025; v1 submitted 11 November, 2025; originally announced November 2025.

Field-Tunable Anisotropic Fulde-Ferrell Phase in NbSe$_2$/CrSiTe$_3$ Heterostructures

Authors: Jiadian He, Xin-Zhi Li, Chen Xu, Yifan Ding, Yueshen Wu, Jinghui Wang, Peng Dong, Yan-Fang Li, Wei Li, Xiang Zhou, Yanfeng Guo, Yulin Chen, Wen-Yu He, Jun Li

Abstract: The emergence of superconductivity in two-dimensional transition metal dichalcogenides with strong spin orbit coupling (SOC) has opened new avenues for exploring exotic superconducting states. Here, we report experimental observation of an anisotropic Fulde-Ferrell (FF) phase in few-layer NbSe$_2$/CrSiTe$_3$ heterostructures under in-plane magnetic fields. Through combined magnetoresistance and no… ▽ More The emergence of superconductivity in two-dimensional transition metal dichalcogenides with strong spin orbit coupling (SOC) has opened new avenues for exploring exotic superconducting states. Here, we report experimental observation of an anisotropic Fulde-Ferrell (FF) phase in few-layer NbSe$_2$/CrSiTe$_3$ heterostructures under in-plane magnetic fields. Through combined magnetoresistance and nonreciprocal transport measurements, we find that due to the couplings from the ferromagnetic CrSiTe$_3$, a half-dome-shaped region emerges in the magnetic field-temperature ($B$-$T$) diagram. Importantly, the half-dome-shaped region exhibits finite second harmonic resistance with in-plane anisotropy, indicating that the superconducting state is an anisotropic FF phase. Through a symmetry analysis combined with mean field calculations, we attribute the emergent anisotropic FF phase to the CrSiTe$_3$ layer induced Rashba SOC and three-fold rotational symmetry breaking. These results demonstrate that heterostructure stacking is a powerful tool for symmetry engineering in superconductors, which can advance the design of quantum devices in atomically thin superconducting materials. △ Less

Submitted 2 November, 2025; originally announced November 2025.

Comments: 19 pages, 5 figures

Preliminary Demonstration of Diamond-GaN pn Diodes via Grafting

Authors: Jie Zhou, Yi Lu, Chenyu Wang, Luke Suter, Aaron Hardy, Tien Khee Ng, Kai Sun, Yifu Guo, Yang Liu, Tsung-Han Tsai, Xuanyu Zhou, Connor S Bailey, Michael Eller, Stephanie Liu, Zetian Mi, Boon S. Ooi, Matthias Muehle, Katherine Fountaine, Vincent Gambin, Jung-Hun Seo, Zhenqiang Ma

Abstract: Ultrawide bandgap (UWBG) semiconductors exhibit exceptional electrical and thermal properties, offering strong potential for high power and high frequency electronics. However, efficient doping in UWBG materials is typically limited to either n type or p type, constraining their application to unipolar devices. The realization of pn junctions through heterogeneous integration of complementary UWBG… ▽ More Ultrawide bandgap (UWBG) semiconductors exhibit exceptional electrical and thermal properties, offering strong potential for high power and high frequency electronics. However, efficient doping in UWBG materials is typically limited to either n type or p type, constraining their application to unipolar devices. The realization of pn junctions through heterogeneous integration of complementary UWBG or WBG semiconductors is hindered by lattice mismatch and thermal expansion differences. Here, we report the preliminary demonstration of diamond GaN heterojunction pn diodes fabricated via grafting. A single crystalline p plus diamond nanomembrane was integrated onto an epitaxially grown c plane n plus GaN substrate with an ultrathin ALD Al2O3 interlayer. The resulting diodes exhibit an ideality factor of 1.55 and a rectification ratio of over 1e4. Structural and interfacial properties were examined by AFM, XRD, Raman, and STEM, providing critical insights to guide further optimization of diamond GaN pn heterojunction devices. △ Less

Submitted 28 October, 2025; originally announced October 2025.

Comments: 21 pages, 3 figures

Ultrafast Charge-Doping via Photo-Thermionic Injection in van der Waals Devices

Authors: Yiliu Li, Esteban Rojas-Gatjens, Yinjie Guo, Birui Yang, Dihao Sun, Luke Holtzman, Juseung Oh, Katayun Barmak, Cory R. Dean, James C. Hone, Nathaniel Gabor, Eric A. Arsenault, Xiaoyang Zhu

Abstract: Van der Waals (vdW) heterostructures of two-dimensional (2D) materials have become a rich playground for the exploration of correlated quantum phases, and recent studies have begun to probe their non-equilibrium dynamics under femtosecond laser excitation. In a time-resolved experiment, optical excitation of the multilayer structure can lead not only to rich dynamic responses from the target layer… ▽ More Van der Waals (vdW) heterostructures of two-dimensional (2D) materials have become a rich playground for the exploration of correlated quantum phases, and recent studies have begun to probe their non-equilibrium dynamics under femtosecond laser excitation. In a time-resolved experiment, optical excitation of the multilayer structure can lead not only to rich dynamic responses from the target layers, such as moiré interfaces, but also to additional device functionality from the layer degree of freedom. Here, we investigate optical excitation in a prototypical moiré device of dual-gated twisted WSe2 bilayers, with few-layer graphite gates and hexagonal boron nitride (hBN) spacers. We establish an ultrafast photodoping mechanism in the moiré bilayer from photo-thermionic emission of the graphite gates. Using transient reflectance experiments, we reveal photo-induced hole injection evidenced by: (i) a shift of gate voltages at which optical signatures of correlated insulators are observed, (ii) a persistent optical signature indicative of charge diffusion at microsecond timescales and local charge buildup from pulse-to-pulse accumulation, and (iii) photoinduced absorption due likely to transient formation of correlated insulators. We further demonstrate that the injected holes can be selectively controlled by tuning the excitation energy, fluence, and gate bias. △ Less

Submitted 23 October, 2025; originally announced October 2025.

Comments: 16 pages, 4 figures, SI

Photoinduced Metal-to-Insulator Transitions in 2D Moiré Devices

Authors: Yiliu Li, Esteban Rojas-Gatjens, Yinjie Guo, Birui Yang, Dihao Sun, Luke Holtzman, Juseung Oh, Katayun Barmak, Cory R. Dean, James C. Hone, Nathaniel Gabor, Eric A. Arsenault, Xiaoyang Zhu

Abstract: Photoexcitation has been utilized to control quantum matter and to uncover metastable phases far from equilibrium. Among demonstrations to date, the most common is the photo-induced transition from correlated insulators to metallic states; however, the reverse process without initial orders has not been observed. Here, we show ultrafast metal-to-insulator transition in gate-doped WS2/WSe2 and WSe2… ▽ More Photoexcitation has been utilized to control quantum matter and to uncover metastable phases far from equilibrium. Among demonstrations to date, the most common is the photo-induced transition from correlated insulators to metallic states; however, the reverse process without initial orders has not been observed. Here, we show ultrafast metal-to-insulator transition in gate-doped WS2/WSe2 and WSe2/WSe2 moiré devices using photo-thermionic hole injection from graphite gates. The resulting correlated insulators are metastable, with lifetimes exceeding microseconds. These findings establish an effective mechanism for the ultrafast control of correlated electronic phases in van der Waals heterostructures. △ Less

Submitted 23 October, 2025; originally announced October 2025.

Comments: 13 pages, 4 figures, SI

Loss investigations of high frequency lithium niobate Lamb wave resonators at ultralow temperatures

Authors: Wenbing Jiang, Xuankai Xu, Jiazhen Pan, Hancong Sun, Yu Guo, Huabing Wang, Libing Zhou, Tao Wu

Abstract: Lamb wave resonators (LWRs) operating at ultralow temperatures serve as promising acoustic platforms for implementing microwave-optical transduction and radio frequency (RF) front-ends in aerospace communications because of the exceptional electromechanical coupling (k^2) and frequency scalability. However, the properties of LWRs at cryogenic temperatures have not been well understood yet. Herein,… ▽ More Lamb wave resonators (LWRs) operating at ultralow temperatures serve as promising acoustic platforms for implementing microwave-optical transduction and radio frequency (RF) front-ends in aerospace communications because of the exceptional electromechanical coupling (k^2) and frequency scalability. However, the properties of LWRs at cryogenic temperatures have not been well understood yet. Herein, we experimentally investigate the temperature dependence of the quality factor and resonant frequency in higher order antisymmetric LWRs down to millikelvin temperatures. The high-frequency A1 and A3 mode resonators with spurious-free responses are comprehensively designed, fabricated, and characterized. The quality factors of A1 modes gradually increase upon cryogenic cooling and shows 4 times higher than the room temperature value, while A3 mode resonators exhibit a non-monotonic temperature dependence. Our findings provide new insights into loss mechanisms of cryogenic LWRs, paving the way to strong-coupling quantum acoustodynamics and next-generation satellite wireless communications. △ Less

Submitted 12 October, 2025; originally announced October 2025.

Comments: Accepted for publication in Applied Physics Letters

Preparation of initial states with open and periodic boundary conditions on quantum devices using matrix product states

Authors: Yibin Guo, Manuel Schneider, Takis Angelides, Karl Jansen, C. -J. David Lin, Yao Ting Su

Abstract: We present a framework for preparing quantum states from matrix product states (MPS) with open and periodic boundary conditions on quantum devices. The MPS tensors are mapped to unitary gates, which are subsequently decomposed into native gates on quantum hardware. States with periodic boundary conditions (pbc) can be represented efficiently as quantum circuits using ancilla qubits and post-select… ▽ More We present a framework for preparing quantum states from matrix product states (MPS) with open and periodic boundary conditions on quantum devices. The MPS tensors are mapped to unitary gates, which are subsequently decomposed into native gates on quantum hardware. States with periodic boundary conditions (pbc) can be represented efficiently as quantum circuits using ancilla qubits and post-selection after measurement. We derive an exact expression for the success rate of this probabilistic approach, which can be evaluated a priori. The applicability of the method is demonstrated in two examples. First, we prepare the ground state of the Heisenberg model with pbc and simulate dynamics under a quenched Hamiltonian. The volume-law entanglement growth in the time evolution challenges classical algorithms but can potentially be overcome on quantum hardware. Second, we construct quantum circuits that generate excited states of the Schwinger model with high fidelities. Our approach provides a scalable method for preparing states on a quantum device, enabling efficient simulations of strongly correlated systems on near-term quantum computers. △ Less

Submitted 8 October, 2025; originally announced October 2025.

Comments: 19 pages, 15 figures, comments are welcome!

Ground state magnetic structure of Mn3Sn

Authors: Jeppe Jon Cederholm, Zhian Xu, Yanfeng Guo, Martin Ovesen, Thomas Olsen, Kristine M. L. Krighaar, Chrystalla Knekna, Jian Rui Soh, Youngro Lee, Navid Qureshi, Jose Alberto Rodriguez Velamazan, Eric Ressouche, Andrew T. Boothroyd, Henrik Jacobsen

Abstract: We use spherical neutron polarimetry to determine the ground state magnetic structure of Mn3Sn. We find that Mn3Sn adopts an inverse triangular structure with spins parallel to <100> (Type III) rather than spins parallel to <110> (Type IV). Density functional theory calculations reveal no energy difference between these two structures, suggesting that the selection is caused by subtle effects such… ▽ More We use spherical neutron polarimetry to determine the ground state magnetic structure of Mn3Sn. We find that Mn3Sn adopts an inverse triangular structure with spins parallel to <100> (Type III) rather than spins parallel to <110> (Type IV). Density functional theory calculations reveal no energy difference between these two structures, suggesting that the selection is caused by subtle effects such as sixth-order anisotropy. Partial control of the magnetic domain population through a moderate magnetic field is key to distinguish between the two models. We find that three of the six domains are approximately equally populated, while the others have negligible population. Upon entering the low temperature incommensurate phase, the domain structure is lost. The domains decouple from the magnetic field, and can therefore not be controlled by any known method. △ Less

Submitted 8 October, 2025; originally announced October 2025.

Comments: 7 pages, 7 figures

Strain-tunability of the multipolar Berry curvature in altermagnet MnTe

Authors: Shane Smolenski, Ning Mao, Dechen Zhang, Yucheng Guo, A. K. M. Ashiquzzaman Shawon, Mingyu Xu, Eoghan Downey, Trisha Musall, Ming Yi, Weiwei Xie, Chris Jozwiak, Aaron Bostwick, Nobumichi Tamura, Eli Rotenberg, Lu Li, Kai Sun, Yang Zhang, Na Hyun Jo

Abstract: The anomalous Hall effect describes the generation of a transverse voltage by a longitudinal current even in the absence of an external magnetic field. While typically observed in ferromagnets, it has also been predicted to arise in altermagnets, materials characterized by rotational symmetries that enable broken time reversal symmetry despite compensated collinear magnetic ordering. These symmetr… ▽ More The anomalous Hall effect describes the generation of a transverse voltage by a longitudinal current even in the absence of an external magnetic field. While typically observed in ferromagnets, it has also been predicted to arise in altermagnets, materials characterized by rotational symmetries that enable broken time reversal symmetry despite compensated collinear magnetic ordering. These symmetries enforce band (anti)crossings that can generate significant contributions to the Berry curvature that drives the anomalous Hall effect. This Berry curvature is predicted to exhibit a characteristic multipolar order, resulting in a symmetry-enforced distribution at or near net compensation which is highly sensitive to perturbations that distort this balance. However, exploring the predicted multipolar Berry curvature of altermagnets and its reversible manipulation remains challenging. Here, we demonstrate evidence for the multipolar nature of the altermagnetic Berry curvature in MnTe by tuning the anomalous Hall effect via uniaxial stress. Upon straining, the magnitude of the anomalous Hall conductivity changes and, at a critical strain of 0.14%, the sign is reversed. Symmetry analysis and density functional theory calculations reveal that this tunability is a direct consequence of the altermagnetic multipolar Berry curvature. Our results provide insight into the role of crystal and magnetic symmetries in the realization of higher-order Berry curvature distributions and their unique tunability. △ Less

Submitted 25 September, 2025; originally announced September 2025.

Generalized Li-Haldane Correspondence in Critical Free-Fermion Systems

Authors: Yuxuan Guo, Sheng Yang, Xue-Jia Yu

Abstract: Topological phenomena in quantum critical systems have recently attracted growing attention, as they go beyond the traditional paradigms of condensed matter and statistical physics. However, a general framework for identifying such nontrivial phenomena, particularly in higher-dimensional systems, remains insufficiently explored. In this Letter, we propose a universal fingerprint for detecting nont… ▽ More Topological phenomena in quantum critical systems have recently attracted growing attention, as they go beyond the traditional paradigms of condensed matter and statistical physics. However, a general framework for identifying such nontrivial phenomena, particularly in higher-dimensional systems, remains insufficiently explored. In this Letter, we propose a universal fingerprint for detecting nontrivial topology in critical free-fermion systems protected by global on-site symmetries. Specifically, we analytically establish an exact relation between the bulk entanglement spectrum and the boundary energy spectrum at topological criticality in arbitrary dimensions, demonstrating that the degeneracy of edge modes can be extracted from the bulk entanglement spectrum. These findings, further supported by numerical simulations of lattice models, provide a universal fingerprint for identifying nontrivial topology in critical free-fermion systems. △ Less

Submitted 17 December, 2025; v1 submitted 24 September, 2025; originally announced September 2025.

Comments: 5 + 10 pages, 7 figures. Any comments and suggestions are welcome!

Observation of mirror-odd and mirror-even spin texture in ultra-thin epitaxially-strained RuO2 films

Authors: Yichen Zhang, Seung Gyo Jeong, Luca Buiarelli, Seungjun Lee, Yucheng Guo, Jiaqin Wen, Hang Li, Sreejith Nair, In Hyeok Choi, Zheng Ren, Ziqin Yue, Alexei Fedorov, Sung-Kwan Mo, Junichiro Kono, Jong Seok Lee, Tony Low, Turan Birol, Rafael M. Fernandes, Milan Radovic, Bharat Jalan, Ming Yi

Abstract: Recently, rutile RuO$_2$ has attracted renewed interest due to expectations of prominent altermagnetic spin-splitting. However, accumulating experimental evidence suggests that in its bulk and thick-film forms, RuO$_2$ does not display any form of magnetic ordering. Despite this, the spin structure of RuO$_2$ remains largely unexplored in the ultra-thin limit, where substrate-imposed epitaxial str… ▽ More Recently, rutile RuO$_2$ has attracted renewed interest due to expectations of prominent altermagnetic spin-splitting. However, accumulating experimental evidence suggests that in its bulk and thick-film forms, RuO$_2$ does not display any form of magnetic ordering. Despite this, the spin structure of RuO$_2$ remains largely unexplored in the ultra-thin limit, where substrate-imposed epitaxial strain can be substantial. Here, we employ spin-resolved angle-resolved photoemission spectroscopy, supported by ab-initio calculations, to reveal the electronic structure of 2.7~nm-thick epitaxial RuO$_2$ heterostructures. We observe an unconventional spin texture characterized by the coexistence of mirror-even and mirror-odd momentum-dependent components. A comprehensive symmetry analysis rules out nonmagnetic origins of this spin texture. These findings suggest an emergent non-relativistic spin structure enabled by epitaxial strain in the ultra-thin limit, marking a distinct departure from the behavior of relaxed or bulk RuO$_2$. Our work opens new perspectives for exploring symmetry-breaking mechanisms and spin textures in oxide heterostructures. △ Less

Submitted 19 September, 2025; originally announced September 2025.

Comments: 45 pages, 5 figures, 1 table

Supersonic flow and hydraulic jump in an electronic de Laval nozzle

Authors: Johannes Geurs, Tatiana A. Webb, Yinjie Guo, Itai Keren, Jack H. Farrell, Jikai Xu, Kenji Watanabe, Takashi Taniguchi, Dmitri N. Basov, James Hone, Andrew Lucas, Abhay Pasupathy, Cory R. Dean

Abstract: In very clean solid-state systems, where carrier-carrier interactions dominate over any other scattering mechanisms, the flow of electrons can be described within a hydrodynamic framework. In these cases, analogues of viscous fluid phenomena have been experimentally observed. However, experimental studies of electron hydrodynamics have so far been limited to the low velocity, linear response regim… ▽ More In very clean solid-state systems, where carrier-carrier interactions dominate over any other scattering mechanisms, the flow of electrons can be described within a hydrodynamic framework. In these cases, analogues of viscous fluid phenomena have been experimentally observed. However, experimental studies of electron hydrodynamics have so far been limited to the low velocity, linear response regime. At velocities approaching the speed of sound, the electronic fluid is expected to exhibit compressible behaviour where nonlinear effects and discontinuities such as shocks and choked flow have long been predicted. This compressible regime remains unexplored in electronic systems, despite its promise of strongly nonlinear flow phenomena. Here, we demonstrate compressible electron flow in bilayer graphene through an electronic de Laval nozzle, a structure that accelerates charge carriers past the electronic speed of sound, until they slow down suddenly in a shock. Discontinuities in transport measurements and local flattening of potential in Kelvin probe measurements are consistent with a viscous electron shock front and the presence of supersonic electron flow, and are not consistent with Ohmic or ballistic flow. Breaking the sound barrier in electron liquids opens the door for novel, intrinsically nonlinear electronic devices beyond the paradigm of incompressible flow. △ Less

Submitted 25 September, 2025; v1 submitted 19 September, 2025; originally announced September 2025.

Comments: v2: fixed affiliations and bibliography

Crystal Orientation Dependence of Extreme Near-Field Heat Transfer between Polar Materials Governed by Surface Phonon Modes

Authors: Wei-Zhe Yuan, Yangyu Guo, Hong-Liang Yi

Abstract: Due to the rapid development of micro- and nano-manufacturing and electronic devices, heat transfer at the transition regime between radiation and conduction becomes increasingly important. Recent work has demonstrated the importance of nonlocal optical response and phonon tunneling. However, it remains unclear how the crystal orientation impacts them. In this work, we study this effect on heat tr… ▽ More Due to the rapid development of micro- and nano-manufacturing and electronic devices, heat transfer at the transition regime between radiation and conduction becomes increasingly important. Recent work has demonstrated the importance of nonlocal optical response and phonon tunneling. However, it remains unclear how the crystal orientation impacts them. In this work, we study this effect on heat transport across vacuum gaps between magnesium oxide (MgO) by nonequilibrium molecular dynamics (NEMD) simulation. At 5~Å~gaps, the overall thermal conductance exhibits 30\% enhancement for [100] orientation versus [110] and [210], while becoming orientation-insensitive beyond 6~Å. When the gap size is extremely small, the crystal orientation significantly impacts the resonance frequencies of spectral thermal conductance which are quite close to those of unique surface phonon modes distinct from bulk counterparts. As the gap size gradually increases, the spectral thermal conductance gradually converges to the predicted results of fluctuation-electrodynamics (FE) theory in the long-wavelength approximation. Our findings reveal how surface phonon modes govern extreme near-field heat transfer across nanogap, providing insights for thermal management in electronic devices. △ Less

Submitted 17 September, 2025; originally announced September 2025.

Comments: 9 pages, 6 figures

The self-assembly behavior of a diblock copolymer/homopolymer induced by Janus nanorods

Authors: Y. Q. Guo, J. Liu, H. R. He, N. Wu, J. J. Zhang

Abstract: We employ cell dynamics simulation based on the CH/BD model to investigate the self-assembly behavior of a mixed system consisting of diblock copolymers (AB), homopolymers (C), and Janus nanorods. The results indicate that, at different component ratios, the mixed system undergoes various phase transitions with an increasing number of nanorods. Specifically, when the homopolymer component is 0.40,… ▽ More We employ cell dynamics simulation based on the CH/BD model to investigate the self-assembly behavior of a mixed system consisting of diblock copolymers (AB), homopolymers (C), and Janus nanorods. The results indicate that, at different component ratios, the mixed system undergoes various phase transitions with an increasing number of nanorods. Specifically, when the homopolymer component is 0.40, the mixed system transitions from a disordered structure to a parallel lamellar structure, subsequently to a tilted layered structure, and ultimately to a perpendicular lamellar structure as the number of nanorods increases. To explore this phenomenon in greater depth, we conduct a comprehensive analysis of domain sizes and pattern evolution. Additionally, we investigate the effects of the repulsive interaction strength between polymers, wetting strength, length of nanorods, and degree of asymmetry on the self-assembly behavior of the mixed system. This research provides significant theoretical and experimental insights for the preparation of novel nanomaterials. △ Less

Submitted 23 September, 2025; v1 submitted 16 September, 2025; originally announced September 2025.

Comments: 16 pages, 9 figures

Journal ref: Condensed Matter Physics, 2025, Vol. 28, No. 3, 33602

Surface reconstruction and orthogonal decoupling in SrAl4 and EuAl4

Authors: Tongrui Li, Leiyuan Chen, Jian Yuan, Zhengtai Liu, Yichen Yang, Zhicheng Jiang, Jianyang Ding, Jiayu Liu, Jishan Liu, Zhe Sun, Yanfeng Guo, Tong Zhang, Dawei Shen

Abstract: Surface-induced symmetry breaking in quantum materials can stabilize exotic electronic phases distinct from those in the bulk, yet its momentum-space manifestations remain elusive due to domain-averaging effects. Here, using angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy (STM), we present a microscopic investigation of the electronic structures of SrAl4 and EuA… ▽ More Surface-induced symmetry breaking in quantum materials can stabilize exotic electronic phases distinct from those in the bulk, yet its momentum-space manifestations remain elusive due to domain-averaging effects. Here, using angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy (STM), we present a microscopic investigation of the electronic structures of SrAl4 and EuAl4, layered tetragonal intermetallic compounds that exhibit well-characterized incommensurate charge-density-wave (CDW) transitions. Below the CDW transition temperatures, we uncover linearly dispersing electronic states and pronounced unidirectional replica bands orthogonal to the bulk CDW wave vector, evidencing the emergence of an in-plane C4 symmetry-breaking electronic order that is not dictated by the bulk incommensurate CDW. STM measurements further reveal a 1 times 2 surface reconstruction with quasi-one-dimensional modulations and half-unit-cell steps, traced to ordered 50 percent Sr/Eu vacancies, which vanish irreversibly upon thermal cycling, indicating decoupled surface and bulk orders. These findings establish SrAl4 and EuAl4 as model platforms for exploring surface-confined nematicity and emergent low-dimensional phases in quantum materials. △ Less

Submitted 4 September, 2025; originally announced September 2025.

Comments: 9 pages,4 figures

Multi-origin driven giant planar Hall effect in topological antiferromagnet EuAl2Si2 with tunable spin texture

Authors: Xiangqi Liu, Ziyi Zhu, Yixuan Luo, Zhengyang Li, Bo Bai, Jingcheng Huang, Xia Wang, Chuanying Xi, Li Pi, Guanxiang Du, Leiming Chen, Wenbo Wang, Wei Xia, Yanfeng Guo

Abstract: In topological materials, the planar Hall effect (PHE) is often regarded as a hallmark of profound quantum phenomena-most notably the Adler-Bell-Jackiw chiral anomaly and Berry curvature-rendering it an indispensable tool for deciphering the topological essence of emergent phases. In this study, we delve into the PHE and anisotropic magnetoresistance in the recently discovered layered topological… ▽ More In topological materials, the planar Hall effect (PHE) is often regarded as a hallmark of profound quantum phenomena-most notably the Adler-Bell-Jackiw chiral anomaly and Berry curvature-rendering it an indispensable tool for deciphering the topological essence of emergent phases. In this study, we delve into the PHE and anisotropic magnetoresistance in the recently discovered layered topological antiferromagnet EuAl2Si2. Our analysis of the robust PHE signal (~3.8 μΩ cm at 2 K and 8 T) unveils a distinct interplay of mechanisms. While Berry curvature plays a minor role, the dominant contributions stem from classical orbital MR in the field-induced ferromagnetic state and field-suppressed spin fluctuations in the paramagnetic regime. These insights not only position EuAl2Si2-with its highly tunable spin texture-as an exemplary system for probing the intricate coupling between spin configurations and band topology in magnetotransport but also pave the way for designing novel materials with tailored PHE responses, highlighting significant application prospects in quantum sensing, spintronic devices, and topologically protected electronic systems. △ Less

Submitted 27 August, 2025; originally announced August 2025.

Comments: 17 pages and 5 figures

Emergent dynamical Kondo coherence and competing magnetic order in a correlated kagome flat-band metal CsCr6Sb6

Authors: Xiangqi Liu, Xuefeng Zhang, Jiachen Jiao, Renjie Zhang, Kaiwen Chen, Ying Wang, Yunguan Ye, Zhenhai Yu, Chengyu Jiang, Xia Wang, Lei Shu, Baiqing Lv, Gang Li, Yanfeng Guo

Abstract: Correlated kagome metals host unique electronic states that enable exotic quantum phenomena. In the recently emerged CsCr6Sb6, these manifest through Kondo behavior from localized Cr-3d electrons and unprecedented band flattening near the Fermi level. Yet the intricate interplay among Kondo screening, magnetic frustration, and electronic correlations remains poorly understood-a fundamental gap we… ▽ More Correlated kagome metals host unique electronic states that enable exotic quantum phenomena. In the recently emerged CsCr6Sb6, these manifest through Kondo behavior from localized Cr-3d electrons and unprecedented band flattening near the Fermi level. Yet the intricate interplay among Kondo screening, magnetic frustration, and electronic correlations remains poorly understood-a fundamental gap we address through multifaceted experimental and theoretical approaches. Our angle-resolved photoemission spectroscopy measurements reveal electronic correlation-renormalized flat bands and muon spin relaxation study detect short-range magnetic order at TN ~ 80 K. Complementing these findings, density-functional theory and dynamical mean-field theory calculations identify a coherent-incoherent crossover at TN, with a remarkable restoration of coherence accompanying local moment suppression-an anomalous hallmark of Kondo behavior. Intriguingly, despite strong interlayer antiferromagnetic coupling, the system evades long-range magnetic order due to competing magnetic configurations separated by sub-meV energy differences. These insights establish CsCr6Sb6 as a prototypical platform for investigating dynamical Kondo screening in correlated flat-band systems, opening new avenues to study flat band physics and frustrated magnetism in correlated kagome lattices. △ Less

Submitted 11 August, 2025; originally announced August 2025.

Comments: Mian Text 17 pages, 4 figures; SI 9 pages, 7 figures, 1 table

Dichotomy of flat bands in the van der Waals ferromagnet Fe$_5$GeTe$_2$

Authors: Han Wu, Jianwei Huang, Chaowei Hu, Lei Chen, Yiqing Hao, Yue Shi, Paul Malinowski, Yucheng Guo, Bo Gyu Jang, Jian-Xin Zhu, Andrew F. May, Siqi Wang, Xiang Chen, Yaofeng Xie, Bin Gao, Yichen Zhang, Ziqin Yue, Zheng Ren, Makoto Hashimoto, Donghui Lu, Alexei Fedorov, Sung-Kwan Mo, Junichiro Kono, Yu He, Robert J. Birgeneau , et al. (6 additional authors not shown)

Abstract: Quantum materials with bands of narrow bandwidth near the Fermi level represent a promising platform for exploring a diverse range of fascinating physical phenomena, as the high density of states within the small energy window often enables the emergence of many-body physics. On one hand, flat bands can arise from strong Coulomb interactions that localize atomic orbitals. On the other hand, quantu… ▽ More Quantum materials with bands of narrow bandwidth near the Fermi level represent a promising platform for exploring a diverse range of fascinating physical phenomena, as the high density of states within the small energy window often enables the emergence of many-body physics. On one hand, flat bands can arise from strong Coulomb interactions that localize atomic orbitals. On the other hand, quantum destructive interference can quench the electronic kinetic energy. Although both have a narrow bandwidth, the two types of flat bands should exhibit very distinct spectral properties arising from their distinctive origins. So far, the two types of flat bands have only been realized in very different material settings and chemical environments, preventing a direct comparison. Here, we report the observation of the two types of flat bands within the same material system--an above-room-temperature van der Waals ferromagnet, Fe$_{5-x}$GeTe$_2$, distinguishable by a switchable iron site order. The contrasting nature of the flat bands is also identified by the remarkably distinctive temperature-evolution of the spectral features, indicating that one arises from electron correlations in the Fe(1) site-disordered phase, while the other geometrical frustration in the Fe(1) site-ordered phase. Our results therefore provide a direct juxtaposition of the distinct formation mechanism of flat bands in quantum materials, and an avenue for understanding the distinctive roles flat bands play in the presence of magnetism, topology, and lattice geometrical frustration, utilizing sublattice ordering as a key control parameter. △ Less

Submitted 6 August, 2025; v1 submitted 4 August, 2025; originally announced August 2025.

Comments: The manuscript was submitted on June 12 2024

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

Propagating Neutral Modes in an Intervalley Coherent State

Authors: Richen Xiong, Yi Guo, Chenxin Qin, Fanzhao Yin, Taige Wang, Samuel L. Brantly, Junhang Qi, Jinfei Zhou, Zihan Zhang, Melike Erdi, Kenji Watanabe, Takashi Taniguchi, Shu Zhang, Seth Ariel Tongay, Andrea F. Young, Liang Fu, Chenhao Jin

Abstract: The emergence of neutral collective modes is a hallmark of correlated quantum phases but is often challenging to probe experimentally. In two-dimensional flatband systems, charge responses have been intensively investigated, yet neutral excitations remain largely unexplored. In particular, intervalley coherent state (IVC) features a neutral Goldstone mode due to spontaneously broken valley U(1) sy… ▽ More The emergence of neutral collective modes is a hallmark of correlated quantum phases but is often challenging to probe experimentally. In two-dimensional flatband systems, charge responses have been intensively investigated, yet neutral excitations remain largely unexplored. In particular, intervalley coherent state (IVC) features a neutral Goldstone mode due to spontaneously broken valley U(1) symmetry. While IVC state has been proposed as a unifying theme across graphene- and semiconductor-based systems, its defining feature - the neutral Goldstone mode - remains elusive in experiment. Here we investigate space-and-time-resolved transport of neutral modes in twisted WSe2 moiré superlattices through a novel ultrafast imaging technique. We uncover two new propagating collective modes with very different velocities, which emerge near the van Hove singularity (VHS) in both intermediate- (3.5~4 degree) and large-angle (~5 degree) twisted WSe2. The fast-propagating mode has a surprisingly large speed of ~3 km/s and is consistent with a Goldstone mode for an IVC state, while the slow-moving mode is likely a gapped amplitude mode. They can be understood as the spin-valley analogues of collective modes of a superfluid, whose propagation are imaged for the first time in a condensed matter system. Our study sets a new paradigm for probing charge-neutral modes in quantum materials and offers key insights into the interplay between charge and spin-valley physics in moiré superlattices. △ Less

Submitted 24 July, 2025; originally announced July 2025.

Ultra-clean interface between high k dielectric and 2D MoS2

Authors: Han Yan, Yan Wang, Yang Li, Dibya Phuyal, Lixin Liu, Hailing Guo, Yuzheng Guo, Tien-Lin Lee, Min Hyuk Kim, Hu Young Jeong, Manish Chhowalla

Abstract: Atomically thin transition metal dichalcogenides (TMDs) are promising candidates for next-generation transistor channels due to their superior scaling properties. However, the integration of ultra-thin gate dielectrics remains a challenge, as conventional oxides such as SiO2, Al2O3, and HfO2 tend to unintentionally dope 2D TMDs and introduce interfacial defect states, leading to undesirable field-… ▽ More Atomically thin transition metal dichalcogenides (TMDs) are promising candidates for next-generation transistor channels due to their superior scaling properties. However, the integration of ultra-thin gate dielectrics remains a challenge, as conventional oxides such as SiO2, Al2O3, and HfO2 tend to unintentionally dope 2D TMDs and introduce interfacial defect states, leading to undesirable field-effect transistor (FET) performance and unstable threshold voltages. Here, we demonstrate that zirconium oxide (ZrO2), a high-k dielectric compatible with semiconductor processing, forms an ultra-clean interface with monolayer MoS2. Using soft and hard X-ray photoelectron spectroscopy and density functional theory, we find that ZrO2 does not measurably interact with MoS2, in contrast to significant doping observed for SiO2 and HfO2 substrates. As a result, back-gated monolayer MoS2 FETs fabricated with ZrO2 dielectrics exhibit stable and positive threshold voltages (0.36 plus/minus 0.3 V), low subthreshold swing (75 mV per decade), and high ON currents exceeding 400 microamperes. We further demonstrate p-type WSe2 FETs with ON currents greater than 200 microamperes per micrometer by suppressing electron doping with ZrO2 dielectrics. Atomic-resolution imaging confirms a defect-free ZrO2/MoS2 interface, which enables top-gate FETs with an equivalent oxide thickness of 0.86 nanometers and subthreshold swing of 80 mV per decade. Moreover, the ultraclean ZrO2/MoS2 interface allows for effective threshold voltage modulation in top-gate FETs via gate metal work function engineering. These findings establish ZrO2 as a highly promising, industry-compatible high-k dielectric for scalable 2D TMD-based electronics. △ Less

Submitted 23 July, 2025; originally announced July 2025.

Comments: 30 pages

Unraveling Magneto-Phononic Coupling and Photoinduced Magnetic Control in Antiferromagnetic Kondo Semimetal CeBi

Authors: Xu-Chen Nie, Chen Zhang, Qi-Yi Wu, Hao Liu, Jie Pang, You-Guo Shi, Zhi-An Xu, Yan-Feng Guo, Ya-Hua Yuan, H. Y. Liu, Yu-Xia Duan, Jian-Qiao Meng

Abstract: We report an ultrafast optical spectroscopy study on the coherent phonon dynamics in the topological semimetal CeBi and its nonmagnetic isostructural compound LaBi, revealing profound insights into their electronic and magnetic interactions. Both materials exhibit prominent $A_{1g}$ longitudinal optical phonons with characteristic anharmonic temperature dependencies. However, in CeBi, the… ▽ More We report an ultrafast optical spectroscopy study on the coherent phonon dynamics in the topological semimetal CeBi and its nonmagnetic isostructural compound LaBi, revealing profound insights into their electronic and magnetic interactions. Both materials exhibit prominent $A_{1g}$ longitudinal optical phonons with characteristic anharmonic temperature dependencies. However, in CeBi, the $A_{1g}$ phonon frequency and amplitude show clear anomalies near its antiferromagnetic (AFM) ordering temperatures ($T_{N1}$ $\simeq$ 25 K and $T_{N2}$ $\simeq$ 12 K), which unequivocally demonstrate strong magneto-phononic coupling. Crucially, in the AFM state at 4 K, CeBi exhibits a pump fluence threshold of $F_C$ $\approx$ 44 $μ$J/cm$^2$, above which the rate of phonon softening accelerates and the amplitude increases sharply. This unique threshold, absent in paramagnetic CeBi and LaBi, points to a photoinduced, non-thermal quenching of the AFM order. Our findings establish coherent phonons as highly sensitive probes of intertwined orders in heavy fermion systems, highlighting the transformative potential of ultrafast pulses in dynamically controlling magnetic states in correlated electron materials and paving the way for the manipulation of emergent quantum phases. △ Less

Submitted 11 July, 2025; originally announced July 2025.

Comments: 6 pages,3 figures

Optoelectronically Active GaAs/GeSn-MQW/Ge Heterojunctions Created via Semiconductor Grafting

Authors: Jie Zhou, Haibo Wang, Yifu Guo, Alireza Abrand, Yiran Li, Yang Liu, Jiarui Gong, Po Rei Huang, Jianping Shen, Shengqiang Xu, Daniel Vincent, Samuel Haessly, Yi Lu, Munho Kim, Shui-Qing Yu, Parsian K. Mohseni, Guo-En Chang, Zetian Mi, Kai Sun, Xiao Gong, Mikhail A Kats, Zhenqiang Ma

Abstract: Traditionally, advancements in semiconductor devices have been driven by lattice-matched heterojunctions with tailored band alignments through heteroepitaxy techniques. However, there is significant interest in expanding the capabilities of heterojunction devices, in particular utilizing extreme lattice mismatches. We demonstrate the manipulation of device behaviors and performance enhancement ach… ▽ More Traditionally, advancements in semiconductor devices have been driven by lattice-matched heterojunctions with tailored band alignments through heteroepitaxy techniques. However, there is significant interest in expanding the capabilities of heterojunction devices, in particular utilizing extreme lattice mismatches. We demonstrate the manipulation of device behaviors and performance enhancement achievable through a lattice-mismatched, single-crystalline GaAs/GeSn-multi-quantum well (MQW)/Ge n-i-p heterojunction by employing advanced semiconductor grafting technology. With engineered band alignment and optical field distribution, the grafted GaAs/GeSn-MQW/Ge n-i-p photodiode achieved outstanding performance: a record-low dark current density of 1.22E10^-7 A/cm^2, an extended spectral response from ~0.5 to 2 um, and improved photoresponsivity of RVIS of 0.85 A/W and RNIR of 0.40 A/W at 520 and 1570 nm, respectively. The dark current density is at least 5 orders of magnitude lower than state-of-the-art GeSn photodiodes. The photoresponsivity demonstrates an approximately sevenfold enhancement in the VIS range and a threefold improvement in the NIR range compared to the reference epitaxial photodiode. This work presents a unique strategy for constructing lattice-mismatched semiconductor heterojunction devices. More importantly, the implications transcend the current GaAs/GeSn-MQW/Ge example, offering potential applications in other material systems and freeing device design from the stringent lattice-matching constraints of conventional heteroepitaxy. △ Less

Submitted 7 June, 2025; originally announced June 2025.

Comments: 25 pages, 6 figures

Reconstructing the wavefunction of magnetic topological insulators MnBi2Te4 and MnBi4Te7 using spin-resolved photoemission

Authors: Xue Han, Jason Qu, Hengxin Tan, Zicheng Tao, Noah M. Meyer, Patrick S. Kirchmann, Yanfeng Guo, Binghai Yan, Zhi-Xun Shen, Jonathan A. Sobota

Abstract: Despite their importance for exotic quantum effects, the surface electronic structure of magnetic topological insulators MnBi2Te4 and MnBi4Te7 remains poorly understood. Using high-efficiency spin- and angle-resolved photoemission spectroscopy, we directly image the spin-polarization and orbital character of the surface states in both compounds and map our observations onto a model wavefunction to… ▽ More Despite their importance for exotic quantum effects, the surface electronic structure of magnetic topological insulators MnBi2Te4 and MnBi4Te7 remains poorly understood. Using high-efficiency spin- and angle-resolved photoemission spectroscopy, we directly image the spin-polarization and orbital character of the surface states in both compounds and map our observations onto a model wavefunction to describe the complex spin-orbital texture, which solidifies our understanding of the surface band structure by establishing the single-band nature of the most prominent states. Most importantly, our analysis reveals a new mechanism for reducing the magnetic gap of the topological surface states based on the orbital composition of the wavefunction. △ Less

Submitted 3 June, 2025; originally announced June 2025.

Topological surface states in γ-PtBi$_2$ evidenced by scanning tunneling microscopy

Authors: Yunkai Guo, Jingming Yan, Wen-Han Dong, Yongkai Li, Yucong Peng, Xuetao Di, Caizhen Li, Zhiwei Wang, Yong Xu, Peizhe Tang, Yugui Yao, Wenhui Duan, Qi-Kun Xue, Wei Li

Abstract: For the application of topological materials, the specific location of their topological surface states with respect to the Fermi level are important. γ-PtBi2 has been demonstrated to be a Weyl semimetal possessing superconducting Fermi arcs by photoemission spectroscopy. However, the evidence of its topological surface states is lacking by scanning tunneling microscopy (STM), which should be rath… ▽ More For the application of topological materials, the specific location of their topological surface states with respect to the Fermi level are important. γ-PtBi2 has been demonstrated to be a Weyl semimetal possessing superconducting Fermi arcs by photoemission spectroscopy. However, the evidence of its topological surface states is lacking by scanning tunneling microscopy (STM), which should be rather sensitive to detect the surface states. Here, we show multiple STM evidences for the existence of topological surface states in γ-PtBi2. We observe not only the step-edge and screw dislocation induced quasiparticle interference fringes, originating from the electron scatterings between the Fermi arcs of γ-PtBi2, but also the back-scattering prohibition related to the spin-flip process, which is the direct evidence for the topological nature of the surface states. Moreover, we demonstrate that the topological surface states are precisely located over a narrow energy range near the Fermi level, within which sharply enhanced intensity and slow spatial decay of quasiparticle interference are observed. △ Less

Submitted 15 May, 2025; originally announced May 2025.

Observing Bethe strings in an attractive Bose gas far from equilibrium

Authors: Milena Horvath, Alvise Bastianello, Sudipta Dhar, Rebekka Koch, Yanliang Guo, Jean-Sébastien Caux, Manuele Landini, Hanns-Christoph Nägerl

Abstract: Bethe strings are bound states of constituent particles in a variety of interacting many-body one-dimensional (1D) integrable quantum models relevant to magnetism, nanophysics, cold atoms and beyond. As emergent fundamental excitations, they are predicted to collectively reshape observable equilibrium and dynamical properties. Small individual Bethe strings have recently been observed in quantum m… ▽ More Bethe strings are bound states of constituent particles in a variety of interacting many-body one-dimensional (1D) integrable quantum models relevant to magnetism, nanophysics, cold atoms and beyond. As emergent fundamental excitations, they are predicted to collectively reshape observable equilibrium and dynamical properties. Small individual Bethe strings have recently been observed in quantum magnets and superconducting qubits. However, creating states featuring intermixtures of many, including large, strings remains an outstanding experimental challenge. Here, using nearly integrable ultracold Bose gases, we realize such intermixtures of Bethe strings out of equilibrium, by dynamically tuning interactions from repulsive to attractive. We measure the average binding energy of the strings, revealing the presence of bound states of more than six particles. We find further evidence for them in the momentum distribution and in Tan's contact, connected to the correlated density. Our data quantitatively agree with predictions from generalized hydrodynamics (GHD). Manipulating intermixtures of Bethe strings opens new avenues for understanding quantum coherence, nonlinear dynamics and thermalization in strongly-interacting 1D systems. △ Less

Submitted 20 June, 2025; v1 submitted 15 May, 2025; originally announced May 2025.

Quantum spin excitations in a dual-core magnetic molecule

Authors: Wenbin Li, Wenwen Shi, Xiaoxiao Xiao, Haiyan Zhu, Cai Cheng, Dongfei Wang, Lan Chen, Masahiro Haze, Huixia Fu, Xiao Zheng, Yang Guo, Zhendong Li, Yukio Hasegawa

Abstract: Magnetic excitations are important quantum phenomena in magnetic systems and have been widely studied in individual magnetic atoms and molecules as well as their assembled structures over the past few decades. Using scanning tunneling microscopy/spectroscopy (STM/S) combined with density functional theory (DFT) and the state-of-the-art ab initio wavefunction calculations, we investigated the prope… ▽ More Magnetic excitations are important quantum phenomena in magnetic systems and have been widely studied in individual magnetic atoms and molecules as well as their assembled structures over the past few decades. Using scanning tunneling microscopy/spectroscopy (STM/S) combined with density functional theory (DFT) and the state-of-the-art ab initio wavefunction calculations, we investigated the properties of a novel dual-core Cr2Br6 molecule, which consists of two Cr ions coupled via superexchange through a single near-90° Cr-Br-Cr scissors bond. Under zero magnetic field, we observed a Fano peak with multi-steps through STS. When an external magnetic field is applied, some steps exhibit additional splitting, while others change little. We find that the Cr2Br6, exhibits a spin-degenerate ground state, and the complex peak splitting arises from the coexistence of vibrational and magnetic excitations in the molecule. Our results reveal rich quantum spin behavior in a well-defined two-core magnetic trihalide complex at the atomic scale, offering not only a minimal model for superexchange-coupled multi-spin quantum excitations but also a possible foundational unit for future molecule-based quantum functionalities. △ Less

Submitted 11 May, 2025; originally announced May 2025.

Comments: 18 pages, 3 figues and 2 tables

Physics-informed Neural Networks Enable High Fidelity Shear Wave Viscoelastography across Multiple organs

Authors: Ziying Yin, Yuxi Guo, Jiayi Pu, Yuxuan Jiang, Shiyu Ma, Guo-Yang Li, Yanping Cao

Abstract: Tissue viscoelasticity has been recognized as a crucial biomechanical indicator for disease diagnosis and therapeutic monitoring. Conventional shear wave elastography techniques depend on dispersion analysis and face fundamental limitations in clinical scenarios. Particularly, limited wave propagation data with low signal-to-noise ratios, along with challenges in discriminating between dual disper… ▽ More Tissue viscoelasticity has been recognized as a crucial biomechanical indicator for disease diagnosis and therapeutic monitoring. Conventional shear wave elastography techniques depend on dispersion analysis and face fundamental limitations in clinical scenarios. Particularly, limited wave propagation data with low signal-to-noise ratios, along with challenges in discriminating between dual dispersion sources stemming from viscoelasticity and finite tissue dimensions, pose great difficulties for extracting dispersion relation. In this study, we introduce SWVE-Net, a framework for shear wave viscoelasticity imaging based on a physics-informed neural network (PINN). SWVE-Net circumvents dispersion analysis by directly incorporating the viscoelasticity wave motion equation into the loss functions of the PINN. Finite element simulations reveal that SWVE-Net quantifies viscosity parameters within a wide range (0.15-1.5 Pa*s), even for samples just a few millimeters in size, where substantial wave reflections and dispersion occur. Ex vivo experiments demonstrate its applicability across various organs, including brain, liver, kidney, and spleen, each with distinct viscoelasticity. In in vivo human trials on breast and skeletal muscle tissues, SWVE-Net reliably assesses viscoelastic properties with standard deviation-to-mean ratios below 15%, highlighting robustness under real-world constraints. SWVE-Net overcomes the core limitations of conventional elastography and enables reliable viscoelastic characterization where traditional methods fall short. It holds promise for applications such as grading hepatic lipid accumulation, detecting myocardial infarction boundaries, and distinguishing malignant from benign tumors. △ Less

Submitted 24 June, 2025; v1 submitted 6 May, 2025; originally announced May 2025.

Anyonization of bosons in one dimension: an effective swap model

Authors: Botao Wang, Amit Vashisht, Yanliang Guo, Sudipta Dhar, Manuele Landini, Hanns-Christoph Nägerl, Nathan Goldman

Abstract: Anyons emerge as elementary excitations in low-dimensional quantum systems and exhibit behavior distinct from bosons or fermions. Previous models of anyons in one dimension (1D) are mainly categorized into two types: those that rely on nontrivial scattering behavior, and those based on density-dependent hopping processes in discrete lattices. Here, we introduce a novel framework for realizing anyo… ▽ More Anyons emerge as elementary excitations in low-dimensional quantum systems and exhibit behavior distinct from bosons or fermions. Previous models of anyons in one dimension (1D) are mainly categorized into two types: those that rely on nontrivial scattering behavior, and those based on density-dependent hopping processes in discrete lattices. Here, we introduce a novel framework for realizing anyonic correlations using the internal degrees of freedom of a spinor quantum gas. We propose a "swap" model, which assigns a complex phase factor to the swapping processes between two different species, referred to as "host particles" and "impurities". The anyonic characteristics are demonstrated through the one-body correlator of the impurity, using a spin-charge separation analysis. For a single impurity, our swap model can be effectively implemented by applying tilt potentials in a strongly interacting quantum gas [Dhar et al., arXiv:2412.21131]. We further explore the dynamical properties of anyonic correlations and extend our analysis to the case of multiple impurities. Our work provides new avenues for engineering many-body anyonic behavior in quantum simulation platforms. △ Less

Submitted 29 April, 2025; originally announced April 2025.

Comments: 5 pages, 4 figures plus supplementary. BW and AV contributed equally

Consistency between the Green-Kubo formula and Lorentz model for predicting the infrared dielectric function of polar materials

Authors: Wei-Zhe Yuan, Yangyu Guo, Hong-Liang Yi

Abstract: Accurate prediction of infrared dielectric functions in polar materials is fundamental for thermal and photonic applications, yet it remains unexplored whether the two main methods, Green-Kubo formula and Lorentz model, can give unified predictions. In this work, we present a detailed comparison of these two approaches using MgO and LiH as prototypical cases employing both empirical rigid ion mode… ▽ More Accurate prediction of infrared dielectric functions in polar materials is fundamental for thermal and photonic applications, yet it remains unexplored whether the two main methods, Green-Kubo formula and Lorentz model, can give unified predictions. In this work, we present a detailed comparison of these two approaches using MgO and LiH as prototypical cases employing both empirical rigid ion model (RIM) and machine learning potential (MLP). We demonstrate that the conventional Lorentz model fails to capture the multi-phonon absorption inherent in Green-Kubo method, which can be resolved via using the phonon self-energy as a generalization of the usual linewidth. In addition, with RIM, a correction factor is required in the ionic contribution to infrared response to account for the electronic polarization effect, which is yet captured by MLP using the Born effective charges for calculating dipole moment. The present benchmark study thus enables cross-validation of dielectric function calculations while providing mechanistic insights into the polarization dynamics. △ Less

Submitted 24 April, 2025; originally announced April 2025.

Comments: 14 pages, 12 figures

Boundary anomalous dimensions from BCFT: O($N$)-symmetric $φ^{2n}$ theories with a boundary and higher-derivative generalizations

Authors: Yongwei Guo, Wenliang Li

Abstract: We investigate the $φ^{2n}$ deformations of the O($N$)-symmetric (generalized) free theories with a flat boundary, where $n\geqslant 2$ is an integer. The generalized free theories refer to the $\Box^k$ free scalar theories with a higher-derivative kinetic term, which is related to the multicritical generalizations of the Lifshitz type. We assume that the (generalized) free theories and the deform… ▽ More We investigate the $φ^{2n}$ deformations of the O($N$)-symmetric (generalized) free theories with a flat boundary, where $n\geqslant 2$ is an integer. The generalized free theories refer to the $\Box^k$ free scalar theories with a higher-derivative kinetic term, which is related to the multicritical generalizations of the Lifshitz type. We assume that the (generalized) free theories and the deformed theories have boundary conformal symmetry and O($N$) global symmetry. The leading anomalous dimensions of some boundary operators are derived from the bulk multiplet recombination and analyticity constraints. We find that the $ε^{1/2}$ expansion in the $φ^6$-tricritical version of the special transition extends to other multicritical cases with larger odd integer $n$, and most of the higher derivative cases involve a noninteger power expansion in $ε$. Using the analytic bootstrap, we further verify that the multiplet-recombination results are consistent with boundary crossing symmetry. △ Less

Submitted 19 October, 2025; v1 submitted 23 April, 2025; originally announced April 2025.

Comments: 51 pages, 3 figures

Fluctuated lattice-driven charge density wave far above the condensation temperature in kagome superconductor KV$_3$Sb$_5$

Authors: Haoran Liu, Shaofeng Duan, Xiangqi Liu, Zhihua Liu, Shichong Wang, Lingxiao Gu, Jiongyu Huang, Wenxuan Yang, Jianzhe Liu, Dong Qian, Yanfeng Guo, Wentao Zhang

Abstract: The kagome material AV$_3$Sb$_5$ exhibits multiple exotic orders, including an unconventional charge density wave (CDW). Elucidating the underlying mechanism behind the CDW transition is crucial for unraveling the complex interactions among these phases. However, the driving force of the CDW remains a topic of debate due to the intertwined interactions among the system's various excitations. Here… ▽ More The kagome material AV$_3$Sb$_5$ exhibits multiple exotic orders, including an unconventional charge density wave (CDW). Elucidating the underlying mechanism behind the CDW transition is crucial for unraveling the complex interactions among these phases. However, the driving force of the CDW remains a topic of debate due to the intertwined interactions among the system's various excitations. Here we investigated the CDW transition in KV$_3$Sb$_5$ by isolating the ultrafast electronic phase transition using time- and angleresolved photoemission spectroscopy. An ultrafast electronic phase transition was observed at a critical photoexcitation fluence, F$_c$, without reduction in CDW lattice-distortion-induced band folding. This folded band persisted up to 150 K under equilibrium heating, well above the CDW condensation temperature of T$_c$ = 78 K. Notably, the pump-induced band shifts at F$_c$ were comparable to those caused by thermal effects at T$_c$. These findings suggest that in KV$_3$Sb$_5$, a fluctuating lattice-driven in-plane CDW emerges above 150 K, with out-of-plane electronic correlations leading to the $2\times2 \times 2$ CDW near T$_c$, offering key insights into the interplay between the electronic and structural dynamics in AV$_3$Sb$_5$. △ Less

Submitted 25 April, 2025; v1 submitted 23 April, 2025; originally announced April 2025.

Comments: 21 pages, 4 figures

Journal ref: Science Bulletin 70, 1211-1214 (2025)

Dissecting coupled orders in a terahertz-driven electron-doped cuprate

Authors: Liwen Feng, Haotian Zhang, Tim Priessnitz, Jiayuan Cao, Tarapada Sarkar, Thales de Oliveira, Alexey N. Ponomaryov, Igor Ilyakov, Fei Yang, Yongbo Lv, Yuheng Guo, Kilian Srowik, Steffen Danzenbacher, Moritz Niethammer, Sergey Kovalev, Jan-Christoph Deinert, Stefan Kaiser, Richard L. Greene, Hao Chu

Abstract: The interplay between superconductivity and charge density wave has often been studied from an equilibrium point of view. For example, using static tuning knobs such as doping, magnetic field and pressure, superconductivity can be enhanced or suppressed. The resulting effect on the co-existing charge density wave order, if any, is judged by variations in its ground state properties such as the ord… ▽ More The interplay between superconductivity and charge density wave has often been studied from an equilibrium point of view. For example, using static tuning knobs such as doping, magnetic field and pressure, superconductivity can be enhanced or suppressed. The resulting effect on the co-existing charge density wave order, if any, is judged by variations in its ground state properties such as the ordering temperature or the spatial correlation. Such an approach can be understood as coordinated static displacements of two coupled order parameters within a Ginzburg-Landau description, evincing their interplay as either co-operative or competing but does not provide further microscopic information about the interaction. In order to assess such information, we dynamically perturb both orders from equilibrium and observe their coupling directly in the time-domain. We show that high-field multicycle terahertz pulses drive both the Higgs amplitude fluctuations of the superconducting order as well as collective fluctuations of the charge order in an electron-doped cuprate, resulting in characteristic third harmonic generation. A notable time delay is manifested between their respective driven dynamics. We propose that this may signify the important energy scale describing their coupling or imply a terahertz field-depinned charge density wave that destroys macroscopic superconductivity. Our work demonstrates a holistic approach for investigating coupled superconducting and charge density wave orders, which may shed novel light on their intertwined presence and widespread fluctuations in many classes of unconventional superconductors. △ Less

Submitted 16 April, 2025; originally announced April 2025.

Two-dimensional perovskites with maximum symmetry enable exciton diffusion length exceeding 2 micrometers

Authors: Jin Hou, Jared Fletcher, Siedah J. Hall, Hao Zhang, Marios Zacharias, George Volonakis, Claire Welton, Faiz Mandani, Isaac Metcalf, Shuo Sun, Bo Zhang, Yinsheng Guo, G. N. Manjunatha Reddy, Claudine Katan, Jacky Even, Matthew Y. Sfeir, Mercouri G. Kanatzidis, Aditya D. Mohite

Abstract: Realizing semiconductors with high symmetry of their crystallographic structures has been a virtue of inorganic materials and has resulted in novel physical behaviors. In contrast, hybrid (organic and inorganic) crystals such as two-dimensional metal halide perovskites exhibit much lower crystal symmetry due to in-plane or out of plane octahedral distortions. Despite their amazing ability for phot… ▽ More Realizing semiconductors with high symmetry of their crystallographic structures has been a virtue of inorganic materials and has resulted in novel physical behaviors. In contrast, hybrid (organic and inorganic) crystals such as two-dimensional metal halide perovskites exhibit much lower crystal symmetry due to in-plane or out of plane octahedral distortions. Despite their amazing ability for photoinduced light emission at room temperature, the Achilles' heel of this attractive class of 2D materials for optoelectronics remains the poor control and lack of performance for charge carrier transport. Inspired by the tremendous charge carrier properties of the 3D cubic perovskite phase of FAPbI3 and combining the use of the appropriate cage cation, the spacer molecule and the temperature and rate of crystallization, we report a new series of FA-based layered two-dimensional perovskites that exhibits the highest theoretically predicted symmetry with a tetragonal P4/mmm space group, resulting in no octahedral distortion in both in-plane and out-of-plane directions. These 2D perovskites present the shortest interlayer distances (4 angstrom), which results in systematically lower bandgaps (1.7 to 1.8 eV). Finally, the absence of octahedral distortions, results in an exciton diffusion length of 2.5 μm, and a diffusivity of 4.4 cm2s-1, both of which are an order of magnitude larger compared to previously reported 2D perovskites and on par with monolayer transition metal dichalcogenides. △ Less

Submitted 14 April, 2025; v1 submitted 10 April, 2025; originally announced April 2025.

Chiral magnetic excitations and domain textures of g-wave altermagnets

Authors: Volodymyr P. Kravchuk, Kostiantyn V. Yershov, Jorge I. Facio, Yaqian Guo, Oleg Janson, Olena Gomonay, Jairo Sinova, Jeroen van den Brink

Abstract: Altermagnets (AMs) constitute a novel class of spin-compensated materials in which opposite-spin sublattices are connected by a crystal rotation, causing their electronic iso-energy surfaces to be spin-split. While cubic and tetragonal crystal symmetries tend to produce AMs in which the splitting of electronic iso-energy surfaces has $d$-wave symmetry, hexagonal AMs, such as CrSb and MnTe, are… ▽ More Altermagnets (AMs) constitute a novel class of spin-compensated materials in which opposite-spin sublattices are connected by a crystal rotation, causing their electronic iso-energy surfaces to be spin-split. While cubic and tetragonal crystal symmetries tend to produce AMs in which the splitting of electronic iso-energy surfaces has $d$-wave symmetry, hexagonal AMs, such as CrSb and MnTe, are $g$-wave AMs. Here we investigate the purely magnetic modes and spin-textures of $g$-wave AMs and show that they are drastically different for easy-axial (CrSb) and easy-planar (MnTe) materials. We show that in CrSb the splitting of the chiral magnon branches possesses $g$-wave symmetry, with each branch carrying a fixed momentum-independent magnetic moment. The altermagnetic splitting is not affected by the easy-axial anisotropy and is the same as that in the nonrelativistic limit. The magnon splitting of MnTe, however, does not strictly possess $g$-wave symmetry due to its easy-planar anisotropy. Instead, the magnetic moment of each branch becomes momentum-dependent, with a distribution that is of $g$-wave symmetry. To generalize the concept of the altermagnetic splitting beyond the nonrelativistic limit, we introduce alternative, directly observable splitting parameter which comprises both the magnon eigenenergy and its magnetic moment and possesses the $g$-wave symmetry in both easy-axial and easy-planar cases. The associated altermagnetic domain walls in easy-axial CrSb possess a net magnetization with an amplitude that depends on their orientation. △ Less

Submitted 26 May, 2025; v1 submitted 7 April, 2025; originally announced April 2025.

Comments: 12 pages, 9 figures

Journal ref: Phys. Rev. B 112, 144421 (2025)

Uncovering the roughness effect on inelastic phonon scattering and thermal conductance at interface via spectral energy exchange

Authors: Jinyuan Xu, Yangyu Guo

Abstract: Understanding the mechanism of interfacial thermal transport is crucial for thermal management of electronics. Recent experiments have shown the strong impact of interfacial roughness on inelastic phonon scattering and interfacial thermal conductance (ITC), while the theoretical modeling and underlying physics remain missing. Through non-equilibrium molecular dynamics simulations with quantum corr… ▽ More Understanding the mechanism of interfacial thermal transport is crucial for thermal management of electronics. Recent experiments have shown the strong impact of interfacial roughness on inelastic phonon scattering and interfacial thermal conductance (ITC), while the theoretical modeling and underlying physics remain missing. Through non-equilibrium molecular dynamics simulations with quantum correction, we predict ITC of both sharp and rough Si/Al interfaces in a good agreement with experimental results in a broad range of temperatures. We further introduce a novel spectral energy exchange analysis, which reveals more annihilation of high-frequency phonons and generation of moderate-frequency phonons around the sharp interface compared to its rough counterpart. However, the low-frequency phonons at rough interface shows unexpected stronger inelastic scattering and larger contribution to ITC due to unique emerging interfacial modes. Our work thus promotes both the methodology and understanding of interfacial thermal transport at solid/solid interfaces, and may benefit the design and optimization of thermal interface materials. △ Less

Submitted 6 April, 2025; originally announced April 2025.

Comments: 22 pages, 8 figures

Orbital-selective band modifications in a charge-ordered kagome metal LuNb$_6$Sn$_6$

Authors: Rui Lou, Yumeng Zhang, Erjian Cheng, Xiaolong Feng, Alexander Fedorov, Zongkai Li, Yixuan Luo, Alexander Generalov, Haiyang Ma, Quanxing Wei, Yi Zhou, Susmita Changdar, Walter Schnelle, Dong Chen, Yulin Chen, Jianpeng Liu, Yanfeng Guo, Sergey Borisenko, Denis V. Vyalikh, Claudia Felser, Bernd Büchner, Zhongkai Liu

Abstract: The origin of the charge order in kagome lattice materials has attracted great interest due to the unique electronic structure features connected to kagome networks and the interplay between electron and lattice degrees of freedom. Recently, compounds with composition $Ln$Nb$_6$Sn$_6$ ($Ln$ = Ce-Nd, Sm, Gd-Tm, Lu, Y) appear as a new family of kagome metals, structurally analogous to $R$V$_6$Sn… ▽ More The origin of the charge order in kagome lattice materials has attracted great interest due to the unique electronic structure features connected to kagome networks and the interplay between electron and lattice degrees of freedom. Recently, compounds with composition $Ln$Nb$_6$Sn$_6$ ($Ln$ = Ce-Nd, Sm, Gd-Tm, Lu, Y) appear as a new family of kagome metals, structurally analogous to $R$V$_6$Sn$_6$ ($R$ = Sc, Y, or rare earth) systems. Among them, LuNb$_6$Sn$_6$ emerges as a novel material hosting charge density wave (CDW) with a $\sqrt{3}$ $\times$ $\sqrt{3}$ $\times$ $3$ wave vector, akin to that in ScV$_6$Sn$_6$. Here, we employ high-resolution angle-resolved photoemission spectroscopy, scanning tunneling microscopy, and density functional theory calculations to systematically investigate the electronic properties of LuNb$_6$Sn$_6$. Our observation reveals the characteristic band structures of the "166" kagome system. A charge instability driven by Fermi surface nesting is decisively ruled out through an analysis of the interactions between van Hove singularities. Across the CDW transition, we observe orbital-selective band modifications, with noticeable evolutions of Lu 5$d$ and Sn 5$p$ electrons, while Nb 4$d$ electrons exhibit minimal change, suggesting that the Lu and Sn sites other than the Nb kagome lattice play a key role in the formation of CDW. Our findings substantiate a universal lattice-driven CDW mechanism rather than a charge-instability-driven one in the "166" kagome compounds, making it a distinct material class compared to other charge-ordered kagome systems, such as $A$V$_3$Sb$_5$ ($A$ = K, Rb, Cs) and FeGe. △ Less

Submitted 4 April, 2025; originally announced April 2025.

Comments: 17 pages, 4 figures

Toward Sustainable Polymer Design: A Molecular Dynamics-Informed Machine Learning Approach for Vitrimers

Authors: Yiwen Zheng, Agni K. Biswal, Yaqi Guo, Prakash Thakolkaran, Yash Kokane, Vikas Varshney, Siddhant Kumar, Aniruddh Vashisth

Abstract: Vitrimer is an emerging class of sustainable polymers with self-healing capabilities enabled by dynamic covalent adaptive networks. However, their limited molecular diversity constrains their property space and potential applications. Recent development in machine learning (ML) techniques accelerates polymer design by predicting properties and virtually screening candidates, yet the scarcity of av… ▽ More Vitrimer is an emerging class of sustainable polymers with self-healing capabilities enabled by dynamic covalent adaptive networks. However, their limited molecular diversity constrains their property space and potential applications. Recent development in machine learning (ML) techniques accelerates polymer design by predicting properties and virtually screening candidates, yet the scarcity of available experimental vitrimer data poses challenges in training ML models. To address this, we leverage molecular dynamics (MD) data generated by our previous work to train and benchmark seven ML models covering six feature representations for glass transition temperature (Tg) prediction. By averaging predicted Tg from different models, the model ensemble approach outperforms individual models, allowing for accurate and efficient property prediction on unlabeled datasets. Two novel vitrimers are identified and synthesized, exhibiting experimentally validated higher Tg than existing bifunctional transesterification vitrimers, along with demonstrated healability. This work explores the possibility of using MD data to train ML models in the absence of sufficient experimental data, enabling the discovery of novel, synthesizable polymer chemistries with superior properties. The integrated MD-ML approach offers polymer chemists an efficient tool for designing polymers tailored to diverse applications. △ Less

Submitted 26 March, 2025; originally announced March 2025.

Quantum Strong-to-Weak Spontaneous Symmetry Breaking in Decohered One Dimensional Critical States

Authors: Yuxuan Guo, Sheng Yang, Xue-Jia Yu

Abstract: Symmetry breaking has been a central theme in classifying quantum phases and phase transitions. Recently, this concept has been extended to the mixed states of open systems, attracting considerable attention due to the emergence of novel physics beyond closed systems. In this work, we reveal a new type of phase transition in mixed states, termed \emph{quantum} strong-to-weak spontaneous symmetry b… ▽ More Symmetry breaking has been a central theme in classifying quantum phases and phase transitions. Recently, this concept has been extended to the mixed states of open systems, attracting considerable attention due to the emergence of novel physics beyond closed systems. In this work, we reveal a new type of phase transition in mixed states, termed \emph{quantum} strong-to-weak spontaneous symmetry breaking (SWSSB). Using a combination of field theory calculations and large-scale matrix product state simulations, we map out the global phase diagram of the XXZ critical spin chain under local strong symmetry preserving decoherence, which features an SWSSB phase and a trivial Luttinger liquid phase, separated by a straight critical line that belongs to the boundary Berezinskii-Kosterlitz-Thouless universality class with a varying effective central charge. Importantly, we analyze this transition from two complementary perspectives: on one hand, through the behavior of order parameters that characterize the symmetry breaking; on the other hand, from a quantum information viewpoint by studying entropic quantities and the concept of quantum recoverability. Remarkably, the SWSSB transition in our case is \emph{purely quantum} in the sense that it can only be driven by tuning the Hamiltonian parameter even under arbitrary decoherence strength, fundamentally distinguishing it from the decoherence-driven SWSSB transitions extensively discussed in previous literature. Importantly, our unified theoretical framework is applicable to a broad class of one-dimensional quantum systems, including spin chains and fermionic systems, whose low-energy physics can be described by Luttinger liquid theory, under arbitrary symmetry-preserving decoherence channels. Finally, we also discuss the experimental relevance of our theory on quantum simulator platforms. △ Less

Submitted 20 October, 2025; v1 submitted 18 March, 2025; originally announced March 2025.

Comments: 21pages. 10 figures

Journal ref: PRX Quantum 6, 040311, 16 October, 2025

Observation of multiple surface states in naturally cleavable chiral crystal PdSbSe

Authors: Zhicheng Jiang, Zhengtai Liu, Chenqiang Hua, Xiangqi Liu, Yichen Yang, Jianyang Ding, Jiayu Liu, Jishan Liu, Mao Ye, Ji Dai, Massimo Tallarida, Yanfeng Guo, Yunhao Lu, Dawei Shen

Abstract: Chiral multifold fermions in solids exhibit unique band structures and topological properties, making them ideal for exploring fundamental physical phenomena related to nontrivial topology, chirality, and symmetry breaking. However, the challenge of obtaining clean, flat surfaces through cleavage has hindered the investigation of their unique electronic states. In this study, we utilize high-resol… ▽ More Chiral multifold fermions in solids exhibit unique band structures and topological properties, making them ideal for exploring fundamental physical phenomena related to nontrivial topology, chirality, and symmetry breaking. However, the challenge of obtaining clean, flat surfaces through cleavage has hindered the investigation of their unique electronic states. In this study, we utilize high-resolution angle-resolved photoemission spectroscopy and density functional theory calculations to investigate the low-energy electronic structure of the cleavable single-crystal PdSbSe. Our combined experimental and theoretical analysis reveals the presence of multifold degenerate fermions within this chiral crystal. We also observe multiple chiral Fermi arc surface states and spin-splitting behavior in the associated bulk bands. These findings provide unique insights into chiral, multifold fermionic states in easily cleavable crystals and offer a robust platform for further research into their unique electronic properties and potential applications in novel electronic devices. △ Less

Submitted 17 March, 2025; originally announced March 2025.

Comments: 7 pages, 4 figures, to be published in Physical Review Materials

Kramers nodal lines in intercalated TaS$_2$ superconductors

Authors: Yichen Zhang, Yuxiang Gao, Aki Pulkkinen, Xingyao Guo, Jianwei Huang, Yucheng Guo, Ziqin Yue, Ji Seop Oh, Alex Moon, Mohamed Oudah, Xue-Jian Gao, Alberto Marmodoro, Alexei Fedorov, Sung-Kwan Mo, Makoto Hashimoto, Donghui Lu, Anil Rajapitamahuni, Elio Vescovo, Junichiro Kono, Alannah M. Hallas, Robert J. Birgeneau, Luis Balicas, Ján Minár, Pavan Hosur, Kam Tuen Law , et al. (2 additional authors not shown)

Abstract: Kramers degeneracy is one fundamental embodiment of the quantum mechanical nature of particles with half-integer spin under time reversal symmetry. Under the chiral and noncentrosymmetric achiral crystalline symmetries, Kramers degeneracy emerges respectively as topological quasiparticles of Weyl fermions and Kramers nodal lines (KNLs), anchoring the Berry phase-related physics of electrons. Howev… ▽ More Kramers degeneracy is one fundamental embodiment of the quantum mechanical nature of particles with half-integer spin under time reversal symmetry. Under the chiral and noncentrosymmetric achiral crystalline symmetries, Kramers degeneracy emerges respectively as topological quasiparticles of Weyl fermions and Kramers nodal lines (KNLs), anchoring the Berry phase-related physics of electrons. However, an experimental demonstration for ideal KNLs well isolated at the Fermi level is lacking. Here, we establish a class of noncentrosymmetric achiral intercalated transition metal dichalcogenide superconductors with large Ising-type spin-orbit coupling, represented by In$_x$TaS$_2$, to host an ideal KNL phase. We provide evidence from angle-resolved photoemission spectroscopy with spin resolution, angle-dependent quantum oscillation measurements, and ab-initio calculations. Our work not only provides a realistic platform for realizing and tuning KNLs in layered materials, but also paves the way for exploring the interplay between KNLs and superconductivity, as well as applications pertaining to spintronics, valleytronics, and nonlinear transport. △ Less

Submitted 29 May, 2025; v1 submitted 11 March, 2025; originally announced March 2025.

Comments: 40 pages, 5 figures. Supplementary information PDF included in TeX Source

Journal ref: Nat. Commun. 16, 4984 (2025)

A hybrid method integrating Green's function Monte Carlo and projected entangled pair states

Authors: He-Yu Lin, Rong-Qiang He, Yibin Guo, Zhong-Yi Lu

Abstract: This paper introduces a hybrid approach combining Green's function Monte Carlo (GFMC) method with projected entangled pair state (PEPS) ansatz. This hybrid method regards PEPS as a trial state and a guiding wave function in GFMC. By leveraging PEPS's proficiency in capturing quantum state entanglement and GFMC's efficient parallel architecture, the hybrid method is well-suited for the accurate and… ▽ More This paper introduces a hybrid approach combining Green's function Monte Carlo (GFMC) method with projected entangled pair state (PEPS) ansatz. This hybrid method regards PEPS as a trial state and a guiding wave function in GFMC. By leveraging PEPS's proficiency in capturing quantum state entanglement and GFMC's efficient parallel architecture, the hybrid method is well-suited for the accurate and efficient treatment of frustrated quantum spin systems. As a benchmark, we applied this approach to study the frustrated $J_1$-$J_2$ Heisenberg model on a square lattice with periodic boundary conditions (PBC). Compared with other numerical methods, our approach integrating PEPS and GFMC shows competitive accuracy in the performance of ground-state energy. This paper provides systematic and comprehensive discussion of the approach of our previous work. △ Less

Submitted 12 March, 2025; v1 submitted 11 March, 2025; originally announced March 2025.

Comments: 8 pages, 4 figures

Journal ref: Chinese Physics B 33 (2024) 117504