Statistical Mechanics · Cross-listed from quant-ph
Chaos, Entanglement and Measurement: Field-Theoretic Perspectives on Quantum Information Dynamics
Anastasiia Tiutiakina
This work develops tools to understand how
quantum information spreads, scrambles, and is reshaped by measurements in many-body systems. First, I study scrambling and pseudorandomness in the Brownian Sachdev-Ye-Kitaev (SYK) model, quantifying pseudorandomness using
unitary k-designs and frame potentials. Using Keldysh path integrals with replicas and disorder averaging, I obtain analytic control of the approach to randomness, identify collective modes that delay convergence to Haar-like behavior, and estimate design times as functions of model parameters, clarifying links between scrambling, complexity growth, and random-
circuit phenomenology. Second, I construct a field theory for weakly measured SYK clusters. Starting from a system-ancilla description and a continuum monitoring limit, and using fermionic coherent states with replicas and disorder averaging, I derive a nonlinear sigma model that captures measurement back-action and the competition between interaction-induced scrambling and information extraction, predicting characteristic crossover scales and response signatures that distinguish weak monitoring from fully
unitary evolution. Third, I develop a strong-disorder renormalization group for measurement-only SYK clusters, based on the SO(2n) replica
algebra and Dasgupta-Ma decimation rules. The flow shows features reminiscent of infinite-randomness behavior, but an order-of-limits subtlety renders the leading recursions non-robust, so the analytic evidence for an infinite-randomness fixed point is inconclusive, even though the average second Renyi
entropy displays logarithmic scaling. Together, these results provide a unified
language to diagnose when many-body dynamics generate operational randomness and how measurements redirect that flow.
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Mesoscale and Nanoscale Physics
Nanoscale magnetometry of a synthetic three-dimensional spin texture
Ricardo Javier Peña Román, Sandip Maity, Fabian Samad et al. (+7 more)
Multilayered synthetic antiferromagnets (SAFs) are artificial three-dimensional (3D) architectures engineered to create novel, complex, and stable
spin textures. Non-invasive and quantitative nanoscale
magnetic imaging of the two-dimensional stray field profile at the sample surface is essential for understanding the fundamental properties of the
spin-structure and being able to tailor them to achieve new functionalities. However, the deterministic detection of
spin textures and their quantitative characterization at the nanoscale remain challenging. Here, we use nitrogen-vacancy scanning probe microscopy (NV-SPM) under ambient conditions to perform the first quantitative vector-field magnetometry measurements in the multilayered SAF [(Co/Pt)$_5$/Co/Ru]$_3$/(Co/Pt)$_6$. We investigate nanoscale static and dynamic properties of
antiferromagnetic domains with boundaries hosting “one-dimensional”
ferromagnetic stripes with ~ 100 nm of width and periodic modulation of the magnetization. By employing NV-SPM measurements in different imaging modes and involving NV-probes with various crystallographic orientations, we demonstrated distinct fingerprints emerging from GHz-range
spin noise and constant stray fields on the order of several mT. This provides quantitative insights into the structure of domains and domain walls, as well as, into
magnetic noise associated with thermal
spin-waves. Our work opens up new opportunities for quantitative vector-field magnetometry of modern
magnetic materials with tailored 3D
spin textures and stray field profiles, and potentially novel
spin-wave dispersions–in a quantitative and non-invasive manner, with exceptional
magnetic sensitivity and nanometer scale spatial resolution.
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All authors Ricardo Javier Peña Román, Sandip Maity, Fabian Samad, Dinesh Pinto, Simon Josephy, Andrea Morales, Attila Kákay, Klaus Kern, Olav Hellwig, Aparajita Singha
Superconductivity
Yamaji effect and quantum oscillation in Yang-Rice-Zhang model of underdoped cuprates
Yicheng Zhong, Fu-Chun Zhang and Kun Jiang
Recent experiments have revealed signatures of small
Fermi pockets in the pseudogap phase of cuprate
superconductors, most notably the Yamaji effect observed in $\mathrm{HgBa}_2\mathrm{CuO}_{4+\delta}$. The Yang-Rice-Zhang (YRZ) model provides a successful phenomenological description of the pseudogap state and naturally predicts such small pockets. In this work, we use a microscopic framework to calculate angle-dependent magnetoresistance and
quantum oscillation within the YRZ model. Our calculations simultaneously reproduce the experimentally observed Yamaji oscillations and the Shubnikov-de Haas oscillation corresponding to a pocket area of about $p/8$, with $p$ the hole density. By further testing the effect of Green's-function zeros, we confirm that isolated zeros leave the oscillation period unchanged, whereas an extended zero segment suppresses and modifies the oscillation. Our findings demonstrate that the YRZ model captures essential features of the pseudogap regime and provides a general
quantum approach that can be applied to more complex electronic structures.
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Materials Science
Interfacial effect on the optoelectronic and piezoelectric properties of Ge-Sn terminated Halide Perovskite heterostructure from first-principles study
L. Celestine, R. Zosiamliana, H. Laltlanmawii et al. (+6 more)
Since the very early stages of research on sustainable technologies, green energy conversion has always been a
prime focus. With the discoveries of countless functional materials in recent years, significant progress has been made to meet the global energy demand for sustainable development. Among them, halide perovskites have emerged as one of the most promising and reliable materials. In this work, we have investigated the lead-free halide perovskites, vis CsGeCl3 and RbSnBr3, within a framework of density functional theory (DFT) to explore their potential applicability in harvesting clean and renewable energy. This study gives a comprehensive analysis of the bulk, surface (001), and Ge-Sn-terminated interfaces within GGA and mGGA functionals. Interestingly, the inherent asymmetric arrangements of the systems exhibit remarkable optoelectronic and piezoelectric properties. The piezoelectric performance of each surface cut has been validated through the electromechanical coupling calculation.
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All authors L. Celestine, R. Zosiamliana, H. Laltlanmawii, B. Chettri, Lalhum Hima, Lalhriat Zuala, S. Gurung, A. Laref, D. P. Rai
Materials Science
Atomistic understanding of two-dimensional monatomic phase-change material for non-volatile optical applications
Hanyi Zhang, Xueqi Xing, Jiang-Jing Wang et al. (+8 more)
Elemental antimony (Sb) is a promising material for phase-change
memory, neuromorphic computing and nanophotonic applications, because its compositional simplicity can prevent phase segregation upon extensive programming. Scaling down the film thickness is a necessary step to prolong the lifetime of amorphous Sb, but the optical properties of Sb are also significantly altered as the thickness is reduced to a few nanometers, adding complexity to device optimization. In this work, we aim to provide atomistic understanding of the thickness-dependent optical responses in Sb thin films. As thickness decreases, both the extinction coefficient and optical contrast reduce in the near-infrared spectrum, consistent with previous optical measurements. Such thickness dependence gives rise to a bottom thickness limit of 2 nm in photonic applications, as predicted by coarse-grained device simulations. Further bonding analysis reveals a fundamentally different behavior for amorphous and crystalline Sb upon downscaling, resulting in the reduction of optical contrast. Thin film experiments are also carried out to validate our predictions. The thickness-dependent optical trend is fully demonstrated by our ellipsometric spectroscopy experiments, and the bottom thickness limit of 2 nm is confirmed by structural characterization experiments. Finally, we show that the greatly improved amorphous-phase stability of the 2 nm Sb thin film enables robust and reversible optical switching in a silicon-based waveguide device.
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All authors Hanyi Zhang, Xueqi Xing, Jiang-Jing Wang, Chao Nie, Yuxin Du, Junying Zhang, Xueyang Shen, Wen Zhou, Matthias Wuttig, Riccardo Mazzarello, Wei Zhang
Mesoscale and Nanoscale Physics
Feynman paradox in a spherical axion insulator
Anastasiia Chyzhykova, Jeroen van den Brink and Flavio S. Nogueira
We show that a small charged probe near a spherical topological
insulator causes the latter to rotate around a
symmetry axis defined by the center of the sphere and the position of the charge outside the latter. The rotation occurs when the distance from the charge to the center of the sphere is changed. This phenomenon occurs due to induced static fields and is a consequence of the
axion electrodynamics underlying the electromagnetic response of a topological
insulator. Assuming a regime where the charged probe can be regarded as a point charge $q=Ne$, where $N$ is a positive integer and $e$ is the elementary electric charge, we obtain that the rotation frequency is given by $\omega=(N\alpha)^2\Upsilon(\epsilon,d/a)/I$, where $I$ is the moment of inertia, $\alpha$ is the fine-structure constant, and the function $\Upsilon$ depends on the dielectric constant $\epsilon$ and the relative distance $d/a$ of the charge from the center of the sphere of radius $a$. Since the point charge also induces
Hall currents on the surface, we compute also their associated angular momentum. This allows us to derive an exact expression for the electronic velocity on the surface as a function of $a/d$.
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Materials Science
Engineering Multifunctional Response in Monolayer Fe3O4 via Zr Adsorption: From Half-Metallicity to Enhanced Piezoelectricity
Sikander Azam, Qaiser Rafiq, Rajwali Khan et al. (+1 more)
Two-dimensional (2D)
magnetic oxides are increasingly studied for their multifunctional potential in fields like spintronics, optoelectronics, and energy conversion. In this research, we conduct a detailed first-principles study of pure monolayer Fe3O4 and its modification through Zr adsorption at two sites: on top of an Fe atom and at the bridge between Fe atoms. Using
spin-polarized density functional theory with the GGA plus U method, we examine how adsorption affects structure, electronic,
magnetic, optical, elastic, and piezoelectric properties. The original monolayer shows half-
metallicity, strong
spin polarization, and a moderate in-plane piezoelectric effect. Zr adsorption causes local
lattice distortions and orbital hybridization, resulting in intermediate electronic states, a reduced bandgap, and increased optical absorption in both
spin channels. Notably, Zr at the bridge site greatly enhances dielectric response, optical conductivity, and piezoelectric coefficients, tripling e11 compared to the pristine layer. Elastic constants indicate mechanical softening after functionalization, and energy loss spectra display shifts in plasmon resonance. These findings suggest Zr adsorption offers a controllable, non-destructive way to tune
spin, charge, and
lattice interactions in Fe4O4 monolayers, connecting
magnetic, optical, and piezoelectric functionalities within a single 2D material platform.
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All authors Sikander Azam, Qaiser Rafiq, Rajwali Khan, Hamdy Khamees Thabet
Materials Science
Electric-Field-Controlled Altermagnetic Transition for Neuromorphic Computing
Zhiyuan Duan, Peixin Qin, Chengyan Zhong et al. (+12 more)
Altermagnets represent a novel
magnetic phase with transformative potential for ultrafast spintronics, yet efficient control of their
magnetic states remains challenging. We demonstrate an ultra-low-power electric-field control of altermagnetism in MnTe through strain-mediated coupling in MnTe/PMN-PT
heterostructures with negligible Joule heating. Application of +6 kV/cm electric fields induces piezoelectric strain in PMN-PT, modulating the Néel temperature from 310 to 328 K. As a result, around the
magnetic phase transition, the altermagnetic
spin splitting of MnTe is reversibly switched "on" and "off" by the electric fields. Meanwhile, the piezoelectric strain generates
lattice distortions and
magnetic structure changes in MnTe, enabling up to 9.7% resistance modulation around the
magnetic phase transition temperature. Leveraging this effect, we implement programmable resistance states in a Hopfield neuromorphic network, achieving 100% pattern recognition accuracy at <=40% noise levels. This approach establishes the electric-field control as a low-power strategy for altermagnetic manipulation while demonstrating the viability of altermagnetic materials for energy-efficient neuromorphic computing beyond conventional charge-based architectures.
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All authors Zhiyuan Duan, Peixin Qin, Chengyan Zhong, Shaoxuan Zhang, Li Liu, Guojian Zhao, Xiaoning Wang, Hongyu Chen, Ziang Meng, Jingyu Li, Sixu Jiang, Xiaoyang Tan, Qiong Wu, Yu Liu, Zhiqi Liu
Materials Science
First-principles study of the phase competition, mechanical and piezoelectric properties of pseudo-binary (SiC)(AlN) alloy
Laszlo Wolf, Geoff L. Brennecka and Vladan Stevanović
The ongoing search for new piezoelectric materials offering adequate balance between piezoelectric response and other application-relevant properties has lead to the investigation of various
alloy systems. In this work we study the
alloy of the widely used AlN with SiC for their relative abundance, current use in other electronics applications and expected phase competition between wurtzite and other polymorphs, the kind of which has lead to some of the most interesting results notably between AlN and ScN. Here the pseudo-binary (SiC)(AlN)
alloy is studied from first-principles over the entire composition range. Relevant crystalline phases are identified using the First-Principles Random Structure Sampling approach which, in accordance with previous bulk experiments, finds wurtzite, zincblende and rhombohedral phases to be the only statistically relevant phases of the
alloy. Further study of these phases is done through Special Quasi-random Structures (SQS) and, in the case of the wurtzite phase, predictions of the stiffness, piezoelectric and dielectric tensors. Analysis of these tensors is done through the scope of a Bulk AcousticWave (BAW) filter application, where trends and trade-offs between the c-axis acoustic velocity and piezoelectric response enable identification of relevant compositions.
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Statistical Mechanics · Cross-listed from hep-th
Reflecting boundary conditions in critical loop models
Max Downing, Jesper Lykke Jacobsen, Rongvoram Nivesvivat et al. (+2 more)
In critical loop models, we call a boundary sticky if loops can attach to it, and reflecting otherwise. Using analytic bootstrap methods, we show that reflecting boundaries are characterised by one complex parameter, analogous to the boundary cosmological constant in Liouville theory. We determine disc 1-point functions, and write an explicit formula for disc 2-point functions as infinite combinations of conformal blocks. We also sketch the
lattice interpretation of reflecting boundaries.
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All authors Max Downing, Jesper Lykke Jacobsen, Rongvoram Nivesvivat, Sylvain Ribault, Hubert Saleur
Mesoscale and Nanoscale Physics
Excitation energies and UV-Vis absorption spectra from INDO/s+ML
Ezekiel Oyeniyi and Omololu Akin-Ojo
The semi-empirical INDO/s method is popular for studies of excitation energies and absorption of molecules due to its low computational requirement, making it possible to make predictions for large systems. However, its accuracy is generally low, particularly, when compared with the typical accuracy of other methods such as time-dependent density functional theory (TDDFT). Here, we present machine learning (ML) models that correct the INDO/s results with negligible increases in the amount of computing resources needed. While INDO/s excitations energies have an average error of about 1.1 eV relative to TDDFT energies, the added ML corrections reduce the error to 0.2 eV. Furthermore, this combination of INDO/s and ML produces UV-Vis absorption spectra that are in good agreement with the TDDFT predictions.
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Mesoscale and Nanoscale Physics
Surface acoustic wave-driven valley current generation in intervalley coherent states
Hiroto Tanaka and Youichi Yanase
Recent experiments have reported valley-gauge-
symmetry-broken phases, identified as intervalley coherent (IVC) states. Exploration of anomalous responses, particularly those analogous to superconductivity, has become an urgent theoretical issue. In this study, we show that the IVC order gives rise to anomalous valley-current generation driven by surface acoustic waves (SAWs). The anomalous valley current exhibits a characteristic power-law dependence for low-frequency SAWs. Furthermore, we demonstrate by numerical analysis that the IVC order significantly enhances valley-current generation in rhombohedral
graphene. These results open a pathway toward exploring exotic phenomena emerging from valley-gauge-
symmetry breaking, in close analogy with gauge-
symmetry breaking in
superconductors.
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Materials Science
Structure Prediction of Ionic Epitaxial Interfaces with Ogre Demonstrated for Colloidal Heterostructures of Lead Halide Perovskites
Stefano Toso, Derek Dardzinski, Liberato Manna et al. (+1 more)
Colloidal epitaxial
heterostructures are nanoparticles composed of two different materials connected at an interface, which can exhibit properties different from those of their individual components. Combining dissimilar materials offers opportunities to create several functional
heterostructures. Yet, assessing structural compatibility (the main prerequisite for epitaxial growth) is challenging when pairing complex materials with different
lattice parameters/
crystal structures. This complicates both the selection of target
heterostructures for synthesis and the assignment of interface models when new
heterostructures are obtained. Here, we demonstrate Ogre as a powerful tool to accelerate the design and characterization of colloidal
heterostructures. To this end we implemented developments tailored for the efficient prediction of epitaxial interfaces between ionic/polar materials, which encompass most colloidal
semiconductors. These include pre-screening candidate models based on charge balance at the interface and using a classical potential for fast energy evaluations, with parameters automatically extracted from the input bulk structures. These developments are validated for CsPbBr3/Pb4S3Br2
heterostructures, where Ogre produces interface models in agreement with density functional theory and experiments. Furthermore, we use Ogre to rationalize the templating effect of CsPbCl3 on the growth of lead sulfochlorides, where perovskite seeds induce the formation of Pb4S3Cl2 rather than Pb3S2Cl2 due to better epitaxial compatibility. Combining Ogre simulations with experimental data enables us to unravel the structure and composition of the hitherto unsolved CsPbBr3/BixPbySz interface and assign a structure to many other reported metal halide/
oxide based interfaces. The Ogre package is available on GitHub or via the OgreInterface desktop application, available for Windows, Linux and Mac.
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All authors Stefano Toso, Derek Dardzinski, Liberato Manna, Noa Marom
Materials Science · Cross-listed from cs.LG
Fitting magnetization data using continued fraction of straight lines
Vijay Prakash S
Magnetization of a
ferromagnetic substance in response to an externally applied
magnetic field increases with the strength of the field. This is because at the microscopic level,
magnetic moments in certain regions or domains of the substance increasingly align with the applied field, while the amount of misaligned domains decreases. The
alignment of such
magnetic domains with an applied
magnetic field forms the physical basis for the nonlinearity of magnetization. In this paper, the nonlinear function is approximated as a combination of continued fraction of straight lines. The resulting fit is used to interpret the nonlinear behavior in both growing and shrinking
magnetic domains. The continued fraction of straight lines used here is an algebraic expression which can be used to estimate parameters using nonlinear regression.
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Statistical Mechanics · Cross-listed from cs.GT
The $k$-flip Ising game
Aleksandr Kovalenko and Andrey Leonidov
The game-theoretic view on the classical Ising model - the noisy binary choice Ising game, - is a well-known conceptual framework that, on the one hand, highlights similar patterns between social or artificial
agent-based systems and ensembles of interacting physical
spins and, on the other hand, helps to stress important differences between the ones. The study considers one of such differences - the possibility of simultaneous decision making of several
agents that is typical for game theoretic interaction. To do this we analyse a partially parallel discrete time dynamics of an Ising-type system of $N$ interacting binary units on a complete graph in which at each time steps $k$ arbitrarily chosen units can change their states is analysed. The particular problem under study is a $k$ - dependence of the decay of a metastable configuration into a stable one. The analysis is based on an explicit analytical calculation, for arbitrary noise, of the transition
matrix characterising the $k$ - flip
evolution as well as the first two moments of the distribution of the fraction of players choosing one of the two available strategies. First two moments of the first hitting time distribution for sample trajectories corresponding to transition from a metastable and unstable states to a stable one are considered. A nontrivial dependence of these moments on $k$ for the decay of a metastable state is discussed. A presence of the minima at certain $k_{\rm min}$ is attributed to a competition between $k$-dependent
diffusion and restoring forces.
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Materials Science
Spin-orbit torques in bulk collinear antiferromagnets:complete classifications and the induced spin dynamics
Yizhuo Song, Jianting Dong, Jiahao Shentu et al. (+1 more)
Electric field induced
spin-orbit torques are the crucial mechanism for electric regulations of
antiferromagnetic order. However, the
spin-orbit torques in antiferromagnets and the induced
spin dynamics remain largely unexplored. In this work, the full classifications of SOTs in bulk collinear AFMs have been achieved based on
magnetic point group. Dependent on the
symmetries connecting the opposite
spin sublattices, the SOTs are classified into six distinct types. Among them, the SOTs and the induced Neel vector dynamics in three representative AFMs have been investigated, where the
spin sublattices are connected by fractional translation, spatial inversion, and neither by translation nor inversion
symmetry respectively. The SOTs on
spin sublattices have been calculated by first-principles calculations based on Kubo linear response theory, and then the induced
spin dynamics are simulated by LLG equations. In typical PT symmetric AFM and the inversion
symmetry breaking altermagnet, the simulations indicate that the deterministic switching of Neel vectors can be driven by field like torques. What's more, the fully electric writing of multiple
antiferromagnetic domains into single domain state with preset Neel vector direction and 180 deterministic switching may also be realized. Our work may shed light on the current control of
antiferromagnetic orders in collinear AFMs. Especially, for inversion
symmetry breaking altermagnet, the electric writing and reading of Neel vector are highly desirable for
antiferromagnetic memory applications.
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All authors Yizhuo Song, Jianting Dong, Jiahao Shentu, Jia Zhang
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Generation of mechanical cat-like states via optomagnomechanics
Hao-Tian Li, Hong-Bin Wang, Zi-Xu Lu et al. (+1 more)
We propose an optomagnomechanical approach for preparing a cat-like superposition state of mechanical motion. Our protocol consists of two steps and is based on the magnomechanical system where the magnetostrictively induced displacement further couples to an optical cavity mode via radiation pressure. We first prepare a squeezed mechanical state by driving the magnomechanical system with two microwave pulses. We then switch off the microwave drives and send a weak red-detuned optical pulse to the optical cavity to weakly activate the optomechanical anti-Stokes scattering. We show that $k$
phonons can be subtracted from the prepared squeezed thermal state, conditioned on the detection of $k$ anti-Stokes
photons from the cavity output field, which prepares the mechanical motion in a cat-like state. The work provides a new avenue for preparing mechanical superposition states by combining opto- and magnomechanics and may find applications in the study of macroscopic
quantum states and the test of collapse theories.
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All authors Hao-Tian Li, Hong-Bin Wang, Zi-Xu Lu, Jie Li
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Optomagnonic generation of entangled travelling fields with different polarizations
Zi-Xu Lu, Huai-Bing Zhu, Xuan Zuo et al. (+1 more)
The optomagnonic coupling between
magnons and optical
photons is an essential component for building remote
quantum networks based on magnonics. Here we show that such a coupling, manifested as the
magnon-induced Brillouin light scattering, can be exploited to entangle two propagating optical fields. The protocol employs two pairs of the whispering gallery modes coupled to the same
magnon mode in a YIG sphere. In each pair a strong pump field is applied to activate either Stokes or anti-Stokes scattering. Due to the
magnon mode involving in the two scattering processes and as a mediation, Stokes and anti-Stokes
photons of different polarizations get entangled. The
entanglement can be extracted by filtering the travelling output fields centered at the Stokes and anti-Stokes sidebands. Optimal conditions are identified under which strong output
entanglement can be achieved.
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All authors Zi-Xu Lu, Huai-Bing Zhu, Xuan Zuo, Jie Li
Mesoscale and Nanoscale Physics
Cascade of topological phase transitions and revival of topological zero modes in imperfect double helical liquids
Anna Ohorodnyk and Chen-Hsuan Hsu
Two parallel helical edge channels hosting interacting electrons, when proximitized by local and nonlocal pairings, can host time-reversal-invariant pairs of topological zero modes at the system corners. Here we show that realistic imperfections substantially enrich the physics of such proximitized double helical
liquids. Specifically, we analyze this platform and its fractional counterparts in the presence of pairing and interaction asymmetries between the two channels, as well as random
spin-flip terms arising from either
magnetic disorder or coexisting charge disorder and external
magnetic fields. Using renormalization-group analysis, we determine how Coulomb interactions, pairings, and
magnetic disorder collectively influence the transport behavior and topological properties of the double helical
liquid. As the system now belongs to class BDI, an additional topological phase supporting a single Majorana zero mode per corner emerges. We further show how additional pairing or Coulomb asymmetry influences the stability of various topological phases and uncovers a revival of Majorana zero modes and cascades of successive topological transitions through topological phases characterized by a $\mathbb {Z}$ invariant, which are accessible through controlling the electrical screening effect. We also analyze the spatial structure of the zero modes and the bulk gap closing through channel-resolved density profiles, revealing observable features through scanning tunneling microscope. In contrast to conventional understanding, disorder is not merely detrimental, as it in general allows for a tuning knob that qualitatively reshapes the topological superconductivity in imperfect helical
liquids.
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Materials Science
Spin Orientation Driven Polarization in Collinear Magnets
Yixun Zhang, Longju Yu, Yizhou Tong et al. (+4 more)
In a collinear magnet, the predominant
magnetic moments are collectively aligned along a specific spatial orientation, and this
alignment may yield intriguing phenomena such as
spin orientation driven polarization. It is well known that
spin orientation driven polarization is a relativistic effect that widely occurs in various type-II multiferroics. However, a universal theory that describes such a phenomenon and directs the corresponding materials discovery is lacking. Here, we revisit the
magnetic structures of collinear magnets and explore the
spin-orientation-dependent phenomena therein. Based on
symmetry principles, we analyze the
spin point groups (SPGs) that are associated with collinear magnets in the non-relativistic regime, demonstrate how relativistic
spin-orbit interaction reduces each SPG to various
magnetic point groups that are associated with different
magnetic alignments, and classify the SPGs with respect to
spin orientation driven polarization. We employ our theory to elucidate the mechanisms of
spin orientation driven polarization in a variety of type-II multiferroics. Combined with first-principles simulations, we further show that polarization may be driven in nonpolar collinear antiferromagnets (e.g., CuFeS$_2$) by reorienting their
magnetic alignments. Our theory provides guidelines for designing and discovering materials with
spin orientation driven polarization, which will benefit the development of spintronics based on type-II multiferroics and related materials.
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All authors Yixun Zhang, Longju Yu, Yizhou Tong, Ying Sun, Xu Li, Hong Jian Zhao, Yanming Ma
Materials Science
Fresnel Magnetic Imaging of Ultrasmall Skyrmion Lattices
Yongsen Zhang, Wei Liu, Meng Shi et al. (+9 more)
Magnetic skyrmions with ultrasmall nanometric dimensions hold significant promise for next-generation high-density spintronic devices. Direct real-space imaging of these topological
spin textures is critical for elucidating their emergent properties at the nanoscale. Here, we present Lorentz transmission electron microscopy studies of nanometric skyrmion
lattices in B20-structured Mn0.5Fe0.5Ge
crystals using Fresnel mode. According to conventional
chiral discrimination methods relying on static bright-dark contrast, we demonstrate an abnormal periodic
chiral-reversal phenomenon retrieved through the transport of intensity equation analysis of defocus-dependent Fresnel images. Through systematic off-axis electron holography experiments and numerical simulations, we attribute these
chiral misinterpretations to the sinusoidal modulation mechanism of the contrast transfer functionthat correlates with both defocus values and skyrmion dimensions. Our findings establish quantitative limitations of conventional Fresnel contrast analysis for ultrasmall skyrmions while revealing fundamental insights into defocus-mediated phase-to-intensity conversion processes in nanoscale
magnetic imaging.
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All authors Yongsen Zhang, Wei Liu, Meng Shi, Yaodong Wu, Jialiang Jiang, Sheng Qiu, Huanhuan Zhang, Hui Han, Mingliang Tian, Haifeng Du, Shouguo Wang, Jin Tang
Materials Science
Infusing Experimental Reality into Complex Many-Body Hamiltonians: The Observable-Constrained Variational Framework (OCVF)
Shaoliang Guo and Ziping Yang
Deep learning potentials for complex many-body systems often face challenges of insufficient accuracy and a lack of physical realism. This paper proposes an "Observable-Constrained Variational Framework" (OCVF), a general top-down correction paradigm designed to infuse physical realism into theoretical "skeleton" models (H_o) by imposing constraints from macroscopic experimental observables (\mathfrak{O}_{\text{exp},s}). We theoretically derive OCVF as a numerically tractable extension of the "Constrained-Ensemble Variational Method" (CEVM), wherein a neural network (\Delta H_\theta) learns the correction functional required to match the experimental data. We apply OCVF to BaTiO3 (BTO) to validate the framework: a neural network potential trained on DFT data serves as H_o, and experimental PDF data at various temperatures are used as constraints (\mathfrak{O}{\text{exp},s}). The final model, H_o + \Delta H_\theta, successfully predicts the complete phase transition sequence accurately (s', s \neq s'). Compared to the prior model, the accuracy of the Cubic-Tetragonal (C-T) phase transition temperature is improved by 95.8% , and the Orthorhombic-Rhombohedral (O-R) T_c accuracy is improved by 36.1%. Furthermore, the
lattice structure accuracy in the Rhombohedral (R) phase is improved by 55.6%, validating the efficacy of the OCVF framework in calibrating theoretical models via observational constraints.
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Quantum Gases · Cross-listed from quant-ph
Tunable discrete quasi-time crystal from a single drive
Xu Feng, Shuo Liu, Shu Chen et al. (+1 more)
The search for exotic temporal orders in
quantum matter, such as discrete quasi-time
crystals (DQTCs), has become an important theme in nonequilibrium physics. However, realizing these phases has so far required complex protocols, such as drives with multiple incommensurate frequencies. Here, we present a significantly simpler mechanism: the emergence of DQTCs in a dissipative collective
spin system subjected to only a single periodic drive. Remarkably, the characteristic frequencies of this novel phase are not fixed but can be continuously tuned by varying the strength of the drive. Even more strikingly, this tunability is punctuated by Arnold tongues, within which the response main frequency locks to rational fractions of the drive. Our model further provides a unified framework that also encompasses stationary, discrete time
crystals and chaotic phases. This discovery simplifies the requirements for generating complex temporal orders and opens a viable route towards the experimental control and manipulation of quasi-time crystalline matter.
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All authors Xu Feng, Shuo Liu, Shu Chen, Shi-Xin Zhang
Materials Science
Development of a Ferromagnetic Resonance Measurement System Using NanoVNA
Reo Fukunaga, Ryunosuke Takahashi, Tetsuro Ueno et al. (+3 more)
Ferromagnetic resonance (FMR) is a fundamental technique for probing magnetization dynamics in spintronic and
magnetic materials. However, conventional FMR measurements rely on broadband vector network analyzers (VNAs), whose high cost limits accessibility for small laboratories and educational environments. To overcome this barrier, we have developed a compact and low-cost FMR measurement platform - the NanoVNA-FMR system-based on a commercially available NanoVNA. The setup integrates an electromagnet and a coplanar waveguide (CPW) and is fully automated using Python scripts. This enables synchronized
magnetic-field sweeping, S-parameter acquisition, and real-time visualization. The system successfully captures clear FMR spectra that exhibit systematic shifts in resonance frequency with increasing
magnetic field. The results are in excellent agreement with those obtained using a conventional VNA-based FMR system, confirming the quantitative reliability of the NanoVNA approach. Additionally, a 3D-printed sample holder further reduces overall system cost. These results demonstrate that the NanoVNA-FMR system provides a practical, accurate, and accessible alternative for quantitative
magnetic characterization and educational applications.
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All authors Reo Fukunaga, Ryunosuke Takahashi, Tetsuro Ueno, Hiroki Shoji, Yoshihiko Togawa, Hiroki Wadati
Superconductivity
Geometric Control of Pairing: Universal Scaling of Superconductivity at KTaO3 Interfaces
Xueshan Cao, Meng Zhang, Yishuai Wang et al. (+3 more)
The superconducting transition temperature Tc at KTaO3-based
oxide interfaces exhibits a dramatic dependence on crystallographic orientation, yet a unifying principle has remained elusive. Here, we discover a universal linear scaling between Tc and a single
geometric parameter - the angle {\theta} between the (hkl) plane and the (100) plane - across ten different orientations of LaAlO3/KTaO3 interfaces. With the exception of (100), all orientations exhibit two dimensional superconductivity, with transition temperatures Tc ranging from ~ 0.12 K to 1.9 K. This linear {\theta}-Tc scaling is robust against variations in growth temperature, device geometry, and transport configuration. By establishing
geometric orientation as a direct control knob for pairing strength, our results impose a critical
benchmark for microscopic theories of superconductivity in KTaO3-based systems.
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All authors Xueshan Cao, Meng Zhang, Yishuai Wang, Ming Qin, Yi Zhou, Yanwu Xie
Strongly Correlated Electrons
Anomalous Hall effect and rich magnetic phase diagram of Mn$_{100-x}$Rh$_{x}$ epitaxial films
Cong Wang, Zheng Li, Jing Meng et al. (+7 more)
A series of Mn$_{100-x}$Rh$_x$ ($20 \le x \le 50$) thin films were epitaxially grown on the MgO substrate using magnetron sputtering technique, and were systematically investigated by magnetization, longitudinal electrical resistivity, and transverse
Hall resistivity. After optimizing the growth conditions, phase-pure Mn$_{100-x}$Rh$_x$ films with a cubic CsCl-type structure were obtained, and their
magnetic phase diagram was built. The manipulation of Rh content leads to a rich
magnetic phase diagram, where three different regimes can be identified: for $x < 40$, Mn$_{100-x}$Rh$_x$ films undergo a
ferromagnetic (FM) transition below $T_\mathrm{C} \approx$ 330-350 K; for $40 \le x \le 45$, in addition to the FM transition at $T_\mathrm{C} \approx$ 200 K, Mn$_{100-x}$Rh$_x$ films undergo a FM-to-
antiferromagnetic (AFM) transition at $T_\mathrm{N} \approx$ 120 K; finally for $x > 45$, only one AFM transition at $T_\mathrm{N} \approx$ 150 K can be tracked. All the Mn$_{100-x}$Rh$_x$ films exhibit distinct anomalous
Hall effect in their magnetically ordered state, which is most likely due to the intrinsic Berry-
curvature mechanism. In addition, all the anomalous
Hall transport properties, including the resistivity, conductivity, and angle exhibit a strong correlation with the
magnetic properties of Mn$_{100-x}$Rh$_x$ films, which become most evident for $x$ = 35. Our systematic investigations suggest a strong correlation between
magnetic properties and electronic band
topology in Mn$_{100-x}$Rh$_x$ films, highlighting their great potential for AFM spintronics.
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All authors Cong Wang, Zheng Li, Jing Meng, Hui Zhang, Haoyu Lin, Jiyuan Li, Kun Zheng, Yang Xu, Tian Shang, Qingfeng Zhan
Strongly Correlated Electrons
Investigating the origin of topological-Hall-like resistivity in Zn-doped Mn2Sb ferrimagnet
BoCheng Yu, JiaLiang Jiang, Jing Meng et al. (+7 more)
Skyrmions and other
chiral spin textures have been extensively studied as potential building blocks for novel spintronic devices.
Hall-resistivity anomalies that deviate from magnetization scaling, known as the topological
Hall effect, have been widely employed as evidence for the presence of
chiral spin textures in
magnetic materials. However, recent studies on
magnetic thin films have revealed a drawback of this approach, as the presumed topological
Hall contribution may in fact originate from trivial mechanisms. Here, we investigate the
magnetic and transport properties of a Zn-doped Mn2Sb ferrimagnet, whose related compounds have previously been suggested to exhibit a topological
Hall effect arising from
chiral spin textures.
Hall-resistivity anomalies are also observed in our sample, yet they show little correlation with the
magnetic or metamagnetic transitions and are therefore clearly distinct from those in
magnetic compounds hosting
chiral spin textures. Most importantly, additional Lorentz transmission electron microscopy measurements rule out the existence of
chiral spin textures in this ferrimagnet. Therefore, instead of a nontrivial origin, we attribute the
Hall-resistivity anomalies to the combined effect of multiple anomalous
Hall channels resulting from sample inhomogeneity. Our work shows that the difficulties of identifying
chiral spin textures through transport measurements also apply to bulk systems, prompting some existing results to be revisited.
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All authors BoCheng Yu, JiaLiang Jiang, Jing Meng, XiaoYan Zhu, Jie Ma, HaiFeng Du, QingFeng Zhan, Jin Tang, Yang Xu, Tian Shang
Materials Science
Defects Engineering of ZrTe5 for Stabilizing Ideal Topological States
Chia-Hsiu Hsu, Zezhi Wang, Sen Shao et al. (+6 more)
ZrTe5 is a highly tunable, high-mobility topological material that hosts a rich variety of
quantum phenomena, making it a promising platform for next-generation
quantum technologies. Despite intensive research efforts, experimental studies have reported inconsistent and sometimes conflicting results for its electronic and topological states, largely due to variations in sample quality. Here, through systematic frst-principles investigations of all intrinsic point defects, we identify a practical route to achieving stable and ideal topological characteristics in ZrTe5. We show that the competition between two dominant charged defects, donor-like Zr interstitials and acceptor-like Te vacancies, governs the
Fermi-level position. Furthermore, variations in defect density determine the topological phases of the samples. We theoretically propose and experimentally confrm that increasing the Te/Zr ratio during
crystal growth effectively suppresses intrinsic defects and stabilizes ZrTe5 in a nearly ideal weak topological
insulator state. These fndings provide clear guidance for defect control and sample optimization, paving the way toward robust and reproducible realization of topological
quantum states in ZrTe5 for future
quantum applications.
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All authors Chia-Hsiu Hsu, Zezhi Wang, Sen Shao, Yoshinori Okada, Feng-Chuan Chuang, Dong Xing, Ilya Belopolski, Cheng-Long Zhang, Guoqing Chang
Mesoscale and Nanoscale Physics
Stable skyrmion bundles at room temperature and zero magnetic field in a chiral magnet
Yongsen Zhang, Jin Tang, Yaodong Wu et al. (+5 more)
Topological
spin textures are characterized by topological
magnetic charges, Q, which govern their electromagnetic properties. Recent studies have achieved skyrmion bundles with arbitrary integer values of Q, opening possibilities for exploring topological spintronics based on Q. However, the realization of stable skyrmion bundles in
chiral magnets at room temperature and zero
magnetic field - the prerequisite for realistic device applications - has remained elusive. Here, through the combination of pulsed currents and reversed
magnetic fields, we experimentally achieve skyrmion bundles with different integer Q values - reaching a maximum of 24 at above room temperature and zero
magnetic field - in the
chiral magnet Co8Zn10Mn2. We demonstrate the field-driven annihilation of high-Q bundles and present a phase diagram as a function of temperature and field. Our experimental findings are consistently corroborated by micromagnetic simulations, which reveal the nature of the skyrmion bundle as that of skyrmion tubes encircled by a fractional Hopfion.
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All authors Yongsen Zhang, Jin Tang, Yaodong Wu, Meng Shi, Xitong Xu, Shouguo Wang, Mingliang Tian, Haifeng Du
Mesoscale and Nanoscale Physics
Deterministic Electrical Control of Single Magnetic Bubbles in Nanostructured Cells
Jialiang Jiang, Yaodong Wu, Lingyao Kong et al. (+10 more)
Localized particle-like
spin textures have been found to exhibit emergent electromagnetic properties, which hold promise for the development of intriguing spintronic devices. Among these textures,
magnetic bubbles represent localized
spin configurations that could serve as data bits. However, the precise methods for their electrical manipulation remain uncertain. Here, we demonstrate the deterministic electrical manipulations and detections of single
magnetic bubbles in kagome-latticed Fe3Sn2
magnetic nanostructured
cells. The current-induced dynamics of
magnetic bubbles were explored using nanosecond pulsed currents. We show single pulsed currents with low and high densities can be applied for the creation and deletion of a single bubble, respectively. The mutual writing-deleting operations on single bubbles are attributed to the thermal heating and non-thermal
spin-transfer torque effects in combination with micromagnetic simulations. We also realized the in-situ detection of a single bubble using the anisotropic magnetoresistance effect through a standard four-probe method. Our results could propel the development of bubble-based spintronic devices.
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All authors Jialiang Jiang, Yaodong Wu, Lingyao Kong, Yongsen Zhang, Sheng Qiu, Huanhuan Zhang, Yihao Wang, Junbo Li, Yimin Xiong, Shouguo Wang, Mingliang Tian, Haifeng Du, Jin Tang