Materials Science
Discovering structural, electronic and excitonic properties of bulk, nanostructured and doped C3N4 in diamond- and graphitic-like phases
Da Chen, Pietro Andreozzi, Giulia Frigerio et al. (+3 more)
In this systematic density functional theory study, we compare a standard gradient corrected functional (PBE) with a long-range hybrid functional (HSE06), with and without correction for the dispersion forces, relative to their ability to correctly reproduce structural and electronic properties of different bulk 3D C3N4 phases, encompassing diamond- and graphitic-like models. Corrugation is found to provide further stabilization to the layered structures with all methods. We observe that HSE06-D3 method provides results in good agreement with experimental data and with more sophisticated G0W0 calculations. Based on that, we exploited the method to investigate the nature of the bulk triplet
excitons in these C3N4 structures to evaluate the S0-T1 energy difference, the self-trapping triplet
exciton energy and the photoluminescence emission energy since this is a promising visible-light photocatalyst. Nanostructuring (0D and 2D) is another relevant aspect of these materials in practical applications; therefore, we have considered the effect of single- or multilayer exfoliation or space confinement in nanoparticles. Finally, we also discuss how the introduction of extrinsic dopants (e.g., S atoms) in the nanostructures modifies the atomic and electronic structure.
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All authors Da Chen, Pietro Andreozzi, Giulia Frigerio, Daniele Perilli, Paulo Siani, Cristiana Di Valentin
Disordered Systems and Neural Networks
Understanding jump discontinuity in disordered system
Anjan Daimari and Diana Thongjaomayum
The response of a complex system to a slow varying external force often displays a jump discontinuity in the order parameter near the critical point. However, this discontinuity is not usually a single jump but rather breaks into smaller jumps which makes it difficult to locate the critical point on approaching its vicinity based only on simulations, in the absence of exact results. Our work is a small effort in understanding these breaks in jump through the hysteretic response of a classical Ising
spin system to an external field, $h$, in the context of a nonequilibrium zero-temperature random field Ising model on dilute systems. We consider a Bethe
lattice with coordination number, $z = 4$, and dilute a fraction $(1-c)$ of the sites. Therefore the
lattice now consists of sites with varying $z = 4, 3, 2, 1$ and possibly few isolated sites $(z=0)$, depending on the concentration $c$. We obtain the exact solution of the magnetization curve, $m(h)$ vs $h$, for the entire
lattice as well as for each sublattice of different $z$ coordinated sites, $m_4(h), m_3(h), m_2(h), m_1(h), m_0(h)$. The discontinuity in total magnetization is the result of the superposition of the jumps of different $z$ coordinated sites and observed at the same value of external field, $h_{crit}$. The dominant contribution to the jump comes from those sites with higher concentration and larger $z$. However, the triggering sites responsible for large jumps are mostly $z\ge3$. We test this on cubic
lattices as well, where exact results are not available. We hope our analysis will help in understanding fluctuations around a jump in numerical simulations as well as experiments.
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Materials Science
Pattern formation during melting of lamellar eutectics
Rahul Nellissery Rajan, Rajesh Kumari Rajendran, Guillaume Boussinot et al. (+3 more)
We present a study of the melting dynamics of a two-phase eutectic solid. In situ, thin-sample experiments using a transparent eutectic
alloy and two-dimensional phase field simulations calibrated for the very same
alloy are combined to assess pattern formation during directional melting in a temperature gradient. Depending on the melting velocity $V_m$ and the spacing $\lambda$ of the pre-solidified lamellar microstructure, an unexpectedly rich diversity of melting patterns is observed, with good agreement between experiments and simulations. We unravel the different physical mechanisms leading to this diversity, and establish the scaling behaviors of (i) the penetration of the
liquid along the solid-solid interface at large $V_m$, (ii) the thickening of the primary-phase fingers at low $V_m$, and (iii) a period-doubling instability for small $\lambda$ values. Our study provides a fundamental basis for further investigations of eutectic melting, including additive manufacturing during which melting/solidification cycles take place.
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All authors Rahul Nellissery Rajan, Rajesh Kumari Rajendran, Guillaume Boussinot, Kamal Sbargoud, Sabine Bottin-Rousseau, Silvère Akamatsu
Mesoscale and Nanoscale Physics
Layer-dependent quantum transport in KV2Se2O-based altermagnetic tunnel junctions
Yue Zhao, Bin Xiao, Jiawei Liu et al. (+2 more)
Magnetic tunnel junction (MTJ) is the key component to enable information access and increasing number of MTJs is integrated to develop high-density spintronic devices. However, continuous miniaturization of the conventional MTJs is hindered by stray
magnetic fields. Altermagnets, combining the advantages of both ferromagnets and antiferromagnets, provide a promising alternative to fabricate versatile MTJs with exotic properties, such as
giant spin splitting, high intrinsic frequency, and absence of stray fields. Inspired by the altermagnetic metal candidate KV2Se2O reported recently, we design an altermagnetic tunnel junction (AMTJ) based on KV2Se2O/SrTiO3/KV2Se2O. Using density functional theory combined with non-
equilibrium Green's function, we investigate the layer-dependent
quantum transport properties and the tunneling magnetoresistance (TMR) of such AMTJ device. Our calculated results reveal that the transmission of the AMTJ device exhibits a pronounced oscillation behavior dependent on the number of layers of the SrTiO3
semiconductor, which is attributed to the interface configuration determined by parity of the layer number. In odd-layer devices, the electron-rich O-Se interface exhibits a smooth effective potential and enables transverse momentum (k||) transport channels, leading to enhanced transmission. In contrast, in even-layer devices, the Ti-Se interface presents a steeper effective potential, impeding
quantum transport through transverse momentum (k||) channels. A
giant TMR of 4.6*10^7% is predicted to be realized by using a 4-layer SrTiO3. Our findings not only provide physical understanding relevant to the
quantum transport in AMTJs, but also unveil that the barrier interface engineering is a strategy to tune the magnetoelectric performance.
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All authors Yue Zhao, Bin Xiao, Jiawei Liu, Hui Zeng, Jun Zhao
Mesoscale and Nanoscale Physics
Weak Magnetic Sensing via Floquet Driving in an Active Cavity Magnon Coupled System
Fan Yang, Xudong Wang, Lijun Yan et al. (+4 more)
While significant advancements have been made in weak
magnetic field detection, conventional high-sensitivity techniques are often limited by requirements for cryogenic operation or bulky setups. In this work, we develop a sensitive alternating
magnetic field sensor based on a coupled system of an active microwave cavity and yttrium iron garnet (YIG), with the components implemented on printed
circuit boards (PCBs). By introducing electrically tunable gain to compensate for cavity losses, we substantially improve both the quality factor and the signal intensity. Under the coupled system, Floquet modulation is induced by the alternating
magnetic field, allowing for weak field detection by driving a specific hybrid mode and measuring the resulting Floquet sidebands. This miniaturized device operates at room temperature, achieving a detection limit of 121 pT/\sqrt{Hz}.
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All authors Fan Yang, Xudong Wang, Lijun Yan, Yue Zhao, Jinwei Rao, Lihui Bai, Shishen Yan
Mesoscale and Nanoscale Physics
Formalizing Poisson-Boltzmann Theory for Field-Tunable Nanofluidic Devices
Zhongyuan Zhao, Chudi Qi, Yuheng Li et al. (+3 more)
Nanofluidic devices support unconventional ion transport appealing to energy and information technologies, thanks to the susceptibility of confined electric double layers (EDLs) to various external physical fields. Although experimental studies advance rapidly, the rationalization of field-tunable nanofluidic transport has not reached a formalized and unified level. Here we reformulate the Poisson-Boltzmann theory and reveal distinct EDL regimes on the parameter space. Based on the regime classification, we establish a formal framework for the tunable nanofluidic transport and discuss the electrostatic modulation (ionic transistor) extensively. The framework reproduces the observed conductivity-concentration scaling behaviors, rationalizes the ionic transistors with reconfigurable polarities, and predicts one fundamental thermodynamic limit for electrostatic modulation (60 mV/dec). Being accurate, generalizable and extensible, this framework can account for a wide range of ion transport in confined spaces.
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All authors Zhongyuan Zhao, Chudi Qi, Yuheng Li, Shoushan Fan, Qunqing Li, Yang Wei
Materials Science
Spin-Valley-Mismatched Altermagnet for Giant Tunneling Magnetoresistance
Kun Yan, Yizhi Hu, Wei-Hua Xiao et al. (+3 more)
Altermagnet-based heterojunctions have demonstrated magnetoresistive effects in experiments, however, a predictive theoretical model for non-
ferromagnetic structures has remained elusive. In this work, we develop a tunneling-based
spin-transport theory that explicitly incorporates the transverse-wavevector ($\bf{k}_\|$)-dependent
spin polarization of an altermagnet's transport channels, enabling the prediction of
giant tunneling magnetoresistance (TMR). Based on the theory, we predict that the altermagnet KV$_2$Se$_2$O can reach the extreme limit of magnetoresistance. By performing first-principles transport calculations, we verify that
magnetic tunnel junctions using the metallic KV$_2$Se$_2$O as the electrodes and few-layer MgO as the spacer exhibit zero-bias magnetoresistance larger than $7.57\times10^7$%, which is robust against the bias and thickness of the spacer. Our research provides a quantitative design principle for next-generation
spin-electronic devices and establishes KV$_2$Se$_2$O/MgO/KV$_2$Se$_2$O as a leading candidate material system for room-temperature ultra-high-density non-volatile
memory.
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All authors Kun Yan, Yizhi Hu, Wei-Hua Xiao, Xiaolong Zou, Xiaobin Chen, Wenhui Duan
Statistical Mechanics · Cross-listed from physics.soc-ph
A convex-geometric framework for fully phase-locked states in the finite Kuramoto model
Antonio Garijo, Sergio Gómez and Alex Arenas
We study the finite-size Kuramoto model of all-to-all coupled phase oscillators with heterogeneous natural frequencies and characterize the minimal coupling strength required for the existence of a fully phase-locked
equilibrium (in a co-rotating frame). To remove the degeneracy due to uniform phase shifts, we move to a reduced co-rotating frame and assess stability through the Jacobian of the reduced system: a fully phase-locked state is stable when this Jacobian is negative definite. This defines a stability region in the phase space. The Kuramoto vector field maps this region to a convex set in frequency space, so a fully-locked state at coupling $K$ exists exactly when the rescaled frequency vector $\hat{\mathbf{\omega}}/K$ lies inside that convex image. The critical coupling $K_{\ell}$ is defined as the smallest coupling strength for which a fully phase-locked
equilibrium exists; geometrically, it corresponds to the first intersection of the ray $t\hat{\mathbf{\omega}}$ with the boundary of this convex set. Building on this convex-
geometric structure, we construct an explicit polytope from analytically computable boundary points of the stability region, providing a closed-form upper bound $K_b \ge K_{\ell}$. The bound is exact for frequencies aligned with polytope vertices and offers a fully explicit outer approximation for general frequency vectors. While not uniformly sharp in a quantitative sense, this construction exposes the underlying geometry of stable fully phase-locking solutions. These results provide a practical use the convex-
geometric structure underlying stable fully-locked states in the Kuramoto model.
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Quantum Gases
Mean-field phase diagrams of spinor bosons in an optical cavity
Maksym Prodius, Mateusz Łącki and Jakub Zakrzewski
The plethora of possible ground states of spinor
bosons placed in an external
lattice and a cavity is revisited. We discuss the simplest configuration when the external
lattice nodes coincide with the antinodes of the cavity field. We analyze the problem within the grand-canonical mean-field approach, considering both the homogeneous system and the nonhomogeneous case with a harmonic trapping potential. Due to the
spin degree of freedom, in the homogeneous case, we treat the system in a twofold manner: we impose the physically relevant total-magnetization constraint, while also discussing the minimization landscape for the full unconstrained problem. In the latter, by combining analytical arguments with numerical calculations based on the Gutzwiller ansatz, we show that the system exhibits two types of
magnetic phases: an
antiferromagnetic Mott
insulator (AFM) and a
ferromagnetic density wave (FDW). In addition, two distinct supersolid phases emerge, characterized by different patterns of
spin and density imbalances. In the case of zero total magnetization, the FDW phases are replaced by charge density waves (CDWs) that lack net
magnetic ordering. Finally, we establish the phase diagram of the trapped system, providing direct guidance for future experiments.
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Mesoscale and Nanoscale Physics
Thermal conductivity tuning of scalable nanopatterned silicon membranes measured with a three-probe method
Jose M. Sojo-Gordillo, Alex Rodriguez-Iglesias, Dominik M. Koch et al. (+5 more)
Phononic silicon structures have emerged as an integrable and scalable nanosystem for tailoring thermal transport. However, their widespread adoption has been limited by their complex fabrication pathways. Alongside, the reliable characterization of thermal properties in suspended nanostructured films remains challenging, as thermal contact resistances often hinder the accuracy of measurements. In this work, we demonstrate a clear and controllable reduction of thermal conductivity in nanopatterned silicon membranes. A block copolymer self-assembly approach is employed to fabricate nanoholed silicon films with a pitch of 63 nm and hole diameters of 35 nm. Additionally, we introduce an extension of the three-probe technique that enables robust, quantitative, and spatially resolved thermal conductivity measurements in complex thin-film systems, accounting for thermal contact artifacts. The method is validated through measurements on unpatterned 40 nm-thick silicon thin films between 30 and 350 K, yielding a room-temperature thermal conductivity of 46.5 W/m.K. Finally, we further show that controlled etching of the nanoholes provides a powerful means to tune thermal transport in the overall studied temperature range, establishing hole etch depth control as an effective parameter in phononic silicon. Specifically, a fivefold reduction in thermal conductivity is achieved, reaching 7.3 W/m.K for fully etched-through membranes at room temperature.
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All authors Jose M. Sojo-Gordillo, Alex Rodriguez-Iglesias, Dominik M. Koch, Arianna Nigro, Iñigo Martin-Fernandez, Marta Fernandez-Regulez, Marc Salleras, Ilaria Zardo
Strongly Correlated Electrons
Nontrivial three-sublattice magnetization in the easy-axis spin-1/2 XXZ antiferromagnet on the triangular lattice
Masahiro Kadosawa, Masaaki Nakamura, Yukinori Ohta et al. (+1 more)
We investigate the ground-state
magnetic structure of the
spin-$1/2$ XXZ antiferromagnet on the triangular
lattice in the easy-axis regime using the density-
matrix renormalization group. By applying spiral boundary conditions, we exactly map finite $L\times L$ clusters onto one-dimensional chains while avoiding the spatial anisotropy inherent in cylindrical geometries. From
symmetry-broken local magnetization profiles, we extract the three-sublattice moments and track their
evolution with anisotropy. At the isotropic point, we obtain a positive sublattice moment of $0.217(3)$, consistent with previous numerical estimates. In the easy-axis regime ($\Delta=J_z/J_\perp>1$), the ordered moments remain close to a Y-like zero-magnetization three-sublattice state, whose $z$-component pattern is of the form $(2m,-m,-m)$, over a broad range of $\Delta$. Extrapolation in $1/\Delta$ shows that the positive sublattice moment stays well below the classical saturation value $1/2$, approaching $0.419(7)$ as $\Delta\to\infty$, while the magnitude of the negative sublattice moment approaches $0.209(4)$. We further compare the energies of the Y state and the up-down-down state and find that the Y state is favored at zero field. Independent thermodynamic-limit energy calculations, performed without assuming any particular ordered pattern, yield an energy consistent with the Y-state solution. These results show that the easy-axis ground state does not simply cross over to a trivially saturated collinear Ising state, but instead remains a nontrivial three-sublattice ordered state selected from the macroscopically degenerate Ising
manifold by
quantum fluctuations.
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All authors Masahiro Kadosawa, Masaaki Nakamura, Yukinori Ohta, Satoshi Nishimoto
Materials Science
Nonmagnetic-magnetic Transitions in Rutile RuO2
Yue-Fei Hou, Siyuan Liu, Wanxiang Fen et al. (+4 more)
Rutile RuO$_2$ has recently attracted great interest, as its
magnetic ground state remains controversial. Experimental studies have reported either nonmagnetic (NM) or altermagnetic (AM) ground states in different crystalline samples of RuO$_2$, highlighting the need for a reasonable explanation to resolve this contradiction. In this study, density functional theory calculations are performed to reveal the correlation-sensitive and strain-dependent magnetism of bulk RuO$_2$. On one hand, multiple AM phases with different magnitudes of the
spin magnetic moment are identified in the Hubbard parameter space for RuO$_2$. On the other hand, when appropriate strains that significantly change the
crystal cell volume are applied, the ground state of RuO$_2$ can undergo transitions between the NM state (with no
spin splitting) and the
magnetic states (with
spin splitting in the band structure). These findings not only demonstrate intriguing physics in 4\textit{d}-electron-correlated RuO$_2$, but also retain its potential for spintronic applications.
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All authors Yue-Fei Hou, Siyuan Liu, Wanxiang Fen, Jiajun Lu, Xinfeng Chen, Gui-Bin Liu, Ping Zhang
Materials Science
Morphological Transition: From Meanders to Mound Structures
Marta A. Chabowska, Hristina Popova and Magdalena A. Załuska-Kotur
Mound formation on flat and miscut
crystal surfaces exhibits distinct growth behaviors. While mound structures are the predominant feature on flat surfaces, miscut surfaces display a smooth transition from meandered patterns to three-dimensional mounds, depending on both internal and external conditions. We investigate this morphological
evolution-from meander-like surface patterns to faceted pyramidal structures-using a Vicinal Cellular Automaton modeling framework. The transition is shown to be governed by the competition between the Ehrlich-Schwoebel barrier and adatom mobility on terraces. Under moderate barrier strengths and sufficiently high terrace diffusivity, the system demonstrates a reversible transition from mounded configurations to regular step meandered patterns. This reveals a complex interplay between kinetic barriers and mass transport. Our simulations cover a wide range of growth conditions, including variations in deposition flux, surface
diffusion rates, temperature, and miscut angle. By applying the height-height correlation function, we calculate the correlation lengths along and across the steps and analyze their scaling behavior. These results offer insight into the continuum pathways that connect distinct classes of surface structures and provide a unified framework for describing pattern
evolution across different
crystal growth regimes.
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Mesoscale and Nanoscale Physics
Orbitals of Artificial Atoms in a Gapped Two-Dimensional Vacuum
Mong-Wen Gu, Aizhan Sabitova, Taner Esat et al. (+4 more)
Advances in nanotechnology now allow the creation of artificial atoms - engineered structures whose electronic states closely mimic those of real atoms. Understanding how these artificial atoms interact and bond is key to designing new materials with tailored electronic properties. Here, we use scanning tunnelling microscopy to visualise the bound states of nanostructures patterned in a two-dimensional molecular film featuring a
parabolic band with multiple partial energy gaps. The lowest-energy states split off from the bottom of the band and resemble the familiar $s$ and $p$ orbitals of natural atoms, even bonding in the same way. Yet, artificial atoms go beyond this analogy: the gapped two-dimensional
vacuum in which they reside gives rise to entirely new orbitals with no counterparts in real atoms. These quasi-one-dimensional localised states enrich the orbital vocabulary of chemistry, adding a new class of orbitals that are predominantly shaped by the surrounding electronic
vacuum.
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All authors Mong-Wen Gu, Aizhan Sabitova, Taner Esat, Christian Wagner, F. Stefan Tautz, Aleksandr Rodin, Ruslan Temirov
Other Condensed Matter
J. Fransson
Indirect long range interactions between localized
magnetic moments are in metals mediated by itinerant electrons. In
insulators and semi-conductor, such interactions need to be small, if not negligible, due to the absence of mediating carriers. The existence of magnetically ordered
insulators, for instance, metal-
oxides, is therefore an everlasting source for proposals of various mechanisms that may support the order. Here,
phonon mediated interactions between localized
magnetic moments is considered as a mechanism that can provide quantifiable symmetric and anti-symmetric anisotropic
spin-
spin interactions. It is demonstrated that while a symmetric anisotropic interaction exists for all types of
phonons, the existence of anti-symmetric anisotropic interactions requires broken inversion
symmetry. The latter mechanism may explain the weak
ferromagnetic order observed in
chiral, e.g., CuO and CoO compounds. Furthermore, the interaction is nearly independent of the temperature at low temperature while approaches a linear growth at high. Spatially, the interactions have an oscillatory power law decay with the inter-
nuclei distance.
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Quantum Gases · Cross-listed from quant-ph
Spectroscopic measurement of the Casimir-Polder force in the intermediate regime
K. Ton, G. Kestler, D. A. Steck et al. (+1 more)
The Casimir-Polder (CP) effect – the force between a neutral atom and an uncharged conducting plate in empty space – is an intriguing consequence of
quantum vacuum fluctuations. The typically attractive CP potential crosses over from a scaling of $z^{-3}$ at short separations to $z^{-4}$ at long distances, where retardation effects due to the finite speed of light become important. At intermediate distances, where the atom–surface separation is of the order of the wavelength of the dominant atomic transition, experiments have so far relied on indirect methods, such as diffraction or
quantum reflection, to observe the CP effect. Here, we directly reveal the CP force between strontium atoms and a dielectric surface via the induced shifts in the atomic energy levels in the intermediate regime. We spectroscopically probe the CP-induced kHz-frequency shift of ultracold atoms confined by a magic-wavelength optical
lattice at 189(2)~nm from the surface – on the scale of the dominant 461-nm transition. Our measurements agree well with QED calculations and differ from the short-range approximation, while excluding the long-distance one. This paves the way for studying the CP effect across various surface properties and geometries, as well as exploring the tensor nature of the atom-surface potential – all important for the development of hybrid atomic optical-
magnetic quantum devices.
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All authors K. Ton, G. Kestler, D. A. Steck, J. T. Barreiro
Disordered Systems and Neural Networks · Cross-listed from cs.AI
The Agentification of Scientific Research: A Physicist's Perspective
Xiao-Liang Qi
This article argues that the most important significance of the AI revolution, especially the rise of large
language models, lies not simply in automation, but in a fundamental change in how complex information and human know-how are carried, replicated, and shared. From this perspective, AI for Science is especially important because it may transform not only the efficiency of research, but also the structure of scientific collaboration, discovery, publishing, and evaluation. The article outlines a gradual path from AI as a research tool to AI as a scientific collaborator, and discusses how AI is likely to fundamentally reshape scientific publication. It also argues that continuous learning and diversity of ideas are essential if AI is to play a meaningful role in original scientific discovery.
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Superconductivity
Interlayer hybridization enables superconductivity in bilayer nickelates
Shilong Zhang, Meng Zhang, Qilin Luo et al. (+10 more)
Ruddlesden-Popper nickelates offer a new route to high-temperature superconductivity beyond the cuprates and iron-pnictides. However, the electronic reorganization that enables superconductivity in
bilayer nickelates remain unresolved, largely due to the difficulty of directly probing the superconducting phase. Here, we overcome this limitation by stabilizing superconducting (La,Pr)$_3$Ni$_2$O$_7$ thin films with a protective capping layer, thereby enabling direct spectroscopic access via X-ray absorption and resonant inelastic X-ray scattering. We resolve the
evolution of in-plane and out-of-plane electronic states,
spin and orbital excitations, and
spin-density-waves across insulating, superconducting, and metallic regimes. Combining experimental results with theoretical analysis, we show that the in-plane $d_{x^2-y^2}$ states form an itinerant backbone, while superconductivity emerges only when coherent $d_{z^2}$-$p_z$-$d_{z^2}$ interlayer hybridization develops, accompanied by suppressed static
spin order and strongly damped
spin excitations. Oxygen stoichiometry and epitaxial strain both act on this interlayer channel, placing superconductivity within a narrow window of interlayer coherence and correlation strength. These findings identify the microscopic ingredients required for superconductivity in
bilayer nickelates and provide a multiorbital picture of its emergence.
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All authors Shilong Zhang, Meng Zhang, Qilin Luo, Zihao Tao, Hsiao-Yu Huang, Kunhao Li, Ganesha Channagowdra, Jie Li, Junchi Fu, Di-Jing Huang, Yanwu Xie, Yi Lu, Yingying Peng
Strongly Correlated Electrons
Level statistics of the disordered Haldane-Shastry model with $1/r^\alpha$ interaction
Vengatesan Ganapathy, Pranay Patil and Ajit C. Balram
Understanding how the interaction range and various types of disorder affect the level statistics of many-body
quantum systems, leading to the emergence of many-body localization (MBL), is a challenging open frontier. We study the level statistics of a variant of the
spin-$1/2$ Haldane-Shastry model with $1/r^{\alpha}$ interactions, where $\alpha{\geq}0$ parametrizes the range of the interactions, in the presence of position disorder and/or random
magnetic fields. We find that neither position disorder nor random
magnetic fields alone yields pristine Poisson statistics in this system; however, Poisson statistics emerge in their combined presence, suggesting the emergence of MBL when both types of disorder coexist. Interestingly, once random
magnetic fields break the $SU(2)$
symmetry, the strength of the position disorder, $\delta$, appears to play an important role, as evidenced by an approximate scaling collapse of the disorder-averaged gap ratios that is parametrized in terms of a single parameter, $\alpha \delta$.
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Materials Science
Anomalous Platinum and Oxygen Transport during Electroforming of NbOx Memristors
Shimul Kanti Nath, Sanjoy Kumar Nandi, Xiao Sun et al. (+9 more)
Electroforming of metal-
oxide-metal memristors is generally attributed to the creation of oxygen-vacancy filaments within the
oxide, with noble metal electrodes such as Pt and Au remaining chemically inert. Here, we demonstrate that electroforming and subsequent operation of Pt/NbOx/Nb2O5/Pt devices can induce an unexpected and highly correlated redistribution of both oxygen and platinum. Time-of-flight secondary ion mass spectrometry reveals a filamentary pathway characterized by micrometer-scale oxygen enrichment extending from the Nb2O5 layer through NbOx and deep into the Pt top electrode. Surprisingly, this is accompanied by the formation of a Pt-rich filament penetrating the
oxide stack along the same filamentary path. Finite-element and lumped-element modelling show that current-controlled negative-differential-resistance operation produces localized Joule heating and high-frequency thermal cycling, which strongly enhances oxygen migration and enables thermally assisted Pt
diffusion along vacancy-rich pathways. These findings reveal a previously unrecognized metal-ion transport mechanism in NbOx memristors and highlight the critical role of post-forming electrical dynamics in determining filament chemistry, stability, and device reliability.
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All authors Shimul Kanti Nath, Sanjoy Kumar Nandi, Xiao Sun, Sujan Kumar Das, Bin Gong, Nicholas J. Ekins-Daukes, Deepak Mishra, Mahesh P. Suryawanshi, William D. A. Rickard, Songyan Yin, Michael P. Nielsen, Robert G. Elliman
Mesoscale and Nanoscale Physics
Effect of Rashba spin-orbit coupling on Faraday rotation in an extended Haldane model
Yuan Fang, Yixiang Wang and Xiaopu Zhang
Utilization of Faraday rotation (FR) properties of topological materials offers a promising route toward novel magneto-optical devices. We systematically investigated the effect of Rashba
spin-orbit coupling (SOC) on FR spectra in an extended Haldane model, which incorporates Rashba SOC and exchange splitting into the original spinless Haldane framework. Using the Kubo formalism, we calculated the FR spectra across the model's rich topological phase diagram. We found that in the Chern number C=2 region, in the absence of exchange splitting, the FR angle can exceed 4$^\circ$ and its peak position is tunable by the Rashba SOC. In contrast, with the inclusion of exchange splitting, a nearly flat FR profile emerges over a broad frequency range, and the FR peak values increase monotonically with the Rashba SOC strength. The Rashba SOC opens additional transition channels, whose net contribution constructively enhances the FR peak. Furthermore, we derived a low-energy effective
Hamiltonian expanded up to quadratic terms, the results of which are in good agreement with tight-binding model calculations, thereby validating our numerical results. Our findings suggest that magneto-optical device characteristics can be designed and optimized through Rashba SOC engineering.
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Superconductivity
Quantum Landscape of Superconducting Diodes
Muhammad Nadeem and Xiaolin Wang
This study maps the
quantum landscape of superconducting diodes (SDs) \cite{nadeem23} onto the
quantum technology architecture, which is currently constrained by fundamental challenges in control and scalability. In the existing non-integrated
quantum technology hardware, control and scalability related issues emerge at two fronts: First, nonlinear and nonreciprocal
circuit elements, which are essential building blocks for
quantum processors, are often complex, bulky, and dissipative. Second, the temperature gradient between classical control electronics ($T_C\gtrsim$ K), which is also dissipative, and the
quantum processor at cryogenic temperatures ($T_Q\sim$ mK) makes scalability even more challenging. The main focus is to reveal how the built-in nonlinearity, nonreciprocity, and
quantum functionalities of SDs are significant for on-chip integrated
circuit quantum electrodynamics (c-QED), enabling scalable integration of noise-resilient
qubit and
qubit-interfaces for efficient power delivery, coherent control and
memory, high-fidelity readout, and
quantum-limited amplification. To this end, this study will also shed light on how thermodynamic constraints and field effects can be harnessed within a
quantum-enhanced SD platform, thereby enabling thermal compatibility between classical and
quantum workflows, isothermal all-electrical control, and on-chip scalability. This perspective is expected to play a pivotal role in the advancement of superconducting
circuit-based
quantum hardware with temperature-matched classical,
quantum, and hybrid workflows.
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Soft Condensed Matter
Absence of solid phase in dense amorphous active granular matter
Cunyuan Jiang
Solid phase of dense granular matter is inevitable because of jamming transition when the packing fraction or the pressure suffered is high enough. The experiment suggests that active Brownian granular matter will keep fluid phase even under the highest packing fraction (higher than the packing fraction of crystallization) if crystallization is prevented by mixing granular particles of different sizes. The findings encourage us to reconsider the role of activity in affecting the global dynamical properties of matter.
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Superconductivity
Wide-field magnetic imaging of shielding-current-driven vortex rearrangement under local heating using diamond quantum sensors
Ryoei Ota, Shunsuke Nishimura, Koki Honda et al. (+6 more)
Understanding and controlling
vortex motion in
superconductors are important both for suppressing dissipation in superconducting devices and for device applications that exploit
vortices. In this work, we quantitatively imaged the stray
magnetic field distribution of
vortices in an NbN thin film by wide-field
magnetic imaging using a perfectly aligned diamond nitrogen-vacancy ensemble. By continuously measuring while stepwise varying the applied
magnetic field under local
laser heating, we captured a rearrangement of the
vortex configuration in real space and in real time over more than 100 min. The observed
vortex rearrangement is consistent with a reduction of the pinning force due to local
laser heating and with the Lorentz force exerted by shielding currents induced by the field variation. These results provide insight into
vortex dynamics and suggest potential applications, including
vortex exclusion from sensitive regions of superconducting devices.
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All authors Ryoei Ota, Shunsuke Nishimura, Koki Honda, Takeyuki Tsuji, Taro Yamashita, Takayuki Iwasaki, Mutsuko Hatano, Kento Sasaki, Kensuke Kobayashi
Soft Condensed Matter
Persistent Free Volume Governs (Anti)plasticization in Chitosan-Water Mixtures
Baris E. Ugur and Michael A. Webb
Chitosan is a highly versatile and sustainable
polymer with a broad range of potential biological and materials engineering applications. Despite its versatility, the native brittleness of chitosan limits its broader utilization. This limitation can be addressed by blending chitosan with small-molecule additives to modulate its thermomechanical properties. We employ molecular dynamics (MD) simulations to investigate the mechanism underlying antiplasticization followed by plasticization at increasing water content. Decomposition of the elastic
moduli reveals a competition between weakened
polymer-
polymer interactions and enhanced
polymer-water interactions, with their relative strengths governing the resulting properties. We introduce a simple model incorporating dynamically accessible free volume regions as a key driver of
polymer mobility, effectively capturing the (anti)plasticization of elastic properties. We show that accessibility of free volume regions is enabled by connectivity of additive-accessible volume regions. This study provides new insights into the molecular interactions that dictate the properties of chitosan-water mixtures and may inform the rational design of chitosan-based materials and other hydrated biopolymers.
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Materials Science
First-principles study of infrared, Raman, piezoelectric and elastic properties of Mg-IV-N\textsubscript{2} (IV = Ge, Si, Sn)
Sarker Md. Sadman and Walter R. L. Lambrecht
Mg-IV-N\textsubscript{2} compounds with IV=Si, Ge, Sn are ultra-wide band gap
semiconductors with various potential electronic and optoelectronic applications. They share the Pna2\textsubscript{1} space group
crystal structure. Here we present Density Function Perturbation Theory (DFPT) calculations of the vibrational modes of these materials. We focus on the vibrational modes at the zone center to establish the relation between vibrational modes and their corresponding point-group
symmetries, which determine the Raman and infrared spectra but also report the full Brillouin zone
phonon dispersions and density of states. We also determine the piezoelectric tensor and the elastic compliance tensor.
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Strongly Correlated Electrons
Discovery of an odd-parity f-wave charge order in a kagome metal
Jiangchang Zheng, Caiyun Chen, Ruiqin Fu et al. (+13 more)
The spontaneous breaking of
symmetries is a cornerstone of physics, defining the phases of matter from the cosmological scale to the
quantum realm. In condensed matter, electronic orders are classified by their behavior under fundamental
symmetries like spatial inversion (parity). While even-parity orders, such as conventional superconductivity and charge density waves, are ubiquitous, their odd-parity counterparts–predicted to host exotic phenomena such as gapless quasiparticle excitations and novel collective modes–are comparatively elusive states of
quantum matter. Here, using high-resolution scanning tunneling microscopy and angle-resolved photoemission spectroscopy on the kagome metal CsV$_3$Sb$_5$, we report the discovery of an inversion
symmetry-breaking $f$-wave charge bond order. We show that this phase, which preserves translation
symmetry, is stabilized by the spontaneous opening of a spectral gap at a previously overlooked Dirac point, providing a textbook condensed-matter realization of the Gross-Neveu model for dynamical mass generation and parity breaking. Intriguingly, this $f$-wave order is itself a intervening phase, vanishing abruptly below a temperature of 10\,K and pointing to a subsequent transition into a `hidden' electronic state that is invisible to local STM probes. Our findings establish odd-parity charge order as a novel phase of matter, here, embedded within the intricate hierarchy of correlated electronic orders on the kagome
lattice.
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All authors Jiangchang Zheng, Caiyun Chen, Ruiqin Fu, Luca Buiarelli, Zihan Lin, Fazhi Yang, Tianhao Guo, Ganesh Pokharel, Andrea Capa Salinas, Sen Zhou, Turan Birol, Stephen D. Wilson, Junzhang Ma, Daniel J. Schultz, Xianxin Wu, Berthold Jäck
Strongly Correlated Electrons
The Two Orbital, Interacting Hatano-Nelson Model
Jonah Huang, Rubem Mondaini, Nancy Aggarwal et al. (+1 more)
The single orbital, one-dimensional, Hatano-Nelson
Hamiltonian provides deep insight into the physics of non-Hermiticity, resulting from asymmetric left/right hopping, and its connections to localization. In the absence of disorder, its single particle
eigenvalues $E_{\alpha}$ lie on an ellipse in the complex plane whose extent in the imaginary direction is controlled by the degree of asymmetry. When randomness is introduced, two sets of real
eigenvalues emerge at the extremes of the largest and smallest real part of $E_{\alpha}$. These real
eigenvalues are associated with localized eigenvectors. For spinless
fermions, increasing near-neighbor interactions first cause a transition to a charge density wave phase, and ultimately, on finite
lattices, a collapse of all
eigenvalues to the real axis. In this paper, we explore the presence of real
eigenvalues in the interacting, two-particle sector for the spinful case (Hubbard model) in a two-chain (two-band) geometry with a Hermitian interchain hopping. Our key results are to obtain the “phase" diagrams for the existence of a purely real spectrum, as a function of the interaction strength, degree of non-Hermiticity, and interchain hopping. We study the sensitivity to boundary conditions of the spectral properties of our two-chain model with winding number analysis and explore the relationship between PBC doublon states and OBC skin modes. To address the question of stability in such non-
equilibrium systems, we solve the dynamics at low filling according to Lindbladian
evolution and find that the non-Hermitian description is able to qualitatively describe such systems.
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All authors Jonah Huang, Rubem Mondaini, Nancy Aggarwal, Richard Scalettar
Quantum Gases
Solitonic Solutions of the One-Dimensional Harmonically Trapped Repulsive Bose-Einstein Condensate via Neural Network Quantum States
Gaoqing Meng and Mingshu Zhao
We demonstrate the existence of bright
solitons in a repulsively interacting, harmonically trapped quasi-one-dimensional Bose-Einstein condensate described by the Gross-Pitaevskii equation. Using a neural-network
quantum state (NNQS) approach, we parametrize the initial wavefunction and optimize it to find solutions that recur after one trap period, effectively balancing repulsion with trap-induced attraction. Aside from the bright solitonic solution, we also report double bright and dark
soliton states. Perturbing the initial state with multiplicative phase and amplitude noise confirms that these periodic orbits are orbitally stable. Our results indicate that NNQS provides a powerful framework for uncovering coherent structures in nonlinear wave systems.
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Mesoscale and Nanoscale Physics
Josephson phase shift and diode effect due to the inverse spin Hall effect
Gen Tatara, Yositake Takane and Aurelien Manchon
We theoretically study the direct and inverse
spin Hall effects in a
superconductor-normal metal-uperconductor junction induced by a
spin-orbit interaction that is invariant under spatial inversion. We show that a supercurrent induces a
spin Hall effect, leading to a static
spin accumulation with opposite polarizations at the two edges, analogous to that in normal conductors. For the inverse effect, we consider a spatially inhomogeneous static
magnetic field and show that it induces an anomalous phase shift, which, in the presence of higher harmonics, results in a diode effect. Unlike Rashba systems studied previously, the present mechanism does not require broken structural inversion
symmetry, since an inhomogeneous
magnetic field, equivalent to a
spin current, breaks the inversion
symmetry extrinsically.
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