Statistical Mechanics
Universal classical and quantum fluctuations in the large deviations of current of noisy quantum systems: Quantum symmetric simple exclusion and inclusion processes
Mathias Albert, Denis Bernard, Tony Jin et al. (+2 more)
We study the fluctuation statistics of integrated currents in noisy
quantum diffusive systems, focusing on the
Quantum Symmetric Simple Exclusion and Inclusion Processes (QSSEP/QSSIP). These one-dimensional fermionic (QSSEP) and bosonic (QSSIP) models feature
stochastic nearest-neighbor hopping driven by Brownian noise, together with boundary injection and removal processes. They provide solvable microscopic settings in which
quantum coherence coexists with
diffusion. Upon noise averaging, their dynamics reduce to those of the classical SSEP/SSIP. We show that the cumulant-generating function of the integrated current, at large scales, obeys a large deviation principle. To leading order in system size and for each noise realization, it converges to that of the corresponding classical process, establishing a classical typicality of current fluctuations in these noisy
quantum systems. We further demonstrate a direct connection with Macroscopic Fluctuation Theory (MFT), showing that the large-scale equations satisfied by biased
quantum densities coincide with the steady-state Hamilton equations of MFT, thereby providing a microscopic
quantum justification of the MFT framework in these models. Finally, we identify the leading finite-size corrections to the current statistics. We show the existence of subleading contributions of purely
quantum origin, which are absent in the corresponding classical setting, and provide their explicit expressions for the second and third current cumulants. These
quantum corrections are amenable to direct experimental or numerical verification, provided sufficient control over the noise realizations can be achieved. Their presence points toward the necessity of a
quantum extension of MFT.
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All authors Mathias Albert, Denis Bernard, Tony Jin, Stefano Scopa, Shiyi Wei
Mesoscale and Nanoscale Physics
Interaction Induced Magnetotransport in a 2D Dirac-Heavy Hole Hybrid Band System
G. M. Gusev, A. D. Levin, V. A. Chitta et al. (+2 more)
While electron-electron (e-e) interactions are known to influence resistivity in non-Galilean invariant two-dimensional (2D) systems, their effect on magnetotransport is not fully understood. Conventional models for simple bands often predict a vanishing magnetoresistivity from e-e interactions alone. In this work, we investigate magnetotransport in a gapless 6.3 nm HgTe
quantum well, a hybrid 2D band system that hosts coexisting holes with both linear (Dirac-like) and
parabolic energy bands. Focusing on the high temperature regime where particle-particle collisions dominate scattering, we observe significant corrections to both the magnetoresistivity and the
Hall effect. The high temperature transport coefficients are in good agreement with the theoretical model describing transport in massive-massless
fermion mixtures governed by a frictional mechanism and intervalley scattering. Our findings provide strong experimental validation for this theoretical framework, demonstrating that collisions between particles with different dispersions are a key mechanism governing magnetotransport in hybrid band semimetals.
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All authors G. M. Gusev, A. D. Levin, V. A. Chitta, Z. D. Kvon, N. N. Mikhailov
Mesoscale and Nanoscale Physics
Magnetosomes in Nature, Biomedicine and Physics
N.A. Usov
Magnetotactic bacteria synthesize linear chains of magnetite nanoparticles within their bodies, which allow the bacteria to navigate the Earth's
magnetic field in search of the best habitat. Biogenic magnetite particles, called magnetosomes, are very promising for use in biomedicine. Magnetosome chains have also been found in ancient fossils and sediments. The study of magnetofossils provides valuable information about the Earth's biological past. The presence of biogenic magnetite in ancient rock samples can be detected by measuring
ferromagnetic resonance spectra, first-order magnetization reversal curves, or quasi-static hysteresis loops. Theoretical analyses of these experiments generally assume that magnetosomes are spherical nanoparticles, although the shape of some types of magnetosomes is close to spheroidal one. In this work, simple formulas for describing the magneto-dipole interaction of oriented spheroids are obtained and quasi-static hysteresis loops of randomly oriented magnetosome chain assembly consisting of elongated spheroids are calculated.
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Statistical Mechanics
Statistical mechanics of a 2D material in a gas reservoir
Moon-ki Choi and Ellad B Tadmor
We derive and validate a partition function for low-dimensional systems interacting with a heat bath, addressing the general issue of thermodynamic modeling of nanoscale systems. In contrast to bulk systems in the canonical (NVT) ensemble where the partition function is solely determined by the
Hamiltonian of the system and the temperature of the heat bath, our formulation demonstrates that accounting for the interactions with the heat bath is essential for describing the statistical mechanics of low-dimensional materials. To validate our theoretical findings, we develop a molecular dynamics (MD)
algorithm for directly modeling the heat bath as a gas reservoir. We first validate our approach using a 1D harmonic oscillator, calculating its length distribution through explicit numerical integration and confirming these results with MD simulations. We then extend our method to investigate the out-of-plane fluctuations of a 2D
graphene monolayer immersed in a gas at finite temperature and pressure. Comparisons with conventional NVT ensemble simulations controlled by a thermostat reveal that environmental interactions significantly influence the properties of the 2D material system.
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Materials Science
Charting the Landscape of Oxygen Ion Conductors: A 60-Year Dataset with Interpretable Regression Models
Seong-Hoon Jang, Shin Kiyohara, Hitoshi Takamura et al. (+1 more)
Oxygen ion conductors are indispensable materials for such as solid
oxide fuel
cells, sensors, and membranes. Despite extensive research across diverse structural families, systematic data enabling comparative analysis remain scarce. Here, we present a curated
dataset of oxygen ion conductors compiled from $84$ experimental reports spanning $60$ years, covering $483$ materials. Each record includes activation energy ($E_a$) and prefactor ($A$) derived from Arrhenius plots, alongside detailed metadata on structure, composition, measurement method, and data source. When the original papers derive these using an erroneous Arrhenius equation $\sigma_T=A\exp{\left(-\frac{E_a}{RT}\right)}$, where ($\sigma_T$ is the oxygen ion conductivity at temperature $T$ and $R$ is the gas constant), we replotted these using the correct one, $\sigma_{T}T=A\exp{\left(-\frac{E_a}{RT}\right)}$. To illustrate how the database can be used, we constructed interpretable regression models for predicting oxygen ionic conductivity. Two symbolic regression models for E_a and A suggest that oxygen ion transport is primarily governed by local coordination environment and the electrostatic interactions, respectively. This
dataset establishes a reliable foundation for data-driven discovery and predictive modeling of next-generation oxygen ion conductors.
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All authors Seong-Hoon Jang, Shin Kiyohara, Hitoshi Takamura, Yu Kumagai
Mesoscale and Nanoscale Physics
Twisted bilayer graphene from first-principles: structural and electronic properties
Albert Zhu, Daniel Bennett, Daniel T. Larson et al. (+3 more)
We present a comprehensive first-principles study of twisted
bilayer graphene (tBLG) for a wide range of twist angles, with a focus on structural and electronic properties. By employing density functional theory (DFT) with an optimized local basis set, we simulate tBLG, obtaining fully relaxed commensurate structures for twist angles down to 0.987{\deg}. For all angles the
lattice relaxation agrees well with continuum elastic models. For angles accessible to plane-wave DFT (VASP), we provide a detailed comparison with our local basis DFT (SIESTA) calculations, demonstrating excellent agreement in both the atomic and electronic structure. The dependence of the
Fermi velocity and band width on the twist angle shows qualitative agreement with results from an `exact' $\mathbf{k \cdot p}$ continuum model, but reveals a small twist angle offset. Additionally, we provide details of the low-energy wavefunction character, band inversion and
symmetries. Our results provide an ab initio reference point for the microscopic structure and electronic properties of tBLG which will serve as the foundation for future studies incorporating many-body effects.
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All authors Albert Zhu, Daniel Bennett, Daniel T. Larson, Mohammed M. Al Ezzi, Efstratios Manousakis, Efthimios Kaxiras
Strongly Correlated Electrons
Intermediate Field Spin(on) Dynamics in $\alpha$-RuCl$_3$
C.L. Sarkis, K.D. Dixit, P. Rao et al. (+11 more)
We present comprehensive inelastic
neutron spectroscopic maps of the
magnetic field-induced disordered phase of the Kitaev
quantum spin liquid candidate material $\alpha$-RuCl$_3$. For fields along both in-plane high-
symmetry directions we observe that the
spin excitation spectrum at and above a
magnetic field of 8~T is gapped. Excitation modes then sharpen for increasing field but are consistently broader than experimental resolution even at 13.5~T. The out-of-plane dispersion diminishes in the 7-10~T regime, signifying enhanced two-dimensional behavior as the in-plane
liquid correlations are established. In this regime, excitations are very broad and largely flat for all accessible energy-momenta, which is kinematically at odds with a
magnon-decay picture. By contrast, a continuum of fractionalized excitations naturally yields a broad continuum response, which crucially may be accompanied by sharper modes of bound states of fractionalized excitations. Their damping by the continuum accounts for the observed spectral broadening and field dependence. Our results provide strong evidence for the existence of fractionalized excitations in $\alpha$-RuCl$_3$ in a
magnetic field.
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All authors C.L. Sarkis, K.D. Dixit, P. Rao, G. Khundzakishvili, C. Balz, J-Q. Yan, B. Winn, T.J. Williams, A. Unnikrishnan, R. Moessner, D.A. Tennant, J. Knolle, S.E. Nagler, A. Banerjee
Superconductivity
Superconducting density of states and vortex lattice of LaRu$_2$P$_2$ observed by Scanning Tunneling Spectroscopy
Marta Fernández-Lomana, Paula Obladen Aguilera, Beilun Wu et al. (+3 more)
We provide the superconducting density of states of the iron based
superconductor LaRu2P2 (Tc= 4.1 K), measured using millikelvin Scanning Tunneling Microscopy. From the tunneling conductance, we extract a density of states which shows the opening of a s-wave single superconducting gap. The temperature dependence of the gap also follows BCS theory. Under
magnetic fields,
vortices present Caroli de Gennes Matricon states, although these are strongly broadened by defect scattering. From the
vortex core size we obtain a superconducting coherence length of {\xi} = 50 nm, compatible with the value extracted from macroscopic Hc2 measurements. We discuss the comparison between s-wave LaRu2P2 and pnictide unconventional multiple gap and strongly correlated Fe based
superconductors.
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All authors Marta Fernández-Lomana, Paula Obladen Aguilera, Beilun Wu, Edwin Herrera, Hermann Suderow, Isabel Guillamón
Superconductivity
Pressure-induced superconductivity in topological insulator Ge2Bi2Te5 and the evolution with Mn doping
Shangjie Tian, Qi Wang, Yuqing Cao et al. (+5 more)
Introducing superconductivity (SC) or magnetism into topological
insulators (TIs) can give rise to novel
quantum states and exotic physical phenomena. Here, we report a high-pressure transport study on the TI Ge2Bi2Te5 and its Mn-doped counterparts. The application of pressure induces a SC in Ge2Bi2Te5, which shows a dome-shape phase diagram with the maximum Tc of 7.6 K at 23 GPa. Doping Mn into Ge2Bi2Te5 introduces an
antiferromagnetic order at ambient pressure and strongly weakens the pressure-induced SC, demonstrating that magnetism and SC compete in this material system. Present study provides a new platform for investigating the interplay among band
topology, magnetism, and SC.
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All authors Shangjie Tian, Qi Wang, Yuqing Cao, Ying Ma, Xiao Zhang, Yanpeng Qi, Hechang Lei, Shouguo Wang
Strongly Correlated Electrons
Non-Abelian fusion and braiding in many-body parton states
Koyena Bose
Fractional
quantum Hall (FQH) states host fractionally charged anyons with exotic exchange statistics. Of particular interest are FQH phases supporting non-Abelian anyons, which can encode topologically protected
quantum information. In this work, we construct quasihole bases for a broad family of non-Abelian FQH states using parton wave functions, which reproduces the fusion-space dimensionality expected from their underlying conformal field theory, consistent with level-rank duality across the parton family. As an application, we numerically compute braiding
matrices for representative parton states for large systems, providing a general framework for diagnosing non-Abelian characteristics in candidate FQH states.
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Quantum Gases
One-dimensional asymmetrically interacting quantum droplets in Bose-Bose mixtures
Huiyun Xiao, Xinran Zhang, Junli Liu et al. (+3 more)
We theoretically investigate ground-state properties and collective excitations of one-dimensional
quantum droplets in asymmetric Bose-Bose mixtures with unequal intraspin interactions. Using the extended Gross-Pitaevskii equation supported by variational, sum-rule, and linearization methods, we show that the intraspin interaction ratio substantially alters the droplet's density profile, driving a transition from Gaussian-like to flat-top shapes. By examining two experimentally relevant parameter regions, we analyze density profiles, radii, peak densities, and excitation spectra to distinguish
quantum phases and to depict phase diagrams in the space of asymmetric interaction ratio and total atom number. We carefully study the frequencies of both well-known dipole and breathing modes and less-explored
spin-dipole and
spin-breathing modes. The breathing-mode frequency decreases monotonically with interaction ratio, approaching asymptotically the result of a conventional weakly interacting Bose gas. It varies nonmonotonically with total atom number, peaking at a critical point that highlights the crucial role of
quantum fluctuations. In contrast,
spin modes display distinct temporal
spin density distributions and reveal in-phase and out-of-phase relative dynamics between components. Their frequencies depend instead monotonically on the interaction ratio and atom number. Our results provide a comprehensive understanding of asymmetric
quantum droplets and link to experimentally accessible regimes in ultracold $^{39}$K atomic gases.
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All authors Huiyun Xiao, Xinran Zhang, Junli Liu, Xucong Du, Xiao-Long Chen, Yunbo Zhang
Strongly Correlated Electrons
Zoology of Altermagnetic-type Non-collinear Magnets on the Maple Leaf Lattice
Pratyay Ghosh and Ronny Thomale
We define unconventional non-collinear
magnetic ground states on the maple leaf
lattice (MLL) distinguished by the selective breaking or preservation of time reversal ($\mathcal{T}$) and parity ($\mathcal{P}$). Depending on the nature of $\mathcal{P}\mathcal{T}$-breaking, linear
spin-wave theory reveals momentum-dependent non-relativistic
magnon spin splitting at different high
symmetry points in the Brillouin zone. From a mean-field analysis of the Hubbard model at weak coupling, we reveal itinerant $\mathcal{P}$-preserving $q=0$ altermagnetic (A$l$M)-type order, while we expect $\mathcal{P}$-broken canted-$120^\circ$ A$l$M-type order at strong coupling. Our findings establish the MLL as a
prime platform for exploring phase transitions and frustration phenomena emanating from competing non-collinear A$l$M-type orders.
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Mesoscale and Nanoscale Physics · Cross-listed from physics.optics
Observation of polaritonic flat-band bound states in the continuum in a 2D magnet
Fuhuan Shen, Jiahao Ren, Zhiyi Yuan et al. (+5 more)
Flat-band bound states in the continuum (BICs) are topological states with suppressed group velocity and robustness against radiation loss, offering a powerful platform for the exploration of non-Hermitian, nonlinear, topological phenomena and device applications. Van der Waals (vdW) metasurfaces have recently emerged as promising candidates for sustaining BICs and hybridizing with material transitions. However, the realization of flat-band BICs remains elusive. Here, we experimentally demonstrate polaritonic high-order BICs on a wide-angle flat band utilizing a subwavelength metasurface made of a vdW magnet CrSBr. The large oscillator strength of direct
excitons in CrSBr enables near ultrastrong coupling with BICs, leading to strongly suppressed polaritonic angular dispersions. Remarkably, second-order polaritonic BICs become flat-band across a wide angular range, with corresponding Q factors exceeding 1500. Additionally, we find that these polaritonic BICs vanish in the transverse
magnetic configuration, while leading to fascinating surface
hyperbolic exciton-polaritons within the Reststrahlen band. Our findings underscore CrSBr as an exceptional platform for exploring flat-band photonics and polaritonics, paving the new avenue for advances in next-generation optical and
quantum technologies.
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All authors Fuhuan Shen, Jiahao Ren, Zhiyi Yuan, Kai Wu, Sai Yan, Kunal Parasad, Hai Son Nguyen, Rui Su
Materials Science
Unified First-Principles Formula for Time-Resolved ARPES Spectra of Coherent and Incoherent Excitons
Gianluca Stefanucci and Enrico Perfetto
Despite major experimental progresses in time-resolved and angle-resolved photoemission spectroscopy, a quantitative, microscopic framework for interpreting
exciton-induced modifications of electronic band structures – applicable even beyond the low-density limit – is still lacking. Here we close this gap by introducing a unified approach that links the dynamics of coherent and incoherent
excitons to distinct and experimentally observable excitonic sidebands. Our central result is a general, first-principles formula for time-resolved photoemission spectra, applicable across a broad range of temperatures, excitation densities, and pump-probe delays. This advance provides a predictive tool for quantitatively tracking excitonic dynamics in complex materials.
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Other Condensed Matter · Cross-listed from hep-lat
Z2 Lattice Gauge Theory on Non-trivial Topology and Its Quantum Simulation
Jiaqi Hu, Shu Tian, Xiaopeng Cui et al. (+3 more)
Wegner duality is essential for Z2
lattice gauge theory, yet the duality on non-trivial
topologies has remained implicit. We extend Wegner duality to arbitrary
topology and dimension, obtaining a new class of Ising models, in which
topology is encoded in non-local domain-wall patterns. Without the overhead of gauge constraints, simulating this model on an L*L
torus requires only L*L
qubits with two-body couplings, halving the conventional four-body coupled 2L*L
qubits, enabling full experimental realization of Z2
lattice gauge theory on near-term devices.
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All authors Jiaqi Hu, Shu Tian, Xiaopeng Cui, Rebing Wu, Man-Hong Yung, Yu Shi
Soft Condensed Matter
Negative Pressure and Cavitation Dynamics in Plant-like Structures
Olivier Vincent
It is well known that a solid (e.g. wood or rubber) can be put under tensile stress by pulling on it. Once a critical stress is overcome, the solid breaks, leaving an empty space. Similarly, due to internal cohesion, a
liquid can withstand tension (i.e. negative pressure), up to a critical point where a large bubble spontaneously forms, releasing the tension and leaving a void (the bubble). This process is known as cavitation. While water at negative pressure is metastable, such a state can be long-lived. In fact, water under tension is found routinely in the plant kingdom, as a direct effect of dehydration, e.g. by evaporation. In this chapter, we provide a brief overview of occurrences of water stress and cavitation in plants, then use a simple thermodynamic and fluid mechanical framework to describe the basic physics of water stress and cavitation. We focus specifically on situations close to those in plants, that is water at negative pressure nested within a structure that is solid, but porous and potentially deformable. We also discuss insights from these simple models as well as from experiments with artificial structures mimicking some essential aspects of the structures found within plants.
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Materials Science
Controlling Mixed Mo/MoS$_2$ Domains on Si by Molecular Beam Epitaxy for the Hydrogen Evolution Reaction
Eunseo Jeon, Vincent Masika Peheliwa, Marie Hrůzová Kratochvílová et al. (+2 more)
Molybdenum disulfide (MoS$_2$) is a prototypical layered transition-metal dichalcogenide whose electrocatalytic performance is governed by a delicate balance between crystallinity, defect density, and electronic conductivity. Here we report a systematic molecular beam epitaxy (MBE) study in which annealing temperature, deposition cycle number, and Mo/S thickness ratio were independently varied to control the structural and electronic properties of MoS$_2$ thin films. The successful epitaxial growth of atomically uniform MoS$_2$ directly on Si substrates enables strong interfacial coupling and efficient charge transfer, offering a viable route toward
semiconductor-integrated catalytic architectures. X-ray diffraction, Raman spectroscopy, and X-ray absorption analyses reveal that higher annealing temperatures and excessive deposition cycles enhance crystallinity but reduce edge-site density and electrical conductivity, leading to diminished hydrogen
evolution reaction (HER) activity. In contrast, intermediate cycle numbers and sulfur-deficient growth conditions yield
heterostructures composed of MoS$_2$ with residual metallic Mo and sulfur vacancies, which activate otherwise inert basal planes while providing conductive pathways. These defect-engineered films deliver the best catalytic performance, achieving overpotentials as low as -0.33 V at -10 mA cm$^{-2}$, enlarged electrochemical surface area (ECSA) up to 8.0 cm$^2$, and mass-based turnover frequencies exceeding 23 mmol H$_2$ g$^{-1}$ s$^{-1}$, more than double those of stoichiometric counterparts. Our findings establish sulfur stoichiometry and growth kinetics as powerful levers to tune the interplay between structural order and catalytic activity in MBE-grown MoS$_2$ and point toward a broader strategy for engineering layered catalysts at the atomic scale.
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All authors Eunseo Jeon, Vincent Masika Peheliwa, Marie Hrůzová Kratochvílová, Tim Verhagen, Yong-Kul Lee
Materials Science
Engineering the electronic structure of TiO$_2$ by transition metal doping: A First Principles DFT Study
Vikash Mishra, Shashi Pandey, Swaroop Ganguly et al. (+1 more)
By means of first-principles density-functional theory (DFT) calculations, we perform a comparative analysis of the electronic and
magnetic properties of transition metal-doped TiO$_2$. The electronic band gaps of Ti$_x$M$_{1-x}$O$_2$, where M represents 3d-transition metals such as Sc, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn have been determined using the PBE functional within the generalized-gradient approximation (GGA) scheme, and also using the hybrid HSE06 functional. In the context of pure TiO$_2$, the partial density of states (PDOS) reveals that the electronic band gap emerges between the O-2p and Ti-3d orbitals. It is suggested that the Ti-3d ($t_{2g}$) states play a more prominent role in bonding compared to the Ti-3d ($e_g$) states. We performed DFT calculations to investigate the impact of doping with other 3d transition metal atoms, leading to the emergence of
impurity states within the band gap. The hybridization between the oxygen 2p orbitals and the titanium 3d orbitals in TiO$_2$ is altered by the introduction of doping with 3d transition metals because of the change in the oxidation state of titanium, shifting from solely 4+ to a combination of 4+ and 3+ states. The calculation of
spin-polarized density demonstrates the emergence of
ferromagnetic properties, particularly in titanium dioxide doped with chromium (Cr), manganese (Mn), and iron (Fe) with large
magnetic moments. Our work demonstrates the significant impact of doping transition metals on TiO$_2$, allowing for the precise manipulation of electrical and
magnetic properties, and thus holds great potential for the development of
spin-based
memory devices with possible neuromorphic applications.
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All authors Vikash Mishra, Shashi Pandey, Swaroop Ganguly, Alok Shukla
Soft Condensed Matter
Shear-Induced Wobbling and Motility Suppression in Swimming Bacteria
Wei Feng, Fanglong Dang, Hao Luo et al. (+3 more)
The intricate wobbling motion of flagellated bacteria, characterized by the periodic precession of the
cell body, is a determinant factor in their motility and
navigation within complex fluid environments. While well-studied in quiescent fluids, bacterial wobbling under ubiquitous flow conditions remains unexplored. In this work, we investigate the wobbling dynamics of Escherichia coli swimming near surfaces under steady shear flow. Our experiments reveal that the wobbling amplitude intensifies with flow strength before reaching a plateau, with this amplification exhibiting a strong dependence on the swimming orientation relative to the flow direction. It turns out that the enhanced wobbling remains governed by the misalignment between the
cell body and the flagellar bundle. Furthermore, we observe that the wobbling frequency increases monotonically with flow strength, and that shorter bacteria exhibit more pronounced variations in both amplitude and frequency. By linking the wobbling motion to the intrinsic body-flagella misalignment, we attribute the flow-enhanced precession to a combination of shear- and chirality-induced torques acting on the flexible flagellar hook. This mechanical coupling ultimately suppresses the net migration velocity as the flow rate increases. These findings elucidate the elastohydrodynamic mechanisms by which shear flow modifies bacterial locomotion near surfaces, with implications for microbial transport in physiological and ecological environments.
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All authors Wei Feng, Fanglong Dang, Hao Luo, Alan C. H. Tsang, Yanan Liu, Guangyin Jing
Statistical Mechanics
What is nonequilibrium?
Christian Maes
Lecture notes on elements of nonequilibrium statistical mechanics: (1) a characterization of the nonequilibrium condition, largely by contrast to
equilibrium; (2) a retelling of some of the great performances of the more distant past, including the perspectives of Boltzmann and Onsager; and (3) more recent methods and concepts, from local detailed balance and the identification of
entropy fluxes to dynamical fluctuation theory, and the importance of dynamical activity.
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Materials Science
Control of helix orientation in chiral magnets via lateral confinement
Maurice Colling, Mariia Stepanova, Mario Hentschel et al. (+7 more)
Helimagnetic materials offer a versatile platform for
spin-based device concepts owing to their long-range, tunable spiral order. Here, we demonstrate controlled manipulation of the helimagnetic propagation vector q by geometrical confinement, using FeGe as a model Dzyaloshinskii-Moriya interaction (DMI)-driven
chiral magnet. Micromagnetic simulations based on the nonlinear sigma model reveal that open boundaries give rise to a
chiral surface twist acting as an effective surface anisotropy, which dictates the preferred helix orientation in the absence of magnetostatic shape effects. This geometry-induced anisotropy is quantitatively captured by an analytical model derived from the DMI boundary condition.
Magnetic force microscopy measurements on focused-ion-beam structured FeGe confirm the predicted orientation behavior and establish geometry-controlled helimagnetic order as a robust, tunable mechanism for steering DMI-stabilized
spin-spiral states. The concept provides a general route toward device-level control of
chiral magnetic order in non-centrosymmetric systems.
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All authors Maurice Colling, Mariia Stepanova, Mario Hentschel, Somasree Bhattacharjee, Erik Lysne, Kasper Hunnestad, Naoya Kanazawa, Yoshinori Tokura, Jan Masell, Dennis Meier
Materials Science
AI-enhanced discovery and accelerated synthesis of metal phosphosulfides
Javier Sanz Rodrigo, Nicholas A. Kryger-Nelson, Lena A. Mittmann et al. (+3 more)
Metal phosphosulfides have emerged as unique multifunctional materials, but they present unique synthesis challenges compared to more established material classes such as
oxides and nitrides. As a consequence, experimental development and theoretical understanding of phosphosulfides have focused on individual compounds rather than on accelerated broad-range exploration. In this work, we first evaluate the synthesizability and band gaps of 909 hypothetical ternary phosphosulfides by density functional theory. We find 19 previously unknown thermodynamically stable compounds, including the first Si- and Ge-based phosphosulfides. For rapid band gap prediction, we then develop a multi-fidelity machine learning model to translate semilocal density functional theory band gaps into experimentally calibrated band gaps. Importantly, we extend the accelerated material development workflow to the experimental domain by demonstrating a route to high-throughput synthesis and characterization of virtually any phosphosulfide material system. The method is based on thin-film combinatorial libraries and yields over 100 unique compositions in each experiment, enabling us to synthesize four distinct phosphosulfide compounds in only four combinatorial experiments without prior synthesis recipes and without compromising on material quality. Thus, we argue that accelerated materials development workflows combining theory, artificial intelligence, synthesis, and characterization can be viable even for experimentally challenging inorganic materials.
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All authors Javier Sanz Rodrigo, Nicholas A. Kryger-Nelson, Lena A. Mittmann, Eugène Bertin, Ivano E. Castelli, Andrea Crovetto
Mesoscale and Nanoscale Physics
Observation of an isolated flat band in the van der Waals crystal NbOCl$_2$
Changhua Bao, Vincent Eggers, Manuel Meierhofer et al. (+11 more)
Dispersionless electronic bands lead to an extremely high density of states and suppressed kinetic energy, thereby increasing electronic correlations and instabilities that can shape emergent ordered states, such as excitonic,
ferromagnetic, and superconducting phases. A flat band that extends over the entire momentum space and is well isolated from other dispersive bands is, therefore, particularly interesting. Here, the band structure of the van der Waals
crystal NbOCl$_2$ is revealed by utilizing photoelectron momentum microscopy. We directly map out an electronic band that is flat throughout the entire Brillouin zone and features a width of only $\sim$100 meV. This band is well isolated from both the conduction and remote valence bands. Moreover, the quasiparticle band gap shows a high tunability upon the deposition of caesium atoms on the surface. By combining the single-particle band structure with the optical transmission spectrum, the optical gap is identified. The fully isolated flat band in a van der Waals
crystal provides a qualitatively new testbed for exploring flat-band physics.
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All authors Changhua Bao, Vincent Eggers, Manuel Meierhofer, Jakob Helml, Lasse Münster, Suguru Ito, Leon Machtl, Sarah Zajusch, Giacomo Inzani, Ludwig Wittmann, Marlene Liebich, Robert Wallauer, Ulrich Höfer, Rupert Huber
Soft Condensed Matter
Simulation of the carbon dioxide hydrate-water interfacial energy
Jesús Algabaa Esteban Acuña, José Manuel Míguez, Bruno Mendiboure et al. (+2 more)
Carbon dioxide hydrates are ice-like nonstoichiometric inclusion solid compounds with importance to global
climate change, and gas transportation and storage. The thermodynamic and kinetic mechanisms that control carbon dioxide nucleation critically depend on hydrate-water interfacial free energy. Interfacial energies show large uncertainties due to the conditions at which experiments are performed. Under these circumstances, we hypothesize that accurate molecular models for water and carbon dioxide combined with computer simulation tools can offer an alternative but complementary way to estimate interfacial energies at coexistence conditions from a molecular perspective. We have evaluated the interfacial free energy of carbon dioxide hydrates at coexistence conditions (three-phase
equilibrium or dissociation line) implementing advanced computational methodologies, including the novel Mold Integration methodology. Our calculations are based on the definition of the interfacial free energy, standard statistical thermodynamic techniques, and the use of the most reliable and used molecular models for water (TIP4P/Ice) and carbon dioxide (TraPPE) available in the literature. We find that simulations provide an interfacial energy value, at coexistence conditions, consistent with the experiments from its thermodynamic definition. Our calculations are reliable since are based on the use of two molecular models that accurately predict: (1) The ice-water interfacial free energy; and (2) the dissociation line of carbon dioxide hydrates. Computer simulation predictions provide alternative but reliable estimates of the carbon dioxide interfacial energy. Our pioneering work demonstrates that is possible to predict interfacial energies of hydrates from a truly computational molecular perspective and opens a new door to the determination of free energies of hydrates.
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All authors Jesús Algabaa Esteban Acuña, José Manuel Míguez, Bruno Mendiboure, Iván M. Zerón, Felipe J. Blas
Soft Condensed Matter
Hard disks confined within a narrow channel
J. M. Brader, E. Di Bernardo and S. M. Tschopp
We employ inhomogeneous integral equation theory to investigate the
equilibrium properties of hard disks confined to a channel of width $L$ by hard parallel walls. If the channel width is narrowed below two disk diameters, then the system enters a quasi one-dimensional regime for which the particles cannot move past each other. In the limit when $L$ is equal to one particle diameter the system reduces to the one-dimensional bulk along the center of the channel. We study first the dimensional crossover properties of the inhomogeneous Percus-Yevick (PY) integral equation as $L$ is reduced and then investigate the behaviour of a quasi one-dimensional system as the packing of the particles is increased for a fixed value of $L$. We find that the inhomogeneous PY equation is highly accurate for situations of quasi one-dimensional confinement and that it predicts the onset of a structural transition to a zigzag state at higher packing. The excellent performance of this integral equation method and the ease with which it handles confinement-induced dimensional crossover is a consequence of the improved resolution which comes from treating explicitly the inhomogeneous two-body correlation functions.
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Materials Science
Microscopic Origin of Piezomagnetism in Mn$_3$Sn: A Dual Real- and $k$-Space Picture
Soichiro Kikuchi, Yuki Yanagi, Thi Ngoc Huyen Vu et al. (+1 more)
We present a comprehensive first-principles study on the origin of the piezomagnetic effect in the non-collinear antiferromagnet Mn$_3$Sn, a material known for exhibiting a large anomalous
Hall effect. We investigate strain-induced variations of electronic and
magnetic states and elucidate the mechanism of the piezomagnetic effect from both real-space and momentum-space perspectives. In real space, the emergence of piezomagnetism is understood to arise from rotations of the
magnetic moments at specific Mn sites, which directly couple to the strain. Through detailed electronic structure analysis, we identify the
Fermi surfaces that play a crucial role in the emergence of piezomagnetism. Our results reveal that specific
Fermi surface features undergo pseudo-degeneracy lifting under applied strain, which significantly contributes to the induced net magnetization. By combining these complementary real-space and momentum-space pictures, our dual-space analysis provides deep insight into the microscopic origins of strain-driven magnetization in Mn$_3$Sn.
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All authors Soichiro Kikuchi, Yuki Yanagi, Thi Ngoc Huyen Vu, Michi-To Suzuki
Mesoscale and Nanoscale Physics
Current-induced magnetization control in dipolar-coupled nanomagnet pairs and artificial spin ice
A. Pac, G. M. Macauley, J. A. Brock et al. (+5 more)
Exploiting current-induced
spin-orbit torques (SOTs) to manipulate the
magnetic state of dipolar-coupled nanomagnet systems with in-plane
magnetic anisotropy, such as artificial
spin ices, provides a route to local, electrically-programmable control of the magnetization, with relevance for applications including neuromorphic computing. Here, we demonstrate how the orientation of a nanomagnet relative to the direction of an applied electrical current impacts the threshold current density needed for all-electrical magnetization switching, and how dipolar coupling between the nanomagnets influences the switching of interacting pairs and ensembles of nanomagnets. Using a material system designed to generate SOTs in response to electrical currents, we find that the current required to switch the magnetization of isolated nanomagnets varies non-monotonically as the angle between the nanomagnet long axis and the current increases. In small artificial
spin ice systems, we observe similar angular dependence of the switching current, which can be used to control the magnetization orientation of specific subsets of nanomagnets. These experimental results are supported by micromagnetic modeling, which illustrates how the various current induced torques can be exploited to control magnetization switching in nanomagnetic systems. These results establish SOT switching as a practical method for programmable manipulation of dipolar nanomagnetic systems.
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All authors A. Pac, G. M. Macauley, J. A. Brock, A. Hrabec, A. Kurenkov, V. Raposo, E. Martinez, L. J. Heyderman
Strongly Correlated Electrons
$d$-wave FFLO state and charge-2e supersolidity in the $t$-$t'$-$J$ model under Zeeman fields
Xing-Zhou Qu, Dai-Wei Qu, Qiaoyi Li et al. (+2 more)
Unconventional superconductivity under strong Zeeman fields–particularly beyond the Pauli paramagnetic limit–remains a central challenge in condensed matter physics. The exotic Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state, in particular, remains in need of definitive study within fundamental electronic models. Here we employ state-of-the-art finite-temperature and ground-state tensor network approaches to systematically explore the superconducting (SC) phase diagram of the $t$-$t'$-$J$ model subjected to Zeeman fields. We find that zero-momentum $d$-wave superconductivity persists until the
spin gap closes, coexisting with charge density waves. A novel $d$-wave FFLO phase emerges under a higher Zeeman field even above the Pauli limit, concomitant with a field-enhanced
spin density waves. We identify these phases, characterized by the simultaneous presence of pairing condensate and density wave orders, as charge-2e supersolids. Analysis of Matsubara Green's function reveals that the FFLO pairing momentum is locked to the underlying
Fermi surface. Our results provide microscopic insights into field-induced unconventional pairing mechanisms and reveal the long-sought FFLO state in a fundamental correlated electron model, offering a promising route for its realization in ultracold atom optical
lattice.
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All authors Xing-Zhou Qu, Dai-Wei Qu, Qiaoyi Li, Wei Li, Gang Su
Materials Science
Role of defects in the thermodynamic stability of grain boundary phases at asymmetric tilt boundaries in copper
Swetha Pemma, Lena Langenohl, Saba Saood et al. (+5 more)
Grain boundaries can exist as different grain boundary phases (also called complexions) with individual atomic structures. The thermodynamics of these defect phases in high-angle grain boundaries were studied mostly with atomistic and phase field computer simulations, but almost exclusively for special, symmetric boundaries. Here, we use molecular dynamics simulations combined with structure search methods, as well as scanning transmission electron microscopy experiments to take a step towards understanding more general grain boundaries. Using the example of $\Sigma$37c $[11\overline{1}]$ tilt boundaries in Cu, we show how the grain boundary phase transition on a symmetric boundary plane is changed by the geometrically necessary defects introduced in inclined, asymmetric boundaries. We analyze the disconnections - which are dislocation-like line defects of grain boundaries - both in the simulations, as well as in experimental Cu and Al samples. A main finding is that defect energies can have a major influence on the stability of grain boundary phases, even at small inclinations. Furthermore, some defects are not able to effect large inclinations. At that point, defective asymmetric GB phases compete with grain boundaries faceting into the adjacent symmetric GB phases.
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All authors Swetha Pemma, Lena Langenohl, Saba Saood, Yoonji Choi, Rebecca Janisch, Christian H. Liebscher, Gerhard Dehm, Tobias Brink
Statistical Mechanics · Cross-listed from hep-th
Generalized Integrable Boundary States in XXZ and XYZ Spin Chains
Xin Qian and Xin Zhang
We investigate integrable boundary states in the anisotropic Heisenberg chain under periodic or twisted boundary conditions, for both even and odd system lengths. Our work demonstrates that the concept of integrable boundary states can be readily generalized. For the XXZ
spin chain, we present a set of factorized integrable boundary states using the KT-relation, and these states are also applicable to the XYZ chain. It is shown that a specific set of eigenstates of the transfer
matrix can be selected by each boundary state, resulting in an explicit selection rule for the Bethe roots. We also derive the overlaps between integrable boundary states and Bethe states in the U(1)-symmetric cases.
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