Soft Condensed Matter
Bayesian inference in active microrheology with wall and particle-particle interactions
Parajal Rai, Michelle M.A. Spanjaards, Ye Wang et al. (+2 more)
Active microrheology infers rheological properties from the motion of a force-driven probe. In small samples, however, the probe is often close to walls or other probes, and the resulting hydrodynamic interactions bias the inferred parameters. We present a
Bayesian framework in which these interactions are built into simplified analytical models for Newtonian and linear viscoelastic fluids and test it on noisy synthetic data from finite-element simulations of Newtonian and Oldroyd-B fluids. Accounting for the interactions substantially improves the accuracy of the inferred parameters. Near a wall, oblique forcing allows the material parameters and the wall distance to be identified jointly from a single experiment. In the nonlinear viscoelastic regime, posterior predictive checks over multiple force levels reveal the inadequacy of the linear model. Finally, when the probe size is comparable to the heterogeneity length scale, the framework distinguishes spatial variations in the modulus from measurement noise.
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All authors Parajal Rai, Michelle M.A. Spanjaards, Ye Wang, Patrick D. Anderson, Nick O. Jaensson
Soft Condensed Matter
Enskog kinetic theory in a model of confined granular mixtures. Heat flux and some applications
David González Méndez and Vicente Garzó Puertos
This work considers the Enskog kinetic theory for moderately dense confined granular mixtures within the framework of the $\Delta$-model, an effective collisional model that accounts for the transfer of energy from the vertical to the horizontal degrees of freedom of grains through an additional velocity increment during collisions. The main objective is to complete the Navier–Stokes hydrodynamic description of dense binary granular mixtures by explicitly determining the heat-flux transport coefficients, namely the Dufour and thermal conductivity coefficients, together with the first-order contributions to the partial temperatures and the cooling rate. These quantities are determined in the steady state from the Enskog kinetic equation by means of the Chapman–Enskog method and are expressed in terms of the masses and diameters of the particles, mixture composition, density, and coefficients of restitution. The results show that finite-density effects have a significant influence on transport, leading to behaviors that differ markedly from those observed in the dilute regime. The complete set of transport coefficients is considered further to study two different problems. First, we perform a linear stability analysis of the homogeneous steady state (HSS). The analysis demonstrates that no unstable transverse or longitudinal hydrodynamic modes are found over the parameter space explored, indicating that the HSS is linearly stable even at moderate densities. As a second problem, the violation of the Onsager reciprocal relations for a confined dense granular mixture is quantified in terms of the parameter space of the problem.
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Disordered Systems and Neural Networks · Cross-listed from cs.CL
A Data-free Universal Prior over Syntactic Structures
Fermín Moscoso del Prado Martín
The probabilities of syntactic structures in human
languages are assumed to emerge fully from
language-specific experience. Here, I show that a universal prior over syntactic structures emerges from a model of human
language production, in which words are progressively integrated into syntactic structure. Without fitting any parameters to specific
language data, the resulting prior assigns higher probabilities to attested than to random dependency trees in all 138 typologically diverse
languages examined. These prior probabilities correlate positively with those estimated from corpora in 33 of 34
languages. The results indicate that part of the probability structure of syntax can arise independently of
language-specific learning. This identifies human
language production as a possible cognitive source of universal statistical structure in
language, while providing a data-independent structural bias for probabilistic models, including large
language models.
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Statistical Mechanics
Odd diffusion and power-law correlations in chiral mass-transport processes
Koushik Das, Animesh Hazra and Punyabrata Pradhan
We study mass-conserving Markov jump processes on a square
lattice, where masses hop with a preferred rotational sense, thus breaking both time-reversal and mirror
symmetries. We consider closed systems with both periodic and open (reflecting) boundaries, the latter supporting a steady-state edge current. We show that odd
diffusion, arising from the chiral transport, generically provides a mechanism for the emergence of scale-invariant two-point density correlations in nonequilibrium steady states even in the presence of
lattice rotation
symmetry – a mechanism that is qualitatively distinct from the well-known mechanism of anisotropic hopping. We exactly calculate the steady-state equal-time density-density correlations, which exhibit an algebraic decay, $C(\mathbf{r}) \sim |\mathbf{r}|^{-4}$ for $|\mathbf{r}| \gg 1$. This algebraic behavior results from the interplay between the off-diagonal components of the
diffusion and mobility tensors, demonstrating that chiral transport alone can generate power-law correlations in isotropic driven systems. Remarkably, the structure factor in the zero-wavenumber limit and the amplitude of the power laws depend nontrivially on chirality. While increasing chirality initially suppresses large-scale density fluctuations, the fluctuations beyond a threshold odd-
diffusion strength vary nonmonotonically with chirality and develop a cusp singularity.
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Mesoscale and Nanoscale Physics
Generation of pure spin currents via nonadiabatic quantum pumping in an antiferromagnetic chain
Leila Eslami, Fatemeh Bourbour, Somaieh Ahmadi et al. (+1 more)
In this study,
quantum spin pumping in an antiferromagnetic chain driven by time-dependent potential is investigated. The aim is to explore the possibility of generating and controlling
spin currents in the absence of external bias and to examine the role of exchange field and periodic driving in the separation of
spin-up and
spin-down currents. The system is described using a tight-binding model, and
spin-resolved currents are calculated employing the Keldysh non-
equilibrium Green's function formalism. Two time-dependent potentials with a specific phase difference are applied to the two ends of the chain, while the chemical potentials of both electrodes are set equal. The results demonstrate that in the adiabatic regime (low frequencies), the response of the two
spin channels is nearly identical. However, as the driving frequency increases and the system enters the nonadiabatic regime, absorption and emission processes of energy quanta become activated, leading to significant differences between
spin-up and
spin-down currents. The pumped current exhibits strong dependence on the chemical potential, allowing for the control of both magnitude and direction of the
spin current through its adjustment. With increasing frequency, the
spin current enhances, and parameters can be tuned such that the charge current nearly vanishes while a considerable
spin current persists. This finding indicates the feasibility of achieving nearly pure
spin pumping without net charge transfer in the antiferromagnetic chain. The results provide a promising perspective for designing
spin-pumping devices based on antiferromagnetic systems.
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All authors Leila Eslami, Fatemeh Bourbour, Somaieh Ahmadi, Santanu K. Maiti
Materials Science
ZStar: An automated toolkit for polarization, Born effective charges, dielectric response, and infrared and Raman spectra calculations
Xudong Zhu, Junhong Li, Gan Jin et al. (+2 more)
Born effective charges (BEC) link atomic displacements to polarization, connecting
lattice vibrations to dielectric response and infrared activity. We present ZStar, an open-source Python toolkit that automates calculations of polarization, BEC,
phonons, static and frequency-dependent dielectric response, and infrared and Raman spectra. ZStar supports calculations across all dimensionalities, including bulk
crystals, two-dimensional materials, one-dimensional structures, and molecules, through an integrated workflow spanning input preparation, execution, and response analysis. Berry-phase polarization and real-space dipoles describe responses along periodic and open directions, respectively. Our unified,
symmetry-adapted finite-displacement framework jointly determines BEC and zone-center force constants from the same calculations, improving computational efficiency while preserving numerical accuracy. Reusing the electronic
Hamiltonian in the ABACUS+PYATB route enables Raman calculations without additional self-consistent calculations. Reproducible examples and a packaged
agent skill support conventional and
agent-assisted use. ZStar enables efficient, automated exploration of polarization, BEC, dielectric response, and vibrational spectra across all dimensionalities.
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All authors Xudong Zhu, Junhong Li, Gan Jin, Zheng Guan, Lixin He
Materials Science
Fractional-Quantum Ferroelectrics: A Route to High-Mobility Ferroelectric Semiconductors
Rong-Tian Pang, Wenjie Hu, Youning Liu et al. (+1 more)
Ferroelectric
semiconductors are promising for multifunctional electronics, yet their typically low carrier mobilities remain a major limitation. Using first-principles
phonon-limited transport calculations for monolayer In$_2$Se$_3$, we show that this limitation depends critically on the microscopic origin of ferroelectricity. In displacive $\beta'$-In$_2$Se$_3$, low-frequency ferroelectric modes dominate carrier scattering, with additional contributions from longitudinal-optical (LO)
phonons, limiting the room-temperature electron mobility to a few cm$^2$/(V s). By contrast, in fractional-
quantum ferroelectric $\alpha$-In$_2$Se$_3$, ferroelectric-mode scattering is absent because polarization arises from discrete
lattice-scale atomic displacements rather than soft-mode condensation. Transport is therefore dominated by LO
phonons, yielding a room-temperature mobility above 70 cm$^2$/(V s). Carrier doping further screens long-range electron-LO-
phonon interactions and raises the mobility beyond 300 cm$^2$/(V s) at experimentally accessible densities. These results establish that fractional-
quantum ferroelectricity can decouple robust polarization from strong intrinsic carrier scattering, offering a route toward high-mobility ferroelectric
semiconductors.
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All authors Rong-Tian Pang, Wenjie Hu, Youning Liu, Jin-Jian Zhou
Materials Science
SpectraFit XPS: a free, browser-based application for X-ray photoelectron spectroscopy peak fitting and quantification
Yongsup Park
SpectraFit XPS is a free web application for the analysis of X-ray photoelectron spectroscopy (XPS) data that runs entirely in the browser, with no installation and no server-side processing: spectra never leave the user's computer. It combines an interactive Levenberg–Marquardt fitting engine with true Voigt, Doniach–Šunjić, and summed Gaussian–Lorentzian line shapes; Shirley (static and dynamic), linear, and Tougaard (two- and four-parameter) backgrounds;
spin–orbit doublet generation; and expression-based inter-peak constraints. Quantitative analysis supports ten relative-sensitivity-factor sets, several kinetic-energy correction schemes including TPP-2M inelastic mean free paths, angular correction, and atomic and weight percentages, with the underlying database and
algorithms adapted from the open-source KherveFitting project. The application reads and writes ISO~14976 (VAMAS) files—including multi-region and depth-profile data and load-time transmission-function correction—and imports common vendor and spreadsheet formats. A publication plotter exports journal-ready SVG/PNG figures. The quantification pipeline reproduces KherveFitting reference values exactly in a 30-case regression suite, part of an automated test set of 100 tests. The application, an illustrated bilingual user guide, and a synthetic demonstration
dataset are freely available at https://spectrafit-xps.web.app/.
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Mesoscale and Nanoscale Physics
Diffusive molecules share the 1/3 shot noise suppression of quantum conductors
Henri Vo Van Qui, Ignacio Madrid, Simon Grall et al. (+7 more)
Electrical noise measurement, especially shot noise, which arises from the discreteness of charge, is an indispensable tool in
quantum transport for probing the nature of charge carriers beyond simple conductance measurements. Diffusive conductors share a universal shot noise reduction of 1/3, a result obtained independently from
quantum scattering theory, semi-classical kinetics, or by classical exclusion processes8. Until now, however, experimental tests of this universality have been limited to cryogenic conditions, leaving its origin incompletely understood. Here we show that ferrocene redox cycling in a microfluidic gap is a room temperature realization of this universality. We derive the full counting statistics of diffusing single-electron molecular shuttles and verify the predicted current noise experimentally, showing that the universal 1/3 shot noise suppression is recovered in the
diffusion-limited regime. Our result identifies
diffusion and sequential charge transfer as sufficient ingredients for this universal noise reduction, rather than
quantum coherence, fermionic statistics or cryogenic conditions. We anticipate that this study will establish electrochemical microfluidics as a room-temperature platform for mesoscopic counting statistics and bring noise-based probes to molecular transport and reaction kinetics. Furthermore, this
liquid-based
quantum-inspired study will provide a novel insight on the yet to be understood links between
quantum and biology.
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All authors Henri Vo Van Qui, Ignacio Madrid, Simon Grall, Thibaut Jonckheere, Akira Fujiwara, Laurent Jalabert, Masayuki Hashisaka, Christophe Demaille, Soo Hyeon Kim, Nicolas Clément
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Initial-Slip Dynamics Enables the Quantum Mpemba Effect
M. Crotti, F. Cavaliere, D. Ferraro et al. (+2 more)
We investigate the
quantum Mpemba effect, whereby a system initially farther from
equilibrium relaxes faster than one initially closer to
equilibrium, emerging in a
quantum harmonic oscillator linearly coupled to a bosonic environment. Starting from factorized thermal states at different temperatures, we derive exact analytical criteria for the occurrence of the
quantum Mpemba effect valid also beyond the typically considered weak-coupling and Markovian approximations. Most importantly, we show that the effect is enabled by the initial-slip dynamics generated by the sudden switch-on of the system-bath interaction. Neglecting this contribution completely suppresses the anomalous relaxation, identifying transient system-bath correlations as the key ingredient underlying the
quantum Mpemba effect.
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All authors M. Crotti, F. Cavaliere, D. Ferraro, G. Benenti, M. Sassetti
Materials Science
Topological spin textures in 2D altermagnetic chromium chalcogenides: Interplay between magnetic frustration and Dzyaloshinskii-Moriya interaction
Zirui Zhang, Shiwei Zhu, Ruixiao Ma et al. (+3 more)
Altermagnetism has recently emerged as a distinct
magnetic paradigm, yet the exploration of topological
spin textures within two-dimensional (2D) altermagnets remains limited. Using first-principles calculations and atomistic
spin simulations, we investigate monolayer $\mathrm{Cr_2X_2}$ and Janus monolayer $\mathrm{Cr_2XY}$ altermagnets ($\mathrm{X, Y}=\mathrm{O, S, Se, Te}$, and $\mathrm{X \neq Y}$). Both systems exhibit strong intrinsic exchange frustration arising from competition between nearest-neighbor and further-neighbor exchange interactions. In Janus $\mathrm{Cr_2XY}$, breaking the out-of-plane mirror
symmetry additionally activates a substantial in-plane Dzyaloshinskii-Moriya interaction (DMI), mediated by the strong
spin-orbit coupling of heavy chalcogen ligands. The interplay between exchange frustration and DMI gives rise to distinct frustration- and DMI-dominated regimes, while
magnetic anisotropy determines the preferred
spin orientation, leading to a diverse range of non-collinear states. Systematic phase-space scans and geodesic nudged elastic band (GNEB) calculations reveal two distinct mechanisms governing this interplay: a synergistic effect, in which frustration lowers the critical DMI for the onset of non-collinear states, and a competitive effect, in which frustration favors high-topological-charge states while DMI favors low-charge states. Our results establish a general framework for understanding the interplay between frustration and DMI and guiding the design of topological
spin textures in two-dimensional altermagnets.
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All authors Zirui Zhang, Shiwei Zhu, Ruixiao Ma, Qiuyao Zhang, Xiaoping Wu, Changsheng Song
Materials Science
Interplay between Interlayer Shift and Twist: Twisted van der Waals Nanowires Driven by Rotational Twinning
Dong-gyu Kim, Kisung Kang, Hani Kang et al. (+8 more)
In van der Waals(vdW) layered materials, interlayer shift and twist have enabled the control of material properties through polytype and moire engineering. Various approaches, including bottom-up synthesis and manual layer-by-layer stacking, have been utilized to engineer targeted stacking configurations. However, the interplay between interlayer shift and twist, as well as reliable mechanisms for fine-tuning these parameters, remains largely unexplored. Here, we report a previously unrecognized twisting mechanism arising from preferred tilted stacking and twinning in vdW
crystals. Electron diffraction and atomic-resolution scanning transmission electron microscopy(STEM) imaging reveal that the
lattice planes of group-IV chalcogenide GeSe_{2-x}Te_x rotate continuously along the nanowire growth axis, with twist rates depending systematically on nanowire radius. Atomic-scale imaging further identifies a continuous rotational twin boundary extending along the central region of the nanowire. First-principles calculations and structural relaxation simulations confirm that the twisting deformation originates from energetic competition between the preferred interlayer stacking registry and the strain cost imposed by rotational twinning. These findings establish rotational twinning as an intrinsic route to spontaneous twist formation and provide a design principle for realizing twist-engineered vdW
crystals with compatible
crystal symmetries and stacking motifs.
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All authors Dong-gyu Kim, Kisung Kang, Hani Kang, Kihyun Lee, Yangjin Lee, Jinsub Park, Joong-Eon Jung, Min Kim, Myeongjin Jang, Aloysius Soon, Kwanpyo Kim
Materials Science
Floquet Spin-Antiferroelectricity in Collinear Antiferromagnets
Yu-hao Wei, Zheng Qin, Shengpu Huang et al. (+3 more)
Multiferroics combining
magnetic and polar orders offer opportunities for optical control of
spin and electric degrees of freedom. Here, using
symmetry analysis and Floquet theory, we establish Floquet
spin-antiferroelectricity coexisting with unconventional magnetism in periodically driven collinear antiferromagnets, qualifying it as an unconventional multiferroic. This driven phase supports compensated,
spin-resolved in-plane electric polarizations perpendicular to the vertical rotation axis, which are strictly forbidden by crystalline
symmetry in
equilibrium. Using a tight-binding model, we elucidate how light polarization controls the emergence of polar order and
spin responses. Moreover, first-principles-based Floquet calculations predict its realization in monolayer $\text{MnPS}_3$, identifying a realistic two-dimensional antiferromagnetic platform. These findings establish a nonequilibrium route to
spin-antiferroelectricity beyond
equilibrium symmetry constraints and connect Floquet engineering, unconventional magnetism, and multiferroicity through optical control of
spin and polar degrees of freedom.
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All authors Yu-hao Wei, Zheng Qin, Shengpu Huang, Dong-Hui Xu, Da-shuai Ma, Rui Wang
Materials Science
Electric-Field-Switchable Altermagnetism via Ligand Rotation in a d0 Metal-Organic Framework
Hongjing Wang, Xiuling Li and Xiaojun Wu
Altermagnetism combines vanishing net magnetization with momentum-dependent
spin splitting. While altermagnetic signatures have been identified in metal-organic frameworks (MOFs), non-invasive reversible control remains challenging. Here we report a route to electric-field-switchable altermagnetism in a flexible d0-MOF, in which polar substituents couple the external field to ligand rotation. In the planar ground state, pz orbitals mediate 180-degree ligand-metal-ligand superexchange (J2), stabilizing antiferromagnetic order. Rotating ligands out of plane activates px/py orbitals, enhances 90-degree pathways (J1), and reverses J1/J2 competition. The antiferromagnetic-to-altermagnetic crossover occurs at approx. 34 degrees, with
spin splitting of 84 meV at 90 degrees. The 90-degree altermagnetic state is switched on by the electric field and switched off upon field removal, as the constrained-rotation landscape decreases monotonically back toward 0 degrees, enabling barrierless relaxation to the antiferromagnetic state and reversible on/off operation. Ab initio molecular dynamics at 300 K shows thermal fluctuations alone cannot synchronize ligand rotation. Polar substituents provide the required coupling for electric-field control; for fluorinated substituents, the critical field is approx. 0.22 V/Angstrom, comparable to field-effect devices. This work establishes ligand p orbitals, rather than transition-metal d orbitals, as the origin of altermagnetic order and shows that polar substituents enable electric-field control for organic spintronics.
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Materials Science
The Closer, the Better: Engineering RGB Thermometric Performance in Tb3+, Eu3+-Doped MOFs
M. Szymczak, L. Giang and L. Marciniak
The effectiveness of luminescence thermometry, which exploits temperature-induced changes in the spectroscopic properties of phosphor materials for temperature sensing, has been extensively demonstrated. However, from a practical perspective, monitoring temperature-induced variations in the color of the emitted light offers a considerably more straightforward and user-friendly alternative to conventional spectral analysis. In this context, establishing a clear relationship between the thermal
evolution of the emission color and the structure of the phosphor is essential for the rational design of visual luminescence thermometers. In this work, we investigate the correlation between the temperature-dependent emission color and the structural characteristics of Tb3+, Eu3+-co-doped metal-organic frameworks (MOFs), with particular emphasis on their potential for filter-free, camera-based thermal sensing. The obtained results demonstrate that, within the investigated series of materials, decreasing the interionic distance between Eu3+ and Tb3+ ions increases the probability of energy transfer and consequently enhances the thermal sensitivity of the camera-based readout derived from the ratio of luminescence intensities recorded in the blue and red channels. These findings establish a direct relationship between the structural characteristics of the luminescent material, the underlying energy-transfer processes, and its thermometric performance. More broadly, this study provides a foundation for the rational design of visual luminescence thermometers with predefined sensing characteristics, opening a pathway toward structure-guided optimization of filter-free, camera-based thermal sensing platforms.
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Materials Science
Electrical Probing of Sub-Néel Spin Dynamics in Two-Dimensional Antiferromagnets Using Graphene Heterostructures
Adrián García-Martín, Sara Gullace, Nicolás Montenegro-Pohlhammer et al. (+4 more)
Low-dimensional antiferromagnetic van der Waals materials have emerged as a versatile platform for exploring exotic
spin dynamics and
magnetic phases, yet electrically accessing these phenomena remains a major challenge because of their vanishing net magnetization and highly insulating nature. Here, we demonstrate that
graphene can act as an ultrasensitive electrical transducer of hidden
spin dynamics in two-dimensional antiferromagnets. By integrating
graphene with the van der Waals antiferromagnet FePS$_3$, low-temperature transport measurements combined with
magnetic-field and gate-voltage control reveal multiple resistance anomalies well below the Néel temperature. Their distinct temperature,
magnetic-field, and carrier-density dependences enable us to associate these anomalies with
magnon excitations and with a low-temperature
magnetic reconfiguration of the antiferromagnetic state, both of which remain largely inaccessible to conventional magnetometry. Density functional theory calculations further show that competing antiferromagnetic
spin configurations in FePS$_3$ are nearly degenerate in energy while producing markedly different electronic responses in the adjacent
graphene layer. The pronounced electrostatic tunability of these signatures demonstrates that
graphene directly transduces interfacial
magnetic dynamics into an electrical signal. Our work establishes
graphene/antiferromagnetic van der Waals
heterostructures as a versatile platform for the electrical readout of
spin dynamics in two-dimensional magnets.
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All authors Adrián García-Martín, Sara Gullace, Nicolás Montenegro-Pohlhammer, María José Martínez-Pérez, Rocío Sánchez-de-Armas, Carmen J. Calzado, Enrique Burzurí
Mesoscale and Nanoscale Physics
1/f frequency noise in mechanical resonators scales inversely with volume, not with quality factor
M.L. Roukes
Mechanical frequency-shift sensors have never reached their fundamental thermomechanical or
quantum limits. Every material, size, and transduction scheme yet examined yields a $1/f$ floor 1-3 orders higher, with a flicker-noise coefficient $h_{-1} \propto 1/V_{\varepsilon}$. Surveying the published record, I find the invariant $h_{-1}\,V_{\varepsilon} \equiv \sigma_A ^2\, V_{\varepsilon}/(2\ln 2)$ independent of device size across 13 decades; volume-independent noise is excluded by 9$\sigma$, site-averaging by 3.8$\sigma$. No $Q$ dependence appears: reported $Q^{-n}$ laws scale equivalently when $Q$ and volume co-vary; only volume scaling survives when they do not. Mass resolution follows as $|\delta m| \propto \sqrt{h_{-1}\,V_{\varepsilon} \cdot V}$.
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Materials Science
Total-energy-assisted Tight-binding Method Based on Density Functional Theory - Design Principles toward Transferability and Extrapolation
Takeo Fujiwara, Yoshiro Nohara and Susumu Yamamoto
The previously proposed tight-binding method derived from the total energy has been extended within the local density approximation (TE-TB method; J. Phys. Soc. Jpn. 87, 064802 (2018)). Unlike the earlier two-parameter formulation, the present method introduces three parameters. These parameters explicitly capture local packing effects and improve transferability. Furthermore, based on physical considerations, several boundary conditions (inductive bias) are imposed on the functionals defining the tight-binding
Hamiltonian and related energy functionals. The revised formalism is tested on crystalline silicon to assess the stability of the diamond structure, a monovacancy, and the (001) surface. These
benchmark tests demonstrate the high transferability and reliability of the present three-parameter TE-TB design philosophy.
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Mesoscale and Nanoscale Physics
Accurate noise spectroscopy using quantum sensing ensembles
Dhilan T Vallury, Nikolai Dontschuk, Alexander M Jakob et al. (+2 more)
Noise spectroscopy with
quantum sensors is a powerful tool for characterising the properties of the sensor environment and detecting critical
magnetic phenomena. While replacing single sensors with large ensembles promises substantial gains in measurement sensitivity and field of view, the output becomes difficult to interpret when there is a variable coupling to targets across the sensing ensemble. In this work we present an analysis procedure for accessing the true source noise spectrum using ensemble coherence from dynamical decoupling measurements. We show that sequence timing plays a dual role in ensemble noise spectroscopy, setting both the frequency selectivity and the weighted collection of signal across the ensemble, and demonstrate how incorporation of the coupling distribution allows accurate parameter extraction of the noise. We apply this procedure to a model system, shallow nitrogen-vacancy centres in diamond, and show that consistent information about the spectral character of MHz-range surface noise can be obtained from two sensing ensembles featuring distinct depth distributions. Our results pave the way for using large
quantum sensor ensembles for quantitative, broadband noise spectroscopy, with straightforward extension to other solid-state and molecular sensing platforms.
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All authors Dhilan T Vallury, Nikolai Dontschuk, Alexander M Jakob, Alexander J Healey, David A Simpson
Materials Science
Application of Regional Chemical Potential Analysis to Si Adsorption on the Diamond (001) Surface
Masahiro Fukuda, Arath E. Marin Ramirez, Yoshiaki Sugimoto et al. (+1 more)
Adsorption of carbon dimers and Si atoms on the reconstructed diamond (001) surface is inves- tigated using density functional theory and regional chemical potential (RCP) analysis. We first demonstrate that the RCP distribution provides a real-space description of the bonding rearrange- ments responsible for the site-selective growth of experimentally observed carbon-dimer ribbons. We then examine the adsorption of single and multiple Si atoms. The calculated adsorption ener- gies show that a single Si atom preferentially bridges a surface carbon dimer and that subsequently adsorbed Si atoms favor neighboring dimer sites through Si-Si bond formation. The RCP analysis identifies electron-donating regions at the ends of finite Si chains, providing an intuitive explanation for their preferential one-dimensional growth and a physically motivated strategy for selecting candi- date adsorption structures. At higher Si coverages, geometry optimizations yield Si stripe and planar square-
lattice structures on the diamond surface. Surface phase analysis indicates that an increase in the effective Si chemical potential favors structures with progressively higher Si coverages, from the Si stripe phase to the Si square-
lattice phase. The calculated band structures reveal a progressive reduction of the surface band gap with increasing Si coverage. In the Si square-
lattice structure, several bands cross the Fermi level, and the conducting states along the two in-plane directions have distinct Si and C character because the underlying diamond (001) substrate lacks fourfold rotational
symmetry. These results establish RCP analysis as a useful approach for interpreting surface covalent bonding and guiding the exploration of adsorption-driven surface structures.
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All authors Masahiro Fukuda, Arath E. Marin Ramirez, Yoshiaki Sugimoto, Taisuke Ozaki
Statistical Mechanics · Cross-listed from quant-ph
Floquet Dressing and Bath Spectral Effects on the Geometric Phase of a Driven Dissipative Qubit
Chirag Arora
The
geometric phase (GP) of a periodically driven symmetricspin-
boson model (SBM) is investigated using the process-tensor time-evolving
matrix product operator (PT-TEMPO) method. A longitudinal monochromatic field drives the
qubit along the same coordinate that couples to an Ohmic bosonic environment. The gauge-invariant kinematic GP is evaluated from the reduced-statetrajectory, and a circular non-additivity measure quantifies the combined effects of driving and dissipation relative to driven-
unitary and undriven-dissipative references. Amplitude, frequency, coupling-strength, and bath-cutoff sweeps reveal regimes in which periodic driving reduces or enhances environmental phase deformation relative to the
unitary counterpart. The one-cycle GP exhibits pronounced nonmonotonic drive frequency dependence, while its bath-induced shift depends sensitively on both coupling strength and cutoff. These trends are interpreted qualitatively in terms of Floquet dressing and bath spectral structure. A two-cycle echo provides a complementary reversibility diagnostic, whose persistence signal does not generally measure the Tong GP. The results characterize the non-additive influence of driving and dissipation on
geometric-phase dynamics and identify parameter regimes of reduced bath-induced deformation.
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Quantum Gases
Weak ferromagnetism in the square-lattice Heisenberg $J_1$-$J_2$-$J_2^\prime$ model with easy-axis single-ion anisotropy
Bin-Zhou Mi and Qiang Gu
Motivated by recent experimental realizations of the Heisenberg model and two-dimensional altermagnetism using ultracold atoms in optical
lattices, we systematically investigate the
magnetic properties of the square-
lattice Heisenberg $J_1$-$J_2$-$J_2^\prime$ model in the presence of easy-axis single-ion anisotropy $D$. Here, $J_1 (>0)$ is the nearest-neighbor antiferromagnetic exchange parameter, while $J_2$ and $J_2^\prime$ are two distinct next-nearest-neighbor superexchange parameters that alternate on the
lattice. We perform numerical calculations of the sublattice magnetization, net magnetization, and critical temperature. Interestingly, the net magnetization is not identically zero at finite temperatures; its absolute value first increases and then decreases with increasing temperature, revealing a temperature-dependent weak ferromagnetism. We find that $J_2\not=J_2^\prime$ is the primary factor responsible for weak ferromagnetism at finite temperatures, while $D$ provides the necessary background for two-dimensional long-range
magnetic ordering. Moreover, for a fixed $J_2+J_2^\prime$, we observe that a larger $|J_2-J_2^\prime|$ leads to a greater maximum net magnetization and critical temperature, as well as a broader temperature range for weak ferromagnetism. The difference between $J_2$ and $J_2^\prime$ originates from the distinct superexchange pathways between
magnetic atoms, with these pathways mediated by two different types of nonmagnetic atoms. This mechanism, which differs from conventional ones such as the Dzyaloshinskii-Moriya interaction, may be detectable in real materials.
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Strongly Correlated Electrons
Hartree-Fock Density-Matrix Renormalization Group for Very Long Chains
Steven R. White
We formulate Hartree–Fock as a density-
matrix renormalization group (DMRG) sweep of a single Slater determinant, assuming a density–density electron–electron interaction. We compress the occupied state and long-range interaction separately, reducing each sweep step to a small local Fock problem. Exchange is retained throughout. Uniform antiferromagnetic hydrogen chains provide an almost ideal setting for this approach, while retaining the Coulomb interaction and its $1/r$ tail. We initialize and converge a chain of 100,000 electrons in 1.8 million spatial basis functions in about two hours on a 64-GB Mac mini, using less than a third of its
memory. The work per sweep is nearly proportional to chain length, and the number of sweeps needed for convergence changes little from 1000 to 100,000 atoms. DMRG's compression of states and environments thus makes large HF calculations with long-range Hartree and exchange practical on an ordinary desktop computer.
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Soft Condensed Matter
Adsorbing Boundaries Stratify the Kinetics of Confined Colloidal Phase Separation
Kui Lin and Haiming Lu
Phase separation in network-forming materials couples mass transport to mechanical relaxation, yet how adsorbing boundaries reshape this coupling remains unclear. We compare fluid-particle-dynamics simulations resolving solvent hydrodynamics with free-draining Brownian dynamics for attractive colloids confined between parallel walls. Adsorbing boundaries do not slow coarsening uniformly but stratify the network into spatially distinct kinetic regimes. With hydrodynamics, the self-similar central network exhibits growth consistent with poroelastic relaxation, Lb~t^(1/2), whereas the adsorbed region follows an effective Lw~t^(1/3) law. In free-draining dynamics, central coarsening approaches t^(1/3), while the boundary exponent remains time dependent over the accessible times. Direction-resolved displacements reveal suppressed wall-normal motion and reduced lateral mobility near the walls. Increasing wall attraction connects adsorbed islands into an extended layer while leaving local dense-phase packing nearly unchanged. For island-like domains, we propose a testable encounter-controlled scaling framework linking boundary growth to domain geometry, size-dependent mobility, and evolving adsorbed mass. Locally self-similar central coarsening thus coexists with distinct or nonstationary boundary kinetics, precluding a common dynamic-scaling length for the central and adsorbed regions over the accessible times; in both regions, the growth law depends on whether solvent hydrodynamics is resolved.
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Materials Science
Nonlinear Photocurrent Spectroscopy and Polarization-Tunable Shift Current in the Layered Semiconductor $\mathrm{CuScP_2S_6}$
Alexander M. Blackston, Md Kazi Rokunuzzaman, Ryan P. Siebenaller et al. (+4 more)
The class of layered metal thiophosphates and selenophosphates are emerging as promising candidates for non-linear photonic and optoelectronic applications. Here we report one-
photon absorption (1PA) and two-
photon absorption (2PA) induced photocurrents in $CuScP_2S_6$, establishing it as an optoelectronically-active non-centrosymmetric
semiconductor. Spectrally-resolved 1PA and 2PA photoresponsivity paired with photoluminescence and differential reflectance measurements reveal a band gap of 2.35 eV, several higher energy interband transitions, and sub-band gap multiphoton excitonic transitions. Vertical graphite/$CuScP_2S_6$/graphite devices exhibit zero-bias photocurrent with a polarity controlled by both
photon energy and optical polarization orientation within the ab-plane. This sign-dependence combined with a characteristic power-law transition from linear to square-root scaling are consistent with a shift-current origin to this bulk photovoltaic effect (BPVE). These findings establish $CuScP_2S_6$ as a multi-functional platform for polarization-sensitive non-linear optoelectronics.
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All authors Alexander M. Blackston, Md Kazi Rokunuzzaman, Ryan P. Siebenaller, Shashu Tomar, Enam Chowdhury, Michael A. Susner, Roberto C. Myers
Materials Science
Origin and Reduction of Coercive Fields in ZnO-based Wurtzite Ferroelectrics
Abhijeet Dhakane, Alireza Sepehrinezhad, William Prudnick et al. (+5 more)
Wurtzite ferroelectrics offer a route to
semiconductor-compatible non-volatile devices, but their large coercive fields (E$_c$) constrain the operating window between polarization reversal, leakage and dielectric breakdown. Atomically localized and non-classical switching fronts have recently been identified in wurtzite nitrides, yet the microscopic feature that sets the coercive field remains unresolved. Here we use large-scale reactive molecular dynamics, parameterized against first-principles data, to follow field-driven reversal in pristine, Mg-modified and heterostructured ZnO. Reversal proceeds through rugged inversion-boundary filaments in agreement with recent observations in other wurtzite ferroelectrics. We find that the field required for switching is controlled by the advancing filament head, which is a under-coordinated reconstructed inversion-boundary region during the transient switching dynamics with a large field-aligned local polar-order amplitude that is only partially compensated by an oppositely oriented surrounding shell. Controlled strain-only and charge-doping-only perturbations show that charge redistribution lowers the coercive field more effectively than strain because it suppresses this field-setting unscreened local polar order at the filament head, with the combined effect lowering E$_c$ by $\sim$ 50 %. Layered ZnO/ZnMgO architectures further create buried nucleation sites and shorten filament propagation lengths. These results connect atomistic switching
topology to a materials-design principle for substantially reducing coercive fields in ZnO-based wurtzite ferroelectrics.
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All authors Abhijeet Dhakane, Alireza Sepehrinezhad, William Prudnick, Jon-Paul Maria, Bobby Sumpter, Adri C. T. van Duin, Kyle P. Kelley, P. Ganesh
Statistical Mechanics
Diffusivity in Dissipative Quantum Transport from an Exactly Solvable Krylov Chain
Zhi-Li Zhou and Jorge Noronha
The computation of transport coefficients in interacting
quantum many-body systems is rarely analytically accessible. Here, we develop a new Krylov-space mechanism that makes the leading density dependent correction to Green-Kubo diffusivity exactly calculable in the strong-dissipation regime of a one-dimensional noisy
spin-$\frac{1}{2}$ XXZ chain. This is done by showing that the density-polarization-dressed bond coherence generates a Krylov subspace where repeated action of the dissipator closes exactly on an explicitly identifiable operator family. Within this subspace, the dissipative dynamics is then mapped onto a self-similar semi-infinite chain with a boundary defect. Surprisingly, all Lanczos coefficients of the Krylov chain and its boundary Green's function can be determined exactly. The latter then determines the exact leading density-dependent correction to the diffusivity. Finally, we calculate analytically the full boundary-to-bulk Green's function and find that it decays exponentially along the emergent Krylov chain.
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Materials Science
Exotic centrosymmetric phase of acentric urea under high pressure
Haw-Tyng Huang, Yedukondalu Neelam, Mei-Shuan Cheng et al. (+6 more)
Urea is a simple prototype supramolecular
crystal that exhibits rich polymorphism at low pressure due to broken and restored N-H-O hydrogen bonds. The high pressure polymorph (phase V') of acentric urea crystallizes in a centrosymmetric structure, which presents an appealing target because of its potential exotic structure, analogous to the symmetric ice phase X. The pressure-induced polymorphism of urea was studied using powder X-ray diffraction, infrared and Raman spectroscopy, second harmonic generation (SHG) measurements up to 20 GPa and ab initio
crystal structure prediction (CSP) based on the constrained evolutionary approach. A strong decrease of the SHG signal at the transition pressure 10 GPa reveals that the high-pressure polymorph is indeed centrosymmetric, further confirmed by the selection rules observed in the
lattice vibration modes, in contrast to chemical intuition for acentric urea. The structural
evolution sequence obtained from X-ray diffraction, SHG and CSP calculations is as follows: phase I (P421m; Z=2) from 0 to 0.5 GPa, Phase III (P212121; Z=4) from 0.5 to 5.2 GPa, and phase V' (P21/m; Z=6) beyond 10.0 GPa which is energetically competitive with the theoretically predicted phase V (Pnma; Z=4). A phase X with distinct spectral and diffraction features forms between 5.2 and 10.0 GPa, which could be explained by a
quantum disorder intermediate state between phase III and V', that is ascribed to the difficulty to disrupt the H-bonding network under extremely compressed environment. The softening of N-H vibrations and the change in intensity of the vibrations associated with the hydrogen bonding provide evidence for
proton tunneling and charge-transfer interaction in phase X.
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All authors Haw-Tyng Huang, Yedukondalu Neelam, Mei-Shuan Cheng, Zhenxian Liu, Lkhamsuren Bayarjargal, Rachel Husband, Anna Pakhomova, John B. Parise, Lars Ehm
Statistical Mechanics · Cross-listed from gr-qc
Bridging Between Statistical Mechanics and Black Hole Evolution: Theoretical Formalism
Suvodip Mukherjee
Black holes in the Universe span nearly ten orders of magnitude in mass over a large
cosmic timescale, dating back to at least the Universe's early history, when it was only a few hundred million years old. The formation and
evolution of these objects remain a mystery because no direct probe can trace each black hole across the full mass range and
cosmic time. This work shows, for the first time, a statistical mechanical description of black hole
evolution. I show that though each black hole and its
evolution are governed by
stochastic processes, one can make a macroscopic description of the distribution function of black holes in the Universe, and its
evolution over the entire mass range and
cosmic time can be expressed in terms of the Kramers-Moyal expansion. This bridging between statistical mechanics and black hole
evolution in terms of the Kramers-Moyal expansion enables the discovery of the underlying physical processes that play a role in the
evolution of black holes. In the future, the application of this technique to data accessible from different messengers, such as gravitational waves and electromagnetic waves, which probe black holes in the Universe, can lead to a data-driven understanding of the underlying physical processes by this statistical mechanics technique despite the ignorance of the underlying microscopic
stochastic processes.
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Materials Science
Orbital-resolved superexchange and topological magnon bands in MXene Fe$_2$C
Qiang Gao, Wei Wang, Shaojin Qi et al. (+5 more)
Magnetic MXenes are promising candidates for future spintronics due to their intriguing properties. Nevertheless, the topological properties of
magnon bands and superexchange mechanism remain relatively underexplored. In this work, we have calculated the
spin wave dispersions for MXene Fe$_2$C using the linear
spin wave method, with the exchange coupling parameters obtained from first-principles calculations. Owing to the staggered stacking of two Fe sub-
lattices, the interlayer exchange coupling lifts the degeneracy of the ferromagnetic
magnon modes. A Dirac point is identified in the
magnon bands at the $K$ point. The topological properties of
magnon bands, including Berry
curvature, valley Chern number and edge states, are further computed by means of a two-band model. We also derive an effective
Hamiltonian to explain the magnonic
topology, which is protected by the $C_{3v}$ rotational
symmetry. To understand the microscopic origin of the exchange couplings that govern the
magnon bands, we then construct a refined model integrating perturbation theory and the tight-binding approach. The ferromagnetic superexchange coupling is mediated by the virtual hopping between the d orbitals of two distinct Fe sites via a pair of orthogonal p orbitals at the bridging C site. In detail, the intralayer exchange coupling is governed by the in-plane $p_x$ and $p_y$ orbitals, while the out-of-plane $p_z$ orbital is responsible for the interlayer exchange coupling. Our results establish a direct link between the orbital-resolved anisotropic superexchange and topological properties of the
magnon bands in
magnetic MXene Fe$_2$C, providing theoretical guidance for future spintronics applications.
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All authors Qiang Gao, Wei Wang, Shaojin Qi, Guimei Shi, Anbang Guo, Xin Jin, Chen Shen, Xing-Qiu Chen