Quantum Gases
Faraday pattern formation in dipolar superfluid and supersolid quantum gases
Sumit Semwal, Shawan K. Jha, G. A. Bougas et al. (+2 more)
We investigate Faraday instabilities in three-dimensional parametrically driven trapped dipolar
quantum gases within the framework of the extended Gross-Pitaevskii equation. In the superfluid regime, periodic modulation of the short-range interactions induces the resonant excitation of discrete polygonal surface modes displaying sub-harmonic response. The resonance frequencies and the parametric windows of instability are accurately captured by an appropriate Mathieu equation, further corroborating our simulations. It is also shown that dipolar interactions in superfluids shift the resonance frequencies to lower values compared to their non-dipolar counterparts. Near the superfluid-to-supersolid transition, intrinsic density undulations associated with the softened roton mode accelerate pattern formation, yielding hybrid surface and bulk excitations. The bulk patterns prevail deeper in the supersolid regime, emerging from droplet collisions with the superfluid background. Our results reveal a crossover from surface collective modes to hybrid surface-bulk excitations and demonstrate how parametric driving dictates pattern formation in long-range interacting
quantum fluids.
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All authors Sumit Semwal, Shawan K. Jha, G. A. Bougas, S. I. Mistakidis, Pankaj Kumar Mishra
Strongly Correlated Electrons
Emergence and Detection of Surface altermagnetism in KV$_2$Se$_2$O
Rodrigo Jaeschke-Ubiergo, Xanthe H. Verbeek, Colin Lange et al. (+4 more)
We demonstrate the recent concept of emergent surface altermagnetism through its unique signatures in \KVSO. We show that for bulk antiferromagnetically ordered \KVSO, the (001) surface exhibits $d$-wave altermagnetism. Our results fully explain the recent seemingly contradicgting experimental evidence, independently showing both an antiferromagnetically ordered bulk from
neutron diffraction, and $d$-wave
spin splitting from photoemission spectroscopy. To fully verify this conecept, we predict, as a key experimental signature, a large nonlinear Edelstein response, which is localized at the surface, and follows the $d$-wave altermagnetic
symmetry. These results are not only relevant for the metallic and room-temperature magnet \KVSO, but also for several other Lieb
lattice systems. Our work expands the pool of techniques that can be used to detect altermagnetism emerging at the surfaces of antiferromagnets.
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All authors Rodrigo Jaeschke-Ubiergo, Xanthe H. Verbeek, Colin Lange, Sergio Rodriguez, Atasi Chakraborty, Alexander Mook, Jairo Sinov
Quantum Gases · Cross-listed from physics.optics
AOM-based ultra-low noise laser intensity control up to the MHz range
Christian Partes, Jonas Auch, Eduard Heidt et al. (+3 more)
High-power
laser sources that exhibit low relative intensity noise and allow simultaneous dynamic control of their light level are required for a broad range of applications in various fields of physics. Acousto-optic modulators (AOMs) are widely used for active power stabilization and regulation due to their simple drive electronics requirements and high optical power handling capability in free-space. However, the rather slow propagation speed of the sound wave within the AOM
crystal typically limits their control bandwidth to a few hundred kHz. In this work, we present a novel AOM-based control system that is capable of significantly suppressing intensity noise of high-power
lasers up to the MHz range. By combining two standard feedback loops with one feedforward control branch and optimizing the beam path in the AOM
crystal, ultra-low relative intensity noise levels down to $-155\, \text{dB}\,\text{Hz}^{-1}$ even at several hundred kHz are achieved. Our results are relevant for applications that require ultra-low intensity noise at
Fourier frequencies up to the MHz range, such as optical
lattice experiments with light ultracold atoms.
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All authors Christian Partes, Jonas Auch, Eduard Heidt, Kirill Karpov, Florian Kiesel, Christian Groß
Strongly Correlated Electrons
Manipulation of localized excitons in CrPS$_4$ by temperature and magnetic field
Dipankar Jana, Swagata Acharya, Amit Pawbake et al. (+9 more)
Layered van der Waals
magnetic semiconductors provide a versatile platform for exploring excitonic phenomena intertwined with
spin and
lattice degrees of freedom, enabling
excitons to act as sensitive probes of
magnetic order. CrPS$_4$ is a layered
antiferromagnetic semiconductor that hosts rich excitonic features whose microscopic origin and connection to
magnetic ordering remain incompletely understood. Here, we investigate the electronic and excitonic properties of bulk CrPS$_4$ using a combination of many-body perturbation theory, dynamical mean-field theory, and photoluminescence-based experiments. Our calculations establish CrPS$_4$ as a direct-gap
semiconductor with a bandgap of 2.48~eV in the
antiferromagnetic phase. Several sub-bandgap excitonic transitions are predicted by theory, comprising multiple
spin-allowed
excitons and an additional
spin-flip excitation, predominantly localized on the Cr$^{3+}$ ions. Temperature- and
magnetic-field-dependent optical measurements reveal thermally driven
exciton redistribution among localized states and identify characteristic energy shifts that provide clear optical signatures of
magnetic phase transitions in CrPS$_4$. These results provide new insights into the excitonic transitions of antiferromagnets and suggest potential routes for all-optical sensing and light-driven control of their
magnetic order.
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All authors Dipankar Jana, Swagata Acharya, Amit Pawbake, Dmitrii Litvinov, Aljoscha Soll, Zdenek Sofer, Clement Faugeras, Dimitar Pashov, Mark van Schilfgaarde, Kostya S. Novoselov, Marek Potemski, Maciej Koperski
Materials Science
The New High-entropy Compound RhMnFeCoGe4 with Cubic Non-centrosymmetric B20 Structure
V. A. Sidorov, V. N. Krasnorussky, A. V. Bokov et al. (+8 more)
A novel high-
entropy compound, RhMnFeCoGe$_4$, with a cubic non-centrosymmetric B20 struc- ture, has been synthesized under conditions of high pressure and temperature. The electrical transport and
magnetic properties of the obtained compound at both ambient and elevated pres- sures have been investigated. In addition,
nuclear magnetic resonance (NMR) spectra were obtained at 4.2 K and ab initio calculations were performed. The new material exhibits ferromag- netic behavior with a critical temperature of $T_C$ = 146 K and a spontaneous moment of 2.5 $\mu_B$ per formula unit. The magnetization data obtained at the critical region yielded the critical temperature and exponents, which were found to be $T_C$ = 146(1) K, $\beta$ = 0.337(1), $\gamma$ = 1.121(1), and $\delta$ = 4.326(1). The
magnetic moments of Mn and Co were determined from NMR spectra to be 2.2 $\mu_B$ and 0.5 $\mu_B$, respectively. Ab initio calculations yielded reasonable values for the
lattice parameter and the
magnetic moments of all constituents. The density of states and band structure are determined for both paramagnetic and
ferromagnetic states.
Lattice compression results in the increase in the $T_C$.
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All authors V. A. Sidorov, V. N. Krasnorussky, A. V. Bokov, Z. N. Volkova, A. P. Gerashchenko, N. M. Chtchelkatchev, M. V. Magnitskaya, D. A. Salamatin, A. V. Semeno, V. V. Brazhkin, A. V. Tsvyashchenko
Mesoscale and Nanoscale Physics
Vector-field control and emergent basal-plane anisotropy of magnetic textures in noncentrosymmetric (Fe$_{0.63}$Ni$_{0.3}$Pd$_{0.07}$)$_3$P
Victor Ukleev, Oleg I. Utesov, Lorenzo Ubilla et al. (+17 more)
(Fe$_{0.63}$Ni$_{0.3}$Pd$_{0.07}$)$_3$P is a room-temperature magnet with $S_4$
symmetry that hosts a rich variety of topological
spin textures. Here, we report a combined resonant small-angle x-ray scattering and ptychography study of (Fe$_{0.63}$Ni$_{0.3}$Pd$_{0.07}$)$_3$P in vector
magnetic fields over a broad temperature range. We demonstrate deterministic vector-field control of
magnetic stripe domains, where in-plane fields continuously rotate their orientation via a transition from a
chiral stripe to an achiral fan configuration. Furthermore, at 50 K and below, the stripe orientation becomes metastably pinned and retains its field-trained direction. While the magnitude of the wavevector is nearly isotropic within the basal plane at room temperature, a pronounced temperature
evolution of anisotropic interactions emerges upon cooling. In particular, non-trivial anisotropy axes develop at 20-50 K reflecting the combined effects of magnetocrystalline anisotropy, anisotropic exchange, and Dzyaloshinskii-Moriya interaction (DMI), whose effective orientation is found to rotate with temperature. These results establish (Fe$_{0.63}$Ni$_{0.3}$Pd$_{0.07}$)$_3$P as a model system for vector-field control of
chiral spin textures and reveal a previously unrecognized temperature-driven
evolution of the effective DMI landscape in a noncentrosymmetric magnet.
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All authors Victor Ukleev, Oleg I. Utesov, Lorenzo Ubilla, Chen Luo, Radu-Marius Abrudan, Peter Wild, Holger Kropf, Moritz Winter, Sebastian Schneider, Alexander Tahn, Bernd Rellinghaus, Tim A. Butcher, Simone Finizio, Sebastian Wintz, Markus Weigand, Max T. Birch, Yoshinori Tokura, Yasujiro Taguchi, Kosuke Karube, Florin Radu
Statistical Mechanics · Cross-listed from physics.app-ph
Thermodynamically consistent initialization of the Maxwell–Cattaneo—Vernotte heat conduction model: Analytical solutions and engineering applications
Zalán Sándor and Róbert Kovács
This paper investigates the numerical initialization of the one-dimensional Maxwell–Cattaneo–Vernotte (MCV) heat conduction model, addressing the critical mathematical challenge of defining the initial time derivative for non-
equilibrium states. In modern high-frequency thermal engineering applications, traditional time-integration schemes and commercial finite-element solvers frequently introduce severe numerical artifacts when handling non-
Fourier models. This study systematically evaluates three initialization strategies: a zero derivative, a spatially uniform non-zero derivative, and an exact space-dependent derivative. Using an explicit staggered finite-difference scheme, the transient responses to an exponentially distributed initial temperature field under adiabatic boundary conditions are compared against an analytical solution using the Galerkin method. The results demonstrate that assuming a zero or spatially uniform initial derivative introduces significant unphysical oscillatory deviations, leading to heat-flux prediction errors as the relaxation time increases. Conversely, mapping the exact space-dependent derivative onto the staggered grid preserves the local thermodynamic structure of the initial state, yielding robust transient responses that match the analytical
benchmark without meaningful computational overhead. These findings establish a thermodynamically consistent initialization technique that can be extended to non-local models as well.
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Materials Science
Spin-Chirality-Driven Bulk Photovoltaic Effect in van der Waals Magnet CrSBr
Dezhao Wu, Yong Xu, Meng Ye et al. (+1 more)
The bulk photovoltaic effect (BPVE) can be greatly enriched in
magnetic materials. Here, we establish vector
spin chirality as a tunable knob for generating an unconventional time-reversal-even
magnetic BPVE, comprising the
chiral shift current (CSC) and
chiral injection current (CIC). Using
bilayer antiferromagnetic (AFM) CrSBr as a prototype, we theoretically demonstrate the emergence of CSC and CIC. Compared with conventional photovoltaic currents arising from noncentrosymmetric
crystal structures or collinear
magnetic orderings, CSC and CIC not only possess comparable magnitudes but also exhibit exceptional tunability. Specifically, they can be switched on and off by
magnetic-field-induced
spin canting, reversed in direction upon canting-direction reversal, and continuously modulated in intensity via canting-angle variation. Furthermore, we reveal an unusual optical transition channel governing both currents in CrSBr. Our work establishes an unconventional
magnetic BPVE with remarkable controllability, paving the way for applications in optoelectronics and
magnetic sensing in noncollinear magnets.
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All authors Dezhao Wu, Yong Xu, Meng Ye, Wenhui Duan
Materials Science
Anisotropic Phonon Heat Flow and Thermoelectric Response in Tetragonal GeS$_2$ and GeSe$_2$
Neeraj Kulhari, Krishna Swaroop Sharma and K. C. Bhamu
The electronic structure,
lattice dynamics, bonding, elastic response, and anisotropic thermoelectric transport properties of tetragonal GeS$_2$ and GeSe$_2$ were investigated using density functional theory, density functional perturbation theory, Wannier interpolation, and scattering-aware Boltzmann transport. The relaxed structures are mechanically and dynamically stable within the calculated harmonic description. The HSE03/Wannier band gaps are 2.48 eV for GeS$_2$ and 1.23 eV for GeSe$_2$, while substitution of S by Se lowers the upper
phonon frequency from approximately 13.6 to 10.3 THz. The
phonon Boltzmann transport calculations reveal pronounced
lattice-transport anisotropy. Within the relaxation-time approximation, the 300 K in-plane and cross-plane
lattice thermal conductivities are 26.86 and 1.19 W m$^{-1}$ K$^{-1}$ for GeS$_2$, and 18.74 and 1.52 W m$^{-1}$ K$^{-1}$ for GeSe$_2$, respectively. At 800 K, these values decrease to 10.22 and 0.46 W m$^{-1}$ K$^{-1}$ for GeS$_2$, and 7.25 and 0.58 W m$^{-1}$ K$^{-1}$ for GeSe$_2$. Frequency-resolved analysis shows that low-frequency
phonons carry most of the heat, whereas the small cross-plane values reflect restricted out-of-plane
phonon transport. Combining the ShengBTE RTA
lattice tensors with AMSET electronic coefficients gives $zT=0.257$ for n-type cross-plane GeS$_2$ at 800 K and $10^{19}$ cm$^{-3}$. The corresponding PBE-AMSET estimate for GeSe$_2$ is $zT=0.066$ for p-type cross-plane transport at 800 K and $3\times10^{20}$ cm$^{-3}$. LOBSTER analysis identifies mixed covalent–ionic Ge–X bonding, with Ge–S bonds having a larger stabilizing ICOHP magnitude than Ge–Se bonds ($-5.27$ versus $-4.74$ eV per bond). These results identify tetragonal GeX$_2$ compounds as strongly anisotropic thermoelectrics with moderate calculated $zT$ values whose cross-plane response benefits from suppressed
lattice heat transport.
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Statistical Mechanics
Fibonacci number systems and the localization criterion in the many-body Aubry-André model
Balázs Hetényi
We introduce an extension of the Fibonacci number system, we call the fractional Fibonacci number system, which interpolates between the Fibonacci number system (used for natural numbers) and the irrational base-$\phi$ number system, which can be used to represent real numbers. The number system finds its use in interpreting the localization phase diagram of the many-body non-interacting Aubry-André model. For finite system sizes a localization criterion can be obtained if the particle density is written in the fractional Fibonacci number system. In the thermodynamic limit, the criterion remains, but in this case the particle density is expressed in base-$\phi$. The nature of the thermodynamic limit is also discussed.
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Strongly Correlated Electrons
Magnetoresistance in Magnetic Weyl semimetal Mn$_{3}$ZnC
Sunil Gangwar and C. S. Yadav
The magnetoresistance (MR) in
magnetic materials reveal an intriguing
spin-dependent electron scattering, highlighting the role of
spin polarization on the electronic transport properties. This becomes even more interesting for the topological
magnetic materials where a finite Berry
curvature leads to an intrinsic scattering channel also. In this report, we investigate MR of Mn$_{3}$ZnC, an antiperovskite
magnetic nodal line semimetal. Mn$_{3}$ZnC shows a
ferromagnetic (FM) transition at $\sim$ 420 K, followed by an ferrimagnetic (FIM) transition at $\sim$ 195 K. We focus on the interpretation of MR data and highlight the relation between MR and its magnetization. The signature of magnetization induced MR shows correlation at low
magnetic fields and displays distinct behaviors in the FIM and FM states. Similar to the isothermal magnetization M(H) curve of FM and FIM state, the MR curves exhibit a sharp increase, followed by a linear behavior at higher fields. As the
magnetic field varies, the cusp-like anomaly becomes more pronounced, and vanishes at the
magnetic phase transition, which then reappears as the temperature increases. The sign change in the MR curves in the FIM state is attributed to a drastic change in the carrier mobility. Interestingly, this system shows a positive MR in FM state at very low field, which is quite unusual.
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Statistical Mechanics
Surface diffusion with lateral interactions: a closed-form intermediate scattering function of an Ising adlayer from the memory-equation formalism
S. Miret-Artés
The intermediate scattering function and its value at zero time, which is the static structure factor, are both characteristic functions. An exact equation of motion for the ISF carrying a local rate and a
memory function is then obtained. To interpret this equation, the ISF is expressed in terms of relaxation modes. The local rate is fixed by a sum rule which reversibility turns into an
equilibrium average. The de Gennes narrowing is establshed as a
theorem. The
memory function being non-negative, the closed form that results is a rigorous lower bound on the ISF at every momentum transfer and every time, and its accuracy is itself predicted. In the diffusive regime, the closed form keeps the single-exponential shape to which
spin-echo data are routinely fitted, with both coefficients renormalized by the interaction: the amplitude becomes the SSF of the layer and the dephasing rate the dressed one-adsorbate rate divided by it, explicit in momentum transfer, time, coverage and temperature. When introducing the lateral interaction, a single correlation parameter fixes the
equilibrium structure and the renormalized hop rate: exactly along a one-dimensional channel, and on the surface as the nearest-neighbour correlation of a pair approximation completed by a collective (random-phase) structure factor. The result contains no adjustable parameter and is exact at vanishing interaction for every coverage and momentum; the Darken relation comes with it, the correlation between successive moves separated off as a computable factor. Applications to Na/Cu(111) and H/Pt(111) are analysed and discussed.
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Soft Condensed Matter
Active wetting/de-wetting of focal adhesions on viscoelastic substrates
Ivana Pajic-Lijakovic, Milan Milivojevic, Boris Martinac et al. (+2 more)
Cell adhesion to viscoelastic substrates is mediated by focal adhesions (FAs), which dynamically couple actomyosin contractility to the extracellular
matrix. Although substrate stress relaxation is known to regulate adhesion stability and
cell migration, a predictive physical framework linking viscoelasticity to force transmission and adhesion dynamics remains lacking. Here we review briefly what is known about the active wetting and de-wetting of FAs on viscoelastic substrates and synthesize existing experimental and theoretical work into a two-timescale physical framework to describe the phenomena reported. At short timescales, oscillatory actomyosin-driven displacements are transmitted through molecular clutches, leading to frequency-dependent energy transfer to the substrate. We show that this transfer is maximized at an optimal frequency set by a balance between elastic energy storage and viscous dissipation, establishing a resonance-like mechanism that selects both the effective FA stiffness and traction force amplitude. At longer timescales, this mechanically optimal state couples to adhesion remodelling through an effective surface tension, enabling FA growth and disassembly to be interpreted as active wetting and de-wetting processes. The model predicts that adhesion stability and steady-state size are controlled by substrate stiffness and viscoelastic timescales, as well as mechanosensitive feedback mediated by Piezo1-dependent calcium signalling.
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All authors Ivana Pajic-Lijakovic, Milan Milivojevic, Boris Martinac, Massimo Vassalli, Peter VE McClintock
Mesoscale and Nanoscale Physics
Helicity in monoaxial chiral magnets
Victor Laliena, Diego Gironés-Magaña and Javier Campo
The
equilibrium state of a monoaxial
chiral magnet surrounded by a non-
magnetic medium (such as air or
vacuum) is a helical texture characterized by a single, well-defined wave vector. No metastable states have ever been observed in such systems. Recently, however, it was demonstrated that when a
chiral magnet is in close contact with two uniaxial ferromagnets, a large number of metastable helical states emerge in addition to the
equilibrium state [Phys. Rev. B 109, 214424]. These helical states are distinguished by their wave number (helicity). In the present work, we elucidate the topological origin of the stabilization of these states –a mechanism we term dynamical topological protection– and investigate their static and dynamic properties. We find that, as a consequence of this dynamical topological protection, the winding number of the helical states remains constant under the application of sufficiently weak
magnetic fields and polarized electric currents. Furthermore, when a polarized current is applied to a metastable helical state, a static configuration is reached. This state retains the original winding number, but its winding number density becomes non-homogeneously distributed, concentrating near the interface with one of the ferromagnets. The dynamic response to sufficiently large
magnetic fields and currents provides mechanisms to switch between different helical states. Since the
magnetic properties depend on helicity, these metastable helical states are highly promising for applications in spintronics and magnonics.
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Materials Science
Magnetic and crystal electric field excitations in a spin-orbit coupled frustrated hyperkagome magnet Nd$_3$Li$_3$W$_2$O$_{12}$
R. Kolay, S. Guchhait, Indrajeet S. Rathore et al. (+4 more)
Rare-earth based garnets provide a viable platform for studying the frustrated driven
magnetic properties of the hyperkagome
lattices. Herein, we report a comprehensive study of the
magnetic properties and
crystal electric field (CEF) scheme of a new Nd$^{3+}$ based hyperkagome antiferromagnet, Nd$_3$Li$_3$W$_2$O$_{12}$ belonging to the garnet family via magnetization, heat capacity, and inelastic
neutron scattering (INS) measurements. Magnetization measurement reveals a dominant
antiferromagnetic interaction with a low temperature Curie-Weiss temperature $\theta_{\rm CW}^{\rm LT} \simeq -0.2$ K. Two broad maxima are observed in the
magnetic heat capacity data under
magnetic fields, implying multilevel Schottky anomalies due to the effect of CEF and display a two-step
magnetic entropy release. No
magnetic long-range order is observed down to 0.1 K. The CEF excitations of the Nd$^{3+}$ ($J=9/2$) ion with $D_2$ point group
symmetry, probed via INS experiments, show non-dispersive excitations characterizing the transitions among the CEF energy levels. The simultaneous fit of the INS spectra at different temperatures enabled the mapping of the CEF
Hamiltonian and the energy
eigenvalues of the Kramers' doublets. The simulation using the obtained CEF parameters reproduces the experimental
magnetic susceptibility,
magnetic isotherms, and
magnetic heat capacity data. The thermodynamic properties and INS-derived
crystal-field scheme confirm a Kramers' doublet ground state with an effective
spin $J_{\rm eff} = 1/2$ at low temperatures.
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All authors R. Kolay, S. Guchhait, Indrajeet S. Rathore, S. Nandi, M. D. Le, N. B. Christensen, R. Nath
Statistical Mechanics
Discrepancy between the H-Function and Entropy: Insights into the rigorously established Boltzmann equation for hard-sphere gases
Li-Xiang Cen
By investigating the origin of the evolutionary discrepancy between the H-function and
entropy, we elucidate that the H-function fails to serve as a valid arrow-of-time criterion in the rigorously derived Boltzmann equation for the hard-sphere gas model under the Boltzmann-Grad limit.
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Materials Science
Alloy engineering of excitonic properties in TMD monolayers
Eirini Katsipoulaki, Adlen Smiri, Panagiotis Spiliotakis et al. (+12 more)
We investigate monolayer MoS$_{2x}$Se$_{2(1-x)}$
alloys across the full composition range using optical spectroscopy. We demonstrate continuous tuning of the optical gap over $\sim$0.35 eV, accompanied by a systematic reduction of the B–A
exciton splitting, in agreement with density functional theory calculations. Temperature-dependent measurements reveal a progressive increase of the average
phonon energy from Se-rich to S-rich
alloys that follows a simple reduced-mass scaling model. Polarization-resolved spectroscopy further shows a monotonic increase of the circular polarization from nearly zero in MoSe$_2$ to $\sim$15% in MoS$_2$ at 78 K. The observed
evolution of the polarization is attributed to
alloy-induced modifications of the electronic structure that modify bright–dark
exciton mixing and the associated valley depolarization. These findings establish
alloy engineering as an effective strategy for controlling excitonic properties in TMD monolayers.
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All authors Eirini Katsipoulaki, Adlen Smiri, Panagiotis Spiliotakis, Konstantinos Mourzidis, Danae Katrisioti, Takashi Taniguchi, Kenji Watanabe, Georgios Kopidakis, Zdenek Sofer, Gang Wang, Emmanuel Stratakis, George Kioseoglou, Iann C. Gerber, Xavier Marie, Ioannis Paradisanos
Materials Science
Picometre-scale real-time drift correction in TEM and STEM by dynamic control of the specimen stage for atomic-resolution imaging
Christophe Gatel, Julien Dupuy, Teresa Hungria et al. (+1 more)
In this work, we show how the specimen drift can be actively compensated by controlling the stage with precision down to the picometre scale. We do this by dynamic control, a generic real-time feedback framework designed to actively stabilize electron microscopy experiments by continuously monitoring an experimental variable from the detector data stream and compensating its
evolution during acquisition. The framework, applicable to a broad range of controllable experimental instabilities, includes automated calibration procedures, operates in parallel with image acquisition and is implemented as a software plugin without requiring any hardware modification of the microscope. Results for live drift correction are shown for a selection of TEM and STEM instruments using conventional mechanical stages as well as piezoelectric stages. Experimental results are presented for medium resolution TEM, high-resolution TEM, HR-STEM and in situ observations. With piezoelectric stages, specimen stabilization down to the picometre scale was achieved allowing drift-corrected atomic-resolution imaging. Specimen stage-based stabilization significantly improves long-exposure imaging and in situ experiments by increasing the effective exposure time, preserving the field of view, maintaining identical optical conditions and eliminating the need for numerical
alignment of large
datasets. Beyond the specific application presented here, dynamic control provides a versatile framework for real-time regulation of electron microscopy experiments and opens new perspectives for quantitative imaging, automated in situ studies and
multimodal acquisitions.
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All authors Christophe Gatel, Julien Dupuy, Teresa Hungria, Martin J. Hytch
Soft Condensed Matter
Hydrodynamic description of proliferating active matter
Nathan Silvano, Emilio Hernandez-Garcia and Cristóbal López
We develop a continuum theory for proliferating active matter starting from a microscopic
stochastic model of self-propelled particles undergoing birth, death, and nonlocal competition. Beginning from the master equation, we derive mean-field
evolution equations for the particle density and polarization fields and close the resulting hierarchy through a von Mises ansatz, providing a coupled hydrodynamic description applicable to a broad class of proliferating active systems. As an application, we study the recently introduced Active Brownian Bug model, in which the form of flocking emerges despite the absence of explicit
alignment interactions. Linear stability analysis predicts both Turing and
Hopf instabilities, whose analytical thresholds agree with numerical simulations. The continuum model reproduces the principal dynamical regimes of the underlying particle system, including homogeneous states, stationary periodic clusters, and coherently propagating flocking states. These results establish a general continuum framework for proliferating active matter and provide a physical interpretation of collective motion driven by the interplay between activity and population dynamics.
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Materials Science
Bias Tunable Transport Modulation and Gas Selectivity in Layered BiOI: A DFT NEGF Study
Jemal Yimer Damte, Jiří Houška, Pavel Baroch et al. (+1 more)
Understanding the interplay between adsorption energetics and charge-transport modulation is essential for the rational design of low-power and bias-tunable gas sensors. Here, we present a comprehensive first-principles study of gas selectivity in layered bismuth oxyiodide (BiOI) by integrating density functional theory with nonequilibrium Green's function transport calculations. The adsorption and bias-dependent transport responses toward NO2, NH3, CO2, and representative volatile organic compounds are systematically examined. While NH3 and NO2 exhibit strong chemisorption and localized electronic perturbations, CO2 interacts through weak physisorption, demonstrating that adsorption strength alone does not determine sensing performance. Instead, the
evolution of transmission channels near the
Fermi level governs the sensing response. Bias-dependent calculations reveal an electrically tunable sensitivity hierarchy, in which weakly adsorbed CO2 preserves conductive pathways and exhibits pronounced low-bias sensitivity despite minimal charge transfer. Recovery-time analysis further highlights the trade-off between transport modulation and reversibility for strongly adsorbed species. These results establish a transport-centered selectivity framework for layered BiOI and provide mechanistic insight into electric-field-controlled gas sensing under ambient conditions.
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All authors Jemal Yimer Damte, Jiří Houška, Pavel Baroch, Xue Yong
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Single-molecule strong optomechanical regimes in SERS via hybrid plasmonic cavities
Miguel Á. Martínez-García, Johannes Feist and Diego Martín-Cano
We identify enhanced strong coherent Surface-Enhanced Raman Scattering (SERS) interactions facilitated by hybridized metallo-dielectric cavities with a resonant fluorescent molecule. By illuminating a detuned electronic transition near saturation via a narrowband hybrid plasmonic mode, we observe enhanced splittings in the Stokes and anti-Stokes spectra, revealing strong optomechanical coupling and nonlinear vibrational modifications at intensities far below irreversible SERS damage thresholds. We compute the second-order
photon correlations that allows identifying the nonclassical character associated to these strong optomechanical interactions and SERS configurations that enables them to optically characterize the anharmonic character of the vibrational modes.
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Materials Science
AccelNet: Exact backward-compatible acceleration of polynomial angular descriptors through Cartesian moment factorization
Yuki Nagai
We present AccelNet, an exact, backward-compatible method for accelerating existing trained aenet and n2p2 neural-network potentials without retraining. For angular terms with separable one-neighbor weights and a finite
polynomial dependence on $\cos \theta$, the method exploits their hidden finite-rank structure to replace explicit neighbor-pair loops by one-neighbor Cartesian moments. AccelNet reads models trained with either package and reproduces their descriptors, energies, and analytic forces to floating-point roundoff. We verified this equivalence for H$_2$O and TiO$_2$ models and tested the resulting potentials in LAMMPS molecular-dynamics simulations. The implementation, model-conversion tools, and LAMMPS interfaces are released as open-source software. AccelNet also enables GPU-accelerated molecular dynamics with existing aenet and n2p2 potentials. Moment evaluation achieves speedups of up to 10.9 on a CPU and 15.8 on a GPU relative to direct evaluation within AccelNet. The implementation, model-conversion tools, and LAMMPS interfaces are released as open-source software.
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Other Condensed Matter
Topological properties and phase diagram of the triangular Hofstadter model with staggered flux
Qi Gao and Wei Chen
We study the topological properties and phase diagram of the triangular Hofstadter model with staggered flux in adjacent triangles in this work. This
lattice can be used to describe the low energy physics of the twisted
bilayer transition metal dichalcogenides (TMD) in a certain range of the electric displacement field between the two layers. We show that the Hofstadter spectrum of this model is generally asymmetric except at specific staggered flux $3\phi= \pi/2 \mod {\pi}$ due to an additional P
symmetry at such $\phi$. Breaking the translation
symmetry by dimerization lifts the P
symmetry and results in rich topological phases in the system. The dimerized model with different rational external
magnetic flux ${\Phi}_B = 2\pi p/q$ has phase diagram with the following common features. For even q, the dimerized model generally has three gapped regimes. The one with small dimerization has finite Chern number and the other two have zero Chern number. For odd q, the model is gapped with zero Chern number at any finite dimerization. For both q even and odd, the two regimes with zero Chern number can be further characterized by the inversion
symmetry of the parametrized one-dimensional chains of the system at \phi = 0 \mod \pi/3$, and one regime is topologically non-trivial and the other is trivial. Our results may be tested in twisted
bilayer TMD with weak interaction or cold atom systems in optical
lattice or photonic
crystals achieved in recent experiments.
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Strongly Correlated Electrons
Fluctuations of topological charges in two-dimensional classical Heisenberg model through high-temperature and low-temperature expansions
Shan-Chang Tang
It is well known that KT transition in 2d XY model is driven by the binding and unbinding of topological defects, which can be characterized by the fluctuation of topological charges inside a region. We extend the idea into the 2d Heisenberg model and calculate the fluctuation through high-temperature and low-temperature expansion respectively. It is found that the fluctuation of topological charges is proportional to the area of the region at high temperatures while obeys the perimeter law at low temperatures.
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Strongly Correlated Electrons
Contrasting anisotropic electron-phonon-spin coupling in Fe$_{3}$GeTe$_{2}$ and Fe$_{5}$GeTe$_{2}$: A helicity-resolved Raman study
Smrutiranjan Mekap, Jyoti Saini, Andrzej Ptok et al. (+4 more)
Two-dimensional van der Waals ferromagnets Fe$_3$GeTe$ _2$ (F3GT) and Fe$_5$GeTe$_2$ (F5GT) exhibit pronounced magneto-optical responses, which open promising platforms for investigating the interplay among
lattice, electronic, and
magnetic degrees of freedom. Here, we present a comparative study of optical resonance-induced anisotropic electron-
phonon coupling and its association with
magnetic ordering in these systems using wavelength- and temperature-dependent helicity-resolved Raman spectroscopy. By resolving the doubly degenerate E modes under left- and right-circularly polarized excitations, we demonstrate that the temperature
evolution of the
chiral mode splitting ($\Delta f$) does not track the magnetization behavior, indicating that the helicity-dependent Raman response arises not solely from time-reversal
symmetry breaking due to
magnetic order, but also from
spin-orbit-coupled electronic interactions. Notably, in F3GT, the out-of-plane magnetization indirectly governs the in-plane anisotropic electron-
phonon coupling under optical resonance, whereas F5GT exhibits static anisotropic interactions. The Fano asymmetry parameter $1/q$ reveals mode- and temperature-dependent coupling strengths between
phonons and the electronic continuum, with pronounced angular anisotropy in F3GT but isotropic behavior in F5GT— a consequence of its multiple Fe sites and enhanced interlayer hybridization in the latter. Our results demonstrate the role of
crystal structure and
magnetic anisotropy in shaping the anisotropically coupled electron-
phonon-
spin dynamics in these layered metallic ferromagnets, and highlight Fe$_n$GeTe$_2$ as a versatile platform for microscopic insight into
chiral light-matter interactions in layered metallic ferromagnets.
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All authors Smrutiranjan Mekap, Jyoti Saini, Andrzej Ptok, Pawan Kumar Srivastava, Changgu Lee, Subhasis Ghosh, Anushree Roy
Soft Condensed Matter · Cross-listed from physics.chem-ph
Negative Differential Capacitance from Composition-Dependent Stern Capacitance in a Binary Mixture
Yuki Uematsu
We develop a thermodynamic theory of electric double layers in binary
liquid mixtures by allowing the Stern-layer capacitance to depend on the local solvent composition. This coupling produces an additional negative contribution to the inverse differential capacitance. As a result, the surface potential can become a nonmonotonic function of the surface charge density, leading to negative differential capacitance and a voltage-induced first-order transition between two electric-double-layer states. We determine the coexistence condition using a common-tangent construction for the surface-charge-controlled grand potential and obtain phase diagrams in terms of the Stern-capacitance contrast, surface charge density, bulk composition, and surface potential. We also compare the theory with capacitance data for tetrabutylammonium chloride in water/1-propanol mixtures, finding semi-quantitative agreement in the continuous-response regime. These results suggest that solvent exchange inside the Stern layer can strongly control the capacitance and interfacial phase behavior of binary mixtures.
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Statistical Mechanics
Exact Resonances Are Not Sufficient for Phonon Energy Diffusion
Wei Lin, Yong Zhang and Hong Zhao
Multi-
phonon resonance conditions underpin kinetic theories of
phonon transport and
lattice thermalization. We show that exact resonance matching, nonzero interaction coefficients, and network connectivity do not guarantee persistent energy
diffusion.
Symmetry-enforced balance relations drive exact-resonant collision currents to nonthermal zero-flux states, producing kinetic arrest from individual resonant sets to connected networks. Complete energy spreading is sustained by quasi-resonances. The thermodynamic and weak-nonlinearity limits do not commute: the leading kinetic behavior is recovered in the former, whereas at fixed finite size the thermalization time diverges through higher-order crossovers as the nonlinearity vanishes. Exact-resonance existence and connectivity are therefore kinematic, not sufficient dynamical, criteria for
phonon energy
diffusion.
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Mesoscale and Nanoscale Physics
Quaternion-Kähler geometry of time reversal symmetric crystals
Hyeongmuk Lim, Junseo Jung, Yuting Qian et al. (+1 more)
Quantum geometry reveals how the shape of Bloch wave functions governs correlated
quantum phenomena. Its standard formulation describes isolated complex bands, where Berry
curvature is Abelian and ideal geometry is Kähler. However, time reversal symmetric
crystals with
spin require a different
language since Kramers degeneracy pairs Bloch states and turns Berry
curvature into a non-Abelian SU(2) field. Here we show that Kramers pair band geometry is quaternionic. A minimal Kramers pair defines a map into quaternion projective space, and its quaternionic
quantum geometric tensor unifies the
quantum metric with the three SU(2) Berry
curvature components. The non-negativity of this tensor imposes local metric-
curvature inequalities, whose saturation defines the non-Abelian counterpart of ideal Chern bands. In four dimensions, the ideal limit further yields an algebraic structure related to the four-dimensional
quantum Hall effect. Our results promote ideal
quantum geometry from the Abelian geometry of Chern bands to the quaternionic, non-Abelian geometry of time reversal symmetric
quantum matter.
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All authors Hyeongmuk Lim, Junseo Jung, Yuting Qian, Bohm-Jung Yang
Materials Science
Apparent Dresselhaus coefficient in (001) GaAs quantum wells: Correlation-time renormalization in D'yakonov-Perel' spin relaxation
Yuzo Ohno, Jun Ishihara and Satoshi Iba
We study the Dresselhaus coefficient inferred from D'yakonov-Perel'
spin relaxation in bulk GaAs and (001) GaAs
quantum wells using nonballistic Monte Carlo simulations. In bulk GaAs, inelastic LO-
phonon simulations reproduce the
spin relaxation with a cubic Dresselhaus coefficient \gamma_{3D}\simeq12.4 eVÅ^3 and a cubic-field correlation time \tau_3^{3D}\simeq150 fs. In a projected two-dimensional
quantum-well model, however, k_z^2 is replaced by the static expectation value \langle k_z^2 \rangle, converting the dominant Dresselhaus field into a term linear in the in-plane wave vector. We show that this projection changes the D'yakonov-Perel' correlation kernel from K_3^{2D} to a first- and third-order hybridized kernel K_{1+3}^{2D}, for which the correlation time \tau_{1+3}^{2D} approaches 235 fs in the strict two-dimensional limit, in contrast to the third-order correlation time \tau_3^{2D} of 130 fs. Consequently, the coefficient entering the projected two-dimensional model is not the intrinsic cubic coefficient itself but an apparent coefficient, \gamma_{2D}^{app}=\gamma_{3D} \sqrt{\tau_3^{2D}/\tau_{1+3}^{2D}}. Since \tau_{1+3}^{2D}\simeq1.8\tau_3^{2D} under LO-
phonon-dominated scattering, \gamma_{2D}^{app}\simeq9.2 eVÅ^3, consistent with
spin relaxation in (001) GaAs
quantum wells. This correlation-time renormalization clarifies why Dresselhaus coefficients extracted from two-dimensional
spin relaxation can differ from the cubic bulk coefficient and provides a useful framework for interpreting linear and cubic Dresselhaus parameters in
quantum wells.
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Statistical Mechanics · Cross-listed from quant-ph
Typical Output States of Monitored Random Clifford Circuits: A Graph-Theoretic Approach
Yu-Xuan Zhang and Yu-Xiang Zhang
In many-body physics, an explicit wavefunction often provides the most thorough understanding, yet for monitored random Clifford
circuit it has remained missing. Here we develop a framework that grants direct access to the typical output states. As every stabilizer state is local-Clifford-equivalent to a graph state, the graph adjacency
matrix, a classical bit
matrix, provides a complete description of the
quantum state. In the large-$N$ limit, we show that these graphs converge to the Erdős–Rényi random graph $G(N,1/2)$, which allows us to resolve the open problem of Greenberger–Horne–Zeilinger (GHZ)
entanglement generated by deep random Clifford
circuits. We obtain analytically the mean GHZ content $\langle g_3\rangle=1.204$ for even $N$ and $1.325$ for odd $N$. For monitored Clifford
circuits with a 1D layout, we uncover an emergent Erdős–Rényi subgraph $G(N_{\mathrm{sub}},1/2)$ in the output states of the volume-law phase, where $N_{\mathrm{sub}}/N\approx \sqrt{1-p/p_c}$ with $p$ the measurement rate and $p_c$ the critical point of the measurement-induced phase transition (MIPT). The output state is thus equivalent to the output of an unmonitored random Clifford
circuit on $N_{\mathrm{sub}}$
qubits, weakly perturbed by the remaining $N-N_{\mathrm{sub}}$
qubits carrying little
entanglement. This result directly accounts for the
quantum error-correcting capability of the volume-law phase, and implies the same GHZ statistics for the whole volume-law phase. We further identify a clustering effect for
qubits in the dense subgraph, which we reproduce with an infection-recovery toy model that exhibits a measurement-induced absorbing-state phase transition. Finally, a mean-field argument on the graph locates the MIPT critical point at $p_c = 0.1608$, in excellent agreement with the numerical value $p_c\approx 0.16$.
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