Soft Condensed Matter · Cross-listed from physics.flu-dyn
Nature of continuous spectra in wall-bounded shearing flows of FENE-P fluids
Pratyush Kumar Mohanty, P. S. D. Surya Phani Tej, Ganesh Subramanian et al. (+1 more)
Owing to the spatially local nature of the constitutive equations typically used to model polymeric stresses, the differential operators governing the linearized dynamics of bounded viscoelastic shearing flows have singular points. As a result, the eigenspectra of such shearing flows contain, in addition to discrete
eigenvalues, continuous spectra (CS) comprising singular eigenfunctions. A clear understanding of the theoretical CS loci is crucial in discriminating physically genuine (discrete)
eigenvalues from the poorly approximated numerical CS. For rectilinear shear flows of Oldroyd-B fluids, the CS are a pair of line segments, with lengths equal to the base-state range of velocities. In this study, we provide the first comprehensive account of the nature of the CS for both rectilinear and curvilinear shearing flows of the FENE-P fluid. In stark contrast to the CS for the Oldroyd-B fluid mentioned above, we show analytically that there are up to six distinct continuous spectra for shearing flows of FENE-P fluids. When the finite extensibility parameter $L > 50$, as appropriate for large molecular weight
polymers used in experiments, three of the CS are nearly identical, and independent of the solvent-to-solution viscosity ratio ($\beta$). The other three CS are $\beta$-dependent, with one of them being the analogue of the solvent (viscous) continuous spectrum in the Oldroyd-B fluid. The remaining two $\beta$-dependent CS are novel features of the FENE-P spectrum, and can have phase speeds outside the base range of velocities, including negative ones. The complexity of the CS predicted here for shearing flows of FENE-P fluids is expected to carry over to other nonlinear viscoelastic models that exhibit a shear-thinning rheology.
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All authors Pratyush Kumar Mohanty, P. S. D. Surya Phani Tej, Ganesh Subramanian, V. Shankar
Strongly Correlated Electrons
Local Irreversible phase reconfiguration and thermal-memory effects in a highly-correlated manganite
Guilherme Kuhl-Soares, Otávio Canton, Eduardo Granado et al. (+5 more)
Phase-separated manganites provide a unique platform to study the dynamics of competing electronic and structural orders in correlated systems. In La0.275Pr0.35Ca0.375MnO3 (LPCMO), we use temperature-cycling Raman spectroscopy to uncover a previously unidentified regime of structural irreversibility, emerging from the interplay between
lattice distortions and phase competition across the phase-separation and charge-orbital ordering temperatures. This irreversible behavior encodes a thermal-
memory effect reflecting the system's history-dependent energy landscape. Correlated
magnetic and transport responses confirm the coupling between
lattice and electronic degrees of freedom, revealing a new form of nonequilibrium phase dynamics in mixed-valence
oxides. These results advance the understanding of metastability and
memory phenomena in strongly correlated materials.
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All authors Guilherme Kuhl-Soares, Otávio Canton, Eduardo Granado, Diego Carranza-Célis, Marcelo Knobel, Gabriel Gomide, Juan Gabriel Ramirez, Diego Muraca
Materials Science
Angle and time-resolved polarization change induced by Kerr effect in amorphous and crystalline SiO2
Lample Pierrick, Weis Mateusz, Boschetto Davide et al. (+1 more)
We measure the polarization change of a beam reflected from the surface of both crystalline alpha and amorphous SiO2 samples while they are photo-excited by an intense light pulse, at intensities above the nonlinear excitation threshold yet below the damage threshold. The polarization change varies with the angle between the polarization of pump and probe light, but is found to be independent of their orientation relative to the
crystal axes. This behavior differs between the reflected and transmitted beams, and can be modeled by taking into account a birefringence induced by the electric field of the pump. These polarization-change effects can be very strong, with polarization rotation exceeding 90{\deg}, at pump intensities well below the damage threshold. We also observe a markedly different behavior of the reflected beam depending on whether the material is crystalline or amorphous.
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All authors Lample Pierrick, Weis Mateusz, Boschetto Davide, Guizard Stéphane
Mesoscale and Nanoscale Physics · Cross-listed from astro-ph.EP
Radial modes of pressure bumps and dips in astrophysical discs
Armand Leclerc, Guillaume Laibe, Elliot Lynch et al. (+1 more)
This study investigates the signatures of pressure extrema on global oscillations in discs. To this end, we use the framework of wave
topology to establish a generalised local dispersion relation that includes pressure gradients. We highlight the influence of a previously unrecognized epicyclic-acoustic frequency and derive an analytical criterion for the existence of a branch of modes transiting between the inertial and the pressure bands. We find that pressure extrema consist of wave guides in which such topological modes propagate. The fundamental mode trapped at a pressure bump can propagate at all frequencies, allowing it to resonate with any temporal forcing, while the mode associated with a pressure gap propagates at a fixed frequency, propagates with arbitrary vertical phase velocity. These specific features make them attractive candidates for future discoseismology.
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All authors Armand Leclerc, Guillaume Laibe, Elliot Lynch, Nicolas Perez
Strongly Correlated Electrons
Sliding phasons in Moiré Ladders
Paula Mellado, Francisco Muñoz and Javiera Cabezas-Escares
An incommensurate charge density wave is a periodic modulation of charge that breaks translational
symmetry at a momentum that does not coincide with the primitive
lattice vectors. Its Goldstone excitation, the phason, comprises collective gapless phase fluctuations. Aiming to unveil the mechanism behind the onset of incommensurate charge order in layered materials, we study a half-filled, four-band tight-binding model on a ladder with a relative shift \(\delta=p/q\) between the legs, induced by the dimerization of one of them. The shift results in a moiré supercell comprising \(q\) composite
cells and a modulated inter-leg tunneling. The moiré potential compresses the leg bands into flat minibands near the
Fermi level, resulting in additional low-energy peaks in the density of states. Including Coulomb interactions, we find an incommensurate charge-density-wave phase in which the charge modulation is out of phase between the legs. The collective excitations of this state are long-lived neutral, acoustic phasons whose speed is controlled by the moiré parameter \(\delta\) and the inter-leg tunneling amplitude. This model sheds light on the role of interlayer incongruities in the formation of excitonic charge-ordered phases in van der Waals and heterostructured materials.
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Materials Science · Cross-listed from physics.chem-ph
Comparing the latent features of universal machine-learning interatomic potentials
Sofiia Chorna, Davide Tisi, Cesare Malosso et al. (+3 more)
The past few years have seen the development of “universal” machine-learning interatomic potentials (uMLIPs) capable of approximating the ground-state potential energy surface across a wide range of chemical structures and compositions with reasonable accuracy. While these models differ in the architecture and the
dataset used, they share the ability to compress a staggering amount of chemical information into descriptive latent features. Herein, we systematically analyze what the different uMLIPs have learned by quantitatively assessing the relative information content of their latent features with feature reconstruction errors, and observing how the trends are affected by the choice of training set and training protocol. We find that uMLIPs encode the chemical space in significantly distinct ways, with substantial cross-model feature reconstruction errors. When variants of the same model architecture are considered, trends become dependent on the
dataset, target, and training protocol of choice. We also observe that fine-tuning of a uMLIP retains a strong pre-training bias in the latent features. Finally, we discuss how atom-level features, which are directly output by MLIPs, can be compressed into global structure-level features via concatenation of progressive cumulants, each adding significantly new information about the variability across the atomic environments within a given system.
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All authors Sofiia Chorna, Davide Tisi, Cesare Malosso, Wei Bin How, Michele Ceriotti, Sanggyu Chong
Materials Science
Exe.py: Ab initio fine structure parameters for trigonal defect qubits within the E$\otimes$e Jahn-Teller case
Balazs Toth, Adam Gali and Gergo Thiering
Trigonal solid-state defects are often subjects of spontaneous
symmetry breaking driven by the $E\otimes e$ Jahn-Teller effect, reflecting strong electron-
phonon coupling. These systems, particularly paramagnetic defect
qubits in solids are central for
quantum technology applications, where accurate knowledge of their fine-structure parameters $-$ shaped by the complex interplay of
spin-orbit and electron-
phonon interactions $-$ is essential. We introduce the Exe.py code part of the jahn-teller-dynamics package, a Python code that implements the first-principles approach of [Phys. Rev. X 8, 021063 (2018)] to accurately compute the
spin-orbit-
phonon entanglement in trigonal defects utilizing the output from density functional theory calculations (DFT). By employing $\Delta$SCF calculations, the method extends naturally to excited states and predicts fine-structure parameters of zero-
phonon lines (ZPLs), including Zeeman shifts under external
magnetic fields. The approach is applicable not only to solid-state defects but also to Jahn-Teller active trigonal molecules such as the $X$CH$_3$ family. We demonstrate the capabilities of Exe.py through applications to negatively charged Group-IV$-$vacancy (G4V) defects in diamond: SiV$^-$, GeV$^-$, SnV$^-$, PbV$^-$ and the neutral N$_3$V$^0$ defect in diamond, and the CH$_3$O methoxy radical.
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Materials Science
In situ mapping of indentation-induced densification and cracking in vitreous silica by nanofocus X-ray scattering
Johan F. S. Christensen, M. Faizal Ussama Jalaludeen, Søren S. Sørensen et al. (+9 more)
The practical strength of
oxide glasses is greatly reduced by surface flaws that form during processing and use. Instrumented indentation can mimic such real-life damage events and induce flaws and cracking under controlled conditions. At the same time, instrumented indentation allows for systematic examination of the deformation and structural changes of the regions of the glass being indented. However, structural probing is nearly always performed after rather than during the sharp contact event, limiting our understanding of the indentation process. To overcome this, we here demonstrate the use of nanofocus X-ray scattering experiments to probe the local mechanical and structural response of vitreous silica during indentation. Two-dimensional mapping of the scattering pattern in the zone below a sharp diamond wedge indenter reveals local changes in the atomic structure and density as well as cracking behavior. These in situ experiments during indentation reveal the formation and
evolution of the densification zone and cracking with nanoscale resolution. Understanding the interplay between structural densification and cracking behavior in glasses is deepened through this work, which is crucial for the development of more damage-resistant and thus stronger glasses as well as fundamental understanding of glass deformation mechanisms.
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All authors Johan F. S. Christensen, M. Faizal Ussama Jalaludeen, Søren S. Sørensen, Anders K. R. Christensen, Xuan Ge, Tao Du, Yuanzheng Yue, Anton Davydok, Christina Krywka, Lothar Wondraczek, Henning F. Poulsen, Morten M. Smedskjaer
Strongly Correlated Electrons
Excitonic Charge Density Waves in Moire Ladders
Paula Mellado, Francisco Muñoz and Javiera Cabezas-Escares
An incommensurate charge density wave (CDW) is a periodic modulation of charge that breaks translational
symmetry incongruently with the underlying
lattice. Its low-energy excitations, the phason, are collective, gapless phase fluctuations. We study a half-filled, four-band ladder model where a shift \(\delta = p/q\) between the legs leads to a supercell of \(q\) composite
cells. The moiré potential narrows minibands near the
Fermi level, resulting in additional peaks in the density of states, whose separation is controlled by \(\delta\). The inclusion of short-range Coulomb interactions leads to an excitonic incommensurate CDW state. We identify the oscillations in its amplitude with a gapped
Higgs collective mode and a lowest-energy Goldstone mode, realized by long-lived neutral phasons whose propagation velocity is governed by the shift \(\delta\) and the inter-leg tunneling amplitude. Our results show that even the slightest interlayer mismatches can strongly modify both charge-ordering patterns and low-energy bosonic excitations in layered materials, and suggest that the enigmatic CDW phase in the quasi-one-dimensional compound \(\rm HfTe_3 \) is excitonic in nature.
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Quantum Gases
Quenching dynamics of vortex in spin-orbit coupled Bose-Einstein condensates
Juan Wang, Zhenze Fan and Yan Li
We investigate the ground states and rich dynamics of
vortices in
spin-orbit coupled Bose-Einstein condensates (BEC) subject to position-dependent detuning. Such a detuning plays the role of an effective rotational frequency, causing the generation of a synthetic
magnetic field. Through scanning the detuning gradient, we numerically obtain static
vortex lattice structures containing 1 to 6
vortices using the coupled Gross-Pitaevskii equations. When quenching detuning gradient below its initial value, the
vortex lattices exhibit interesting periodic rotation motion, and their dynamical stability can persist for up to 1000ms. In particular, depending on the detuning gradient, the twin
vortices exhibit either a scissors-like rotational oscillation or a clockwise periodic rotation, reflecting the response to the
magnetic field gradient experienced by the condensates. We fit the numerical results to quantitatively analyze the relation between rotation dynamics and
magnetic field gradients. When quenching the detuning gradient beyond its initial value, additional
vortices appear. Our findings may motivate further experimental studies of
vortex dynamics in synthetic
magnetic fields and offer insights for engineering a BEC-based
magnetic field gradiometer.
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Materials Science
Improving 2D-ness to enhance thermopower in oxide superlattices
Dongwon Shin, Inseo Kim, Min-Su Kim et al. (+6 more)
The transport dynamics of itinerant charge carriers and their interactions with the environment. For two-dimensional
oxide thermoelectrics, predominantly represented by doped SrTiO3-based superlattices, reduced spatial dimensions and increased effective mass are known to enhance thermopower (S). However, because of their large effective Bohr radius resulting from their high dielectric constant, SrTiO3-based systems have limitations in exhibiting the 2D characteristic. Here, we focus on EuTiO3 as an alternative perovskite platform in which fractional LaxEu1-xTiO3/EuTiO3 artificial superlattices demonstrate the improvement in 2D nature for the dimensionality-induced improvement of S. We observed a quasi-2D thermopower S2D of -950 uV K-1 and S2D/S3D of ~20 resulting from the improved 2D confinement. Thermopower measurements, combined with hybrid density functional theory calculations, show the enhanced S originates from the confinement of Ti 3dxy-states within the LaxEu1-xTiO3 layers and the associated increase in the 2D density of states. In detail, a smaller effective Bohr radius and modified electronic band structures, in conjunction with the presence of the Eu 4f-states in EuTiO3 which modified the local electronic potential and strengthened the spatial confinement of Ti 3d-states. This approach to improving the dimensional confinement establishes a small effective Bohr radius and Eu 4f-state assisted 2D confinement provides valuable insights into the design of high-performance applications in artificial
oxide superlattices.
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All authors Dongwon Shin, Inseo Kim, Min-Su Kim, Yu-Qiao Zhang, Woo Tack Lim, Si-Young Choi, Minseok Choi, Hiromichi Ohta, Woo Seok Choi
Statistical Mechanics · Cross-listed from physics.flu-dyn
Uncertainty Growth in Stably Stratified Turbulence
Mrinal Jyoti Powdel and Samriddhi Sankar Ray
We investigate uncertainty growth and chaotic dynamics in statistically steady, stably stratified three-dimensional
turbulence. Using direct numerical simulations of the Boussinesq equations, we quantify the divergence of initially infinitesimal perturbations via twin simulations and decorrelator diagnostics. At short times, perturbations exhibit exponential growth, allowing us to define a (largest) Lyapunov exponent. We systematically examine how this exponent depends on stratification strength, quantified by the Brunt–Väisälä frequency and the Froude number, in a parameter regime relevant to oceanic flows. We find that increasing stratification leads to a monotonic reduction of the Lyapunov exponent, indicating suppressed chaoticity. Despite this reduction, uncertainty growth retains the universal temporal sequence observed in homogeneous isotropic
turbulence – initial decay, exponential growth, and saturation. The growth phase is characterized by self-similar decorrelator spectra, but exhibits strong anisotropy: uncertainty spreads much more slowly along the stratification direction than horizontally, with the disparity increasing with stratification strength. An analysis of the decorrelator
evolution equation reveals that the suppression of chaos arises primarily from strain-mediated
alignment dynamics rather than direct buoyancy coupling. Our results provide a quantitative characterization of predictability and uncertainty growth in stratified
turbulence and highlight the utility of decorrelator-based methods for anisotropic geophysical flows.
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Mesoscale and Nanoscale Physics
Excitation of quasiparticle pairs in superconducting nanodevices by 1/f noise
Clare C. Yu, M. C. Goffage, Yifan Wang et al. (+3 more)
Superconducting nanodevices such as
qubits, resonators, and photodetectors, have revolutionized our capabilities for probing and controlling
quantum phenomena. Nonequilibrium quasiparticles, which are broken Cooper pairs that cause decoherence and energy loss, can limit their performance. The number of these quasiparticles is often tens of orders of magnitude greater than would be present in thermal
equilibrium. Background radiation has been shown to excite quasiparticles, but quasiparticles are observed even when the devices are carefully shielded. Here we show that the high-frequency components of 1/f noise can excite quasiparticle pairs and that this mechanism is consistent with previously unexplained experimental results. We also propose new experiments that exploit this quasiparticle excitation mechanism to non-invasively characterize high-frequency charge noise as well as the locations and nature of the defects producing the noise. The proposed experiments would also investigate how this noise changes as the defects that give rise to it evolve towards thermal
equilibrium.
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All authors Clare C. Yu, M. C. Goffage, Yifan Wang, A. Alase, M. C. Cassidy, S. N. Coppersmith
Statistical Mechanics
The geometric control of boundary-catalytic branching processes
Denis S. Grebenkov and Yilin Ye
Boundary-catalytic branching processes describe a broad class of natural phenomena where the population of diffusing particles grows due to their spontaneous binary branching (e.g., division, fission or splitting) on a catalytic boundary located in a complex environment. We investigate the possibility of the
geometric control of the population growth by compensating the proliferation of particles due to catalytic branching events by their absorptions in the bulk or on absorbing regions of the boundary. We identify an appropriate Steklov spectral problem to obtain the phase diagram of this out-of-
equilibrium stochastic process. The principal
eigenvalue determines the critical line that separates an exponential growth of the population from its extinction in a bounded domain. In other words, we establish a powerful tool for calculating the growth-regulating absorption rate that equilibrates the opposite effects of branching and absorption events and thus results in steady-state behavior of this
diffusion-reaction system. Moreover, we show the existence of a critical catalytic rate above which no compensation is possible, so that the population cannot be controlled and keeps growing exponentially. The proposed framework opens promising perspectives for better understanding, modeling and control of various boundary-catalytic branching processes, with applications in physics, chemistry, and life sciences.
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Quantum Gases · Cross-listed from quant-ph
Squeezing Classical Antiferromagnets into Quantum Spin Liquids via Global Cavity Fluctuations
Charlie-Ray Mann, Mark A. Oehlgrien, Błażej Jaworowski et al. (+4 more)
Cavity
quantum electrodynamics with atomic ensembles is typically associated with collective
spin phenomena, such as superradiance and
spin squeezing, in which the atoms evolve collectively as a macroscopic
spin ($S\sim N/2$) on the Bloch sphere. Surprisingly, we show that the tendency toward a collective
spin description need not imply collective
spin phenomena; rather, it can be exploited to generate new forms of strongly correlated
quantum matter. The key idea is to use uniform cavity-mediated interactions to energetically project the system into the total-
spin singlet sector ($S=0$) - a highly entangled subspace where the physics is governed entirely by cavity fluctuations. Focusing on Rydberg atom arrays coupled to a single-mode cavity, we show that global cavity fluctuations can effectively squeeze classical antiferromagnets into
quantum spin liquids, characterized by non-local
entanglement, fractionalized excitations, and emergent gauge fields. This work suggests that cavity QED can be a surprising resource for inducing strongly correlated phenomena, which could be explored in the new generation of hybrid tweezer-cavity platforms.
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All authors Charlie-Ray Mann, Mark A. Oehlgrien, Błażej Jaworowski, Giuseppe Calajó, Jamir Marino, Kyung S. Choi, Darrick E. Chang
Statistical Mechanics
Sticky eigenstates in systems with sharply divided phase space
Hua Yan
We investigate mixed eigenstates in systems with sharply divided phase space, using different piecewise-linear maps whose regular-chaotic boundaries are formed by marginally unstable periodic orbits (MUPOs) or by quasi-periodic orbits. With the overlap index and the
entropy localization length, we classify mixed eigenstates and show that the contribution from dynamical tunneling scales as $\sim \hbar\, \exp(-b/\hbar)$, with $b>0$ associated with the relative size of the regular region. The dominant fraction of states that remain sticky to the boundaries, referred to as sticky eigenstates, scales approximately as $\hbar^{1/2}$ in the MUPO case and oscillates around this algebraic behavior in the quasiperiodic case. This behavior generalizes established predictions for hierarchical states in Kolmogorov-Arnold-Moser (KAM) systems, which scale as $\hbar^{1 - 1/\gamma}$, with $\gamma$ set by the corresponding classical stickiness reflected in the algebraic decay of cumulative recurrence-time distributions $t^{-\gamma}$. For the piecewise-linear maps studied here, $\gamma = 2$. These results reveal a clear
quantum signature of classical stickiness in non-KAM systems.
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Mesoscale and Nanoscale Physics
Toward a Theoretical Roadmap for Organic Memristive Materials
Salvador Cardona-Serra
Neuromorphic computing aspires to overcome the intrinsic inefficiencies of von Neumann architectures by co-locating
memory and computation in physical devices that emulate biological
neurons and synapses. Memristive materials stand at the core of this paradigm, enabling non-volatile, history-dependent electronic responses. While inorganic
oxides currently dominate the field, molecular and polymeric systems can offer untapped advantages in terms of chemical tunability, structural flexibility, low-cost processing, and biocompatibility. However, progress has been hindered by the absence of a theoretical framework able to rationalize how molecular structure translates into memristive function. Here, a multiscale computational perspective is presented, outlining how
quantum chemistry and molecular dynamics, among other approaches, can be integrated into a coherent methodology to design next-generation organic memristors. Three mechanisms, ionic migration, redox-driven switching, and conduction interplay in
chiral molecules are examined as representative routes toward molecular neuromorphic hardware. The opportunities and challenges associated with each mechanism are discussed, together with a view on how a theoretically guided roadmap can accelerate the emergence of chemically engineered synaptic materials.
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Materials Science
Suppression of stripe-ordered structural phases in monolayer IrTe$_2$ by a gold substrate
Kati Asikainen, Frédéric Chassot, Baptiste Hildebrand et al. (+12 more)
Metal-assisted exfoliation of two-dimensional (2D) materials has emerged as an efficient route to isolating large-area monolayer
crystals, yet the influence of the supporting metal substrate on their intrinsic properties remains poorly understood. Here, we demonstrate successful gold-assisted exfoliation of monolayer IrTe$_2$ up to the millimeter scale. Angle-resolved photoemission spectroscopy (ARPES), combined with first-principles calculations, reveals that the low-energy electronic structure closely resembles that of a freestanding monolayer 1T-IrTe$_2$. We find that quasi-covalent hybridization together with substrate-induced strain leads to only modest modifications of the electronic bands. Although strain contributes to phase stability, it is essentially hybridization that drives the stabilization of the 1T-phase of the monolayer IrTe$_2$ by suppressing stripe-ordered phase transitions. These results establish gold-assisted exfoliation as a robust route to prepare a large-area monolayer IrTe$_2$ and highlight the role of metal-substrate interaction in engineering 2D materials with tailored structural phases.
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All authors Kati Asikainen, Frédéric Chassot, Baptiste Hildebrand, Aymen Mahmoudi, Joel Morf, Mahault Berset, Pascal Turban, Matti Alatalo, S. Assa Aravindh, Marko Huttula, KeYuan Ma, Fabian O. von Rohr, Jean-Christophe Le Breton, Thomas Jaouen, Claude Monney
Materials Science
Prussian Blue and Prussian Blue Analogs as Emerging Memristive Materials
L.B. Avila
Prussian blue analogues (PBAs) and related organic materials are promising platforms for next-generation
memory and energy-storage technologies due to their redox activity, ionic mobility, and compatibility with low-cost and scalable fabrication. Electrodeposited Prussian Blue (PB) and Prussian White (PW) thin films show robust resistive switching with ON/OFF ratios from one to three orders of magnitude in both bipolar and unipolar modes. Structural and spectroscopic analyses reveal homogeneous films with well-defined grain boundaries and ionic pathways that enable filamentary conduction. Current-voltage measurements, impedance spectroscopy, and
quantum transport modeling indicate switching mechanisms governed by ohmic or space-charge-limited conduction, driven by potassium-ion migration and reversible redox processes. PB-based devices also exhibit conductance quantization with discrete steps at integer and half-integer multiples of G0, consistent with ballistic electron transport through atomic-scale channels. Complementary studies on perylene-based
liquid crystals and FeHCF on
graphene oxide highlight the versatility of PBAs for
memory and supercapacitor applications. Together, these results demonstrate the multifunctionality and scalability of PBAs for future ReRAM, neuromorphic computing, multilevel
memory, cryptographic hardware, and high-performance energy-storage devices.
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Other Condensed Matter
Plasmascopy of ultrafast hot charges in solids
Dmitry A. Zimin, Raja Sen, Muhammad Qasim et al. (+2 more)
We demonstrate an electric field-resolved approach for probing ultrafast dynamics of photoinjected charges in solids. Direct access to the electric field of few-cycle pulses enables us to measure a broadband response of a medium with associated
plasma frequency. We prepare an ensemble of photoinjected hot charge carriers with energies sufficient to trigger impact ionization and establish a framework to measure its dynamics. Our study reveals the first time-resolved observation of the short-lived ultrafast impact ionization in germanium counteracted by trapping of mobile charges at later times. This approach provides a promising route for studying ultrafast many-body physics in photoexcited solids, with predictions from advanced theoretical models.
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All authors Dmitry A. Zimin, Raja Sen, Muhammad Qasim, Jelena Sjakste, Vladislav S. Yakovlev
Materials Science
Revealing interstitial energetics in Ti-23Nb-0.7Ta-2Zr gum metal base alloy via universal machine learning interatomic potentials
Miroslav Lebeda, Jan Drahokoupil, Veronika Mazáčová et al. (+1 more)
Understanding the behavior of light interstitial elements in multicomponent
alloys remains challenging due to the complexity of local chemical environments and the high computational cost of first-principles calculations. Here we demonstrate that three universal machine-learning interatomic potentials (uMLIPs) - MACE-MATPES-PBE-0, Orb-v3, and SevenNet-0 can efficiently map the energetics of C, N, O, and H interstitials in a Ti-23Nb-0.7Ta-2Zr (at.%) gum metal base
alloy while being several orders of magnitude faster than density functional theory (DFT). All uMLIPs predict broad energy distributions (~1-3 eV) across the four interstitial elements, reflecting their strong sensitivity to local
lattice chemistry. Despite
alloy disorder, MACE-MATPES-PBE-0 and Orb-v3 reproduce the expected site preferences of the bcc structure: C, N, and O relax into octahedral sites, whereas H stabilizes in tetrahedral positions. In contrast, SevenNet-0 predicts H to be most stable in octahedral coordination, indicating a limitation of this model. Correlation analysis reveals two dominant chemical trends: Ti-rich environments strongly stabilize interstitials, whereas close proximity to Nb is destabilizing. Zr and Ta show no statistically significant influence, likely due to their low concentrations. Benchmarking representative O interstitial configurations against DFT confirms that the uMLIPs reasonably reproduce the energetic ordering of chemically distinct environments. DFT validation confirms that tetrahedral configurations are energetically more favorable than octahedral sites for H interstitials, further illustrating the SevenNet-0 limitation. Overall, we demonstrated that uMLIPs enable computationally efficient, statistically broad characterization of defect energetics in Ti-23Nb-0.7Ta-2Zr gum metal base
alloy and provide insight into how local chemical environments govern interstitial stability.
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All authors Miroslav Lebeda, Jan Drahokoupil, Veronika Mazáčová, Petr Vlčák
Strongly Correlated Electrons
Interplay of Orbital Degeneracy and Vacancies in Stabilizing Collinear Magnetic Order in Cr$_{1+\delta}$Te$_2$
Prasanta Chowdhury, Jyotirmoy Sau, Mohamad Numan et al. (+7 more)
Cr$_{1+\delta}$Te$_2$, a two-dimensional van der Waals ferromagnet, displays a contested
magnetic structure, poised between collinear and non-collinear
spin configurations. In this work, we investigate the
magnetic structure of Cr$_{1.33}$Te$_2$ at the microscopic level by combining single-
crystal neutron diffraction, X-ray absorption spectroscopy, and first-principles calculations.
Neutron diffraction measurements reveal a distinct collinear
spin alignment, whereas spectroscopic analyses reveal inherent structural vacancies at both Cr and Te sites. These vacancies lead to local
symmetry breaking that elevates the orbital degeneracy of the Cr 3$d$ states, as demonstrated by our first-principles analysis. The resulting modification of magnetocrystalline anisotropy emerges as the key mechanism stabilising the collinear
magnetic ground state over the non-collinear one in the presence of vacancies. Our findings uncover a vacancy-driven route to control
spin anisotropy and
magnetic ordering in layered ferromagnets, offering new insights into the design of tunable 2D
magnetic materials.
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All authors Prasanta Chowdhury, Jyotirmoy Sau, Mohamad Numan, Jhuma Sannigrahi, Matthias Gutmann, Gangadhar Das, D. T. Adroja, Saurav Giri, Manoranjan Kumar, Subham Majumdar
Strongly Correlated Electrons
Sub 1 K Adiabatic Demagnetization Refrigeration with Rare-Earth Borates Ba$_3$XB$_9$O$_{18}$ and Ba$_3$XB$_3$O$_9$, X = (Yb, Gd)
Marvin Klinger, Tim Treu, Felix Kreisberger et al. (+4 more)
Adiabatic demagnetization refrigeration (ADR) is regaining relevance for the refrigeration to temperatures below 1 K as global helium-3 supply is increasingly strained. While ADR at these temperatures is long established with paramagnetic hydrated salts, more recently frustrated rare-earth
oxides were found to offer higher
entropy densities and practical advantages since they do not degrade under heating or evacuation. We report structural,
magnetic and thermodynamic properties of the rare-earth borates Ba$_3$XB$_9$O$_{18}$ and Ba$_3$XB$_3$O$_9$ with X = (Yb, Gd). Except for Ba$_3$GdB$_9$O$_{18}$, which orders at 108 mK, the three other materials remain paramagnetic down to their lowest measured temperatures. ADR performance starting at 2 K in a field of 5 T is analyzed and compared to literature results.
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All authors Marvin Klinger, Tim Treu, Felix Kreisberger, Christian Heil, Anna Klinger, Anton Jesche, Philipp Gegenwart
Mesoscale and Nanoscale Physics · Cross-listed from physics.optics
How to measure laser chirp rate at single-emitter excitation energies
Timothée Mounier, Moritz Kaiser, Mert Tuncel et al. (+8 more)
We present a simple and direct method for measuring
laser chirp rate, i.e., group delay dispersion (GDD) of ultrashort
laser pulses at power levels compatible with single-
quantum-emitter excitation. Traditional pulse characterization techniques rely on nonlinear optical processes that require high peak powers, making them unsuitable for the attojoule-to-femtojoule regime relevant to
quantum photonics. Our approach utilizes a wavelength-to-time mapping method in which the arrival times of spectrally filtered components of a broadband pulse are recorded using a superconducting nanowire single-
photon detector and correlated via a high-resolution time-tagging system. The resulting linear relationship between wavelength and arrival time directly yields the dispersion parameter and, subsequently, the GDD. Beyond single-emitter excitation, this technique can be applied in areas such as single-
photon spectroscopy, ultralow-power optical communications, and time-domain
quantum control, where linear and non-destructive dispersion characterization is essential.
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All authors Timothée Mounier, Moritz Kaiser, Mert Tuncel, Iker Avila Arenas, René Schwarz, Ria G. Krämer, Stefan Nolte, Florian Kappe, Yusuf Karli, Gregor Weihs, Vikas Remesh
Materials Science
Mode-resolved logarithmic quasiballistic heat transport in thin silicon layers: Semianalytic and Boltzmann transport analysis
Jae Sik Jin
Nonequilibrium
phonon transport driven by nanoscale hotspot heating in silicon device layers governs heat dissipation in advanced microelectronics and underscores the need for a better microscopic understanding of such processes. Yet the origin of the frequently observed logarithmic (ln) dependence of the apparent thermal response on hotspot size in crystalline silicon, and the role of individual
phonon modes in this regime, remain unclear. Here, we develop a semianalytical, mode-resolved framework in the spectral
phonon mean free path (MFP) domain and validate it against a full-
phonon-dispersion Boltzmann transport model for heat removal from a 10 x 10 nm^2 hotspot in a thin Si layer (thicknesses of 41, 78, and 177 nm) representative of a silicon-on-
insulator transistor. We show that ln-type quasiballistic scaling arises only for modes that lie on a log-uniform conductivity plateau and are diffusive-side or quasiballistic with respect to the hotspot size, whereas fully ballistic long-MFP modes contribute a saturated, nonlogarithmic background, leading to extremely slow suppression of their heat-carrying capability. The resulting
phonon-modal nonlocal spectrum establishes spectral selection rules for ln-regime transport in confined Si and provides a compact basis for incorporating mode-selective quasiballistic corrections into continuum thermal models and for interpreting
phonon-resolved thermometry experiments.
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Soft Condensed Matter
Electrically Tunable Heliconical Smectic Superstructure in Polar Fluids
Hiroya Nishikawa, Dennis Kwaria, Atsuko Nihonyanagi et al. (+3 more)
The ferroelectric nematic (NF) phase and related polar
liquid-crystalline phases form a new class of strongly polarized yet fluid soft matter. Well-recognized heliconical ferroelectric phases such as NTBF and SmC_P^H exist, but their electro-optic functionality in smectic systems has been largely unexplored. Here, we report a newly designed single-component achiral molecule exhibiting a hierarchical polar phase sequence: SmAF-NTBF-HEC-SmC_P^H. The key feature of the SmC_P^H phase is its ability to form a stable macroscopic orientation without any
alignment layers and to enable continuous, reversible pitch modulation over a wide spectral range at ultralow electric fields, approximately one-third of those required for conventional heliconical nematics. The system exhibits characteristic electro-optic properties in the sub-kilohertz range, differentiating it from heliconical materials controlled by dielectric-elastic balance at higher frequencies. In addition, the SmC_P^H phase's polar heliconical smectic structure facilitates enhanced second-harmonic generation via favorable phase matching, thereby establishing a simple and robust platform for low-voltage photonic applications.
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All authors Hiroya Nishikawa, Dennis Kwaria, Atsuko Nihonyanagi, Koki Sano, Hiroyuki Yoshida, Fumito Araoka
Superconductivity
Guest metal-driven quantum anharmonic effects on stability and two-gap superconductivity in carbon-boron clathrates
Xianghui Meng, Yanqing Shen, Xin Yang et al. (+4 more)
Traditionally, strong
quantum anharmonic effects have been considered a characteristic of hydrogen-rich compounds. Here we propose that these effects also play a decisive role in boron-carbon clathrates. The stability and superconducting transition temperature (Tc) of carbon-boron clathrates XYB6C6, whose metal atoms have an average oxidation state of +1.5, have long remained under debate. At this oxidation state, some combinations (e.g., RbSrB6C6) are dynamically stable, whereas others (e.g., RbPbB6C6) are not. Using the
stochastic self-consistent harmonic approximation combined with machine learning, we find that the anharmonicity originates primarily from guest metal atoms. For comparison, we find that
quantum fluctuations have negligible influence on SrB3C3, but remove the
lattice instability of RbPbB6C6. The predicted Tc of RbPbB6C6 (88 K) is nearly twice that of SrB3C3. Moreover, RbPbB6C6 exhibits two-gap superconductivity due to the higher C/B ratio in the density of states at the
Fermi level compared to SrB3C3, weakening the sp3 hybridization. These findings demonstrate that
quantum anharmonicity crucially governs the stability and superconductivity of XYB6C6 clathrates.
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All authors Xianghui Meng, Yanqing Shen, Xin Yang, Xinyu Wang, Qing Ai, Yong Shuai, Zhongxiang Zhou
Soft Condensed Matter
Equation of state for the hard sphere fluids
Can Cui and Jianxiang Tian
Based on the survey of the literatures on the new improvements on the equation of state (EOS) for the hard sphere fluids, we here compare lots of different EOSs and present a very accurate equation of state for this kind of fluids. The new equation is built up on the basis of (1) the best estimated virial coefficients B5-B11 by Tian et al. [ Phys. Chem. Chem. Phys., 2019, 21, 13070] and (2) the newest numerical simulation data of the compressibility factor versus the density by Pieprzyk et al. [Phys. Chem. Chem. Phys., 2019, 21, 6886]. Our results show that this equation is accurate in not only the stable density range but also the metastable density range with the proper closest packing fraction pole, and well derives the predictive values of the high order virial coefficients B13-B16.
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Mesoscale and Nanoscale Physics
Quantum geometry and $X$-wave magnets with $X=p,d,f,g,i$
Motohiko Ezawa
Quantum geometry is a differential geometry based on
quantum mechanics. It is related to various transport and optical properties in condensed matter physics. The Zeeman
quantum geometry is a generalization of
quantum geometry including the
spin degrees of freedom. It is related to electromagnetic cross responses.
Quantum geometry is generalized to non-Hermitian systems and density
matrices. Especially, the latter is
quantum information geometry, where the
quantum Fisher information naturally arises as
quantum metric. We apply these results to the $X$-wave magnets, which include $d$% -wave, $g$-wave and $i$-wave altermagnets as well as $p$-wave and $f$-wave magnets. They have universal physics for anomalous
Hall conductivity, tunneling magneto-resistance and planar
Hall effect. We also study magneto-optical conductivity,
magnetic circular dichroism and Friedel oscillations in the $X$-wave magnets. Various analytic formulas are derived in the case of two-band
Hamiltonians. This paper presents a review of recent progress together with some original results.
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Statistical Mechanics
Observation-Time-Induced Crossover from Fluctuating Diffusivity
Masahiro Shirataki and Takuma Akimoto
A sharp change in apparent mobility at a characteristic temperature that depends on the observation time has been reported in experiments and simulations of hydrated
proteins. Such behavior is often discussed in the context of the
protein dynamical transition, yet its general physical origin remains unclear. Here we show that fluctuating diffusivity within a Langevin framework naturally gives rise to an observation-time-induced crossover in translational
diffusion: the effective
diffusion coefficient exhibits a temperature-dependent change whose crossover point systematically shifts with the observation time. Through analytical and numerical analyses, we elucidate the mechanism of this crossover and identify the minimal conditions required for its emergence. Our results establish observation-time-induced crossover as a generic non-
equilibrium phenomenon in systems with slowly relaxing mobility fluctuations. While distinct from internal dynamical transitions probed in
neutron scattering, this framework provides a unified perspective that encompasses related finite-time crossover phenomena observed in hydrated
proteins and other complex soft-matter systems.
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