Soft Condensed Matter
Fluctuation-Dissipation Framework for Size-Dependent Surface Tension
Sergii Burian, Yevhenii Shportun, Liudmyla Klochko et al. (+3 more)
The size-dependent
liquid-vapor surface tension controls phase change, wetting, and transport at nanoscales, yet its first
curvature correction, the Tolman length, remains difficult to determine. We develop a thermodynamic and statistical-mechanical framework that relates this correction to bulk response properties of a one-component
liquid near
liquid-vapor coexistence. For curved interfaces, the analysis considers two local formulations of the same capillary-chemical balance, in excess pressures and in relative density deviations. For weakly compressible
liquids in the regime emphasized here, the adopted asymmetric density-based formulation is the practically relevant one, with finite-
curvature effects entering through vapor supersaturation under capillary
equilibrium. At coexistence, the planar-limit value of the same Tolman length reduces to a combination of the
liquid isothermal compressibility and its pressure derivative and can be recast as a bulk fluctuation-response observable of the homogeneous
liquid in the isothermal-isobaric ensemble. In this representation, the planar-limit coefficient is determined by second and third central moments of the volume distribution, equivalently by the pressure response of the relative fluctuation width. For water, homogeneous (N,P,T) simulations of SPC/E and TIP4P/2005 sample the bulk
liquid, not an explicit
liquid-vapor interface, and yield estimates near -0.7 Angstrom at 300 K. An independent evaluation based on the IAPWS-IF97 industrial formulation gives -0.713 +/- 0.004 Angstrom at the same coexistence state and predicts a weakly nonmonotonic temperature dependence along coexistence. Beyond water, the framework applies to other one-component
liquids in regimes where an accurate thermal equation of state or sufficiently converged bulk volume statistics are available.
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All authors Sergii Burian, Yevhenii Shportun, Liudmyla Klochko, Leonid Bulavin, Dmytro Gavryushenko, Mykola Isaiev
Statistical Mechanics
Crossover and universality breaking in the dilute Baxter-Wu model
Dimitrios Mataragkas, Alexandros Vasilopoulos, Dong-Hee Kim et al. (+1 more)
The critical behavior of the Baxter-Wu model belongs to the universality class of the four-state Potts model. While the introduction of annealed vacancies does not alter the criticality of the four-state Potts model, the dilute Baxter-Wu model has remained the subject of several competing scenarios. Here we investigate the phase diagram of the
spin-$1$ Baxter-Wu model in the presence of a
crystal field using transfer-
matrix calculations and large-scale Monte Carlo simulations. Our results reveal a systematic
evolution of the effective critical behavior with increasing
crystal field, accompanied by increasingly strong finite-size corrections near the crossover to the first-order regime. Along the line of continuous transitions, the central charge remains close to $c=1$, while the scaling dimensions systematically deviate from the
spin-$1/2$ limit as the
crystal field increases, consistent with either continuously varying effective critical exponents or a slow crossover between competing critical behaviors. The first-order regime is independently characterized through multicanonical simulations, which confirm the expected finite-size scaling and interfacial behavior. Taken together, our results provide a unified picture of the dilute
spin-$1$ Baxter-Wu model, substantially narrowing the range of possible scenarios for the crossover between continuous and first-order phase transitions.
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All authors Dimitrios Mataragkas, Alexandros Vasilopoulos, Dong-Hee Kim, Nikolaos G. Fytas
Statistical Mechanics · Cross-listed from physics.bio-ph
A hyperbolic cell cycle law for early embryonic developmental timing
Adrián Aguirre-Tamaral, Johanna Royer, Magdalena Schindler-Johnson et al. (+4 more)
Across metazoans, early embryos exhibit a strikingly conserved slowing down of their
cell duplication speed, despite widely varying developmental paces and underlying molecular mechanisms. Here we show that this common behavior arises because early development unfolds along a biochemical rather than a chronological timescale, resulting from the coupling of finite maternal resource consumption to the Michaelis-Menten-like kinetics governing the rates of the biochemical reactions involved in
cell duplication. This leads to a
hyperbolic growth of the
Cell Cycle Length (CCL), approaching a mathematical singularity, which would correspond to developmental arrest. Data from a wide range of organisms – cnidarians, nematodes, arthropods, molluscs, echinoderms, tunicates, amphibians, and fish – collapse on a single curve, quantitatively capturing not only a universal CCL dynamical behaviour, but also key hallmarks of early metazoan development, including
cell-number temporal
evolution, the dependency of CCL on
cell size, and, remarkably, gastrulation timing at the predicted singularity. Crucially, experimental modulation of resource availability and consumption rates validate the model and further demonstrate that a source of heterochrony in early development is an altered biochemical timescale of resource depletion. Overall, this work reveals resource consumption rates as a fundamental mechanism driving developmental timing in early embryogenesis across species.
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All authors Adrián Aguirre-Tamaral, Johanna Royer, Magdalena Schindler-Johnson, Jun-Ru Lee, Daniel R. Amor, Nicoletta I. Petridou, Bernat Corominas-Murtra
Materials Science
Conditional probability density functional theory for solids
Peiwei You, Ryan Pederson, Kieron Burke et al. (+1 more)
The recently developed conditional probability density functional theory (CP-DFT) yields direct access to the exchange-correlation hole of a system, an important correlation function that is not available in standard DFT. We present the first results for extended materials with periodic boundary conditions. We validate CP-DFT for weakly correlated Na and Si. We apply it to a stretched hydrogen chain, the prototype of strong correlation. When applied to the Kagome material CsV$_3$Sb$_5$, we find $d$-orbital correlations that are missing in standard DFT, implying an enhanced finding probability between two separated electrons and a local charge density wave related modulation.
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All authors Peiwei You, Ryan Pederson, Kieron Burke, E. K. U. Gross
Mesoscale and Nanoscale Physics
Highly Efficient Exciton Modulation in MoSe$_2$/PdSe$_2$ Heterostructures
Petr Rozhin, Emma Contin, Danae Katrisioti et al. (+15 more)
Controlling
exciton recombination in atomically thin
semiconductors is central to their optoelectronic functionality, as the competition between radiative and non-radiative decay channels governs emission efficiency. Existing approaches, such as defect passivation, chemical doping, dielectric engineering, and strain tuning, primarily aim to suppress non-radiative losses. Here, we report a pronounced $\sim$6-fold enhancement of room-temperature A-
exciton emission in a type-I MoSe$_2$/PdSe$_2$ van der Waals
heterostructure, yielding a photoluminescence
quantum yield of 6 %, compared to $\sim$1 % for as-exfoliated monolayer MoSe$_2$. This enhancement is accompanied by strong quenching of the B-
exciton, consistent with interlayer electronic coupling that redistributes
exciton populations toward the radiative A-
exciton channel. Power- and temperature-dependent measurements reveal a suppression of
exciton-
exciton annihilation and a crossover to quenched emission at low temperature, indicating a redistribution of
exciton relaxation pathways. Photoluminescence excitation spectroscopy further reveals a broadband enhancement spanning 450-725 nm, ruling out a resonance-specific mechanism. These results demonstrate that interlayer electronic coupling can be used as an efficient means to redirect
exciton populations toward radiative channels, enhancing emission efficiency in two-dimensional
semiconductors without chemical modification or strain.
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All authors Petr Rozhin, Emma Contin, Danae Katrisioti, Till Weickhardt, Muhammad Sufyan Ramzan, Micol Bertolotti, Nouha Loudhaief, Bing Wu, Zdeněk Sofer, Takashi Taniguchi, Kenji Watanabe, Leonardo Puppulin, Stefano Dal Conte, Caterina Cocchi, Ioannis Paradisanos, Giancarlo Soavi, Giovanni Antonio Salvatore, Domenico De Fazio
Quantum Gases
Observation of an aperiodic polariton monotile
Sergey Alyatkin, Yaroslav V. Kartashov, Kirill Sitnik et al. (+2 more)
A plethora of unconventional localization phenomena and fractal features of linear spectrum observed in quasiperiodic structures have been accompanied by a long-standing quest for the geometrical elements and structures that permit tilings of the plane, but only in a non-periodic manner. Until 2024, it was believed that such quasiperiodic structures, or quasicrystals, could only be composed of at least two different tiles. Surprisingly, a newly discovered class of quasicrystals requires only one elementary monotile. However, its physical realization and study of propagating coherent excitations in this novel setting remained elusive. Here we optically sculpt aperiodic quasicrystals composed of "einstein" monotiles in an inorganic microcavity and observe nontrivial relative phases of the
exciton-polariton condensates nonresonantly excited at the vertices of each monotile. Utilizing energy-resolved
tomography in momentum-space, we reveal the formation of distinct Bragg peaks with six-fold
symmetry and Dirac-like spectral fingerprints, intrinsic to the underlying
graphene-like structure, while interferometric phase reconstruction shows a nontrivial synchronization pattern distinct from both periodic triangular
lattices and Penrose quasicrystals. Our work demonstrates that monotiles can be converted into a programmable driven-dissipative artificial material, where long-range coherence coexists with enforced
geometric aperiodicity, producing synchronization and spectral responses distinct from both periodic and conventional quasicrystalline tilings.
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All authors Sergey Alyatkin, Yaroslav V. Kartashov, Kirill Sitnik, Philipp Grigoryev, Pavlos G. Lagoudakis
Soft Condensed Matter · Cross-listed from physics.bio-ph
Onsager-variational formulation of diffuse-domain methods for computational modeling of microscale fluid-structure interactions
Xinpeng Xu
Direct numerical simulation of microscale fluid–structure interactions in multicomponent and multiphase flows requires methods that can represent moving boundaries together with fields constrained to evolving interfaces. Diffuse-domain methods (DDMs) address this
geometric difficulty by replacing sharp surfaces with diffuse volumetric representations on regular computational domains. Here we formulate DDMs using Onsager's variational principle. Instead of extending sharp-interface equations and boundary conditions term by term, we embed sharp-surface free-energy and dissipation functionals into the bulk through a diffuse surface delta density and derive the governing equations from the Rayleighian. The framework distinguishes balance-law fields, internal nonconserved order parameters, and kinematic or constitutive rate variables. It also clarifies a key moving-surface distinction: conserved surface densities are transported by the full material surface velocity, whereas explicitly tangential vector and tensor internal variables require projected objective or co-rotational rates within their admissible tangential state spaces. For scalar transport on rigid and deformable interfaces, and for interfacial hydrodynamics near rigid walls, the formulation recovers established DDM models and their sharp-interface limits. The same variational construction yields coupled diffuse-domain models for multicomponent deformable vesicles with surface viscosity, tangential slip, and finite areal compressibility, and for active shells carrying chemical and tangential vector order. These results provide a unified route to thermodynamically consistent passive DDMs for interfacial and surface dynamics, while allowing active stresses through active work power. The framework is relevant to soft matter, microfluidic interfaces, biological membranes, and morphogenetic surface dynamics.
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Materials Science
Magnesium-graphene interphase boundaries created by high-pressure torsion enhance hydrogen storage kinetics:Mechanisms and significance of activation energy and frequency factor
Runchen Zhou, Payam Edalati, Anthony Alhayek et al. (+6 more)
A strategy to overcome sluggish hydrogenation/dehydrogenation of magnesium is demonstrated by creating magnesium-
graphene interphase boundaries via high-pressure torsion (HPT). HPT reduces the grain size of pure magnesium from 1 mm to 850 nm, with 70% of grain boundaries having high misorientation angles.
Graphene addition leads to even finer grain sizes of 10-500 nm with a bimodal morphology. The magnesium-
graphene composites exhibit superior kinetics at 623 K while maintaining high air resistance. Kinetic modeling reveals that the rate-controlling mechanism transits from interfacial reaction in coarse-grained magnesium to atomic
diffusion in magnesium-
graphene nanocomposites. Kissinger analysis shows that the activation energy for hydrogen desorption remains unchanged at 145 +/- 2 kJ/mol, regardless of the presence of grain or interphase boundaries. However, the frequency factor (number of successful attempts to overcome the activation energy) increases with the generation of interfaces, which serve as sites for hydrogen
diffusion and heterogeneous metal/hydride nucleation. These findings highlight the impact of interphase boundary engineering via severe plastic deformation for enhancing the kinetics and air resistance of hydrogen storage materials.
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All authors Runchen Zhou, Payam Edalati, Anthony Alhayek, Shivam Dangwal, Marc Novelli, Md. Amirul Islam, Baran Bidyut Saha, Thierry Grosdidier, Kaveh Edalati
Materials Science
Structural, electronic, and optical properties of hexagonal GeSn from density functional theory
Yetkin Pulcu, János Koltai, Andor Kormányos et al. (+1 more)
Unlike cubic GeSn, which undergoes an indirect-to-direct bandgap transition only above a finite Sn concentration, lonsdaleite (2H) germanium is an intrinsic direct-gap
semiconductor. We employ first-principles density functional theory to investigate the structural, electronic, and optical properties of 2H-Ge$_{1-x}$Sn$_{x}$ random
alloys in the dilute Sn regime ($x \le 0.10$). Substitutional disorder is modeled using 48-atom special quasirandom structure (SQS) supercells, and the coherent effective band structure is recovered via spectral band unfolding. We show that the semiconducting
alloy configurations retain a direct bandgap at the $\Gamma$ point, with a moderate, nearly linear reduction of the bandgap in the dilute regime that shifts the fundamental absorption edge toward the mid-infrared. As the gap approaches zero, its calculated value becomes increasingly sensitive to the atomic configuration and supercell size. Evaluation of the optical transition
matrix elements shows that the polarization anisotropy characteristic of pristine 2H-Ge remains observable under dilute Sn alloying. Although
alloy disorder relaxes the
crystal selection rules, the band edge response remains dominated by light polarized perpendicular to the
crystal $c$ axis, whereas the parallel component remains weaker. These results identify dilute hexagonal GeSn as a tunable direct-gap system with a strongly polarization-dependent optical response in the infrared.
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All authors Yetkin Pulcu, János Koltai, Andor Kormányos, Guido Burkard
Materials Science
Helium Bubbles in Liquid Lead Lithium Solutions: Pressure Inhomogeneities at Interfaces and Non Ideal Mixture Effects
Edgar Alvarez-Galera, Jordi Marti and Lluis Batet
The extremely low solubility of helium in
liquid metals may lead to rapid supersaturation, promoting spontaneous formation of helium bubbles by nucleation. Once nucleated, the stability of these bubbles is governed by the properties of the helium
liquid metal interface. In particular, interfacial tension between the immiscible phases controls bubble interactions and induces local pressure inhomogeneities. This work is motivated by the need of a better understanding of helium bubble formation in
liquid Pb Li
alloys, which are of particular relevance for the design of breeding blankets in the future
nuclear fusion reactors. We employ classical molecular dynamics simulations to investigate helium segregation in a range of lead lithium systems, including the limiting cases of pure lead and pure lithium. Changes in local pressure are evaluated from direct mechanical calculations, enabling the characterization of interfacial properties. Interfacial tension and radius of the bubble are subsequently determined across multiple thermodynamic conditions, spanning temperatures starting near the melting points of the constituent metals up to 1021 K. The impact of
curvature and composition of the
alloy on the interfacial behaviour are also investigated.
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Materials Science
Ultrafast Critical Slowing of Spin Dynamics and Emergent Nonequilibrium Fano Interference in Fe3GeTe2
Anupama Chauhan, Sidhanta Sahu, Satyabrata Bera et al. (+5 more)
Fe$_3$GeTe$_2$ is a prototypical metallic van der Waals ferromagnet with itinerant magnetism and a highly tunable Curie temperature, yet how electronic excitations couple to
spin and
lattice degrees of freedom across its
magnetic transition remains largely unexplored. Here, we use two-color pump-probe reflectivity to investigate the coupled electronic,
spin, and
lattice dynamics. The time-resolved reflectivity exhibits a tri-exponential relaxation, in which the intermediate component shows an anomaly near the Curie temperature due to enhanced interlayer
spin-
lattice interactions, while the slowest component displays pronounced critical slowing down with an exponent of ~ 0.3, revealing non-universal relaxation dynamics associated with intralayer
spin correlations. Furthermore, we observe an emergent nonequilibrium A1g
phonon Fano asymmetry that is suppressed in the
ferromagnetic phase but anomalously enhanced in the paramagnetic regime, driven by thermally activated anharmonic decay pathways that bridge the kinematic gap to a hot electronic continuum. The pronounced enhancement of the acoustic strain pulse amplitude near T$_c$ further evidences robust magnetoelastic coupling. Overall, our results reveal how
magnetic order governs the interplay among critical
spin dynamics, electronic continuum excitations, and
lattice response in metallic van der Waals ferromagnets
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All authors Anupama Chauhan, Sidhanta Sahu, Satyabrata Bera, Tuhin Debnath, Mintu Mondal, Anamitra Mukherjee, Siddhartha Lal, N. Kamaraju
Mesoscale and Nanoscale Physics
Observation of end-to-end pumping in a quasiperiodic Fibonacci-type photonic chain
Arnob Kumar Ghosh, Ang Chen, Ashraf El Hassan et al. (+3 more)
End-to-end pumps utilizing edge-localized states offer a promising route to operate as connecting buses, supplying efficient and robust connectivity between non-neighboring elements in a network. Here, we investigate a finite quasiperiodic Fibonacci-type photonic chain and demonstrate its ability for end-to-end pumping, with only small and simple changes to the system. First, we use a tight-binding formalism to numerically show that a localized pumping state can be transferred between opposite ends of the system, with only a small structural change to the chain. Then, we experimentally implement this end-to-end pump in an array of coupled optical waveguides, where light propagation is effectively described by the tight-binding model under the paraxial approximation, enabling direct correspondence between theory and experiment. We numerically simulate and experimentally demonstrate pumping by injecting light into a single waveguide at one end of the setup, which activates a localized pumping state. As the light propagates along the wave guide array, it is also pumped to the other end. We further show that pumping remains robust against structural deformation, such as controlled defects in the waveguide array. Our results establish that quasiperiodic Fibonacci-type photonic
lattices are a robust and experimentally viable platform for disorder-resilient state transfer.
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All authors Arnob Kumar Ghosh, Ang Chen, Ashraf El Hassan, Patric Holmvall, Mohamed Bourennane, Annica M. Black-Schaffer
Materials Science
Apparent Ferroelectric Polarization Hysteresis and a Simple Method to Observe Piezoelectric Strain Loops with a Microphone
Mamoru Fukunaga
Extra components in series to non-ferroelectric capacitance can cause apparent ferroelectric D-E hysteresis loops even with the double-wave method (DWM). Characteristics of fake loops are studied withsimple
circuit models, and suspicious loops of actual materials are found in some papers using the DWM. Inverse piezoelectric strain also reverses along with the polarization by the electric field, and S-E loops are considered more reliable to prove ferroelectricity than the D-E loops. But measurement of S-E loops usually requires expensive instruments in contrast to D-E loops with a simple
circuit. A very simple method is developed to observe S-E loops of bulk samples with an inexpensive small electret microphone and a little expansion to the
circuit for D-E loops. S-E loops of a commercial ceramic capacitor by this method reveal that its D-E loops apparent.
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Mesoscale and Nanoscale Physics
Quantized Transport in Floquet Topological Insulators
Rekha Kumari, Manas Kulkarni and Abhishek Dhar
We study
quantum transport in a periodically driven (Floquet) topological system coupled to static fermionic reservoirs. Using the Floquet nonequilibrium Green's-function (NEGF) formalism we show, from exact numerics for a strip geometry, that the two-terminal (longitudinal) conductance is quantized as $|W_{\varepsilon}|\,e^2/h$, while the
Hall (transverse) conductance is quantized as $W_{\varepsilon}\,e^2/h$, where $W_{\varepsilon}$ is the Floquet winding invariant associated with the quasienergy gap at $\varepsilon = 0$ or $\varepsilon = \Omega/2$. Quantization is achieved only after summing over the contribution of all Floquet sidebands. We provide an analytic understanding of this Floquet conductance sum rule, by considering the
Hall conductance in the weak coupling limit. In that limit, we show that the Floquet
Hall conductance gets contributions from the Floquet sidebands, which includes the signs of the velocities of the edge modes. Their sum yields exact quantization, as predicted by the Floquet sum rule. We find that in a wide range of parameter regime, the convergence is fast, making observation of the sum rule and Floquet winding numbers accessible to experiments.
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Materials Science
Selective Octahedral Accommodation of Cr$^{3+}$ and Weak Magnetic Connectivity in the Sugilite Analogue KNa$_2$Cr$_2$Li$_3$Si$_{12}$O$_{30}$
Yuya Haraguchi, Taishu Aoki, Daisuke Nishio-Hamane et al. (+1 more)
We report the synthesis of the Cr analogue of sugilite, KNa$_2$Cr$_2$Li$_3$Si$_{12}$O$_{30}$, in the milarite-type framework. Rietveld refinement of a composition-conserving antisite model gives $x = 0.0024(18)$ in KNa$_2$[Cr$_{2-x}$Li$_x$][Li$_{3-x}$Cr$_x$]Si$_{12}$O$_{30}$, corresponding to a T2-site Cr occupancy of $0.0008(6)$. X-ray MEM analysis shows no detectable Cr-like density at T2.
Magnetic susceptibility indicates weak
antiferromagnetic interactions with $\theta_{\mathrm{W}} = -4.78(7)$ K and no ordering above 1.8 K.
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All authors Yuya Haraguchi, Taishu Aoki, Daisuke Nishio-Hamane, Hiroko Aruga Katori
Statistical Mechanics
Matrix-noise Jacobians in stochastic-calculus inference and optimal paths
Surachate Limkumnerd
Multiplicative noise makes
stochastic dynamics depend on how the white-noise limit is interpreted. In multidimensional systems with
matrix-valued noise amplitudes $\sigma(x)$, this dependence includes a local Jacobian contribution that is absent from the scalar examples most often used to build intuition. We formulate a finite-step path-likelihood framework for $\theta$-discretized
diffusions and show that its short-time expansion isolates the scalar $J_\sigma=\partial_j\sigma_{ik}\partial_i\sigma_{jk}-(\partial_i\sigma_{ik})(\partial_l\sigma_{lk})$. For a specified noise-amplitude representation $\sigma$, this quantity vanishes in one-dimensional, scalar-isotropic, and strictly diagonal cases, but can survive when state-dependent noise directions mix different components. We then test its consequences using paired comparisons that hold the drift,
diffusion matrix, interpolation point, and Gaussian increment term fixed. In Model A, removing only the off-diagonal determinant contribution produces a shift in the fitted
stochastic prescription that vanishes when $J_\sigma=0$. In Model B, removing the corresponding state-dependent action term changes a stable optimized transition path. These results show that a genuinely
matrix-noise part of the short-time path measure can survive the scalar cancellations familiar from simpler settings and produce measurable changes in fitted
stochastic prescriptions and Onsager–Machlup paths.
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Strongly Correlated Electrons
Frustrated Magnetism of the $S = 1$ Trillium-Lattice Oxide Li$_2$NiGe$_3$O$_8$
Yuya Haraguchi
We report magnetization and heat-capacity measurements on the ordered-spinel
oxide Li$_2$NiGe$_3$O$_8$, where Ni$^{2+}$ ions with $S = 1$ form a single three-dimensional trillium
lattice. Powder x-ray diffraction confirms a cubic ordered-spinel structure with space group $P4_{1}32$ or $P4_{3}32$. The inverse susceptibility $H/M$ follows Curie–Weiss behavior above 50 K with an effective
magnetic moment $\mu_{\mathrm{eff}} = 3.124(4)\,\mu_{\mathrm{B}}$ per Ni and a Weiss temperature $\theta_{\mathrm{W}} = -0.21(1)$ K, but deviates smoothly below about 10 K. The
magnetic heat capacity $C_{\mathrm{mag}}/T$ shows a broad maximum near 3 K with a wide tail to about 10 K, and the
entropy recovered between 2 and 40 K is about 88% of $R \ln 3$. The broad heat-capacity maximum is compared with Monte Carlo results for the local
ferromagnetic Ising model on the trillium
lattice using a characteristic scale $J$ of order 7 K, while the inverse susceptibility shows only qualitative similarity to the theoretical curve. These results establish Li$_2$NiGe$_3$O$_8$ as a rare $S = 1$ single-trillium
oxide with frustrated
magnetic correlations. The present data provide an experimental platform for discussing the relation between Heisenberg-like and
spin-ice-like regimes on the trillium
lattice.
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Mesoscale and Nanoscale Physics
Terahertz detection within charge density wave state
Zhi Li
Terahertz (THz) technology enables multi-Tbps satellite communications, but conventional
semiconductor detectors suffer from fundamental performance degradation above 1 THz due to the Drude limit of free electrons. Here, we theoretically demonstrate that charge density wave (CDW) materials offer a paradigm-shifting solution via their collective electronic response. We show that a static bias electric field can continuously tune the THz resonant absorption frequency of CDW states from 0 to cutoff frequency, and enhance the nonlinear rectification current by more than one order of magnitude. This unprecedented electric-field tunability makes CDW materials ideal candidates for next-generation ultrafast THz detectors working at room-temperature.
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Strongly Correlated Electrons
Grassmann tensor networks
Jian-Gang Kong, Jia-Ji Zhu and Z. Y. Xie
Developing non-perturbative methods to reveal exotic properties of strongly correlated fermionic systems remains one of the most essential tasks of theoretical physics. Tensor network methods with Grassmann
algebra offer powerful numerical tools for fermionic many-body systems in the coherent-state path-integral representation. Despite their vast potential for both condensed-matter and particle-physics communities, Grassmann tensor network methods are somewhat underexploited in practical simulations. In this work, we provide a detailed, self-contained introduction to Grassmann tensor network methods, from the basics of the Grassmann tensor operations to the Grassmannization of typical tensor network
algorithms. Furthermore, the resulting Grassmann tensor network methods are validated in several interesting models in both particle physics and condensed matter physics.
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Materials Science · Cross-listed from nlin.PS
Whitham modulation equations for the regularized Boussinesq equation with cubic nonlinearity
Mark A. Hoefer and Anna Vainchtein
A regularized Boussinesq equation is studied as a dispersive, long-wave (quasicontinuum) approximation of the
Fermi-Pasta-Ulam
lattice with a general cubic interaction force. Explicit periodic traveling wave solutions in terms of Jacobi
elliptic functions are classified, and their solitary-wave, kink, and trigonometric limits are obtained. The Whitham modulation equations describing slow modulations of periodic traveling wave solutions are derived using an averaged variational principle. The convexity (strict hyperbolicity, genuine nonlinearity) of the resulting hydrodynamic-type equations is examined numerically in general and analytically in the solitary-wave and harmonic limits. In particular, the loss of hyperbolicity and the formation of complex conjugate characteristic speeds is shown to lead to modulational instability of periodic traveling waves. The onset of modulational instability is verified by numerical computations of linearized spectra for periodic traveling waves and initial value problems that also reveal additional short-wave instabilities.
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Soft Condensed Matter
Topological and morphological signatures of disorder in a self-assembled, soft matter sponge network
Xueyang Feng, Suman S. Kulkarni, Michael S. Dimitriyev et al. (+4 more)
Many soft matter systems exhibit ordered, polycontinuous network morphologies, such as the cubic (double) gyroid or diamond, as well as disordered network morphologies known generically as “random sponges". While presumed to share similar local packing geometry, the structural relationship between these ordered and disordered network morphologies has remained obscure. We use slice and view scanning electron microscopy to analyze and compare multi-scale morphological features of an ordered double-gyroid morphology to the amorphous sponge morphology formed in the same block copolymer sample. We find that node valence of the minority component network of the sponge is mostly gyroidal (trivalent), with a small fraction of diamond-like (tetravalent) connections. We analyze mesoatoms – space-filling volumes occupied by chains around each network node – finding significant differences in shape and size between ordered and amorphous regions. Local block thickness and inter-domain
curvature within mesoatomic units of the disordered sponge exhibits a surprisingly similar degree of dispersity to the ordered double-gyroid. The mean differences in local packing geometry derive from topological distinction: loops of the minority networks of the ordered double-gyroid are intercatenated, while loops of the disordered sponge are not. In this way, the sponge may be viewed as disordered variant of a single-gyroidal morphology. We exploit these topological differences to demarcate the boundary region between ordered and disordered networks and highlight modulations of the mesoatom motifs at the boundary. These observations point to new questions about potential metastability of disordered networks and their possible role as kinetic precursors to long-range ordered network morphologies.
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All authors Xueyang Feng, Suman S. Kulkarni, Michael S. Dimitriyev, Dani S. Bassett, Randall D. Kamien, Edwin L. Thomas, Gregory M. Grason
Statistical Mechanics
Competing Effect of Biquadratic and Heisenberg Coupling on Magnetic Tunnel Junction Molecular Spintronics Devices
Andoniaina Mariah Randriambololona, Hayden Brown, Eva Mutunga et al. (+3 more)
Heisenberg exchange coupling (HC) and biquadratic exchange coupling (BQC) are known to occur in
magnetic tunnel junctions (MTJ) and nanoscale spintronics structures. MTJ-based molecular spintronics devices (MTJMSD) provide a platform to study these interactions and the correlated
magnetic behavior they generate. Molecular
spin channels formed along the exposed MTJ edge have been shown to produce strong exchange interactions that include HC and BQC, which can drive perpendicular
alignment of
spin vectors in adjacent
ferromagnetic electrodes. Despite their importance, the competing roles of HC and BQC in MTJMSDs remain unclear. Monte Carlo simulations using a three-dimensional Heisenberg model were performed to systematically vary BQC strength under three conditions: no molecular HC, strong parallel HC, and strong antiparallel HC. The resulting
magnetic and physical properties of the MTJMSDs were analyzed. Increasing BQC strength produced minimal changes in overall magnetization when strong HC was present, indicating that HC dominates device magnetization. Temporal
evolution studies showed that devices with only BQC failed to reach
magnetic stability, while devices with both HC and BQC achieved stable
magnetic states due to the stabilizing influence of HC. These results show that BQC plays a secondary role in magnetization dynamics and cannot overcome the stronger stabilizing effect of HC. The presence of BQC offers a plausible explanation for experimentally observed
magnetic phase orientations beyond simple parallel and antiparallel states in MTJMSDs.
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All authors Andoniaina Mariah Randriambololona, Hayden Brown, Eva Mutunga, Andrew Grizzle, Christopher DAngelo, Pawan Tyagi
Soft Condensed Matter
PACSim: A Flexible Simulation Framework for Polymer-Attenuated Coulombic Self-Assembly
Philipp Höllmer, Nicole Smina, John P. Marquardt et al. (+4 more)
Polymer-Attenuated Coulombic Self-Assembly (PACS) is a flexible experimental approach for generating
crystals from simple colloidal building blocks. The central components are charged spherical particles coated with a
polymer brush that prevents irreversible aggregation. Whether oppositely charged colloids crystallize, and which structures they form, depends on several factors, including colloid concentration, charge, and size, as well as the salt concentration of the solution. Molecular dynamics (MD) simulations are a powerful tool for predicting the outcomes of PACS assembly experiments and also provide particle-level insight into the assembly processes. Here, we present an open-source simulation framework, PACSim, that enables MD simulation studies of assembly by PACS across a range of experimentally relevant scenarios. PACSim is built on top of OpenMM, a flexible MD simulation framework that readily supports the implementation of different interaction potentials, as well as integration with other tools such as enhanced-sampling and machine-learning frameworks. We describe the motivation for PACSim, outline its features, report methodological advancements inspired by this framework, and provide examples of its use.
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All authors Philipp Höllmer, Nicole Smina, John P. Marquardt, Michael S. Chen, Steven van Kesteren, Stefano Sacanna, Glen M. Hocky
Materials Science
Ultraviolet plastic scintillators based on naphthalene-doped polystyrene and polyvinyltoluene
Nicolás Agustín Molina, Victoria Alejandra Gómez Andrade, Javier Martín Abbas et al. (+6 more)
This work reports the fabrication and optical characterization of ultraviolet-emitting plastic scintillators based on polystyrene [-(CH2-CH(C6H5))n-] and polyvinyltoluene [-(CH2-CH(C6H4CH3))n-] doped with different concentrations of naphthalene (Naph). Photoluminescence (PL) measurements show that Naph incorporation enhances the emission intensity, inducing a red shift in the emission wavelength of the polystyrene (PS), while Naph-doped polyvinyltoluene (PVT) exhibits a bimodal emission with peaks around 335 and 350 nm. Time-resolved photoluminescence (TRPL) reveals fast decay components for the undoped
matrices and a dominant slow component of approximately 87 ns in the doped samples. Scintillation light yield measurements indicate moderate performance for the undoped
polymers and a significant enhancement upon Naph doping.
Proton irradiation experiments reveal a reduction in light yield for all samples, with Naph-doped PVT retaining a larger fraction of its initial light yield compared to PS-based scintillators, indicating improved radiation tolerance. Overall, these results demonstrate the effectiveness of Naph as a UV emission enhancer and highlight Naph-doped PVT as a promising candidate for compact and radiation-resistant scintillation detectors.
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All authors Nicolás Agustín Molina, Victoria Alejandra Gómez Andrade, Javier Martín Abbas, Alan Fuster, Luciano Ferreyro, Martín Alurralde, Martin Mirenda, María Dolores Pérez, Paula Guidici
Soft Condensed Matter
Wall accumulation of confined active Janus colloids due to effective active diffusivity
Sandeep Ramteke, Alicia Boymelgreen and Jarrod Schiffbauer
Electrokinetically-driven Janus colloids, e.g., with one metallic and one dielectric hemisphere, confined between parallel walls exhibit a boundary-accumulation mechanism enabled by an effective cross-channel diffusivity which is distinct from wall accumulation of active Brownian or run-andtumble particles. Using density-matched suspensions and three-dimensional confocal imaging, we directly measure the full time-dependent redistribution of particles across the channel under an applied AC electric field. The wall population grows exponentially while the bulk depletes, and data obtained over multiple field strengths collapse onto a single curve when rescaled by the measured relaxation rate, revealing one dominant, confinement-controlled timescale. Propulsion follows the expected induced-charge electrophoretic scaling, with a mean orientation angle lying between 2 degrees and 10 degrees above horizontal, leading to a top-biased accumulation. Comparison with an overdamped Ornstein-Uhlenbeck turning model suggests that persistent
stochastic turning about a small out-ofplane angle results in a cross-channel effective drift and
diffusion. The drift governs the dominant timescale and the
diffusion is strong enough to provide significant accumulation on the bottom wall despite a mean upward orientational bias.
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Materials Science
Ultrafast electron dynamics of electron-irradiated graphene
Yifan Yao and Andre Schleife
Electron irradiation is essential for materials characterization and modification, though the fundamental interactions between incident electrons and host materials remain under investigation. Here, we employ first-principles simulations to study electron dynamics under external electron irradiation. We quantify differences in key observables, including kinetic energy loss, secondary electron emission, and backscattered electrons, between classical and
quantum mechanical descriptions of the incident electron. Around 400 eV incident energy, we identify significant differences in backscattered electron yields between classical point-charge and
quantum wave-packet descriptions, whereas the
quantum-mechanical effects diminish at incident energies above 600 eV. These differences highlight the critical importance of
quantum effects in electron irradiation phenomena that occur in a specific energy range of the incident electron. Our results provide clear guidance for selecting appropriate incident, electron descriptions based on kinetic-energy regimes, identify a targeted experimental window for isolating
quantum-only backscattering, and enable the rational design of 2D materials for nanofabrication and high-resolution electron-beam technologies.
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Statistical Mechanics · Cross-listed from physics.soc-ph
Empirical confirmation of bosonic wealth statistics in Bitcoin UTXOs
Chanhee Park, Claudio J. Tessone, Yu Zhang et al. (+1 more)
Digitalisation transforms money from distinguishable physical objects into fungible informational units. A recent theoretical framework predicts that such indistinguishable wealth obeys bosonic occupancy statistics, leading to
geometric ownership distributions and enhanced inequality. Using Bitcoin blockchain data, we test this prediction on 63 UTXO denominations across 72 monthly snapshots (2018–2023). A one-parameter
geometric model describes the ownership distributions, reproducing both mean holdings and their temporal
evolution; Jensen–Shannon divergence values lie below $0.08$ in $99.74\%$ of cases. The inferred inverse-temperature parameter satisfies the analytic mean–temperature relation to better than $0.1\%$ in every sample – a self-consistency test that two-parameter alternatives cannot pass – and remains within a narrow band across eight orders of magnitude in denomination and over six years. Bitcoin UTXO ownership statistics are therefore consistent with bosonic occupancy laws, suggesting that the informational nature of electronic money may act as a structural driver of inequality in digital economies.
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All authors Chanhee Park, Claudio J. Tessone, Yu Zhang, Jeong-Hyuck Park