Materials Science
Designing new Zintl phases SrBaX (X = Si, Ge, Sn) for thermoelectric applications using ab initio techniques
Vivek Gusain, Mohd Zeeshan and B. K. Mani
Slack's
phonon-glass and electron-
crystal concept has been the guiding paradigm for designing new thermoelectric materials. Zintl phases, in principle, have been shown as great contenders of the concept and thereby good thermoelectric candidates. With this as motivation, we design new Zintl phases SrBaX (X = Si, Ge, Sn) using state-of-the-art computational methods. Herein, we use first-principles simulations to provide key theoretical insights to thermal and electrical transport properties. Some of the key findings of our work feature remarkably low
lattice thermal conductivities ($<$~1~W~m$^{-1}$~K$^{-1}$), putting proposed materials among the well-known thermoelectric materials such as SnSe and other contemporary Zintl phases. We ascribe such low values to antibonding states induced weak bonding in the
lattice and intrinsically weak
phonon transport, resulting in low
phonon velocities, short lifetimes, and considerable anharmonic scattering phase spaces. Besides, our results on electronic structure and transport properties reveal tremendous performance of SrBaGe ($ZT\sim$ 2.0 at 700~K), highlighting the relevance among state-of-the-art materials such as SnSe. Further, the similar performances for both $p$- and $n$-type dopings render these materials attractive from device fabrication perspective. We believe that our study would invite experimental investigations for realizing the true thermoelectric potential of SrBaX series.
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Statistical Mechanics
Electrical conductivity of randomly placed linear wires: a mean field approach
Yuri Yu. Tarasevich, Andrei V. Eserkepov and Irina V. Vodolazskaya
Using the mean-field approximation, a formula for the effective electrical conductivity of a two-dimensional system of randomly arranged conducting sticks with a given orientation distribution was obtained. Both the resistance of the sticks themselves and the resistance of the contacts between them were taken into account. The accuracy in the resulting formula was analyzed. A comparison of the theoretical predictions of mean-field approach with the results of direct electrical conductivity calculations for several model orientation distributions describing systems with crossed sticks demonstrated good agreement. Our study showed that cross-
alignment of nanowires should lead to a decreasing in the electrical conductivity compared to electrodes with isotropically arranged nanowires. We suppose that the widely used model with zero-width sticks is quite acceptable for systems of cross-aligned nanowires, but overestimates their connectivity in isotropic systems. Thus, the enhancement of the electrical conductivity of conducting films with cross-aligned nanowires may be due to a significant difference in the network
topology.
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Soft Condensed Matter
Why Extensile and Contractile Tissues Could be Hard to Tell Apart
Jan Rozman, Sumesh P. Thampi and Julia M. Yeomans
Active nematic models explain the topological defects and flow patterns observed in epithelial tissues, but the nature of active stress-whether it is extensile or contractile, a key parameter of the theory-is not well established experimentally. Individual
cells are contractile, yet tissue-level behavior often resembles extensile nematics. To address this discrepancy, we use a continuum theory with two-tensor order parameters that distinguishes
cell shape from active stress. We show that correlating
cell shape and flow, whether in coherent flows in channels, near topological defects, or at rigid boundaries, cannot unambiguously determine the type of active stress. Our results demonstrate that simultaneous measurements of stress and
cell shape are essential to fully interpret experiments investigating the nature of the physical forces acting within epithelial
cell layers.
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Strongly Correlated Electrons
Low Temperature Two Fluid State in SmB6
Sayantan Ghosh, Sugata Paul, Tamoghna Chattoraj et al. (+3 more)
Comprehensive study using DC transport, specific heat, magnetization, and two-coil mutual inductance measurements unveils an understanding of three temperature regimes in SmB$_6$: (i) $T \geq T^{*}$ ($\sim66$K), (ii) $T_g$ ($\sim40$ K) $\leq T < T^{*}$, and (iii) $T < T_g$. Onset of Kondo breakdown below $T^{*}$ releases disorder-driven
magnetic fluctuations, which splits the bulk ($\sim116$K) and surface Kondo temperature ($T_k^{s} \approx 7$ K). Below $T_g$, as
magnetic fluctuations subside, surface Kondo screening revives, stabilizing the topological surface state and generating an in-gap feature ($\sim2.2$ meV) across which Dirac-like carriers are excited. Nyquist impedance analysis reveals a crossover from purely capacitive to capacitive-inductive behavior, signalling a disorder-driven two-fluid phase of heavy quasiparticles and light, high-mobility carriers below $T_g$. We identify a characteristic length scale, $L_{\nu_0}(T)$, associated with the high-mobility phase, exhibiting an almost divergent trend below $T_k^{s}$. These findings underscore the complex nature of the surface conducting state in SmB$_6$.
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All authors Sayantan Ghosh, Sugata Paul, Tamoghna Chattoraj, Ritesh Kumar, Zachary Fisk, S. S. Banerjee
Strongly Correlated Electrons
Microscopic origin of period-four stripe charge-density-wave in kagome metal CsV$_3$Sb$_5$
Yuma Murata, Rina Tazai, Youichi Yamakawa et al. (+2 more)
The interplay between unconventional density waves and exotic superconductivity has attracted growing interest. Kagome
superconductors $A\rm{V}_3\rm{Sb}_5$ ($A = \rm{K}, \rm{Rb}, \rm{Cs}$) offer a platform for studying
quantum phase transitions and the resulting
symmetry breaking. Among these
quantum phases, the $4a_0$ stripe charge-density-wave (CDW) has been widely observed for $A=\rm{Rb}$ and $\rm{Cs}$ by scanning tunneling microscopy (STM) and
nuclear magnetic resonance (NMR) measurements. However, the microscopic origin of the $4a_0$ stripe CDW remains elusive, and no theoretical studies addressing this phenomenon have been reported so far. In this paper, we propose a microscopic mechanism for the emergence of the $4a_0$ stripe CDW. We analyze the CDW instability in the 12-site kagome
lattice Hubbard model with the $2\times2$ bond order driven by the paramagnon-interference mechanism by focusing on the short-range
magnetic fluctuations due to the geometrical frustration of kagome
lattice. We reveal that the nesting vector of the reconstructed
Fermi surface, formed by the $2\times 2$ bond order, gives rise to a $4a_0$-period CDW. Remarkably, the obtained stripe CDW is composed of both the off-site hopping integral modulations and on-site potentials. The real-space structure of the stripe CDW obtained here is in good qualitative agreement with the experimentally observed stripe pattern.
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All authors Yuma Murata, Rina Tazai, Youichi Yamakawa, Seiichiro Onari, Hiroshi Kontani
Materials Science
The Microscopic Structure of Stacking Faults in Sr$_2$NaNb$_5$O$_{15}$
Robin Sjökvist, Yining Xie, Zabeada Aslam et al. (+4 more)
Stacking faults and other topological defects in ferroics can have a significant influence on the electronic and mechanical properties of the material. Here, regular stacking faults in the tetragonal tungsten bronze material Sr$_2$NaNb$_5$O$_{15}$ are investigated through transmission electron microscopy,
symmetry mode analysis and machine-learned force-field calculations. It is shown that the faults, with a fault vector of $\frac{1}{4}[\bar{2}12]_o$, annihilate in sets of four in the material, owing to the $\frac{1}{4}$ unit
cell displacement along the b-axis. The four resulting domains emerge as four possible directions of the S$_3$ order parameter, related to NbO$_6$ octahedral tilts in the material. Force-field calculations reveal that the stacking faults are likely placed at positions where the octahedra in neighbouring domains have similar magnitudes of rotation, and that the estimated stacking fault energy is 46 mJ/m$^2$. The investigation shows that the stacking faults have a significant local effect on the polar modes present in the structure, and therefore could affect the ferroelectric properties.
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All authors Robin Sjökvist, Yining Xie, Zabeada Aslam, Andy P. Brown, Nicholas C. Bristowe, Mark S. Senn, Richard Beanland
Soft Condensed Matter
Controlling viscosity to engineer focal conic domains in photonic cellulose nanocrystal films
Diogo V. Saraiva, Lotte Polling, Ivo R. Vermaire et al. (+3 more)
Cellulose nanocrystals (CNCs) form cholesteric architectures that can have color specific reflectivity and enable sustainable photonic films. However, achieving uniform color, suppressing iridescence, and accessing ordered defect structures such as focal conic domains remain challenging. Here, we control the photonic properties of CNC films by steering the self assembly process. Across 24 dish-cast films with varying salt concentrations and sonication doses, we combine viscosity measurements, timelapse polarized optical microscopy, and angle-resolved reflectance spectroscopy to correlate evaporation dynamics with photonic structure. We show that viscosity, jointly controlled by NaCl-mediated electrostatic screening and sonication-induced bundle fragmentation, dictates the extent of tactoid coalescence. Low-viscosity suspensions generate large, homogeneous cholesteric domains and narrow spectral responses, while high viscosity leads to arrested, heterogenous domains and increased diffuse light reflection. Critically, within a narrow parameter window of intermediate ionic strength and moderate sonication, we reproducibly engineer photonically active focal conic domains. These results identify viscosity-driven flow as a key, previously underappreciated factor in CNC self-assembly and establish design rules for producing structurally colored films with tunable photonic response, reduced iridescence, and controllable defect architectures.
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All authors Diogo V. Saraiva, Lotte Polling, Ivo R. Vermaire, Sander J. W. Vonk, Freddy T. Rabouw, Lisa Tran
Statistical Mechanics · Cross-listed from math.DS
Nonlinear Thermodynamic Formalism: Mean-field Phase Transitions, Large Deviations and Bogoliubov's Variational Principle
Jean-Bernard Bru, Walter de Siqueira Pedra and Artur O. Lopes
Let $\Omega =\{1,2,\ldots ,d\}^{\mathbb{N}}$, $T$ be the shift acting on $\Omega $, $\mathcal{P}(T)$ the set of $T$-invariant probabilities. Given a Hölder potential $A$ and a continuous function $F$, we investigate the probabilities $\rho _{F,A}$ that are maximizers of the nonlinear pressure $\mathfrak{P}_{F,A}:=\sup_{\rho \in \mathcal{P}(T)}\{ F(\int A(x)\rho (\mathrm{d}x))+h(\rho )\} .$ $\rho _{F,A}$} is called a nonlinear
equilibrium; a nonlinear phase transition occurs when there is more than one. In the case $F$\ is convex or concave, we combine Varadhan's lemma and Bogoliubov's variational principle to characterize them via the linear pressure problem and self-consistency conditions. Let $\mu \in \mathcal{P}(T)$ be the maximal
entropy measure, $\varphi _{n}(x)=n^{-1}(\varphi (x)+\varphi (T(x))+\cdots +\varphi (T^{n-1}(x)))$ and $\beta >0$.}\newline (I) We also consider the limit measure $\mathfrak{m}$ on $ \Omega $, so that $\forall \psi \in C(\Omega )$, $\int \psi (x)\,\mathfrak{m}\,( \mathrm{d}x)\,\,=\lim_{n\rightarrow \infty }\frac{\,\int \,\psi (x)\,\,\,e^{ \frac{\beta n}{2}\,\,A_{n}((x)^{2}}\,\,\mu \,(\mathrm{d}x)\,}{\int e^{\frac{ \beta n}{2}\,\,A_{n}((x)^{2}}\mu \,(\mathrm{d}x)\,\,}.$ We call $\mathfrak{m}$ a \textit{quadratic mean-field Gibbs probability (II) Via subsequences $n_{k}$, $k\in \mathbb{N}$, we study the limit measure $\mathfrak{M}$ on $\Omega $, so that $\forall \psi \in C(\Omega )$, $\int \psi (x)\mathfrak{M}(\mathrm{d} x)=\lim_{k\rightarrow \infty }\frac{\,\int \psi _{n_{k}}(x)e^{\frac{\beta n_{k}}{2}A_{n_{k}}(x)^{2}}\mu (\mathrm{d}x)}{\int e^{\frac{\beta n_{k}}{2} A_{n_{k}}(x)^{2}}\mu (\mathrm{d}x)}.$ We call $\mathfrak{M}$ a quadratic mean-field
equilibrium probability; it is shift-invariant. Explicit examples are given.
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Mesoscale and Nanoscale Physics
Non-local synchronization of continuous time crystals in a semiconductor
Alex Greilich, Nataliia E. Kopteva, Vladimir L. Korenev et al. (+6 more)
Synchronization resulting in unified collective behavior of the individual elements of a system that are weakly coupled to each other has long fascinated scientists. Examples range from the periodic oscillation of coupled pendulum clocks to the rhythmic behavior in biological systems. Here we demonstrate this effect in a solid-state platform: spatially remote, auto-oscillating electron-
nuclear spin systems in a
semiconductor. When two such oscillators separated by up to 40 ${\mu}$m are optically pumped, their individually different frequencies lock to a common value, revealing long-range coherent coupling. For larger separations, the synchronization breaks. The interaction distance matches the electron
spin diffusion length, identifying
spin transport as the coupling-mediating mechanism and establishing phase coherence over mesoscopic distances. As a consequence, a wide-area optical pump drives all oscillators within the illuminated spot into a single synchronized state, despite their inhomogeneity. This synchronization accounts for the exceptional stability of the resulting auto-oscillations, enabling collective motion in distributed
spin systems and paving the way toward coherent
spin networks in spintronics.
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All authors Alex Greilich, Nataliia E. Kopteva, Vladimir L. Korenev, Philipp A. Haude, Linus Kunze, Ben W. Grobecker, Sergiu Anghel, Markus Betz, Manfred Bayer
Materials Science
Wafer-Scale Films of Two-Dimensional Materials via Roll-to-Roll Mechanical Exfoliation
Yigit Sozen, Thomas Pucher, Bhagyanath Paliyottil Kesavan et al. (+6 more)
In this study, we demonstrate an improved version of the roll-to-roll mechanical exfoliation method, incorporating a controlled sliding motion into the exfoliation process to achieve uniform nanosheet films of two-dimensional materials at wafer-scale. This scalable technique enables the fabrication of high-quality films suitable for electronic and optoelectronic applications. We validate the process by fabricating WSe2 phototransistors directly on the exfoliated films, achieving performance metrics comparable to the best reported devices based on electrochemically exfoliated material. The all-dry transfer method employed ensures minimal contamination and preserves the intrinsic properties of the material. This work highlights the potential of high-throughput mechanical exfoliation as a cost-effective and reliable route for large-scale production of 2D material-based devices.
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All authors Yigit Sozen, Thomas Pucher, Bhagyanath Paliyottil Kesavan, Nuria Jimenez-Arevalo, Julia Hernandez-Ruiz, Zdenek Sofer, Carmen Munuera, Juan J. Riquelme, Andres Castellanos-Gomez
Materials Science
Perspective on Moreau-Yosida Regularization in Density-Functional Theory
Markus Penz, Michael F. Herbst, Trygve Helgaker et al. (+1 more)
Within density-functional theory, Moreau-Yosida regularization enables both a reformulation of the theory and a mathematically well-defined definition of the Kohn-Sham approach. It is further employed in density-potential inversion schemes and, through the choice of
topology for the density and potential space, can be directly linked to classical field theories. This perspective collects various appearances of the regularization technique within density-functional theory alongside possibilities for their future development.
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All authors Markus Penz, Michael F. Herbst, Trygve Helgaker, Andre Laestadius
Soft Condensed Matter
Coupling of Lipid Phase Behavior and Protein Oligomerization in a Lattice Model of Raft Membranes
Subhadip Basu and Oded Farago
Membrane
proteins often form dimers and higher-order oligomers whose stability and spatial organization depend sensitively on their lipid environment. To investigate the physical principles underlying this coupling, we employ a
lattice Monte Carlo model of ternary lipid mixtures that exhibit
liquid-disordered ($L_d$) and
liquid-ordered ($L_o$) phase coexistence. In this framework,
proteins are represented as small membrane inclusions with tunable nearest neighbor interactions with both lipids and other
proteins, allowing us to examine how
protein-lipid affinity competes with
protein-
protein interactions and lipid-lipid demixing. We find that the balance of these interactions controls whether
proteins remain dispersed, assemble into small oligomers, or form large stable clusters within $L_o$ domains, and that increasing the
protein concentration further promotes coarsening of the ordered phase. To incorporate ligand-regulated activation, we extend the model to a kinetic Monte Carlo scheme in which
proteins stochastically switch between inactive and active states with distinct affinities. The inverse switching rate, relative to the time required for a
protein to diffuse across the characteristic size of the $L_o$ domains, governs the aggregation behavior. Rapid switching yields only transient small oligomers, slow switching reproduces the static limit with persistent large clusters, and intermediate rates produce broad cluster-size distributions. These results highlight the interplay between lipid phase organization,
protein-lipid affinity, and activation dynamics in regulating membrane
protein oligomerization, a coupling that is central to signal transduction and membrane organization in living
cells.
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Superconductivity
High-resolution magnetostriction measurements of the Pauli-limited superconductor Sr2RuO4
Shunichiro Kittaka, Yohei Kono, Toshiro Sakakibara et al. (+4 more)
We performed high-resolution magnetostriction measurements on the Pauli-limited
superconductor Sr$_2$RuO$_4$ using high-quality single
crystals. A first-order superconducting transition, accompanied by pronounced hysteresis, was observed under in-plane
magnetic fields, where the relative length change of the sample, $\Delta L/L$, was on the order of $10^{-8}$. To ensure the reliability of the measurements, particular
attention was paid to minimizing the influence of
magnetic torque, which can significantly affect data under in-plane field configurations, via field-angle-resolved magnetostriction. Within the hysteresis regime, slightly below the Pauli-limited upper critical field, a hump-like anomaly in the magnetostriction coefficient was identified. Furthermore, a characteristic double-peak structure in the field-angle derivative of the magnetostriction provides additional support for this anomaly. Although these findings may reflect a
lattice response associated with the emergence of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase in Sr$_2$RuO$_4$, the possibility of a broadened first-order transition cannot be excluded. Notably, this magnetostriction anomaly qualitatively deviates from the FFLO phase boundary suggested by previous NMR measurements, highlighting the necessity for further experimental and theoretical investigations to elucidate the nature of the FFLO state in this material.
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All authors Shunichiro Kittaka, Yohei Kono, Toshiro Sakakibara, Naoki Kikugawa, Shinya Uji, Dmitry A. Sokolov, Kazushige Machida
Materials Science
Challenges in predicting positron annihilation lifetimes in lead halide perovskites: correlation functionals and polymorphism
Kajal Madaan, Guido Roma, Jasurbek Gulomov et al. (+3 more)
Halide perovskites have emerged in the last decade as a new important class of
semiconductors for a variety of optoelectronic applications. A lot of previous studies were thus devoted to the characterisation of their point defects. Positron annihilation spectroscopy is a well recognized tool for probing vacancies in materials. Recent applications of this technique to APbX$_3$ halide perovskites are sparse, and the rare theoretical predictions of positron lifetimes in these materials, published in association with experiments, do not fully agree with each other. These works suggest that vacancies on the A site are not detected. In our theoretical study we focus on the role of the electron-positron correlation functional. We thoroughly revisit and compare several approximations when applied to methylammonium lead iodide (MAPbI$_3$) with or without vacancies, as well as inorganic perovskites CsPbI$_3$ and CsPbBr$_3$, in various phases. We show also the relationship between the size of the voids, through Voronoi volumes, and the calculated lifetimes. For the cubic phases we investigate in detail the role of polymorphism, including the distribution of vacancy formation energies and positron annihilation lifetimes. In our lifetimes calculations, apart from older and more recent semi-local approximations for the electron-positron correlation potential, we also consider the weighted density approximation (WDA), which is truly non-local and should better describe positron annihilation in regions with strong electronic density variations. We show that for this class of materials, and especially for cations vacancies, the influence of the chosen approximation is crucial, much stronger than in metals,
alloys and conventional
semiconductors. This influence may induce to reconsider the interpretation of experimentally determined lifetimes.
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All authors Kajal Madaan, Guido Roma, Jasurbek Gulomov, Pascal Pochet, Catherine Corbel, Ilja Makkonen
Strongly Correlated Electrons · Cross-listed from physics.comp-ph
The noiseless limit and improved-prior limit of the maximum entropy method and their implications for the analytic continuation problem
Thomas Chuna, Nicholas Barnfield, Paul Hamann et al. (+3 more)
Quantum Monte Carlo (QMC) methods are uniquely capable of providing exact simulations of
quantum many-body systems. Unfortunately, the applications of a QMC simulation are limited because extracting dynamic properties requires solving the analytic continuation (AC) problem. Across the many fields that use QMC methods, there is no universally accepted analytic continuation
algorithm for extracting dynamic properties, but many publications compare to the maximum
entropy method. We investigate when
entropy maximization is an acceptable approach. We show that
stochastic sampling
algorithms reduce to
entropy maximization when the
Bayesian prior is near to the true solution. We investigate when is Bryan's controversial optimization
algorithm [Bryan, Eur. Biophys. J. 18, 165-174 (1990)] for
entropy maximization (sometimes known as the maximum
entropy method) appropriate to use. We show that Bryan's
algorithm is appropriate when the noise is near zero or when the
Bayesian prior is near to the true solution. We also investigate the mean squared error, finding a better scaling when the
Bayesian prior is near the true solution than when the noise is near zero. We point to examples of improved data-driven
Bayesian priors that have already leveraged this advantage. We support these results by solving the double Gaussian problem using both Bryan's
algorithm and the newly formulated dual approach to
entropy maximization [Chuna et al., J. Phys. A: Math. Theor. 58, 335203 (2025)].
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All authors Thomas Chuna, Nicholas Barnfield, Paul Hamann, Sebastian Schwalbe, Michael P. Friedlander, Tobias Dornheim
Mesoscale and Nanoscale Physics
Controlling the Size of Nanoparticles Using a Magnetic Field: A Sphere Packing Approach
Yazeed Tawalbeh, Marwa Ghazi and Mauro Fernandes Pereira
We present an analytical framework that predicts and controls nanoparticle size through external
magnetic fields, uniting first-principles thermodynamics with a sphere packing approach. Calibrated to diamagnetic silver nanoparticles (20 nm at zero field and 5 nm at 250 mT), the model yields a closed-form relation between radius and field that reproduces the observed shift in most-probable size. Within the limits of classical capillarity and spherical demagnetization, the field lowers the nucleation barrier and drives the distribution toward smaller particles. Our results are robust for radii above 3 nm (5740 atoms). Below this scale non-extensive effects likely dominate, as discussed in detail in Supplementary Information. The approach generalizes to both diamagnetic and paramagnetic systems and the limitations expected for very small or ferromagnetically ordered nanoparticles are discussed.
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Soft Condensed Matter · Cross-listed from physics.bio-ph
Theory of Semi-discontinuous DNA Replication
Janani G and Deepak Bhat
The replisome, a
protein complex that drives DNA replication, comprises multiple DNA polymerases. During replication, one polymerase synthesizes the leading strand continuously, while another synthesizes the lagging strand discontinuously, producing short transient segments known as Okazaki fragments and gaps between them. After the synthesis of each Okazaki fragment, the lagging-strand polymerase dissociates either spontaneously or upon collision with the preceding fragment; however, the relative contributions of these mechanisms remain unclear. Here, we develop a biophysical model of semi-discontinuous replication by incorporating the
stochastic dynamics of the lagging-strand polymerase. By computing the Okazaki fragment and gap-size distributions, we show the significance of polymerase dissociation in shaping these statistics. Applying the model to the T4 bacteriophage and B. subtilis replisomes, we find that collisions with preceding Okazaki fragments predominantly trigger polymerase dissociation.
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Mesoscale and Nanoscale Physics
Plasmon resonance in a sub-THz graphene-based detector: theory and experiment
I.M. Moiseenko, E. Titova, M. Kashchenko et al. (+1 more)
We present a combined experimental and theoretical study of photovoltage generation in a
bilayer graphene (BLG) transistor structure exposed to subterahertz radiation. The device features a global bottom and split top gate, enabling independent control of the band gap and
Fermi level, thereby enabling the formation of a tunable p-n junction in
graphene. Measurements show that the photovoltage arises primarily through a thermoelectric mechanism driven by heating of the p-n junction in the middle of the channel. We also provide a theoretical justification for the excitation of two-dimensional plasmons at a record-low frequency of 0.13 THz, which manifests itself as characteristic oscillations in the measured photovoltage. These plasmonic resonances, activated by a decrease in charge carrier concentration due to opening of the band gap, lead to a local enhancement of the electromagnetic field and an increase in the carrier temperature in the junction region. The record-low frequency of plasmon resonance is enabled by the low carrier density achievable in the
bilayer graphene upon electrical induction of the band gap.
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All authors I.M. Moiseenko, E. Titova, M. Kashchenko, D. Svintsov
Mesoscale and Nanoscale Physics
Ultra-long-range spin coupling in graphene revealed by atomically resolved spin excitations
Beatriz Viña-Bausá, Antonio. T. Costa, Joao Henriques et al. (+6 more)
Magnetic interactions between localized
spins-1/2 play a central role in
quantum magnetism,
spin-based
quantum computing, and
quantum simulation. The range and strength of these interactions are key figures of merit. Here, we probe exchange interactions in pairs and trimers of
spins-1/2 introduced by chemisorption of individual hydrogen atoms on
graphene. Using scanning tunneling microscopy and inelastic electron tunneling spectroscopy, supported by large-scale mean-field Hubbard calculations, we demonstrate 3 meV exchange couplings at separations beyond 10 nm, surpassing all prior systems. The couplings can be ferro- or
antiferromagnetic depending on the relative sublattice arrangement. Real-space mapping of
spin excitation amplitudes enables characterization with atomic-resolution. Through atomic manipulation we extend this control to
spin trimers, revealing collective
spin excitations when pairwise exchange couplings are comparable.
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All authors Beatriz Viña-Bausá, Antonio. T. Costa, Joao Henriques, Eva Cortés-del Río, Roberto Carrasco, Pierre Mallet, Jean-Yves Veuillen, Joaquín Fernández-Rossier, Iván Brihuega
Materials Science · Cross-listed from physics.bio-ph
Beyond the tip: Lattice dynamics, seams, and the mechanism of microtubule fracture
Amir Zablotsky, Subham Biswas, Laura Schaedel et al. (+1 more)
The structural integrity of microtubules is paramount for cellular function. We present a theoretical analysis of their
lattice fracture, focusing on the influence of multi-seam structures arising from monomer defects and aiming to provide a more accurate estimation of GDP
lattice parameters. Our findings reveal that seams function as pre-existing pathways that accelerate damage propagation. Consequently, monomer vacancies destabilize the
lattice due to the inherent structural loss of tubulin-tubulin contacts and the additive acceleration of fracture through multiple seams. Importantly, the comparison of our simulations with experiments on
lattice fracture suggests that the intrinsic ratio of longitudinal to lateral binding energies is bounded at approximately 1.5, challenging previous predictions of
lattice anisotropy from tip-growth models and highlighting the urgent need to incorporate into current growth models parameters obtained from
lattice dynamics.
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All authors Amir Zablotsky, Subham Biswas, Laura Schaedel, Karin John
Materials Science
Density-dependent sodium-storage mechanisms in hard carbon materials
Alexis Front, Tapio Ala-Nissila and Miguel A. Caro
Understanding the sodium-storage mechanism in hard carbon (HC) anodes is crucial for advancing sodium-ion battery (SIB) technology. However, the intrinsic complexity of HC microstructures and their interactions with sodium remain not fully elucidated. We present a multiscale methodology that integrates grand-canonical Monte Carlo (GCMC) simulations with a machine-learning interatomic potential based on the Gaussian approximation potential (GAP) framework to investigate sodium insertion mechanisms in hard carbons with different levels of porosity, achieved by simulating structural models with densities ranging from 0.7 to 1.9 g cm$^{-3}$. Structural and thermodynamic analyses reveal the interplay between pore size and accessibility and the relative contributions of adsorption, intercalation, and pore filling to the overall storage capacity. Low-density carbons favor pore-filling, achieving extremely high capacities at near-zero voltages, whereas high-density carbons primarily store sodium through adsorption and intercalation, leading to lower but more stable capacities. Intermediate-density carbons ($1.3-1.6$ g cm$^{-3}$) provide the most balanced performance, combining moderate capacity (480 and 310 mAh g$^{-1}$), safe operating voltages, and minimal volume expansion ($<10$%). These findings establish a direct correlation between carbon density and electrochemical behavior, providing atomic-scale insight into how hard carbon morphology governs sodium-storage. The proposed framework offers a rational design principle for optimizing HC-based SIB anodes toward high energy density and long-term cycling stability.
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Materials Science
Physical properties and first-principles calculations of an altermagnet candidate Cs$_{1-\delta}$V$_2$Te$_2$O
Chang-Chao Liu, Jing Li, Ji-Yong Liu et al. (+4 more)
We report the
crystal growth, structure, physical properties, and first-principles calculations of a vanadium-based oxytelluride Cs$_{1-\delta}$V$_2$Te$_2$O. The material possesses two-dimensional V$_2$O square nets sandwiched by tellurium layers, with local crystallographic
symmetry satisfying the
spin symmetry for a $d$-wave altermagnet. An
antiferromagnetic transition at 293 K is unambiguously evidenced from the measurements of
magnetic susceptibility and specific heat. In addition, a secondary transition at $\sim$70 K is also observed, possibly associated with a Lifshitz transition. The first-principles calculations indicate robust Néel-type collinear antiferromagnetism in the V$_2$O plane. Consequently,
spin splittings show up in momentum space, in relation with the real-space mirror/rotation
symmetry. Interestingly, the V-$d_{yz}/d_{xz}$ electrons, which primarily contribute the quasi-one-dimensional
Fermi surface, turns out to be fully orbital- and
spin-polarized, akin to the case of a half metal. Our work lays a solid foundation on the potential applications utilizing altermagnetic properties in vanadium-based oxychalcogenides.
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All authors Chang-Chao Liu, Jing Li, Ji-Yong Liu, Jia-Yi Lu, Hua-Xun Li, Yi Liu, Guang-Han Cao
Statistical Mechanics
On the thermodynamic analogy of intracellular diffusivity fluctuations
Yuichi Itto
Two recent topics on a formal thermodynamic analogy of intracellular diffusivity fluctuations observed experimentally in normal/anomalous
diffusion are reported. Not only the analogs of the quantity of heat and work as well as the internal energy but also that of the Clausius inequality are identified. Then, the analog of the heat engine is constructed to characterize extraction of the diffusivity change as the analog of work during a cycle, the efficiency of which is formally equivalent to that of the Carnot engine, making the total change of the
entropy concerning the fluctuations vanish. The effect of the slow variation of the fluctuations on the efficiency is also briefly discussed.
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Soft Condensed Matter
Mobility of Lactose in Milk Powders
Armin Afrough, Pernille Andersen, Tanja Ninette Angelika Weihrauch et al. (+4 more)
Lactose is the major component of milk powders and is normally found to be in a glassy/amorphous state. During storage, lactose is known to participate in physicochemical processes, including crystallization on the surface and reaction with
proteins such as $\beta$-lactoglobulin. Lactose needs to be mobile to participate in such processes. However, there is a lack of evidence of its mobility in milk powders. In this study, we demonstrate that some of the lactose becomes mobile when milk powders are exposed to humid air $-$ an inappropriate storage condition. This mobility is evidenced by peaks in magic angle spinning $^{1}\mathrm{H}$ NMR spectra of milk powders in the range of 3.5 ppm to 4.0 ppm, which stem from lactose molecules displaying considerable rotational mobility. These signals have a longitudinal relaxation time constant T1 similar to that of mobile water according to 2D T1$-\delta(^{1}\mathrm{H})$ experiments under magic angle spinning. Furthermore, 2D $^{1}\mathrm{H}-^{13}\mathrm{C}$ HSQC magic angle spinning experiments of skim milk powder demonstrate the same fingerprint as that of lactose in the solution, confirming our observations.
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All authors Armin Afrough, Pernille Andersen, Tanja Ninette Angelika Weihrauch, Dennis Wilkens Juhl, Serafim Bakalis, Kirsten Gade Malmos, Thomas Vosegaard
Disordered Systems and Neural Networks
Tunable phononic transparency and opacity with isotopic defects
Zhun-Yong Ong
In an isotopically disordered harmonic chain,
phonon transmission attenuates exponentially with distance because of multiple scattering by the isotopic defects. We propose a simple and systematic method, which is based on the static structure factor, for arranging the isotopic defects to suppress or enhance
phonon scattering within a targeted frequency window (TFW), resulting in frequency-selective maximization or minimization of
phonon transmission. The phononic transparency and opacity effects are demonstrated numerically from the changes in the transmission coefficient and the
phonon inverse participation ratio. We briefly discuss how the underlying concept can be extended to the design of aperiodic superlattices to improve or block phononic transmission and control coherent
phonon transport.
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Materials Science
Machine Learning Approach to Predict the Curie Temperature of Fe- and Pt-Based Alloys
Svitlana Ponomarova, Oleksandr Ponomarov and Yurii Koval
Various techniques can be employed to determine the temperature of
magnetic transformation, whether it be the Curie or Neel temperature. The standard procedure typically involves creating
alloys with defined compositions and performing measurements experimentally. Alternatively, these temperatures can be predicted based on a material known physical and chemical properties prior to experiments. We identified an optimal feature set and selected the most effective
algorithm. Our findings show that the Voting Ensemble model, when combined with Monte Carlo cross-validation, achieves the highest prediction accuracy. The normalized root mean squared error serves as the primary performance metric. For implementation, we utilize the Azure Machine Learning framework for its robust computational and integration capabilities. This approach offers an efficient and reliable strategy for designing and predicting the Curie temperature of ternary
alloys. The paper also highlights potential applications of the model and its extensions for other systems.
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Soft Condensed Matter
Anomalous Enhancement of Yield Strength due to Static Friction
Ryudo Suzuki, Takashi Matsushima, Tetsuo Yamaguchi et al. (+2 more)
Friction is fundamental to mechanical stability across scales, from geological faults and architectural structures to granular materials and animal feet. We study the mechanical stability of a minimal friction-stabilized structure composed of three cylindrical particles arranged in a triangular stack on a floor under
gravity. We analyze the yield force, defined as the threshold compressive force applied quasi-statically from above at which the structure collapses due to sliding at the floor contact. Using singular perturbation analysis, we derive an expression which quantitatively predicts the yield force as a function of the static friction coefficient and a small dimensionless parameter $\epsilon$ characterizing elastic deformation.
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All authors Ryudo Suzuki, Takashi Matsushima, Tetsuo Yamaguchi, Marie Tani, Shin-ichi Sasa
Materials Science
Polarization-Magnetization Coupling in Visible Light Ferroelectric Double Perovskites
Sathiyamoorthy Buvaneswaran, Trilochan Sahoo and Saurabh Ghosh
The bulk photovoltaic effect (BPVE), arising from broken inversion
symmetry in ferroelectrics, offers a distinct pathway toward high-efficiency next-generation photovoltaics. We propose and investigate A/A$^\prime$-ordered double perovskites KLaFeMoO$_6$ and NaLaFeMoO$_6$ as promising single-phase ferroelectric photovoltaic (FE-PV) materials. First-principles calculations reveal robust P2$_1$
symmetry with A-site layer and B-site rock-salt ordering, accompanied by hybrid improper ferroelectricity driven by $a^{-}a^{-}c^{+}$ octahedral tilts. Both compounds exhibit significant spontaneous polarization and indirect band gaps of $\sim$ 1.8 eV, well suited for visible-light absorption ($>$10$^5$ cm$^{-1}$). Low carrier effective masses along the polar axis indicate efficient charge transport. Ab initio molecular dynamics simulations (AIMD) show that polarization-coupled magnetization switching is feasible above room temperature, making these materials suitable for room-temperature applications.
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Mesoscale and Nanoscale Physics
Heat Coulomb blockade in a double-island metal-semiconductor device
A. V. Parafilo
We study the thermal transport properties of a mesoscopic device comprising two metallic islands embedded in a two-dimensional electron gas in the integer
quantum Hall regime. It is shown that the $2M$ ballistic edge channels connecting the islands to the external reservoirs and the $N$ inter-island channels play a central role in the phenomenon of heat Coulomb blockade. Unlike the single-island case, where the heat flux is reduced by exactly one
quantum of thermal conductance, we predict an additional suppression proportional to the factor $M^2/(2N+M)^2$. We further examine a configuration in which the islands are placed between electrodes at different temperatures and identify the conditions under which the Wiedemann-Franz law is violated.
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Mesoscale and Nanoscale Physics
Universal two-stage dynamics and phase control in skyrmion formation
Shiwei Zhu, Xinyuan Guan, Zhen Sun et al. (+2 more)
We uncover a universal two-stage dynamics during skyrmion formation and establish its connection to
equilibrium phases through the introduction of a
chiral correlation $\chi$. Stage I involves stripe coarsening governed by the exchange-to-DMI ratio $J'$, while stage II entails stripe contraction driven by the synergy between $J'$ and the anisotropy-to-DMI ratio $K'$. The
magnetic field-to-DMI ratio $B'$ influences both stages. By combining symbolic regression with neural networks, we model the competition and cooperation among these parameters and derive a skyrmion formation criterion, $0.58 K'J' + \mu B'J' > 1$. Our model disentangles their distinct roles: $J'$ sets the stripe width, $K'$ primarily controls the skyrmion size, and $B'$ strongly affects the topological charge. This approach provides a general framework for predicting and controlling
magnetic phases in
chiral magnets.
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All authors Shiwei Zhu, Xinyuan Guan, Zhen Sun, Qiuyao Zhang, Changsheng Song