Soft Condensed Matter · Cross-listed from q-bio.CB
Modeling Tissue Detachment and Rupture Using an Extended Vertex Model with T2-inverse Transitions
Shota Nishimoto and Yuichi Togashi
The vertex model is widely used to describe the mechanics of epithelial tissues, but its conventional formulation assumes that all
cells remain tightly packed and always share edges with their neighbors, making it difficult to represent local detachment or gap formation. Here, we propose a minimal extension of the vertex model that enables
cell detachment by introducing a new topological transformation, T2-inverse, which acts as the inverse of the classical T2 transition. When the imbalance of forces acting on a vertex, quantified by a tension metric $T$, exceeds a threshold, the T2-inverse splits the vertex into multiple vertices and creates a closed polygon that is incorporated as a pseudo-
cell. This operation allows the model to represent the emergence and propagation of local detachment events. Using this framework, we simulate the stretching of a
cell sheet and show that force-induced local detachments can accumulate to produce macroscopic tissue rupture. These results demonstrate that the proposed model extends the capability of the vertex model to describe tissue-level breakdown processes, including detachment and tearing, and provides a foundation for studying a broader class of epithelial mechanical phenomena.
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Strongly Correlated Electrons
Hidden Magnetic Octupolar Order driven by Spin-Orbit coupling in KFeF$_3$
C. A. Crawford, C. I. Hiley, N. C. Bristowe et al. (+6 more)
Phase transitions are typically driven by
symmetry-breaking structural distortions that lift electronic degeneracies, yet in some cases, these transitions may be driven by a hidden order without conventional structural signatures. Here, we demonstrate that the 3$d$ perovskite, KFeF$_3$, hosts such a hidden instability. Using a combination of high-resolution powder diffraction, magnetometry,
symmetry-based analysis and first principles calculations, we reveal that while the 90 K cubic to rhombohedral transition arises from conventional magnetostriction accompanying antiferromagnetic order, a second transition at 40 K lowers the
symmetry to monoclinic without any detectable Jahn-Teller distortion or translational
symmetry-breaking.
Symmetry-based Landau analysis supports a hidden zone centered
magnetic octupole order parameter, whose improper coupling accounts for the weak ferromagnetism and pronounced
symmetry-breaking strain. Density functional calculations show that
spin-orbit coupling suppresses the competing Jahn-Teller instability, and thereby favors higher rank
magnetic multipolar degrees of freedom. These findings establish KFeF$_3$ as a model system in which the competing energy scales between
spin-orbit coupling and orbital degeneracy result in the emergence of hidden, multipolar order. We show that the control of such
magnetic, multipolar order could, in principle, provide a route to induce altermagnetism.
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All authors C. A. Crawford, C. I. Hiley, N. C. Bristowe, C. Stock, J. Gainza, C. Ritter, M. R. Lees, R. I. Walton, M. S. Senn
Mesoscale and Nanoscale Physics
Weak-coupling theory of half-metals and other fractional metallic phases in biased doped Bernal bilayer graphene
D. V. Zhitov, A. V. Rozhkov, A. O. Sboychakov et al. (+1 more)
The paper presents a theoretical study of many-body electronic phases in doped and electrically biased Bernal-stacked (AB) bilayer
graphene. We develop a variational mean-field theory with no fitted parameters. For the electron-electron interaction, we employ a parameter-free random-phase approximation to model the short-range screened Coulomb repulsion. The remaining long-range Coulomb potential energy is dictated by the geometry of the sample, behaving as a parallel-plate capacitor. We formulate the theory directly in terms of the experimentally controlled displacement field $\frak D$ rather than the interaction-renormalized interlayer potential difference. It makes our theory better suited for direct comparison with experiment. The resulting phase diagram is quite rich. It hosts several fractional-metal states connected by first- and second-order transitions. At higher bias and doping, three distinct fractional metallic states emerge. We classify these phases by the number of doped sectors and the
symmetry of the order parameters. Our results - obtained without any parameter fitting - reproduce key qualitative and quantitative features of recent experiments. This includes the energy scale associated with the loss of fractional metallic order. At lower bias and doping, the model stabilizes a broad spectrum of fractional-metal phases with more exotic
symmetry-breaking patterns. This suggests that further experimental exploration of the latter regime is warranted.
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All authors D. V. Zhitov, A. V. Rozhkov, A. O. Sboychakov, A. L. Rakhmanov
Quantum Gases
Finite-temperature mass gap and quench dynamics of mobile impurities in a Fermi gas
Baihua Gong
Recently, a mass-gap description of mobile impurities in a Fermi gas was introduced, which connects Anderson's orthogonality catastrophe for static impurities to the quasiparticle picture of Fermi polarons through a recoil-induced energy gap in the fermionic dispersion. That description, however, was restricted to zero temperature and did not address dynamics. Here we generalize the mass-gap model to finite temperature by combining the Lee–Low–Pines transformation with a self-consistent Hartree–Fock decoupling of the recoil-induced interaction, and we study the quench dynamics within this framework using the functional-determinant approach. At finite temperature the effective mass gap obeys the self-consistency equation $\Delta(T)=2U_F\tanh[\Delta(T)/4k_B T]$, with $U_F=k_F^2/2M$ and $M$ the impurity mass. This equation admits a nonzero solution below the characteristic temperature $T^*=U_F/(2k_B)$ and closes as $(T^*-T)^{1/2}$. We identify this closing as the mean-field signature of the thermal melting of the polaron and molecule quasiparticles. Computing the Ramsey response $S(t)$ after a sudden quench of the impurity–
fermion interaction, we find that its long-time oscillations—
quantum beats between the bound and in-gap states—disappear precisely above $T^*$. Our work ties the thermodynamic and dynamical fingerprints of polaron formation to a single temperature-dependent mean-field parameter.
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Mesoscale and Nanoscale Physics
Low-Frequency Charge Noise in Bilayer Graphene Quantum Dots
Jessica Richter, Max J. Ruckriegel, Jonas D. Gerber et al. (+12 more)
Bilayer
graphene (BLG)
quantum dots (QDs) are a promising platform for
semiconductor qubits. However, the low-frequency charge noise that may ultimately limit coherence has remained largely unexplored. Here, we systematically characterize charge noise in gate-defined BLG QDs using transport-based noise spectroscopy. We extract a median amplitude of $ S_\mu^{1/2} (1~\text{Hz}) = 1.16~\mu\text{eV}/\sqrt{\text{Hz}}$, placing BLG well within the range reported for established
semiconductor quantum-dot platforms. Across variations in charge occupation, confinement, source-drain bias, and charge-sensor operating conditions, neither the noise amplitude nor the spectral dependence shows a reproducible trend in electrostatic tuning, indicating that we extracted the intrinsic
semiconductor noise. Consistent noise levels are further observed in double QDs and confirmed using an independent superconducting resonator-based dispersive readout. Extending the study to BLG devices incorporating transition metal dichalcogenide layers reveals no measurable charge noise increase in weakly proximitized QDs. These results validate BLG as a viable platform for coherent
quantum information processing.
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All authors Jessica Richter, Max J. Ruckriegel, Jonas D. Gerber, Tijl Degroote, Christoph Adam, Markus Niese, Lara Ostertag, Clara Galante, Kenji Watanabe, Takashi Taniguchi, Petar Tomic, Artem O. Denisov, Hadrien Duprez, Klaus Ensslin, Thomas Ihn
Soft Condensed Matter
Pseudospectral Methods and Critical Phenomena
Jake Skelton, Joseph Brader, Salomée Tschopp et al. (+1 more)
We employ pseudospectral methods to solve the homogeneous Ornstein-Zernike (OZ) equation for a model fluid in the vicinity of the critical point. Focusing on the Mean-Spherical Approximation (MSA) as a closure to the OZ equation, we obtain numerical estimates for the critical exponents $\eta$, $\delta$ and $\gamma$ for a system of hard-core Yukawa particles both in two and three dimensions. The three-dimensional MSA exponents are already well-known from an analytic solution and are recovered by our numerical methods. The two-dimensional exponents are a new output of this work. The pseudospectral method allows for rapid and highly accurate solution of
liquid-state integral equation theories, and enables calculations on truely infinite domains, as needed for highly correlated states. In addition, we analyse the standard Picard iteration scheme and propose a variation of it which provides increased stability and speed of convergence.
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All authors Jake Skelton, Joseph Brader, Salomée Tschopp, Benjamin Goddard
Disordered Systems and Neural Networks
Spectral properties of deterministic matrices multiplied by rotationally invariant random non-Hermitian ensembles
Pierre Bousseyroux and Marc Potters
In this paper, we study spectral properties of multiplicative deformations of non-Hermitian random
matrices. We consider
matrices of the form $\mathbf{A}\mathbf{B}$, where $\mathbf{A}$ is a deterministic $N\times N$
matrix (not necessarily Hermitian) and $\mathbf{B}$ is a rotationally invariant random
matrix. We show that, as $N\to\infty$, the boundary of the complex
eigenvalue distribution of $\mathbf{A}\mathbf{B}$ is governed by simple equations involving the $\mathcal{R}_1$ and $\mathcal{R}_2$ transforms of $\mathbf{B}$.
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Statistical Mechanics
Frenkel line of Yukawa fluids within the self-consistent relaxation theory
Ilnaz I. Fairushin and Anatolii V. Mokshin
For a simple model fluid, the Yukawa fluid, the condition for dynamic crossover, known as the Frenkel line, is defined. The condition is related to the fact that the roton minimum in the dispersion relation of longitudinal acoustic-like excitations exists only when the collective vibrational dynamics of particles dominates in the
liquid. Based on the self-consistent relaxation theory for the Yukawa fluid, thermodynamic states are determined in which the roton minimum disappears. The obtained values of the state parameters for the Frenkel line are consistent with the results of studies in which the position of this line on the phase diagram of the Yukawa fluid was determined using molecular dynamics simulations. It is shown that the Frenkel line in this system can be determined directly from the structural characteristic – the static structure factor. A physical interpretation of the roton minimum frequency for the simple
liquids near the Frenkel line is proposed.
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Soft Condensed Matter
Patterned Substrates Unlock Self-Electrophoretic Phenomenon in Active Janus Microswimmers
Jyoti Sharma, Yashpal Singh Brar, Omar Tricinci et al. (+3 more)
Inert colloids half-coated with platinum (Pt) are a standard model of chemically powered active particles, yet the microscopic origins of their propulsion in hydrogen peroxide (H2O2) remain difficult to dissect experimentally. Whereas self-diffusiophoresis was the prevailing theory, self-electrophoresis has been more recently suggested as the main mechanism of propulsion. According to the latter mechanism, the pole-to-equator Pt-thickness gradient produced by directional metal deposition is sufficient to create anodic and cathodic regions on the metal cap and thereby generate an electric field sustained by H2O2 decomposition. Enhancing self-propulsion performance of such particles thus requires precise control over the Pt thickness distribution, which is currently not achievable with standard methods (e.g. evaporation or sputtering). Here, we propose a method to fabricate Janus active particles by assembling silica microspheres on patterned substrates containing spherical grooves whose depth and spacing set the degree of particle coating while simultaneously suppressing proximity-led defects (Pt bridges). The resulting particles exhibit a tunable platinum-thickness contrast, as verified by Focused-Ion-Beam cross-sections. In 2.5% H2O2, our results suggest that this control can significantly increase propulsion efficiency, while providing evidence indirectly supporting the hypothesis that self-electrophoresis is the dominant mechanism. These results demonstrate that our patterned-substrate route can enhance control over the catalyst deposition and enable novel Janus morphologies, allowing for more precise engineering of active colloids.
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All authors Jyoti Sharma, Yashpal Singh Brar, Omar Tricinci, Paola Parlanti, Mauro Gemmi, Stefano Palagi
Soft Condensed Matter
Effects of Charge Regulation on the Conformations and Dynamics of a Polyelectrolyte during Nanoparticle Adsorption
Kawaljeet Kaur, Rashmi Kandari, Sunita Kumari et al. (+1 more)
Customizing the surface characteristics and stimuli-responsive behavior of polyelectrolyte (PE) during interaction with nanoparticles (NP) have potential applications ranging from biological interactions to advanced diagnostic technologies. Using numerical simulations, we investigate how charge regulation (CR) shapes the conformation, dynamics and adsorption of PE on a oppositely charged NP and compared the results with constant charge (CC) conditions. At low solvent ion concentrations, CR barely affects the adsorption fraction, while significantly enhancing the dynamical response of the PE. However, at high ion concentrations, while complexation is suppressed in the CC case, the CR environment helps to overcome the energy barriers related to Debye screening and thermal fluctuations, thereby promoting the adsorption. By maintaining the strong PE-NP electrostatic interaction, PE exhibits a more directed ballistic-like dynamics towards NP during adsorption, in comparison to the diffusive and sub-diffusive behavior observed in the CC case. Our results emphasize that in high ion concentrations, with a strong Debye screening effect, a small fraction of charge-fluctuating sites suffices for adsorption to happen. A tunable CR mechanism is thus an efficient and robust strategy to control the biomolecular interaction and stability in complex environments.
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All authors Kawaljeet Kaur, Rashmi Kandari, Sunita Kumari, Subhajit Paul
Materials Science
High-Throughput Computational Discovery of Inverted Resistive Switching in Two-Dimensional Materials
Sanchali Mitra, Arnab Kabiraj, Benjamin W. J. Chen et al. (+8 more)
Atomristors, non-volatile resistive switching devices based on two-dimensional (2D) monolayers, are promising building blocks for energy-efficient
memory and neuromorphic computing. However, their design remains restricted to a few materials such as MoS2 and h-BN, limiting functional diversity and design flexibility. Here, a high-throughput computational framework combining density functional theory, machine-learning molecular dynamics, and
quantum transport simulations screens about 2,900 exfoliable monolayers for vacancy-mediated resistive switching, identifying 17 thermally stable candidates in two mechanistically distinct classes. In Class 1 monolayers, such as GaS, Au adsorption at the native vacancy introduces conducting states, switching the insulating monolayer from a high- to a low-resistance state (HRS-to-LRS). Class 2 monolayers, comprising ionically bonded metal oxyhalides and nitrohalides such as BiOCl, exhibit previously unreported inverted switching. Vacancy-released electrons delocalize and push the Fermi level into the conduction band, placing the device natively in the LRS; Au adsorption re-localizes these carriers and returns the Fermi level to the gap, driving LRS-to-HRS switching.
Quantum transport simulations confirm both mechanisms, while migration-barrier calculations identify the electrode-2D separation as a key parameter governing Au migration and the resistance window. These findings expand the atomristor landscape and establish complementary switching as a design paradigm for multifunctional
memory and neuromorphic hardware.
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All authors Sanchali Mitra, Arnab Kabiraj, Benjamin W. J. Chen, Han Zhang, Haiyu Meng, Shi-Jun Liang, C. S. Lau, Lei Shen, Lain-Jong Li, Kah-Wee Ang, Yee Sin Ang
Materials Science
SALTED: a symmetry-adapted machine-learning program for predicting electron-densities in molecules and materials
Zekun Lou, Alan M. Lewis, Théophane Bernhard et al. (+5 more)
SALTED provides an open-source Python package for machine learning the
quantum-mechanical electron density, $n(\mathbf{r})$, in molecular and condensed-phase systems based on input atomic coordinates and species. The program adopts a linear atom-centered decomposition of the electron density, which makes it highly transferable across diverse atomistic configurations sharing similar chemical environments. Because of this representation choice, SALTED is naturally interfaced with state-of-the-art electronic-structure programs based on atomic orbitals, namely CP2K, FHI-aims, and PySCF, from which reference electron-density data can be generated and used to train a model. The learning
algorithm is based on a
symmetry-adapted extension of Gaussian process regression, making SALTED especially efficient in small-data regimes. Thanks to the implementation of vector-field kernel functions, SALTED can also learn the first-order response of the electron density to applied electric fields, $\partial n(\mathbf{r})/\partial \mathbf{E}$. The application of SALTED within computational workflows has already shown its utility in a wide variety of contexts, including the calculation of polarization vectors and polarizability tensors, the accurate evaluation of Coulomb forces in QM/MM molecular-dynamics simulations, and electronic-structure studies of large-scale 2D materials.
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All authors Zekun Lou, Alan M. Lewis, Théophane Bernhard, Lukas Seifert, Agustin Salcedo, Florian Kleemiss, Mariana Rossi, Andrea Grisafi
Soft Condensed Matter
Heterogeneous collapse in thermoresponsive copolymer microgels varying molar composition
Jacopo Vialetto, Francesco Brasili, Letizia Tavagnacco et al. (+5 more)
Understanding the internal architecture of copolymer microgels is crucial for establishing how nanoscale
polymer organization controls their stimuli-responsive behavior. Here we focus on thermoresponsive P(N-isopropylacrylamide-co-N-isopropyl-methacrylamide), P(NIPAM-co-NIPMAM), microgels with varying mole fraction of the components, synthesized via radical precipitation polymerization, and we demonstrate that changes in their volume phase transition and
equilibrium swelling are governed by composition-dependent internal heterogeneity. Comparison between small-angle
neutron scattering (SANS) with isotopic labeling and monomer-resolved simulations show a block-like monomer distribution of the two components. SANS analysis reveals a universal maximum in the
polymer mesh correlation length near the transition, evidencing coexistence of collapsed NIPAM-rich and swollen domains. The correlation length increases with increasing NIPMAM content, with a maximum for 75 mol % NIPMAM, implying sparse collapsed regions within the network and thus a large degree of heterogeneity induced by the presence of an increasingly large fraction of intercalated, non-collapsing PNIPMAM. The maximum heterogeneity correlates with the
equilibrium swelling ratio, indicating that collapsed microgels retain a structural
memory of the transition and present a less-compliant structure in response to temperature variations. Overall, these insights highlight a complex effect of the block-like monomer distribution on the responsive properties of copolymer microgels with different compositions, thus providing a design rule for tailoring responsive colloids for functional soft materials.
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All authors Jacopo Vialetto, Francesco Brasili, Letizia Tavagnacco, Gavino Bassu, Elena Buratti, Stephen King, Emanuela Zaccarelli, Marco Laurati
Statistical Mechanics
Sample-specific rectification-like response in a boundary-driven exclusion process
Issei Sakai and Takuma Akimoto
We investigate the current response of a boundary-driven symmetric exclusion process with quenched site disorder. Hard-core particles hop symmetrically on a one-dimensional
lattice with site-dependent rates and are injected and removed at the boundaries by two reservoirs of different densities. We approximate the steady-state density profile using a Galerkin projection at linear order and a mean-field closure at higher orders, and thereby obtain the current as a nonlinear function of the reservoir density difference. At linear order in the reservoir density difference, the current-response coefficient depends on the mean reservoir density $\rho$, in contrast to the homogeneous case. Through the linear-response relation, this dependence leads to an
equilibrium current-fluctuation coefficient that is asymmetric under $\rho\rightarrow 1-\rho$. Beyond linear response, nonzero even-order current contributions break the antisymmetry of the current under reversal of the reservoir density difference, producing rectification-like behavior in individual disorder realizations. We further show that spatial-reflection
symmetry of the
equilibrium density profile rules out such behavior, so broken spatial-reflection
symmetry of the profile is a necessary condition for rectification-like behavior. Within the present approximation, we further find that, for continuously distributed site disorder, rectification-like behavior occurs arbitrarily close to
equilibrium for almost every disorder realization. At the ensemble level, however, the disorder-averaged current remains antisymmetric because the disorder ensemble is invariant under spatial reflection. These results provide a mechanism for rectification-like transport arising from sample-specific spatial heterogeneity rather than from an explicitly imposed directional asymmetry.
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Mesoscale and Nanoscale Physics
Spectral Function Method and Janus Quantum Numbers in Quasiperiodic Systems
Tian-Le Wu, Shi-Ping Ding, Miao Liang et al. (+2 more)
The absence of translational
symmetry in quasiperiodic systems invalidates conventional band theory, posing the central challenge in the field. Building upon the incommensurate energy band (IEB) concept, we establish a unified spectral theory for quasiperiodic systems by introducing two key advances. First, we develop an efficient spectral function method that calculates $A(k,\omega)$ using a small truncated
Hamiltonian matrix, bypassing full diagonalization. It converges via a distinctive successive locking of energy moments, yielding exact thermodynamic-limit results without finite-size scaling. Second, we introduce that quasiperiodic eigenstates possess Janus
quantum numbers: a single eigenstate, continuously tracked across localization transitions, carries dual labels in momentum and real space, which naturally reduce to the familiar Bloch momentum and band index in the commensurate limit. Together with IEB, these advances constitute a “band theory” for quasiperiodic systems, enabling us to define, compute, and label states with the same facility as in periodic ones.
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All authors Tian-Le Wu, Shi-Ping Ding, Miao Liang, Jing-Tao Lü, Jin-Hua Gao
Other Condensed Matter
Magnetic Couplings in Half-Filled Bipartite Graphs
Georges Bouzerar
We break from perturbative frameworks to establish a non-perturbative generalization of
magnetic exchange rules in half-filled bipartite networks. While historical models remain strictly tied to the debatable perturbation approach in the dilute limit and require the absence of zero-energy modes, our universal mechanism governs exchange interactions across arbitrary bipartite graphs. By bypassing traditional expansion bottlenecks, this framework provides an analytical predictive tool for magnetism in complex
lattices, offering key design principles to engineer stable, long-range order in next-generation 2D spintronic devices
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Soft Condensed Matter · Cross-listed from physics.comp-ph
BU-MBAR: A hybrid solution strategy for the MBAR equations
Fabio Müller, Francesco Alesiani and Henrik Christiansen
The multi-state Bennett acceptance ratio (MBAR) equations combine the data collected under different thermodynamic conditions in a statistically optimal way. Due to their practical importance, several solution strategies have been devised to optimize the convergence of the resulting set of coupled equations. However, even with graphics processing unit (GPU) acceleration, the convergence of these methods can still be either unstable or slow. We propose a new approach where the equations are interpreted as the limit of infinitesimal bin width of the respective weighted histogram analysis method (WHAM). In the proposed binned-to-unbinned MBAR (BU-MBAR) method, the bin width is adapted dynamically to ensure a stable and efficient convergence to the asymptotic solution.
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Soft Condensed Matter
Near-surface colloidal dynamics in jammed and slipping microgel suspensions
Masoodah Gunny, Frédérick Caetano, Matilde Bureau et al. (+4 more)
Jammed suspensions of soft microgel particles may exhibit slippage along smooth boundaries. Owing to their expected sub-micrometric dimensions, direct observations of dynamics within the near-surface layers supposed to be responsible for this slippage have been difficult to achieve. Here, we use total internal reflection fluorescence microscopy (TIRFM) to observe nanoparticle dynamics near glass/microgel-suspension interfaces. Indicating near-wall dynamic heterogeneity, velocity profiles for suspensions are nonlinear. These profiles tend to a constant slippage velocity at submicrometric distances from the wall, consistent with macroscopic wall slip measurements. Furthermore, nanoscale particle altitude distributions are strongly dependent on the slip velocity, revealing a dynamically-mediated and nanoscale particle-organisation effect. The collected observations give support for the existence of near-wall heterogeneity as a dominant mechanism contributing to microgel wall slip. Our work also opens new perspectives for the study of particle dynamics and organisation in complex interfacial environments.
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All authors Masoodah Gunny, Frédérick Caetano, Matilde Bureau, Alexandre Vilquin, Marie Le Merrer, Joshua D Mcgraw, Catherine Barentin
Strongly Correlated Electrons
Non-Resonant Impulsively Stimulated Raman Scattering by a Terahertz Field: a Case Study of 1T-TaS2
Haotian Zhang, Yuheng Guo, Zidu Yu et al. (+7 more)
Time-domain ultrafast and nonlinear terahertz spectroscopy techniques are recently applied to many condensed matter systems for investigating their collective excitations. In centrosymmetric systems, these collective modes are typically Raman-active and therefore do not couple directly to the terahertz electric field. The mechanism by which light-matter interaction realizes in these studies has not been explicitly discussed in detail. In this work, we perform terahertz pump - optical probe and terahertz third harmonic generation investigations on 1T-TaS2, a material exhibiting a rich charge-density-wave (CDW) phase diagram including the commensurate, nearly-commensurate and incommensurate CDW phases. The transition between these distinct states leaves a clear signature on the dynamical Raman response. We investigate how the Raman-active
phonons couple to a broadband monocycle terahertz field as well as a narrowband multicycle terahertz field. Our results indicate that a modified impulsively stimulated Raman scattering mechanism involving two-
photon absorption, also known as non-resonant Raman scattering, underlies the coherent excitation and observation of the
lattice modes. These results are relevant for future spectroscopy investigation and coherent control of collective modes using low-energy terahertz field as well as cavity electrodynamical dressing of solids.
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All authors Haotian Zhang, Yuheng Guo, Zidu Yu, Yongbo Lv, Yiting Wang, Liwen Feng, Jiaying Xu, Tianlong Xia, Xinbo Wang, Hao Chu
Materials Science
Orbital-Free DFT-Assisted Machine-Learned Molecular Dynamics for Electric-Field-Driven Ionic Transport
Yusuke Nishiya, Hiroya Nakata, Yosuke Harada et al. (+1 more)
We propose an orbital-free density functional theory (OFDFT)-assisted machine-learned molecular dynamics method in which field-independent interatomic forces are evaluated using a machine-learned potential and atomic charges that depend on the local environment are obtained from OFDFT calculations. The atomic charges obtained by Bader partitioning of the OFDFT electron density are multiplied by the electric-field vector and added to the forces from the machine-learned potential. This approach enables molecular dynamics simulations under an electric field at a lower computational cost than Kohn-Sham DFT (KSDFT)-based molecular dynamics. As a proof of concept, the method was applied to beta-Li3PS4 bulk and an S8/Li3PS4
heterostructure under periodic boundary conditions. For Li3PS4 bulk, OFDFT yielded Li charges and a total charge of the PS4 unit consistent with those obtained using KSDFT. In the
heterostructure, Li ions migrated from the Li3PS4 region into the S-rich region within a simulation time of approximately 170 ps. Accompanying this migration, the mean Bader charge of the S atoms that initially formed S8 rings changed from nearly neutral to negative. A comparison with KSDFT for a representative interfacial structure also confirmed that the negative charging of the S atoms upon the arrival of Li and the magnitude of the Li charges were qualitatively reproduced. These results demonstrate the possibility of treating field-driven ionic transport and changes in interfacial charge states using a universal machine-learned potential without training an additional material-specific charge-prediction model.
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All authors Yusuke Nishiya, Hiroya Nakata, Yosuke Harada, Yu-ichiro Matsushita
Materials Science
Electron-phonon coupled hydrodynamics in semimetal TaAs_2
Shan Jiang, Wei Xie, Xiaokang Li et al. (+2 more)
Hydrodynamic corrections to diffusive transport can arise when momentum-conserving collisions between quasiparticles become prominent, and they have been documented for both electrons and
phonons. An emerging frontier topic is coupled electron-
phonon (e-ph) hydrodynamics. Here, through electrical and thermal transport measurements on TaAs2
crystals with different impurity levels, we document the emergence of an e-ph bifluid in the temperature window of 5 to 15 K. Within this range, the
lattice thermal conductivity exhibits a faster-than-T^3 temperature dependence, as a consequence of non-monotonic and purity-dependent
phonon mean free paths, a signature of
phonon Poiseuille flow. However, strong e-ph coupling impedes the emergence of a ballistic regime. This is corroborated by the observation of
quantum oscillations in the
lattice thermal conductivity. Prominent
phonon-mediated momentum exchange between electrons amplifies the violation of the Wiedemann-Franz law and yields a two-order-of-magnitude discrepancy between
quantum and transport lifetimes, a signature of electron hydrodynamics in semimetals. Our results imply that in semimetals with optimized e-ph coupling, thanks to matching between the cryogenic
phonon wave?length and the Fermi wavelength, momentum and energy flow between the electron and
phonon reservoirs as frequently as within each reservoir.
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All authors Shan Jiang, Wei Xie, Xiaokang Li, Kamran Behnia, Zengwei Zhu
Strongly Correlated Electrons
Competing lattice structures induced by Sn substitution in CsV$_3$Sb$_5$
Anshu Kataria, Ilija K. Nikolov, Armando Consiglio et al. (+8 more)
Understanding the effect of chemical substitution on competing phases of kagome metals is crucial for disentangling the interplay between local structural distortions and electronic instabilities. In \cvs, Sn substitution strongly modifies the electronic phase diagram, yet the microscopic mechanism driving this remains unclear. Here, we combine $^{121}$Sb nuclear quadrupole resonance (NQR) measurements and density functional theory calculations to investigate the atomic-scale effects of Sn substitution in CsV$_3$Sb$_{5-x}$Sn$_x$. At low Sn concentrations, the observed satellite NQR peaks exhibit signatures of local structural distortion induced by Sn substitution, qualitatively consistent with our computational analysis. These impurity-induced features persist across the entire experimentally investigated doping range, up to $x$ = 0.65, and remain observable up to room temperature. For $x=1$, the fully doped idealized case, the estimated dynamical instabilities of the kagome
lattice suggest the stabilization of two nearly energy-degenerate
equilibrium structures characterized by V-trimers, distinguished by a zero- or $\pi$-phase shift between adjacent layers along the $c$-axis. Together, these results show that Sn substitution drives a complex interplay between local impurity-induced distortions and competing structural instabilities in vanadium-based kagome compounds.
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All authors Anshu Kataria, Ilija K. Nikolov, Armando Consiglio, Giuseppe Allodi, Ginevra Corsale, Andrea Capa Salinas, Stephen D. Wilson, Domenico Di Sante, Vesna F. Mitrović, Samuele Sanna, Pietro Bonfà
Materials Science
Interplay of B-Site Off-Centering and Molecular Orientations in the Mixed Hybrid Perovskite MAGe1xSnxI3
Erik Fransson, Apinya Ngoipala, Oskar Öjstedt et al. (+3 more)
B-site mixing is a common strategy for tuning properties of halide perovskites. In the lead-free system MAGe1-xSn_xI3, it brings tilting and off-centering into competition. Using large-scale molecular dynamics driven by a machine-learned interatomic potential, we map the structural behavior across the full composition range. MAGeI3 exhibits strong polar B-site off-centering that remains nearly constant up to the cubic transition, together with methylammonium (MA) orientational order that weakens progressively on heating. By contrast, MASnI3 combines octahedral tilting with weaker, predominantly antipolar off-centering. Ge-like behavior persists upon alloying and gives way to Sn-like behavior only beyond roughly 65 % Sn. In the high-temperature phases, the B-site cations remain locally off-centered but directionally disordered. On the Ge-rich side, the distorted inorganic framework biases the soft MA orientational landscape toward a restricted set of preferred directions. This coupling shows how the composition of the inorganic sublattice can tune molecular ordering in lead-free hybrid perovskites.
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All authors Erik Fransson, Apinya Ngoipala, Oskar Öjstedt, Maths Karlsson, Paul Erhart, Julia Wiktor
Soft Condensed Matter
Exact Scaling Laws and Non-Hermitian Topological Phase Transitions of Active Continuum on Hyperbolic Manifolds
Yu-Xin Xie
The macroscopic collective motion of active continuum on curved
manifolds is conventionally addressed through perturbative dynamic renormalization or finite-element simulations, often obscuring the underlying
geometric mechanisms. Here, an exact algebraic framework is established to reformulate the active phase transition on
hyperbolic spaces $\mathbb{H}^2$. By rigorously expanding the covariant Navier-Stokes-like equations and applying the Weitzenböck identity, we derive the exact critical threshold $\alpha_c = \frac{5}{4}D\kappa^2$ for macroscopic polarization, which is dictated by the
geometric mass gap of the Hodge-de Rham
Laplacian. We strictly define the parameter subspace $\alpha = 2D\kappa^2$ where the topological free energy reaches the Bogomolny-Prasad-Sommerfield (BPS) limit. This enables the reduction of the complex velocity field to Blaschke products via Möbius gauge
symmetry. The flat-space limit ($\kappa \to 0$) exactly degenerates to the topological phase of the classical O(2) model, demonstrating that the constant negative
curvature acts as an un-perturbative infrared regularization for non-linear amplitude saturation. Furthermore, mapping the non-variational active convective modes onto the defect translational zero-modes yields an intrinsically non-reciprocal interaction
matrix. By analytically extending the singular integral operator of the dynamically condensed defect ring, we identify a macroscopic second-order exceptional point (EP2) characterized by a strictly algebraic dynamic scaling law $\tau \sim |\Delta \nu|^{-1/2}$. This closed-form theoretical paradigm provides exact solutions for
geometric frustration and non-Hermitian
topology in soft mechanics.
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Strongly Correlated Electrons
Such stuff as magic is made on: compact operator algebra, stabilizer polytope and the structure of reduced density matrices in a Kitaev spin liquid
Snigdh Sabharwal, Nic Shannon and Paul Skrzypczyk
Quantum many-body systems exhibit rich and complex behaviour. Magic has recently emerged as a powerful new diagnostic for probing such systems, complementing other key features such as many-body
entanglement. Here, starting from an investigation of the onset of magic within subsystems of a larger many-body
quantum system, we show that intricate structures emerge which shed important light on the underlying many-body physics. Focusing on the Kitaev honeycomb model, we first identify the temperature below which local subsystems acquire magic. Remarkably, we find that the optimal magic witnesses active at the onset of magic reveal compact operator spaces that continue to capture the local thermal states throughout their subsequent
evolution. For the six-site hexagonal marginal, this connection can be made stronger: the same operator space emerges independently from the
symmetries of the local marginal and forms the
symmetry-resolved plaquette
algebra. When these
symmetries are realized exactly, the local state lies entirely within this
algebra and the reduced robustness of magic is equal to the full robustness of magic. The same reduced description can also be applied to other local
quantum resources, which we illustrate using genuine multipartite
entanglement. Furthermore, the operator spaces possess a rich algebraic structure in the form of finite-dimensional Euclidean Jordan
algebras, with a natural interpretation in terms of bond and bond-cycle operators. Our general methodology therefore show how the onset of local magic can reveal a compact, physically meaningful operator structure underlying the finite-temperature Kitaev
spin liquid, and opens up a new avenue towards reduced descriptions of
quantum resources in many-body systems.
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Mesoscale and Nanoscale Physics
Built-In Electric Field Modulation of Spontaneous Magnetism and Thermospin Transport in Boron-Nitrogen Doped Zigzag Graphene Nanoribbons
Ma Luo, Yiyi Xie and Xinxiu Wu
Zigzag-edged
graphene nanoribbons (ZGNRs) host large
magnetic moments at two zigzag edges due to spontaneous magnetism, whose ground state is antiferromagnetically coupled
spin-order edge state (AF state). In this paper, the spontaneous magnetism and thermoelectricity of ZGNRs with periodic substituted doping of boron and nitrogen atoms along the axial direction are investigated by first principle calculation. The doping induces an internal electric field, which modulates the
magnetic moments at the two zigzag edges and the band structure with
spin splitting. For varying doping configuration, the ground state could be AF state, ferromagnetically coupled
spin-order edge state (FM state), or degenerated pair of AF and FM states. External transversal static electric field can further modulate the
magnetic moments and the band structure. By designing the doping configuration and the external field, pure thermal
spin current with the absence of thermal charge current can be generated at room temperature, which can be switched on and off by flipping the
magnetic configuration between AF and FM states. Thus, the doped ZGNRs can be applied as prototype devices for
spin-caloritronic.
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Soft Condensed Matter
Granular Rods Fall Faster in Denser Obstacle Fields
Fumiaki Nakai and Hiroaki Katsuragi
How does particle shape affect driven transport through obstacle fields? We simulate a dissipative rod falling under
gravity through randomly placed fixed obstacles. For sufficiently slender rods, the mean descent speed before trapping decreases, increases, and then decreases again as obstacle density rises, opening a window of densities in which rods fall faster in denser fields. Scaling arguments based on collision rates and rod geometry explain the three regimes and their crossovers. Particle shape can thus reverse the expectation that crowding slows driven transport.
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Strongly Correlated Electrons
Studying line defect at Deconfined Quantum Criticality via fuzzy sphere regularization
Shutao Liu, Shuai Yang, Jie Lou et al. (+1 more)
The interplay between bulk critical fluctuations and nontrivial
topology can enrich defect physics and give rise to novel defect universality classes. Understanding the fate of such defects therefore constitutes an important open problem. In this work, we studied a particularly simple setting: a (0+1)-dimensional pinning-field defect coupled to a (2+1)-dimensional deconfined
quantum critical bulk. Using the fuzzy-sphere regularization, we numerically investigated the defect operator spectrum and extracted several universal quantities characterizing the defect conformal fixed point, including the scaling dimensions of defect-changing(creating) operators and the defect \(g\)-function. These results establish the first numerical characterization of line-defect conformal data at deconfined
quantum criticality and may stimulate further investigations of defect critical phenomena in topological
quantum critical matter.
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All authors Shutao Liu, Shuai Yang, Jie Lou, Yan Chen
Quantum Gases
Universal scaling of fluctuations and correlations across the superfluid transition
Paul Paquiez, Géraud Dupuy, Maxime Allemand et al. (+6 more)
The critical behavior of a system near a continuous phase transition is commonly characterized by power laws and a set of universal critical exponents. Yet universality at phase transitions has even more fundamental manifestations. It dictates that all observables follow universal scaling functions, which may extend beyond simple power laws. Furthermore, microscopic details are captured entirely by only two system-specific scale factors, that rescale any measured quantity onto its universal form. In this work, we report the experimental validation of this prediction in ultracold
lattice Bose gases undergoing the superfluid transition. We extract the scale factors by collapsing the order-parameter cumulants measured at varying
entropies. We show that these factors specify scaling functions governing both the order-parameter distribution and two-point correlations. By measuring these scaling functions, we also determine three critical exponents $\beta$, $\gamma$ and $\nu$. Our results provide an experimental demonstration that universal scaling is simultaneously obeyed by multiple observables in a
quantum many-body system.
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All authors Paul Paquiez, Géraud Dupuy, Maxime Allemand, Henri Coquinot, Tommaso Roscilde, Nicolas Dupuis, Adam Rançon, Thomas Chalopin, David Clément
Soft Condensed Matter
Computing stable configurations of confined smectic liquid crystals with a deep variational framework
Yuchen Xie, Baoming Shi, Yucen Han et al. (+1 more)
Smectic
liquid crystals are layered
liquid-crystalline phases characterized by orientational order and periodic density modulation. Although their structures can be modeled using continuum theories, computing stable configurations remains challenging in complex geometries, particularly when the high-frequency density modulations associated with smectic layering should be resolved. We propose a deep variational framework (DVF) for computing these configurations within the modified Landau–de Gennes model, in which the coupled orientational and positional order parameters are represented on a regular reference domain while physical confinement is incorporated through coordinate mappings. A warmup penalty mitigates the spectral bias of neural networks toward smooth, nonlayered fields, enabling robust recovery of oscillatory smectic states. Comparisons with a neural-network baseline and finite-difference relaxation demonstrate the essential role of this penalty and the numerical stability of the resulting layered states. The DVF reproduces experimentally established smectic-A defect structures and layer morphologies across diverse confinement geometries and further predicts a chevron-like smectic-C state in a tangent-anchored sphere. Together, these results demonstrate the applicability of the DVF to computing stable smectic configurations across experimentally relevant confinement geometries and anchoring conditions.
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All authors Yuchen Xie, Baoming Shi, Yucen Han, Lei Zhang