Strongly Correlated Electrons
Prominent Dimensional Effects on High-order Harmonic Generation in Strongly Correlated Electron Systems
Kento Uchida, Shintaro Takayoshi, Yuta Murakami et al. (+6 more)
Dimensionality strongly affects elementary excitations in correlated
quantum materials, yet its impact on extreme nonlinear optical responses remains largely unexplored. Here, we combine high-harmonic generation (HHG) experiments on quasi-one-dimensional SrCuO$_2$ and quasi-two-dimensional Pr$_2$CuO$_4$ with nonequilibrium simulations of Hubbard models. We find a pronounced dimensional contrast: SrCuO$_2$ exhibits a robust plateau-like high-harmonic spectrum with weak temperature dependence, whereas Pr$_2$CuO$_4$ shows a monotonic decrease in harmonic yield and strong thermal suppression, especially at higher harmonics. The simulations qualitatively reproduce these trends and identify dimensionality-dependent doublon–holon dephasing, governed by
spin–charge coupling, as their microscopic origin. These results establish dimensionality and
spin–charge coupling as key control parameters for extreme nonlinear optical responses in correlated
insulators.
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All authors Kento Uchida, Shintaro Takayoshi, Yuta Murakami, Dongjoon Song, Alannah M. Hallas, Masayuki Watanabe, Takashi Konishi, Aiko Nakano, Koichiro Tanaka
Statistical Mechanics
Impedance in Periodically Driven Stochastic Systems
Bart Wijns, Branko Meeus, Jef Hooyberghs et al. (+1 more)
We study the time-dependent currents arising in periodically driven
stochastic systems. In the linear regime of small driving, a closed expression is obtained for the impedance/admittance associated with these currents. This expression leads directly to an interpretation in terms of an equivalent electrical
circuit. For a
stochastic system with $N$ states, the electrical
circuit consists of precisely $N$ parallel branches, with each branch comprising a resistor and a capacitor in series. The low- and high-frequency limits of these currents are calculated, and the results are generalized to more general current expressions. We demonstrate our findings across several archetypal settings, illustrating the potential to detect specific broken
symmetries or the graph
topology associated with the
stochastic process.
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All authors Bart Wijns, Branko Meeus, Jef Hooyberghs, Bart Cleuren
Strongly Correlated Electrons
Thermodynamic Electric Toroidal Dipole and Intrinsic Longitudinal Spin Transport
Taisei Yamanaka, Takumi Sato and Satoru Hayami
Electric toroidal dipoles (ETDs) characterize ferroaxial order, yet their bulk definition in periodic
crystals has remained elusive because conventional multipole operators involve the ill-defined position operator. Here we formulate a thermodynamic ETD by coupling a spatially varying electric field to the relativistic
spin-induced electric polarization. The resulting expression is gauge invariant and provides a bulk order parameter for ferroaxial phases. We further establish a direct relation between the chemical-potential derivative of the ETD and the intrinsic longitudinal
spin conductivity in insulating systems. To demonstrate the formulation, we construct a minimal ferroaxial extension of the Kane–Mele model. The ETD becomes finite exclusively in the ferroaxial phase and is strongly enhanced near a small band gap, accompanied by a sizable longitudinal
spin current. Our results establish a thermodynamic theory of ETDs in crystalline solids and identify the longitudinal
spin conductivity as a direct transport manifestation of ferroaxial order.
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Materials Science
Chemical pressure and vacancies in crystals under nonhydrostatic stress
Michiel Sprik
Inhomogeneous stress is a driving force for
diffusion of vacancies in
crystals. The other way around a non-uniform distribution of vacancies induces stress. The accepted theory of composition-stress coupling in
crystals is Larché-Cahn (LC) theory. Composition is defined in terms of the population of
lattice sites with a limit of one-particle per site. Coupling is modelled by adding a compositional strain term to the elastic strain in the constitutive relation for stress. An alternative mechanism, proposed here, is letting the site binding energy vary with spatial (deformed) density. This generates a chemical pressure adding to the elastic stress. The governing equations for this model are derived using non-
equilibrium continuum thermodynamic methods. The gradient of the chemical pressure has a dual function acting both as the drift force for migration and as an effective internal one body force in the Cauchy equation for the elastic stress. The practical evaluation presented in the paper is restricted to
equilibrium properties. We examine the effect of externally applied non-hydrostatic stress, either in the form of surface tractions or a one-body force density (gravitation). The model system is a one component
crystal with a fixed number of
lattice sites. The number of particles can be variable but is always smaller than the number of
lattice sites. The linear elastic response is modelled by the standard Lamé stress tensor. The results for systems deformed by surface tractions are in qualitative agreement with LC theory allowing for differences in the expression for the elastic moduli. Deviations are more serious for the
crystal deformed by gravitation.
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Mesoscale and Nanoscale Physics
Rank-Selective Optical Tomography of Higher-Wave Altermagnetism
Meysam Bagheri Tagani, Carmine Autieri and Sahar Izadi Vishkayi
Identifying the spatial rank of higher-wave altermagnetic order optically is challenging because local electric-dipole response does not uniquely resolve distinct continuum harmonics. We show that finite
photon momentum turns one-
photon spin-resolved absorption into a rank-selective
tomography. For the planar $|m|=\ell$ sector of an even-parity $\ell$-wave component, a joint
Fourier projection in polarization and momentum angle isolates $\mathcal T_\ell\propto\eta_\ell q^{\ell-2}$, yielding the hierarchy $d:q^0$, $g:q^2$, and $i:q^4$; phase changes track rotations of the selected
magnetic harmonic. A Ward-consistent finite-$q$ microscopic calculation reproduces these powers without imposing them. Although discrete
crystal symmetry can generate lower-order local aliases, they are orthogonal to the selected momentum harmonic and cannot contaminate it below $q^{\ell-2}$. In MnTe, whose nonrelativistic parent order is three-dimensional $g$ wave while
spin–orbit coupling lowers the exact relativistic
spin-momentum-locking
symmetry, first-principles calculations show that more than $99.9\%$ of the
Fourier power of the Néel-projected $A$-region
spin-energy contrast remains in the parent $g$-wave-derived $m=3$ harmonic. Structured near fields place the required momentum window within experimental reach.
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Mesoscale and Nanoscale Physics
Direct observation of flat bands in near-magic-angle twisted bilayer CVD graphene
Gianluigi Baiardi, Alex Boschi, Giulia Piccinini et al. (+13 more)
Advances in chemical vapor deposition (CVD) growth have driven
graphene crystal quality to unprecedented levels, yet it is still unknown whether this route can realize the fragile flat-band and correlated states of the magic-angle (MA) twisted bilayer
graphene (TBG). Here, we report on the experimental observation by room-temperature nano-angle-resolved photoemission spectroscopy (nano-ARPES) of flat bands in a TBG sample close to the MA, assembled via a grow-and-stack protocol based on low-pressure CVD of
graphene on copper. Our study indicates electronic bands fully comparable to those measured in exfoliation-based samples and determines the size of the largest near-MA domain to be compatible with electronic transport experiments, motivating further experiments on flat band physics in CVD-
graphene.
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All authors Gianluigi Baiardi, Alex Boschi, Giulia Piccinini, Vaidotas Mišeikis, Lorenzo Cavicchi, Aaron Bostwick, Chris Jozwiak, Eli Rotenberg, Kenji Watanabe, Takashi Taniguchi, Marco Polini, Fabio Beltram, Antonio Rossi, Stiven Forti, Sergio Pezzini, Camilla Coletti
Materials Science
Symmetry-based modal analysis of heat transport in molecular dynamics of quasi-1D systems
Yu-Jie Cen, Sandro Wieser, Georg K. H. Madsen et al. (+1 more)
Detailed analysis of thermal conductivity results obtained from molecular dynamics (MD) trajectories conventionally relies on knowledge of the harmonic vibrational modes of the system. This is the case in methods like Green-Kubo modal analysis (GKMA) and homogeneous nonequilibrium modal analysis (HNEMA). However, arbitrary mixing within degenerate
phonon subspaces makes individual modal contributions basis dependent and can obscure their
symmetry character. We propose an alternative for quasi-one-dimensional (quasi-1D) systems: we construct the modal basis for the decomposition of the thermal conductivity from line-group projection operators, so that every projected component carries well-defined
symmetry labels (including rotational information and parities) and the decomposition is unique at the level of irreducible representations (irreps). Applying the idea to a (10, 0)-(20, 0) WS2-MoS2 double-walled nanotube (DWNT) described by a neuroevolution potential (NEP), we find that at 300 K both HNEMA and GKMA yield statistically consistent total conductivities and allow the identification of several prominent
symmetry-adapted conduction channels. The GKMA pair
matrix shows that within-block and same-channel cross-k terms account for 75.6% of the total conductivity, while cross-channel correlations contribute 24.4%.
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All authors Yu-Jie Cen, Sandro Wieser, Georg K. H. Madsen, Jesús Carrete
Disordered Systems and Neural Networks · Cross-listed from cs.LG
Percolation Dynamics in Optimization: Variance Cascades and Nested Symmetry
Sai Niranjan Ramachandran and Suvrit Sra
We study the dynamics of
Stochastic Gradient Descent (SGD), which is known to steer deep neural networks toward invariant sets that correspond to simpler subnetworks. How this steering unfolds over time remains poorly understood. We answer this by modeling the
stochastic gradient flow (SGF) as a percolation process, in which nested architectural
symmetries force subnetworks to merge in discrete blocks rather than by single-edge attachment. These structural transitions register as variance spikes in a macroscopic order parameter echoing physical phase transitions. We further state sufficient conditions under which the trapping argument carries over to Adam and AdamW under heavy-tailed gradient noise and measure them on a trained
Transformer.
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Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Implementation of quantum gates by Floquet analysis of kicked quantum system
Andrea De Luca, Carola Ciaramelletti and Simone Paganelli
Precise control of multi-
qubit architectures remains a critical bottleneck in superconducting
quantum processors. In this work, we investigate the synthesis of high-fidelity
quantum operations and state transfer protocols within an extended superconducting linear chain, scaling from three to seven sites. Using Floquet theory, we model the periodic drive as a train of delta-like pulses, mapping the
quantum control problem onto quasi-energy resonance conditions. Combining the Baker-Campbell-Hausdorff expansion with Floquet spectral decomposition, we analytically identify optimal driving parameters, refined via the Covariance
Matrix Adaptation
Evolution Strategy (CMA-ES). In the three-
qubit architecture, this enables high-fidelity synthesis of the iSWAP gate. Extending to a seven-site chain, we implement periodic trains of finite-width Gaussian pulses to activate distinct double-excitation transport channels with ultra-short gate durations t_gate (~170 ns). This achieves a clear scale separation from energy-relaxation times (T1) typical of fixed-frequency transmon devices with tunable couplers, such as IBM
Quantum hardware. Finally, we
benchmark stability under realistic imperfections, revealing a heightened sensitivity to static parameter disorder at the sub-percent level (eta ~ 10^-3) driven by spectral crowding, and discuss how closed-loop
topologies could mitigate this constraint. This framework bridges time-periodic control theory and practical
quantum gate engineering.
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Other Condensed Matter · Cross-listed from hep-th
Surprises of Klein paradox
T. R. Ahmadov, E. T. Akhmedov and V. I. Lapushkin
We consider second quantized $1+1$ dimensional Dirac
fermions with mass $m$ in background electric fields. This theory mimics the following situations. We consider two parallel capacitors with opposite directions of the electric field $E$ in them. The potential energy difference in one of them is equal to $V_0 > 2m$ and in the other to $V+V_0$, with $0<V<2m$. According to general physical understanding of the Schwinger effect, each capacitor separately will create pairs and there will be oppositely directed currents, which will not be equal to each other. The total current will not vanish. In this paper we show that this is too naive an observation: the limiting expectation value of the current operator, as $t\to +\infty$, is actually zero, if the above form of the potential with $0<V<2m$ is instantaneously turned on. The non-vanishing current is obtained only if $V>2m$. We also consider the same theory in the presence of the infinite wall and a deep well $V_0>2m$. We show that in such a potential the limiting expectation value of the current is zero in the Gaussian approximation. We discuss the relation of these observations to the Schwinger effet and to the decay of supercritical
nuclei.
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Materials Science
Magneto-Structural Coupling Enables Cryogenic Cation Redistribution in a Spinel Oxide
Yifeng Han, Yixing Zhao, Yunbo Ou et al. (+11 more)
Ionic transport in oxides is generally frozen at cryogenic temperatures, where thermal energy lies far below typical cation-migration barriers.
Neutron powder diffraction reveals progressive Fe/Mg redistribution between tetrahedral (A) and octahedral (B) sites in the spinel Mg0.5Fe0.5TiFeO4 upon cooling from 200 K to 5 K. A-site Fe occupancy increases toward near completion at 5 K within Rietveld resolution, while Ti remains on the B site. This exchange coincides with complex
magnetic correlations rather than a classical thermally activated window. Low-temperature magnetostrictive volume changes indicate strong
spin-
lattice coupling, but do not identify magnetostriction as the sole thermodynamic driver. Room-temperature high-pressure X-ray diffraction produces the opposite occupancy trend, showing that volume contraction alone cannot explain the cryogenic site exchange. These results point to magneto-structural free-energy minimization as a plausible mechanism for unlocking cryogenic cation mobility in a correlated spinel oxide.
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All authors Yifeng Han, Yixing Zhao, Yunbo Ou, Feiran Shen, Lunhua He, Ligang Xu, Mingxue Tang, Jared Matteucci, Zexiao Zhang, Xiaoli Ma, Xiaohui Yu, Zheng Deng, Man-Rong Li, Alexandra Navrotsky
Soft Condensed Matter
Collective Cell Fluidity Controls Active Prestress Transmission in Cell-Extracellular-Matrix Tissues
Liyang Wang, J. M. Schwarz and Tao Zhang
Tissues are active composites in which multicellular collectives and extracellular
matrices mechanically reorganize one another. We develop a three-dimensional micromechanical model that couples deformable, rearranging
cell clusters to a disordered network of semiflexible fibers through a dynamic, force-generating interface.
Cell clusters are represented as solid-like or fluid-like vertex-model spheroids and coupled to the
matrix by passive or contractile linkers renewed as the cluster boundary reorganizes. Matched intact, voided, and passive-linker controls separate cavity formation, interfacial tethering, and active loading. At small strain, passive tethering provides modest reinforcement, whereas active contraction prestresses and strongly stiffens the
matrix. Solid-like clusters preserve coherent force transmission and exhibit an excess modulus scaling approximately as $|\sigma|^{1.4}$ across changes in activity, cluster size, and cluster number. Fluid-like clusters undergo greater interfacial renewal, producing weaker and nonmonotonic coupling between prestress and stiffness. Increasing cluster number produces collective stiffening when prestressed regions become connected through sufficiently persistent interfaces. At large strain, both solid-like and fluid-like systems approach the corresponding voided-network response as the residual fiber backbone becomes mechanically dominant. Thus,
cell-generated prestress controls macroscopic stiffness only together with the organization and persistence of its transmission across the
cell-
matrix interface.
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Statistical Mechanics
Effect of reactive targets on diffusive transport with intermittent restarts
Samali Ghosh, Suvam Pal, Dibakar Ghosh et al. (+1 more)
We study search processes in a complex environment using the strategy of
stochastic resetting. A common occurrence in these environments is targets with finite reactivity.
Stochastic resetting has emerged as a powerful mechanism for optimizing search processes by curtailing long, unproductive excursions inherent to diffusive dynamics. Most theoretical studies, however, assume perfectly absorbing targets – an idealization that overlooks the finite reactivity commonly encountered in realistic chemical and biological systems. In this work, we investigate the interplay between
stochastic resetting and finite-target reactivity in reaction -
diffusion processes. Considering a one-dimensional system with multiple reactive targets, we demonstrated that the target reactivity modifies the optimization landscape. We uncover distinct regimes in which resetting enhances transport efficiency towards specific targets based on their chemical kinetics. As a consequence, the optimal resetting rate becomes intrinsically reactivity dependent. Our results identify target reactivity as a crucial control parameter governing
stochastic transport and provide insights into reaction-
diffusion processes in complex media.
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All authors Samali Ghosh, Suvam Pal, Dibakar Ghosh, P. S. Pal
Statistical Mechanics
Nonequilibrium corrections to conserved Ising criticality in scalar active matter: Ward identities, spectrum, and long crossovers
Piotr Zdybel
We identify the slowest-decaying nonequilibrium perturbations near the three-dimensional conserved Ising critical point and determine their impact on finite-size observables. We study two classes of perturbations: a field-dependent noise-to-mobility ratio $\Theta(\phi)=D(\phi)/M(\phi)$ and the gradient activity of Active Model B+. Starting from the Martin-Siggia-Rose-Janssen-De Dominicis action, we compute the linearized flow using the functional renormalization group. The transport sector is block triangular, with leading odd
eigenvalue $y_{\Theta_1}=-\Delta_\phi$, where $\Delta_\phi=(d-2+\eta)/2$. In the gradient sector, removing the detailed-balance direction leaves two genuinely nonequilibrium modes, chemical and current-like. Two smooth regulators give $y_{\Theta_1}\simeq-0.52$, $y_J\simeq-0.56$, and $y_{\rm ch}\simeq-0.89$. A translation Ward identity expresses the current operator as the divergence of the stress tensor. Together with conservation and Itô causality, this forbids chemical operators from generating the current mode, making the nonequilibrium stability
matrix triangular; an independent two-loop calculation in $d=4-\varepsilon$ finds no additional current contact counterterm. Within the FRG truncation, $y_J-y_{\Theta_1}=-\eta$; beyond it, this relation requires the absence of an additional contact anomaly. Using the 3D Ising value $\eta=0.0362978(20)$ [Kos et al., 2016] gives $y_{\Theta_1}\simeq-0.5181$ and $y_J\simeq-0.5544$. Because these exponents nearly coincide, single-power fits yield amplitude-dependent apparent exponents and crossover lengths may exceed accessible system sizes. We derive the resulting finite-size scaling rules: odd block observables respond linearly to activity, while even observables receive only quadratic corrections.
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Mesoscale and Nanoscale Physics
Room-temperature local strain control of moiré excitons in MoS$_2$/WSe$_2$ heterobilayers
T. O. Oskolkova, Y. Koo, A. A. Shubnic et al. (+8 more)
Moiré superlattices in heterobilayers of atomically thin transition metal dichalcogenides provide a versatile platform for exploring
quantum many-body physics as they can trap
excitons, leading to the formation of quantized moiré
exciton states. However, such moiré
excitons have been predominantly studied at cryogenic temperatures, which severely limits their practical applications. Here, we demonstrate room-temperature activation and control of moiré
excitons in MoS$_2$/WSe$_2$ heterobilayers using local strain engineering. Applying mechanical strain with a modified atomic force microscopy tip, we observe a series of resonances attributed to interlayer
exciton states confined in the moiré potential. Power-dependent photoluminescence measurements elucidate the population dynamics of the moiré
exciton states, while controlled local strain enables continuous tuning of their emission wavelength to the center of the second telecom window. We provide a theoretical model that captures all experimentally observed features, including the unconventional spectral shape of the moiré
exciton emission. Our findings establish local tip-induced strain as a powerful tool for the on-demand manipulation of moiré
excitons, paving the way for room-temperature
quantum excitonic devices.
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All authors T. O. Oskolkova, Y. Koo, A. A. Shubnic, I. Yu. Chestnov, I. Choi, C. Cheng, D. Huang, T. Jiang, K.-D. Park, I. V. Iorsh, V. Kravtsov
Mesoscale and Nanoscale Physics
In silico design of magnonic lasing in constricted waveguides
Jean F. Oliveira da Silva, Rai M. Menezes and Milorad V. Milosevic
Analogue black-hole systems have been proposed in various physical platforms, including
magnetic materials, offering rich physics and promising applications such as wave lasing. However, their practical realization and characterization remain largely unexplored. Here, we present an in silico study of magnonic black-hole phenomena in constricted ferromagnetic waveguides driven by
spin-polarized currents. Using micromagnetic simulations with a two-dimensional Poisson solver to obtain realistic current-density profiles, we demonstrate the formation of a double-hole cavity bounded by analogue event horizons, enabling resonant
spin-wave amplification. We characterize the resonances as a function of
magnetic and
geometric parameters and identify the corresponding
spin-wave modes. We further show that gradual tapers enhance transmission by suppressing
spin-wave reflections, while interfacial Dzyaloshinskii-Moriya interaction can mimic the current-induced Doppler shift, substantially reducing the critical current density required for applications and, consequently, Joule heating. Finally, we demonstrate a
spin-wave
laser in which thermally excited
spin waves undergo selective amplification and coherent emission at well-defined resonance frequencies. These results provide design principles for magnonic analogues of gravitational systems and point toward their potential for advanced spintronic applications.
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Materials Science
Ferroelastic domain switching by ultrafast photoinduced strain
Daniel G. Lourens, Maarten Kwaaitaal, Carl S. Davies et al. (+1 more)
The
crystal lattice underpins the fundamental properties of condensed matter, with ferroic order emerging sensitively from atomic coordination. Manipulating the lattic therefore promises a direct way to switch ferroics between their states. Infrared excitation provides an efficient pathway to drive
lattice motion and generate transient
crystal deformations and strains. Ferroelastics constitute a uniquely direct platform for such control, their order parameter being strain itself. However, whether ultrafast
laser-induced
lattice distortions can switch ferroelastic order remains unknown. Here we use ultrafast pump-probe microscopy to demonstrate that a single high-amplitude infrared pulse induces strain within the first nanosecond, followed by ferroelastic domain switching several nanoseconds later. The spatial distribution follows that expected from the photoinduced strain field, while their temporal
evolution is closely coupled to the strain dynamics. Our observations identify transient strain as the driving field for ferroelastic switching and suggest a general
lattice-mediated pathway for controlling ferroic order using infrared light.
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All authors Daniel G. Lourens, Maarten Kwaaitaal, Carl S. Davies, Andrei Kirilyuk
Superconductivity
Quantum Structural Renormalization and Anharmonic Stabilization of Superconductivity in P4/mmm YScH8
Xiaorui Dong, Mi Pang, Wenjie Ma et al. (+2 more)
The recent synthesis of P4/mmm-YScH$_{8}$ at 191.7 GPa with a superconducting critical temperature Tc of 113 K has attracted considerable interest in the study of ternary superhydrides. Here we systematically evaluate the effects of
quantum and anharmonic motion of ions in P4/mmm-YScH$_{8}$ using the
stochastic self-consistent harmonic approximation (SSCHA). We find that these effects renormalize the
crystal structure and lower the dynamical stability threshold pressure from $\sim$140 GPa to $\sim$84 GPa, a reduction of about 40%. Furthermore, neglecting these effects causes a significant overestimation of the $T_{c}$, for instance by $\sim$20 K at 190 GPa. Our prediction of $T_{c}$ at 190 GPa is 113 K ($\mu^{*}$= 0.13), close to the experimental observation. Analysis of the
phonon density of states and Eliashberg spectral function further reveals site-dependent contributions to superconductivity. These results establish that a consistent treatment of nuclear
quantum motion and anharmonicity is essential for accurately predicting superconductivity in compressed ternary hydrides.
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All authors Xiaorui Dong, Mi Pang, Wenjie Ma, Yao Ma, Pugeng Hou
Materials Science
Vitrification-Devitrification Enables Tunable Photonic and Gas Sorption Properties of Zeolitic Imidazolate Frameworks
Zhencai Li, Zihao Wang, Minhyuk Kim et al. (+14 more)
Zeolitic imidazolate framework (ZIF) glasses represent an emerging family of melt-quenched glasses, which exhibit immense potential for applications in gas separation, energy storage, and optics. However, their intrinsic porosity remains elusive due to the inherent challenges in resolving their disordered atomistic structures. Here, we systematically investigate the porosity of ZIF-4 and ZIF-62
crystals and their corresponding glasses. CO2 sorption at 195 K enables quantitative assessment of microporosity in both crystalline and glassy states, allowing the accessible micropore volume of the ZIF glasses to be determined. Moreover, establishing a direct relationship between photonic properties and structural porosity in Zn-based ZIF glasses remains challenging. Here we demonstrate striking broadband blue-light emission from ZIF-4 glass annealed under optimized conditions. A pronounced red shift is observed when increasing the annealing temperature above the glass transition temperature. By correlating the
evolution of photoluminescence with structural porosity, we reveal the interplay between the photonic and gas sorption properties of ZIF glasses. These findings provide new insights into the structure-property relationships of ZIF glasses and offer a pathway toward the rational design of multifunctional MOF glasses.
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All authors Zhencai Li, Zihao Wang, Minhyuk Kim, Huotian Zhang, Bozhao Yin, Yong Li, Qi Zhang, Fengming Cao, Xuan Ge, Laurent Calvez, Daniel Irving, Guoping Dong, Feng Gao, Haomiao Zhu, Morten M. Smedskjaer, Hoi R. Moon, Yuanzheng Yue
Mesoscale and Nanoscale Physics · Cross-listed from math-ph
Heat transfer problem of a dense gas described by the Enskog equation with a modification of the Enskog factor
Shigeru Takata, Soma Sakata and Masanari Hattori
Heat transfer in a dense gas between two parallel plates is studied for assessing the quantitative difference of two variants of the Enskog equation, i.e., the original Enskog equation and the Enskog equation with a modified Enskog factor recently proposed in Phys. Rev. E 111, 065108 (2025). The main advantage of the latter is that the H
theorem, which the former lacks, has been established. The influence of the modification is assessed by comparing the macroscopic quantities in detail. It is found that the impact of this modification is quite limited and the two variants reasonably agree as a whole.
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Superconductivity
Anomalous Superfluid Response in Altermagnetic Superconductors
Christian Wiedemann, Danilo Nikolić, Matthias Eschrig et al. (+1 more)
We report on the emergence of the anomalous (paramagnetic) superfluid response in altermagnetic
superconductors at arbitrary impurity concentrations. Due to anisotropic gapless superconductivity, altermagnetic
superconductors with an out-of-plane Zeeman field display an anisotropic paramagnetic Meissner effect. The effect is strongest for parallel altermagnetic and Zeeman exchange field vectors and in the clean sample. The presence of nonmagnetic impurities leads to isotropisation and, consequently, weakens the effect; however, the paramagnetic response sustains intermediate amounts of impurities in the system. As demonstrated in recent experiments, microwave superfluid stiffness measurements can serve as a sensitive probe of gapless superconductivity.
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All authors Christian Wiedemann, Danilo Nikolić, Matthias Eschrig, Wolfgang Belzig
Superconductivity
Vortex-core Majorana coupling to a chiral edge in a $p_x+ip_y$ superconductor: Nonmonotonic spectral reorganization and coherent fermion-parity dynamics
Peiyao Liu and Yi Zhou
We study how
vortex–edge coupling reorganizes the low-energy sector of a finite two-dimensional \(p_x+ip_y\) superconducting disk as a function of the
vortex–boundary separation \(d\) and examine what this reorganization implies for the parity
memory associated with a prescribed
vortex-core Majorana wave packet, a resource relevant to Majorana-based
quantum operations. Bogoliubov–de Gennes calculations reveal nonmonotonic core–edge reorganization of the lowest positive-energy finite-disk eigenstate, with particularly rapid variation near \(d\simeq7\xi\), where \(\xi\) is the coherence length. To separate this eigenstate reorganization from the spectral representation of a prescribed state, we rigidly translate a centered-
vortex core-reference packet to each fixed
vortex position, restrict it to the target disk, and project it, without intermediate normalization, onto the particle-hole-complete low-energy subspace. For \(\Delta_0/E_F=0.36\) and disk radius \(R=30\xi\), the resulting retained norm exceeds \(0.98\) at all six sampled separations, \(4.25\leq d/\xi\leq8.25\), while, depending on \(d\), the spectral measure is concentrated near zero energy, fragmented over several low-energy levels, or dominated by finite-energy weight. Correspondingly, the signed parity correlator displays slow temporal variation, rapid coherent dephasing, or sign-changing oscillations, with possible finite-size recurrences at later times. Thus a large retained norm does not by itself imply spectral concentration or persistent parity
memory.
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Materials Science
Linker Functionalization and pH Tuning Enhance Solar-Driven Catalytic CO$_2$ Reduction in MOF-5
Julia Santana-Andreo, Joshua Edzards, Surender Kumar et al. (+1 more)
The wide band gap of metal-organic framework (MOF) 5 constrains its use in photocatalytic carbon dioxide (CO$_2$) reduction despite its high porosity and favorable mass-transport properties. Adopting a state-of-the-art first-principles approach, we systematically investigate the effects of volumetric strain, metal-node substitution, linker functionalization, and pH control as knobs to improve the CO$_2$ photocatalytic ability of MOF-5. Strain and metal-node substitution negligibly affect the gap, whereas linker functionalization narrows it into the visible range via in-gap states while preserving reduction-side
alignment at pH = 0. The resulting reduction energetics are strongly sensitive to both linker functionalization and pH. Halogenated and hydroxylated frameworks provide access primarily to HCOOH, CO, and HCHO under alkaline conditions, principally with the Mg and Zn nodes, whereas COOH functionalization offers the broadest thermodynamic accessibility across the full CO$_2$ reduction sequence. NH$_2$ retains thermodynamic feasibility for all target reduction pathways but with larger overpotentials, while NO$_2$ generally yields unfavorable reduction energetics. Crucially, within the COOH series, the choice of the metal node tunes the fundamental gap by over 1 eV with only minor changes in the reduction overpotentials, placing Sr- and Ba-based architectures as the most favorable ones for broad product selectivity with visible-light excitation. Linker functionalization substantially reduces the spatial overlap of the frontier states, promoting photoinduced charge separation. Taken together, these results establish linker functionalization and solution pH as complementary design levers for independently tuning light absorption and CO$_2$-reduction energetics in MOF-5, establishing a rational and viable route for designing efficient MOF-based photocatalysts.
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All authors Julia Santana-Andreo, Joshua Edzards, Surender Kumar, Caterina Cocchi
Materials Science
Decoding Oxygen K-edge Fingerprints of NCM-811 Degradation via Ab Initio Many-Body Theory and High-Throughput Screening of Crystal Proxies
Daniel Duarte-Ruiz, Timo Reents, Elmar Kataev et al. (+4 more)
The degradation of LiNi$_{0.8}$Co$_{0.1}$Mn$_{0.1}$O$_2$ (NCM-811) in Li-ion batteries produces complex transition-metal oxides and binary phases that fundamentally limit cathode performance. While identifying these degradation products via X-ray absorption spectroscopy (XAS) is essential for mitigating electrochemical performance loss, interpretation remains challenging due to the structural complexity of real-world samples. In this work, we present an integrated theoretical-experimental framework combining high-resolution oxygen K-edge XAS with ab initio simulations based on many-body perturbation theory and high-throughput screening from density functional theory. We first evaluate the spectroscopic fingerprints of eight layered, spinel, and nominal rock-salt reference oxides, identifying discrepancies between the idealized single-
crystal bulk phase and experimental spectra. Using high-throughput screening to analyze the oxygen $p$-projected density of states of 38 distinct polymorphs of NiO, CoO, and MnO, we propose that the spectral differences can emerge, among other factors, from a structural ensemble of local variations represented here by simplified structural proxies. Our work establishes a viable and rigorous computational pathway to interpret the complex landscape of degraded battery materials.
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All authors Daniel Duarte-Ruiz, Timo Reents, Elmar Kataev, Raul Garcia-Diez, Regan G. Wilks, Marcus Baer, Caterina Cocchi
Soft Condensed Matter · Cross-listed from physics.bio-ph
Trypanosome motility in blood and particle suspensions
Florian A. Overberg, Marie Kater, Timothy Krüger et al. (+3 more)
Motile microorganisms often navigate crowded and structurally complex environments, where surrounding obstacles can strongly influence locomotion. The bloodstream form of the flagellate parasite Trypanosoma brucei circulates in blood, a dense suspension of red blood
cells (RBCs), yet the physical mechanisms governing its locomotion under such conditions remain poorly understood because direct experimental observations are challenging. Here, we combine numerical simulations with in vitro experiments to investigate trypanosome motility in concentrated RBC suspensions and in suspensions of spherical colloidal particles. Simulations reveal that the parasite swimming speed increases by up to $50\%$ at RBC volume fractions comparable to those in blood. To identify the origin of this enhancement, we perform controlled studies in colloidal suspensions with particles of different sizes. We find that suspended particles substantially increase the anisotropy between the perpendicular and parallel friction coefficients acting on the beating flagellum, thereby enhancing propulsion. This effect is most pronounced when the suspended particles are comparable to or smaller than the characteristic wavelength of the flagellar beat. Experiments with microparticle suspensions confirm an increase in trypanosome propulsion with increasing particle concentration, in qualitative agreement with the simulations. Our results uncover a general physical mechanism by which concentrated particle suspensions can enhance flagellar-beat-driven locomotion and suggest that the densely crowded, particulate environment of blood may facilitate trypanosome propulsion. These findings provide new insight into trypanosome motility in the bloodstream and may apply broadly to other flagellated microswimmers in complex suspensions.
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All authors Florian A. Overberg, Marie Kater, Timothy Krüger, Gerhard Gompper, Markus Engstler, Dmitry A. Fedosov
Materials Science
The Locality Cost of Fully Flat Hopf Insulators
Feng Liu, Qifeng Liang and Wenlong Gao
Hopf
topology permits a strictly finite-range
Hamiltonian with one exactly flat topological band. We prove, however, that extending flatness to the complete two-band spectrum necessarily sacrifices strict locality or the gap: any gapped, Hermitian, translationally invariant two-band
Hamiltonian with strictly finite-range hopping and two exactly flat bands has vanishing Hopf invariant. Equivalently, within this two-band setting, a Hopf band admits no compactly supported, translation-covariant, orthonormal Wannier generator. For factorized one-flat-band Hopf parents, the unavoidable partner dispersion equals the Gram symbol of translated compact localized states and encodes their nonorthogonality. Full flattening converts this dispersion into exponentially decaying but infinitely supported hopping. Model-independent bounds provide a sufficient criterion for finite-range approximants to retain the Hopf phase. An explicit model yields the axial decay length $\xi_z/a=1/\ln 2$, parameter-free hopping tails, and residual bandwidths testable in
circuit and photonic
lattices. Hopf
topology therefore does not prohibit a flat band but forces the locality–flatness cost to appear as either partner-band dispersion or nonlocal hopping.
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Disordered Systems and Neural Networks · Cross-listed from cs.NE
Memory as an Energy Landscape—Hopfield
Nima Dehghani
This chapter reconstructs the Hopfield network as a physical theory of
memory rather than merely an early neural-network
algorithm. It begins with the problem as it stood before 1982-threshold logic, Hebbian association, correlation
memories, and recurrent binary networks-and isolates what Hopfield's synthesis added: a dynamical definition of content-addressable
memory, a symmetric recurrent architecture with a Lyapunov function, a Hebbian
embedding of patterns in its couplings, and a physical account of basins, robustness, and graceful degradation. The binary and graded-response energy functions are derived in full, together with the signal-crosstalk decomposition governing pattern stability, the mean-field theory of
retrieval at extensive load, and the zero-temperature
retrieval spinodal at (alpha 0.138) established by Amit, Gutfreund, and Sompolinsky. The energy-based program is then followed through analog optimization networks,
polynomial dense associative
memories, exponential interactions, and modern continuous Hopfield updates, including the precise conditions under which the update becomes scaled dot-product
attention. Throughout, capacity claims are tied to their disorder ensemble, scaling limit, and success criterion, showing why numerically different storage limits need not conflict. A closing assessment distinguishes established results from surviving principles, assumption-bound limitations, and open problems, treating the Hopfield network as an effective theory whose
symmetry, locality, and point-
neuron assumptions delimit its biological reach. Fixed-seed numerical experiments expose the mechanisms discussed but do not substitute for analytical results.
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Disordered Systems and Neural Networks · Cross-listed from q-bio.NC
Neural Logic, Invariance, and the Retina—McCulloch and Pitts
Nima Dehghani
This chapter reconstructs the McCulloch-Pitts program as a physics of neural computation rather than the familiar cartoon of a binary
neuron. The 1943 logical calculus is developed in both directions: given a net, characterize the propositions realized by its activity; given an admissible logical expression, construct a net that realizes it. We recover the original distinction between thresholded excitatory summation and absolute inhibitory veto-one the weighted-threshold form cannot preserve for arbitrarily large excitatory inputs-and read unit-time delay as the physical realization of logical depth. Recurrence is treated exactly: an autonomous, deterministic network of finitely many binary units has a finite state space, so every trajectory eventually enters a periodic orbit-a fact about finite-state dynamics, not unbounded Turing computation. A single threshold element realizes only linearly separable Boolean functions, whereas finite feedforward networks of them synthesize any Boolean function on a finite domain. We then follows McCulloch and Pitts beyond threshold logic. The 1945 heterarchy paper turns cyclic preference into an obstruction to representation by a scalar utility. The 1947 work on universals asks how a physical network can identify inputs related by nuisance transformations, developed here via group averaging and feedback canonicalization. The 1959 frog-retina study makes the adequate-stimulus question experimental, revealing parallel invariant operations before the
brain proper. Spike-triggered analysis shows how a nonlinearly driven
neuron can have a vanishing first-order average while second-order statistics recover its hidden selectivity: methodological failure can masquerade as physiological absence. Modern mathematical tools are used without projecting their notation onto the historical papers, and limitations of the idealization are stated explicitly.
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Materials Science · Cross-listed from physics.optics
Multidimensional Light Detection with Symmetry-engineered Heterojunctions
Yucai Lin, Yaoqiang Zhou, Ruijuan Tian et al. (+11 more)
Miniaturised multidimensional light detection, encompassing full-Stokes polarimetry and spectroscopy in ultracompact footprints, is attracting growing interest for its potential to capture a comprehensive set of light properties in portable platforms. Although significant progress has been made in miniaturised schemes for independent polarisation and spectral detection, achieving simultaneous high-dimensional light detection remains an outstanding challenge that limits their development toward full integration. We overcome this limitation by breaking the rotational and inversion
symmetries in a
symmetry-engineered van der Waals heterojunction to realise an ultracompact multidimensional photodetector. The dual
symmetry breaking gives rise to non-trivial
quantum geometric and topological features, enabling simultaneous broadband polarisation- and spectrum-resolved light detection, in contrast to previous van der Waals material-based devices, which could detect only one of these modalities. Our device, with an effective area of only 10 micron x 10 micron, reconstructs full-Stokes polarisation with overall root-mean-square errors below 0.05 and resolves spectral peaks separated by 0.4 nm, capabilities not previously achieved in single-pixel detectors. By unifying high-fidelity polarimetry and sub-nanometre spectroscopy in a single electrically tunable junction, our work eliminates the need for cascaded detection architectures and establishes a foundation for multidimensional detector arrays for integrated photonics,
quantum information processing, and precision imaging.
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All authors Yucai Lin, Yaoqiang Zhou, Ruijuan Tian, Faisal Ahmed, Andreas C. Liapis, Youqiang Huang, Yawei Dai, Yuwei Chen, Weiwei Cai, Zongyin Yang, Weida Hu, Tawfique Hasan, Luojun Du, Zhipei Sun
Materials Science
Charge-Transfer Electronic Structure of NiX$_2$ (X = S, Se)
Atsushi Hariki, Takaki Okauchi, Daisuke Takegami et al. (+8 more)
We investigate the electronic structures of NiS$_2$ and NiSe$_2$ using density functional theory combined with dynamical mean-field theory (DFT+DMFT). A realistic electronic structure within DFT+DMFT was determined by optimizing the double-counting correction to reproduce experimental valence-band photoemission spectra. The validity of the present model is further confirmed by its successful description of the Ni 2$p$ core-level photoemission and Ni $L$-edge x-ray absorption spectra of NiS$_2$. Our results reveal a smaller charge-transfer energy than previously assumed, resulting in substantial ligand-to-Ni charge transfer and a reduced Ni local moment. We clarify how the relative position and interaction between the Ni upper Hubbard band and the antibonding chalcogen-dimer states shape the
evolution of the low-energy electronic structure across the NiS$_{2-x}$Se$_x$ series.
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All authors Atsushi Hariki, Takaki Okauchi, Daisuke Takegami, Naoki Ito, Mizuki Furo, Ayako Yamamoto, Tomoya Higo, Satoru Nakatsuji, Masato Yoshimura, Takashi Mizokawa, Jan Kunes