Materials Science
Molecular Precursor Chemistry Shapes Early-Stage Reaction Pathways in Nitrogen-Doped Carbon Nanotube Synthesis
Narayan N. Som, Lukasz Nowicki, Tomasz Gizewski et al. (+10 more)
The structural characteristics of carbon nanotubes are usually discussed in terms of processes occurring during nanotube nucleation and subsequent growth from an already formed catalyst nanoparticle. Here, we show that their structural trajectory can begin much earlier, within the first nanoseconds of precursor decomposition and catalyst formation. We combine experiment and reactive molecular dynamics to compare nitrogen-free CNT synthesis with two closely related aromatic nitrogen precursors, pyridine and pyrazine, containing one and two nitrogen atoms per molecule, respectively. Experimentally, both nitrogen-containing precursors promote bamboo-like CNT formation and produce substantially more structurally disordered CNTs than the nitrogen-free reference. Notably, nitrogen incorporation does not scale simply with the amount of nitrogen supplied, demonstrating a strong contribution from precursor chemistry. Reactive molecular dynamics reveals that nitrogen-containing precursors significantly modify local Fe-carbon and Fe-SiO2 interactions during catalyst
evolution, while pyridine and pyrazine exhibit distinct decomposition pathways, with pyrazine showing significantly greater decomposition within the simulated timescale. These results demonstrate that precursor chemistry influences the local chemical environment and early catalyst
evolution, highlighting its potential role in the initial stages of CNT growth.
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All authors Narayan N. Som, Lukasz Nowicki, Tomasz Gizewski, Karolina Z. Milowska, Anna Wroblewska, Caghan Tuncer, Maciej Trzaskowski, Olga Iwasinska-Kowalska, Tomasz Plocinski, Mariusz Zdrojek, Krzysztof K. Koziol, Malgorzata Jakubowska, Agnieszka Lekawa-Raus
Disordered Systems and Neural Networks · Cross-listed from cs.IT
Information-Theoretic Limits for Rectangular Spiked Matrix Models with Rotationally Invariant Noise
Qun Chen, Rudy Skerk, Jean Barbier et al. (+3 more)
We study the information-theoretic limits of inference in rectangular rank-one spiked
matrix models with additive rotationally invariant noise, thereby going beyond the standard assumption of independent noise entries. Using the replica method from statistical physics, we derive a variational formula for the mutual information between the signal and the data, together with a system of saddle point equations predicting the minimum mean squared error in estimating the rank-one spike. We further show that, in the Bayes-optimal setting, these saddle point equations coincide with the fixed point equations of the state
evolution of a recently proposed orthogonal approximate message passing
algorithm with Bayes-optimal denoisers. This equivalence provides an algorithmic interpretation of the replica prediction and supports the Bayes-optimality of orthogonal approximate message passing whenever the relevant fixed point is unique. Numerical evaluations of the saddle point equations for several rotationally invariant noise ensembles and signal priors, together with finite-size simulations of the
algorithm, confirm the asymptotic predictions. They illustrate both regimes with a unique informative fixed point, where orthogonal approximate message passing is predicted to attain the minimum mean squared error, and regimes with multiple fixed points, where a statistical-to-computational gap exists.
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All authors Qun Chen, Rudy Skerk, Jean Barbier, Francesco Camilli, Junjie Ma, Haochuan Zhang
Soft Condensed Matter
Self-phoresis on a one-dimensional periodic domain
Leah Anderson and David S. Dean
We study the spontaneous motion and collective dynamics of self-phoretic particles on a one-dimensional periodic domain. The particles act as localized chemical sources (of a particle-dependent strength) of a field and the particles themselves respond to the gradients of the field they generate (with a particle-dependent phoretic mobility). The chemical field itself diffuses and evaporates. For a single particle, we derive the exact threshold for spontaneous propulsion and establish the emergence of stable constant-velocity states near onset through a supercritical pitchfork bifurcation. We then consider an active source coupled to a non-emitting tracer and determine the conditions for slipping and stable phase-locked motion. For two mutually coupled sources, the stationary antipodal configuration can lose stability through either a pitchfork or a Hopf bifurcation, depending on the relative source strengths and phoretic mobilities. We determine the competing instability thresholds and compare them with direct numerical simulations of the coupled particle-field equations. Beyond onset, the resulting translating and oscillatory states provide qualitative counterparts to modes of motion observed experimentally for camphor disks in annular water channels. These results connect the onset of individual propulsion, tracer entrainment, and collective motion within a common analytically tractable framework.
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Quantum Gases
Information Entropy as a Sensitive Diagnostic of Relaxation Dynamics in a Quasiperiodic Mott Insulator
N. D. Chavda, Antônio M. S. Macêdo, Robin P Sagar et al. (+1 more)
We study the nonequilibrium dynamics of a bosonic Mott
insulator following a sudden quench from a periodic to a quasiperiodic
lattice. Using ab initio multiconfigurational (MCTDHB) continuum many-body dynamics, we characterize the
evolution through momentum distributions, fragmenta- tion, correlation functions, and information
entropy. We find that melting of Mott correlations does not necessarily imply relaxation of the many-body state. In the weakly interacting regime, the initial Mott-like correlation undergo recurrent melting and partial recovery, while the information
entropy displays large, intermittent fluctuations within the simulated time window. In contrast, a strongly interacting and fully fragmented Mott
insulator retains its characteristic Mott correla- tions, up to partial distortions, while the many-body information
entropy approaches a well-defined stationary regime plateau with comparatively small fluctuations. These results indicate that Mott- correlation dynamics and many-body relaxation can be dissociated in this finite system and support the use of information
entropy, evaluated in the multiconfigurational representation, as a sensitive complementary diagnostic of nonequilibrium relaxation.
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All authors N. D. Chavda, Antônio M. S. Macêdo, Robin P Sagar, Barnali Chakrabarti
Strongly Correlated Electrons
Quantum Ising transition on the Cayley tree: boundary criticality, universality, and an effective Bethe line
Pietro Richelli and Natalia Chepiga
We investigate
quantum criticality in the transverse-field Ising model on finite Cayley trees and demonstrate that their extensive boundary fundamentally changes the nature of the
quantum phase transition compared with the infinite, boundary-free Bethe
lattice. Using tree tensor-network simulations for systems with up to $N=12286$ sites, we identify a boundary-driven continuous transition at $h_x^c\approx1.76$, distinct from the mean-field Bethe-
lattice transition at $h_x^c\approx2.23$. We characterize this transition through finite-size scaling of the magnetization and
magnetic susceptibility and extract a consistent set of critical exponents. By introducing next-nearest-neighbor interactions, we demonstrate the robustness of the extracted critical exponents, providing numerical argument for the Ising boundary universality class on the Cayley tree. Furthermore, we show that the physics of the boundary-free Bethe
lattice can be efficiently recovered on a finite Cayley tree by fine-tuning a local boundary field. The resulting effective Bethe line, whose existence is tied to the mean-field nature of the bulk transition, effectively screens the extensive boundary and restores both the critical point and the mean-field critical scaling of the infinite Bethe
lattice.
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Materials Science
Engineering Ferroelectric Phases in BaTiO$_3$ Films via Buffer-Layer Induced Misfit Strain Reversal
A.S. Mikheykin, N.V. Lyanguzov, A.S. Konstantinov et al. (+4 more)
Controlling ferroelectric phase
symmetry through strain engineering is crucial for tailoring polarization
topology and functional properties in oxide-based devices. Here, we show that a thin conductive buffer layer can override substrate-induced strain in BaTiO$_3$ (BTO) films on MgO. Although the
lattice parameter of MgO(001) would be expected to induce tensile misfit strain, in 500~nm BaTiO$_3$ films the thermal-expansion mismatch dominates, resulting in effective compressive stress upon cooling. Inserting a 50-nm La$_{0.67}$Sr$_{0.33}$MnO$_3$ (LSMO) buffer layer reverses the effective strain state from compressive to tensile. Using temperature-dependent polarized Raman spectroscopy, X-ray diffraction, and piezoresponse force microscopy, we reveal an unconventional phase sequence upon cooling: paraelectric $\rightarrow$ orthorhombic ($\textit{aa}$-phase, $\sim$407 K) $\rightarrow$ monoclinic ($\textit{r}$-phase, $\sim$300-345 K), characterized in-plane and tilted polarization components. The LSMO layer not only serves as a bottom electrode but also modifies the strain state, while interfacial charge redistribution induces a built-in electric field, evidenced by self-polarization and asymmetric PFM hysteresis. These findings highlight the critical role of conductive buffer layers in controlling ferroelectric
symmetry and enabling oxide
heterostructures with tailored polarization textures for low-power spintronics, tunable microwave devices, and neuromorphic computing.
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All authors A.S. Mikheykin, N.V. Lyanguzov, A.S. Konstantinov, V.B. Shirokov, E.D. Linnik, T. Bondar, A.G. Razumnaya
Mesoscale and Nanoscale Physics
Transport Determines Spectral Distance in Mesoscopic Thermodynamics
Giorgio Sonnino
We derive a distance between thermodynamic states from a positive Hermitian transport tensor within a mesoscopic canonical model. An exact first-order factorization of the
evolution generator gives a commutator norm and the metric $G=2g^{-1}$, where $g$ denotes the symmetric transport tensor. Gradients of the antisymmetric tensor can change the
evolution, but they leave this distance unchanged. The construction allows coordinate-dependent coefficients. For constant Onsager coefficients, a Clifford representation gives the same metric. In a two-channel thermoelectric system, the ratio of normalized principal distances is $\sqrt{1+ZT}+\sqrt{ZT}$. Transport coupling thus fixes the anisotropy of this metric. The construction requires neither an independent metric nor a physical
spin variable.
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Soft Condensed Matter
Impact of shear and dilational membrane viscosities on capsule shape and dynamics under shear flow: a theoretical study
Paul Regazzi and Marc Leonetti
In artificial (micro)capsules or
cells such as red blood
cells for example, the two-dimensional (2D) rheology of the membrane (or the shell) is viscoelastic and not only elastic. The deformation and inclination of such a capsule are theoretically studied under shear and extensional flows. The membrane mechanics is described by the Kelvin-Voigt model: the 2D dissipation with the Boussinesq-Scriven law associated to specific dilational and shear Boussinesq numbers $Bq_d$ and $Bq_d$ respectively while the elastic constitutive law is either Hookean, strain-softening (neoHookean) or strain-hardening (Skalak). The dynamics depends on the elastic capillary number $Ca$, the Poisson ratio (or $C$ in Skalak law), the viscosity ratio $\lambda$, the nonlinearities included in the constitutive law and both boussinesq numbers. Three dynamics are identified in the limit of weak deformations: a tank-treading motion in the limit of small elastic capillary number with a characteristic time depending on $\lambda$, $Bq_s$ and $Bq_d$, an oscillation without any elasticity and a damped oscillation leading to a tank-treading motion in the limit of large Boussinesq numbers. In all cases, both shear and dilational 2D dissipations contribute differently leading to non-trivial results. In the case of a Skalak law with $C=1$, $Bq=Bq_s=Bq_d$ and $Bq>>\lambda$, the deformations in the limits $Ca<<1$, $Bq=O(1)$ and $Ca=O(1)$, $Bq>>1$ determined in the seminal work of \cite{barthes1985role} are recovered.
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Mesoscale and Nanoscale Physics
Emergent Spinorial Structure in Mesoscopic Irreversible Thermodynamics
Giorgio Sonnino
We reconstruct a geometry of thermodynamic coordinates from transport coefficients within a mesoscopic canonical model. Self-adjoint flux observables determine a compatible
evolution generator containing symmetric and antisymmetric transport coefficients. When the Hermitian transport tensor is positive, an exact graded first-order factorization reproduces this generator on its scalar sector. Its commutators define a spectral distance whose metric depends only on the symmetric tensor. Gradients of the antisymmetric tensor can change the
evolution while leaving the metric unchanged. The construction allows coordinate-dependent coefficients. In the constant Onsager regime, a Clifford representation gives the same distance and an
algebra fixed by the transport
matrix. Published transport data for a $\mathrm{Bi_2Te_3}$ film give a principal-distance ratio of approximately $2.12$ in normalized coordinates at $ZT\simeq0.68$. We also examine a separate quadratic
entropy-production observable and distinguish its discrete spectrum from the spectrum of the
evolution generator. The spinorial representation adds no physical
spin degrees of freedom.
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Mesoscale and Nanoscale Physics
1/f frequency-noise reduction in nanomechanical resonators by dissipation dilution
Kostas Kanellopulos and Silvan Schmid
The frequency noise of a resonant nanomechanical sensor is well understood down to its thermomechanical limit, but the longest useful averaging time is set by a flicker, or $1/f$, frequency-noise floor whose origin has remained unknown. We show that this floor is the thermal noise of the tension. By the fluctuation-dissipation
theorem, the tension of a resonator with fixed ends fluctuates by an amount set by the loss angle of its material; for structural damping, these fluctuations produce $1/f$ frequency noise with a flicker coefficient $h_{-1}=E k_{\mathrm{B}} T/(2\pi V\sigma_0^2 Q_{\mathrm{el}})$, with $Q_{\mathrm{el}}$ the intrinsic loss under elongation, that contains no free parameter and is diluted by the tensile stress $\sigma_0$ in the same way as damping is in dissipation dilution. Silicon nitride strings and membranes from 30 to 340~nm thickness follow the predicted volume scaling, the predicted $\sigma_0^{-2}$ dilution across resonators and within stress-engineered strings, and the predicted thickness dependence, which places noise-active two-level systems in the volume and at the surfaces of the resonators, all at the absolute level set by the independently measured intrinsic loss. The same relation accounts for published data between 78 and 296~K; below 78~K, the loss measured at the resonance no longer represents the loss probed by the noise, marking the limit of the structural-damping assumption. Dissipation dilution therefore lowers the $1/f$ floor, and the longest useful integration time of a resonant sensor is set by its prestress, volume, temperature, and intrinsic loss angle.
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Soft Condensed Matter
Colloid-Colloid Interactions Impact Network Morphology of Confined Colloidal Drying Patterns
Andreas Andersen Hennig, Natalia Kizilova, Ilaria Beechey-Newman et al. (+1 more)
Colloidal suspensions that are confined between two closely spaced plates and left to evaporate slowly form maze-like labyrinth patterns in the final stage of evaporation. The fingers in these patterns form bifurcations and occasionally loops, which we may quantify with a skeletonization method. We compare drying patterns formed with two different salt concentrations in the droplet which changes the screening length and therefore the effective colloid interactions. We find that the junctions generally follow Murray's law for optimal transport networks, and that the typical bifurcation angles peak around 53. Screened droplets additionally show more loopy networks, and is characterized by bands of transversal fingers before merging into a central non-fingering colloidal aggregate. Our observations suggest that colloid-colloid interactions can strongly influence the large-scale
topology of the pattern while leaving the local geometry of the individual fingers unchanged.
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All authors Andreas Andersen Hennig, Natalia Kizilova, Ilaria Beechey-Newman, Erika Eiser
Strongly Correlated Electrons
Destructive Interference of a Charge Density Wave in the Skyrmion Magnet GdRu2Si2
G. D. A. Wood, D. A. Mayoh, F. Orlandi et al. (+10 more)
In skyrmion magnets, charge density waves induce higher-order exchange interactions that can select multi-Q ground states. Using resonant X-ray scattering and
neutron diffraction, we measure temperature-dependent
spin-charge coupling in GdRu2Si2. A minimal Landau model with one critical exponent and two ordering temperatures reproduces all six observed order parameters.
Spin-density wave components of the multi-Q ground state drive charge ordering, but the onset of a
magnetic helix suppresses it via destructive interference.
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All authors G. D. A. Wood, D. A. Mayoh, F. Orlandi, A. Bombardi, D. D. Khalyavin, P. Manuel, S. H. Moody, P. D. Hatton, R. D. Johnson, T. W. Chamberlain, O. A. Petrenko, M. R. Lees, G. Balakrishnan
Materials Science
Domain-wall-to-domain interconversion in a polar conducting oxide
Martin F. Sarott, Majid Ahmadi, Johanna van Gent González et al. (+13 more)
Domain walls in ferroic
crystals are topological defects with a
symmetry distinct from the domain interior, allowing them to display functionalities that are otherwise forbidden in the host material. Despite their unique properties, domain walls are strictly confined to two-dimensional interfaces, which hinders unveiling their true nature and limits their applicability. Here, we demonstrate reversible dimensionality control by expanding nanoscale domain walls into three-dimensional functional regions in polar epitaxial tungsten trioxide ($\text{WO}_3$). This domain-wall-to-domain interconversion is enabled by the conducting, non-polar domain walls adopting the parent-phase structure. An alternating electric field applied through a scanning probe tip induces localized heating, which expands this domain-wall phase into the adjacent polar domains. This approach enables reversible spatial control to switch between mutually exclusive properties of domains (polarity) and domain walls (conductivity), offering a new paradigm for reconfigurable oxide electronics.
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All authors Martin F. Sarott, Majid Ahmadi, Johanna van Gent González, Ewout van der Veer, Mads C. Weber, Jacopo Pinna, Daniel A. Chaney, Arijit Sinha, Hamideh Hassani, Horatio R. J. Cox, Thomas Perrault, Amir Sabet Ghorabaei, Maria A. Loi, Philippe Ghosez, Bart J. Kooi, Beatriz Noheda
Strongly Correlated Electrons
Confinement-deconfinement transitions in the dimer-loop models on two-dimensional non-bipartite lattices
Jay Pandey, Souvik Kundu and Kedar Damle
Recent work [Kundu, Damle, Phys. Rev. X 15, 011018 (2025)] has demonstrated that a class of $S=1$ kagome
lattice antiferromagnets with competing anisotropies can exhibit unusual low-temperature behavior that is best described in terms of the statistical mechanics of an interesting interpolation between the fully-packed dimer model and the fully-packed loop model on the bipartite honeycomb
lattice. On this and other bipartite
lattices in two and three dimension, such fully-packed dimer-loop models generically have two distinct power-law correlated Coulomb phases, both of which admit a low-energy description in terms of a fluctuating divergence-free polarization vector field [Phys. Rev. X 15, 011018 (2025); arXiv:2510.11607]. The transition between these phases corresponds to a confinement transition for the $Z_2$ part of the corresponding $U(1)$ flux [Phys. Rev. X 15, 011018 (2025); arXiv:2510.11607]. Here we demonstrate that a variant of such a topological confinement transition can also exist in dimer-loop models on non-bipartite
lattices such as the kagome and triangular
lattices although the low-energy description does not feature any conserved $U(1)$ flux. In these non-bipartite dimer-loop models, both phases are short-range correlated
liquids, and the topological distinction between them is in terms of a $Z_2$-valued winding number instead of the flux of a divergence-free polarization field. In spite of this key difference, this transition appears to be in the same Ising universality class as the analogous transition of the bipartite dimer-loop models. These kagome and triangular
lattice dimer-loop models correspond respectively to the low-energy limit of a class of $S=1$ antiferromagnets with competing anisotropies on the ruby
lattice comprising a corner-sharing arrangement of fully-frustrated squares and a
lattice of corner-sharing fully-frustrated hexagons.
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Strongly Correlated Electrons
Topological Chiral Superconductivity from Doping Correlated Charge Transfer Insulator with Orbital Magnetism
Wen Sun, Yuan Yang, Shou-Shu Gong et al. (+1 more)
Topological chiral superconductivity has been extensively studied from the perspective of electronic structures in momentum space, while its emergence from real-space processes in strongly interacting systems remains largely unexplored. Here, we study a doped charge-transfer
insulator in a strongly repulsive spinless-
fermion model with three sublattices and $2\pi$ flux per unit
cell. Combining perturbative analysis, exact diagonalization, and density
matrix renormalization group simulations, we establish a topological superconducting ground state with $p+ip$
symmetry. In the large charge-transfer gap limit, chiral charge-transfer excitations generate a correlated-hopping process that provides a microscopic mechanism for electron pairing and its chiral structure. The chiral superconductivity persists into the smaller-gap regime, where chiral excitonic two-particle bound state can emerge. Our results establish a concrete real-space route to topological chiral superconductivity upon doping strongly interacting charge-transfer
insulators with orbital magnetism.
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All authors Wen Sun, Yuan Yang, Shou-Shu Gong, Wen Huang
Statistical Mechanics · Cross-listed from q-fin.ST
Asymmetric $q$-Gaussian Distributions from Tsallis Maximum Entropy
Francesco Cesarone, Massimiliano Corradini, Nicolò Giunta et al. (+1 more)
Within the framework of non-extensive statistical mechanics, $q$-Gaussian distributions arise as maximum-
entropy solutions of Tsallis
entropy under suitable escort moment constraints. Although widely used in physics, biology, geology, finance, and related fields, standard $q$-Gaussians are intrinsically symmetric and cannot capture asymmetric fluctuations often observed in empirical data. We ask whether asymmetry can arise from the Tsallis maximum-
entropy principle without externally skewing or joining distributions. We show that this is achieved by retaining the Tsallis
entropy and imposing a global escort mean together with distinct downside and upside escort semi-variances. The key step is to reformulate the problem of maximum Tsallis
entropy in terms of the escort density. The nonlinear escort constraints then become affine, while maximizing Tsallis
entropy becomes equivalent to maximizing a strictly concave functional over a convex feasible set. Consequently, any admissible stationary solution is the unique global maximizer of the corresponding variational problem. The finite-sample approximation properties of the proposed asymmetric $q$-Gaussian are studied through Monte Carlo experiments using synthetic data generated from Azzalini skew-Student distributions. Compared with the classical symmetric $q$-Gaussian, the asymmetric specification systematically provides a closer approximation to synthetic asymmetric heavy-tailed distributions. Finally, we fit the model to return series from major equity indices, a commodity, and cryptocurrencies, and compare its in-sample goodness of fit with that of a symmetric $q$-Gaussian. The results show that the asymmetric model offers a closer in-sample description of unconditional return distributions, most clearly in the tails.
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All authors Francesco Cesarone, Massimiliano Corradini, Nicolò Giunta, Serena Rocci
Mesoscale and Nanoscale Physics
Nontrivial topological properties from the cooperation of static perturbations and Floquet fields in type-II semi-Dirac semimetals
Wen-Hao Bian and Jing Wang
In this work, we present a comprehensive theoretical study for the topological and anomalous transport properties of type-II SDSMs under three scenarios, i.e., static
symmetry-breaking perturbations, periodic Floquet driving by two-frequency orthogonally polarized light (TFOPL), and their cooperative effects in the hybrid scenario. We first show that a static mass $m_z$ opens a bulk gap and drives the system into a Chern
insulator with Chern number $C^{\rm per}=\pm 2\,{\rm sgn}(m_z)$. In comparison, TFOPL alone only shifts the positions of Dirac points and cannot open a full gap. Nevertheless, it produces a Berry
curvature odd in the $x$-direction, yielding a finite Berry
curvature dipole (BCD) along $x$ proportional to the sine of the initial phase, while the $y$-component vanishes. The hybrid scenario, by contrast, exhibits a remarkably rich phenomenology. Specifically, its gap-closure criterion becomes cubic and thus admits up to three real roots when the effective parameter along the $x$-direction is negative, thereby producing multiple light-tunable gap-closing points and a series of topological phase transitions. In particular, the BCD exhibits a double-peak structure with strong enhancement near gap-closing
manifolds and synchronized sign reversal of the full vector under external tuning. We further analyze the anomalous Hall conductivity (AHC), anomalous Nernst conductivity (ANC), and anomalous thermal Hall conductivity (ATHC). The AHC and ATHC exhibit quantized plateaus that serve as signatures of Chern-
insulator phases, while the ANC, being a Fermi-surface probe, provides complementary local information and can identify light-induced gaps even when global topological invariants remain unchanged. Taken together, these results offer useful insights into the topological properties of 2D type-II SDSMs and related systems.
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Soft Condensed Matter
Solubility of poorly soluble species in bulk and nanopores from grand-canonical Wang-Landau sampling
Russell Kajouri, Adyant Agrawal, Philipp Stärk et al. (+2 more)
Poorly soluble species can have mean populations below one in small systems such as nanopores. In this regime, the grand-potential minimum, which identifies the most probable particle number, differs from the ensemble-averaged solute loading. We use grand-canonical Wang-Landau sampling (GCWLS) to calculate the density of states $\Omega(N_\mathrm{A}, N_\mathrm{B})$ for a binary Lennard-Jones mixture of solute B in solvent A, both in bulk and in slit pores. One set of GCWLS simulations gives ensemble averages over a range of chemical potentials, whereas conventional grand-canonical Monte Carlo (GCMC) simulation requires a separate simulation at each state point. Independent GCMC simulations confirm the GCWLS ensemble averages. The solvent number distribution is nearly Gaussian, whereas the dilute solute distribution is skewed and Poisson-like. The most probable solute number therefore lies below the ensemble-averaged loading $\langle N_\mathrm{B}\rangle$ and is zero whenever $\langle N_\mathrm{B}\rangle<1$. Reading the solute loading from the grand-potential minimum underestimates it and can falsely indicate that no solute is present. Defining the oversolubility as $\mathcal{O}_\mathrm{B}=x_\mathrm{B}^{\mathrm{conf}}/x_\mathrm{B}^{\mathrm{bulk}}$, where $x_\mathrm{B}$ is the solute mole fraction, we find $\mathcal{O}_\mathrm{B}\approx12$ in a pore of 3.5 particle diameters width when both wall interactions are repulsive. Adding wall-solute attraction moderately raises it to $\approx13$, whereas wall-solvent attraction lowers it to $\approx3.4$. This comparison shows that the wall-solvent interaction controls most of the enhancement. As the pore widens, $\mathcal{O}_\mathrm{B}$ decreases toward unity. In bulk and in nanopores alike, the solubility of poorly soluble species should be obtained from ensemble averages rather than from grand-potential minima.
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All authors Russell Kajouri, Adyant Agrawal, Philipp Stärk, Alexander Schlaich, Christian Holm
Mesoscale and Nanoscale Physics
Admittance extraction of quantum dot arrays for charge sensing
Conor Power, Mathieu Moras, Andrii Sokolov et al. (+2 more)
This work demonstrates admittance extraction of
quantum dot arrays using a rate equation frame- work matching experimental reflectometry measurements. Using a semiclassical rate equation, we consider a perturbation of the source/drain chemical potential to model reflectometry readout in a
quantum dot array. This is a time-dependent extension of the rate equation which has been employed in literature for pumped arrays of
quantum dots and capacitance extractions. Here we extend this to a double
quantum dot for admittance extraction. The simulations are calibrated us- ing Fermi-Hubbard parameters extracted from experimental data, which it is then shown to closely approximate to.
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All authors Conor Power, Mathieu Moras, Andrii Sokolov, Robert Bogdan Staszewski, Elena Blokhina
Superconductivity
Tailored VxOy Metal–Insulator-Transition Oxides for Temperature-Triggered Smart Insulation in Superconducting Coils
Mattia Ortino, Davide Uglietti, Andrea Testino et al. (+5 more)
Smart insulation is a turn-to-turn layer that insulates in normal operation and conducts only near a hot spot. It could combine the fast ramping of insulated coils with the passive energy dump of non-insulated coils. Metal-
insulator transition (MIT) oxides are natural candidates, but the only one tested in a coil so far, V2O3, switches at 150-170 K, far above the 30-70 K window useful for REBCO magnets. We explore the vanadium-oxygen system to lower the transition. TGA redox processing produced multi-phase powders with an effective transition near 127 K, about 25 K below V2O3. Hydrothermal V3O7, hydrated or annealed, was far too resistive and showed no usable transition. V2O3-epoxy specimens provided a robust reference and an acceptance criterion. Cryogenic measurements revealed a reproducible thermal hysteresis, and the measured specific heat of V2O3 corrects earlier model inputs by close to two orders of magnitude. A first electro-thermal model reproduces current sharing through the smart-insulation layer. Doped V2O3 and V8O15 are identified as the next targets.
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All authors Mattia Ortino, Davide Uglietti, Andrea Testino, Nicola Casati, Alexander Steppke, Wiktoria Wnetkowska, Andrea Masi, Kamil Sedlak
Mesoscale and Nanoscale Physics
Probing quantum nonlinear phononics in multilayer graphene with time-resolved Raman scattering
Jakob Dolgner, Michael Rübhausen and Dirk Manske
Coherently driven
phonons are conventionally described classically. Nonlinear
phonon-
phonon interactions, however, allow an infrared drive to reshape the fluctuation spectrum and generate substantial nonthermal enhancement of
phonon fluctuations, motivating a description beyond the coherent displacement alone. We
benchmark classical and semiclassical approximations against the full
quantum theory and find that the semiclassical treatment substantially improves agreement with the
quantum dynamics. We propose nonequilibrium spontaneous Raman scattering as a sensitive probe of these effects and apply our framework to recent experiments suggesting
quantum nonlinear phononics involving the $\mathrm{E}_{1u}$ and $\mathrm{E}_{2g}$ modes in multilayer
graphene. At very strong pump fields, driving the $\mathrm{E}_{1u}$ mode significantly modifies the $\mathrm{E}_{2g}$ Raman spectrum; however, reproducing the reported response at experimental field strengths requires accounting for pump-induced Raman
matrix element dynamics or alternative energy pathways into the $\mathrm{E}_{2g}$ mode. Our findings extend nonlinear phononics beyond average atomic displacements to the dynamics of
lattice fluctuations, highlighting the interplay between coherent motion and
quantum correlations in driven materials.
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Soft Condensed Matter
Activity-Induced Structural and Dynamical Heterogeneity in Colloidal Gels
Santu Nath, Sudipta Mandal and Smarajit Karmakar
Active gels are intrinsically non-
equilibrium materials whose structural and dynamical heterogeneity emerges from the interplay of attractive interactions, thermal fluctuations, and self-propulsion. We investigate a model active gel, simulated using large-scale Brownian dynamics simulations, to explore the effects of temperature $T$, active force strength $f_0$, persistence timescale $\tau_p$, and active particle concentration $\rho_a$. We characterize the structure of the evolving gel network through morphological analysis, while dynamical changes are quantified by the relaxation timescale and dynamical heterogeneity (DH). We show that an optimal choice of activity parameters yields a percolating gel network with faster gelation and larger voids and clusters, enhancing mechanical stability. Conversely, the structural relaxation timescale and DH decrease with increasing activity, indicating enhanced particle rearrangements and reduced spatial correlations of mobile and immobile regions. An effective temperature ($T_\text{eff}$) framework for colloidal gels maps structural quantities and relaxation timescales in an active gel onto those of a passive gel. More interestingly, the growth of DH with increasing swim force can also be described by the same effective-temperature framework, in stark contrast to observations in active glasses. Our findings show that, in colloidal gels, temperature and active force compete, giving rise to similar structural ordering and, consequently, similar DH at the same $T_\text{eff}$. These findings highlight the crucial role of structural ordering in governing DH in active colloidal gels, as compared to active glasses.
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Materials Science
Real-space obstruction control of the shift current in two-dimensional Quantum Spin Hall insulators
Michele Bagaglini, Mattia Iannetti, Jonas Erhardt et al. (+4 more)
The search for materials exhibiting a large bulk photovoltaic effect has recently expanded to low-band-gap systems capable of operating in the infrared regime, with potential applications in optoelectronics. Among the microscopic mechanisms contributing to this phenomenon, the shift current is one of the dominant sources of photocurrent generation. Owing to its
geometric origin, the shift current is not only determined by the optical transition probability but also by the real-space displacement associated with the optical excitation, making non-centrosymmetric materials with obstructed electronic wave functions particularly promising candidates. In this work, using a tight-binding model of a
quantum spin Hall
insulator on a triangular
lattice, we investigate the nonlinear photocurrent across trivial,
quantum spin Hall, and higher-order topological insulating phases. We show that obstructed topological phases exhibit a substantially enhanced shift-current response, despite the similar electronic band structure. We identify the origin of this enhancement in optical transitions between states belonging to distinct Wannier-center sectors, which allow for a large real-space displacement upon photoexcitation and, depending on the topological phase, control the sign of the shift current. Our results extend the search for controllable bulk photovoltaic effects to materials characterized by real-space electronic obstruction and identify indenene, a monolayer of In on SiC(0001), as a promising candidate for realizing this phenomenon.
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All authors Michele Bagaglini, Mattia Iannetti, Jonas Erhardt, Jörg Schäfer, Ralph Claessen, Giorgio Sangiovanni, Gianni Profeta
Materials Science
Interlayer Registry Controls Polar Topology in Twisted Bilayer h-BN
Di Fan, Changming Ke and Shi Liu
Twisting van der Waals bilayers creates a moir'e stacking field with periodically varying local interlayer registry, enabling spatially patterned polarization. However, a systematic understanding of how this registry-controlled polar
topology evolves with twist angle, temperature, and mechanical strain is still lacking. Here, using first-principles-trained deep-potential molecular dynamics simulations, we show that spatially varying interlayer registry governs the polarization texture and can be directly tuned by twist and relative layer deformation. As the twist angle decreases, the moir'e polarization texture evolves from compact, nearly circular
vortex-like patterns to extended triangular AB/BA domains. This crossover arises from enhanced
lattice relaxation at small twist angles, which expands low-energy, oppositely polarized AB/BA regions and confines in-plane polarization mainly to domain boundaries. Despite this reconstruction, the local in-plane winding remains tied to interlayer registry and persists up to 1000 K, indicating robust
topology against thermal fluctuations. We further show that the mechanical response is dictated by whether deformation changes the relative registry: homogeneous deformation of both layers produces only weak distortions, whereas layer-selective deformation strongly reconstructs the moiré polarization texture. A mismatch-
matrix registry-mapping model is developed to capture this response, explaining deformation-induced changes in
vortex radii at larger twist angles and triangular-domain geometry at smaller twist angles. These results identify interlayer registry as the central control parameter for forming and tuning moir'e polar
topology in twisted bilayer h-BN.
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Quantum Gases
Bogoliubov excitations of a Bose-Einstein condensate in the presence of the non-Hermitian skin effect
Carlo Panu, Ulf Peschel, Oleg A. Egorov et al. (+2 more)
The non-Hermitian skin effect is one of the most remarkable topological features of non-conservative physics. It causes a macroscopic accumulation of states at the boundaries of a confined system, opening new ways for controlling and directing waves in non-Hermitian settings. This effect has recently been observed in experiments with Bose-Einstein condensates of
exciton polaritons and ultracold bosonic
quantum gases. The underlying physics is captured by a mean-field
Hamiltonian with a trapping potential and an imaginary gauge field. While prior work has examined the effect of the imaginary gauge field term on the condensate itself, its effect on the collective excitations on top of the condensate remained unexplored. Here, we develop a new theory for the Bogoliubov excitations in a non-Hermitian framework and systematically study their spectrum across different interaction regimes. By analysing the position expectation values, we find that while the repulsive interactions oppose the localisation of the condensate due to the skin effect, the excitations remain strongly affected by the imaginary gauge field. As a consequence, in the presence of harmonic confinement, we predict a strong shift in the dipole oscillation frequency, which can be observed in experiments. This is in contrast to Hermitian systems, where this frequency is fixed by the trap dimensions. Furthermore, we develop a consistent second-quantised field theory of the collective excitations in this non-Hermitian system. Strikingly, we find that a second-quantised treatment removes the shift of the dipole oscillation frequency entirely. This intriguing discrepancy between the two theoretical approaches to the treatment of elementary excitations in a non-Hermitian system can be resolved in experiments.
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All authors Carlo Panu, Ulf Peschel, Oleg A. Egorov, Elena A. Ostrovskaya, Eliezer Estrecho
Materials Science
Theoretical Investigation of Oxygen-Vacancy Diffusion in SrTiO$_3$ using Neural Network Potentials
Kazutaka Nishiguchi, Ryota Yamamoto and Seiichiro Ten-no
Oxygen-vacancy formation and
diffusion play important roles in determining the electronic and atomic transport properties of SrTiO$_3$ (STO). Accurate analysis of such point defects requires sufficiently large-scale and long-time molecular dynamics (MD) simulations; however, direct investigations of oxygen-vacancy dynamics using ab initio MD (AIMD) based on density functional theory (DFT) are limited to relatively small systems and short time scales because of their high computational cost. In this study, we develop a neural network potential (NNP) for pristine and oxygen-deficient STO using a reference
dataset generated from AIMD simulations. The trained NNP model accurately reproduces the DFT reference energies, atomic forces, and virials for both pristine STO and STO containing an oxygen vacancy. The NNP also reproduces the supercell-size dependence of the total energies and oxygen-vacancy formation energies, including the formation energy extrapolated to the dilute limit. Large-scale and long-time MD simulations using the NNP (NNP-MD) are then performed to investigate oxygen-vacancy
diffusion. The resulting oxygen-vacancy
diffusion coefficients show substantially better agreement with experimental data than those obtained from conventional classical MD simulations. An Arrhenius analysis yields an oxygen-vacancy migration enthalpy of 0.64 eV, in close agreement with the experimental value of 0.67 eV. These results demonstrate that NNPs trained on first-principles data provide an accurate and computationally efficient framework for investigating defect formation and long-time vacancy transport in perovskite oxides.
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Other Condensed Matter
Optically driven ultrafast lattice contraction in a topological crystalline insulator
M. H. Berntsen, W. Chen, D. Phuyal et al. (+9 more)
The ability to dynamically control topological order remains a central challenge in the exploration of
quantum materials. Here, we investigate the
lattice and electronic response of the topological crystalline
insulator (TCI) Pb$_{1-x}$Sn$_x$Se to ultrafast optical excitation using time- and angle-resolved photoemission spectroscopy (tr-ARPES) in combination with X-ray diffraction (XRD) and first-principles calculations. Static XRD measurements establish the
lattice constant as the key control parameter for the topological transition, with a critical value $a_\mathrm{c}=6.073$ Åseparating the normal-
insulator and topological phases. Despite generating electronic temperatures far above the topological-to-normal transition temperature $T_\mathrm{c}$, optical excitation in the TCI phase does not induce a phase transition. Instead, it drives an ultrafast
lattice contraction of $\Delta a \approx -0.45$ pm within less than 1 ps that counteracts thermal expansion and prevents the system from reaching $a_\mathrm{c}$. The optical excitation therefore pushes the system deeper into the topological phase, providing a direct explanation for the absence of an optically driven transition. Total-energy calculations reveal that this behavior originates from the band inversion in the topological regime, which reverses the character of the photoinduced charge transfer and transiently strengthens atomic bonding. These findings identify band inversion as a mechanism that fundamentally alters the nonequilibrium
lattice response, with general implications for ultrafast optical control of topological materials.
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All authors M. H. Berntsen, W. Chen, D. Phuyal, J. Wu, A. Grubišić-Čabo, M. Dendzik, Q. Guo, A. Orthaber, C. Li, R. M. Geilhufe, J. Weissenrieder, O. Tjernberg
Superconductivity
Superconductivity from altermagnetic fluctuations: the crucial role of sublattice polarization
Mats Barkman, Andreas Kreisel and Brian M. Andersen
Unconventional superconductivity in correlated systems often appears in the vicinity of a magnetically ordered state. This situation is also relevant for altermagnets, characterized by a nonrelativistic
spin-split electronic structure in the presence of Néel order. Many proposed altermagnetic candidates, however, never cross the
magnetic instability. We study superconductivity arising from altermagnetic fluctuations in such systems and show that the sublattice polarization (SLP) of the normal-state bands plays a pivotal role in determining the superconducting state. SLP, an inherent property of altermagnetic band structures that persists even without
magnetic order, prevents Cooper pairs from forming between different sublattices. This suppresses pairing mediated by the nearest-neighbor antiferromagnetic exchange, which favors
spin-singlet superconductivity, and leaves longer-range same-sublattice bonds dominant. When the next-nearest-neighbor exchange is ferromagnetic, as expected for frustration-free Néel order, this results in
spin-triplet superconductivity. This mechanism is fundamentally different from that in altermagnets with long-range Néel order, where the
spin-split Fermi surfaces favor equal-
spin pairing. Finally, when longer-range interactions in the disordered phase instead favor singlet pairing, SLP leads to singlet states with characteristic properties distinct from nearest-neighbor pairing states.
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Strongly Correlated Electrons
Scalable Quantum Monte Carlo for Shannon-Rényi Entropy: An Experiment-visitable Probe of Quantum Phases and Criticality
Dong-Xu Liu, Zhe Wang, Zenan Liu Yi-Ming Ding et al. (+1 more)
The Shannon-Rényi (SR)
entropy characterizes the probability distribution of many-body wave functions in a chosen basis and is directly accessible from single-shot measurement snapshots in cold-atom experiments, yet its theoretical evaluation in interacting systems carries exponential cost. Here we construct a field-theoretic spacetime
manifold for the SR
entropy in which $q$ replicas are glued at the imaginary-time boundaries, recasting it as a ratio of generalized partition functions amenable to large-scale
quantum Monte Carlo simulation. On this basis we develop a reweight-annealing framework with two complementary strategies: a virtual-parameter scheme interpolating between unglued and fully glued limits via binomial-weighted partial gluing, and a real-parameter scheme using a physical coupling constant as the annealing variable within
stochastic series expansion. Both reduce the computational cost from exponential to
polynomial. Most importantly, we establish for the first time a finite-size scaling theory for the SR
entropy near a
quantum critical point, $S_q=a(g)L^2+S_q^0\left((g-g_c)L^{1/\nu}\right)$; data collapse of its first derivative yields the correlation-length exponent $\nu$ for both the O(3) and Ising universality classes, realized in the
spin-$\frac{1}{2}$ columnar dimerized Heisenberg model and the bilayer Heisenberg-Ising model. The same simulations extract the Goldstone-mode count $N_G=2$ and the $Z_2$ ground-state degeneracy $\ln 2$ from subleading terms. These results elevate the SR
entropy to a standalone, order-parameter-free diagnostic of
quantum criticality with the same scaling status as the
entanglement entropy, and close the loop between theory and
quantum simulation by enabling quantitative benchmarking of experimental snapshots from state-of-the-art
quantum simulators.
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All authors Dong-Xu Liu, Zhe Wang, Zenan Liu Yi-Ming Ding, Zheng Yan
Mesoscale and Nanoscale Physics
Emergence of Nonlocal Hydrodynamics in Many-Body Radiative Heat Transport
Mauricio Gomez Viloria, Florian Herz, Riccardo Messina et al. (+1 more)
We develop a nonlocal hydrodynamic theory of radiative heat transport in many-body systems by coarse graining their microscopic electrodynamic interactions. Long-range radiative exchange naturally generates a spatially nonlocal constitutive relation in which the heat current at a given position depends on temperature gradients over an extended region, while energy conservation retains its local conservative form.
Fourier transport emerges as a controlled long-wavelength limit when the interaction kernel has a finite second spatial moment. When this moment fails to converge, spatial nonlocality survives coarse graining and gives rise to non-
Fourier transport. The resulting framework establishes a systematic bridge between discrete many-body fluctuational electrodynamics and a continuous description of radiative heat transport.
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All authors Mauricio Gomez Viloria, Florian Herz, Riccardo Messina, Philippe Ben-Abdallah