Disordered Systems and Neural Networks
On the robustness of noisy solutions in non-convex neural networks
Enrico M. Malatesta, Alessandra Passalacqua and Riccardo Zecchina
Optimization in non-convex neural network models is strongly influenced by the geometry of the solution space: sparse, isolated, point-like clusters are typically algorithmically inaccessible, whereas wide and flat regions can be found efficiently despite being relatively rare. At zero temperature this picture has been formalized in binary perceptrons through the overlap gap property (OGP), which limits algorithmic access to configurations with zero training error above a critical constraint density $\alpha_{\rm OGP}$. Here we extend this description to finite temperature, where a positive training error is allowed and statistically penalized. We first show that the frozen one-step replica-
symmetry-breaking solution, dominating the zero temperature
equilibrium measure, survives at any finite temperature. We furthermore derive a general criterion, based on the smoothness of the single-pattern Gibbs weight near the decision boundary, that determines when a finite-temperature relaxation of the loss removes freezing. We then extend the OGP construction to finite temperature and show that dense, algorithmically accessible regions of finite-energy configurations persist beyond $\alpha_{\rm OGP}$, up to a threshold $\alpha_{\rm OGP}(\epsilon)$ that grows with the allowed training error $\epsilon$. Finally, in the teacher-student setting, we show that these wide, finite-energy regions still retain good generalization. Using a finite energy message-passing
algorithm, we demonstrate numerically that thermal noise enables effective generalization in the regime of constraint densities where both recovering the teacher and finding a zero temperature solution are computationally hard.
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Statistical Mechanics · Cross-listed from quant-ph
Two-state generator extraction: property currents and a two-layer arrow of time in pre- and post-selected quantum dynamics
Seiki Saito
Conditioning on both past and future assigns intermediate-time properties a causal observer does not; these time-symmetric assignments obey exact
symmetry theorems and are measurable from trajectories. We use two-state generator extended dynamic mode decomposition (gEDMD): because weak values obey $dA_w/dt=i\langle[H,A]\rangle_w$ exactly, generator extraction, with an exact-derivative baseline, applies unchanged to them. First, a reflection involution on the pre-/post-selected ensemble splits every window-fitted friction uniquely as $\gamma_{fwd}=\gamma_A+\gamma_S$: $\gamma_A$, antisymmetric about the midpoint, carries the modes' boundary-condition physics; $\gamma_S$, symmetric, comes from the differencing scheme; both follow from the same data as $(\gamma_{fwd}\pm\gamma_{bwd})/2$. At a fixed inference resolution the arrow of time has two layers: the coherent-mode arrow reverses at the midpoint, the fluctuation-level one does not, $\gamma_S$ dominating $\gamma_A$ at every size and class. The difference is one of degree: $\gamma_S$ is 34 times larger there than at the mode layer, and with the exact derivative both layers reverse: immunity belongs to the inference, not the ensemble. Second, in a
lattice interferometer conditioned only at its ports, the
quantum Cheshire-cat structure emerges unimposed: particle and polarization obey separate continuity equations, and a local field in the polarization-carrying arm rotates that phase alone, at exactly twice the field strength, entering the generator as a rigid imaginary shift, while the particle's weak density stays invariant to machine precision. We verify the sample-level identity and the two layers from $2^8$ to $2^{20}$ dimensions: $|\gamma_A|/\gamma_S=0.09$ to $0.27$ across five classes; self-averaging makes it insensitive to class among those sharing a boundary modulation, removing the $2^{-N/2}$ overlap obstruction for $N$
qubits.
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Materials Science
Generation of representative powder particle packing in 2D/3D: which tool for which application?
Antoine Tainturier, Louis Lemarquis, Victor Szczepan et al. (+1 more)
Although dense sphere packings serve as the initial state for simulations in powder metallurgy, additive manufacturing and granular physics, the choice of a packing generator is rarely guided by a systematic
benchmark. A representative packing must be (i)-(ii) physically admissible (non-overlapping particles in gravitational
equilibrium); (iii) faithful to the target particle size distribution (PSD); (iv) representative in relative density Phi; and (v) computationally affordable. Four open-source tools have been benchmarked, meeting (i)-(ii) by construction: the sequential DR (dropping-and-rolling) and its densified variant DR-ME, and the discrete element method (DEM) codes LAMMPS (
gravity) and dp3D (isostatic compression). Across four configurations (2D/3D lognormal, 3D bimodal, and a 3D domain-size study), they are compared against an industrial MIM-grade powder, with PSD fidelity measured by the bin-width-independent Hellinger distance and Phi against the feedstock solid loading (phi_exp = 0.62, by Archimedes' method). In 3D, the DEM codes reach the densest packings but run more than three orders of magnitude slower: for approximatively 20 000 particles, DR shows a 9% phi shortfall relative to dp3D while running 1800x faster. These idealised model packings yield application-driven tool-selection guidelines.
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All authors Antoine Tainturier, Louis Lemarquis, Victor Szczepan, Marc Bernacki
Superconductivity
Density-wave phases, anisotropic transport, and Planckian dissipation in single crystals of the superconductor La3Ni2O7
Zhehong Liu, Masamichi Nakajima, Markus Kriener et al. (+14 more)
Pressure-induced superconductivity in
bilayer nickelates provides a platform for investigating intertwined roles of charge/
spin orders and electric transport in unconventional superconductivity. However, important quantitative information on the transport, such as the absolute value of the resistivity, the anisotropy, and the scattering rate of carriers, remains insufficient due to the lack of accurate measurements using large single
crystals. Here we establish a high-precision pressure-temperature phase diagram of high-quality La3Ni2O7 single
crystals, by measuring the in-plane and out-of-plane resistivities. We resolve two distinct anomalies associated with density-wave formation with contrasting pressure dependences. The pressure-induced structural transition enhances not only the resistivity values for both directions, but also its anisotropy at low temperatures, demonstrating a pronounced effect of density-wave order on the charge dynamics. Superconductivity with zero-resistance emerges near the boundary where the density-wave phases are fully suppressed, and above Tc, the resistivity exhibits a temperature-linear dependence over a wide temperature range while the scattering rate falls within a regime of the Planckian limit. Our results show that pressure dramatically changes the anisotropic charge transport via modifying density-wave orders, and eventually produces a pronounced strange-metal state with strong scatterings, from which superconductivity develops. This establishes robust density-wave correlations and Planckian dissipation as remarkable features of La3Ni2O7.
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All authors Zhehong Liu, Masamichi Nakajima, Markus Kriener, Shunsuke Kitou, Xiaowei Lyu, Chieko Terakura, Kosuke Karube, Ka Man Yip, Sorin Lazar, Nobuto Nakanishi, Keiko Shimada, Akiko Kikkawa, Yukako Fujishiro, Xiuzhen Yu, Taka-hisa Arima, Yoshinori Tokura, Yasujiro Taguchi
Materials Science
Theory of phonon-magnon hybridization and angular momentum in CrI$_3$ and CrBr$_3$
Maxime Mignolet, Miquel Royo, Massimiliano Stengel et al. (+1 more)
In
magnetic materials angular momentum can be mediated by different carriers, including electrons,
magnons, and
phonons. The
magnons can interact with circularly polarized
phonons which are close in energy, provided specific
symmetry conditions are met. If the interaction is strong enough the
phonons and
magnons shift in frequency and start to mix to form hybrid magneto-elastic quasi-particles. In this paper, we develop a constrained
Hamiltonian framework which incorporates hybrid stiffness
matrices and Berry
curvatures. We quantify the degree of hybridization between
phonons and
magnons (up to 8% in CrI$_3$ and 25% in CrBr$_3$) using a decomposition of the total energy, which is a generalization of the norm decomposition for atomic contributions to
phonons used in the literature. We also explore how the total angular momentum is conserved but shared between the phononic and magnonic subsystems upon hybridization.
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All authors Maxime Mignolet, Miquel Royo, Massimiliano Stengel, Matthieu J. Verstraete
Statistical Mechanics · Cross-listed from math-ph
Lee-Yang Zeros And Particle Fluctuations
Mohamed El Hedi Bahri, Ian Jauslin and Joel L. Lebowitz
We consider classical particles in the continuum in the grand canonical ensemble, with a stable, tempered and lower-regular pair potential and boundary conditions of uniformly bounded density. We prove that if the Lee–Yang zeros of the grand canonical partition function in the complex fugacity plane $z = e^{\beta\mu}$ remain bounded away from a real point $z_0 > 0$ for all sufficiently large volumes, then along cubes the thermodynamic limit and differentiation commute at $z_0$: every derivative of the finite-volume pressure in the chemical potential converges, uniformly in a neighborhood of $z_0$, to the corresponding derivative of the limiting pressure. The limiting values of all derivatives are independent of the boundary condition; in particular, the density and the particle-number variance per unit volume converge to $\beta^{-1}\partial_\mu p$ and $\beta^{-2}\partial^{2}_{\mu} p$, respectively. The result extends to the unbounded boundary conditions of Procacci and Yuhjtman for super-stable potentials in addition to Ruelle's tempered boundary conditions.
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Mesoscale and Nanoscale Physics
Two-magnon scattering in the framework of the Lippmann-Schwinger equation
Jorge Marquez Chavez, Ondřej Wojewoda, Yixuan Song et al. (+2 more)
Controlling
magnetic losses requires identifying the microscopic origin of extrinsic linewidth broadening. We introduce a Lippmann–Schwinger framework for two-
magnon scattering from weak defect potentials, showing that scattering is set by the overlap between the perturbation of the effective field and degenerate
spin-wave states. Applied to iron garnet films, YIG/GGG(111) and YIG/GGG(110), we identify crystallographic directions along which these perturbation are elongated. This approach provides a link between the crystallography, effective field on the sample scale and two-
magnon scattering.
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All authors Jorge Marquez Chavez, Ondřej Wojewoda, Yixuan Song, Geoffrey S. D. Beach, Caroline A. Ross
Materials Science
Ferroelectric switchable altermagnetic-like compensated ferrimagnets with charge ordering
Xinyu Yang and Shuai Dong
Unconventional collinear magnets with almost zero magnetization but prominent nonrelativistic
spin-splitting, such as altermagnets, can inherit the advantages of both ferromagnets and antiferromagnets. By incorporating more degrees of freedom such as ferroelectricity and charge ordering, these unconventional magnets can be even more interesting and functionalized. With this design principle, the Fe$_3$O$_5$ monolayer is predicted to exhibit a hybrid
spin-splitting mechanism, with the superposition of the altermagnetic-like $k$-path alternating splitting and ferrimagnet-like Zeeman splitting. Benefiting from the hidden magnetoelectricity based on the
spin-charge coupling, such
spin-splitting can be fully switched by an electric field. Its conductivity is highly
spin-polarized, with a polarization ratio above $99\%$, comparable to half-metals but with zero magnetization.
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Mesoscale and Nanoscale Physics
Depth-Resolved Lattice Distortions in a Silicon-Germanium Qubit Host
Jonathan C. Marcks, E. S. Joseph, J. Reily et al. (+6 more)
Semiconductor qubits, promising for
quantum computation, inherit properties from their host
lattice.
Quantum dot
spins, occupying the local lowest energy states in the conduction band, necessarily couple to structural disorder and interfaces. While silicon-based systems promise low noise alongside industrially compatible manufacturing, the growth of SiGe—a leading platform—unavoidably introduces
lattice dislocations, inhomogeneous strain, and crosshatch patterns, expected to cause fluctuations between devices,
qubit failure, and subsequently higher operational overhead. Through X-ray nano-structural mapping of an Intel Si/SiGe chip, we reveal, with 30$~$nm lateral and 200$~$nm functional depth resolution, how extended
lattice defects introduced during growth propagate through the
heterostructure, creating permanently distorted
lattice planes and strain. We correlate these at the $\approx1~\mu$m scale of a
quantum dot device and calculate the impact on
qubit energy spectra. We observe crosshatch fine structure and find that substrate miscut and growth correlate with the final crosshatch pattern.
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All authors Jonathan C. Marcks, E. S. Joseph, J. Reily, Talise Oh, Abigail Postlewaite, Tao Zhou, M. A. Eriksson, Mark Friesen, Martin V. Holt
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Two-photon interference from as-grown InAsP/InP quantum dots under detuned excitation
Maja Wasiluk, Anna Musiał, Paweł Mrowiński et al. (+3 more)
In this study, we investigate as-grown InAsP/InP
quantum dots emitting in the third telecommunication window under detuned quasi-resonant excitation. A large excitation-emission detuning of 32 meV enables efficient suppression of scattered
laser light while retaining several advantages of near-resonant excitation. The single-
photon nature of the emission is confirmed by a Hanbury Brown and Twiss experiment, yielding a raw second-order autocorrelation value of $g_{\mathrm{raw}}^{(2)}(0)=0.076(6)$. Hong-Ou-Mandel measurement is used to determine the degree of indistinguishability of single
photons and reveal as measured visibilities of $V=0.094(4)$ and $V=0.106(5)$ for excitation pulse separations of 13.1 ns and 5.3 ns, respectively. These results demonstrate the potential of as-grown InAsP/InP
quantum dots grown via molecular beam epitaxy under not experimentally demanding detuned excitation for generating indistinguishable telecom single
photons. Further improvements are to be achieved through Purcell enhancement in optical cavities.
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All authors Maja Wasiluk, Anna Musiał, Paweł Mrowiński, Johann Peter Reithmaier, Mohamed Benyoucef, Wojciech Rudno-Rudziński
Mesoscale and Nanoscale Physics
Majorana current induced by charge current in Kitaev magnet/graphene bilayers
Takehito Yokoyama
We investigate Majorana current induced by charge current in Kitaev magnets coupled with
graphene through the mechanism by which Majorana
fermions in the Kitaev magnet are dragged by electrons in
graphene. We calculate Majorana current density based on the perturbation with respect to a Kondo type Majorana-electron coupling and obtain an analytical expression of the Majorana current induced by charge current, indicative of electronic control of charge-neutral Majorana
fermions. We also discuss Majorana heat current induced by charge current and give estimations of their magnitudes.
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Soft Condensed Matter
Instability-induced bistable shape-morphing kirigami structures
Xiaoyuan Ying and Marcelo A. Dias
Deployable shape-morphing structures that transform from flat sheets into stable three-dimensional configurations are highly desirable for applications ranging from soft robotics and biomedical devices to adaptive architecture and aerospace systems. Existing kirigami-based morphing systems primarily rely on isotropic deployment, compliant soft materials, or external constraints to maintain deployed shapes, which limits
geometric programmability, structural integrity, and applicability in rigid-material systems. Here, we present an inverse design framework for anisotropic bistable kirigami structures that enables programmable shape morphing through controlled
geometric frustration and instability-induced deployment. The framework combines a semi-analytical mechanical model with geometry to establish a direct connection between
geometric transformation and the underlying energy landscape. We show that instability-induced shape morphing leads to tunable bistability and directional deployment in anisotropic kirigami structures. The results are validated through finite element simulations and experiments, demonstrating stable deployed configurations and programmable anisotropic morphing. The proposed framework further provides a general design strategy that can be integrated with various active actuation systems, enabling broader engineering applications.
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Mesoscale and Nanoscale Physics
Symmetry-Selective Strain Control of Anisotropic Magnetic Response in a Silicon FinFET Double Quantum Dot
Yuze Lu, Xiaoyan Liu and Fei Liu
Strain naturally develops in three-dimensional
quantum-dot structures such as silicon FinFETs during fabrication and cooling. Such strain becomes especially important in a double
quantum dot, because the two dots can experience different local strain and therefore acquire different
magnetic responses. To understand how this dot-to-dot strain difference affects coupled hole
spins, we theoretically study the local \(g\) tensors of a silicon FinFET double
quantum dot by combining a three-dimensional Poisson–Schrödinger calculation based on a six-band \(k\!\cdot\!p\) model with configuration interaction. We find that the effect of strain depends on both its tensor component and its spatial
symmetry. For the diagonal components \(\epsilon_{yy}\) and \(\epsilon_{zz}\), strain mainly changes the principal \(g\) values, with only a small opening of the maximum-response axes. In contrast, the shear component \(\epsilon_{yz}\) can also change the orientation of the local
magnetic response. When the strain profile preserves the transverse mirror
symmetry, the shear-induced rotation is strongly suppressed. Breaking this local constraint permits a pronounced off-diagonal response and rotates the principal
magnetic axes. The same component- and
symmetry-selected trends appear in a Zeeman-only calculation, showing that the valence-band Zeeman coupling is sufficient to generate them, while the full
Hamiltonian determines their quantitative expression. Together, these results show how the tensor component and spatial
symmetry of strain can be used to control both the magnitude and orientation of the
magnetic response in coupled hole-
spin qubits.
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Strongly Correlated Electrons
The electric field gradient tensor as a symmetry-adapted order parameter in Landau theory
L. Scalise and A. W. Carbonari
Quadrupolar hyperfine spectroscopies, including
Nuclear Quadrupole Resonance (NQR),
Nuclear Magnetic Resonance (NMR), Time-Differential Perturbed Angular Correlations (TDPAC), and Mössbauer spectroscopy, have long used the electric field gradient (EFG) at a
nuclear site as an empirical proxy for order parameters in structural and electronic phase transitions, yet the EFG has never been systematically incorporated into Landau theory. Here we provide that framework. The EFG is an exactly traceless, symmetric rank-2 tensor defined at a crystallographic site. Decomposing it under the site-
symmetry group and inducing over the Wyckoff orbit determines its irreducible representation content in the parent space group. Whenever the representation of a zone-center transition is present,
symmetry requires the corresponding EFG combination to vanish above the transition and grow linearly with the order parameter below it, inheriting its critical exponent, sign, and domain structure.
Symmetry-orthogonal channels are quadratic, recovering the classic empirical relations. This yields a falsifiable classification of primary, secondary, and forbidden EFG responses. The framework is validated against five decades of quadrupolar experiments, reproducing critical exponents, first-order discontinuities, and a null result, and by first-principles calculations satisfying the predicted parity and zero
theorems. All-electron calculations for $\alpha$-quartz confirm the orbit-selection rule: only the EFG combination transforming as the soft-mode irreducible representation varies linearly with distortion amplitude, while the orthogonal combination remains suppressed by two orders of magnitude. A proposed study of the $^{75}$As site across the nematic transition in BaFe$_2$As$_2$ provides five falsifiable predictions, including a previously unstated null result.
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Statistical Mechanics
Boundary-Driven Anisotropic Coarsening in Conserved Phase Separation
Emilio N.M. Cirillo, Nicklas Jävergård, Adrian Muntean et al. (+1 more)
Universal scaling in phase separation is typically assumed to be isotropic in systems with conserved dynamics. Here we show that boundary forcing alone can break this dynamical scaling
symmetry, leading to anisotropic coarsening, with different effective global growth laws observed parallel and perpendicular to the boundary. We consider a ternary mixture with two conserved components and a passive species undergoing surface evaporation, which provides a simple setting to investigate this effect. In this case, evaporation leads to a progressive mass loss and to the formation of macroscopic concentration gradients, which, in turn, drive anisotropic coarsening, with different effective growth laws observed parallel and perpendicular to the boundary. At the same time, bulk regions appear to retain the standard Model B scaling, suggesting that the observed anisotropy is mainly induced by boundary fluxes rather than by changes in the intrinsic dynamics. Our results indicate that boundary conditions can play an important role in breaking scaling
symmetry and may offer a way to influence coarsening behavior in nonequilibrium phase separation.
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All authors Emilio N.M. Cirillo, Nicklas Jävergård, Adrian Muntean, Stela Andrea Muntean
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Revival of transport reciprocity via quantum interference in asymmetric nonlinear devices
Rupak Bag and Dibyendu Roy
Structural asymmetry combined with optical nonlinearity often leads to nonreciprocal light transport. We explore the mechanism by which 1-
photon interference effects can revive reciprocity in such nonlinear models. To this end, we study correlated 2-
photon scattering where an artificial atom is asymmetrically (a) side-coupled to an infinite waveguide at two spatially separated points, and (b) direct-coupled to two semi-infinite waveguides. The setup (a) gives robust reciprocal transport for the two
photons. However, the setup (b) shows a transition from a nonreciprocal to a reciprocal regime by tuning the interference effect via an additional tunneling path for
photons between the two waveguides.
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Statistical Mechanics · Cross-listed from physics.flu-dyn
Disentangling intermittent flow structure contributions to anomalous scaling and multifractality in turbulence
Ritwik Mukherjee and Siddhartha Mukherjee
Intermittency in
turbulence manifests as intense
vortices and sharp peaks of dissipation. Causing the breakdown of Kolmogorov's simple self-similar theory, it leads to anomalous scaling, multifractality and so far remains beyond the scope of a complete theoretical description. How intermittent flow structures influence these different measurements is not known quantitatively. With a simple filtering procedure-thresholding vorticity and inverting the Biot-Savart law to generate filtered velocity fields-we show the effects of intermittent flow structures can be disentangled. As extreme vorticity contributions to the velocity field are filtered out, the energy spectrum scaling persists, while the bottleneck is flattened, and structure function scalings tend towards their Kolmogorov values. The approach is more rapid for transverse exponents, revealing the selective importance of intensely swirling flow regions. Similarly, the extent of multifractality reduces as intermittency is filtered, shrinking the range of roughness singularity exponents. The residual fields are curiously more multifractal, but their structure begins to break away from an underlying
turbulence skeleton. The effects on
vortex stretching and strain self-amplification are quantified. Our work shows that a Biot-Savart approach can selectively remove the effects of intermittency from
turbulence, and hence from its scalings.
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Materials Science
Structure-Property Correlation of Cr/Cu-MnFeCoNi High-Entropy Alloys for Alkaline Water Electrolysis
Shreyasi Chattopadhyaya, Raphael B. de Oliveira, Deepti Gangwar et al. (+10 more)
High-
entropy alloys (HEAs), with their unique compositional-complexity and tunable surface chemistry, have emerged as promising electrocatalysts for energy conversion. The catalytic activity of HEA often arises from the interplay between the intrinsic activity of the individual elements and the synergistic effects generated at the interfaces. Even a single-element substitution in a multicomponent HEA can substantially alter the surface-chemistry and electrochemical kinetics of the active surface. Here we investigated the structure-property relationship of CrMnFeCoNi (HEA-Cr) and MnFeCoNiCu (HEA-Cu) HEAs by comparing the alkaline hydrogen
evolution reaction (HER) and oxygen
evolution reaction (OER) activity. Under the same experimental condition, HEA-Cu outperforms HEA-Cr towards both HER and OER. Substituting Cr with Cu significantly enhances the bifunctional activity, where HEA-Cu achieved a lower overpotential (538 mV) and Tafel slope (165 mVdec-1) when compared with HEA-Cr. Computational analysis corroborates these findings, showing that Cu substitution modulates the electronic-structure to provide favorable binding energies for reaction intermediates (H*, O*, OH*, and OOH*). Interestingly, unlike HER, recovered HEA-Cu after OER showed migration of Cu forming a Cu-rich outer layer shell with a multimetallic core. These findings demonstrate the potential of single-element substitution in HEAs as a strategy for designing high-performance, cost-effective catalysts for efficient water electrolysis.
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All authors Shreyasi Chattopadhyaya, Raphael B. de Oliveira, Deepti Gangwar, Tymofii S Pieshkov, Marcelo L. Pereira Junior, Dhiman Banik, Astrid Campos-Mata, Atin Pramanik, Soumyabrata Roy, Douglas S. Galvão, Chandra Sekhar Tiwary, Krishanu Biswas, Pulickel M Ajayana
Materials Science
Crystal forming ability of amorphous refractory metals under nanoindentation: a molecular dynamics study
Prashant Dwivedi, Alberto Fraile and Tomas Polcar
Amorphous refractory metal coatings combine high hardness with chemical inertness, yet their metastability makes them prone to mechanically induced crystallisation (devitrification) under contact loading, and how readily such a glass re-orders to its parent body centred cubic (bcc)
crystal is unknown across the refractory series. We prepared amorphous V, Nb, Mo, Ta and W by melt quenching to 300 K, validated each interatomic potential against ab initio
liquid radial distribution functions, and probed them by large scale molecular dynamics nanoindentation. Indentation drives a localised amorphous to bcc transformation by bulk nucleation, growth and coalescence. A
crystal forming ability (CFA), the maximum slope of the sigmoidal bcc fraction versus depth curve, spans about a factor of four and decreases as V > Mo > Nb > Ta > W; it falls with indenter velocity as CFA $\propto v^{-m}$ with a mean exponent of 1.08, so CFA$\cdot v$ is nearly constant and the transformation rate is almost velocity independent. Transforming atoms carry excess non affine displacement and local shear strain, not hydrostatic pressure, marking a shear associated displacive pathway; the bulk driving force is largest for the most resistant element, W, so resistance tracks cohesive bond strength rather than the thermodynamic driving force. Early bcc like order sets the sharpness and depth of the transition, whereas the mechanical work to half transformation sets the persistent
nucleus density. A grain population balance links nucleation, growth and coalescence to a terminal microstructure whose completeness does not follow the CFA order.
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Soft Condensed Matter
Squirming motion near corrugated surfaces
Sagnik Garai, Thomas G. Fai and Christina Kurzthaler
Swimming microorganisms often operate in complex confinement, where an interplay of long-ranged hydrodynamic interactions and a short-ranged repulsive interaction can give rise to interesting dynamical behaviors. Here, we theoretically investigate the trajectories of microswimmers - modeled as squirmers - in the presence of periodic boundaries. The latter modify their swimming velocity, leading to behaviors that differ qualitatively from swimming near planar walls. Using a perturbative approach based on bispherical coordinates and the Lorentz reciprocal
theorem, we characterize the interaction between a squirmer and a periodic surface in the limit of small surface amplitude and systematically explore its dependence on the boundary corrugation wavelength, squirmer type, orientation, and swimmer-surface distance. Most importantly, our results reveal that pullers become trapped in the valley of the surface corrugations, in contrast to their sliding motion near planar walls. Furthermore, the near-surface dynamics of pushers display oscillations, reflecting the periodicity of the surface structure. A tilt of the swimmer orientation with respect to the surface corrugations results in a wave-length dependent drift that sorts pushers from pullers. These findings highlight the impact of hydrodynamic interactions in shaping microswimmer transport near structured boundaries with potential implications for microbiological phenomena, such as biofilm formation, and technological applications.
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Strongly Correlated Electrons
Microscopic Emergence of Ancilla Lattice Physics in the Emery Model
Mikołaj Walicki, Johannes Knolle and Krzysztof Wohlfeld
We derive a controlled low-energy effective theory for the three-band Emery model on the Lieb
lattice near (n=2) filling. Starting from the positive charge-transfer regime, a sequence of Schrieffer–Wolff transformations rigorously establishes a direct microscopic mapping onto an ancillary
lattice structure. For realistic cuprate-like parameters, this framework naturally reproduces the conventional
Fermi-
liquid (FL) phase at a filling shifted by one electron per site. Our analysis identifies the precise microscopic conditions required to access the exotic fractionalized
Fermi-
liquid (FL$^*$) phase. We show that realizing FL$^*$ requires nonstandard cuprate parameter regimes together with additional interactions that stabilize a
quantum spin liquid in the background ancilla layer. These results establish a microscopic foundation for ancilla physics in multiorbital materials and clarify the conditions for realizing FL$^*$. We discuss the possibility to replicate ancilla model physics in Lieb
lattice cold atom simulations.
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Strongly Correlated Electrons
Electronic and magnetic properties of small one-dimensional Wigner crystals from an ab initio approach
Daniele Lagasco and Jan Arjan Berger
We present an ab initio method to study the electronic and
magnetic properties of small one-dimensional Wigner
crystals. In particular, we focus on the calculation of the electronic charge distribution and the exchange coupling constant. Our theoretical studies are motivated by the experimental observation of few-electron Wigner
crystals in a carbon nanotube [Science 364, 870 (2019)]. We model the experimental setup by confining electrons in a one-dimensional potential well with infinite side barriers. We represent the
Hamiltonian of the system in a basis of Slater determinants and perform full configuration interaction to ensure we capture all the electron correlation for a given basis set. As the one-particle basis set we use particle-in-a-box wave functions which by construction satisfy the boundary conditions. With our approach, we obtain accurate electronic density profiles of small one-dimensional Wigner
crystals. These profiles clearly show the localisation of the electrons. Finally, we present a simple approach to obtain the exchange coupling constant by mapping our ab initio method on a Heisenberg
Hamiltonian. We illustrate our approach on a Wigner dimer. We obtain excellent agreement with a result in the literature.
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Materials Science
Magnetic hopfions at room temperature
Kaixin Zhu, Wenli Gao, Zhan Wang et al. (+12 more)
Hopfions are three-dimensional (3D) topological
solitons predicted to exist in diverse
magnetic systems, yet their practical utility has been largely restricted to cryogenic environments. Here, we overcome this temperature constraint by demonstrating stable
magnetic hopfions in the
chiral magnet Co8Zn8Mn4 at and above room temperature. Using a transmission electron microscope equipped for in situ optical excitation, we generate
magnetic hopfions with femtosecond
laser pulses. Long-term observations further reveal Brownian-like motion at room temperature and thermally activated collapse upon approaching the high-temperature regime. Together with micromagnetic simulations and homotopy group analysis, our experimental observations uncover the hopfion formation mechanism through the fusion of bimeron pairs. These findings establish room-temperature
magnetic hopfions and provide a framework for their further studies under technologically relevant conditions.
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All authors Kaixin Zhu, Wenli Gao, Zhan Wang, Shuaishuai Sun, Siyuan Huang, Junxi Tong, Jun Li, Huanfang Tian, Zian Li, Huaixin Yang, Ying Zhang, Olle Eriksson, Filipp N. Rybakov, Nikolai S. Kiselev, Jianqi Li
Materials Science
Inferring Magnetic Material Parameters from Statistical Measures in Strongly Fluctuating Magnetization Dynamics
Kübra Kalkan, Atreya Majumdar, Ross Knapman et al. (+5 more)
Magnetic material parameters such as the exchange stiffness and
magnetic anisotropy govern the behavior and functionality of
magnetic systems, yet their local inference from magnetization data remains challenging, particularly in strongly fluctuating regimes with polycrystalline or multiphase microstructure, where conventional texture-based methods become unreliable. We introduce a magnetization-only framework for inferring material parameters from thermally driven magnetization dynamics. Using micromagnetic simulations, we extract statistical quantities such as temporal mean and latent
entropy from the magnetization dynamics, fit models to these descriptors, and invert the models to infer material parameters. We show that this framework enables material-parameter inference as well as grain-boundary detection in a heterogeneous sample. Among the descriptors considered, latent
entropy yields more accurate parameter estimates than the temporal mean. Our results establish latent
entropy as an efficient descriptor for inferring
magnetic material parameters from dynamical magnetization data and point toward its use for experimental parameter extraction at high temperatures and, more broadly, under strongly fluctuating conditions.
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All authors Kübra Kalkan, Atreya Majumdar, Ross Knapman, Omer Fetai, Franziska Scheibel, Sabrina Disch, Illia Horenko, Karin Everschor-Sitte
Statistical Mechanics
The Role of Odd Diffusivity in Multipoint Statistics of State-Dependent Observables
Jong-Min Park
Odd diffusivity is a transverse transport coefficient that appears when time-reversal and parity
symmetries are broken. Its most distinctive signature is a probability flux perpendicular to a density gradient, generated by the antisymmetric part of the
diffusion tensor. Here we show that for an arbitrary number of state-dependent observables measured at arbitrary times, their joint statistics are independent of the antisymmetric part of the
diffusion tensor. Thus, the Lorentz flux does not contribute to any multipoint state-observable measurements. The result clarifies the separate roles of two effects that are often linked together by fluctuation–dissipation relations, i.e., odd mobility and odd diffusivity. This observation demonstrates that the anomalous correlations in odd-diffusive systems originate solely from odd mobility. It also allows the statistics of state-dependent observables in odd-diffusive systems to be computed using conventional Langevin dynamics without the antisymmetric
diffusion part while preserving the antisymmetric mobility tensor. It implies that universal relations associated with state-dependent observables alone, such as nonlinear fluctuation–dissipation relations and generalized Green–Kubo relations, remain valid in odd-diffusive systems without modification. We verify our findings through mean back relaxation, the
diffusion coefficient, the nonlinear fluctuation–dissipation relation, and a generalized Green–Kubo relation in diverse systems.
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Materials Science
End-to-End Modeling of a Volatile TiO2 Memristor for Neuromorphic Circuit Simulation
Lukas Endres, Hannes Töpfer, Michaela Blum et al. (+2 more)
Memristors are promising devices for applications such as non-volatile
memory, neuromorphic computing, logic
circuits, and analog signal processing. The development of such systems requires accurate simulations based on models that reproduce the electrical behavior of real devices under both continuous and pulsed excitation. This work presents the development of a simulation environment for a volatile TiO2-based memristor. Experimental measurement data are analyzed to verify the memristive behavior of the device and to identify a suitable model. The model parameters are then optimized to match the measured characteristics. The resulting model is implemented in SPICE and validated by comparing simulation results with measurement data. The comparison shows a good agreement between simulation and experiment, demonstrating that the developed model is suitable for reproducing the electrical behavior of the investigated memristor and can be applied in
circuit-level simulations, as demonstrated by a leaky integrate-and-fire
neuron.
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All authors Lukas Endres, Hannes Töpfer, Michaela Blum, Hauke Honig, Peter Schaaf
Strongly Correlated Electrons
Disentangling bulk and surface states in the electronic structure of PtBi$_2$(0001)
Stefanie Suzanne Brinkman, Xin Liang Tan, Anders Christian Mathisen et al. (+13 more)
Recent reports of surface-localized topological superconductivity in trigonal PtBi$_2$ highlight the importance of understanding its surface electronic structure. We investigate the bulk and surface band structure of PtBi$_2$ using angle-resolved photoemission spectroscopy (ARPES) and first-principles calculations. Through
photon-energy- and polarization-dependent measurements, we disentangle bulk dispersions from surface states on the two distinct surface terminations of PtBi$_2$(0001). For both terminations, we assign several different surface states and find good agreement between experiment and calculations. Based on our calculations, we analyze the orbital composition in the surface and bulk bands and compare the results to polarization-dependent ARPES measurements. Together, our results provide a coherent picture of the surface electronic structure of PtBi$_2$ across both surface terminations.
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All authors Stefanie Suzanne Brinkman, Xin Liang Tan, Anders Christian Mathisen, Fabian Göhler, Øyvind Finnseth, Chul-Hee Min, Grigory Shipunov, Falk Pabst, Manuel Alonso Lemos, Balasubramanian Thiagarajan, Craig Polley, Masashi Arita, Kenya Shimada, Anna Isaeva, Jorge I. Facio, Hendrik Bentmann
Soft Condensed Matter · Cross-listed from physics.bio-ph
Navigation driven by bidirectional information transmission between sensing and actuation
Avishek Das and Pieter Rein ten Wolde
A wide variety of biological functions are driven by feedback between sensing and actuation. A paradigmatic example is cellular
navigation. During
navigation, the sensory system maps the environmental input signal onto a sensory output, which then drives an actuation response, thereby changing the future sensory input. How the accuracy of this bidirectional information transmission controls
navigation is not currently understood. Here, we study how information controls
navigation by analytically solving two generic models that describe two major classes of biological navigators: spatial- and temporal-sensing
cells. We find that, in the linear-response regime of shallow gradients,
navigation performance is fully determined by bidirectional information transmission alone, as quantified by feedforward and feedback transfer
entropies. Elementary system parameters affect
navigation performance only through their effect on these information flows. We call these relations Behavioral Equations of State (BESTs): equalities that map information to function in a system-independent way. BESTs predict an experimentally testable data collapse for the performance of navigators with different sensing and actuation parameters. We test the validity of our theory by performing
stochastic simulations of chemotaxis of the bacterium Escherichia coli, computing the relevant transfer
entropies exactly with the TE-PWS
algorithm. The observed performance obeys the BEST without any fitting or scaling parameters. Thus, our theory identifies bidirectional information transmission between sensing and actuation as an organizing principle for
navigation.
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Disordered Systems and Neural Networks
High-dimensional theory of the glass transition revisited: hopping and local defects
Harukuni Ikeda and Francesco Zamponi
The replicated
liquid theory provides a microscopic mean-field description of the glass transition by combining the density functional theory of
liquids with the replica method originally developed for
spin glasses. In the conventional replica
liquid theory, a glassy state is described by assuming that particles in different replicas undergo vibrational motion around common centers of mass, thereby forming molecules that contain one particle from every replica. Here we revisit this assumption by allowing each molecule to contain only a subset of replicas. This generalized formulation describes particle-level replica mismatches, which may be associated with non-vibrational motions such as particle hopping. We apply the theory to high-dimensional hard and harmonic spheres, where the mean-field description is expected to become exact. For hard spheres, replica mismatches destabilize the glassy metastable state and shift the dynamical transition to a significantly higher packing fraction, while leaving the leading thermodynamic glass transition unchanged. The resulting transition density agrees, at leading order in high dimensions, with the recent rigorous lower bound for random sphere packings obtained by Campos, Jenssen, Michelen, and Sahasrabudhe by using a discretized version of greedy Random Sequential Absorption, suggesting an algorithmic interpretation of the transition: grandcanonical dynamics is more efficient in high dimensional spaces than canonical one. For harmonic spheres at finite temperature, the glassy state contains a finite replica-mismatch fraction even at the thermodynamic ideal-glass transition, thereby shifting the transition point from that predicted by the conventional replica ansatz.
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Disordered Systems and Neural Networks
Quenched fluctuation-induced force arising from polarization disorder
Bing-Sui Lu
We investigate the zero-temperature behavior of the fluctuation force induced by the quenched disorder of electric dipoles frozen randomly into a material. Examples of such materials include relaxor ferroelectrics. In terms of the setup and geometry, we focus on a layered system comprising two coplanar semi-infinite slabs separated by a distance $\ell$ as well as a system comprising a neutral atom in the
vacuum located at a distance $\ell$ above the surface of a semi-infinite slab. For both systems, we consider the cases where the quenched random dipolar disorder occurs inside the bulk as well as on the surface of the slabs. In all of these cases, we find that the bulk (surface) dipolar disorder-induced force grows with the mean square quenched electric dipole moment per unit volume (area). The bulk (surface) dipolar disorder-induced pressure between two semi-infinite single-layered slabs decays with $\ell^{-3}$ ($\ell^{-4}$), whereas the bulk (surface) dipolar disorder-induced force on an atom in the
vacuum near a slab containing the disorder decays with $\ell^{-4}$ ($\ell^{-5}$). We also find that the quenched dipolar disorder-induced force between two coplanar slabs can be repulsive in a three-layered dielectric system that obeys a zero-frequency analogue of the Dzyaloshinskii-Lifshitz-Pitaevskii condition, and serve to enhance the “nanolevitation effect" if the latter is present in the disorder-free system.
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