Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
A photonic source with half-a-GHz single-photon flux
P. Zahalka, S. Huijser, A. Pancaldi et al. (+10 more)
Advanced optical
quantum technologies demands high quality
quantum light generation at very high rates. Here, we report on a deterministic single-
photon source that simultaneously combines high excitation rates with high system efficiency to reach over 500 MHz of in-fibre single-
photon flux. The source delivers optical power of over 100 pW, as is measured with an off-the-shelf powermeter, enabling a simple and direct way of determining the single-
photon source fiber efficiency.
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All authors P. Zahalka, S. Huijser, A. Pancaldi, S. Kruger, X. Zhao, Z. Liu, I. Suleiman, R. Jensen, L. Stefan, A. Ludwig, V. Remesh, J. C. Loredo, P. Lodahl
Materials Science
Customized spin spirals in ferromagnetic thin films
Anjali Panchwanee, Kai Schlage, Dieter Lott et al. (+8 more)
The advancement of spintronic nanoscale devices hinges on the ability to flexibly engineer
magnetic spin structures in thin-film stacks with precision and control. Meeting this demand remains a challenge for stable non-collinear
spin configurations and, more specifically, vertical
spin spirals in thin films. Innovative methods are required for their fabrication, stabilization and control. Here, we use oblique-incidence deposition to design and stabilize vertical
spin spirals at room temperature and without an external field in
magnetic thin films. We induce two crossed uniaxial
magnetic anisotropies at the thin film boundaries. These anisotropies are tunable in direction and strength, thus providing control over the angular range and depth profile of the resulting
spin spiral. The combination of polarized
neutron reflectometry and nuclear resonant scattering enables precise and direct determination of the depth-dependent
spin configurations. Our results establish a single-film design approach, in which the surface anisotropies independently serve as controllable design parameters for tailoring the vertical
spin-spiral profile. Potential applications include nanoscale energy-storage devices,
magnetic sensors, and ferromagnetic-resonance filters, advancing all-
spin-based device engineering in general.
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All authors Anjali Panchwanee, Kai Schlage, Dieter Lott, Sven Velten, Thomas Saerbeck, David L. Cortie, Sakshath Sadashivaiah, Ilya Sergeev, Guido Meier, Lars Bocklage, Ralf Röhlsberger
Soft Condensed Matter
Molecular interfacial rheology: Lipid membrane shear viscosity
Zhi-Xun Xu and Amaresh Sahu
We develop a method to extract the shear viscosity of a lipid membrane from
equilibrium molecular dynamics simulations. The method characterizes the rheology of general interfacial systems embedded in three-dimensional media; we term it molecular interfacial rheology. In our simulations the planar bilayer and surrounding water are confined between solid, parallel walls. Following Onsager's regression hypothesis, membrane and water fluctuations are assumed to relax according to the coupled continuum-mechanical equations governing the confined system—which predict that the membrane transverse velocity autocorrelation function (TVACF) decays exponentially, at a rate set by the membrane and water viscosities. The measured TVACF, however, exhibits damped oscillations followed by a slowly decaying tail. We reconcile these behaviors using the Mori–Zwanzig formalism, and extract the wavevector-dependent membrane viscosity from the time-integral of the TVACF. Results from theory and simulations agree over a decade of wavevectors, and extrapolating to long wavelengths yields shear viscosities ranging from 0.064 to 0.18 pN*us/nm across two representative single-component, fluid-phase bilayers. Our results are corroborated by nonequilibrium simulations where a spatially varying in-plane body force is applied to lipid molecules, thus validating the framework of molecular interfacial rheology.
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Materials Science
Remote epitaxy beyond polarity
Ching-Tai Fu, Pei-Jan Hung, Xudong Li et al. (+21 more)
Remote epitaxy through a monolayer two-dimensional material-covered substrate establishes a crystallographic registry across the van der Waals (vdW) surface that enables the epitaxial growth, lift-off and transfer of single-crystalline films. A central belief in remote epitaxy is that the substrate facilitating the phenomenon must be a material with strong ionicity, as the interatomic electrostatic potential fluctuation in covalent and metallic materials is substantially attenuated by two-dimensional materials. Here, we show remote epitaxy is possible when the substrate is a metallic or covalently bonded material and experimentally demonstrate non-polar remote homo- and heteroepitaxy across a wide range of material systems, including both metals and
semiconductors. The achieved non-polar remote interactions are designed and engineered by harnessing substrate conductivity and vicinal surface step-edge density. These findings indicate that remote epitaxy is universal and applicable to ionic, metallic, and covalent materials, expanding its capabilities and stimulating a plethora of new fundamental scientific questions about the mechanism of remote epitaxy.
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All authors Ching-Tai Fu, Pei-Jan Hung, Xudong Li, Xiaolong Zhu, Yu Han, Sayantan Mahapatra, Zhiheng Zhao, Qingsong Fan, Xubing Wu, Qizhang Li, Chenxi Sui, Zirui Zhou, Ting-Hsuan Chen, Cheng-Hao Lei, Ivan Kuzmenko, Xiaobing Zuo, Byeongdu Lee, Alexander S. Filatov, Jeffrey R. Guest, Fengyuan Shi, Yuzi Liu, Hua Zhou, Yunfeng Shi, Po-Chun Hsu
Quantum Gases
How dipolar interactions structure molecular droplets
Wiiliam Freitas, Panagiotis Giannakeas and Jan M. Rost
We investigate how dipolar interactions between microwave-shielded polar molecules structure the self-bound droplets formed under variation of the interaction strength. We identify the transition from droplets to
crystals as a finite-size first order transition. With droplet-ring states and transitional supersolid states we predict additional structure in the
crystal and droplet phases, respectively. To describe this strongly correlated regime, and in particular the reconfiguration of
quantum ground states, we design a variational Monte Carlo framework based on neural
quantum states. It is especially suitable to describe ground states and almost degenerate states with very different configurations. Moreover, one can easily determine the superfluid fraction. Our results reveal the sequence of finite-size structures through which dipolar interactions reorganize molecular droplets into
crystals.
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Strongly Correlated Electrons · Cross-listed from hep-th
The Junction That Remembers: Infrared Response of Two Coupled SYK Majorana Systems
Ali Vahedi
Two strongly interacting Majorana systems of the Sachdev–Ye–Kitaev type, each with its own independent disorder, are joined by a link that is switched on in time. We ask how the infrared structure of the link is imprinted on the response and whether the system remembers how it was opened. At large $N$ the leading cross-correlation between the two systems is an exact product of two
equilibrium propagators and the switching profile; because the disorder is independent, no ladder dresses it. The link operator has scaling dimension one half, which gives its susceptibility a universal logarithm whose coefficient and phase we fix and verify numerically, while the gap of the coupled
equilibrium problem grows more slowly than the naive crossover estimate. Exact dynamics for up to twelve Majoranas per side show strong parity transfer and
entanglement several times the free-
fermion ceiling. The work done by the switch has a first-order part that does not depend on the switching time and a second-order part that grows in magnitude with it. Once the work is held fixed, the protocol dependence of the
entanglement, the link expectation value and a scrambling diagnostic nearly vanishes, and the small residuals do not depend on whether the protocols differ at low or at high frequency. These small systems have no infrared window, so they neither confirm nor exclude
memory at large $N$.
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Strongly Correlated Electrons
Breakdown of Anomalous Hall Scaling in Dilute Kondo System
Arnab Bhattacharya, Prashant Singh, Ajay Kumar et al. (+4 more)
The confluence of strong electronic correlations and Berry
curvature-driven transport constitutes a largely underexplored frontier in
quantum materials research, particularly in systems where electronic correlations arise from flat-band physics rather than conventional $f$-electron states. Here, we report an intrinsic Berry
curvature driven anomalous Hall transport in the dilute Kondo system Ru$_2$Mn$_{0.5}$Ti$_{0.5}$Ge, a non-$f$-electron Heusler
alloy hosting flat bands with van Hove singularity proximate to the Fermi level. The anomalous Hall response is strikingly non-monotonic, violating the Fermi-
liquid scaling relation near the
magnetic transition and is restored only at low temperature, coincident with the onset of Kondo coherence. Ab initio calculations strongly establish that the Berry
curvature originates from the Kondo hybridization induced interplay of flat bands and
spin-orbit coupling mediated anticrossings at the Fermi level. Our findings demonstrate that Kondo coherence of flat bands bears a profound impact on Berry
curvature associated ferroic responses, mandating a rigorous theoretical understanding of anomalous transport in the regime where reciprocal space
topology and strong correlations are intrinsically intertwined.
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All authors Arnab Bhattacharya, Prashant Singh, Ajay Kumar, Afsar Ahmed, Yaroslav Mudryk, I. Das, Anis Biswas
Quantum Gases
Fluctuations of a Photon Bose-Einstein Condensate Coupled to a Reservoir: Describing Coherence Properties in a Free-Energy Model
Martin Weitz, Andreas Redmann, Riccardo Panico et al. (+4 more)
Photons are mutually nearly noninteracting particles, so thermalized
photon ensembles are commonly obtained not from direct particle-particle-interactions but rather from contact with matter, which can constitute a reservoir for the
photon gas. We develop a theory model for
photons in a material-filled (e.g.
liquid dye) optical microcavity, with the aim to study the fluctuation properties using a free-energy description for noninteracting
photons coupled to a reservoir of material electronic excitations. To begin with, we use a single mode description for the condensate. For a small relative size of the material reservoir, corresponding to the canonical regime, condensate number fluctuations are small, and the derived free energy landscape takes the usual Mexican-hat shaped form such that spontaneous
symmetry breaking occurs. In contrast, for a large relative size of the reservoir, corresponding to the grand canonical regime, fluctuations become as large as the average particle number. We show that the resulting free energy landscape acquires a bowl-shaped form, with a single minimum at the origin. Thus, a macroscopic occupation of the ground state (i.e., Bose-Einstein condensation) in the absence of spontaneous
symmetry breaking is expected. We also provide a model for the treatment of a
photon gas trapped in a box-shaped potential with spatially distributed coupling to a reservoir. The model predicts, for example, a statistically fluctuating pattern of islands with long-range coherence, resembling transient microcondensates.
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All authors Martin Weitz, Andreas Redmann, Riccardo Panico, Leon Kleeblank, Kevin J.H. Peters, Frank Vewinger, Julian Schmitt
Disordered Systems and Neural Networks
Connecting heterogeneous dynamics with local entropy
Jun Wu, Walter Kob, Yujie Wang et al. (+1 more)
Establishing a robust and physically interpretable link between static structure and heterogeneous relaxation dynamics remains a fundamental challenge in glass physics. Here, we introduce a weighted pair-
entropy descriptor based on the conventional two-body excess
entropy. For this, we multiply the integrand used to calculate the excess
entropy by a weight function that is directly related to the length scale of the pair correlation function. This multiplication does not affect the contribution of the short range order to the local excess
entropy, but allows to take into account the structure present on intermediate distances, i.e., the medium-range order. For a canonical two-dimensional Lennard-Jones glass former, the resulting descriptor exhibits a strong correlation with particle-level dynamical propensity at long times (multiples of the alpha-relaxation time), with a maximum structure–dynamics correlation reaching about 0.9, substantially outperforming the predictive power of the conventional local pair excess
entropy. These results demonstrate that incorporating a physically motivated structural length scale into
entropy-based descriptors markedly enhances their predictive power while preserving physical interpretability. Our findings provide a simple and general framework for investigating structure–dynamics correlations in glass-forming systems.
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All authors Jun Wu, Walter Kob, Yujie Wang, Zhen Zhang
Materials Science · Cross-listed from physics.app-ph
Thermoelectric properties of metal-semiconductor percolation composites
Oleksandr Porubaniyi, Sergii Tomko, Mihailo Cherkez et al. (+2 more)
We analyze thermoelectric response of composite materials comprising homogeneous
semiconductor hosts with randomly distributed metallic inclusions. We demonstrate that the properties of such materials are strongly affected by the percolation transition (with background conductivity). We show that in vicinity of percolation threshold, the power factor and the thermoelectric figure of merit strongly depend on both the concentration and arrangement of inclusions. Finally, we identify promising regimes for enhancing the power factor in realistic composites.
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All authors Oleksandr Porubaniyi, Sergii Tomko, Mihailo Cherkez, Viktor Podolskiy, Radion Cherkez
Statistical Mechanics
Diffusion under competing bulk and surface stopping mechanisms
Yilin Ye
We investigate reflected
diffusion in a bounded domain subject to two independent, competing stopping mechanisms: an exponentially distributed bulk lifetime of rate $p$ and a surface reaction triggered when the boundary local time exceeds an independent exponential threshold of rate $q$. Denoting by $T$ the stopping time and by $L$ the acquired boundary local time at stopping, we derive their marginal distributions, joint Laplace transform, and complete hierarchy of mixed moments. These statistics are determined by the splitting probability $\phi$ that surface reaction occurs before bulk decay. In particular, we establish the identity $p\expect{T}+q\expect{L}=1$ and show that the cumulative risk $pT+qL$ is exponentially distributed with unit rate. We further obtain equivalent representations of $\phi$ in terms of the Robin-
Laplacian and the generalized Steklov spectra. Explicit results for a three-dimensional ball reveal how competing rates $p,q$ control $\phi$ and the $(T,L)$ statistics. Monte Carlo simulations test the universal cumulative-risk law.
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Mesoscale and Nanoscale Physics
Robustness of RKKY interactions across a Weyl node-annihilation transition
João V. F. Alves, Joelson F. Silva and Luis G. G. V. Dias da Silva
Weyl semimetals (WSMs), with their unique topological properties and distinct electronic structure, exhibit intriguing properties when either time-reversal or inversion
symmetries are broken. In this work, we consider the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between
magnetic impurities in time-reversal
symmetry-breaking WSMs. We derive analytical expressions for the full RKKY exchange tensor in arbitrary two-band spinful
lattice systems. Our approach reveals both Heisenberg, anisotropic Ising and Dzyaloshinsky-Moriya terms, which can be calculated by energy-integrating real-space Green's functions across the entire Brillouin zone, with the band edge acting as a natural energy cutoff. We apply this framework to study a two-band tight-binding model for a time-reversal
symmetry-breaking WSM that interpolates between a Weyl phase with well-separated chiral nodes and a quadratic band-touching semimetal phase. Remarkably, the spatial profile, magnitude, and anisotropic tensor structure of the exchange couplings remain persistent across the node-annihilation transition. This topological robustness reveals that short- and intermediate-range RKKY interactions are mediated by the global, Brillouin-zone-integrated
quantum metric of the full valence band rather than being strictly dictated by local low-energy Berry
curvature monopoles. These findings demonstrate the necessity of full-band tight-binding formulations when predicting real-space
magnetic interactions, providing key insights for electric-field tuning of
magnetic anisotropy and constructing realistic models of heavy-
fermion and Weyl-Kondo semimetals.
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Soft Condensed Matter
Coarse-graining far-from-equilibrium dynamics using oblique projectors
Gerhard Jung
We generalize the Mori-Zwanzig projection operator formalism by introducing an oblique projector using biorthogonal variables to coarse-grain the dynamics of systems far from
equilibrium, such as active or living matter. Improving on previously used orthogonal projectors, the oblique projector correctly decomposes the emergent interactions of the coarse-grained particles into systematic and
stochastic contributions. We show that the formalism directly connects to established results in non-
equilibrium linear response theory and adiabatic perturbation theory. Based on this formalism, we develop a coarse-graining
algorithm which we apply to extract the emergent non-
equilibrium chiral dynamics of a passive tracer in a chiral active bath. Our theory correctly predicts the odd transport properties and a confinement-induced shift of the chiral frequency of the tracer.
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Superconductivity
Dynamical Reduction of Two Series Josephson Junctions to a Synthetic High-Transparency Josephson Element
Claudio Guarcello, Sergio Pagano, Carlo Barone et al. (+3 more)
Two conventional Josephson junctions connected in series can reproduce, in the static limit in which the currents through the capacitive and resistive channels are negligible, the current-phase relation of a single effective weak link with tunable transparency. Therefore, the two-junction series can be treated as a single synthetic high-transparency element. Here, we investigate to what extent this mapping remains valid under finite-frequency drive and retaining the junctions' resistive and capacitive terms. The full resistively and capacitively shunted junction equations are compared with an effective synthetic element with tunable transparency that retains the synthetic tunable-transparency current-phase relation together with effective capacitive and dissipative terms, thus reducing the two second order degree of freedom system to a single second order degree of freedom. The resulting single-element dynamics is compared with the complete two-junction system under ac excitation. The agreement is quantified through a normalized root-mean-square error between the full and effective voltage waveforms. A broad low-error region is found at low drive frequency, while pronounced deviations emerge as the drive frequency approaches the relevant
plasma-frequency scale and at larger drive amplitudes. The results provide a quantitative dynamical criterion for using the reduced single-element description of a synthetic high-transparency Josephson element in superconducting
circuits.
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All authors Claudio Guarcello, Sergio Pagano, Carlo Barone, Alessandro Bruno, A. Mert Bozkurt, Giovanni Filatrella
Mesoscale and Nanoscale Physics
Electrostatic splitting of an Edge Magnetoplasmon Resonator
Sloän Kouamé, Elric Frigerio, Giacomo Rebora et al. (+10 more)
Edge-magnetoplasmon resonators have been proposed as a powerful tool to detect anyons by introducing a
quantum point contact into an isolated
quantum Hall system probed via radiofrequency radiation. In this paper, we study the effect of a
quantum point contact embedded within an edge-magnetoplasmon resonator and how its polarization influences the propagating magnetoplasmonic mode. Combining dc and rf measurements, we unambiguously evidence the signature of both integer ($\nu = 1$ and $2$) and fractional
quantum Hall states ($\nu = 4/3$ and $2/3$) within the radiofrequency transmission signal. Using electrostatic gating, we determine the physical parameters characterizing the electrostatic edge of an AlGaAs/GaAs based two-dimensional electron gas. We extract the dependence of the cavity perimeter with the gate voltage of the
quantum point contact and fully characterize the path followed by edge magnetoplasmons in this system. Finally, we provide a
geometric model in good agreement with experimental results.
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All authors Sloän Kouamé, Elric Frigerio, Giacomo Rebora, Suvankar Purkait, Yong Jin, Ulf Gennser, Antonella Cavanna, Jean-Marc Berroir, Emmanuel Baudin, Pascal Degiovanni, François D. Parmentier, Gwendal Fève, Gerbold C. Ménard
Superconductivity
Ni-O hybridization as a stabilizer for $s^{\pm}$ superconductivity in La$_3$Ni$_2$O$_7$: a DFT+RPA study
Lauro B. Braz, Daniel D. Rivera, Emmanuel V. C. Lopes et al. (+3 more)
The superconducting gap
symmetry of high-pressure bilayer nickelates remains under debate, with weak- and strong-coupling approaches yielding different pairing tendencies. In this work, we investigate how the weak-coupling treatment of electronic states away from the Fermi level influences
magnetic fluctuations and superconductivity in La$_3$Ni$_2$O$_7$. We employ a full-spectrum model based on orthonormalized projections of Kohn-Sham states onto local Ni-$e_g$ orbitals, which preserves the density-functional band structure while redistributing spectral weight over a wide energy range. Compared to a low-energy description, this approach yields enhanced interlayer
spin fluctuations and a commensurate
magnetic instability. Within a
spin-fluctuation framework, these features favor a sign-changing $s^\pm$ superconducting state, whereas low-energy models tend to stabilize $d$-wave pairing. Our results suggest that interlayer coupling in full-energy models may play an important role in shaping the predicted pairing
symmetry of bilayer nickelates.
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All authors Lauro B. Braz, Daniel D. Rivera, Emmanuel V. C. Lopes, George B. Martins, Gustavo M. Dalpian, Luis G. G. V. Dias da Silva
Statistical Mechanics
Markov chains at the onset of non-reversibility
Gustave Robichon, Cecile Monthus and Werner Krauth
For a one-dimensional path graph and a lifted path graph constructed from a duplication of each of its sites, we study how a reversible Markov chain can be perturbed and gradually driven into non-reversibility. The reversible Markov chain has a transition
matrix that is diagonalizable and features real-valued
eigenvalues and eigenvectors. The left and right eigenvectors form a biorthogonal system. We discuss in concrete examples how the transition
matrix of a non-reversible Markov chain may be diagonalizable or non-diagonalizable, and it may have real
eigenvalues and complex-conjugate pairs. For a number of steady states (flat, square-wave, wedge, V-shape), we compute
eigenvalue spectra on both graphs and discuss the speedup that can be achieved through lifting. We develop a Green's
matrix formalism, which we use to compute Kemeny times and mean first-passage times, and which provides valuable information and allows us to interpret the results for the characteristic times.
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Strongly Correlated Electrons
Dipolar and quadrupolar spin supersolid states in a spin-1 triangular antiferromagnet
Yixuan Huang, Yuan Gao, Wei Li et al. (+2 more)
We present a systematic numerical study of the
spin-1 antiferromagnetic Heisenberg model on the triangular
lattice in an out-of-plane
magnetic field, using Density
Matrix Renormalization Group (DMRG) methods. By mapping out the
quantum phase diagram as a function of the single-ion anisotropy $D_z$ and
magnetic field, we identify distinct dipolar and quadrupolar
spin supersolid states, characterized by spontaneous U(1)
symmetry breaking with finite
spin superfluid stiffness coexisting with longitudinal translational
symmetry breaking. At zero field, the dipolar
spin supersolid with a 'Y'-type
spin configuration persists down to $D_z = 0$, whereas the quadrupolar
spin supersolid prevails at large $D_z$. At intermediate fields, the phase diagram is dominated by an up-up-down phase. At high fields below saturation, a quadrupolar
spin superfluid emerges in the large-$D_z$ regime, whereas a dipolar
spin supersolid with a 'V'-type
spin configuration dominates at small $D_z$. These phases are characterized through their order parameters and
spin superfluid stiffness using calculations on various system sizes. Furthermore, the dynamical
spin structure factor is obtained across the phase diagram, where characteristic spectral signatures of different phases are observed, including the gapless Goldstone mode and the roton-like minima. These features are directly accessible to inelastic
neutron scattering experiments. Our results provide a theoretical understanding of the interplay between frustrations, anisotropy, and Zeeman interactions in driving distinct
spin supersolid phases in the
spin-1 system, which are relevant to various triangular-
lattice antiferromagnets such as Na$_2$BaNi(PO$_4$)$_2$ and K$_2$Ni(SeO$_3$)$_2$.
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All authors Yixuan Huang, Yuan Gao, Wei Li, Seiji Yunoki, Sadamichi Maekawa
Superconductivity
Transparency-engineered SQUID cells for Kerr-free three-wave-mixing Josephson metamaterials
Claudio Guarcello, A. Mert Bozkurt, Carlo Barone et al. (+3 more)
We introduce a transparency-engineered rf-SQUID
cell for Kerr-free three-wave-mixing Josephson metamaterials. This design replaces the conventional tunnel-junction element with an effective Josephson element formed by two junctions in series, yielding a non-sinusoidal energy-phase relation that can be used as a tunable nonlinear design resource. We show that the asymmetry between the two series junctions and the applied flux bias provide independent control over the local expansion of the rf-SQUID potential, enabling operating points where the leading quartic Kerr term is suppressed while the cubic nonlinearity remains finite. We derive the corresponding Kerr-free condition, identify the resulting operating ridge in parameter space, and analyze the local stability and passive-matching constraints that bound its physically accessible portion. Our results provide a compact unit-
cell design principle for three-wave-mixing Josephson metamaterials and suggest a route toward Kerr-suppressed Josephson traveling-wave parametric amplifiers.
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All authors Claudio Guarcello, A. Mert Bozkurt, Carlo Barone, Giovanni Filatrella, Alessandro Bruno, Sergio Pagano
Materials Science · Cross-listed from physics.app-ph
What Photocurrent Versus Effective Voltage Tells Us About Charge Generation in Organic Solar Cells
Ardalan Armin, Austin M. Kay, Drew B. Riley et al. (+2 more)
The photocurrent of an organic solar
cell is routinely plotted against an effective voltage and used to extract an
exciton dissociation probability, and through it a free-charge generation efficiency. The photocurrent measures neither. Using a drift-
diffusion model in which free-charge generation is field independent and losses occur only by bimolecular recombination, we show that the apparent dissociation probability returned by this procedure lies well below unity even for complete dissociation. Across wide variations of carrier mobility and recombination strength it is a single-valued function of the fill factor and coincides with the short-
circuit charge collection efficiency, reporting neither the generation yield nor anything about collection beyond what the fill factor already shows. Even for ideal transport the normalised photocurrent saturates below unity at an intensity-independent first-order limit set by recombination of photogenerated carriers with injected
equilibrium charge. Applied to four organic solar
cells whose generation efficiencies are known independently, the apparent dissociation probabilities track the short-
circuit collection efficiency rather than the generation yield. We therefore suggest this construction not be used, particularly in the high-efficiency non-fullerene acceptor systems that are now state of the art.
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All authors Ardalan Armin, Austin M. Kay, Drew B. Riley, Oskar J. Sandberg, Paul Meredith
Materials Science
Neural-field design of broadband Rayleigh-wave carpet cloaks under microstructure realisability constraints
David Aznaurov, Davit Piliposyan, Danila Rukhovich et al. (+1 more)
Transformation elasticity provides appropriate material distributions for elastodynamic cloaks but the required stiffness tensors generally violate the minor
symmetries of Cauchy elasticity and are difficult to realise using conventional materials. Existing approaches restore these
symmetries by modifying the transformed tensor, producing only an approximate cloak. In this work rather than modifying the transformed tensor we seek the best performing cloak within the class of Cauchy materials. We formulate 2D Rayleigh wave carpet cloak design as an optimisation problem governed by partial differential equations. Using a coordinate based neural-field and a differentiable finite element model solver we optimise symmetric stiffness and density fields by minimising wave field distortion. Both single frequency and broadband optimisation are considered, with the broadband model trained over multiple frequencies. Physical realisability is addressed using a database of homogenised microstructures through conditional
diffusion, neural-field inverse design, and nearest-neighbour selection. FEM simulations show that the optimised Cauchy design approaches the ideal transformation-based cloak. After projection onto explicit microstructures, the homogenised representation recovers approximately 97% of the defect free reference surface-displacement magnitude, while direct FEM simulation of the fully resolved microstructured geometry recovers approximately 76%
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All authors David Aznaurov, Davit Piliposyan, Danila Rukhovich, Sebastien Guenneau
Soft Condensed Matter
Glassy dynamics, crossover temperature and density scaling in fragile glass-formers
Ankit Singh, Vinay Vaibhav, Swarn Lata Singh et al. (+1 more)
We investigate the slowing down of dynamics in a glass-forming mixture interacting via an inverse-power-law (IPL) potential using a combination of theory and large-scale molecular dynamics simulations. We measure the static pair-correlation function, configurational
entropy, inherent-structure energy, and structural relaxation time. We employ a theoretical framework to calculate the structural relaxation time $\tau_{\alpha}$, which is found to be in very good agreement with the simulation results. The theory identifies a local structural order which defines the cooperativity of the relaxation and brings forth a fluctuation induced parameter $\psi ( T )$ and a crossover temperature $T_a$ that characterize the density and temperature dependence of the glassy dynamics. Furthermore, we determine a crossover temperature using independent dynamical and thermodynamic criteria and compare with the theoretically predicted crossover temperature $T_a$. Relaxation dynamics is shown to obey density-temperature scaling, similar to thermodynamic properties, in terms of a variable $\Gamma$ formed by an appropriate combination of density and temperature, characteristic of IPL interactions. Finally, we show that, when the excess thermodynamic and dynamic quantities obtained at different densities are plotted as functions of the reduced temperature $T/T_a$ (or $T_a/T$), the data collapse onto master curves with excellent agreement between theory and simulation. These scaling relations provide a unified description of the thermodynamics and dynamics in IPL systems, enabling the prediction of relaxation behavior over a wide range of densities from data at a single state point.
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All authors Ankit Singh, Vinay Vaibhav, Swarn Lata Singh, Yashwant Singh
Materials Science
Interfacial Accommodation as a Candidate Ductility Pathway in Intermetallic-Rich Alloys
Avik Mahata
Heterophase interfaces are increasingly recognized as active participants in plastic deformation, yet quantitative methods for comparing their strain-accommodation capacity remain limited. Here, we present an atomistic framework for quantifying interface-mediated strain accommodation using molecular dynamics simulations. Interface broadening, roughening, and migration are extracted from atomistic trajectories and combined into an Interface Accommodation Index, with a normalized counterpart accounting for differences in initial interface structure. A weighting sensitivity analysis demonstrates that the relative ranking of interfaces is robust to the specific form of the index. The framework is demonstrated for three experimentally motivated interfaces, Al/Al3Ti, Al/Al9M2, and Al9M2/Al3Ti (M = Fe, Co, Ni), under tensile, compressive, and shear loading. Bulk simulations show that Shockley partial dislocations dominate plastic deformation, with
alloy chemistry governing the transition toward mixed-character dislocation networks. Tensile loading produces the greatest interface accommodation, while shear produces comparatively limited structural
evolution. The Al9M2/Al3Ti interface exhibits both the highest yield resistance and the largest accommodation response, suggesting that intermetallic-intermetallic interfaces can simultaneously sustain load and redistribute strain. These simulations quantify structural accommodation rather than ductility or fracture directly; their connection to macroscopic ductility therefore requires experimental validation. The framework provides a transferable approach for comparing interface accommodation in multiphase
alloys and identifies interface chemistry and crystallography as important design variables for damage-tolerant structural materials.
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Strongly Correlated Electrons
Environment-assisted transport in a strongly correlated boundary-driven Fermi-Hubbard chain
Hakan Yeler and Özgür Çak{\i}r
We study steady-state transport in a one-dimensional Fermi-Hubbard chain coupled to particle reservoirs at the boundaries and to local dephasing baths at each site, using the time-evolving block decimation (TEBD) method to solve the Lindblad master equation. In the absence of dephasing, the current exhibits two well-separated maxima as a function of the boundary driving rate, reflecting the distinct charge and
spin energy scales of the strongly correlated regime. Upon introducing dephasing, we find two distinct dephasing-induced transport-enhancement regimes, in contrast to the single enhancement previously reported for spinless
fermions. Analysis of the non-
equilibrium steady state in the
Hamiltonian eigenbasis reveals that the two regimes originate from distinct dephasing-induced redistribution processes: the first involves redistribution within the uppermost Hubbard band, while the second involves transitions between Hubbard bands. Our results demonstrate how many-body correlations shape the interplay between coherent driving, dephasing, and
quantum Zeno physics in strongly correlated open systems.
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Materials Science
Semiclassical thermoelectric transport in disordered Dirac electron system Ag2Te
Kentaro Kuga, Keisuke Hirata, Daiki Goto et al. (+3 more)
We investigated the thermoelectric effects of the Dirac electron system Ag2Te under
magnetic field. Our anal-ysis based on the Boltzmann semiclassical model associated the disorder with the unconventional
magnetic field responses such as linear magnetoresistance, linear Nernst effect, step-like Nernst effect, and sign change in Nernst effect. The analysis also revealed the impurity band near the Fermi energy. We simultaneously clari-fied the serious impact of the thermal Hall effect on the measurement of the Nernst effect, and we proposed the definitive solution. Our careful measurement and analysis will be the standard for the thermoelectric study under
magnetic field.
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All authors Kentaro Kuga, Keisuke Hirata, Daiki Goto, Ryogo Ishihara, Masaharu Matsunami, Tsunehiro Takeuchi
Materials Science
Anharmonic Lattice Dynamics and Anisotropic Electron-Phonon Coupling in Quasi-1-Dimensional Charge Density Wave Ta2NiSe7
Prithwija Mandal, S. Nanthini, Aditya Singh et al. (+4 more)
The microscopic origin of charge density wave formation in quasi one dimensional Ta2NiSe7 remains actively debated, particularly regarding the relative contributions of Fermi surface nesting, electron
phonon coupling, and
lattice instabilities. Here, we combine temperature and orientation dependent polarized Raman spectroscopy with first principles calculations to uncover the anisotropic electronic and
lattice interactions governing the CDW state in Ta2NiSe7. Heat capacity and electrical transport measurements identify an incommensurate CDW transition at 61 K. Raman spectroscopy reveals pronounced in plane anisotropy, with e ph coupling strength along intrachain b axis exceeding five times that along interchain c axis, whereas
lattice anharmonicity is enhanced by threefold along c axis. First principles calculations identify Ta2 Se octahedral vibrations and Ta Se electronic states near the Fermi level as dominant channels mediating the anisotropic e ph interaction. Exceptionally strong and directional e ph coupling along b axis establishes
lattice driven electronic instability as the primary mechanism underlying CDW modulation and highlights the dominance of intrachain interactions in strongly coupled Ta2NiSe7. Despite this strong coupling, the CDW remains incommensurate, indicating that
lattice anharmonicity provides an additional degree of freedom. Enhanced anharmonicity along c axis suggests that anisotropic
phonon phonon interactions reshape the free energy landscape and contribute to stabilizing incommensurate phase. These findings reveal a cooperative interplay between anisotropic e ph coupling and
lattice anharmonicity in governing CDW formation in low dimensional
quantum materials.
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All authors Prithwija Mandal, S. Nanthini, Aditya Singh, Kewal S. Rana, Dibyendu Dey, Kanishka Biswas, Ajay Soni
Disordered Systems and Neural Networks · Cross-listed from cs.LG
Coarse-Graining Hidden Representations: Unsupervised Neuron Selection via Mapping Entropy
Margherita Mele, Andrea Castagna, Roberto Menichetti et al. (+2 more)
Overparameterized neural networks carry far more hidden units than a task nominally requires, raising the question of which
neurons are essential and whether that distinction is legible in the representation itself, without labels or gradients. We cast
neuron selection as the problem of coarse-graining the hidden layer by retaining a subset of its
neurons, and score each putative selection by the mapping
entropy (ME). This quantity measures the loss of discriminatory power inherent in discarding part of the network
neurons, and the selection that minimises the ME is taken as particularly informative. This criterion is fully unsupervised, in that it depends only on hidden-activation statistics. In teacher-student networks, ME optimisation recovers the minimal teacher-consistent representation and retains extra units in proportion to the hidden layer's residual variability; in a non-linear Gaussian process task, it selects coherent functional-class mappings whose preferred class shifts across training. On this task and on translation-augmented MNIST, ME-selected subnetworks outperform random subsets of equal size, most clearly under strong compression - linking configurational distinguishability to predictive performance.
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All authors Margherita Mele, Andrea Castagna, Roberto Menichetti, Raffaello Potestio, Alessandro Ingrosso
Statistical Mechanics
On the growth of operator entanglement in brickwork circuits with Yang–Baxter gates
Balázs Pozsgay
We study the operator
entanglement of local operators in one-dimensional brickwork
circuits whose two-site gate satisfies the braid relation; throughout this work, we call such a gate a Yang–Baxter gate. We establish upper bounds for several structured, overlapping classes of Yang–Baxter gates. We show that the operator Schmidt rank remains uniformly bounded in time for all
qubit Yang–Baxter gates and, in arbitrary local dimension, for permutation gates obtained from non-degenerate Yang–Baxter maps. We also show that it grows at most polynomially for involutive dual-
unitary Yang–Baxter gates and for arbitrary phase dressings of permutation gates obtained from non-degenerate Yang–Baxter maps. These results imply, respectively, constant and logarithmic upper bounds on the operator
entanglement. Conversely, we construct a seven-state involutive Yang–Baxter gate without dual unitarity and a one-site operator whose exact operator Schmidt rank grows exponentially, although the corresponding operator
entropies remain undetermined.
Entanglement growth in the general Yang–Baxter case remains open. All proofs and selected examples were constructed by ChatGPT 5.6 Sol.
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Materials Science
Symmetry-protected triplet Weyl complexes
Yun-Yun Bai, Ke-Xin Pang, Yan Gao et al. (+2 more)
The Nielsen-Ninomiya
theorem dictates that Weyl nodes must appear in pairs of opposite chirality to preserve global charge neutrality. However, in
crystals, specific crystalline
symmetries can stabilize multi-Weyl nodes, circumventing this pairwise constraint and enabling compensated Weyl complexes with mixed chiral charges. The minimal configuration of this type is a triplet Weyl complex (TWC), comprising exactly three Weyl nodes. Here, we systematically investigate the
symmetry conditions required to realize TWCs. By screening all 1651
magnetic space groups (MSGs) in both spinless and spinful systems, we establish that: (i) Only TWCs with charge magnitudes of $\{1,1,2\}$ and $\{1,2,3\}$ are permitted; (ii) the $\{1,1,2\}$ configuration can be realized in 166 spinless MSGs and 70 spinful MSGs; and (iii) the $\{1,2,3\}$-TWCs, which has not been reported before, can occur in 10 MSGs for both spinless and spinful cases. We explicitly demonstrate the existence of $\{1,2,3\}$-TWC in a tight-binding model. Furthermore, we present the first electronic realization of $\{1,1,2\}$-TWC topological semimetal state in the chiral carbon allotrope DZQH-C$_{36}$, in which the three Weyl nodes form a collinear configuration, leading to a characteristic “S”-shaped surface Fermi arc pattern. Our findings uncover novel topological states featuring mixed chiral charges and provide guidance for exploring their physics in concrete material systems.
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All authors Yun-Yun Bai, Ke-Xin Pang, Yan Gao, Weikang Wu, Shengyuan A. Yang
Materials Science
Cross-Layer Anomalous Hall Transport driven by Néel-Vector rotating in the Altermagnet candidate V2Te2O
Yanan Pan, W. Z. Zhuo, Pan Gao et al. (+7 more)
In van der Waals (vdW) materials, weak interlayer coupling generally suppresses vertical dispersion, reinforcing the conventional paradigm that in-plane transport dominates over cross-layer channels. Here, using first-principles calculations and
magnetic symmetry analyses, we uncover a giant,
symmetry-unlocked cross-layer anomalous Hall conductivity (AHC) in the vdW altermagnet V2Te2O. In the
magnetic ground state with Neel vector N//z, horizontal mirror
symmetry protects a
spin-polarized nodal chain near the Fermi level and strictly enforces zero anomalous Hall response. Tilting the Neel vector explicitly breaks this mirror protection, allowing
spin-orbit coupling to gap the nodal chain and activate a sharp cross-layer Hall response. When the Neel vector is rotated into the in-plane configuration (N//x), cross-layer orbital hybridization generates intensive Berry
curvature hotspots, boosting the cross-layer component of AHC {\sigma}_{yz} to approximately 255 S/cm, which exceeds in-plane component {\sigma}_{xy} by nearly two orders of magnitude. Furthermore, varying the azimuthal angle systematically redistributes the anomalous Hall response, enabling full directional control of transverse transport. Our findings demonstrate a highly sensitive cross-layer anomalous Hall switch activated by low-barrier
spin canting, offering promising avenues for directional tensor selection and low-power multi-axial vdW spintronics.
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All authors Yanan Pan, W. Z. Zhuo, Pan Gao, Ziyu Zhou, Junqing Xu, Lijie Shao, Damin Meng, Weiwei Chen, Zhongjun Li, Ye Yang