Superconductivity
Nodal nematic superconductivity in moiré graphene
Shuwen Sun, Grgur Palle, Kenji Watanabe et al. (+4 more)
Unconventional superconductivity can emerge in various forms in strongly correlated systems. Historically, the most extensively studied examples include nodal and triplet pairing, which were experimentally detected in cuprates and superfluid helium-3, respectively. Beyond these canonical cases, there are also nematic
superconductors, in which the rotational
symmetry of the
lattice is broken in the superconducting state. While there are several examples of nematic
superconductors whose pairing emerges inside a preexisting nematic normal state, experimental evidence for superconducting states that intrinsically break rotational
symmetry on their own has been exceedingly scarce. Here, we report the experimental realization and identification of an intrinsic multi-component nodal nematic superconducting state in magic-angle twisted trilayer
graphene (MATTG). By integrating tunneling spectroscopy with
quantum transport measurements, we directly probe the
symmetry of low-energy superconducting quasiparticles. Deep inside the superconducting state, we observe a pronounced two-fold anisotropy in the zero-bias tunneling conductance under an in-plane
magnetic field, which is strongly suppressed together with superconductivity as the temperature or perpendicular
magnetic field is increased. Remarkably, the major axis of anisotropy rotates by up to $90^{\circ}$ across the superconducting dome, indicating an intrinsic, field- and density-tunable
symmetry of the low-energy excitations. These behaviors imply a nodal superconducting state in MATTG that spontaneously breaks the six-fold rotational
symmetry of the moiré superlattice. Our results establish moiré
graphene as a versatile platform for realizing and interrogating nodal nematic superconductivity, opening a new avenue for exploring unconventional
symmetry-breaking superconducting states in two-dimensional materials.
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All authors Shuwen Sun, Grgur Palle, Kenji Watanabe, Takashi Taniguchi, Rafael M. Fernandes, Pablo Jarillo-Herrero, Jeong Min Park
Mesoscale and Nanoscale Physics
Landau quantization of $C_3$ high-fold fermions in honeycomb lattices
Luisa Madail and Joaquín Fernández-Rossier
We present the theory of the Landau levels of $C_3$ high-fold
fermions in honeycomb
lattices. These
fermions arise as a generalization of the tight-binding model in a honeycomb
lattice with one orbital per site, known to describe
graphene, to a family of models with several orbitals per site transforming according to representations of $C_3$, relevant for triangulene two-dimensional
crystals. The models are defined by the number of orbitals $n_a$ and $n_b$ at the $a$ and $b$ sites of the unit
cell. They feature energy bands that combine flat bands and Dirac cones, that are isomorphic to those of
graphene, the Lieb, $p_{xy}$ honeycomb, and the Kagome tight-binding models. Combining tight-binding and $k\cdot p$ methods, here we compute the Landau levels of the $(1,1)$, $(1,2)$, $(2,2)$ and $(3,3)$ models, we compare them to those of the reference models, and we explore the similarities and differences with the Landau levels in
graphene. Our findings reveal that the nature of $C_3$ high-fold
fermions combine Dirac-type Landau quantization, originating from the linear crossings and associated relativistic band dispersion, with anomalous Landau quantization rooted in the
quantum geometry of the singular flat bands.
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Statistical Mechanics
Droplets obstruct Onsager-type solutions of the Ising model in a magnetic field
Ran Luo and Jiahua Tian
Onsager solved the two-dimensional Ising model in zero field, but no solution is known in a
magnetic field. We prove that in any dimension $d\ge2$, at every fixed dimensionless field outside a countable set, the free energy obeys no algebraic differential equation in the coupling, even locally. The obstruction arises from droplet geometry: the maximal droplet volume grows as the $d/(d-1)$ power of its boundary size, while an integer band in the pressure coefficients protects the extremal contributions against cancellation. Our result excludes Onsager-type solutions and closed forms in elliptic, hypergeometric, or Painlevé functions of the coupling at these fields.
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Materials Science
Exchange Interactions and Magnon Spectra in bcc Fe(001) Thin Films: A Computational Study
Joanna Marciniak, Wojciech Marciniak, Jorge Luis Briseño-Gómez et al. (+1 more)
We combined density functional theory with atomistic
spin dynamics to understand how surfaces influence
magnon dispersion. For this purpose, we investigate thin layers of body-centered cubic iron and compare them with the bulk material. We present how the broken
symmetry affects exchange interactions and
magnon behavior. Our results reveal enhanced
magnetic moments and exchange interactions for surface atoms compared to bulk Fe. The increase in exchange interaction integrals is mostly visible for first- and second-nearest neighbors. We also find a significant spread in exchange values within each coordination shell.
Magnon dispersion analysis shows, for the layered system, pronounced band blurring, a significant reduction of maximum frequencies relative to the previously reported bulk values, and the emergence of a low-frequency band outside the \g{}-point. Our study shows that relying on bulk exchange parameters introduces errors in the
magnon spectra of ultrathin systems, underscoring the need for a detailed, system-specific approach.
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All authors Joanna Marciniak, Wojciech Marciniak, Jorge Luis Briseño-Gómez, Jan Rusz
Strongly Correlated Electrons
Metallic electron crystals in rhombohedral graphene as a bridge to twisted WSe$_2$
Wentai Deng, Chenyuan Li, Naoto Nakatsuji et al. (+4 more)
Superconducting phases have recently been discovered both in twisted bilayers of transition metal dichalcogenide WSe$_2$ (tWSe$_2$) and in rhombohedral multilayer
graphene (RMG). While both have generated extensive interest, they appear to be driven by qualitatively different physics. Here, we propose a unified picture in which the superconductivity in RMG arises from a strongly correlated metallic state with a spatial length scale that is compatible with the moiré length scale of tWSe$_2$. Central to this mechanism is a Wigner
crystal phase in RMG that is metallic, driven by a "W"-shaped dispersion in the flat part of the underlying
graphene band structure. We demonstrate this effect through calculations of Wigner
crystal states in pentalayer RMG, focusing on dilute electrons in the quarter-metal regime relevant to experiment. In a region of the phase diagram we find the Wigner
crystal breaks three-fold rotation
symmetry, which guides our construction of a $t$-$V$ model on a triangular
lattice as an effective description of the low-energy electronic physics. This construction suggests a surprisingly similar low-energy description of RMG and tWSe$_2$. Broader implications for superconductivity in dilute carrier systems are also discussed.
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All authors Wentai Deng, Chenyuan Li, Naoto Nakatsuji, Fang Xie, Lei Chen, Qimiao Si, Jennifer Cano
Materials Science
Growth-induced trade-off between polarity, electrical isolation, and structural quality in AlN grown on Si(111) by plasma-assisted molecular beam epitaxy
Hossein Yazdani, Nhu Tran, Xin Du et al. (+3 more)
We investigate the effects of substrate temperature and Al flux, at a fixed N flux, on the polarity, electrical properties, and structural quality of AlN films grown on high-resistivity Si(111) by
plasma-assisted molecular beam epitaxy. N-rich conditions result in relatively highly resistive Al-polar AlN/Si, whereas Al-rich conditions promote N-polarity and improved structural quality but simultaneously lead to increased p-type conductivity of AlN/Si stacks, consistent with unintentional Al doping of the Si substrate during AlN growth. Increasing the substrate temperature further improves the structural quality while enhancing the unwanted conductivity, revealing a growth-induced trade-off among polarity, electrical isolation, and structural quality. By reducing the substrate temperature to 575{\deg}C while maintaining slightly Al-rich conditions, an N-polar AlN/Si stack with a sheet resistance of 276 k{\Omega}/sq is achieved. These results provide guidelines for optimizing AlN/Si templates for various nitride device
heterostructures.
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All authors Hossein Yazdani, Nhu Tran, Xin Du, Vit Hornik, Roman Gröger, YongJin Cho
Strongly Correlated Electrons
Anyons at impurities: Fractional charge measurement and "wrong sign" binding
Haydn S. Adlong, Arthur Christianen, Atac Imamoglu et al. (+1 more)
Recent photoluminescence experiments in twisted MoTe$_2$ have reported signatures of anyons binding to trapped trions. The measured binding energies near the fractional Chern
insulators at fillings of $\nu=-2/3$ and $-3/5$ have a ratio close to the fractional-charge ratio $5/3$, even though such scaling is not generally guaranteed for the expected short-range trion-anyon interaction. We model the trapped trion as a fixed impurity, and investigate anyon-impurity binding using a lowest-Landau-level model with exact diagonalization and Jain wavefunctions. Surprisingly, we find that the anyon-impurity binding energy ratio between $\nu=-2/3$ and $-3/5$ is close to $5/3$ for either short- or long-ranged impurity-electron interactions. However, the ratio departs strongly from the charge ratio at intermediate ranges or different Jain states. Remarkably, we also uncover "wrong-sign" binding, whereby both quasiholes and quasiparticles can bind to either sign of a short-range impurity potential by selecting orbital channels with favorable local density oscillations. Our findings show that localized
excitons or trions can be used to probe the internal density profile of anyons.
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All authors Haydn S. Adlong, Arthur Christianen, Atac Imamoglu, Glenn Wagner
Materials Science
Structural identification in general crystalline systems via Voronoi cell topology
Emanuel A. Lazar and Chris H. Rycroft
Widely used methods for identifying
crystal structure in atomistic simulations are limited in practice to a handful of simple structures, leaving many important crystalline systems without automated classification techniques. Voronoi
topology analysis offers a route to classifying arbitrary crystalline and defect environments, but realizing this potential first requires enumerating the Voronoi
cell topologies that can arise under thermal perturbation of a structure of interest. We present an
algorithm that deterministically enumerates all Voronoi
cell topologies arising from generic infinitesimal perturbations of an arbitrary
crystal structure, producing structural classifiers that extend automated identification to general crystalline systems. We demonstrate the approach on several structures of general interest.
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Disordered Systems and Neural Networks
Testing Replica Symmetry Breaking in the three-dimensional Edwards-Anderson model by using vanishing fields
Miguel Aguilar-Janita, Silvio Franz, Victor Martin-Mayor et al. (+4 more)
Replica
Symmetry Breaking (RSB) theory for
spin glasses, which is exact in infinite dimensions, provides detailed predictions for the behavior of these systems. One of these predictions is that vanishing
magnetic fields induce chaotic behavior. Here, vanishing has a precise meaning: we refer to an externally applied
magnetic field with intensity scaling as $1/\sqrt{N}$, where $N$ is the number of
spins in the system. RSB predicts that this chaotic behavior depends only on the probability density function of the overlap, $P(q)$, as computed at zero field. We proceed to test the RSB prediction in the 3D Edwards-Anderson model, by first computing the $P(q)$ numerically in the absence of a
magnetic field. We then use this function as input to analytically compute the statistics of the states in the regime of a vanishing
magnetic field, using a representation based on the Bolthausen-Sznitman coalescent process (which is exact for the mean-field Sherrington-Kirkpatrick model). This mixed numerical-analytical approach allows us to determine the prediction of RSB for the overlap distribution function measured in the presence of a small vanishing field, as well as the increase in chaoticity as the field strength grows. The above RSB predictions are quantitatively compared with the outcome of numerical simulations of the three-dimensional Edwards-Anderson in the presence of a small vanishing field, finding very good agreement. This agreement provides strong support for the idea that three-dimensional
spin glass at zero
magnetic field and low temperature is well described by RSB theory.
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All authors Miguel Aguilar-Janita, Silvio Franz, Victor Martin-Mayor, Javier Moreno-Gordo, Giorgio Parisi, Federico Ricci-Tersenghi, Juan J. Ruiz-Lorenzo
Statistical Mechanics
Physical limits to stochastic classifiers
Timur Aslyamov and Massimiliano Esposito
Stochastic physical computers use random transitions between states to process inputs. We quantify their ability to solve distinct tasks as the control parameters of a device vary. For Markov jump devices, we bound the number of classification tasks attainable at a prescribed output margin, with each task defined as a binary labeling of fixed inputs. Combining
geometric packing with fluctuation-response inequalities, we bound this number in terms of the control range and dimension, rate sensitivities, output fluctuations, and
entropy production. For state and net-current observables, when controls change kinetics without changing thermodynamic forces and energies, the number of tasks is shaped by
entropy production and output fluctuations. If the product of their maximum values over the allowed control settings and inputs is too small, the device can perform at most one task. An exactly solvable two-state switch illustrates how sufficient driving and observation time enable barrier tuning to select copying or inversion.
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Superconductivity
Magnetic Susceptibility of Superconducting Films in the Meissner-London Regime
Ruslan Prozorov
Extracting the London penetration depth, $\lambda(T)$, from the measured
magnetic susceptibility, $\chi(T)$, of a superconducting platelet in a perpendicular
magnetic field requires knowing the function $\chi(\lambda)$ computed for the actual sample geometry. Thin films are increasingly important in
quantum computing and superconducting electronics, most of which operate at ultra-low excitation fields in the
vortex-free regime. Understanding their electromagnetic response in the Meissner–London (finite-$\lambda$, no
vortices) state is therefore essential for extracting intrinsic properties such as the London penetration depth and superfluid phase stiffness. While numerous prior works have addressed different aspects of this problem, here we focus on providing an analytical semi-empirical representation of $\chi(\lambda)$ based on the 2D sheet-current model and establishing the limits of its applicability using two independent full 3D numerical solutions: finite-element modeling and a volume-current integral equation. As a result, we provide $\chi(\lambda)$ for a disc of radius $a$ and thickness $d$ in closed form, valid for all $\lambda$ and for aspect ratios $\delta\equiv d/(2a)\le0.05$, and accurate to $0.1\%$. The two-dimensional sheet description with Pearl length $\Lambda=2\lambda^2/d$ is adequate for $\delta \lesssim10^{-4}$ and $\lambda \gtrsim 4d$. Thicker films require the full closed form, which includes the three-dimensional corrections. Using the same numerical analysis, we provide an empirical formula that maps rectangular samples—the geometry most commonly used in experiments—onto a disc with an “effective radius” for subsequent calculation of $\chi(\lambda)$, and formulate a complete calibration protocol for whole-sample susceptibility measurements.
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Mesoscale and Nanoscale Physics
Orbitronics in Zero-dimensional Graphene Nanoflakes via Electrode Coupling
Washington F. dos Santos, Eudes Gomes da Silva, Denis R. Candido et al. (+1 more)
We show that
graphene nanoflakes realize a previously unexplored form of orbitronics in which orbital currents emerge in the absence of intrinsic angular momentum of the constituent atoms. Starting with a hexagonal
graphene nanoflake, we demonstrate the presence of energy-degenerate eigenstates with opposite non-zero expectation values of the angular momentum. Placing electrodes in an appropriate configuration on the flake couples the reservoirs more strongly to one of the two opposite-angular-momentum states, yielding a chiral current that carries a net orbital angular momentum. The resulting circulating orbital currents generate
magnetic fringe fields that are experimentally accessible with
spin centers or superconducting
quantum interference magnetometers, providing avenues for their experimental realization. Finally, our work establishes a new platform for exploring and studying orbitronics in zero-dimensional systems.
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All authors Washington F. dos Santos, Eudes Gomes da Silva, Denis R. Candido, Alexandre Reily Rocha
Strongly Correlated Electrons
Large-Tiny Spin-Stripe SDW Order in La$_3$Ni$_2$O$_7$ via $^{139}$La-NQR Spectroscopy: Reconsideration Based on the $Am2m$ Structure
Mitsuharu Yashima, Hongnam Lee, Takumi Ino et al. (+5 more)
The lower-
symmetry $Am2m$ structure was recently proposed as the intrinsic ambient-pressure phase of La$_3$Ni$_2$O$_7$ based on synchrotron x-ray diffraction, whereas earlier studies investigated its properties assuming the commonly accepted $Amam$ structure. Here, we reexamine the
crystal structure in La$_3$Ni$_2$O$_7$ and the
spin configuration of
spin-density-wave (SDW) state via $^{139}$La nuclear quadrupole resonance (NQR). The observation of two distinct La(2) sites in the NQR spectra is naturally accounted for by the $Am2m$ structure without any special assumptions, whereas it cannot be reconciled within the $Amam$ framework. Within the $Am2m$ framework, we reanalyze the
spin configuration of the SDW phase and identify it as a large-tiny
spin-stripe structure, arising naturally from two inequivalent Ni sites with large and tiny
magnetic moments. These results establish the itinerant nature of the SDW order at ambient pressure in La$_3$Ni$_2$O$_7$, providing a basis for understanding its relationship to the emergence of high-$T_c$ superconductivity under high pressure.
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All authors Mitsuharu Yashima, Hongnam Lee, Takumi Ino, Nina Seto, Masataka Kakoi, Hiroya Sakurai, Yoshihiko Takano, Hidekazu Mukuda
Quantum Gases
Universal enhancement of the pairing gap in a dilute Fermi superfluid
Silas R. Beane, Roland C. Farrell and Cameron P. Shotwell
At zero temperature, a dilute Fermi gas with an attractive contact interaction forms a superfluid with gapped fermionic excitations. We show that the gap at weak coupling can be organized as a trans-series expansion in the interaction strength and the asymptotic Gor'kov-Melik-Barkhudarov gap. Low-energy virtual quasiparticles generate corrections that are linear in the gap with a leading coefficient nearly 25$\times$ larger than the other known coefficients. This substantially increases the gap at intermediate densities, highlighting that systematic corrections are crucial for quantitative predictions.
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Statistical Mechanics · Cross-listed from math.PR
Asymptotic behaviour for escaping an interval by Lévy flights under stochastic resetting
Bartosz Zbik and Zbigniew Palmowski
The resetting of
stochastic processes has become a key mechanism appearing in many research fields, such as searching for a target, the transmission control protocol, biology, chemistry, finance, insurance, etc., with the main interest concerning the first passage time (FPT) by the process under resetting. In this paper, we focus on the exit time $\mathcal{T}_L$ from the interval $(-L, L)$ of Lévy flights (LF) under resetting, but we also consider spectrally negative Lévy processes (SNLP). As the main result, we find the asymptotics of the mean first passage time (MFPT) as $L$ tends to $+ \infty$. For LF with $\alpha \in (0, 2)$, the scaling behaves as $L^\alpha$ regardless of the reset rate and the asymmetry of the initial condition, a behaviour completely different from that for the known case of Brownian Motion ($\alpha=2$). For the symmetric $\alpha$-stable case with $\alpha \in (0, 2)$, we also found that taking $r \to \infty$ with fixed $L$ yields a finite MFPT, which therefore may be used as a valid approximation. For completely asymmetric stable processes, we show that the scaling is very different from that for LF, and point out a method to obtain the exact distribution of FPT under resetting. The analytical calculations are verified by numerical simulations of the processes under resetting.
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Strongly Correlated Electrons
Influence of the Néel vector on the bulk electronic structure of MnTe measured from the $(1 \bar1 00)$ surface
D.A. Usanov, A.B. Hellenes, S. Hahn et al. (+7 more)
Altermagnetism gives rise to momentum-dependent
spin splitting without net magnetization. Here, we use angle-resolved photoemission spectroscopy (ARPES) to investigate bulk $\alpha$-MnTe single
crystals cleaved along the $(1\bar{1}00)$ plane - an orientation that preserves the compensated
magnetic symmetry at the surface and substantially reduces surface effects and $k_z$ broadening. We resolve the three-dimensional bulk band structure with markedly enhanced spectral clarity. The $d$-wave band splitting, driven by the altermagnetic order and
spin-orbit coupling in the $\mathbf{\Gamma}-\mathbf{K}-\mathbf{M}$ nodal plane, shows a perfect match to theoretical predictions. We further establish that the valence-band maximum occurs near the $\mathbf{A}$ point, identifying the corresponding hole pockets as the states governing the transport properties. Spatially resolved measurements reveal systematic variations of the band dispersion along $\mathbf{\Gamma}-\mathbf{K}$ and $\mathbf{A}-\mathbf{L}$, associated with different pinning of the Néel vector at the surface. Our results establish a surface-sensitive route to resolving the bulk altermagnetic electronic structure of MnTe and provide direct spectroscopic evidence for Néel-vector-dependent band splitting.
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All authors D.A. Usanov, A.B. Hellenes, S. Hahn, M. Leandersson, J. Osiecki, K. Uhlířová, D. Evtushinsky, L. Šmejkal, T. Jungwirth, J.H. Dil
Quantum Gases
Analog Cosmology in a Quenched Bose-Einstein Condensate Bubble
Ruotong Zhai, Brendan Rhyno, Zain Mehdi et al. (+3 more)
Recent interest and realization of ultracold
bosons confined in shell-shaped, or bubble, traps have opened up several directions in the study of Bose-Einstein condensates (BECs) in intrinsically curved geometries. Here, we explore the prospect of using thin spherical shell-shaped BECs as analog
gravity simulators of an expanding or contracting curved universe. We study an interacting BEC bubble subject to a temporal quench of the interaction strength. Our theoretical approach, which uses a Bogoliubov treatment following a dimensional reduction of a spherical BEC to the low-energy excitations of a shell-shaped structure, demonstrates how this system serves as a laboratory analog for a positively curved universe having a time-varying scale factor. We investigate spontaneous pair production triggered by quenches associated with exponentially decaying or growing interaction strengths, focusing on the emergence of oscillations in the structure factor—analogous to Sakharov oscillations in the
Cosmic Microwave Background angular power spectrum. We quantify the
entanglement of the produced pairs via logarithmic negativity, and show how this measure may be extracted from the power spectrum. These findings establish a bridge between
quantum information science and early-universe cosmology in a laboratory setting.
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All authors Ruotong Zhai, Brendan Rhyno, Zain Mehdi, Naceur Gaaloul, Smitha Vishveshwara, Daniel E. Sheehy
Mesoscale and Nanoscale Physics
Designing Hamiltonians with Exactly Flat Higher-Vortexable Bands
Daniel Spasic-Mlacak and Nigel R. Cooper
The zero modes of the Aharonov-Casher
Hamiltonian form an exactly flat, vortexable Chern band in any nonuniform
magnetic field, analogous to the lowest Landau level. We ask which local
Hamiltonians host exactly flat higher-vortexable bands. For a scalar
Hamiltonian, an exactly flat first-vortexable band requires a mass proportional to the local field; the Dirac analogue has the same structure. For periodic Bernal bilayer
graphene with nonzero mean flux, the exact zero-mode pair is genuinely first-vortexable if and only if the interlayer hopping has nonzero mean; zero-mean hopping instead gives a decomposable pair. Multiorbital models yield exact higher-vortexable chains to arbitrary order, while remaining first order in momentum.
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Soft Condensed Matter
Effective Graph Neural Representation of Chain Architectures of Block Copolymers Tested by Predicting RPA Instability Limits
Xiyue Zhang, Yutong Wu and Yi-Xin Liu
Advances in
polymer synthesis and computational modeling are expanding the block-copolymer architecture space accessible for phase-behavior design. Machine learning can accelerate this exploration, yet a common representation capable of learning across diverse chain
topologies remains lacking. Here, we present a graph neural network (GNN) representation of acyclic AB multiblock architectures, tested by random-phase approximation (RPA) instability prediction. Each chain is represented as a graph, enabling a common model to learn across diverse
topologies. This representation, which organizes RPA-related information, retains predictive capability when extrapolated to architectures with more blocks and demonstrates its potential for reuse across tasks through transfer to instability-wavenumber prediction. By effectively linking block-copolymer chain architecture to field-theoretic response, this graph representation not only reconstructs stability-limit curves but also provides a practical route for future self-consistent field theory exploration of ordered phase space across complex
topologies.
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Materials Science
Modeling electrodeposition of thin films with compact, dendritic, and random morphologies
Fábio D. A. Aarão Reis, Dung di Caprio, Sidiney G. Alves et al. (+1 more)
We summarize previously published computer simulation studies of a metal electrodeposition model that considers diffusive cation flux, a fast reaction in contact with the electrode or with the growing deposit, and adsorbed atom
diffusion in finite time windows. Simulations with various parameters show compact, fractal, dendritic deposits, and dynamic transitions between different morphologies during the growth of individual samples. The dendritic shapes are characterized by hierarchical organizations in which branches of a given order reproduce the shape and crystalline orientation of the branches of the previous order, in contrast to the random branching of the fractal deposits formed by DLA and related models. The simulations show dendrites with maple leaf shape in SC
lattices, pine tree shape in FCC
lattices, and flower-like shape in HCP
lattices, with surfaces predominantly oriented in the lowest-energy configurations of each
lattice. Simulations with nucleation restricted to a nanoscale seed show the initial formation of faceted particles followed by dendrite formation, in agreement with silver electrodeposition on substrates patterned with gold nanoparticles. A quantitative application to faceted and dendritic silver obtained in the same experiment provides values of the model parameters which are consistent with the characteristic widths of these structures being of the same order of magnitude of the
diffusion lengths of atoms on (111) and (001) surfaces. Using an extended model for iron electrodeposition on Si(100), the simulations qualitatively reproduce the initial formation of multilayer islands, small oscillations of the roughness of a polycrystalline compact film after island coalescence, and instability development. Possible directions for applying this modeling to the electrodeposition of other materials are suggested.
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All authors Fábio D. A. Aarão Reis, Dung di Caprio, Sidiney G. Alves, Ismael S. S. Carrasco
Soft Condensed Matter
Dynamic morphing of non-Euclidean active shells enabled by flutter under a steady stimulus
Roberto Marchello, Pietro Maria Santucci and Giovanni Noselli
Synthetic active surfaces are usually designed to attain a prescribed static configuration, with dynamic shape changes typically requiring modulation of the actuation. We show that thin active shells can instead sustain dynamic morphing under a steady stimulus by harnessing flutter instability. We focus on polyelectrolyte hydrogel shells immersed in a viscous fluid and subjected to a constant and uniform electric field, and specialize the non-Euclidean framework for thin structures to account for field-induced activity through a spontaneous
curvature evolving in time with the system configuration. Examining elliptic plates and cylindrical shells as test cases, we integrate linear stability analyses with nonlinear simulations to first locate the onset of flutter and then unveil the resulting dynamics, characterized by thrust-generating shape changes. In all cases, the emergent behavior stems from the interplay between active reconfiguration and elasticity in the fluid environment. For plates, the problem is purely flexural in the linear regime, while the competition between bending and stretching becomes crucial in selecting the ensuing shapes and swimming trajectories at large deformations. Conversely, for cylindrical shells bending and stretching are coupled at all levels, with the latter becoming essential to sustain flutter. Experiments on millimeter-sized hydrogel plates provide tangible support for our theoretical findings through shape reconstructions performed by combining digital image correlation with optical stereo microscopy. Flutter thus offers a route to untethered soft robotic and microfluidic devices based on active shells and operating under a stimulus carrying neither an intrinsic frequency nor a characteristic length scale.
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Mesoscale and Nanoscale Physics
Coherent and dissipative coupling of multiple photon-magnon hybrids in a chiral microwave resonator
Supanat Chantarattana, Charlie W. F. Freeman, Daniel Prestwood et al. (+3 more)
We demonstrate control between level repulsion and level attraction of
photon-
magnon coupling spectra in a chiral microwave-
photon resonator loaded with a 2 mm YIG sphere. By systematically varying the coupling mode volume via the YIG position and the dc-field orientation, we tune the ratio between coherent and dissipative coupling strengths, $J/\Gamma$, and thereby switch between level repulsion and level attraction in the hybrid spectra. Full-wave electromagnetic and magnetization-dynamics simulations reveal multiple
photon-
magnon hybrid modes with distinct spatial overlap factors, which quantitatively account for gap sizes and their angular dependence. Strong nonreciprocity appears near $J/\Gamma \approx 1$, yielding 28.6 dB isolation ratio in agreement with a unified single-bath input-output model and full-wave simulations. Angular dependence of spectral characterization confirms a picture of the chirality-selection rule and our method of
geometric tuning might be useful for considering reconfigurable on-chip isolators.
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All authors Supanat Chantarattana, Charlie W. F. Freeman, Daniel Prestwood, Nimisha Arora, Vincent Castel, Hidekazu Kurebayashi
Mesoscale and Nanoscale Physics
Making Weak Interlayer Excitons Absorb: Manipulating the Effective Oscillator Strength via Purcell Engineering of Critical Coupling
Saroj Poudyal, Anabel Atash Kahlon, Michael Klein et al. (+7 more)
Interlayer
excitons (IXs) in transition metal dichalcogenide bilayers possess unique dipolar properties, providing a path for exploring correlated many-body phases, electrically tunable dipole-dipole interactions, and long-range
exciton transport. However, the large electron-hole separation underlying their dipolar character also results in a significantly reduced oscillator strength, limiting their direct optical interaction with light, and thus the direct probing of their dynamics and many-body interactions. Here, we show that by using Purcell engineering of critical coupling, a weak interlayer transition can absorb as strongly as the dominant intralayer transition, despite its much smaller intrinsic oscillator strength. Using this approach, in an open cavity architecture we demonstrate an order of magnitude IX absorption modulation in bilayer and trilayer MoS2, with doubling of the IX to A-
exciton interaction strength weight from ~23% to ~53%. Furthermore, we demonstrate that in a tailored closed cavity architecture, the IX enhancement can reach beyond an order of magnitude, from ~5% to ~83% excitonic absorption, enabling IX absorption similar to intralayer
excitons. An analytical description of the interaction is obtained via a closed-form transmission-line model which separates the excitonic and photonic contributions to the optical response, revealing how cavity architecture can be designed towards critical coupling. Our findings establish Purcell engineering of critical coupling as a general route to controlling and enhancing weak excitonic transitions.
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All authors Saroj Poudyal, Anabel Atash Kahlon, Michael Klein, Matan Meshulam, Yonatan Gershuni, Thomas Poirier, James H. Edgar, Mukesh Kumar, Seth Ariel Tongay, Itai Epstein
Soft Condensed Matter
A Sideways Crack-Path Instability Amplified by Slow Loading
G. Pallares, O. Ramos and L. Vanel
Crack-path instabilities in solids are typically associated with high propagation velocities. In contrast, we show that nanoparticle-filled elastomers exhibit a sideways crack-path instability that is amplified as the pulling velocity decreases and nearly vanishes at high pulling velocities. The sideways deviation amplitude decreases logarithmically with increasing pulling velocity and scales as the square root of the filler fraction. Large deviations develop at low mean crack velocities and are associated with effective fracture energies up to two orders of magnitude lower. These findings are consistent with subcritical rupture kinetics and suggest that the deviation amplitude is limited by the elasto-adhesive length.
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Statistical Mechanics · Cross-listed from physics.bio-ph
Memory-resolved prediction of ligand residence times on the minutes timescale
Hossein Batebi, Lucas Tepper and Roland R. Netz
AI-enabled computational drug discovery is advancing rapidly in predicting molecular structures, binding poses and affinities, but ligand dissociation kinetics remain harder to access. Bound-state residence time, important for biological response and kinetic selectivity, is not fixed by
equilibrium affinity but depends on the dissociation free-energy landscape and dissipative friction effects. Here, we show that restrained umbrella-sampling trajectories can be used to calculate residence times on the minutes timescale. Time-resolved coordinate fluctuations yield friction profiles that incorporate non-Markovian effects on dissociation kinetics. Combining them with the free-energy profile, we predict a residence time of $\tau_{\rm res}$ = 275 s for the adenosine A$_{2A}$ receptor with ZM241385 (comparable to the experimental value of 125 s) and reproduce the experimental ranking of wild type and two receptor mutants. For HSP90 with compound 18 and RNase S with the S15 peptide, we predict $\tau_{\rm res}$ = 2,169 s and 2,259 s (experimental values are 833 s and 2,439 s). Neglecting
memory effects on residence kinetics overestimates $\tau_{\rm res}$ by factors of 2.6 to 29.
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Superconductivity
Transport regimes in tunnel ferromagnetic Josephson junctions
R. Satariano, A. A. Golubov, E. Raja et al. (+13 more)
We present a systematic study of the temperature-dependent transport properties of Nb- and Al-based
superconductor–
insulator–thin
superconductor–ferromagnet–
superconductor (SIsFS) Josephson junctions. By varying the superconducting material and the thickness of the intermediate superconducting layer, we identify three distinct transport regimes: a tunnel-dominated SIS-like regime, a temperature-driven crossover, and a complex weak-link regime. A unified Usadel-based description connects these regimes through the self-consistent pair potential of the intermediate s-layer. While for Al-based devices an SIS-like transport regime is observed, a self-consistent calculation of the s/F/S proximity electrode, combined with perturbative tunnel coupling to the outer electrode, accounts for Nb devices with different thickness of the superconducting interlayer. The calculation places the 10-nm-interlayer sample in a proximity-supported, strongly suppressed s state, close to the SInFS limit in which the interlayer is effectively driven normal (n). A reduced nonlinear long-junction description captures the same limiting physics. The
evolution of I_cR_N(T) thereby provides a direct experimental signature of the three transport regimes. Beyond the fundamental interest, the results establish practical design guidelines: Nb junctions with sufficiently thick s interlayers are well suited for high-speed cryogenic
memory elements and tunable superconducting parametric amplifiers, while Al junctions are natural candidates for coherent superconducting
quantum circuits
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All authors R. Satariano, A. A. Golubov, E. Raja, R. Ferraiuolo, F. Calloni, H. G. Ahmad, A. Vettoliere, N. Poccia, L. Parlato, G. Ausanio, C. Granata, G. P. Pepe, M. Yu. Kupriyanov, F. Tafuri, D. Montemurro, D. Massarotti
Superconductivity
Bulk superconductivity in quintuple-layer square-planar nickelate La6Ni5O12
Mengzhu Shi, Mei Du, Hongyu Li et al. (+5 more)
Nickelate
superconductors, sharing a similar electronic environment with cuprate
superconductors, offer a promising platform for unraveling the mechanism of high-temperature superconductivity. However, the realization of superconductivity in these systems has so far been restricted to thin films or bulk samples under high-pressure. This limits the applicability of various experimental probes to study the mechanism of superconductivity, and hinders the potential application of the nickelate
superconductors. Exploring bulk superconductivity at ambient pressure is therefore essential to understand its origin and enable broader experimental research. Here, we report the realization of bulk superconductivity at ambient-pressure in quintuple-layer square-planar (SP) nickelate La6Ni5O12. The SP phase is obtained by performing topotactic reaction on the quintuple-layer Ruddlesden-Popper (RP) compound La6Ni5O16. Optimized reduction condition endows La6Ni5O12 with a superconducting state that exhibits onset transition temperature of ~ 18 K, as verified by both zero resistance and diamagnetic shielding effect. Pronounced hysteresis loops revealed by magnetization and torque magnetometry demonstrate the occurrence of
vortex pinning. Specific heat measurements on a polycrystalline pellet of La6Ni5O12 reveal a clear superconducting transition at ~18 K and a superconducting volume fraction of ~ 25%, which strongly supports the presence of bulk superconductivity. Our results establish an unprecedented bulk sample platform for investigating superconductivity in nickelates at ambient pressure, which paves the way for further experimental studies into the superconducting mechanism.
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All authors Mengzhu Shi, Mei Du, Hongyu Li, Zhiwei Wang, Zhengjie Wang, Ziji Xiang, Tao Wu, Xianhui Chen
Materials Science
A Topological\-Geometrical Descriptor (TGD) for Scalable and Interpretable Modeling of Two\-Dimensional Carbon Networks
Rômulo Uriel Liberal de Oliveira and Raphael Matozo Tromer
We introduce a compact Topological-Geometrical Descriptor (TGD) for planar two-dimensional carbon networks. Atomic coordinates are mapped to a periodic planar graph and represented through ring populations, topological-charge statistics, projected ring geometry, and dual-graph defect adjacency. The resulting modeling vector contains 19 physically interpretable features. We evaluate TGD on 120 published planar carbon allotropes using the DFT relative energy per atom with respect to
graphene as the target. Repeated five-fold cross-validation with gradient boosting yields a mean absolute error (MAE) of 0.0826 +/- 0.0138 eV/atom and R2 = 0.803 +/- 0.074. Under the same validation protocol, TGD gives a mean MAE of 0.0828 eV/atom, compared with 0.0929 eV/atom for a 203-feature Matminer representation. We further analyze 360 vacancy-defected
graphene configurations spanning 12 vacancy concentrations from 2 to 24 percent. When entire vacancy concentrations are held out, TGD gives a pooled MAE of 0.269 eV/vacancy and R2 = 0.861, outperforming simple baselines based on vacancy concentration alone or non-hexagonal-ring fraction alone. Sensitivity tests show that the inferred edge sets are stable to moderate changes in the adaptive bond factor. Finally, the mean absolute topological charge is examined as a one-variable empirical surrogate for the allotrope
dataset and is treated explicitly as
dataset-specific rather than universal. These results show that TGD combines compact prediction with direct structural interpretation while making clear the present restriction to single-layer planar carbon networks.
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Materials Science
High-Frequency Mass Transfer Enabling Over-Limiting Currents in Porous Electrodes
Md Abdul Hamid and Kyle C. Smith
Classical film theory predicts a finite
diffusion-limited current at porous electrodes. However, over-limiting currents (OLCs), which exceed this limit, are often observed and have been attributed to surface charge, confinement, or electrokinetic effects. Here, we use a frequency-domain framework to identify a different mechanism governed by the time scale of concentration variation. For perfectly reactive interfaces, the spectral Sherwood number, a frequency-dependent dimensionless measure of interfacial mass transfer relative to molecular
diffusion, grows as $\Shnd\sim\omega^{1/2}$ at high frequency, while its phase approaches $\pi/4$. This response corresponds to the semi-infinite Warburg limit of the electrochemical impedance. A scaling analysis shows that the exponent and prefactor are determined by
diffusion within a thin layer adjacent to the interface and are therefore independent of the global pore geometry. Numerical results for parallel plates, circular tubes, and twelve porous microstructures confirm this scaling. Geometry, flow strength, and flow direction affect the low-frequency response and crossover frequency, but not the asymptotic scaling in the high-frequency limit. This temporal route to OLCs requires neither surface charge nor confinement and could inform the design of systems for pulsed electrodeposition, mineral recovery and renewable-energy storage.
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Materials Science
Access Rate-Dependent Endurance Behavior of Ferroelectric Hafnium Zirconium Oxide Capacitors
Roberto Guido, Julie Laguerre, Pramoda Vishnumurthy et al. (+6 more)
Fluorite-structured ferroelectrics, such as hafnium zirconium oxide ($Hf_{1-x}Zr_{x}O_{2}$), are among the most promising materials for developing the next generation of low-power nonvolatile
memories. Emulating realistic operating scenarios for ferroelectric
memories requires performing access rate-dependent endurance tests. The access rate-dependent reduction of the switched polarization cannot be described as a mere superposition of fatigue and imprint effects, which are observed in conventional endurance and retention tests, respectively. The interplay between these degradation mechanisms and its correlation with the delay time in between the programming pulses remains unclear. Combining electrical testing through voltage pulses with ab initio and drift-
diffusion simulations provides a comprehensive perspective on the microscopic origin of the access rate-dependent reduction of the switched polarization of ferroelectric capacitors based on product-relevant 5 nm thick $Hf_{0.5}Zr_{0.5}O_{2}$ films. The role of oxygen vacancy defects accumulating at the electrode-ferroelectric interface with delay time in reducing the fraction of switchable domains is elucidated considering electron transfer processes which change the defect charge state. Building upon this theoretical understanding, a physics-based model to extrapolate the long-term access rate-dependent endurance performance is developed and experimentally verified for temperatures up to 135{\deg}C and delay times up to 2 ms.
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All authors Roberto Guido, Julie Laguerre, Pramoda Vishnumurthy, Florian Wunderwald, Kristina Holsgrove, Thomas Mikolajick, Sou-Chi Chang, Alfred Kersch, Uwe Schroeder