Soft Condensed Matter · Cross-listed from physics.optics
Label-free quantitative imaging of two-dimensional concentration gradients using Fabry-Pérot interferometry
Taieesa Peshkovsky, Stefan Andreas Schmid, David Taylor et al. (+3 more)
Concentration gradients at the microscale play a central role in many physical, chemical, and biological systems, yet their quantitative visualization remains challenging due to the limited optical contrast associated with changes in concentration. Here, we present RIO (the Refractive Index Observer), a label-free interferometric tool for quantitative imaging of refractive index, and thus concentration fields in microfluidic systems. Implemented using a Fabry-Pérot microfluidic chip mounted on a standard optical microscope, RIO achieves a per-pixel refractive index precision on the order of $1\times 10^{-5}$ refractive index units (RIU) using a standard CMOS camera, enabling high sensitivity two-dimensional chemical imaging. We Characterize the refractive index resolution and spatiotemporal performance of the instrument and demonstrate its capabilities by measuring concentration gradients of dissolved NaCl in a co-laminar flow. RIO provides an accessible, label-free platform for quantitative studies of microscale concentration fields in systems where molecular labeling is undesirable or impractical, and enables investigations of a broad range of out-of-
equilibrium phenomena, from polymerization and enzymatic reactions to
cell signaling and electrochemical processes.
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All authors Taieesa Peshkovsky, Stefan Andreas Schmid, David Taylor, Robert W. Style, Lucio Isa, Federico Paratore
Statistical Mechanics
Exactly solvable Russian-doll model: Renormalization-group cycles meet fractality
Ilya Liubimov and Alexander Gorsky
We consider the Bethe ansatz integrable Russian Doll (RD) model of superconductivity with time-reversal
symmetry breaking, which exhibits a cyclic renormalization group. By obtaining an exact solution for the renormalization group flows, we investigate the phase structure in the one-pair sector, which includes localized, fractal, and delocalized phases. We show that the
quantum number Q, arising from the Bethe ansatz equations, counts the number of cycles and parametrizes the towers of states. Using the action of the renormalization group on the eigenstates, we demonstrate that Q serves as an order parameter, providing a new mechanism for the formation of the fractal phase in the deterministic systems and an example of the interplay between fractality and cyclic RG.
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Superconductivity
Superconducting Lanthanum Nickel Oxides with Bilayered and Trilayered Crystal Structures
Hiroya Sakurai and Yoshihiko Takano
In 2023, superconductivity in La$_3$Ni$_2$O$_7$ was discovered under high pressures above approximately 14 GPa. In addition to its high transition temperature ($T_{\mathrm{c}} \simeq 80$ K), the structural resemblance to high-$T_{\mathrm{c}}$ cuprates has strongly stimulated research, soon followed by the discovery of superconductivity in La$_4$Ni$_3$O$_{10}$. These compounds belong to the Ruddlesden–Popper phases, comprising double- and triple-layered NiO$_2$ square
lattices separated by LaO rock-salt slabs. Research on these systems has rapidly developed along three major directions, as in other prominent families of
superconductors such as the cuprates and iron arsenides: expanding the chemical variety of compounds, enhancing $T_{\mathrm{c}}$ through elemental substitution, and elucidating the superconducting mechanism. These challenges, being closely interconnected, continue to drive the field. The clarification of the pairing mechanism encounters a particular difficulty, since the key experiments must be performed under high pressures. This situation highlights the significance of developing nickel
oxides that exhibit superconductivity at much lower pressures, ideally at ambient pressure, which would in turn broaden the scope of chemical tuning and detailed physical characterization. In this context, it is timely and meaningful to summarize the present state of knowledge. Here, we emphasize sample synthesis and characterization, which are already well established and often decisive for progress in unconventional
superconductors, while providing a brief overview of the currently available electronic properties.
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Quantum Gases · Cross-listed from quant-ph
Implementation of non-local arbitrary two-qubit controlled gates via geometric quantum computation with Rydberg anti-blockade
Le-Jiang Yu, Jia Zheng, Kun Pu et al. (+1 more)
In the context of Rydberg anti-blockade, this paper proposes a new scheme for a high-fidelity controlled-
unitary gate based on non-adiabatic holonomic
quantum computation. Under specific detuning and interaction conditions, the scheme achieves a suitable
evolution path for non-adiabatic holonomic
quantum computation through reverse engineering of pulse parameters. This scheme can implement arbitrary two-
qubit controlled gates with favorable robustness. We also evaluate the effects of spontaneous emission and
laser intensity errors on the fidelity; numerical simulations show that the
geometric gate scheme still exhibits excellent performance under these errors. Furthermore, we extend the scheme to non-local gates via
entanglement transfer and
quantum teleportation techniques, and demonstrate its application in the mutual conversion among four-
qubit entangled states (GHZ, cluster, and W states). This finding indicates the potential applicability of our scheme to complex
quantum information processing tasks.
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All authors Le-Jiang Yu, Jia Zheng, Kun Pu, Chao Gao
Soft Condensed Matter
Collective dynamics of macroscopic photoactive matter under alternating excitation patterns
Sára Lévay, Axel Katona, Raúl Cruz Hidalgo et al. (+1 more)
We present experiments on the collective dynamics of macroscopic photoactive self-propelled particles subjected to spatiotemporally varying excitation. The particles move within an arena divided into two regions with different illumination intensities, creating alternating bright (more active) and dark (less active) zones. Under such conditions, the system exhibits a robust migration from the more active region toward the less active region, demonstrating a strong response to external modulation. This response depends sensitively on the frequency of the illumination pattern: at low frequencies, particles follow the changing landscape, whereas at higher frequencies, the response diminishes. We show that this behavior arises from the interplay between the imposed excitation and the intrinsic dynamics of the particle clusters that form spontaneously. To explain these features, we extend a kinetic model previously introduced in Lévay et al. [Phys. Rev. Lett. 135, 098301 (2025)], hence revealing the most important parameters governing the transition between the responsive and unresponsive regimes.
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All authors Sára Lévay, Axel Katona, Raúl Cruz Hidalgo, Iker Zuriguel
Strongly Correlated Electrons
Field-induced quasi-bound state within the two-magnon continuum of a square-lattice Heisenberg antiferromagnet
F. Elson, M. Nayak, A. A. Eberharter et al. (+14 more)
Quantum magnets in two dimensions display strong
quantum interaction effects even when magnetically ordered. Using the metal-organic framework material CuF$_2$(D$_2$O)$_2$(pyz), we investigate the field-dependent
spin dynamics of the $S = 1/2$ square-
lattice Heisenberg antiferromagnet by high-resolution inelastic
neutron scattering to applied fields beyond one third of saturation. We discover an anomalously sharp, dispersive “shadow mode” residing within the two-
magnon continuum, which shadows the dispersion of the transverse one-
magnon branches across the Brillouin zone at an offset equal to the Larmor energy. We perform cylinder
matrix-product-state (MPS) calculations that reproduce the field-induced spectrum quantitatively and apply a spectrally consistent $1/S$
spin-wave theory to deduce that the “Larmor-shadow mode” is a composite two-
magnon resonance: a dispersing
magnon at wavevector ${\bf Q}$ couples to the uniform Larmor precession at $\Gamma$, its small intrinsic linewidth indicating a non-perturbative effect of attractive
magnon-
magnon interactions. Another
quantum-fluctuation phenomenon, the zero-field $(\pi,0)$ anomaly, is lost at increasing fields, which tighten the spectral weight into the one-
magnon and Larmor-shadow modes. To our knowledge, these results constitute the first observation of a sharp quasi-bound state embedded in the continuum of a gapless two-dimensional antiferromagnet.
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All authors F. Elson, M. Nayak, A. A. Eberharter, M. Skoulatos, S. Ward, U. Stuhr, N. B. Christensen, D. Voneshen, C. Fiolka, K. W. Krämer, Ch. Rüegg, H. M. Rønnow, B. Normand, M. Mourigal, F. Mila, A. M. Läuchli, M. Månsson
Other Condensed Matter · Cross-listed from quant-ph
Postselection-induced localization and coherence in quantum walks on heterogeneous networks
Adithya L J, Suraj S Hegde and Chandrakala Meena
Postselection of
quantum trajectories is known effectively introduce nonlinearity into dynamics of open
quantum systems. We study the effect of such non-linearity in continuous-time
quantum walks (CTQWs) on networks with homogeneous and heterogeneous degree distributions. Using the recently proposed nonlinear Lindblad master equation (NLME), we investigate the dynamics under two decoherence mechanisms: Haken-Strobl and
quantum stochastic walk (QSW). Our analysis reveals a striking dichotomy: under Haken-Strobl decoherence the nonlinear contributions precisely cancel, yielding a uniform steady state independent of postselection details under imperfect detection. In stark contrast, QSW decoherence permits postselection in this regime to break dynamical balance on heterogeneous networks, inducing robust localization preferentially at low-degree (peripheral) nodes. Remarkably, this localized state maintains finite
quantum coherence. Extending our results to many-body
spin systems, we demonstrate that degree heterogeneity similarly stabilizes localization of
spin-up excitations in
spin-down backgrounds, enhancing
entanglement preservation. These findings establish degree heterogeneity and postselection as joint control parameters for engineering
quantum transport and localization in dissipative dynamics.
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Materials Science
Polaron-mediated anisotropic exchange in 2D magnets
Johanna P. Carbone, Jakob Baumsteiger and Cesare Franchini
Two-dimensional (2D) magnets offer a rich platform for exploring emergent
spin phenomena due to their unique and diverse
magnetic properties. Beyond intrinsic magnetism, external manipulation$\unicode{x2013}$such as defect engineering, molecular adsorption, or charge doping$\unicode{x2013}$offers powerful routes to control their
magnetic behavior. In this work, we demonstrate that localized electron polarons provide an effective means to modulate magnetism in 2D magnets. Using first-principles calculations, we investigate polaron formation in monolayer MnPS$_3$ and compute the resulting changes in
magnetic exchange interactions. Our results reveal that polarons can locally break
magnetic symmetry and induce anisotropic exchange couplings, highlighting a novel mechanism for tuning
magnetic textures. This insight opens promising pathways for designing atomic-scale control of magnetism, with potential impact on spintronic technologies.
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Soft Condensed Matter
Local composition controls pattern formation in conserved active emulsions
Florian Raßhofer and Erwin Frey
Phase separation in passive systems leads to uncontrolled droplet growth, limiting structural control in soft materials and
cells. We identify a generic mechanism to arrest coarsening based on chemical interconversion between molecular species with different diffusivities. Sharp-interface theory and simulations show that when the faster-diffusing species becomes enriched inside droplets, composition gradients emerge that oppose mass influx. This transport asymmetry stabilizes droplet sizes even without interaction asymmetries, offering a minimal route to regulate structure formation in active emulsions.
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Materials Science
Sub-angstrom many-body localization driven by phononic flat bands in real quantum materials
Yingpeng Qi, Jianmin Yang, Zhihui Zhou et al. (+10 more)
Defects, fluctuations, degenerate states and correlated interactions facilitate the emergence of exotic properties in condensed matter systems while also inducing atomic-scale local correlated structures that deviate from the average long-range order. Establishing the structure-property relationship from the perspective of these atomic-scale local correlated structures remains ambiguous and controversial due to the lack of direct methods for identifying such local correlated structures. In this work, based on the photoexcited ultrafast structural response, we propose a Bragg scattering phase breaking regime to identify sub-angstrom local correlated structures in
quantum materials. With this regime, we unambiguously identify the many-body-interaction driven local correlated structures in the low temperature ground state of AgCrSe2, characterized by static off-center displacements of Ag atoms ranging from 0 to 0.5 angstrom. The competition between Ag-Ag Coulomb correlations and potential wells induced by CrSe2 layers, leading to phononic flat bands and driving the system into a many body localization (MBL) regime. As temperature rising, these static local correlated structures transform to a dynamic state where the thermal fluctuations overwhelm the multiple localized states. These distinctive local correlated structures constitute the first experimental observation of MBL with
vortex-like topological characteristic in a real material system. Emergent vibrational modes arising from MBL have been confirmed and show excellent agreement with inelastic
neutron scattering experiments. Our work not only offers a universal approach to characterize sub-angstrom local correlated structures across a wide range of
quantum materials but also deepens our understanding of the fundamental mechanism behind exotic properties from the perspective of atomic-scale local correlated structures.
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All authors Yingpeng Qi, Jianmin Yang, Zhihui Zhou, Qing Xu, Yang Lv, Xiao Zou, Tao Jiang, Pengfei Zhu, Dongxue Chen, Zhenrong Sun, Lin Xie, Dao Xiang, Jiaqing He
Soft Condensed Matter
Non-contact mechanics of soft and liquid interfaces by hydrodynamic confinement using a frequency-modulated AFM
Lucie Corral, Christian Curtil, Medhi Lagaize et al. (+2 more)
Measuring the mechanical response of
liquid interfaces without direct contact remains a major experimental challenge, particularly in
liquid-
liquid systems where no solid reference exists. Here, we develop a frequency-modulation atomic force microscopy (FM-AFM) method that probes
liquid interfaces through the hydrodynamic confinement of a viscous
liquid film between an oscillating probe and the interface. This approach provides simultaneous access to the in-phase and dissipative components of the effective mechanical response under confinement. The method is first validated on a
liquid-solid interface, where the measured confinement thickness and the
evolution of the mechanical impedance are consistent with elastohydrodynamic theory over nearly one decade in elastic modulus. It is then applied to a
liquid-
liquid interface, which exhibits a predominantly viscous response with a finite in-phase contribution and a confinement thickness in the micrometric range. These results show that hydrodynamic confinement provides a sensitive, non-contact approach to compare the mechanical response of soft and
liquid interfaces, and opens new perspectives for investigating complex and highly deformable systems such as
polymer films, biological membranes, and rafts of nanoparticles.
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All authors Lucie Corral, Christian Curtil, Medhi Lagaize, Marc Leonetti, Hubert R. Klein
Materials Science
Interface-dependent Phase Transitions and Ultrafast Hydrogen Superionic Diffusion of H2O Ice
Pengfei Hou, Yumiao Tian, Zifeng Liu et al. (+5 more)
High-pressure experiments using diamond anvils have revealed novel properties and phase behavior of H2O under extreme conditions. When contained in diamond-anvil
cells, the H2O samples are usually in direct contact with the diamond anvil. However, the extent to which this interface affects measured pressure-induced properties and behavior, including coexistence lines of ice phases, remains unknown. Combining artificial neural network methods and active learning schemes with large-scale molecular dynamics simulations, we elucidate the interfacial effects on various properties of high-pressure ice phases, including superionic states, solid-solid phase transitions, and melting. The results reveal that the presence of this interface can significantly lower the hydrogen superionic transition temperature. Remarkably, the interface can also induce a spontaneous transition from bcc- to fcc-based ice following the inverse Bain mechanism. Further, we redefined a stability field of bcc and fcc ice below the melting line and predicted the existence of fcc ice at much lower pressures than previously thought. More broadly, the results emphasize the importance of interface effects in understanding a wide range of phenomena reported in experimental studies of ice under pressure, including inconsistencies between theoretical and experimental results of this fundamental system.
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All authors Pengfei Hou, Yumiao Tian, Zifeng Liu, Junwen Duan, Hanyu Liu, Xing Meng, Russell J. Hemley, Yanming Ma
Statistical Mechanics · Cross-listed from eess.SY
Optimal Control for Steady Circulation of a Diffusion Process via Spectral Decomposition of Fokker-Planck Equation
Norihisa Namura and Hiroya Nakao
We present a formulation of an optimal control problem for a two-dimensional
diffusion process governed by a Fokker-Planck equation to achieve a nonequilibrium steady state with a desired circulation while accelerating convergence toward the stationary distribution. To achieve the control objective, we introduce costs for both the probability density function and flux rotation to the objective functional. We formulate the optimal control problem through dimensionality reduction of the Fokker-Planck equation via eigenfunction expansion, which requires a low-computational cost. We demonstrate that the proposed optimal control achieves the desired circulation while accelerating convergence to the stationary distribution through numerical simulations.
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Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Bloch sphere picture and restoration of the quantum Mpemba effect beyond the weak coupling regime in the spin boson model
P. Chirico, G. Di Bello, G. De Filippis et al. (+1 more)
Understanding relaxation dynamics in open
quantum systems is a central problem in nonequilibrium
quantum physics. Here we investigate the
quantum Mpemba effect in the
spin boson model. In the weak coupling Markovian regime we show that the occurrence of the effect strongly depends on the choice of distance measure at low temperature: while it appears in the trace distance, it can disappear in the
quantum relative
entropy. Going beyond the weak-coupling approximation, numerically exact simulations of the full system bath dynamics reveal that increasing coupling enhances the effect in the trace distance and restores it in the
quantum relative
entropy. We uncover a simple Bloch sphere picture of the effect: within the excited-state hemisphere, pairs of states related by rotations and having the same Bloch-vector modulus generically exhibit an inversion of their relaxation ordering. This behavior is robust across sub Ohmic, Ohmic, and super Ohmic bath spectra. In the Ohmic and sub Ohmic regimes, the crossing time becomes strongly suppressed upon approaching the critical region, whereas in the super Ohmic regime the effect remains enhanced despite the absence of a finite-coupling localization transition. These results highlight the interplay between geometry, distance measures, system–environment coupling, and bath spectral properties in anomalous
quantum relaxation.
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All authors P. Chirico, G. Di Bello, G. De Filippis, C. A. Perroni
Other Condensed Matter
Imaginary Gauge Field and Non-Hermitian Topological Transition Emerging Through Attenuation-Gauge Duality in Conservative Systems
Haoran Nie, Chaoran Jiang, Xiangying Shen et al. (+1 more)
Non-Hermitian physics traditionally relies on active gain–loss modulation or non-reciprocal couplings, which often introduce significant complexity, compromise stability, and offer very limited scalability in conservative systems. Here we propose an attenuation-gauge duality paradigm in which non-Hermitian
topology emerges within fully passive, conservative systems through coupling to a structured reservoir. We derive that a spatially varying reservoir can establish an attenuation-gauge duality, where the spatial variation manifests as an emergent imaginary gauge field in the effective dynamics. It drives the boundary accumulation of skin modes while preserving energy conservation, analogous to Feshbach projection in
quantum open systems. We validate this universal wave paradigm via macroscopic mechanical metamaterials, demonstrating that the direction of the skin effect can be reversed by tuning a single passive coupling parameter$t_\perp$, driven by a topological phase transition characterized by the spectral winding number. This framework also allows for a nonlinear extension, where amplitude-dependent coupling can induce intrinsic topological transitions.
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All authors Haoran Nie, Chaoran Jiang, Xiangying Shen, Lei Xu
Statistical Mechanics
Study of Meta-Fibonacci Integer Sequences by Continuous Self-Referential Functional Equations
Klaus Pinn
I propose and investigate the use of continuous functional equations for the study of meta-Fibonacci integer sequences. This exploratory study includes three sequences with quite different behavior: Conway's famous sequence $A(n)= A(A(n-1))+A(n-A(n-1))$, the sequence $D(n)= D(D(n-1))+D(n-1-D(n-2))$ introduced by the present author more than 25 years ago, and Hofstadter's well-known $Q(n)= Q(n-Q(n-1))+Q(n-Q(n-2))$. The sequences are studied in their equivalent detrended forms $(a,d,q)(n)=2\,(A,D,Q)(n)-n$. For $a(n)$ and $d(n)$, a highly symmetric functional equation admits exact continuous solutions that nicely model the global behavior (backbone) of the sequences. For the Hofstadter sequence, a continuous functional model is developed that leads to a random
matrix approach for the generation and study of fractal solutions. Two remarkable properties of the Q-sequence are reproduced by the model: the anomalous scaling of the generation length, which scales $\sim (2-\eta)^k$, and the anomalous amplitude growth that scales like $2^{\alpha k}$.
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Soft Condensed Matter
Free-Energy Analysis of Bubble Nucleation on Electrocatalytic Surfaces
Qingguang Xie, Paolo Malgaretti, Othmane Aouane et al. (+2 more)
Bubble nucleation at catalyst surfaces plays a critical role in the operation of electrolyzers. However, achieving controlled bubble nucleation remains challenging due to limited understanding of the underlying mechanisms. Here, we present a free-energy model that quantitatively predicts both the activation energy and critical
nucleus size of bubbles at given supersaturation, temperature, pressure, and surface wettability. We find that the activation energy $\Delta G_{max}$ decreases with increasing supersaturation $\zeta$, following a power-law scaling of $\Delta G_{max} \sim \zeta^{-2}$, while the critical
nucleus radius $R_c$ scales as $R_c\sim \zeta^{-1}$. Our theoretical predictions for the critical
nucleus radius of hydrogen, oxygen and nitrogen bubbles are in quantitative agreement with experimental measurements. Finally, we present a simple model that couples gas
diffusion and electrochemical reaction kinetics to determine the maximum gas supersaturation at a given current density. Our results advance the fundamental understanding of bubble nucleation at catalyst surfaces and provide practical guidelines for catalyst layer design to improve the performance of electrolyzers.
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All authors Qingguang Xie, Paolo Malgaretti, Othmane Aouane, Simon Thiele, Jens Harting
Statistical Mechanics
Information-Geometric Signatures from Nonextensivity in the $1$-D Blume-Capel Model
Amijit Bhattacharjee, Himanshu Bora and Prabwal Phukon
We study the thermodynamic geometry of the one-dimensional Blume–Capel model within the Tsallis nonextensive framework to understand how generalized statistics modify correlation structure and pseudo-critical behaviour. Using the transfer
matrix method, we construct the Tsallis
entropy based thermodynamic metric as its negative Hessian on the parameter space $(\beta, J)$, with the
crystal-field anisotropy $D$ as a control parameter, and compute the associated scalar
curvature $R(T)$ as a measure of correlations. Although no true phase transition occurs in one dimension, $R(T)$ exhibits finite peaks signaling pseudo-critical crossovers. We analyze both $D < J$ and $D > J$ regimes and show that deviations from the Boltzmann–Gibbs limit ($q=1$) systematically deform the
curvature profile: for $q>1$ the peak shifts and correlations persist beyond the crossover, whereas for $q<1$ the peak is weakened or suppressed. Our results demonstrate that the Tsallis parameter $q$ geometrically reshapes the
entropy surface, providing a clear information-
geometric interpretation of nonextensive effects in
spin-1 systems.
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Materials Science
Hydrogen uptake and hydride formation in Al$_x$CoCrFeNi high-entropy alloys: First-principles, universal-potential, and experimental study
Fritz Körmann, Yuji Ikeda, Konstantin Glazyrin et al. (+9 more)
Hydrogen uptake in complex multicomponent
alloys, including high-
entropy alloys (HEAs), governs both hydrogen storage capacity and resistance to hydrogen-induced degradation. We combine high-pressure experiments, density-functional theory (DFT), and a GRACE universal interatomic potential to investigate hydrogen absorption in Al$_{0.3}$CoCrFeNi and Al$_3$CoCrFeNi HEAs. In H$_2$ as a pressure-transmitting medium, the FCC Al$_{0.3}$CoCrFeNi
alloy forms hydrides at ambient temperature above 3 GPa, whereas the Al-rich B2 Al$_3$CoCrFeNi
alloy shows no evidence of hydride formation even upon heating at pressures up to 50 GPa. Experiments and calculations show that aluminum suppresses hydrogen uptake by increasing solution energies and destabilizing interstitial sites. The universal potential, employed in the calculations and pretrained on large DFT databases, closely reproduces DFT energetics and demonstrates transferability from the dilute limit to the hydride-forming regime. Simulations further disentangle the roles of local ordering, volume changes, composition, and
crystal structure. Overall, our results indicate that hydrogen solubility in Al-containing HEAs is governed primarily by composition, with Al-driven B2 ordering as a strong secondary effect.
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All authors Fritz Körmann, Yuji Ikeda, Konstantin Glazyrin, Maxim Bykov, Kristina Spektor, Shrikant Bhat, Nikita Y. Gugin, Anton Bochkarev, Yury Lysogorskiy, Blazej Grabowski, Kirill V. Yusenko, Ralf Drautz
Superconductivity
${H}$-linear magnetoresistance in the ${T^2}$ resistivity regime of overdoped infinite-layer nickelate La$_{1-x}$Sr$_{x}$NiO$_2$
Yong-Cheng Pan, Tommy Kotte, Toni Helm et al. (+3 more)
We report a systematic magnetotransport study on high-crystallinity La$_{1-x}$Sr$_{x}$NiO$_2$ (LSNO) thin films with $x=0.20-0.24$. By conducting pulsed-field transport experiment up to 62 T, we reveal two salient features of the normal-state transport in overdoped LSNO thin films: (1) the magnetoresistance does not follow the Kohler's rule but exhibits a $H$-linear behavior in the high $H/T$ limit and (2) the normal-state $\rho(T)$ below 30 K consistently follows a $T^2$ behavior across the overdoped regime. Our results demonstrate a coexistence of $H$-linear magnetoresistance and $T^2$ resistivity in a model unconventional
superconductor and provide new information on the transport characteristics of the normal ground state that host superconductivity in infinite-layer nickelates.
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All authors Yong-Cheng Pan, Tommy Kotte, Toni Helm, Motoki Osada, Atsushi Tsukazaki, Yu-Te Hsu
Disordered Systems and Neural Networks
Exploring the role of connectivity in disordered system
Anjan Daimari, Shivanee Borah and Diana Thongjaomayum
We study a minimal model of disordered systems, the random field Ising model (RFIM) on a generalized Petersen Graph, GP(N,k). This graph has a connected inner and outer loop, where both the loops consist of N nodes constituting a total of 2N nodes. The parameter k satisfies the condition 1<=k<=N/2, such that any site i in the inner loop has i-k and i+k as its two nearest neighbours, apart from its connection to a node on the outer loop. Thus, each node in GP(N,k) has coordination number z=3, and by varying k different connections between the nodes in the inner loop can be obtained. The objective is to study whether different connectivity between nodes in these graphs affects the system's response to an external field when the coordination number is fixed. This is of interest because critical behaviour is absent for z<=3 on a random graph which has been solved exactly as well as on the honeycomb
lattice in the context of RFIM. Using single-
spin-flip Glauber dynamics at zero temperature, we compare the system's response with the known case of a z=3 random graph and the generalized Petersen graph for various connectivity k, albeit for the same z. Our study finds the absence of critical behaviour on GP(N,k) highlighting the importance of coordination number over varying connectivity between the nodes. Additionally, we explore the case of directed GP(N,k) and compare it with the undirected GP(N,k) results.
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Mesoscale and Nanoscale Physics
Polarization-Aligned, Spectrally Consistent Quantum Emitters in As-Exfoliated Carbon-Doped Hexagonal Boron Nitride
Sofiya Karankova, Yeunjeong Lee, Seungmin Park et al. (+6 more)
Solid-state
quantum emitters constitute an essential building blocks of integrated
quantum photonic
circuits. Among potential emitter platforms, hexagonal boron nitride (hBN) hosts single-
photon emitters in an atomically thin
lattice amenable to photonic integration. However, multi-step fabrication approaches, limited defect specificity, and poor emission wavelength repeatability limit the performance of hBN
quantum light sources relative to established solid-state architectures. Developing methods to induce emitters that are both suitable for planar photonic devices and that exhibit consistent optical properties remains a key objective. In this work, we identify
quantum emitters in as-exfoliated carbon-doped hBN that exhibit both stable and repeatable emission energies together with polarization-aligned dipoles. Owing to the high
lattice crystallinity, these single-
photon light sources demonstrate exceptional spectral stability with a standard deviation of 7 ${\mu}$eV. The emission energy is reproducible and confined within a narrow range of 2.2825 ${\pm}$ 0.0042 eV. Notably, consistent dipole
alignment for absorption and emission polarization suggests that the intrinsic defects are of the same nature. The color centers are observed in as-exfoliated hBN without any post-treatment, significantly facilitating further interfacing with planar photonic structures. These reproducible, polarization-aligned
quantum emitters in as-exfoliated hBN provide a versatile platform for scalable integration, offering a pathway toward a broad range of
quantum technologies.
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All authors Sofiya Karankova, Yeunjeong Lee, Seungmin Park, Kenji Watanabe, Takashi Taniguchi, Jin-Dong Song, Young Duck Kim, Yong-Won Song, Hyowon Moon
Mesoscale and Nanoscale Physics
Symmetry-Enforced Nodal $f$-Wave Magnets
Moritz M. Hirschmann, Akira Furusaki and Max Hirschberger
Owing to their relevance for spintronics, electronic band splitting and
spin-polarization textures in magnets are active areas of research. In non-collinear magnets, alternating
spin textures can arise both for isolated bands and for intersecting band pairs with nodal splitting. This raises the question of whether $p,f,...$-wave magnets should be defined by their
spin polarization or their band splitting. To resolve this ambiguity, we introduce
spin-space
symmetries that couple the
spin polarization and splitting textures for all bands. Focusing on the nodal $f$-wave magnet, we construct a tight-binding model of itinerant electrons on a honeycomb
bilayer coupled to a non-collinear
magnetic texture. Analytic expressions for
spin polarization and splitting reveal the dependence on hopping and exchange coupling. We predict a canting-induced
spin conductivity arising from the nodal structure of the splitting. Furthermore, the $f$-wave magnet in the bulk can induce $p$-wave magnetism on the surface. This surface $p$-wave character leads to a bulk-forbidden Edelstein effect with $f$-wave anisotropy.
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Disordered Systems and Neural Networks · Cross-listed from quant-ph
Anomalous localization and duality in non-Hermitian quasiperiodic models
Wenzhi Wang, Tianyu Li and Wei Yi
We develop a general framework based on the sign patterns of Lyapunov exponents for engineering and characterizing counterintuitive localization properties in one-dimensional non-Hermitian quasiperiodic
lattices. On the one hand, for the Anderson localized states in the bulk under the periodic boundary condition, we find that their localization features can be boundary-sensitive, becoming boundary-localized skin modes under the open boundary condition. On the other hand, for non-localized states, the well-known extended-localized duality relation can break down, as their counterparts in the dual model can also be nonlocal. We discuss how these remarkable phenomena can be understood from the perspective of Lyapunov exponents, highlighting the interplay of non-Hermiticiy and quasiperiodicity.
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Materials Science
Electronic excitation of ultrafast collective amorphous-amorphous transitions in glassy phase-change material
Yingpeng Qi, Nianke Chen, Zhihui Zhou et al. (+10 more)
The intrinsic nature of glass states and glass transitions remain a fundamental open question in condensed-matter physics and materials science. The key to solving the glass transition problem lies in achieving a complete understanding of the physics governing the structural relaxation. Nonetheless, directly probing dynamic atomic-scale structural changes in order to identify the precise local structural motifs and establish quantitative structure-property relationships remains an outstanding challenge. By combining femtosecond electron diffraction with time-dependent density-functional theory molecular dynamics simulations, we directly capture ultrafast amorphous-amorphous transitions indicated by collective bond stretching (0.2 ps) and angle bending (0.5-2 ps) in glassy phase-change material GeTe. The ultrafast bond stretching is accompanied by localized oscillation modes with the frequency of 3.10 THz, unambiguously signaling the local Peierls-like bonding structure and the flexibility of these polarized bonds. These ultrafast collective atomic motions, captured across timescales ranging from femtoseconds to picoseconds, directly reveals the structural origin of the
boson peak and provide compelling evidence for many-body interactions in amorphous materials. Furthermore, the ultrafast amorphous-amorphous transitions induce a drastic
insulator-metal transition, directly revealing both the underlying switching mechanism and the fundamental speed limit of the ovonic threshold switch. These insights establish a fundamental framework for rationally engineering relaxation pathways and phase-change/threshold switch in amorphous materials. Femtosecond electron diffraction provides a powerful novel approach to deciphering the structural complexity and functional mechanisms of amorphous materials by resolving collective atomic motions from random
diffusion dynamics in the time domain.
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All authors Yingpeng Qi, Nianke Chen, Zhihui Zhou, Qing Xu, Yang Lv, Xiao Zou, Tao Jiang, Pengfei Zhu, Min Zhu, Dongxue Chen, Zhenrong Sun, Xianbin Li, Dao Xiang
Soft Condensed Matter
The role of polyelectrolyte brushes in tunable synaptic devices
Esli Diepenbroek, Leon A. Smook and Sissi de Beer
With the ever-increasing digitization of society, the development of materials with low-power
memory storage -similar to synapses- is becoming more relevant. The field of iontronic artificial synapses has gained traction, in particular with
polymers as the
memory-active material which allows for additional bio-compatibility, flexibility and tunability. Polyelectrolyte brushes are an example of stimulus-responsive materials that can be used in iontronic devices. However, the complexity of current neuromorphic devices does not allow us to isolate and understand the role of polyelectrolyte brushes in their synaptic response. In this paper, we show that polyelectrolyte brushes are capable of synaptic behavior in the most simple of electrochemical
cell designs. Furthermore, by combining theory and experimental work, we shed light on the role of brushes in this synaptic behavior and their dynamic stimuli-responsiveness to polarity changes for different salt concentrations. The obtained trends and interpretations of the nonlinear potential-current response, paired-pulse experiments, and accumulative learning lay the foundation for designing and developing
polymer brush-based neuromorphic devices.
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Soft Condensed Matter
Phase Transition of Hard Disk Systems with Vicsek-type Interactions
Nobuaki Murase and Masaharu Isobe
The phase diagram of self-propelled hard disk systems with Vicsek-type
alignment interactions was investigated by event-driven molecular dynamics simulations. The model incorporates two competing order parameters: the polar order-disorder transition associated with collective velocity
alignment (Vicsek model) and the orientational order arising from solid-fluid transitions (Alder transition) induced by excluded volume effects. The incompressibility of hard disks suppresses motility-induced phase separation at high packing fractions. Distinctive fluctuations were observed near the transition point, accompanied by anomalous shifts in the transition point as functions of noise intensity and packing fraction. Analysis of local configurational parameters – specifically, orientational order and circularity of free volume – provides insight into the microscopic origins of these anomalous phase transition shifts.
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Soft Condensed Matter
Rapid Neural Network Prediction of Linear Block Copolymer Free Energies
Ian Chen and Alfredo Alexander-Katz
Free energies are fundamental quantities governing phase behavior and thermodynamic stability in
polymer systems, yet their accurate computation often requires extensive simulations and post-processing techniques such as the Bennett Acceptance Ratio (BAR). While BAR provides reliable estimates when applied between closely related thermodynamic states, evaluating free energies across large changes in interaction strength typically requires a sequence of intermediate simulations to maintain sufficient phase-space overlap, substantially increasing computational cost. In this work we develop a machine learning framework for rapidly predicting excess free energies of linear diblock copolymer systems from simulation-derived energetic descriptors. Using dissipative particle dynamics simulations of freely-jointed chain
polymers, we construct a
dataset of per-chain energetic statistics, including heterogeneous interaction energies, homogeneous interaction energies, and bonded spring energies, and train feed-forward neural networks to learn the relationship between these descriptors and free energies computed using a stratified BAR procedure. The resulting models accurately reproduce the reference free energies across a range of chain lengths, compositions, and densities, including
polymer architectures held out from training. In regimes where direct, brute-force BAR estimates become unreliable due to poor phase-space overlap, the neural network predictions remain consistent with the reference values. These results demonstrate that physically informed machine learning models can serve as efficient surrogates for expensive free-energy calculations and provide a promising approach for accelerating thermodynamic analysis of
polymer systems.
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Strongly Correlated Electrons
Exactly Solvable Disorder-free Quantum Breakdown Model: Spectrum, Thermodynamics, and Dynamics
Kinya Guan and Hosho Katsura
We introduce and study a disorder-free version of the
quantum breakdown model with all-to-all interactions. The
Hamiltonian factorizes into the product of the zero-momentum-mode occupation number and a quadratic
Hamiltonian including only pairing terms. This structure makes the model exactly solvable and produces an extensive zero-energy degeneracy. We obtain the spectrum and partition function in closed form and analyze the thermodynamics, spectral form factor, two-point functions, and a regulated out-of-time-ordered correlator (OTOC). The OTOC is time independent at leading order in the large-$N$ limit, while its time-dependent contributions first appear at order $1/N$. At infinite temperature, the time-dependent correction reduces to a two-point function arising from the zero-momentum component of the
fermion operators. The model therefore provides a controlled setting for isolating the consequences of the breakdown interaction in the absence of disorder, spatial structure, and environmental coupling.
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Materials Science
GPUMDkit: A User-Friendly Toolkit for GPUMD and NEP
Zihan Yan, Denan Li, Xin Wu et al. (+20 more)
Machine-learned interatomic potentials have revolutionized molecular dynamics simulations by providing
quantum-mechanical accuracy at empirical-potential speeds. The graphics processing unit molecular dynamics (GPUMD) package, featuring the highly efficient neuroevolution potential (NEP) framework, has emerged as a powerful tool in this domain. However, the complexity of force field development, active learning, and trajectory post-processing often requires extensive manual scripting, imposing a steep learning curve on new users. To address this, we present GPUMDkit, a comprehensive and user-friendly toolkit that streamlines the entire simulation workflow for GPUMD and NEP. GPUMDkit integrates a suite of essential functionalities, including format conversion, structure sampling, property calculation, and data visualization, accessible through both interactive and command-line interfaces. Its modular, extensible architecture ensures accessibility for users of all experience levels while allowing seamless integration of new features. By automating complex tasks and enhancing productivity, GPUMDkit substantially lowers the barrier to using GPUMD and NEP programs. This article describes the program architecture and demonstrates its capabilities through practical applications.
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All authors Zihan Yan, Denan Li, Xin Wu, Zhoulin Liu, Chen Hua, Boyi Situ, Hao Yang, Shengjie Tang, Benrui Tang, Ziyang Wang, Shangzhao Yi, Huan Wang, Dian Huang, Ke Li, Qilin Guo, Zherui Chen, Ke Xu, Yanzhou Wang, Ziliang Wang, Gang Tang, Shi Liu, Zheyong Fan, Yizhou Zhu