Strongly Correlated Electrons
A density matrix renormalization group approach to quantum point contacts
Nair Aucar Boidi and Mikhail Kiselev
Using the density
matrix renormalization group (DMRG) combined with the correction-vector method, we investigate the competition between an harmonic potential and repulsive interactions in a one-dimensional fermionic system. The
parabolic confinement induces spatial inhomogeneity, and by tuning its
curvature one can continuously interpolate between a potential well–relevant for cold-atom setups–and a
quantum barrier, as realized in mesoscopic systems such as
quantum point contacts. We analyze how the ground-state particle distribution evolves with the strength and sign of the confining potential and how the confinement reshapes the spectral weight of the local density of states (LDOS) at the center of the chain. In the barrier regime, a localized peak emerges in the electron part of the spectrum ($\omega >0$) as a direct consequence of the potential. In contrast, in the well configuration and for weak interactions, a localized feature persists but shifts to the hole sector ($\omega <0$). However, for stronger interactions, the LDOS no longer displays clear signatures of the external potential, indicating that correlations dominate over single-particle confinement.
Read the full abstract ▾
Materials Science
Coherent two-dimensional electronic spectroscopy integrated with confocal back focal plane microscopy
Trideep Kawde, Pavel Trofimov, Anton Trenczek et al. (+3 more)
We introduce a setup for coherent two-dimensional electronic spectroscopy in the pump-probe reflection geometry that is integrated with a confocal back focal plane imaging microscope. The angle-resolved capability is utilized to control pump and probe wavevectors, while real space imaging enables co-localization of the collection spots for linear and ultrafast experiments. Compression of pulses down to 20 fs is achieved. We demonstrate the capabilities of this approach on an exfoliated WSe$_2$ monolayer on Si/SiO$_2$. The setup is suited to investigate
excitons and
exciton-polaritons in 2D Materials and their
heterostructures.
Read the full abstract ▾
All authors Trideep Kawde, Pavel Trofimov, Anton Trenczek, Matteo Russo, Jasper Wilhelm Schwering, Hélène Seiler
Disordered Systems and Neural Networks · Cross-listed from math.PR
Fluctuations of the Sherrington-Kirkpatrick free energy at critical temperature
Hang Du and Brice Huang
We consider the Sherrington-Kirkpatrick
spin glass model at the critical inverse temperature $\beta = 1$ with zero external field. We prove that the free energy $F_N = F_{N,\beta=1}$ of this model has variance \[ \mathrm{Var}(F_N) = \frac16 \log N + O(1)\,, \] confirming a physics prediction of Aspelmeier \cite{aspelmeier2008free}, and that the centered and scaled $F_N$ satisfies a Gaussian CLT. We also identify the critical two-replica overlap scale, proving \[ \mathbb{E} \langle R_{1,2}^2\rangle \asymp N^{-2/3}\,, \] as conjectured by Talagrand \cite{talagrand2011mean2}, together with a uniform exponential moment bound for $N^{1/3} |R_{1,2}|$. The key input is a critical reweighted moment method, in the spirit of the “small subgraph conditioning” technique from probabilistic combinatorics, but capable of capturing diverging fluctuations. Through this reweighting, we relate the critical SK model to the BBP critical edge, which determines the overlap and fluctuation scales.
Read the full abstract ▾
Statistical Mechanics
Theory of collective learning in populations of adaptive agents
Gerhard Jung, Johann Asnacios, Misaki Ozawa et al. (+2 more)
We investigate homogeneous populations of smart active
agents that exchange information with their neighbors to perform a decentralized learning process aimed at achieving a prescribed macroscopic state. Such
agents may, for example, represent simple microrobots. The exchanged information comprises tunable parameters governing the
agent dynamics, referred to as the individual policy, together with an internal
memory encoding previously visited states. This
memory is used to evaluate a reward that quantifies the success of a policy to achieve the prescribed state. We extend the kinetic-theory description of collective learning in spatially homogeneous systems [Phys. Rev. Lett. 134, 248302 (2025)] and derive formal
evolution equations for the distribution of policies across the population. A central outcome of our theory is the emergence of an effective reward function that fully determines the
evolution of the policy distribution and encapsulates the microscopic details of the
agents physical and
memory dynamics. We obtain closed equations for the policy mean and variance which admit explicit time-dependent solutions under the assumption of Gaussian-distributed
memories and polices. To illustrate the framework, we present a series of minimal microscopic models, considering both perfect and partial separation of physical,
memory and policy exchange time scales, as well as models with one- and two-dimensional policies. The obtained theoretical results compare well with
agent-based numerical simulations. The theory captures key aspects of collective learning, including the influence of population diversity and reward fluctuations on learning performance. Finally, we discuss potential applications to swarm robotics and machine learning, and highlight connections with classical models of biological
evolution, including the Replicator equation and the Moran model.
Read the full abstract ▾
All authors Gerhard Jung, Johann Asnacios, Misaki Ozawa, Olivier Dauchot, Eric Bertin
Disordered Systems and Neural Networks · Cross-listed from quant-ph
Thermodynamics of Quantum Reservoir Computing
Lixiang Ding and Xingze Qiu
Quantum reservoir computing provides a framework for processing complex temporal data, yet its fundamental computational and energetic limits remain unresolved. Here, we establish a non-
equilibrium thermodynamic framework that links the macroscopic predictive performance of driven open
quantum systems to their microscopic energetic costs. By mapping Holevo capacities onto the Bogoliubov-Kubo-Mori
geometric manifold, we analytically prove that the computational peak within the
quantum critical region originates from a spectral resonance: the closing of the intrinsic energy gap forces the reservoir's internal transition frequencies to align with the chaotic drive. To evaluate the associated thermodynamic costs, we introduce
quantum informational dissipation to quantify the non-predictive historical data retained by the reservoir. This allows us to derive a generalized Landauer bound for continuous temporal processing, which reveals a fundamental thermodynamic trade-off: the critical resonance that maximizes predictive capacity simultaneously maximizes informational dissipation and the irreversible work required for environmental erasure. Furthermore, coherence decomposition demonstrates that
quantum coherences amplify predictive capacity without demanding additional mechanical work. These findings establish the fundamental energetic limits of
quantum learning devices, providing theoretical principles for designing energy-efficient
quantum neuromorphic hardware.
Read the full abstract ▾
Statistical Mechanics
Path-Measure Dynamics of Attention-Driven World Models: A Nonlocal Onsager–Machlup Approach
Gunn Kim
Attention enables a world model to condition on its entire history, providing long-term
memory that facilitates long-range predictions. While the local Onsager–Machlup theory in our companion paper assumes a temporally local predictive action, we investigate the conditions under which this locality holds. We derive the predictive path measure for latent dynamics that become non-Markovian due to
attention-induced
memory, demonstrating that this measure is the projection of a hidden linear Markov augmentation. Eliminating the auxiliary field results in a nonlocal Onsager–Machlup action, where
memory manifests as a nonlocal quadratic form rather than a force. These kernels are completely monotone and exactly match a hidden Markov
embedding with a finite relaxation spectrum; otherwise, the dynamics remain fundamentally nonlocal. By expanding the action in terms of the scale-separation parameter $\epsilon=\tau_{\text{mem}}/\tau_{\text{dyn}}$, we show that the leading order recovers the local action of the companion paper, establishing locality as the short-
memory limit of a nonlocal theory. We verify the reversible sector of this expansion term by term against an exactly solvable vector linear model.
Read the full abstract ▾
Soft Condensed Matter
Pore-scale distribution and transport of active particles in a two-dimensional lattice
Akhil Varma and David Saintillan
Suspensions of motile microswimmers such as bacteria and other active colloids frequently encounter porous environments where obstacles and complex shear flows strongly influence their dynamics. Here, we study the distribution and transport of a dilute suspension of active particles in a square
lattice of pillars, which serves as a model porous medium. The microswimmers are modeled as slender point particles, and Brownian Dynamics simulations are performed to determine how their number density and polarization fields change with systematic variations in the medium porosity, polydispersity, flow strength, and self-propulsion strength. We find that in the absence of flow, self-propulsion drives particle accumulation and radial polarization at the pillar surfaces. In the presence of a background flow, particles preferentially accumulate in the wake of pillars and exhibit upstream polarization near their surface, consistent with experimental observations. At moderate flow strengths, topological defects nucleate in the polarization field. These defects are of purely kinematic origin and mark the transition from global upstream swimming at low flow strengths to the coexistence of upstream and downstream swimming regions in the
lattice at high flow strengths. The structured
lattice studied here provides a controlled framework for isolating the physical mechanisms governing active transport in complex geometries, with direct relevance to transport in structured microfluidic settings.
Read the full abstract ▾
Strongly Correlated Electrons
Phonon spectral function of Holstein polaron: Investigation of many-body effects with self-energy and vertex correction
Lawrence Rai and Sudhakar Pandey
We study the impact of the many-body effects on the
phonon spectral function of Holstein polaron in one-dimension in the antiadiabatic regime by incorporating the contributions from the electron self-energy and vertex corrections within a weak-coupling approach that respects the charge-conserving Ward identity. We find that while the polaronic spectral weight is suppressed due to contribution from the electron self-energy, on the other hand, the same is enhanced due to contribution from the vertex corrections. While strength of both the contributions increases with increasing the wave vector ($\q$) of
phonons, they nearly cancel each other for the small-$\q$ modes so that the polaronic spectral weight is weakly affected due to the many-body effects. For the large-$\q$ modes near the zone boundary, the net many-body correction is dominated by the contribution of the electron self-energy which increases faster in comparison to that of the vertex corrections with increasing the wave vector thereby resulting in a significant suppression of the polaronic spectral weight. We find that while the weak-coupling perturbative approach provides a reliable estimation of the impact of the many-body effects deep inside the antiadibatic regime, the renormalization of quasiparticle spectrum must be taken into account for an accurate estimation when the
phonon energy approaches the electronic bandwidth.
Read the full abstract ▾
Mesoscale and Nanoscale Physics
Electrical transport in ultra-thin films: from Fuchs-Sondheimer to quantum-confinement
Alessio Zaccone
Ultra-thin films are fundamental components of modern nanoelectronics, where reducing thickness to the few-nanometer scale leads to a dramatic increase in electrical resistivity. For decades, this behavior has been interpreted in terms of classical size effects, primarily surface scattering within the Fuchs–Sondheimer theory and grain-boundary scattering in the Mayadas–Shatzkes model. While these approaches successfully describe transport when the film thickness is comparable to the electronic mean free path, growing experimental evidence indicates that they become insufficient under extreme confinement. This review discusses the crossover from classical scattering to a
quantum-confinement regime in which the electronic states available for transport are fundamentally restructured by finite size. We review the recently proposed reciprocal-space confinement theory, which predicts an exponential increase of resistivity with decreasing thickness at the nanoscale, and discuss how it can be combined with classical surface-scattering models to provide a unified description of ultra-thin metallic and semiconducting films. Finally, we summarize recent experimental evidence supporting this picture and discuss its implications for future nanoelectronic devices, nanoscale interconnects, and
quantum transport under extreme spatial confinement.
Read the full abstract ▾
Strongly Correlated Electrons
Unconventional Mixed-Parity Magnetism in Rare-Earth Tetraborides
Dong-Choon Ryu, Jae-Ho Han, Bongjae Kim et al. (+1 more)
Altermagnetism has advanced the study of compensated magnets by revealing non-relativistic
spin splitting, traditionally classified into strictly even- or odd-parity
spin textures. Here, we unveil a fundamentally different regime: component-resolved mixed-parity
spin splitting in a fully three-dimensional compensated magnet. Using first-principles calculations, tight-binding and $\mathbf{k} \cdot \mathbf{p}$ models, along with
spin-group
symmetry analysis, we demonstrate that the non-coplanar ground state of $\mathrm{TbB}_4$ enforces a unique momentum-space
spin texture. The in-plane
spin components exhibit odd-parity $p$- and $f$-wave-like textures, whereas the out-of-plane component retains an even-parity $d$-wave altermagnetic character. Crucially, the coexistence of the in-plane odd-parity textures is driven not by relativistic
spin-orbit coupling, but by a staggered Berry phase arising from the inherent scalar
spin chirality. This mixed-parity structure dictates distinct transport fingerprints, including bulk non-relativistic Edelstein and
spin Hall responses, as well as a
symmetry-allowed Berry
curvature dipole. These results establish the rare-earth tetraborides as a robust platform for engineering complex
spin-charge conversion phenomena.
Read the full abstract ▾
All authors Dong-Choon Ryu, Jae-Ho Han, Bongjae Kim, Chang-Jong Kang
Strongly Correlated Electrons
Plaid-Like Spin Splitting and Chirality of Magnon Bands in Antiferromagnetic MnTe$_2$
Dirk Wulferding, Daehyeon An, Jiwon Choi et al. (+8 more)
Altermagnets constitute an emerging class of
magnetic materials that combine compensated
antiferromagnetic order with
spin-split excitations arising from crystalline
symmetries. Despite strong theoretical interest, their experimental identification remains challenging. Here, we demonstrate that helicity- and angle-resolved Raman scattering measurements reveal reduced rotational
symmetries of
magnons and a pronounced imbalance between left- and right-circular polarization channels, indicating momentum-dependent
magnon handedness. First-principles DFT+$U$ calculations combined with linear
spin-wave theory uncover a characteristic plaid-like
spin-splitting structure in momentum space. The resulting
magnon spin textures are dictated by the unconventional sublattice
symmetries of MnTe$_2$ and closely emulate those of altermagnetic electronic bands. Our work provides evidence of
chiral spin-wave excitations unique to this non-coplanar antiferromagnet.
Read the full abstract ▾
All authors Dirk Wulferding, Daehyeon An, Jiwon Choi, Dongmin Mun, Youngsu Choi, Sivasakthi Kuppusamy, Sritharan Krishnamoorthi, Raman Sankar, Myung Joon Han, Se Kwon Kim, Kwang-Yong Choi
Mesoscale and Nanoscale Physics
A 2048-spin bulk acoustic wave Ising machine for number partitioning and Sudoku
Venkatesh Vadde, Roman Ovcharov, Victor H. González et al. (+3 more)
Optical coherent Ising machines based on time-multiplexing have demonstrated significant progress in terms of connectivity and
spin scalability. However, they are constrained by large physical footprints, high power consumption, poor thermal stability, and high cost. Here, we present a time-multiplexed Ising machine leveraging propagating wave packets in solid-state delay lines at microwave frequencies, enabling thermally stable, robust, low-power, tabletop, and affordable design. We use two serially connected 20.5 MHz, 707 microseconds bulk acoustic wave delay lines supporting 2,048
spins. Our design provides all-to-all connectivity with 15-bit coupling resolution and finds approximate MAX-CUT solutions in 341 ms, potentially scalable to sub-ms by using higher frequency delay lines. Additionally, we demonstrate solutions to number partitioning and Sudoku problems. Compared with state-of-the-art Coherent Ising machines, our machine exhibits four orders of magnitude higher thermal stability. Against the simulated bifurcation
algorithm, our design achieves comparable results on the MAX-CUT problem, while outperforming it on the more complex number-partitioning and Sudoku problems.
Read the full abstract ▾
All authors Venkatesh Vadde, Roman Ovcharov, Victor H. González, Roman Khymyn, Artem Litvinenko, Johan Åkerman
Mesoscale and Nanoscale Physics
Quantum-geometric shift of quasiequilibrium: Origin of nonreciprocal current driven by quantum-metric dipole
Sota Kitamura, Takahiro Anan and Takahiro Morimoto
We study nonlinear DC electric transport of
quantum-metric origin by combining adiabatic perturbation theory with the nonequilibrium Green function approach. The adiabatic ansatz provides a basis for directly treating a DC electric field in the velocity gauge, rather than introducing it as the zero-frequency limit of an AC field. The resulting adiabatic-basis
Hamiltonian takes the same form as in the length gauge, enabling a systematic comparison across different formulations. Applying this fully
quantum formulation, we find a longitudinal nonreciprocal current governed by the
quantum-metric dipole. The essential ingredient is a
quantum correction to the distribution function that is absent in semiclassical treatments. We trace this correction to the finite spread of an electron wave packet during relaxation under a bias field, thereby identifying shifted quasiequilibrium as the physical origin of
quantum-metric nonreciprocal transport.
Read the full abstract ▾
Mesoscale and Nanoscale Physics
The Wigner function for Integer quantum Hall effect
Yao Wang, Qi-Ming Fu, Huawei Fan et al. (+2 more)
Wigner's quasi-probability distribution function in phase space is a specialized representation of the density
matrix, possessing significant physical importance. In this article, we first review the wave function describing electronic motion in an electromagnetic field under the Landau gauge. Next, based on an introduction to the properties of the Wigner function, we calculate the Wigner function for the integer
quantum Hall effect using the integral method.
Read the full abstract ▾
All authors Yao Wang, Qi-Ming Fu, Huawei Fan, Li Yu, Kang Li
Statistical Mechanics · Cross-listed from math-ph
Open-boundary integrable quantum circuits with different geometries
Miguel García Fernández, Chiara Paletta and Ana L. Retore
We present a complete classification of integrable Yang-Baxter
quantum circuits with open boundary conditions and arbitrary
circuit geometries. Starting from the standard transfer-
matrix construction with two types of staggered inhomogeneities, we derive a general mapping that determines the arrangement of
circuit gates in terms of the inhomogeneities and the system size. We
conjecture that time-periodic
quantum circuits are integrable whenever the local bulk and boundary gates satisfy the Yang-Baxter equation and the same bulk gate is applied exactly once per period to every nearest-neighbor pair of
spins. Our construction also provides an
algorithm to detect Yang-Baxter integrability for
circuits with arbitrary geometries. Furthermore, we introduce a third type of inhomogeneity, denoted by $\rho$, and demonstrate that the minimum possible
circuit depth is four. We show that when these $\rho$-inhomogeneities are placed at the endpoints and in their immediate neighborhood, the resulting boundary gates can be interpreted as single gates acting on multiple sites. Our construction is fully general and applies to regular $R$-
matrices, both of difference and non-difference type, together with their associated boundary
matrices. As an application, we consider two-
qubit gates corresponding to 6- and 8-vertex $R$-
matrices of non-difference form satisfying the Yang-Baxter equation, and we construct the associated reflection
matrices that generate integrable
quantum circuits.
Read the full abstract ▾
Mesoscale and Nanoscale Physics
Anisotropic tunneling through magnetic barriers in 8-Pmmn borophene
Rachid El Aitouni, Sanae Zriouel, Clarence Cortes et al. (+2 more)
We present a theoretical study of electron tunneling through a
magnetic barrier in 8-Pmmn borophene, created by depositing two
ferromagnetic strips on the borophene sheet. Using a low-energy effective
Hamiltonian that captures the anisotropic Dirac spectrum, we solve the Dirac equation in three regions and impose wave-function continuity at the interfaces. From the resulting spinor solutions, we compute current densities and determine transmission and reflection probabilities as functions of incident energy, angle, and barrier parameters. The transmission exhibits strong anisotropy due to the tilted Dirac cones, with pronounced suppression for specific incident directions, suggesting directional filtering of carriers. We further calculate the conductance using the Landauer-Büttiker formalism, revealing that both
magnetic strength and barrier width can tune the charge transport properties. The results demonstrate that engineered
magnetic barriers in 8-Pmmn borophene enable precise control over electron flow, offering a platform for anisotropic transport control and tunable
quantum devices. The interplay between the intrinsic anisotropy of borophene and external
magnetic barriers provides rich opportunities to manipulate Dirac
fermions in two-dimensional systems.
Read the full abstract ▾
All authors Rachid El Aitouni, Sanae Zriouel, Clarence Cortes, David Laroze, Ahmed Jellal
Materials Science
Anisotropic nanoscale coherent polariton transport in CrSBr
Paritosh Malik, Dogyun Ko, Vita Solovyeva et al. (+11 more)
In a combined experimental and theoretical study, we demonstrate anisotropic polariton transport on the nanoscale in the van der Waals antiferromagnet CrSBr. While effective cavity-polariton formation emerges via the self-hybridization of ultra-high oscillator strength
excitons with a thin slab photonic mode, the absence of external mirrors facilitates spectroscopic investigation of these polaritons via cathodoluminescence (CL) on length scales determined by the electron wavelength. This direct access allows us to perform precise charting of the polariton landscape with nanometric resolution, and to probe polariton interference phenomena. The main finding of the work highlights that the coherent polariton transport follows the $C_{2v}$
symmetry of CrSBr, allowing exclusive transport along the crystallographic a-axis, while no coherent feature is found along the b-axis direction. Our work sets the foundation to use CL spectroscopy in cavity-polaritonics in more advanced landscapes, such as photonic
crystals or optical
lattices, and establishes the technique as a powerful tool to probe anisotropic expansion and relaxation phenomena on the nanoscale
Read the full abstract ▾
All authors Paritosh Malik, Dogyun Ko, Vita Solovyeva, Chirag Chandrakant Palekar, Imad Limame, Sven Rodt, Kseniia Mosina, Zdeněk Sofer, Alexander Steinhoff, Martin Esmann, Stephan Reitzenstein, Bo Han, Christopher Gies, Christian Schneider
Quantum Gases · Cross-listed from quant-ph
Undamped Modes in an N-Qubit Heisenberg Chain with Collective Dissipation
Chun Hei Leung
We investigate the undamped behaviors in a
spin-1/2 Heisenberg chain coupled with an environment via collective
spin jump operators. Using the Bethe ansatz basis, we show that undamped modes exist for any chain length N >= 3. These modes remain robust against variations in the system parameters, including the specific form of the collective dissipation, and the external field. Exploiting the Bethe ansatz solution, we further characterize the number of undamped modes and their oscillation frequencies, uncovering long-lived coherent dynamics in open integrable
quantum systems.
Read the full abstract ▾
Statistical Mechanics
Sandpile Models on complex networks
Komlan Fiagbe, Jean-François de Kemmeter and Timoteo Carletti
We investigate the sandpile model on complex networks by developing a branching-process framework that explicitly incorporates dissipation during avalanche propagation. Unlike classical branching descriptions, which assume conservative transport and locally tree-like independence, the present approach introduces grain-loss effects directly into the offspring distribution, yielding generalized generating functions for dissipative avalanche dynamics. In the dissipative regime, avalanche-size distributions acquire exponential cutoffs while preserving
topology-dependent scaling behavior. Numerical simulations confirm the theoretical predictions on sparse random networks and reveal systematic deviations in highly structured
topologies. In particular, by using Holme-Kim clustered scale-free networks, we show that increasing clustering continuously lowers the avalanche exponent and enhances the probability of large cascades, demonstrating that short cycles generate strong correlations that invalidate the classical independent-branch approx imation. Surprisingly, trees also exhibit substantial deviations from power-law because low edge density and the abundance of leaves constrain avalanche propagation. These results show that dissipation, clustering, and sparse connectivity fundamentally reshape avalanche size distribution of the sandpile model on networks and establish quantitative limits for branching-process descriptions of avalanche dynamics.
Read the full abstract ▾
Materials Science
A depth resolved investigation of hydrogen uptake in carbon based nanostructures by soft-to-hard photoemission spectroscopy
Orlando Castellano, Alice Apponi, Luca Cecchini et al. (+11 more)
Hydrogen chemisorption on graphitic carbon modifies the carbon orbital hybridization from sp2 to sp3, altering both structural and electronic properties. Understanding not only the lateral extent but also the depth distribution of hydrogen uptake in three-dimensional carbon architectures is essential for both fundamental studies and storage applications. To this end, we investigate here the
evolution of the C 1s core-level lineshape in nanoporous
graphene (NPG) and vertically aligned carbon nanotubes (CNTs) upon hydrogenation, exploiting soft-to-hard X-ray photoemission spectroscopy to achieve a depth-resolved analysis. Decomposition of the C 1s spectra reveals the formation of an sp3 rich overlayer, indicating hydrogen chemisorption limited to the outermost accessible surfaces in both systems. These results clarify the depth distribution of hydrogen in curved and porous graphitic networks and provide quantitative constraints on its chemisorption for carbon-based hydrogen storage applications.
Read the full abstract ▾
All authors Orlando Castellano, Alice Apponi, Luca Cecchini, Daniele Paoloni, Simone Ritarossi, Francesco Pandolfi, Ilaria Rago, Tien-Lin Lee, Samuel Jeong, Yoshikazu Ito, Carlo Mariani, Gianluca Cavoto, Francesco Offi, Alessandro Ruocco
Mesoscale and Nanoscale Physics
An efficient formalism for inertial spin waves: Dzyaloshinskii-Moriya antiferromagnets as case studies
De-Yun Zhao, Ri-Xing Wang, Meng-Qiu Cai et al. (+2 more)
Magnetic inertia, emerging in the ultrafast regime, supports inertial
spin waves (SWs) as novel
magnetic excitations. Despite considerable efforts devoted to inertial SWs, a systematic formalism for fully characterizing their intrinsic properties, especially chirality and polarization, is still lacking, and inertial SWs in spatially nonuniform
magnetic configurations remain poorly explored. Here, we develop a framework for calculating inertial SWs and establish a general definition of their chirality and polarization via the ellipticity angle, a unified parameter encoding frequency sign, phase difference, and elliptical axis ratio. Using this method, we systematically investigate precessional and nutational SWs in uniaxial antiferromagnets with staggered and homogeneous Dzyaloshinskii-Moriya interactions (DMIs), covering uniform collinear, canted, and spiral
magnetic configurations. The results reveal that small staggered DMI preserves
spin-wave degeneracy, whereas small homogeneous DMI lifts it. Further space-time inversion
symmetry breaking in canted and spiral structures fully removes
spin-wave degeneracy across the entire Brillouin zone. Long-wavelength nutational SWs behave as backward waves, and flat bands emerge in canted and spiral configurations near a critical inertial relaxation time. In canted and spiral configurations, nutational modes are always lefthanded whereas precessional modes are always righthanded; additionally, the dispersion spectra of the canted configuration can be derived from those of the spiral configuration via band folding. Polarization is wavenumber insensitive for uniform configurations but becomes strongly dispersive for nonuniform ones. This work advances the fundamental understanding of
magnetic inertial dynamics and provides theoretical insights for the development of ultrafast magnonic devices.
Read the full abstract ▾
All authors De-Yun Zhao, Ri-Xing Wang, Meng-Qiu Cai, Mikhail Cherkasskii, Peng-Bin He
Materials Science
Transition-Metal Tailored $Ga_{2}O_{2}$ Monolayer: From Room-Temperature Gas Sensing to Chemical Scavenging
Afreen Anamul Haque and Aniket Singha
Pristine $Ga_{2}O_{2}$ monolayers suffer from poor sensitivity and weak molecular capture, limiting their application in toxic gas detection and environmental detoxification. Here, we employ first-principles density functional theory (DFT) calculations to investigate the gas sensing and scavenging properties of $Ga_{2}O_{2}$ monolayers substitutionally tailored via seven transition-metals (TM): Pd, Zn, Zr, Mo, Ag, Ti, and Pt. All TM-substituted monolayers exhibit negative formation and binding energies, negligible
lattice distortion, and structural stability in molecular dynamics simulations. Performance evaluation against eight toxic industrial and three environmental gases reveals functionalities ranging from selective, reusable room-temperature sensing to permanent molecular capture. Ag substitution exhibits exceptional selectivity for $NO$ with moderate adsorption strength (~-0.83eV), an up to eight-order-of-magnitude conductivity enhancement, besides facilitating reusable $O_2$ and $NO_2$ detection. Additionally, Pd-, Zn-, Zr-, and Mo substitutions tune selectivity toward $NO$, $NO_2$, $CO_2$, $CO$, and $O_2$. Coming to applications towards toxic gas capture, Zr- and Mo-substituted systems selectively scavenge oxidizing gases, whereas Ti and Pt act as universal scavengers. Further analysis reveals that Pd- and Ag-substituted monolayers remain selective for $NO$, while Zn substitution favors $NO_2$ detection even in ambient atmospheric conditions. Thus, these tailored $Ga_{2}O_{2}$ monolayers offer a practical platform for atmospheric monitoring and detoxification.
Read the full abstract ▾
Materials Science
HVAF Spraying of NiTi Coatings: Microstructure, Phase Transformation and Shape Memory Behavior
Sneha Samal, Shrikant Joshi, Stefan Björklund et al. (+8 more)
Depositing various coatings on surface of engineering components with the aim to improve their performance concerning wear, corrosion, friction and thermal protection is already a standard practice. Depositing metallic NiTi shape
memory alloy coatings may be a viable alternative for hard ceramic coatings. NiTi coatings offer additional benefits originating from unique functional thermomechanical properties. However, fabrication of thick NiTi coatings turned out to be difficult. Standard electroplating and
laser cladding methods are not suitable for NiTi the most widely used
plasma spray methods tend to produce chemically inhomogeneous coatings that do not transform martensitically, cold sprayed NiTi coatings suffer from poor adhesion to the substrates. In this work we report on first ever successful fabrication of thick NiTi coatings (100-300 um) that display functional thermomechanical properties and simultaneously show very good adherence to the substrate. We used high velocity air fuel thermal spray method to fabricate NiTi coatings deposited on mild steel using four different sets of processing parameters. Chemical composition, porosity, microstructure, phase transformation and functional thermomechanical properties of the NiTi coatings were evaluated. Although the coatings contain inhomogeneous microstructure, voids,
oxide particles, high density of dislocation defects and internal stress, they undergo martensitic transformation upon cooling and or mechanical loading. As sprayed NiTi coatings need to be annealed to display functional thermomechanical properties. Despite their limited tensile strength, the coatings displayed thermal actuation in 3 point bending tests and shape
memory effects in nanoindentation and scratch tests.
Read the full abstract ▾
All authors Sneha Samal, Shrikant Joshi, Stefan Björklund, Mohit Chandra, Akhil Bhardwaj, Jaromír Kopeček, Stanislav Habr, Lukáš Václavek, Jan Tomáštík, Ondřej Tyc, Petr Šittner
Statistical Mechanics · Cross-listed from quant-ph
False vacuum decay in a two-dimensional quantum spin system
Luka Pavešić, Ian G. Moss and Simone Montangero
False
vacuum decay describes the relaxation of a metastable state through the nucleation and growth of bubbles of the stable phase. Despite describing a broad variety of phenomena across different fields, the
quantum version of the nucleation theory has little experimental or numerical support. Testing its predictions is particularly important in two or more spatial dimensions, where bubble nucleation acquires its true geometrical nature. Here, we study false
vacuum decay in the
quantum Ising model in two dimensions. Through tree tensor network simulations we extract the decay rate, the effective interface tension and the critical bubble size. We compare them to new semi-classical field theory calculations, and find excellent agreement. These results provide numerical evidence that the critical-bubble picture survives in an interacting
quantum spin system in 2+1 dimensions.
Read the full abstract ▾
Disordered Systems and Neural Networks · Cross-listed from physics.soc-ph
The ring wants to be broken
Alexei Vazquez
The Ramsey community number $r_\kappa$ is the minimum network size at which a graph's connectivity is better described by a partition into communities than by no partition, under a prescribed community-detection rule. It was introduced through numerical simulations of networks grown by local rules, which suggested that community structure can emerge without any node heterogeneity. Here I compute $r_\kappa$ analytically for the simplest homogeneous, locally wired graph: the circulant ring
lattice $C_n(1,\dots,c)$. Using a Bernoulli
stochastic block model with symmetric $\mathrm{Beta}$ priors as the detection rule, the
Bayesian evidence for a balanced two-community partition and for the unpartitioned network are both obtained in closed form, so the transition between them can be located exactly. The result is a sharp dependence on the interaction range: the plain cycle ($c=1$) is never partitioned, its two-community posterior decaying as $n^{-(2\alpha+3)}$, so $r_\kappa=\infty$; but the next-nearest-neighbour ring ($c=2$) acquires a finite $r_\kappa\simeq 35$ nodes, above which the partition is preferred with a log-evidence growing as $(\ln 2)\,n$. This provides an exactly solvable instance of community emergence in a network with no built-in communities, and shows that a minimal amount of local connectivity is enough to break the ring.
Read the full abstract ▾
Soft Condensed Matter
Curvature-driven wall accumulation in chiral active particles
Alessandro Petrini, Raphaël Maire, Umberto Marini Bettolo Marconi et al. (+1 more)
We study a dilute system of non-motile
chiral active particles confined in geometries ranging from straight channels to circular enclosures. Activity is introduced through
chiral particle-wall interactions, modeled as tangential wall forces that generate the edge currents characteristic of
chiral active matter. Remarkably, although the particles lack self-propulsion, these boundary currents induce density inhomogeneities. We show that boundary
curvature drives a wall accumulation phenomenon: particles remain uniformly distributed in straight channels but accumulate near the boundaries of circular confinements. Numerical simulations and a hydrodynamic theory for the density and momentum fields consistently capture this
curvature-induced wall-accumulation. These results identify boundary
curvature as a fundamental control parameter for
chiral edge transport and confinement-induced organization, with potential experimental relevance to spinning colloids and granular spinners.
Read the full abstract ▾
All authors Alessandro Petrini, Raphaël Maire, Umberto Marini Bettolo Marconi, Lorenzo Caprini
Superconductivity
Fermiology and spin polarization of topological surface states in PtBi$_2$
Anders Christian Mathisen, Xin Liang Tan, Stefanie Suzanne Brinkman et al. (+12 more)
Layered PtBi$_2$ is a candidate for topological superconductivity arising in
Fermi-arc surface states. Using
spin- and angle-resolved photoemission spectroscopy, we demonstrate that the
Fermi arcs in PtBi$_2$ are singly degenerate and
spin-polarized, which establishes their nontrivial
topology and constitutes a necessary condition for topological superconductivity. We further uncover a pronounced surface-termination dependence of the
Fermi-arc dispersion, yielding either nearly flat or approximately linear bands in agreement with first-principles calculations. Together, the observed
spin polarization and termination-dependent bandwidth of the
Fermi-arc surface states identify key ingredients underlying the potential emergence of topological superconductivity in PtBi$_2$.
Read the full abstract ▾
All authors Anders Christian Mathisen, Xin Liang Tan, Stefanie Suzanne Brinkman, Kristian Mæland, Fabian Göhler, Øyvind Finnseth, Grigory Shipunov, Falk Pabst, Manuel Alonso Lemos, Balasubramanian Thiagarajan, Craig Polley, Björn Trauzettel, Anna Isaeva, Jorge I. Facio, Hendrik Bentmann
Quantum Gases
Interaction-rotation driven localization-delocalization crossover in Fock space: An exact diagonalization study on trapped Bose gas
Mohd Talib and M. A. H. Ahsan
We study the localization-delocalization crossover and
quantum entanglement with varying numbers of interacting
bosons for the nonrotating and the rotating cases. The many-body ground state within subspaces of given total angular momentum is obtained via exact diagonalization and analyzed using the inverse participation ratio (IPR), the information (Shannon)
entropy and the von Neumann
entanglement entropy. In the non-rotating case, a crossover from localization to delocalization is observed with increasing interaction, characterized by decreasing value of IPR with corresponding increase in information
entropy and von Neumann
entanglement entropy, arising from interaction-induced depletion of Bose-Einstein condensate. When subjected to rotation, the system is driven further towards delocalization due to rotation-induced depletion of Bose-Einstein condensate. The crossover from localization to delocalization is indicated by distribution of the eigenstate weights over an increasing number of basis states in the many-body
Hilbert space. The consistent behavior of IPR, information
entropy and von Neumann
entanglement entropy with respect to interaction and rotation demonstrates that these quantities provide a unified characterization of the localization-delocalization crossover. Results on computed von Neumann
entropy show that localized states exhibit weak
entanglement while delocalized states are characterized by strong
entanglement within the
quantum many-body system.
Read the full abstract ▾
Quantum Gases
Elastic Modulus in One-Dimensional Quantum Droplets
Rui Zhang, Tianmiao Zhang, Huan-Bo Luo et al. (+1 more)
Quantum droplets (QDs) are self-bound states of ultradilute
quantum fluids stabilized by the interplay between the Lee Huang-Yang (LHY)
quantum-fluctuation correction and the mean-field interaction, providing a useful platform for exploring macroscopic
quantum phenomena. Recent studies on three-dimensional QDs have introduced the concept of bulk modulus and revealed its connection with the breathing-mode frequency, thereby linking the elastic response of QDs to their collective dynamics. Motivated by this progress, we investigate the elastic modulus of one-dimensional QDs. Based on a super Gaussian variational ansatz, we systematically derive the elastic modulus B and analyze its dependence on the interaction strength and particle number. The analytical predictions are further validated by numerical simulations based on imaginary time
evolution and the spatial scaling method. We also establish a quantitative relation between the elastic modulus and the eigenfrequency of the breathing mode. In addition, by incorporating corrections to the droplet width beyond the Thomas
Fermi approximation, we obtain the dependence of the ratio {\eta} = B/2 on the control parameters g and N. Unlike the three-dimensional case, where the corresponding ratio follows a simple power-law scaling, the one-dimensional system is affected by the
soliton-to-droplet crossover, leading to a more intricate dependence of {\eta} on g and N. Our results show that, in the high-particle-number regime, the elastic modulus asymptotically approaches a limiting value determined mainly by the interaction strength, whereas in the low-particle-number regime it depends on both the particle number and the interaction strength.
Read the full abstract ▾
All authors Rui Zhang, Tianmiao Zhang, Huan-Bo Luo, Zibin Zhao
Materials Science
Quantifying angular momentum of coherently driven circular phonons
Roman Mankowsky, Serhane Zerdane, Shih-Wen Huang et al. (+9 more)
The use of intense terahertz (THz) pulses to manipulate low-energy excitations offers a powerful approach for ultrafast control of electronic and
magnetic properties in materials. Theory suggests that circular ionic motions driven by THz fields carry angular momentum, potentially generating internal
magnetic fields. Recent experiments in nonmagnetic SrTiO3 (STO) have hinted at such THz-induced fields, but their origin remains debated. Here, we employ ultrafast x-ray diffraction to resolve the time-dependent ionic trajectories in STO following excitation by circularly polarized THz pulses. Our analysis reveals that oxygen ions, despite their lower mass, contribute around 90% of the
phonon angular momentum. The resulting imbalance between the negatively and positively charged ions provides a clear explanation for the mechanism behind induced magnetism in STO. This work further provides the first quantitative measurement of circular ionic motions and their angular momentum and establishes a general methodology for the investigation of angular momentum transfer in solids, paving the way for new strategies to control topological
phonon transport and
phonon-driven magnetism in
quantum materials.
Read the full abstract ▾
All authors Roman Mankowsky, Serhane Zerdane, Shih-Wen Huang, Mathias Sander, Xin Liu, Danylo Babich, Martina Basini, Puneet Kaur, Jan-Chi Yang, Michael Fechner, Urs Staub, Henrik Lemke