Materials Science · Cross-listed from physics.app-ph
On the Generation of Phononic Frequency Combs Using Defect Modes of Phononic Crystals
Suhas Suresh Bharadwaj, Murtaza Rangwala and Adarsh Ganesan
This paper proposes a method for generating phononic frequency combs (PFCs) using defect-localized modes in a two-dimensional hexagonal phononic
crystal. Localized vibration modes from a singular point defect produce evenly spaced spectral lines corresponding to PFCs. Numerical modelling reveals robust energy transfer under a single-tone drive, generating spectral sidebands. These results demonstrate defect engineering in phononic
crystals as a tunable platform for PFC generation with significant applications in high-resolution sensing, timing, and
quantum-acoustic technologies.
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Mesoscale and Nanoscale Physics
Quantum Wigner solid in two-dimensional electron systems in semiconductors
Alexander A. Shashkin and Sergey V. Kravchenko
We review recent transport experiments that reveal two-threshold voltage-current characteristics, marked by a significant increase in noise between the two threshold voltages, at low electron densities in the insulating regime in two-dimensional (2D) electron systems, specifically in silicon metal-
oxide-
semiconductor field-effect transistors (MOSFETs) and SiGe/Si/SiGe
heterostructures. The double-threshold voltage-current characteristics closely resemble those observed in the collective depinning of the
vortex lattice in type-II
superconductors. By adapting the model used for
vortices to the case of an electron solid, good agreement with the experimental results is achieved, which supports a
quantum electron solid forming in the low electron density state. When a perpendicular
magnetic field is applied, the double-threshold behavior occurs at voltages an order of magnitude lower and at significantly higher electron densities than the zero-field case. This indicates the stabilization of the
quantum electron solid, aligning with theoretical predictions. Interestingly, the double-threshold voltage-current curves, indicative of electron solid formation at low densities, are not observed in the
quantum Hall regime. This lack of observation does not confirm the existence of a quasi-particle
quantum Hall Wigner solid and indicates that quasi-particles near integer filling do not form an independent subsystem.
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Materials Science
EPW-VASP interface for first-principles calculations of electron-phonon interactions
Danylo Radevych, Aidan Thorn, Manuel Engel et al. (+5 more)
We present an interface between the Vienna Ab initio Simulation Package (VASP) and the EPW software for calculating materials properties governed by electron-
phonon (e-ph) interactions. Computation of the e-ph
matrix elements with the finite-difference supercell approach in VASP and their fine-grid interpolation in EPW enable accurate modeling of temperature-dependent materials properties and
phonon-assisted
quantum processes with VASP's extensive library of exchange-correlation functionals and pseudopotentials. We demonstrate the functionality of the EPW-VASP interface by examining the superconducting gap and critical temperature in MgB$_2$ using the anisotropic Migdal-Eliashberg equations, and the carrier mobility in cubic BN using the ab initio Boltzmann transport equation.
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All authors Danylo Radevych, Aidan Thorn, Manuel Engel, Aleksey N. Kolmogorov, Sabyasachi Tiwari, Georg Kresse, Feliciano Giustino, Elena R. Margine
Materials Science
Perspective: Magnon-magnon coupling in hybrid magnonics
Wei Zhang, Yuzan Xiong, Jia-Mian Hu et al. (+10 more)
The internal coupling of
magnetic excitations (
magnons) with themselves has created a new research sub-field in hybrid magnonics, i.e.,
magnon-
magnon coupling, which focuses on materials discovery and engineering for probing and controlling
magnons in a coherent manner. This is enabled by, one, the abundant mechanisms of introducing
magnetic interactions, with examples of exchange coupling, dipolar coupling, RKKY coupling, and DMI coupling, and two, the vast knowledge of how to control
magnon band structure, including field and wavelength dependences of frequencies, for determining the degeneracy of
magnon modes with different
symmetries. In particular, we discuss how
magnon-
magnon coupling is implemented in various materials systems, with examples of
magnetic bilayers, synthetic antiferromagnets, nanomagnetic arrays, layered van der Waals magnets, and (DMI SOT materials) in
magnetic multilayers. We then introduce new concept of applications for these hybrid magnonic materials systems, with examples of frequency up/down conversion and
magnon-
exciton coupling, and discuss what properties are desired for achieving those applications.
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All authors Wei Zhang, Yuzan Xiong, Jia-Mian Hu, Joseph Sklenar, Mitra Mani Subedi, M.Benjamin Jungfleisch, Vinayak S. Bhat, Yi Li, Luqiao Liu, Qiuyuan Wang, Yunqiu Kelly Luo, Youn Jue Bae, Benedetta Flebus
Materials Science
Effect of Magneto-Mechanical Synergism in the Process-Structure Correlation in Fe-C Alloys: A Phase-Field Modeling Approach
Soumya Bandyopadhyay, Sourav Chatterjee, Dallas R. Trinkle et al. (+4 more)
Applied
magnetic fields can alter phase
equilibria and kinetics in steels; however, quantitatively resolving how
magnetic, chemical, and elastic driving forces jointly influence the microstructure remains challenging. We develop a quantitative magneto-mechanically coupled phase-field model for the Fe-C system that couples a CALPHAD-based chemical free energy with demagnetization-field magnetostatics and microelasticity. The model reproduces single- and multi-particle
evolution during the alpha to gamma inverse transformation at 1023 K under external fields up to 20 T, including ellipsoidal morphologies observed experimentally at 8 T. Chemically driven growth is isotropic; a
magnetic interaction introduces an anisotropic driving force that elongates gamma precipitates along the field into ellipsoids, while elastic coherency promotes faceting, yielding elongated cuboidal or “brick-like" particles under combined magneto-elastic coupling. Growth kinetics increase with C content, and decrease with field strength and misfit strain. Multi-particle simulations reveal dipolar interaction-mediated coalescence for field-parallel neighbors and ripening for field-perpendicular neighbors. Incorporating field-dependent diffusivity from experiment slows kinetics as expected; a first-principles-motivated anisotropic diffusivity correction is estimated to be small (<2%). These results establish a process-structure link for magnetically assisted heat treatments of Fe-C
alloys and provide guidance for microstructure control via chemo-magneto-mechanical synergism.
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All authors Soumya Bandyopadhyay, Sourav Chatterjee, Dallas R. Trinkle, Richard G. Hennig, Victoria Miller, Michael S. Kesler, Michael R. Tonks
Statistical Mechanics · Cross-listed from cs.SI
Evaluating Global Measures of Network Centralization: Axiomatic and Numerical Assessments
Majid Saberi and Samin Aref
Network centralization, driven by hub nodes, impacts communication efficiency, structural integration, and dynamic processes such as
diffusion and synchronization. Although numerous centralization measures exist, a major challenge lies in determining measures that are both theoretically sound and empirically reliable across different network contexts. To resolve this challenge, we normalize 11 measures of network centralization and assess them systematically using an axiomatic framework and numerical simulations. Our axiomatic assessment tests each measure against the six postulates of centralization, ensuring consistency with minimal theoretical requirements. In addition, our numerical assessment examines the behavior of normalized centralization measures over different random graphs. Our results indicate major differences among the measures, despite their common aim of quantifying centralization. Together, our assessments point to the relative suitability of three measures: normalized betweenness centralization, normalized closeness centralization, and normalized degree centralization. Applying these three measures to real-world networks from diverse domains reveals meaningful variation in the organization of the networks with respect to hubs. Normalized betweenness centralization highlights path-based dominance; normalized closeness centralization reflects accessibility and efficiency of reach; and normalized degree centralization captures degree-based hub concentration. When used jointly, the three measures demonstrate the required sensitivity to varying levels of centralization and provide complementary aspects of network centralization that no single measure can offer alone. Our dual evaluation framework clarifies conceptual differences among existing measures and offers practical guidance for selecting reliable centralization metrics.
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Mesoscale and Nanoscale Physics
Exceptional points and spectral cusps from density-wave fluctuation
Zixi Fang and Chen Fang
We report two types of singularities that arise from fluctuations during the formation of charge- or
spin-density waves. The first is the exceptional point (EP), corresponding to a higher-order pole of the retarded Green's function. Such EPs lead to algebraic corrections in the decay of quasiparticle occupations and are observable through time-resolved angle-resolved photoemission spectroscopy (Tr-ARPES). The second is a spectral cusp, defined by the coalescence of three extrema in the real-frequency spectral function $A(\mathbf{k}, \omega)$. This cusp enforces the formation of
Fermi arcs and induces a "threading" structure in the nearby band structure, both of which are directly observable in ARPES.
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Materials Science
IRSSG: An Open-Source Software Package for Spin Space Groups
Sheng Zhang, Ziyin Song, Zhong Fang et al. (+2 more)
We present an open-source software package IRSSG for investigating
magnetic systems with
spin space groups (SSGs). The package works within the density functional theory (DFT) framework and requires wavefunctions from DFT codes, such as VASP,
Quantum ESPRESSO, as well as any other code that has an interface to Wannier90. We introduce a set of compact SSG international symbols by combining non-crystallographic point groups with the 230 crystallographic space groups. The program first identifies all SSG operations and determines the SSG international symbol for a given
magnetic system. It then generates the SSG character tables of little groups at any $k$ point. Finally, it computes the traces of
matrix representations of SSG operations and assigns irreducible corepresentation labels to
magnetic energy bands. The program is not only timely but also essential for advancing research on the study of
magnons, altermagnetism,
magnetic topology, and novel high-degeneracy excitations in SSG systems.
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All authors Sheng Zhang, Ziyin Song, Zhong Fang, Hongming Weng, Zhijun Wang
Strongly Correlated Electrons
Obstruction to Ergodicity from Locality and $U(1)$ Higher Symmetries on the Lattice
Ramanjit Sohal and Ruben Verresen
We argue that the presence of any exact $U(1)$ higher-form
symmetry, under mild assumptions, presents a fundamental obstruction to ergodicity under
unitary dynamics in
lattice systems with local interactions and finite on-site
Hilbert space dimension. Focusing on the two-dimensional case, we show that such systems necessarily exhibit
Hilbert space fragmentation and explicitly construct Krylov sectors whose number scales exponentially with system size. While these sectors cannot be distinguished by
symmetry quantum numbers, we identify the emergent integrals of motion which characterize them. Our
symmetry-based approach is insensitive to details of the
Hamiltonian and the
lattice, providing a systematic explanation for ergodicity-breaking in a range of systems, including
quantum link models.
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Strongly Correlated Electrons
Thermodynamics of the Heisenberg antiferromagnet on the maple-leaf lattice
Robin Schäfer, Paul L. Ebert, Noah Hassan et al. (+3 more)
We study the Heisenberg antiferromagnet on the maple-leaf
lattice using several numerical approaches, focusing on the numerical linked-cluster expansion (NLCE), which exhibits an unconventional convergence extending to low and even zero temperatures. We evaluate thermodynamic properties as well as
spin-
spin correlations through the equal-time structure factor. Within NLCE the specific heat capacity reveals a two-peak structure at $T_1 \approx 0.479\,J$ and $T_2 \approx 0.131\,J$, reminiscent of the corresponding result for the triangular
lattice. At intermediate temperatures, the
spin-
spin structure factor develops features that reflect the absence of reflection
symmetry in the
lattice. The zero-temperature convergence of NLCE enables reliable estimates of the ground-state energy and points to a short-range correlated paramagnetic ground state composed of resonating hexagonal motifs. The NLCE results are benchmarked against Pseudo-Majorana Functional Renormalization Group, finite-temperature Lanczos, and classical Monte Carlo simulations.
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All authors Robin Schäfer, Paul L. Ebert, Noah Hassan, Johannes Reuther, David J. Luitz, Alexander Wietek
Statistical Mechanics · Cross-listed from quant-ph
Holographically Emergent Gauge Theory in Symmetric Quantum Circuits
Akash Vijay and Jong Yeon Lee
We develop a novel
holographic framework to study dynamical phases in random
quantum circuits with a global
symmetry $G$. Viewing the
circuit as a tensor network, we decompose it into two parts: a symmetric layer, which defines an emergent gauge wavefunction in one higher dimension, and a non-symmetric layer, composed of random multiplicity tensors. For $G\,{=}\,\mathbb{Z}_N$ symmetric
circuits consisting of local
unitary gates interspersed with local symmetric noise channels, averaging over the non-symmetric layer yields a dynamically generated noisy $\mathbb{Z}_{N}$ surface code. This allows us to interpret $\mathbb{Z}_{N}$ symmetric
circuits in the volume-law phase as
quantum error-correcting codes with a distinguished set of logical
spin states that inherit the topological protection of the bulk code. By establishing equality of bulk and boundary coherent information, we show that
quantum information encoded in these logical states is maximally protected against symmetric noise up to a finite threshold. We further study weakly monitored $\mathbb{Z}_{N}$ symmetric
circuits which exhibit a charge-sharpening transition. We show that the point at which the observer gains classical information about the global charge coincides with the point at which measurements destroy the underlying
quantum information encoded in the bulk surface code. This also allows for a natural interpretation of the sharpening transition as a confinement transition in the gauge theory. For $N\,{\leq}\,4$, weak measurements drive a single transition from a charge-fuzzy phase with exponential sharpening time $t_{\#}\sim e^{L}$ to a charge-sharp phase with $t_{\#}\sim \mathcal{O}(1)$. On the other hand, for $N>4$, the
circuit can enter an intermediate phase with a linear sharpening time $t_{\#}\sim \mathcal{O}(L)$. In this regime, the bulk gauge theory realizes a Coulomb phase with emergent gapless
photons.
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Strongly Correlated Electrons
Mean-field Modelling of Moiré Materials: A User's Guide with Selected Applications to Twisted Bilayer Graphene
Yves H. Kwan, Ziwei Wang, Glenn Wagner et al. (+3 more)
We review the theoretical modelling of moiré materials, focusing on various aspects of magic-angle twisted
bilayer graphene (MA-TBG) viewed through the lens of Hartree-Fock mean-field theory. We first provide an elementary introduction to the continuum modelling of moiré bandstructures, and explain how interactions are incorporated to study correlated states. We then discuss how to implement mean-field simulations of ground state structure and collective excitations in this setting. With this background established, we rationalize the power of mean-field approximations in MA-TBG, by discussing the idealized "
chiral-flat" strong-coupling limit, in which ground states at electron densities commensurate with the moiré superlattice are exactly captured by mean-field ansätze. We then illustrate the phenomenological shortcomings of this limit, leading us naturally into a discussion of the intermediate-coupling incommensurate Kekulé spiral (IKS) order and its origins in ever-present heterostrain. IKS and its placement within an expanded Hartree-Fock
manifold form our first "case study". Our second case study involves time-dependence, and focuses on the collective modes of various broken-
symmetry insulators in MA-TBG. As a third and final case study, we return to the strong-coupling picture, which can be stabilized by aligning MA-TBG to an hBN substrate. In this limit, we show how mean field theory can be adapted to the translationally non-invariant setting in order to quantitatively study the energetics of domain walls in orbital Chern insulating states. We close with a discussion of extensions and further applications. Used either as a standalone reference or alongside the accompanying open-source code, this review should enable readers with a basic knowledge of band theory and many-body physics to systematically build and analyze detailed models of generic moiré systems.
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All authors Yves H. Kwan, Ziwei Wang, Glenn Wagner, Nick Bultinck, Steven H. Simon, Siddharth A. Parameswaran
Materials Science
On the generalized Keffer form of the Dzyaloshinskii constant: its consequences for the spin, momentum and polarization evolution
Pavel A. Andreev
Different analytical features of the Dzyaloshinskii-Moriya interaction are related to different contributions to the Dzyaloshinskii constant in the microscopic
Hamiltonian. Consequences appear in the macroscopic Landau–Lifshitz–Gilbert equation. It leads to various phenomena. Three contributions to the Dzyaloshinskii constant are reviewed and combined in the generalized Keffer form of the Dzyaloshinskii constant. The fourth possible form of the Dzyaloshinskii constant is suggested as well. Macroscopic consequences of these three mechanisms are well-known, but further possible generalizations of the Keffer form of the Dzyaloshinskii constant are suggested. Consequences for the
spin evolution equations, the momentum balance equations, and polarization
evolution equations are considered. Some analog of the Keffer form is suggested for the exchange integral in symmetric Heisenberg
Hamiltonian demonstrating the nontrivial contribution of the ligands in this regime.
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Superconductivity
Edge-Dependent Superconductivity in Twisted Bismuth Bilayers
Isaías Rodríguez, Renela M. Valladares, Alexander Valladares et al. (+3 more)
Twisted
bilayers offer a compelling and, at times, confounding platform for the engineering of new twistronic materials. Whereas standard studies almost exclusively focus on the explicit enigma that is presented by twist-angles, perhaps better epitomized by the related phenomena that have been observed in twisted
bilayer graphene, functional devices necessarily face a fundamental concern: boundary heterogeneity in their structures. In this study, we address this concern by strictly investigating the electronic properties of twisted bismuth
bilayers at the flake's edges and the vibrational properties of the flake. Twisted flakes exhibit continuous variations of these properties, away from the bulk, as we herein report using ab initio density functional theory, by systematically mapping the drastic
evolution of band
topology, electronic density of states, and possible superconductivity. Our work reveals a dramatic, non-fortuitous consequence of the structural disorder at the edges of the flakes: an enhanced electronic density of states at the
Fermi level. This enhancement reaches a maximum of 10 times that of perfect-crystalline bismuth. Given that the superconducting critical temperature, Tc, is exponentially dependent on the electronic density of states at the
Fermi level, this substantial structural variation immediately suggests a powerful mechanism for vastly increasing Tc. We also identify the twist-angle as a new critical parameter in designing novel engineering devices with topologically enhanced properties. Our results provide a necessary theoretical framework for interpreting new data for the upcoming generation of twistronic heterogeneous materials, and pave the way to search for atomic disordered metastable structures that could lead to enhanced superconducting transition temperatures.
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All authors Isaías Rodríguez, Renela M. Valladares, Alexander Valladares, David Hinojosa-Romero, Flor B. Quiroga, Ariel A. Valladares
Disordered Systems and Neural Networks · Cross-listed from math-ph
Spectral Density and Eigenvector Nonorthogonality in Complex Symmetric Random Matrices
Gernot Akemann, Yan V. Fyodorov and Dmitry V. Savin
Non-Hermitian random
matrices with statistical spectral characteristics beyond the standard Ginibre ensembles have recently emerged in the description of dissipative
quantum many-body systems as well as in non-ergodic wave transport in complex media. We investigate the class AI$^\dag$ of complex symmetric random
matrices, for which available analytic results remain scarce. Using a recently proposed framework by one of the authors, we analyze this class for Gaussian entries and derive an explicit, closed-form expression for the joint distribution of a complex
eigenvalue and its right eigenvector for arbitrary
matrix size $N\ge 2$ in the entire complex plane. From this, we obtain the distribution of the eigenvector non-orthogonality overlap and the mean
eigenvalue density, both for finite $N$ and in the large-$N$ limit. Notably, at the spectral edge both the
eigenvalue density and eigenvector statistics exhibits a limiting behavior that differs from the Ginibre universtality class. This behavior is expected to be universal, as further supported by numerical evidence for Bernoulli random
matrices.
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Other Condensed Matter · Cross-listed from quant-ph
Using the wavelet transform to separate scales in the Schrödinger equation and subsequently derive the Boltzmann equation
A. P. Meilakhs
Here we continue our investigation aimed at the derivation of the Boltzmann equation from the first principles of
quantum mechanics. The key difficulty that we overcome in this manuscript is the incompatibility between traditional methods employed in the derivation of classical mechanics from
quantum mechanics and methods used to describe transitions between
quantum states due to interaction. Here we use a novel technique that is similar to the wavelet transform method that originally appeared in the context of signal processing. With this method, we can simultaneously work with slowly varying potentials that give rise to classical-like wave-function behaviour, motion along a prescribed trajectory, and sharp potentials that lead to behaviour that is best understood in terms of
quantum transitions. Working with smooth potentials in this framework, we derive the Liouville equation from the Schrödinger equation. When using this method for sharp potentials, we naturally obtain the description of system dynamics in terms of a transition-rate
matrix. The transition rates between system states, which characterize the process, are determined by
Fermi's golden rule. We observe that, through the Liouville equation, we can deduce the non-collision part of the Boltzmann equation, and that, through the transition-rate
matrix, we can deduce the collision integral. We combine the results to derive the Boltzmann equation, the main formula of physical kinetics.
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Mesoscale and Nanoscale Physics
Dichroism from Chiral Thermoelectric Probes: Generalized Sum Rules for Orbital and Heat Magnetizations
Baptiste Bermond, Lucila Peralta Gavensky, Anaïs Defossez et al. (+1 more)
We introduce a unified framework that relates orbital and heat magnetizations to experimentally accessible excitation spectra, through thermoelectric probes and generalized sum rules. By analyzing zero-temperature transport coefficients and applying Kramers-Kronig relations, we derive spectral representations of magnetization densities from thermoelectric correlation functions. Excitation rates under
chiral thermoelectric drives then naturally emerge as direct probes of these Kubo-type correlators, placing orbital and heat magnetizations on equal footing with the topological Chern number. As a direct consequence of our formalism, we introduce a hierarchical construction that organizes orbital and heat magnetizations into distinct physical contributions accessible through sum rules, and also naturally obtain real-space markers of these magnetizations. Besides, non-
chiral thermal probes identify a heat
quantum metric, which is defined over the space of gravitomagnetic deformations. From an experimental standpoint, we propose concrete implementations of thermoelectric dichroic measurements in
quantum-engineered platforms based on modulated strain fields. These results establish thermoelectric dichroic measurements as a versatile route to access and disentangle fundamental ground-state properties.
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All authors Baptiste Bermond, Lucila Peralta Gavensky, Anaïs Defossez, Nathan Goldman
Strongly Correlated Electrons
Unconventional orders in the maple-leaf ferro-antiferromagnetic Heisenberg model
Lasse Gresista, Dominik Kiese, Simon Trebst et al. (+1 more)
Motivated by the search for unconventional orders in frustrated
quantum magnets, we present a multi-method investigation into the nature of the
quantum phase diagram of the
spin-$1/2$ Heisenberg model on the maple-leaf
lattice with three
symmetry-inequivalent nearest-neighbor interactions. It has been argued that the parameter regime with
antiferromagnetic couplings on hexagons $J_h$ and
ferromagnetic couplings on triangles $J_t$ and dimer $J_d$ bonds, is potentially host to a cornucopia of emergent phases with unconventional orders. Our analysis indeed identifies an extended region where any conventional dipolar
magnetic order is absent. A hexagonal singlet state is found in the region around $J_{d}=J_{t}=0$, while a dimerized hexagonal singlet order of a
lattice nematic character appears proximate to the phase boundary with the c$120^\circ$
antiferromagnetic order. Interestingly, upon traversing the bulk of the paramagnetic (PM) region, we find a variety of distinct correlation profiles, which are qualitatively different from those of the hexagonal singlet and dimerized hexagonal singlet orders but feature no appreciable
spin-nematic response, while the boundary with the
ferromagnetic phase shows evidence of
spin-nematic order. This PM region is thus likely host to an ensemble of nonmagnetic phases which could putatively include
quantum spin liquids. Our phase diagram is built from a complementary application of state-of-the-art implementations of the cluster mean-field and pseudo-
fermion functional renormalization group approaches, together with an unconstrained Luttinger-Tisza treatment of the model providing insights from the semi-classical limit.
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All authors Lasse Gresista, Dominik Kiese, Simon Trebst, Yasir Iqbal
Mesoscale and Nanoscale Physics
Phonon-tunable THz magnonic emission in multiferroic heterostructures
Sylvain Massabeau, Amr Abdelsamie, Florian Godel et al. (+13 more)
Collective excitations such as
magnons and polar
phonons provide natural access to the terahertz (THz) regime, but efficient generation and tunability remain elusive. Multiferroic BiFeO3 combines both orders at room temperature, offering a unique platform for narrowband THz emission. Here, we achieve efficient sub-bandgap optical rectification of coupled
phonon-polaritons near 2 THz in bare epitaxial thin films. In Pt/BiFeO3
bilayers, we demonstrate that coupling the electromagnon branch with ultrafast strain waves, optically generated in Pt layers with various thicknesses, can produce tunable and narrowband emission between 0.4-0.8 THz. These results uncover the intertwined role of
phonons,
magnons, and magneto-acoustic dynamics in
antiferromagnetic multiferroics, and establish these hybrid platforms as versatile engineered narrowband THz sources.
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All authors Sylvain Massabeau, Amr Abdelsamie, Florian Godel, Filip Miljevic, Noela Rezi, Pascale Gemeiner, Karim Bouzehouane, Thomas Buttiens, Sukhdeep Dhillon, Thomas Maroutian, Jean-Marie George, Henri Jaffres, Brahim Dkhil, Stephane Fusil, Vincent Garcia, Romain Lebrun
Mesoscale and Nanoscale Physics
Formation of Light-Emitting Defects in Ag-based Memristors
Diana Singh, Maciej Ćwierzona, Régis Parvaud et al. (+2 more)
Optical memristors are innovative devices that enable the integration of electro-optical functionalities - such as light modulation, multilevel optical
memory, and nonvolatile reprogramming - into neuromorphic networks. Recently, their capabilities have expanded with the development of light-emitting memristors, which operate through various emission mechanisms. One notable process involves the electroluminescence of defects generated within the switching
matrix during device activation. In this study, we explore the early-stage formation and
evolution of the species responsible for light emission in Ag-based in-plane memristors. Our approach combines electrical stimulation with correlated optical electroluminescence and photoluminescence measurements. The findings provide valuable insights into controlling emission processes in memristors, paving the way for their integration as essential components in neuromorphic
circuits.
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All authors Diana Singh, Maciej Ćwierzona, Régis Parvaud, Sebastian Maćkowski, Alexandre Bouhelier
Strongly Correlated Electrons
Saturation Field as a Direct Probe of Exchange and Single-Ion Anisotropies in Spin-1 Magnets
M. A. R. Griffith, S. Rufo, H. Caldas et al. (+3 more)
High
magnetic fields provide a direct route to probe the anisotropies that govern
spin dynamics in layered magnets. Using the SU(3) bond operator framework for
spin 1 systems, we derive analytic expressions for the
magnon spectrum and the critical fields delimiting the field induced ordered phase. We show that the upper critical field $h_{c2}$ carries a simple and quantitative fingerprint of both exchange anisotropy and single ion
symmetry breaking, enabling high field experiments to serve as sensitive probes of microscopic anisotropy. We further map how these anisotropies, together with interlayer coupling, control the extent and location of the
magnon Bose Einstein condensation dome. Our results provide experimentally accessible criteria for identifying
symmetry breaking mechanisms in real
spin 1 materials.
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All authors M. A. R. Griffith, S. Rufo, H. Caldas, F. Dinola Neto, Minos A. Neto, J. R. Viana
Materials Science · Cross-listed from physics.optics
High resolution 3D imaging of diamonds with multiphoton microscopy
Elana G. Alevy, Samuel D. Crossley, Lam T. Nguyen et al. (+2 more)
Diamonds offer unique benefits for optical technology development due to their optical, chemical, electrical, mechanical, and thermal properties. These attributes also contribute to their aesthetic appeal, high commercial value, and utility in geological studies. Thus, there is high demand for nondestructive techniques that enable rapid analysis of natural and synthetic diamonds as well as diamond-like simulants. Here, we demonstrate sub-micrometer, nondestructive, three-dimensional imaging and spectral analysis of diamonds using multiphoton microscopy (MPM). This approach stimulates nonlinear optical emissions to provide unique insights into the interior structure, fluorescent defects, and formational conditions of diamonds. As a result, MPM can be used to investigate gemstone quality, vacancy centers used in
quantum technologies, and the various inclusions and fluorescent emitters that may trace gemstone provenance and treatment history.
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All authors Elana G. Alevy, Samuel D. Crossley, Lam T. Nguyen, Vu D. Phai, Khanh Q. Kieu
Mesoscale and Nanoscale Physics
Muralidhar Nalabothula, Davide Sangalli, Fulvio Paleari et al. (+2 more)
Excitons, bound electron-hole pairs, are responsible for strong optical resonances near the bandgap in low-dimensional materials and wide-bandgap
insulators. Although current ab initio methods can accurately determine
exciton energies and eigenstates, their
symmetries have been much less explored. In this work, we employ standard group-theory methods to analyse the transformation properties of excitonic states, obtained by solving the BSE, under
crystal symmetry operations. We develop an approach to assign irreducible-representation labels to excitonic states, providing a state-of-the-art framework for analysing their
symmetries and selection rules (including, for example, the case of
exciton-
phonon coupling). Complementary to the
symmetry classification, we introduce the concept of total
crystal angular momentum for
excitons in the presence of rotational
symmetries, allowing the derivation of conservation laws. Furthermore, we demonstrate how these
symmetry properties can be exploited to greatly enhance the computational efficiency of
exciton calculations with the BSE. We apply our methodology to three prototypical systems to understand the role of
symmetries in different contexts: (i) For LiF, we present the
symmetry analysis of the entire excitonic dispersion and examine the selection rules for optical absorption. (ii) In the calculation of resonant Raman spectra of monolayer MoSe2, we demonstrate how the conservation of total
crystal angular momentum governs
exciton-
phonon interactions, leading to the observed resonant enhancement. (iii) In bulk hBN, we analyze the role of
symmetries for the coupling of finite-momentum
excitons to finite-momentum
phonons and their manifestation in the
phonon-assisted luminescence spectra. This work establishes a general and robust framework for understanding the
symmetry properties of
excitons in
crystals, providing a foundation for future studies.
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All authors Muralidhar Nalabothula, Davide Sangalli, Fulvio Paleari, Sven Reichardt, Ludger Wirtz
Strongly Correlated Electrons
Charge carrier relaxation dynamics in the one-dimensional Kondo lattice model
Arturo Perez-Romero, Mica Schwarm and Fabian Heidrich-Meisner
A generic question in the field of ultrafast dynamics is concerned with the relaxation dynamics and the subsequent thermalization of optically excited charge carriers. Among several possible relaxation channels available in a solid-state system, we focus on the coupling to
magnetic excitations. In this paper, we study the real-time dynamics of a paradigmatic model, the Kondo
lattice model in one dimension. We conduct a comprehensive study of the relaxation processes by evaluating the
spin polarization of the conduction electron, the local
spin-
spin correlation between localized and conduction electrons, and the electronic momentum distribution. While in the well-studied cases of one or two charge carriers in a
ferromagnetic background, no thermalization occurs, we demonstrate that the stationary state is compatible with thermalization if either the electronic filling is finite or the
magnetic background is in the singlet sector. Our real-time simulations using the time-dependent Lanczos method are corroborated by a direct comparison with finite-temperature expectation values and an analysis of the spectrum in terms of the gap ratio.
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Statistical Mechanics
Giant enhancement of transport driven by active fluctuations: impact of inertia
K. Białas and J. Spiechowicz
Recently, a paradoxical effect has been demonstrated in which transport of a free Brownian particle driven by active fluctuations in the form of white Poisson shot noise can be significantly enhanced when it is additionally subjected to a periodic potential. This phenomenon can emerge in an overdamped system, but it may also be inertia-induced. Here, we considerably extend previous studies and comprehensively investigate the impact of inertia on the effect of free transport enhancement observed in the overdamped system. We detect that inertia can not only induce this phenomenon, but depending on a parameter regime, it may also strengthen, weaken, or even destroy it. We exemplify these different scenarios and explore the parameter space to identify the corresponding regions where they emerge. The variance of the active fluctuations amplitude distribution is a key determinant of the inertia influence on the effect of free transport amplification. Our results are relevant not only for microscopic physical systems but also for biological ones, such as, e.g., living
cells, where fluctuations generated by metabolic activities are active by default.
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Statistical Mechanics · Cross-listed from quant-ph
Modeling dissipation in quantum active matter
Alexander P. Antonov, Sangyun Lee, Benno Liebchen et al. (+5 more)
Active matter is characterized by a constant influx and dissipation of energy that gives rise to directed motion. Dissipation requires interactions with an external environment, such that extending the paradigm of active matter to a
quantum framework requires an appropriate description of this environment. In this work, we consider a driven
quantum particle undergoing noise and dissipation, with external driving exhibiting characteristics of classical activity. We model the non-
unitary dynamics with time-local master equations and analyze the particle motion at different time scales for different forms of the master equations, satisfying different criteria. We systematically compare predictions on the dynamics of particle trajectories and thereby we uncover how the particle motion evolves under the interplay of
quantum effects, dissipation, and active-like dynamics. These results are essential for guiding possible experiments aimed at realizing
quantum analogues of classical active systems.
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All authors Alexander P. Antonov, Sangyun Lee, Benno Liebchen, Hartmut Löwen, Jannis Melles, Giovanna Morigi, Yehor Tuchkov, Michael te Vrugt
Materials Science
Unified interface dipole theory for Fermi level pinning effect at metal-semiconductor contacts
Ziying Xiang, Jun-Wei Luo and Shu-Shen Li
We present a unified bond dipole theory for metal-
semiconductor interfaces to explain the microscopic origin of interface dipoles and
Fermi level pinning (FLP) in terms of Harrison's bond-orbital model. By combining first-principles calculations with tight-binding analysis, we show that localized bonding between
semiconductor surface dangling bonds and metal orbitals is sufficient to generate a large interface dipole and induce strong FLP, even when only a single metal monolayer is present. Within this framework, metal-induced gap states (MIGS), dangling-bond-induced surface states (DBSS), and bonding states embedded in the valence band are all understood as different outcomes of the same underlying interface bonding mechanism, rather than as independent causes of FLP. We further establish that the key parameter governing FLP strength is the density of surface dangling bonds that can form new chemical bonds with the metal, which directly controls the magnitude of the bond-induced interface dipole. This picture naturally explains the weaker pinning observed in more ionic
semiconductors than in covalent ones and provides practical guidance for engineering metal-
semiconductor interfaces and tuning Schottky barrier heights.
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Statistical Mechanics
Thermodynamic response functions of the Curie-Weiss cell fluid model. I. Supercritical region
O.A. Dobush, M.P. Kozlovskii, R.V. Romanik et al. (+2 more)
In this work, we present an analytical study of the thermodynamic response functions of a multiple-occupancy
cell fluid model with competing Curie-Weiss attraction and local repulsion. In the grand canonical ensemble, explicit expressions are derived for the three independent response functions: the isothermal compressibility, the thermal pressure coefficient, and the isochoric heat capacity. The thermal expansion coefficient and the isobaric heat capacity are subsequently obtained from exact thermodynamic identities. The analytical formulas are used to investigate the behavior of the response functions in the supercritical region. The isothermal compressibility, the thermal expansion coefficient, and the isobaric heat capacity exhibit critical divergences, whereas the thermal pressure coefficient and the isochoric heat capacity remain finite at the critical points despite developing pronounced extrema. The thermal pressure coefficient displays a non-monotonic oscillatory dependence on density and becomes negative over a limited range of temperatures and densities, leading to negative values of the thermal expansion coefficient. The obtained analytical expressions provide a consistent theoretical framework for investigating the thermodynamic properties of the model and establish a basis for future analysis of the subcritical regime and multiphase
equilibrium.
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All authors O.A. Dobush, M.P. Kozlovskii, R.V. Romanik, I.V. Pylyuk, M.A. Shpot
Soft Condensed Matter
Fluidization induced by Magnetic Interactions in Confined Active Matter
Marco Musacchio, Markus Felber, Matteo Paoluzzi et al. (+3 more)
We investigate
magnetic active matter in confined geometries using both experiments with
magnetic toy
robots Hexbugs and simulations of elongated
magnetic active Brownian particles in circular domains. Standard active particles tend to accumulate at boundaries, forming clusters even at relatively low densities. In the presence of
magnetic interactions, we provide evidence for a fluidization effect that inhibits clustering and shifts its onset to higher packing fractions. Moreover,
magnetic dipolar interactions give rise to novel collective behaviors, such as train-like formations, rotating pairs, and particle
vortices.
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All authors Marco Musacchio, Markus Felber, Matteo Paoluzzi, Andrea Gnoli, Andrea Puglisi, Luca Angelani
Materials Science
Fast machine learned interatomic potential for hydrogen-induced embrittlement in {\alpha}-Fe
Eetu Makkonen, Alvaro Lopez-Cazalilla and Flyura Djurabekova
In this work, we present a machine-learned interatomic potential for the ${\alpha}$-Fe-H system based on the tabulated Gaussian Approximation Potential (tabGAP) formalism. Trained on a Density Functional Theory (DFT)
dataset of atomic configurations, energies, forces, and virials, the potential is designed for simulations on the mechanisms of hydrogen embrittlement (HE), the issue of H-induced acceleration of mechanical failure of metals. The proposed potential is shown to outperform the widely used classical and machine-learned interatomic potentials in fundamental properties of the ${\alpha}$-Fe-H system. We show that the tabGAP model reproduces H-point defect properties, H-dislocation interaction, H-H interaction, and elastic constants with nearly DFT-level accuracy at a computational cost that is competitive with the efficient classical Embedded Atom Method (EAM) potentials. As an application of the tabGAP model we simulate the effect of H on the mobility of the $\tfrac{1}{2}\langle 111\rangle$ screw dislocation, which show that the model predicts an enhancement of the mobility of the screw dislocation via trapped H atoms lowering the energy barrier of kink-pair nucleation, resulting in a decreased critical shear stress of dislocation motion at $300\,\mathrm{K}$.
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