Mesoscale and Nanoscale Physics
Environmental Effects and Brillouin's Paradox in Nonlinear Electrical Circuits
Lucas Désoppi and Bertrand Reulet
We present a
stochastic approach to calculate the full statistics of classical voltage fluctuations across an arbitrary, nonlinear, dissipative device embedded in a
circuit in the presence of a DC bias. We show how the feedback resulting from the
circuit, made of an ohmic resistor and a capacitor, affects the statistics of voltage fluctuations, and in particular resolves Brillouin's paradox to satisfy thermodynamics: feedback cancels rectification. We apply our very general results to the case of a tunnel junction and a diode.
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Materials Science
Molecular beam epitaxy of wafer-scale O-band InAs/InGaAs quantum dots on GaAs for quantum photonics
Pavel S. Avdienko, Lukas Hanschke, Quirin Buchinger et al. (+13 more)
We report a scalable molecular beam epitaxy strategy to achieve a low density of O-band electrically tunable InAs/InGaAs
quantum dots (QDs) on GaAs(001) substrates. Our approach is based on a gradient deposition of InAs in the sub-ML regime and subsequent capping with an InGaA strain-reducing layer to
redshift the emission wavelength. For different growth conditions, we investigate the optical properties of the dots using photoluminescence mapping and correlate with structural properties determined by scanning transmission electron microscopy. Using a surface roughness modulation technique and synchronizing InAs sub-monolayer deposition cycles with substrate rotation, we control the dot density and position low-density regions (< 1 QD per um^2) on the substrate. Hyperspectral imaging is used to map the spatial and spectral characteristics of many individual dots in the low-density region, confirming that our approach is universally applicable to conventional MBE growth on (001) surfaces. Finally, we tune the QD emission wavelength within the O-band using electric fields and demonstrate single-
photon emission with g(2)(0) = 0.020(14).
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All authors Pavel S. Avdienko, Lukas Hanschke, Quirin Buchinger, Nikolai Bart, Hubert Riedl, Bianca Scaparra, Yu Xia, Ziria Herdegen, Knut Müller-Caspary, Gregor Koblmüller, Tobias Huber-Loyola, Arne Ludwig, Andreas Pfenning, Sven Höfling, Kai Müller, Jonathan J. Finley
Statistical Mechanics
Bethe Ansatz with a Large Language Model
Balázs Pozsgay and István Vona
We explore the capability of a Large
Language Model (LLM) to perform specific computations in mathematical physics: the task is to compute the coordinate Bethe Ansatz solution of selected integrable
spin chain models. We select three integrable
Hamiltonians for which the solutions were unpublished; two of the
Hamiltonians are actually new. We observed that the LLM semi-autonomously solved the task in all cases, with a few mistakes along the way. These were corrected after the human researchers spotted them. The results of the LLM were checked against exact diagonalization (performed by separate programs), and the derivations were also checked by the authors. The Bethe Ansatz solutions are interesting in themselves. Our second model manifestly breaks left-right invariance, but it is PT-symmetric, therefore its solution could be interesting for applications in Generalized Hydrodynamics. And our third model is solved by a special form of the nested Bethe Ansatz, where the model is interacting, but the nesting level has a free fermionic structure lacking $U(1)$-invariance. This structure appears to be unique and it was found by the LLM. We used ChatGPT 5.2 Pro and 5.4 Pro by OpenAI.
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Mesoscale and Nanoscale Physics
Deep-UV bleaching of charge disorder in encapsulated graphene
Daniil Domaretskiy, Ned Hayward, Van Huy Nguyen et al. (+11 more)
Disorder masks much of the rich physics in two-dimensional electronic systems, with charged
impurities often the limiting factor. In
graphene, progress in reducing disorder has largely stagnated since boron nitride encapsulation was introduced a decade ago. Here we show that a brief deep-UV exposure enhances the electronic quality of encapsulated
graphene - typically by two orders of magnitude - by neutralizing charged
impurities within boron nitride. Following illumination, standard
graphene devices exhibit numerous evendenominator fractional
quantum Hall states, including non-Abelian candidates, and frequently reveal hidden superlattice minibands. Even macroscopically inhomogeneous devices, seemingly unusable for transport studies, recover after deep-UV illumination and display Landau quantization in millitesla fields. This finding provides a straightforward route to exceptional-quality
graphene, enabling further exploration of interaction-driven, topological and other
quantum phenomena.
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All authors Daniil Domaretskiy, Ned Hayward, Van Huy Nguyen, Simone Benaglia, Kornelia Indykiewicz, Hadrien Vignaud, Jing Zhang, Kenji Watanabe, Takashi Taniguchi, V. I. Fal'ko, Laura Fumagalli, L. A. Ponomarenko, I. V. Grigorieva, A. K. Geim
Other Condensed Matter
Kubo-Martin-Schwinger-Gated Imaginary-Time Reconstruction of Time-Resolved Electronic Circular Dichroism in Organic Excitonic Aggregates
Christian Tantardini and Caterina Cocchi
Time-resolved electronic circular dichroism (TR-ECD) and time-resolved circular dichroism (TRCD) probe
chiral exciton dynamics prepared by an ultrafast pump and interrogated by a weak circular probe. The measured signal is a causal mixed electric–
magnetic response, whereas imaginary-time methods require a sufficiently stationary reference. Here, we introduce a Kubo–Martin–Schwinger-gated criterion that determines, at each pump–probe delay, whether the selected TRCD-like response can be represented by a conditional one-
exciton Gibbs ensemble or requires explicit real-time or Keldysh dynamics. The diagnostic combines a state-level distance from the conditional reference with an integrated spectral distance for the reciprocal E1–M1 response. We apply the protocol to three literature-constrained Frenkel-
exciton models: a Ress-type squaraine-
polymer squeezed helix, a cisoid indolenine squaraine B hexamer, and a helical perylene-bisimide stack. The results show that early nonthermal states are non-admissible, whereas intramanifold population relaxation and the decay of coherence
memory can open a Matsubara-admissible delay window before complete excited-state recovery. The resulting gate identifies when imaginary-time methods can be used without imposing a stationary description on a genuinely nonequilibrium chiroptical response.
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Materials Science · Cross-listed from physics.chem-ph
Gap edge eigenpairs from density matrix purification using moments of the Dirac distribution
Lionel Alexandre Truflandier
In this work, we propose a simple method to resolve the eigenstates located at the band gap edges of an electronic eigenspectrum using only the quasi-purified one-particle density
matrix as input. The theoretical framework relies on the decomposition of the occupation number variance into a particle and a hole moment. These moments, when purified using power narrowing iterations, allow us to isolate the highest occupied and lowest unoccupied single-state projectors, \colp{giving ready access} to the corresponding eigenpairs. We demonstrate that when degeneracy is encountered, power narrowing remains able to deliver relevant mixed states. From a
benchmark of selected molecules, we show that the method is robust and efficient since it requires from four to sixteen
matrix-
matrix multiplications in the worst case. The possibility of reducing the computational cost using the Lanczos subspace approach is discussed. The
algorithm simplicity of power narrowing makes it very easy to implement in electronic structure codes or libraries already featuring
Fermi operator expansion or density
matrix purification.
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Disordered Systems and Neural Networks · Cross-listed from q-bio.NC
Copy-Spread-Annihilate Dynamics in Degree-Assortative Networks
Yan Hao, Daniel J. Graham and Marc-Thorsten Hütt
In many systems, communication proceeds by broadcasting rather than single source-target routing, but network structures that maximize signal lifetime are not well understood. Degree correlations are known to influence robustness and spreading, yet their effect on signal persistence has remained unclear. Here we introduce Copy-Spread-Annihilate dynamics, a minimal synchronous broadcasting model with annihilation. We show that signal lifetimes vary non-monotonically with assortativity and are maximized near neutral assortativity, where hub-driven amplification is strong but annihilation via short cycles is still limited. Applying this framework to the mouse connectome suggests assortativity as a structural control parameter for broadcast signal persistence in
brain-like and other complex networks.
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Mesoscale and Nanoscale Physics
Angular anisotropy landscape of vortex ensembles in polarized small-angle neutron scattering
Michael P. Adams, Elizabeth M. Jefremovas and Andreas Michels
We present a
symmetry-resolved classification of two-dimensional
spin-flip small-angle
neutron scattering (SANS) patterns arising from dilute ensembles of spherical nanoparticles hosting
magnetic vortex states. Based on a linear
vortex ansatz with an axially symmetric distribution of
vortex axes and the corresponding analytical expression for the orientationally averaged
spin-flip SANS cross section, we show that the angular scattering patterns organize into four distinct
symmetry regimes: a four-fold anisotropy corresponding to coherent field-aligned magnetization, vertical and horizontal two-fold anisotropies associated with aligned and isotropically distributed
vortex ensembles, and an isotropic ring-like condition separating the two two-fold regimes. The corresponding
symmetry boundaries are obtained analytically and define a compact
symmetry landscape in the parameter space of
vortex amplitude and
vortex-axis distribution width. Comparison with a nonlinear
vortex profile shows that these
symmetry regions are robust with respect to the detailed radial structure of the
vortex core. The angular anisotropies are therefore governed primarily by rotational
symmetry and by the statistical distribution of
vortex axes, providing a compact and model-transparent classification framework of experimental polarized SANS data.
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Disordered Systems and Neural Networks
Inverse Design of Strongly Localized Topological $\pi$ Modes in One-Dimensional Nonperiodic Systems
Fumitatsu Iwase
This study investigates the spatial confinement of topological $\pi$-modes in one-dimensional
chiral-symmetric systems. In conventional periodic and quasiperiodic structures, edge-mode wave functions inevitably penetrate the bulk. To suppress this, inverse design of a potential sequence is performed using a generative model under a global topological constraint. The generated sequence reveals a characteristic structure consisting of a topological boundary layer and a macroscopic S-dense domain, leading to enhanced confinement ($\xi=0.85$) while preserving
topology. Based on the physical principle extracted from this result, a minimal
heterostructure composed of only two S-blocks is manually constructed, which further reduces the localization length to $\xi=0.75$. These results provide a compact design principle for strongly localized topological states.
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Materials Science · Cross-listed from physics.chem-ph
Short-lived memory in multidimensional spectra encodes full signal evolution
Thomas Sayer, Ethan H. Fink, Zachary R. Wiethorn et al. (+9 more)
Ultrafast multidimensional spectroscopies are powerful tools that can access charge and energy flow in complex materials, shifting chemical kinetics, and even many-body interactions in correlated matter. However, current implementations typically involve complex apparatuses and long averaging times. As a result, these methods have been limited to detailed mechanistic investigations of a few samples, precluding the broad characterization of molecular systems and/or the optimization of material ones. For example, converging the statistical noise in 2D spectra becomes exponentially expensive with increasing waiting times, and extended
laser exposure heightens the probability of sample degradation. We address this fundamental challenge by developing a new technique, the spectral generalized master equation (GME), that enables one to employ short-waiting time 2D spectra to determine the full
evolution of 2D spectra over arbitrary waiting times with high temporal resolution. In addition to reducing the cost of experiments by multiple orders of magnitude, our approach accurately removes statistical noise, reducing the need for time averaging, while circumventing the increasing convergence costs with longer waiting times. We provide a rigorous theoretical footing for the spectral GME and demonstrate its applicability on theoretically generated and experimentally measured 2D electronic and 2D infrared spectra. We anticipate that this advance has the potential to enable the investigation of systems that are too delicate for study with current multidimensional spectroscopies and accelerate the progress of 2D spectroscopy-based microscopies that can offer highly resolved excitation dynamics with spatial resolution over heterogeneous environments.
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All authors Thomas Sayer, Ethan H. Fink, Zachary R. Wiethorn, Devin R. Williams, Anthony J. Dominic III, Luke Guerrieri, Yi Ji, Veronica Policht, Jennifer Ogilvie, Gabriela Schlau-Cohen, Amber Krummel, Andrés Montoya-Castillo
Materials Science · Cross-listed from cs.LG
AMShortcut: An Inference- and Training-Efficient Inverse Design Model for Amorphous Materials
Yan Lin, Jonas A. Finkler, Tao Du et al. (+2 more)
Amorphous materials are solids that lack long-range atomic order but possess complex short- and medium-range order. Unlike crystalline materials that can be described by unit
cells containing few up to hundreds of atoms, amorphous materials require larger simulation
cells with at least hundreds or often thousands of atoms. Inverse design of amorphous materials with probabilistic generative models aims to generate the atomic positions and elements of amorphous materials given a set of desired properties. It has emerged as a promising approach for facilitating the application of amorphous materials in domains such as energy storage and thermal management. In this paper, we introduce AMShortcut, an inference- and training-efficient probabilistic generative model for amorphous materials. AMShortcut enables accurate inference of diverse short- and medium-range structures in amorphous materials with only a few sampling steps, mitigating the need for an excessive number of sampling steps that hinders inference efficiency. AMShortcut can be trained once with all relevant properties and perform inference conditioned on arbitrary combinations of desired properties, mitigating the need for training one model for each combination. Experiments on three amorphous materials
datasets with diverse structures and properties demonstrate that AMShortcut achieves its design goals.
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All authors Yan Lin, Jonas A. Finkler, Tao Du, Jilin Hu, Morten M. Smedskjaer
Statistical Mechanics
Optimal Control of a Mesoscopic Information Engine
Emanuele Panizon
We analytically solve the finite-time control problem of driving an overdamped particle via an optical trap under costly measurement. By formulating this mesoscopic information engine within the Partially Observable Markov Decision Process (POMDP) framework, we demonstrate that the underlying Linear-Quadratic-Gaussian (LQG) dynamics decouple the optimal measurement and driving protocols. We derive the optimal feedback control law for the trap placement, which recovers the discontinuous Schmiedl-Seifert driving protocol in the open-loop limit and extends it to any measurement scheduling. For a costly, binary (on/off) sensor, we evaluate the optimal measurement protocol and derive physical bounds on the maximum net gain that can be extracted from thermal fluctuations. We show the emergence of deadline-induced blindness, a phenomenon where all measurements cease as the deadline approaches regardless of their cost. Taking the infinite-horizon limit, we find the exact periodic measurement schedules for the steady state as a function of the measurement cost $C$ and derive the macroscopic velocity envelopes beyond which viscous drag forces the engine into a net-dissipative regime. Finally, we generalize the results to a variable-precision sensor.
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Materials Science
Superlinear Temperature-Dependent Resistivity and Structural Phase Transition in BaNi$_2$P$_4$
E. H. Krenkel, M. A. Tanatar, E. I. Timmons et al. (+13 more)
The mechanism of anomalous superlinear temperature-dependent resistivity, $\rho (T)$, in the metallic unconventional clathrate BaNi$_2$P$_4$ was studied by examining its
evolution with artificial disorder induced by low-temperature ($\sim$ 20 K) 2.5 MeV electron irradiation. We find a dominant effect of the tetragonal-orthorhombic transition at $T_s$ ($ \sim$373 to 378 K, depending on heat cycle rate and direction) on $\rho (T)$, with standard metallic $T-$linear resistivity above the transition and anomalous behavior in the orthorhombic phase below. The transition is accompanied by the formation of structural domains and a notable (about 4~K) hysteresis in the magnetization and resistivity measurements, clearly showing its first order character. Matthiessen rule is obeyed both above and below the transition, suggesting negligible changes in the electronic structure. This conclusion is supported by the smooth
evolution of the
Hall effect through the transition. The
Hall number is in good agreement with band structure calculations both above and below the transition. The transition temperature is notably suppressed with electron irradiation. Raman scattering at temperatures above room temperature find softening of local Ba vibration mode in the orthorhombic phase on approaching the transition. $^{31}P$ NMR line splits in the orthorhombic phase, suggesting a partial shift of the Ba atom from the central position in the cage. We suggest that local Ba rattling leads to enhanced residual contribution to resistivity in the high temperature tetragonal phase, the decay of which is responsible for the anomalous temperature-dependent resistivity in the orthorhombic phase.
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All authors E. H. Krenkel, M. A. Tanatar, E. I. Timmons, S. L. Bud'ko, P. C. Canfield, Qing-Ping Ding, Y. Furukawa, Lin-Lin Wang, M. Konczykowski, R. Grasset, J. L. Niedziela, O. Delaire, G. Viswanathan, J. Wang, K. Kovnir, R. Prozorov
Mesoscale and Nanoscale Physics
Emergence of Non-Hermitian Magic Angles and Topological Phase Transitions in Twisted Bilayer $\alpha$-$T_3$ Lattices
Shaina Gandhi, Gourab Paul, Srijata Lahiri et al. (+1 more)
We investigate the flat-band properties and topological phase transitions in a non-Hermitian twisted
bilayer $\alpha-T_3$
lattice. Here, non-Hermiticity is introduced via Hatano-Nelson-type asymmetric hopping, while an aligned hexagonal boron nitride substrate provides a staggered sublattice mass to the system. We find that the introduction of non-reciprocal hopping splits the conventional single magic angle into three distinct non-Hermitian magic angles (NHMAs). Unlike the exceptional magic angles driven by spectral singularities, these NHMAs host perfectly isolated flat bands where the real and imaginary parts of the bandwidth simultaneously vanish. By mapping the complex eigenspectrum across the moiré Brillouin zone, we show that the scattered energy
eigenvalues coalesce into well-defined, closed loop-like structures as the non-Hermitian parameter strength increases, indicating emergence of a nontrivial point-gap
topology and hence the non-Hermitian skin effect. Furthermore, we characterize the topological phases by computing the direct band gap and the biorthogonal Chern number. While the system exhibits a transition to a higher topological phase at weak non-Hermiticity, we demonstrate that stronger non-Hermiticity drives the gap-closing boundaries to merge and their topological charges to mutually annihilate. This convergence results in a trivial gap closing and a complete suppression of the intermediate topological phase, confirming that non-Hermiticity fundamentally plays a crucial role with regard to destabilizing the robust topological features of this moiré system.
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All authors Shaina Gandhi, Gourab Paul, Srijata Lahiri, Saurabh Basu
Strongly Correlated Electrons
Quantitative thermodynamic study of superconducting and normal states in UTe2 under pressure
T. Vasina, M. Pfeiffer, R. Borth et al. (+7 more)
We report a quantitative calorimetric study of UTe2 under pressure with a direct measurement of the Sommerfeld gamma coefficient, showing a three-fold enhancement of electronic effective mass when approaching the critical pressure where superconductivity is suppressed and ordered states occur. We analyse the
evolution of gamma with the amplitude of the jumps in the specific heat at the two superconducting transitions, and the superconducting critical temperature with pressure. This analysis would suggest that the high pressure superconducting phase nucleates only on a fraction of the
Fermi surface. It also points to the possible major role of a
quantum critical point of the unidentified phase that has been called weak
magnetic order, rather than to the critical pressure of the
antiferromagnetic phase. Just at the border of long-range
antiferromagnetic order, where superconductivity emerges from the weak
magnetic order phase, a significant increase in the specific heat jump for both superconducting transitions is found, accompanied by a noticeable change of their shapes.
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All authors T. Vasina, M. Pfeiffer, R. Borth, M. Nicklas, M. Amano Patino, G. Lapertot, J.-P. Brison, E. Hassinger, G. Knebel, D. Braithwaite
Mesoscale and Nanoscale Physics
Magnetically Induced Switching-Current Jumps in InAs/Al Josephson Junctions
Ofelia Durante, Roberta Citro, Elia Strambini et al. (+8 more)
We report Barkhausen-like switching at millitesla fields in an $n$-doped InAs/Al nanowire Josephson junction, which serves as an interferometric probe of intrinsic
magnetic reconfigurations, as evidenced by discrete switching-current jumps. At $T=30$~mK the device displays a Fraunhofer-like modulation with $I_{\mathrm{sw}}(0)\approx 0.24~\mu\mathrm{A}$ and an abrupt transition at $|B|\approx 3~\mathrm{mT}$ between two branches differing by $\Delta I_{\mathrm{sw}}\approx 0.13~\mu\mathrm{A}$. By tracking the characteristic field scales from $30$ to $900$~mK, we find that the jump field is essentially temperature-independent, whereas the superconducting critical field decreases with temperature, as expected for thin Al films. The sharp discontinuity, sweep-direction asymmetry, and reproducibility across repeated scans point to avalanche-like switching between metastable
magnetic configurations of the local
magnetic texture, which are directly coupled to the weak link. Within an effective-field framework, each reconfiguration modifies a local field offset, thereby reshaping the interference response and leading to an abrupt reorganization of the switching-current pattern.
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All authors Ofelia Durante, Roberta Citro, Elia Strambini, Valeria Demontis, Mirko Rocci, Alessandro Braggio, Sergio Battiato, Valentina Zannier, Lucia Sorba, Francesco Giazotto, Claudio Guarcello
Materials Science · Cross-listed from eess.SY
RHINO-MAG: Recursive H-Field Inference based on Observed Magnetic Flux Density under Dynamic Excitation
Hendrik Vater, Oliver Schweins, Lukas Hölsch et al. (+3 more)
Driven by the MagNet Challenge 2025 (MC2), increased research interest is directed towards modeling transient
magnetic fields within ferrite materials. An accurate time-resolved and temperature-aware H-field prediction is essential for optimizing
magnetic components in applications with quasi-stationary / non-stationary excitation waveforms. Within the scope of this investigation, a selection of model architectures with varying degrees of physically motivated structure is compared. Based on a Pareto investigation, a rather black-box gated recurrent unit (GRU) model structure with a graceful initialization setup is found to offer the most attractive model size vs. model accuracy trade-off in the small-model regime, while the examined physics-inspired models performed worse. For a GRU-based model architecture with only 325 parameters (trained separately per material), an average sequence relative error of 8.02 % and an average normalized energy relative error of 1.07 % across five different materials are achieved on unseen test data. With this excellent parameter efficiency, the proposed model won the first place in the performance category of the MC2.
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All authors Hendrik Vater, Oliver Schweins, Lukas Hölsch, Wilhelm Kirchgässner, Till Piepenbrock, Oliver Wallscheid
Quantum Gases
Phase diagram of rotating Bose-Einstein condensates trapped in power-law and hard-wall potentials
G. M. Kavoulakis
We investigate the rotational phase diagram of a quasi-two-dimensional, weakly-interacting Bose-Einstein condensate confined in power-law and in hard-wall trapping potentials. For weak interactions, the system undergoes discontinuous transitions between multiply-quantized
vortex states as the rotation frequency of the trap increases. In contrast, stronger interactions induce continuous phase transitions toward mixed states involving both singly and multiply-quantized
vortex states. A central result is the qualitative (and experimentally observable) difference between power-law and hard-wall confinement: In hard-wall traps, the leading instability always involves states with nonzero density at the trap center, whereas in power-law traps the density vanishes as the rotation frequency increases. The two different types of confinement give rise to scaling properties in the derived phase diagrams.
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Soft Condensed Matter · Cross-listed from physics.bio-ph
Nucleoid clustering drives stepwise expansion and segregation of replicating bacterial chromosomes
Giada Forte, Enzo Orlandini and Davide Marenduzzo
Bacterial chromosome replication occurs in the absence of a canonical spindle apparatus; yet it reliably produces organised and segregated genomes. While both passive and active mechanisms have been investigated, DNA replication itself is a non-
equilibrium process that continuously generates new genetic material and reorganizes the nucleoid. Here, we investigate how replication-driven dynamics, combined with nucleoid-associated
protein (NAP) interactions, shape spatiotemporal chromosome organisation using a three-dimensional
polymer model that explicitly simulates DNA synthesis. We show that NAP-mediated interactions induce dynamic clustering of DNA, generating density fluctuations in the nucleoid. When coupled to replication, these clusters undergo cycles of stress buildup and release that produce stepwise expansion dynamics consistent with experimental observations. Chromosome segregation occurs naturally in this regime, but only within a finite range of interaction strengths: weak interactions fail to structure the nucleoid, whereas strong interactions hinder replication progression. Within this optimal balance, replication also promotes the spontaneous formation of replication factories. Our results demonstrate that bacterial chromosome organisation can be understood as a non-
equilibrium system in which the interplay between replication forces and
protein-mediated interactions generates nucleoid mechanics, dynamics, and segregation.
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Superconductivity
Ultrafast Two-Dimensional Spectroscopy Uncovers Ubiquitous Electron-Paramagnon Coupling in Cuprate Superconductors
Francesco Proietto, Alessandra Milloch, Paolo Franceschini et al. (+20 more)
The coupling between electronic excitations and collective bosonic modes is fundamental to the emergence of high-temperature superconductivity in cuprates. Despite extensive effort, conventional
equilibrium and pump-probe optical spectroscopies still struggle to disentangle couplings to different bosonic modes when their energy scales overlap. Here we overcome this limitation using ultrafast two-dimensional electronic spectroscopy (2DES), which correlates coherent excitation and detection
photon energies with femtosecond time resolution. Applied to optimally doped Bi$_2$Sr$_2$Ca$_{0.92}$Y$_{0.08}$Cu$_2$O$_{8+\delta}$, 2DES reveals a pronounced off-diagonal resonance arising from the ultrafast generation of non-thermal
bosons with energy $\hbar\Omega_\mathbf{q}\simeq200$ meV. By comparing the measured spectra with a theoretical framework that explicitly includes the interaction between charge-transfer and
magnetic excitations, we identify these
bosons as paramagnons with momenta centered near $(\pi/2,\pi/2)$ and extending toward $(0,\pi)$ and $(\pi,0)$. The resonance persists across a large range of temperatures and doping concentrations, demonstrating that high-energy paramagnons are ubiquitously and strongly coupled to electronic excitations throughout the cuprate phase diagram. Time-domain analysis constrains the build-up of the paramagnon population to $\lesssim 10$ fs, placing a lower bound $\lambda \gtrsim 0.7$ on the coupling strength. More broadly, our results establish 2DES as a powerful approach for disentangling mode-selective electron-
boson interactions and addressing decoherence dynamics, thereby establishing a new avenue for investigating strongly correlated
quantum materials. These findings also provide a direct framework for future time-resolved resonant inelastic X-ray scattering experiments aimed at tracking the ultrafast dynamics of
magnetic excitations.
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All authors Francesco Proietto, Alessandra Milloch, Paolo Franceschini, Mohammadjavad Azarm, Niccolò Sellati, Rishabh Mishra, Peter C. Moen, Steef Smit, Martin Bluschke, Martin Greven, Hiroshi Eisaki, Marta Zonno, Sergey A. Gorovikov, Pinder Dosanjh, Stefania Pagliara, Gabriele Ferrini, Fabio Boschini, Lara Benfatto, Giacomo Ghiringhelli, Fulvio Parmigiani, Jeffrey A. Davis, Andrea Damascelli, Claudio Giannetti
Mesoscale and Nanoscale Physics
Theory of quantum decoherence and its application to anomalous Hall effect
Xian-Peng Zhang, Yan-Qing Feng, Haiwen Liu et al. (+2 more)
Coherent
quantum phenomena can only emerge when decoherence is minimized, and mastery over decoherence is technologically crucial for designing and operating functional
quantum devices. However, its microscopic mechanisms in
spin-orbit-coupled ferromagnets remain elusive, and quantitative treatments have long been challenging. To solve this fundamentally significant and technologically crucial problem, we develop a
quantum master-equation framework with a general ansatz for the off-diagonal density
matrix that simultaneously captures electric-field-driven coherence and
impurity-scattering-induced decoherence. This unified approach enables quantitative analysis of how decoherence reshapes the intrinsic anomalous
Hall effect, revealing a clear crossover between intrinsic and extrinsic regimes. Remarkably, we identify a previously unrecognized extrinsic contribution: a second-order scattering process tightly relative to
quantum decoherence-that is fundamentally distinct from both skew scattering and side jump mechanisms, yet substantially more significant than the skew scattering mechanism. Our work establishes decoherence as a key element in
quantum transport and provides a systematic extension of the Boltzmann transport equation to incorporate decoherence, with broad implications for robust spintronic functionality.
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All authors Xian-Peng Zhang, Yan-Qing Feng, Haiwen Liu, Wanxiang Feng, Yugui Yao
Mesoscale and Nanoscale Physics
Fano Resonances in Mismatched C$_3$N Nanoribbon Junctions
Andor Che Papior, Van-Truong Tran, Roberto D'Agosta et al. (+1 more)
Mismatched junctions formed by two C$_3$N zigzag nanoribbons of different widths provide a useful setting for studying
quantum interference effects involving edge state transport. A crucial ingredient for this interference to appear is, besides the presence of edge states, the formation of localized interface states at the mismatched interface of the junction. At the level of a tight-binding model it is shown that, by means of an external gate potential, one of the edge state energy bands can selectively be shifted into the energy range of the localized interface states. The resulting coupling between the edge and localized interface states gives rise to pronounced Fano resonances in both the density of states and the transmission spectrum with line shapes well described by the canonical Fano formula. Furthermore, it is found that the geometrical mismatch of the junction not only determines the number of resonances but also the energetic orientation of their asymmetric line shapes. These results identify mismatched C$_3$N nanojunctions as a tunable and robust platform for engineering interference-driven transport.
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All authors Andor Che Papior, Van-Truong Tran, Roberto D'Agosta, Stefan Kurth
Mesoscale and Nanoscale Physics
Nonlinear response theory for orbital photocurrent in semiconductors
Kakeru Tanaka and Hiroaki Ishizuka
Recent theoretical studies on the nonlinear response of
spin and orbital degrees of freedom have discovered
spin and orbital analogs of the photocurrent, with potential for characterizing topological materials and for applications. In this paper, we develop a general theory for calculating
spin and orbital currents in
semiconductors and study the properties of optical responses in the Bernevig-Hughes-Zhang and Luttinger models, where nonlinear orbital responses and a topological phase transition occur. We study the
evolution of optical responses at the topological phase transition and how they manifest. In addition, we find that the relaxation time dependence of the orbital conductivity is somewhat distinct from that of the photocurrent. The theory is straightforwardly applicable to complex models of real materials, allowing quantitative predictions of the nonlinear responses of orbital and
spin.
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Quantum Gases · Cross-listed from quant-ph
Non-Equilibrium Sock Dynamics: Spontaneous Symmetry Breaking in the Agitated Wash
Ahmad Darwish, Matteo Murdaca and Jami J. Kinnunen
It is a universal empirical observation that socks become unpaired in the laundry. We propose a quasiparticle theory of sock dynamics in which individual socks are modelled as bosonic excitations of the agitated laundry condensate. The sock dispersion relation is material-dependent: nondispersive materials retain their shape, while dispersive materials give rise to the well-documented phenomenon of sock shrinkage. In the convex regions of the dispersive spectrum, socks undergo Beliaev decay and spontaneously split into two lower-momentum socks, while in the concave regions the dominant process is Landau-Khalatnikov scattering, which degrades socks into lint and loose threads. In addition, the rotating drum creates sock-antisock pairs from the laundry
vacuum via the dynamical Casimir effect. The coexistence of these creation and destruction channels gives rise to a fundamental ambiguity: an unpaired sock at the end of a wash cycle is equally consistent with the destruction of its partner or the spontaneous creation of an entirely new sock.
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Statistical Mechanics
Enhanced synchronization with proportional coupling in Kuramoto oscillator networks under a fixed coupling budget
Amit Pando, Eran Bernstein, Tomer Hacohen et al. (+5 more)
We propose an explicit coupling scheme for enhancing the synchronization of Kuramoto oscillator networks under a fixed coupling budget. We show that by scaling the interaction strength between oscillators according to their frequency detuning, synchronization is enhanced. The coupling scheme produces a crossover from a smooth Kuramoto onset to an abrupt, hysteretic synchronization transition as a single allocation parameter is varied. Our work offers a general route to efficient synchronization in engineered Kuramoto networks and provides insight into their critical behavior.
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All authors Amit Pando, Eran Bernstein, Tomer Hacohen, Nathan Vigne, Hui Cao, Oren Raz, Asher Friesem, Nir Davidson
Mesoscale and Nanoscale Physics
Intrinsic Temporal Coherence Governs Heat Transport of Zone-Folded Phonons
Xiaoyu Huang, Yuxiang Ni, Zhongwei Zhang et al. (+4 more)
While spatial
phonon coherence manifested through band folding is believed to be a key factor governing the anomalous thermal conductivity of periodic structures, we investigate
phonon transport from the perspective of temporal coherence. Using mode-resolved analyses, we quantify temporal coherent contributions and elucidate the interplay between
phonon coherence time and lifetime in heat conduction of
graphene/hexagonal boron nitride superlattices. We find that intrinsic coherence of folded
phonon modes dominates the enhancement in ultrashort-period superlattices. In contrast, Wigner transport equation yields only a minor effect of band folding on thermal conductivity. The predictions in temperature dependence of models with and without temporal coherence provide a falsifiable experimental signature of this effect. Temporal coherence therefore constitutes a previously overlooked but fundamental channel for heat conduction, extending the conventional picture of spatially coherent transport and deepening the understanding of
phonon dynamics in superlattices.
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All authors Xiaoyu Huang, Yuxiang Ni, Zhongwei Zhang, Yangyu Guo, Marc Bescond, Masahiro Nomura, Sebastian Volz
Other Condensed Matter
Femtosecond all-optical coherent control of spin polarization in altermagnets
Kevin Jäckel, Holger Grisk, Niklas Dornquast et al. (+5 more)
Altermagnets constitute an emerging materials platform for spintronic technologies by combining compensated
magnetic order with ferromagnet-like
spin-split electronic bands. Here, we investigate the proposed d-wave altermagnetic material RuO2 using circularly polarized ultrashort
laser pulses. Time-resolved magneto-optical Kerr effect measurements, which are intrinsically sensitive to surface and interface states, reveal the ultrafast
spin response of RuO2. In contrast to the demagnetization dynamics characteristic of conventional ferromagnets, we observe a distinct coherent contribution to the complex Kerr rotation that appears during the light-matter interaction and lasts for about 200 fs. Similar signatures have been associated with
spin-momentum locking and directional band splitting in
spin-split surface states of topological
insulators as well as
spin-orbit-coupled
semiconductors. They are governed by a finite Raman coherence time. We interpret this coherent response as evidence for transient
spin-polarized surface states in RuO2, consistent with the emergence of altermagnetic surface states that are directly relevant to
spin-polarized transport at surfaces and interfaces.
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All authors Kevin Jäckel, Holger Grisk, Niklas Dornquast, Maik Gaerner, Günter Reiss, Timo Kuschel, Jakob Walowski, Markus Münzenberg
Soft Condensed Matter
The continuum limit of the Poland-Scheraga DNA denaturation model
Richard Dengler
Using a field theory equivalent to a
lattice version of the Poland-Scheraga model, the phase diagram for a long DNA molecule is derived in closed form. For the generalized model with excluded-volume interactions a one-loop renormalization group calculation shows that there are two stable fixed points. At both fixed points, the excluded-volume effect plays a role. At the fixed point reached when the original excluded-volume effect is weak, the phase transition is continuous. At the other fixed point, the phase transition is first order.
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Statistical Mechanics
Thermalization in high-dimensional systems: the (weak) role of chaos
Marco Baldovin, Marco Cattaneo, Dario Lucente et al. (+2 more)
In their seminal work,
Fermi, Pasta, Ulam and Tsingou explored the connection between statistical mechanics and dynamical properties, such as chaos and ergodicity. Even today, seventy years later, the topic is not fully understood: while most results of statistical mechanics require the ergodic hypothesis to be rigorously proved, there are many indications that these predictions, both in and out of
equilibrium, hold even in the absence of a rigorous form of ergodicity. Motivated by the above considerations, in this work we reconsider the point of view that the relevant ingredients for the validity of statistical mechanics are the large number of degrees of freedom and the choice of extensive observables, while the details of the dynamics do not play an essential role. This is the idea behind Khinchin's famous proof of the typicality of macroscopic observables at
equilibrium. We extend this perspective to the context of non
equilibrium, by investigating the thermalization properties of both harmonic (integrable) and nonharmonic (chaotic) oscillator chains initially prepared in out-of-
equilibrium conditions. In integrable systems, thermalization occurs, or not, depending on the observable. In the chaotic regime, instead, thermalization is reached by any observable, although the relaxation timescale might be larger than the observation time.
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All authors Marco Baldovin, Marco Cattaneo, Dario Lucente, Paolo Muratore-Ginanneschi, Angelo Vulpiani
Disordered Systems and Neural Networks
The different localisation properties of the eigenmodes of the Laplacian and adjacency matrix of 2D random geometric graphs
Luca Schaefer and Barbara Drossel
We compare the spectrum and the localisation properties of the eigenmodes of the
Laplacian and the adjacency
matrix of 2D random
geometric graphs, using numerical diagonalization of these
matrices for different system sizes and connectivities. For sufficiently large ensembles of systems, we evaluate the spectrum, the probability distribution of the participation ratio and the relation between participation ratios and
eigenvalues. While all eigenmodes of the adjacency
matrix are localised for sufficiently large system sizes, the
Laplacian matrix always leads to a small proportion of system-spanning modes due to a conservation law, and therefore to power-law tails in the probability distribution of the participation ratio and its relation to the
eigenvalues. By disentangling the effects of finite system size, of mean degree, of component size distribution, and of network motifs, we provide a thorough understanding of the data.
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