Materials Science
Atomistic mechanism of corrosion-induced grain boundary migration in NiCr alloys in molten FLiNaK
Sadia Khan, Hamdy Arkoub and Miaomiao Jin
Corrosion of Ni-Cr structural
alloys in molten fluoride salts is a persistent material degradation problem, yet the atomistic role of grain boundaries in this process remains poorly understood. Here we use reactive molecular dynamics to investigate corrosion of NiCr
alloys in molten FLiNaK across four representative grain boundaries ($\Sigma3(111)$, $\Sigma11(113)$, $\Sigma5(012)$, and $\Sigma5(013)$) and corresponding bulk surfaces. Surface crystallography controls the initial dissolution stage, while grain boundary character governs the spatial localization and longer-time
evolution of corrosion. We further identify a corrosion-driven grain boundary migration mechanism in which fluorine localization, preferential chromium dissolution, and vacancy-mediated mobility together drive interfacial motion away from the dealloyed region. The coherent $\Sigma3(111)$ boundary suppresses these processes, indicating low-energy special boundaries as targets for grain boundary engineering of corrosion-resistant Ni-Cr
alloys.
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Strongly Correlated Electrons
Yuan Fang, Lei Chen, Mounica Mahankali et al. (+4 more)
Strange metals exemplify highly collective
quantum many-body systems that call for new means of characterization, and there is considerable potential for
quantum information approaches contributing to the cause. We investigate multipartite
entanglement across the
quantum phase transition of a Kondo
lattice model using the
quantum Fisher information (QFI). We show that the QFI associated with the
spin components transverse to the order parameter characterizes the destruction of heavy quasiparticles in the Kondo-destroyed
magnetic-ordered phase. The physical origin of this observation is elucidated through an analysis of the
antiferromagnetic Heisenberg model. We propose to test the results in terms of both unpolarized and polarized inelastic
neutron scattering measurements in the ordered part of the heavy
fermion phase diagram. Our findings illustrate how different operators of a many-body system can be employed to not only witness multipartite
entanglement in different sectors and but also elucidate the overall physics across different parts of the phase diagram.
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All authors Yuan Fang, Lei Chen, Mounica Mahankali, Fang Xie, Yiming Wang, Shouvik Sur, Qimiao Si
Mesoscale and Nanoscale Physics
Excitonic structure in CsPbBr$_3$ nanocubes, nanorods and nanoplatelets: the effect of dimensionality
Jose L. Movilla, Josep Planelles and Juan I. Climente
We present a theoretical study comparing the excitonic ground state properties of CsPbBr$_3$ nanocrystals with different dimensionality: nanorods (quasi-1D), nanoplatelets (quasi-2D) and nanocubes (quasi-3D). All three systems are described on equal footing, by means of a general variational effective mass model, which captures the influence of
quantum confinement, dielectric confinement, electron-hole correlations and polaronic effects (within a Haken model). The strongly confined directions squeeze the
exciton (X) wavefunction and enhance Coulomb attractions along the weakly confined directions. This stimulates superradiance, thus making radiative recombination rates speed up from cubes to platelets and to rods, in line with recent experiments. The anisotropic local field factor is a secondary, yet non-negligible, mechanism further enhancing radiative rates. X binding energies are also determined primarily by the directions of strong confinenement, which is also consistent with experiments. Weakly confined directions become however influential for small aspect ratios. Dielectric confinement plays a major role in determining the binding energies, and less so in the interparticle-distances. For all dimensionalities, the biexciton (XX) geometry is that of a distorted tetrahedron, rather than squared or linear distributions that would result in Coulomb-governed 2D and 1D structures.
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Strongly Correlated Electrons · Cross-listed from quant-ph
Quantum-classical crossover in fault-tolerant quantum dynamics simulation
Jinzhao Sun, Bozhen Zhou, Jue Xu et al. (+28 more)
While
quantum computers promise to solve classically intractable problems, identifying the point at which fault-tolerant
quantum computation outperforms the best classical
algorithms for practical applications remains an outstanding challenge. Here we establish a concrete
quantum-classical crossover for
quantum many-body dynamics under realistic hardware conditions. We introduce a scalable fault-tolerant framework that combines coherent observable estimation with a space-time-efficient implementation of non-Clifford rotations, suppressing the residual logical errors that limit existing partially fault-tolerant approaches. A
benchmark against state-of-the-art tensor-network and variational Monte Carlo
algorithms reveals a concrete crossover for mixed-field Ising dynamics at modest system sizes. For a physical error rate of $p=10^{-3}$, fault-tolerant simulation requires approximately 2 hours and $3.7 \times 10^5$ physical
qubits for a 100-site 1D system, whereas tensor network approaches would require about 100 years. For 2D models, where rapid
entanglement growth limits the classical
evolution time, we project
quantum runtimes within minutes. A physical error rate of $p=10^{-4}$ leads to at least an order of magnitude reduction in
qubit count ($3.1 \times 10^4$ physical
qubits) and runtime (minutes for 1D and seconds for 2D). The reduction in
quantum runtime arises from our improved rotation-state injection and co-design of
quantum error correction and observable-estimation protocols, which jointly suppress logical-error accumulation and reduce sampling overhead. Our results establish a scalable route towards practical
quantum advantage and identify quantitative engineering targets for future fault-tolerant architectures.
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All authors Jinzhao Sun, Bozhen Zhou, Jue Xu, Yuan Yao, Zhenyu Du, Zixu Zhang, Yuntian Gu, Junxiang Huang, Shuo Zhou, Ziruo Wang, Alexander Yosifov, Wenzheng Dong, Yiming Huang, Daniel Serrano, Xinzhao Wang, Tianfeng Feng, Shreyas Sadugol, Wenjun Yu, Zhou You, Dayue Qin, Xiao-Ming Zhang, Yantao Wu, Aditya Iyer, You Zhou, Tongyang Li, Ying Li, Xiongfeng Ma, Qi Zhao, Pei Zeng, Pan Zhang, Xiao Yuan
Materials Science
Subgrain-resolved Analysis of Degradation in Cu Metallization via Scanning 3DXRD and Thermomechanical Modeling
Nikhil Prabhu, Laura Neumann, Michael Reisinger et al. (+7 more)
Metallization layers play a key role in the performance and reliability of modern power
semiconductor devices. During short-
circuit events, rapid heating of power metallization layers induces thermomechanical incompatibility stresses, which may contribute to material degradation and impact device performance. In this work, potential degradation hotspots associated with thermomechanical loading in Cu power metallization are investigated using a combined experimental–computational approach. Scanning three-dimensional X-ray diffraction measurements are coupled with thermomechanical
crystal plasticity simulations to probe the
evolution of grain-resolved plastic deformation during rapid cyclic loading. This integrated approach provides insight into the microstructural processes governing degradation hotspot formation, laying the groundwork for future microstructure-informed, physics-based reliability assessment of Cu metallization.
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All authors Nikhil Prabhu, Laura Neumann, Michael Reisinger, James A. D. Ball, Cedric Corley-Wiciak, Manuel Petersmann, Agnieszka Corley-Wiciak, Jonathan Wright, Carsten Detlefs, Martin Diehl
Strongly Correlated Electrons · Cross-listed from hep-th
Symmetry extension by condensation defects II: general dimensions and higher-groups
Matteo Bertolini, Lorenzo Di Pietro, Stefano C. Lanza et al. (+1 more)
We discuss a class of
symmetry structures in general spacetime dimension that arise when gauging
symmetries in theories with a cubic 't Hooft anomaly. The anomaly mixes two Abelian discrete
symmetries $A$ and $B$ with a characteristic class for an additional
symmetry $C$, and we gauge $A\times B$. The novelty of this construction is that the resulting
symmetry structure involves certain condensation defects of the dual
symmetry $\widehat{A}\times\widehat{B}$. Specifically, these defects generate an invertible
symmetry that extends $C$, either as an ordinary group extension or as a higher-group, depending on the characteristic class. We describe the corresponding charged operators and states, and illustrate the mechanism in several examples.
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All authors Matteo Bertolini, Lorenzo Di Pietro, Stefano C. Lanza, Antonio Santaniello
Materials Science
Emergent Interfacial Magnetism in Epitaxial RuO$_2$
Yudi Yang, Zhuang Qian, Shi Liu et al. (+1 more)
The
magnetic ground state of the altermagnet candidate RuO$_2$ remains controversial, with
magnetic signatures observed mainly in epitaxial films. Here we show, using first-principles calculations, that magnetism in epitaxial RuO$_2$ can emerge as an interfacial boundary phase at TiO$_2$/RuO$_2$ interfaces. While TiO$_2$-induced epitaxial strain alone does not make (001)-oriented RuO$_2$
magnetic, explicit TiO$_2$/RuO$_2$ interfaces stabilize sizable Ru moments confined to the first few Ru layers. Charge-density and orbital-resolved analyses reveal interfacial electronic reconstruction, and substrate doping provides a route to tune the induced moments. In symmetric TiO$_2$/RuO$_2$/TiO$_2$
heterostructures, the two
magnetic interfaces couple through the metallic RuO$_2$ spacer, producing a thickness-dependent alternation between weak-
ferromagnetic and compensated altermagnetic states. Our results identify interface engineering as a practical route to stabilize and control fragile magnetism in RuO$_2$.
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All authors Yudi Yang, Zhuang Qian, Shi Liu, Congjun Wu
Soft Condensed Matter
Programmable transport of rotating particles in obstacle arrays
Marcos Puerto, Alfredo Alexander-Katz, Juan L. Aragones et al. (+1 more)
Rotating colloids, or spinners, in obstacle arrays exhibit frequency-set stationary orbits and currents set by the competition between an inertial, Magnus-like lift and short-range attraction. Fully resolved
lattice-Boltzmann simulations reveal the hydrodynamic coupling and identify the lift mechanism, while a
symmetry-based Langevin model captures the resulting balance. In periodic
lattices, the superposition of scalar and vector potentials produces two robust orbital regimes: corner states, in which spinners orbit individual posts, and inner states, in which orbits couple across four neighboring obstacles. Slow frequency modulation toggles these states and produces directed, stepwise transport across the grid. This establishes a minimal hydrodynamic mechanism, controlled by a single driving parameter, for programmable guidance of active rotors in structured environments.
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All authors Marcos Puerto, Alfredo Alexander-Katz, Juan L. Aragones, J.V. Alvarez
Superconductivity
Coherent driving of displacive Higgs fluctuations in superconductors
Jacopo Fiore, Irene Zanotti, Kota Katsumi et al. (+4 more)
Intense phase-stable terahertz (THz)
laser pulses can drive collective modes coherently via multi-
photon excitation pathways in a manner different than the standard resonant mechanism operative in linear response. Here we show that in
superconductors the nonlinear optical response can be enhanced when excited quasiparticles activate a (non-resonant) static displacement of the superconducting order parameter, in full analogy with the displacive excitation of coherent
phonons in opaque materials. By combining numerical simulations with analytical results we demonstrate that the displacive mechanism to excite the
Higgs mode is operative in both $s$-wave and $d$-wave
superconductors. We validate this prediction experimentally by the temperature dependence of the phase of the nonlinear first harmonic in superconducting $s$-wave NbN. We also discuss how the order-parameter relaxation at large times, which can be experimentally accessed via pump-probe protocols is connected to energy-dissipative processes. Our results offer a novel perspective on the ability of intense THz fields to measure, and eventually control, the parametric dependence of the optical response on collective degrees of freedom.
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All authors Jacopo Fiore, Irene Zanotti, Kota Katsumi, N. P. Armitage, Claudio Castellani, Goetz Seibold, Lara Benfatto
Materials Science
Structural Relaxation Enables Millisecond Infrared Photodetection in Selenium Iodine Semiconductors
Biman Jana
The optoelectronic performance of amorphous and partially crystalline
semiconductors is strongly governed by structural disorder, yet establishing direct correlations between structural
evolution and carrier transport remains challenging. Here, we show that the solid state optoelectronic response of selenium iodine (SeI2) is dictated by its transformation from a metastable glassy phase into an ordered lamellar structure. Vertically resolved transport measurements reveal pronounced depth-dependent electrical conductivity within thick SeI2 films, arising from compositional and structural inhomogeneity developed during solidification. Immediately after solidification, the glassy SeI2 network exhibits sluggish carrier transport and persistent photoconductivity. Upon prolonged structural relaxation, however, the material undergoes significant transport enhancement, enabling millisecond-scale infrared photodetection with a response time of 4.3 ms, stable operation up to 8 kHz modulation frequency, and shot-noise-limited detectivities of 108 Jones at 1550 nm and 1011 Jones in the visible. Spatial photocurrent mapping demonstrates highly uniform carrier collection despite the self-assembled lamellar morphology, while infrared thermal imaging confirms practical imaging capability over a broad temperature range. These results establish structural relaxation as a powerful strategy for engineering carrier transport in selenium-based
semiconductors and position SeI2 as a promising solution-processable platform for infrared photodetection and thermal imaging.
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Strongly Correlated Electrons
Deconfined quantum critical point in a dissipative spin-1/2 chain
Longye Lu, Shifeng Cui and Wenan Guo
Open
quantum spin systems offer a previously unexplored route to realizing deconfined
quantum criticality. We consider a
spin-1/2 $J$-$Q_3$ chain, consisting of an
antiferromagnetic (AFM) Heisenberg exchange and a competing multi-
spin interaction favoring a valence-bond solid (VBS) state, with each
spin component coupled to a bosonic bath. Using non-Abelian bosonization and renormalization-group (RG) analysis, combined with large-scale
quantum Monte Carlo (QMC) simulations, we determine the phase diagram and the associated phase transitions of the model. We show that strong dissipation stabilizes an AFM phase for sub-Ohmic, Ohmic, and super-Ohmic baths. Continuous AFM-VBS transitions at finite dissipation are found upon increasing the multi-
spin interaction in both the sub-Ohmic and Ohmic regimes. Critical properties are obtained through perturbative RG analysis and QMC simulations. In the Ohmic case, the critical point features spinon deconfinement and emergent O(4)
symmetry. In the sub-Ohmic regime, the transition may also involve spinon deconfinement, provided that spinons remain deconfined in the dissipative VBS phase. In addition, in the super-Ohmic regime, we propose a transition from AFM phase to a quasi-long-range ordered phase.
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Mesoscale and Nanoscale Physics
Raphael Ayache, Nilotpal Chakraborty, Manabendra Kuiri et al. (+11 more)
Although individual skyrmions are topologically protected objects, their cooperative crystalline order is fragile, easily disrupted by thermal fluctuations or other external perturbations. Probing the internal dynamics of such a
crystal is both compelling and challenging, as its intricate and delicate
spin texture must remain stable during measurement. Here, we engineer a nanoscale
graphene junction hosting a skyrmion Wigner
crystal, embedded between
magnon emitters and detectors. The skyrmion
crystal geometry leaves a striking imprint on
magnon transport: as the gate voltage is varied, near-periodic windows of sharp fluctuations in
magnon count are detected across the entire sample. We develop an interpretation that this results from skyrmions being added one by one to a quasi-one-dimensional array. Each burst of the fluctuations thus corresponds to the entry of an additional skyrmion, during which the
lattice stiffness reduces. The impinging
magnons induce and act as a probe of non-
equilibrium collective dynamics of the
crystal. These results establish a real-space probe of topological
spin textures in
quantum Hall-type insulating ground states via
magnon transport and open opportunities to explore correlated, topologically ordered phases in moire and multilayer
graphene systems.
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All authors Raphael Ayache, Nilotpal Chakraborty, Manabendra Kuiri, Quentin Benichou, Antonio Lacerda-Santos, Lilian Seyve, Himadri Chakraborti, Leo Pugliese, Kenji Watanabe, Takashi Taniguchi, Cosimo Gorini, Roderich Moessner, Benoit Doucot, Preden Roulleau
Mesoscale and Nanoscale Physics
Negative quantum friction in nanoscale water flows: the Wigner picture
Adriano Tiribocchi, Marco Lauricella, Efthimios Kaxiras et al. (+1 more)
We explore the phenomenon of "
quantum" friction based on a single-particle model patterned after the Wigner equation describing electrons flow in a solid wall confining nanoscale water flows. The numerical simulations show a clear signature of negative
quantum friction, namely a net momentum transfer from the electrons in the solid wall to the flowing water molecules. Such net momentum transfer results into a sizeable reduction of the water friction, up to forty percent, depending on the strength of the coupling between classical and
quantum fluctuations. Our results offer the prospect of a theoretical framework bridging classical and
quantum description by using continuum kinetic theories and particle-based simulations.
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All authors Adriano Tiribocchi, Marco Lauricella, Efthimios Kaxiras, Sauro Succi
Superconductivity
Drosophila of phonon-mediated superconductivity: Full Eliashberg theory of the jellium model
Christophe Berthod, Louk Rademaker and Dirk van der Marel
We present a full numerical solution of the Migdal–Eliashberg equations for the jellium model of
phonon-mediated superconductivity. We find very low critical temperatures below 1~K, in contrast to earlier claims that the jellium model for hydrogen solids might reach room-temperature superconductivity. Our results suggest that full momentum and frequency dependence of the gap function and normal self-energy should be taken into account for accurate $T_c$ estimates.
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Mesoscale and Nanoscale Physics
Qubit encodings in the p-orbital-valley spectrum for enhanced coherence and tunable two-qubit interaction
John H. Caporaletti and J. P. Kestner
We propose encoding a
qubit in a two-level subspace spanned by the lowest $p$-orbital state in the excited valley of an anisotropic
quantum dot and the excited $p$-orbital in the ground valley, which we dub the $pOv$
qubit. There is an avoided crossing between these states due to valley-orbit coupling (VOC) induced by
alloy disorder, enabling complete single-
qubit control using baseband electrical control of the dot anisotropy. We find that `sweet spots' exist at specific dot orientations where the instantaneous eigenstates are first-order insensitive to charge noise. Using a phenomenological two-level fluctuator (TLF) dipole noise model, we estimate an average dephasing time of $T_2^*\approx 10\,\mu\text{s}$ and a quality factor of $Q\sim 10^4$. Alternatively, encoding in the $p$-orbital states in the ground valley near the isotropic dot point, we show that one can induce a similar sweet spot via an out-of-plane
magnetic field. Finally, we find that two-
qubit gates for the $pOv$
qubit are mediated by the quadrupole-quadrupole Coulomb interaction and can be electrically tuned from zero to $\sim 1~\text{GHz}$ by adjusting the relative orientation of the anisotropic dots, providing a novel pathway towards scalable
quantum computation.
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Mesoscale and Nanoscale Physics
Phase-controlled quasi-bound states in the continuum and thermoelectric enhancement in Majorana-quantum-dot nanostructures
Alejandro Garrido, David Zambrano, Hishan Farfán-Bachiloglu et al. (+3 more)
We investigate how the interplay between Majorana zero modes (MZMs) and bound states in the continuum (BICs) governs the electronic thermoelectric response of a crossbar-shaped
quantum dot (QD) coupled to two topological-
superconductor nanowires. Using the Green-function formalism, exact linear-response energy integrals, and their low-temperature Sommerfeld expansion, we analyze the spectral and thermoelectric properties of the system. We show that
symmetry breaking converts BICs into quasi-BICs, allowing them to contribute to electrical and thermal transport and thereby generate a finite thermoelectric response. While unequal nanowire lengths, reflected in different intra-Majorana coupling strengths, produce only a modest enhancement of $ZT_{el}$, detuning the QD level increases $ZT_{el}$ by approximately one order of magnitude. Superconducting-phase control produces a much stronger enhancement, reaching $ZT_{el} \simeq 0.75$ through a quadratic transmission zero and a pronounced violation of the Wiedemann-Franz law. The low-temperature values $ZT^{max}_{el} \simeq 0.755$ and $\mathscr{L} /\mathscr{L}_{0} = 21/5$ are universal consequences of this quadratic antiresonance. Our results establish phase-tunable thermoelectric signatures of the Majorana-coupled interference structure and identify superconducting-phase control as an efficient means of engineering the electronic response of topological hybrid nanostructures.
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All authors Alejandro Garrido, David Zambrano, Hishan Farfán-Bachiloglu, Juan Pablo Ramos-Andrade, Vladimir Juričić, Pedro Orellana
Soft Condensed Matter
Fast temperature up steps as a test of the Tool-Narayanaswamy formalism
Armand Rykner, François Ladieu and Marceau Hénot
We investigated the aging dynamics of a glass-forming
liquid triethyl-2-acetylcitrate (TEAC), following fast temperature up steps with amplitudes ranging from 0.3 to 13.6 K. The initial states were either at
equilibrium or prepared at increasing levels of out-of-
equilibrium through a prior down step experiment. Our goal was to test the predictive power of the Tool-Narayanaswamy (TN) formalism which assumes that the non-linear re-equilibration of a
liquid can be linked to its linear response to a small perturbation. We determined the TN parameters for steps with small to moderate amplitude ($\leq$ 3.3 K) and crucially took advantage of down step aging experiments below the glass transition temperature to constrain the determination of the
equilibrium relaxation time. We tested the TN predictions and found very good agreement for differences in fictive temperature characterizing the distance from
equilibrium as high as 10 K. For larger steps, however, the prediction progressively fails to capture the aging dynamics. This likely indicates that the re-equilibration mechanism is no longer related to the
equilibrium dynamics. Finally, we discuss the possibility of obtaining a general criterion for the limit of validity of the TN formalism, which we compare to other systems from the literature.
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Soft Condensed Matter · Cross-listed from q-bio.CB
A phenomenological multiscale framework for orientational interactions and viscoelasticity in migrating epithelial monolayers
Ivana Pajic-Lijakovic, Milan Milivojevic and Peter V.E. McClintock
Collective migration of epithelial monolayers emerges from the interplay between mechanical interactions and biochemical signalling. Here, we present a phenomenological mechanobiological framework linking
cell-scale orientational interactions to tissue-scale mechanics. We distinguish reversible and irreversible head-on and glancing collisions, showing that reversible interactions store orientational mechanical energy while preserving collision geometry, whereas irreversible interactions dissipate energy and alter
cell orientation. The balance between energy storage and dissipation governs collective migration, mechanical feedback, and density-dependent processes including
cell jamming and live
cell extrusion. These interactions regulate
cell elasticity, contractility, and adhesion, thereby modifying epithelial surface tension and the effective viscoelastic response of the monolayer. We quantify these effects using orientational interaction potentials, an effective second virial coefficient, and dimensionless measures of stored and dissipated orientational energy. The relative contribution of these mechanisms increases with
cell packing density, becoming dominant near the jamming transition. This framework provides a constitutive interpretation connecting collision-induced orientation dynamics with emergent epithelial rheology and suggests how density-dependent interaction regimes shape collective migration and tissue viscoelasticity.
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Materials Science
Nonuniform pressure helps structural superlubricity
Melisa M. Gianetti, Viet Hung Ho, Bjørn Haugen et al. (+2 more)
Structural superlubricity, nearly vanishing friction between two structurally incommensurate crystalline surfaces, is a promising avenue for reducing friction in applications, but requires very specific and well-controlled conditions. One of those conditions is perfectly uniform atomically flat surfaces. Real-world surfaces are generally rough, leading to nonuniform pressure distributions. We investigate the effects of nonuniform pressure distributions on structural superlubricity, using analytical calculations for rigid contacts as a basis, and molecular-dynamics simulations for a simple model to include the crucial effects of elasticity. We show that a key ingredient is the vanishing pressure at the edge of the contact, and that this leads to improved scaling depinning and scaling behaviour, leading to lower friction. We thus show that nonuniform pressure distributions actually help structural superlubricity, rather than hinder it.
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All authors Melisa M. Gianetti, Viet Hung Ho, Bjørn Haugen, Graham Cross, Astrid S. de Wijn
Strongly Correlated Electrons
Altermagnetism without a long-range order
V. E. Valiulin, A. V. Mikheyenkov and K. I. Kugel
The Kugel-Khomskii
spin-pseudospin model, originally developed for transition-metal compounds with orbital degrees of freedom, has recently been reinterpreted in the context of altermagnetism. In this work, we theoretically investigate the emergence of altermagnetic behavior in the absence of long-range
magnetic or orbital order. Using the rotation-invariant Green's function method for the SU(2) x SU(2) symmetric model on a square
lattice and on a linear chain, we analyze
spin-
spin and
spin-pseudospin correlation functions, excitation spectra, heat capacity, and susceptibilities. We show that beyond a critical intersubsystem exchange Kc(T), a composite state arises with nonzero
spin-pseudospin correlations, even though the average
spin and pseudospin at each site are zero. The excitation spectrum splits into acoustic and optical branches, with nodal lines along qx = qy - a direct signature of altermagnetic
symmetry. A peak in heat capacity and a jump in susceptibility are observed at the phase boundary. In 1D, the phase boundary is nonmonotonic and demonstrates reentrant transition. These results establish the concept of an "altermagnetic paramagnet" or "altermagnetic
liquid" without long-range order, relevant for low-dimensional and strongly fluctuating systems.
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Strongly Correlated Electrons · Cross-listed from quant-ph
Conditional Euclidean-Hamiltonian reductions for sign-problem toy models
Tsogtgerel Gantumur
Euclidean Monte Carlo methods are effective when the path-integral weight is real and nonnegative, but finite-density
fermion systems often produce sign-changing or complex scalar weights after the fermionic sector is traced out.
Hamiltonian formulations avoid this complex-weight sampling problem but face rapid
Hilbert-space growth. This paper studies a conditional Euclidean-
Hamiltonian (CEH) reduction that combines these two descriptions. The calculation is organized around a Monte Carlo-tractable reference problem and a residual active sector. Instead of tracing the active sector into a determinant or scalar weight, CEH keeps it operator-valued and uses the reference calculation to determine projected correlation or transfer
matrices. These
matrices define a finite effective
Hamiltonian, with the remaining finite-density dependence introduced after projection. At finite rank, the result is an effective model whose accuracy must be tested through basis enlargement, metric conditioning,
stochastic matrix-element errors, and number-sector diagnostics. The construction is examined in three finite
benchmarks. A two-channel oscillator tests conditional basis compression; a positive-measure
stochastic calculation tests correlation-
matrix harvesting and GEVP extraction, including a comparison with a PDMS-style
estimator; and a four-site Hubbard ring combines a finite-budget determinant-sign stress test with finite-density continuation in non-target active spaces. The
benchmarks support the proposed trade from scalar sign reweighting to a monitored active-space approximation in structured finite models, but they do not provide an end-to-end
stochastic CEH treatment of the Hubbard sign problem or establish favorable scaling. Usefulness requires both low-rank approximability and efficient extraction of the required projected
matrix data.
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Mesoscale and Nanoscale Physics
Disentangling topological and anomalous Hall contributions of skyrmions using Kerr microscopy and thermal transport measurements
H.Heyen, M. Vogel, F. Gossing et al. (+4 more)
The topological
Hall effect is a valuable tool to indicate the presence of topologically protected
magnetic structures. In this work, we present topological
Hall effect measurements originating from topologically protected skyrmions in Ta/CoFeB/MgO single-layer thick films with a one nanometer thick
magnetic layer. The simultaneous occurrence of the small topological
Hall effect and the dominating anomalous
Hall effect in this material system makes direct detection challenging as compared to bulk or multilayer systems. In electronic transport measurements, both effects' contributions impact electron trajectories in the same way, overlapping in the measurement signal, and require disentanglement. Magneto-optical Kerr microscopy was used to image the surface magnetization, enabling the separation of the topological
Hall effect from other
Hall effect contributions. These measurements reveal a topological
Hall resistivity of $249(18)\,$\si{\pico\ohm\meter} for Ta/CoFeB/MgO layer stacks at room temperature. Magneto-optical Kerr effect (MOKE) measurements also allow tracking skyrmion formation during external
magnetic field sweeps to confirm their occurrence when measuring the topological
Hall effect. We verify this outcome by comparing the results with thermal and electrical transport measurements from which we calculate the overall topological quantity that gives rise to the topological Nernst and
Hall effect, respectively.
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All authors H.Heyen, M. Vogel, F. Gossing, J. Walowski, K. Dahmen, J. McCord, M. Münzenberg
Mesoscale and Nanoscale Physics · Cross-listed from physics.optics
Sub-microsecond conformational dynamics in an optical nanocavity
Heehun Sung, Sam C Scholten, Pavlina Sasheva et al. (+2 more)
Microsecond conformational changes underlie many
protein functions, but ensemble averaging has been needed to observe them without labels. Single-shot measurements on individual
proteins have had insufficient speed, while
protein Brownian-motion has obscured signals. Here, we report a fibre-integrated silicon-photonic sensor that overcomes these barriers, resolving
protein dynamics at sub-microsecond speeds in continuous single-shot measurements that can extend over minutes. This is achieved by combining far-sub-wavelength optical field confinement with high optical field uniformity that suppresses
protein Brownian-motion by a factor of sixty. In single-shot measurements on ferritin molecules, we observe tens of thousands of transitions consistent with conformational fluctuations of the ferritin shell, resolving them over timescales as short as 400 ns. The ability to continuously monitor transitions over long times reveals switching kinetics,
memory effects and molecular heterogeneity hidden in ensemble averages. This opens a new path to improved mechanistic understanding of
protein function.
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All authors Heehun Sung, Sam C Scholten, Pavlina Sasheva, Igor Marinkovic, Warwick P Bowen
Soft Condensed Matter
Property-dependent material times
Aude Y. Amari, Lorenzo Costigliola and Jeppe C. Dyre
We analyze simulations of physical aging following large temperature up-jumps from equilibrated, slowly relaxing states. Specifically, we consider up-jumps from temperatures T=0.43 and T=0.37 to T=0.48 in a binary Lennard-Jones mixture. The Tool-Narayanaswamy (TN) concept of a universal material time was recently shown to become less effective in rationalizing the aging response for such large jumps [Amari et al., Phys. Rev. E 113, 045411 (2026)]. Here, we investigate whether the performance of the TN formalism can be improved by assigning a separate material time to each observable. We examine the potential-energy time-autocorrelation function, the self-intermediate scattering function, and the time-dependent mean-square displacement. As part of this study, we perform a detailed analysis of the extent to which the triangular relation, a necessary condition for the existence of a material time, is satisfied. We find that, for all three properties, the best data collapse is obtained when each property is parameterized by its own material time. The degree of improvement varies considerably among the observables, however; it is most pronounced for the mean-square displacement.
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Statistical Mechanics
Zigzag ordering, defects, and anomalous relaxation in antiferromagnetic Kuramoto lattices
Priyanka D. Bhoyar and Prashant M. Gade
We investigate the nonequilibrium ordering dynamics of coupled Kuramoto oscillators with negative nearest-neighbor coupling, which induces a zigzag
antiferromagnetic ordering. In one dimension, the defect density exhibits anomalously slow coarsening, decaying as $(D(t)\sim t^{-1/4})$ before saturating at a system-size-dependent time $(t_c(N)\sim N^z)$ with (z=2). The local persistence probability follows a stretched-exponential form, $(P(t)\sim \exp(-c t^\alpha))$, with $(\alpha=1/4)$. These exponents are observed are independent of the magnitude of the coupling, which merely rescales the characteristic time scale. The equality $(\alpha=\delta=1/4)$ together with (z=2) is consistent with a distinct universality class. These results demonstrate that deterministic nonlinear dynamics and
geometric frustration alone are sufficient to generate slow relaxation and anomalous scaling, without quenched disorder or
stochastic noise. A continuum approximation and the corresponding coarse-grained partial differential equation provide a theoretical explanation for the observed anomalous exponents, while linear stability analysis accounts for the emergence of the zigzag ordered state. In two dimensions,
geometric frustration inhibits complete ordering and gives rise to long-lived metastable domain-wall structures. An initial transient defect decay is observed before crossover and saturation. These results demonstrate how frustration and continuous phase variables can fundamentally modify coarsening dynamics and generate anomalously slow relaxation in deterministic many-body systems.
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Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Reconstruction of the noise correlation spectral density from the cavity emission in a two-qubit system
Nadine Lenke and Guido Burkard
A significant challenge in the field of large-scale fault-tolerant
quantum computation is the influence of noise. In addition to the influence of noise on individual
qubits, the smaller additional effect of noise correlations is also of high significance because correlated errors pose a challenge for
quantum error correction. We describe the dynamics of two cavity-coupled
qubits that are subject to correlated noise, assuming that the
qubits are affected by longitudinal noise and not coupled directly. We find that the cavity emission enables the characterization of the noise correlations and describe the cases of white noise, quasi-static noise, and Ornstein-Uhlenbeck noise. For a known frequency spectrum, the reconstruction of the noise correlation spectral density from the cavity emission is possible by averaging over many different noise realizations. We demonstrate that, in the case of white noise, the noise correlation effects scale with the fifth order of the cavity-
qubit coupling constant and are thus strongly suppressed compared with the case of quasi-static noise, where they scale with the third order. Furthermore, we present a method for extracting the noise correlation spectral density from the cavity emission in the case where the underlying noise type remains unidentified. This can be achieved by applying the convolution
theorem.
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Statistical Mechanics
Ultrametric organization of energy landscapes on random Erdős–Rényi graphs: topological origin of barrier hierarchy
A.P. Zubarev
In the present work, we investigate the hypothesis of the ultrametric organization of abstract energy landscapes defined on random Erdős–Rényi graphs. Within the proposed model, each vertex of the graph is assigned a random free energy uniformly distributed on a given interval, and the kinetics of the system is described by a Markov process with a Kramers transition rate
matrix. Based on the spectral decomposition of this
matrix, a kinetic metric between basins of attraction is constructed. Computational experiments for graphs with $V=5000$ vertices and $E=5000$ edges (average degree $\langle k\rangle=2.0$) demonstrate that this metric reveals a high degree of nontrivial ultrametricity, which monotonically increases from $\approx42\%$ at an energy interval width of $\Delta F=10$ kJ/mol to $\approx96\%$ at $\Delta F=1000$ kJ/mol. For a rigorous mathematical justification of this phenomenon, a limit
theorem is formulated and proved, establishing that as the width of this interval tends to infinity, the logarithmic asymptotics of the proposed metric converges pointwise to the classical single-linkage ultrametric. The analysis of computational experiments shows that for finite values of the interval width, suboptimal paths and thermal fluctuations introduce corrections that violate the strong triangle inequality; however, in the regime of large energy fluctuations, their contribution is exponentially suppressed, and consequently the metric asymptotically acquires ultrametric properties. The obtained results indicate that the ultrametric organization of energy landscapes represents a universal asymptotic property of networks of arbitrary
topology with a strongly rugged relief, which for sparse, locally tree-like graphs manifests itself already at moderate energy spreads.
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Mesoscale and Nanoscale Physics
Photoelectrical readout and Ramsey interferometry of single shallowly implanted NV centers in diamond
Ilia Chuprina, Christoph Findler, Johannes Lang et al. (+2 more)
Photoelectrical readout of the electronic
spin state of the nitrogen-vacancy (NV) center in diamond is attracting significant interest due to the numerous advantages it possesses compared with conventional fluorescence readout. The higher charge carrier rate compared to the
photon rate and the integration of the detection scheme on a chip can significantly advance
quantum sensing and computing with color centers in diamond. Until now, photoelectric readout has been performed on ensembles of NV centers or single NV centers deep in ultrapure diamond substrates. However, many applications require the artificial creation and precise placement of shallow NV centers, and photoelectric detection of such centers has been challenging. Here we demonstrate photoelectrical readout and coherent control of the electronic
spin of implanted shallow ($\sim$10 nm) NV centers buried by diamond overgrowth. The photoelectrically measured Ramsey $T_2^*$ agrees with conventional fluorescence readout and shows no measurable dependence on the readout photocurrent, for both shallow implanted and deep ingrown NV centers. We further find that overgrowth improves photoelectric readout by suppressing the background photocurrent. These results establish photoelectric readout as a viable route to chip-integrated, electrically detected nanoscale sensing and to
spin registers based on engineered shallow NV centers.
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All authors Ilia Chuprina, Christoph Findler, Johannes Lang, Petr Siyushev, Fedor Jelezko
Mesoscale and Nanoscale Physics
Electrothermal control of spin-reorientation transition in Co/Fe_3GaTe_2 heterostructures
Po-Wei Chen, Ming-Hsien Hsu, Cheng-Ying Hsiao et al. (+12 more)
Electrical control of
magnetic anisotropy in van der Waals (vdWs) magnets is a key step toward reconfigurable two-dimensional spintronics, yet how a conventional metallic ferromagnet competes with a van der Waals magnet across a direct interface has remained largely unexplored. Here we demonstrate reversible thermal and electrothermal control of a
spin-reorientation transition in Co/Fe_3GaTe_2 (FGaT)
heterostructures. As Joule heating weakens the FGaT anisotropy, the
heterostructure switches from an out-of-plane- to an in-plane-dominated state at a reorientation temperature of approximately 311 K, well below the Curie temperature, consistent with an exchange-mediated anisotropy competition between the Co overlayer and FGaT. An electrically driven device shows a closely matching loop
evolution within an 80-100 mW power window, reversibly over five measurement cycles, consistent with an electrothermal origin. In a Co-free FGaT device, Kerr microscopy traces the switching to a power-tunable domain nucleation barrier and demonstrates power-thresholded, field-assisted magnetization reversal at a threshold near 15 mW. These results demonstrate electrothermal anisotropy competition as a route to heat-assisted and device-level control of vdWs magnetism.
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All authors Po-Wei Chen, Ming-Hsien Hsu, Cheng-Ying Hsiao, Ming-Yang Ho, Masahiro Haze, Yan-Ru Chu, Yu-Cheng Shao, Po-Chun Chang, Chen-Yu Ou, Ruei Chen, Ko-Fan Chen, Chung-Ting Ke, Chao-Hung Du, Yukio Hasegawa, Wen-Chin Lin.
Strongly Correlated Electrons
Thermal Order by Disorder in Resonating-Valence Bond States on the Checkerboard Lattice
Giorgi Gogaberishvili, Nika Kurdadze and Kirill Shtengel
We derive a local
spin-1/2
Hamiltonian with a resonating valence bond ground state on the checkerboard
lattice. The state is characterized by the exponential decay of singlet-singlet correlations, whereas dimer-dimer correlations decay with a power law in the corresponding
Quantum Dimer model. This observation leads to a novel mechanism for thermal Order by Disorder whereby thermal decoherence suppresses destructive
quantum interference between different contributions to the correlations in the ground state and results in a qualitatively different, quasi-long-range ordered mixed state.
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