Mesoscale and Nanoscale Physics
Switchable heavy-hole/light-hole spin qubit
Zoltán György, Dmitry Miserev, Jelena Klinovaja et al. (+1 more)
Compressively strained Ge
quantum wells in planar SiGe/Ge
heterostructures are the state-of-the-art platform for hole
spin qubits. While they exhibit robust coherence times, they possess weak intrinsic
spin-orbit interaction (SOI) due to the heavy-hole (HH) character of the wavefunction. Recently, light-hole (LH)
qubits were proposed in GeSn/Ge
heterostructures, offering strong, intrinsic, linear-in-momentum SOI. In this work, we propose a switchable HH-LH
spin qubit in a bilayer Ge
heterostructure with SiGeSn barriers, combining the advantages of HH and LH devices. The character of the
qubit can be changed by shuttling from an LH well to an HH well, which also enables fast, hopping-based single-
qubit rotations. Additionally, we observe an HH-LH resonance introduced by the in-plane confinement, resulting in $g$-factor peaks and first-order charge noise sweet spots. Our calculations reveal a sweet spot with Rabi frequencies on the order of 100 MHz, comparable to the LH regime, but with a more than tenfold increase in coherence time, on the order of 100 $\mu$s.
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All authors Zoltán György, Dmitry Miserev, Jelena Klinovaja, Daniel Loss
Quantum Gases · Cross-listed from quant-ph
Structured Non-Locality and Emergent Locality in Cavity-QED Many-Body Dynamics
Mark A. Oehlgrien, Błażej Jaworowski, Darrick E. Chang et al. (+1 more)
Cavity
quantum electrodynamics (QED) modifies many-body systems by combining cavity-mediated collective interactions with microscopic short-range interactions. The resulting dynamics lies between the local and fully collective limits, such that neither locality nor collectivity alone provides a complete organizing principle. In the clean conceptual limit of dominant collective coupling, we show that the effective dynamics within each energetically isolated subspace is generically controlled by whether that subspace admits a local product-state basis, and identify exceptions imposed by angular-momentum selection rules. Product-state subspaces generically retain the spatial structure of the microscopic interaction. Entangled subspaces instead generically dress local processes with global operators, generating non-local but highly structured dynamics. We illustrate this by deriving the corresponding effective
Hamiltonians in two representative cavity-QED
spin models. The cavity-isolated subspace thus becomes a resource for generating competing short-range interactions or globally conditioned local processes, opening a class of many-body dynamics without local or fully collective counterparts.
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All authors Mark A. Oehlgrien, Błażej Jaworowski, Darrick E. Chang, Charlie-Ray Mann
Disordered Systems and Neural Networks · Cross-listed from physics.optics
From rings to resonance: an inverse method links biophotonic structural color to inverse photonic glasses
Florin Hemmann, Matthias Saba, Ullrich Steiner et al. (+2 more)
Structural color arises from the interaction of light with nanoscale structures and is widespread in nature. As structural complexity increases, the mechanisms governing coloration become progressively less understood. The optical response of periodic photonic
crystals with a spatially periodic refractive index is well described by Bloch theory, whereas that of photonic glasses composed of randomly assembled uniform spheres is more subtle yet well studied. In contrast, disordered photonic networks found in many beetles are among the most complex natural photonic architectures, and the fundamental relationships between their structure and color remain unclear. Here, we use an inverse method to identify the structural features encoded in the reflectance spectrum. By comparing the spectrum of an unknown system with a database of simulated spectra from computer-generated photonic networks, we infer its structural properties. Applying this approach to both simulated networks and the biophotonic network responsible for the blue coloration of the weevil Pachyrhynchus congestus mirabilis, we identify rings and pores as the key local scattering motifs. Their characteristic sizes govern the spectral position of the reflectance peak, whereas short-range disorder controls its width. The inverse method reveals clear spectral signatures of short-range order, whereas the influence of hyperuniformity and primitive similarity appears comparatively weak. This suggests that blue structural coloration is governed by local scattering mechanisms rather than photonic band-gap effects. We propose an analogy to an inverse photonic glass, in which pores and rings act as correlated local resonators. This perspective provides new design principles for bio-inspired structural-color materials.
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All authors Florin Hemmann, Matthias Saba, Ullrich Steiner, Mauro S. Ferreira, Felipe A. Pinheiro
Mesoscale and Nanoscale Physics · Cross-listed from physics.optics
Room-temperature graphene sub-terahertz detector integrated on a silicon dielectric waveguide
A. Titchenko, K. Shein, M. Titova et al. (+6 more)
Terahertz (THz) photonics offers a promising platform for next-generation 6G wireless communications, on-chip spectrometers, and non-invasive biomedical sensors. In the near- and mid-infrared, monolithically integrated photodetectors are a cornerstone of photonic integrated
circuits (PICs). In the THz range, however, such integration on low-loss dielectric waveguides remains an open challenge: to date, room-temperature on-waveguide detection has been realized only through hybrid flip-chip assembly of discrete elements, which leads to poor mode coupling, larger footprint, and reduced mechanical stability. Here we address this gap by demonstrating a room-temperature
graphene sub-THz detector monolithically integrated on a high-resistivity silicon dielectric waveguide for D-band (110-170 GHz) operation. We couple an hBN-encapsulated
graphene channel to the guided mode using a tapered slot-line
antenna patterned directly onto the silicon surface. The detector achieves a voltage responsivity of 11.5 V/W and a 3 dB bandwidth of 1.94 GHz, with the latter currently limited by parasitic inductance of the readout interconnects rather than by the intrinsic
graphene response. This platform provides a practical pathway to fully integrated room-temperature THz photonic
circuits, where electrostatic gating and impedance matching can improve both responsivity and bandwidth by roughly an order of magnitude.
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All authors A. Titchenko, K. Shein, M. Titova, M. Kashchenko, O. Popova, R. Izmaylov, E.I. Titova, I. Gayduchenko, G. Goltsman
Soft Condensed Matter
Residual semi-crystalline particles released during enzymatic degradation of plastics
Michael Schindler and Ludwik Leibler
Enzymatic recycling of plastics is limited by the presence of semi-crystalline spherulites that are recalcitrant to enzymatic depolymerization. Depending on the quality of the waste stream and its treatment history, a large volume fraction of the material actually remains in form of connected clusters of such spherulites. We build on a recently published numeric method to predict the number, the connectivity, and the morphology of these clusters as an outcome of enzymatic degradation. When applied to PET waste, our method predicts that the resulting aggregates are loosely connected, "fluffy" structures with a high surface-to-volume ratio, accompanied by smaller clusters following a continuous size distribution. By providing a quantitative framework for understanding the microparticle production during the depolymerization, these findings should assist choosing a suitable downstream treatment, such as filtering or flocculation. This work could thus help to advance the enzymatic depolymerization technologies.
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Mesoscale and Nanoscale Physics
Topological phases of a generalised tripartite Haldane model
Ahmed Al-kharusi, Alessandro Principi and Niels R. Walet
We present a generalised tripartite Haldane model with a complex nearest neighbour hopping parameter. The total
magnetic flux through the primitive unit
cell, which consists of three hexagonal unit
cells is zero, and thus the model has the structure of a loop-current model. We calculate topological phase diagrams of the Chern numbers as a function of the phases of the nearest and next-nearest neighbour hopping parameters for a fixed ratio of the magnitude of the hopping parameters. We show that, unlike the Haldane model, the topological phase diagram of this model is very complex, but some aspects can still be dealt with analytically. Furthermore, the Chern numbers of the topological phases are as large as $7$ in absolute value. The analysis is supported by explicit expressions for energy bands crossing at high
symmetry points in the Brillouin zone, which show as linear phase boundaries in the phase diagram. We show that such lines explain many features in the topological phase diagrams. Finally, we analyse a few representative examples of the nature of level crossings away from high
symmetry and their
evolution with model parameters.
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Mesoscale and Nanoscale Physics
Light-Hole Spin Qubits in Strained SiGe Lattice-Matched to Ge
Edmondo Valvo, Davide Costa, Patrick Del Vecchio et al. (+3 more)
Strained germanium ($\varepsilon$-Ge)
quantum wells on metamorphic SiGe buffers have enabled advanced hole-based
spin qubit devices. Alternatively, unstrained Ge with
lattice-matched strained silicon-germanium ($\varepsilon$-SiGe) barriers eliminates the need for metamorphic buffers altogether. The ground state character of both these platforms is predominantly heavy-hole (HH) with a largely anisotropic
spin response. We propose and study an alternative
heterostructure,
lattice-matched to Ge, in which both the SiGe
quantum well and barriers are tensile strained, with their composition contrast providing the band offset for confinement and the tensile strain stabilizing a light-hole (LH) ground state. We show large
spin-orbit coupling (SOC), both linear and cubic, along with a significantly more isotropic
spin response compared to strained HH
qubits. We also study the decoherence properties of the proposed device, showing an appreciable gain in the quality factor compared to their HH counterparts. Finally, we propose a bilayer
heterostructure that allows for electrical switching between HH and LH ground state character.
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All authors Edmondo Valvo, Davide Costa, Patrick Del Vecchio, Stefano Bosco, Giordano Scappucci, Maximilian Rimbach-Russ
Quantum Gases
Mass-anisotropy driven stripe pattern formation and directional modulational instability in polariton condensate
Hari Sadhan Ghosh, Soumyadeep Halder, Subrata Das et al. (+1 more)
Motivated by recent experimental advances toward electrical control of the effective mass and the realization of anisotropic mass distributions, we investigate the impact of mass anisotropy on driven-dissipative polariton condensates, focusing on modulational instability, pattern formation, and the collective dynamics of the emergent patterns. We show that unequal effective masses along the two orthogonal directions induce stripe pattern formation in an
exciton-polariton condensate pumped by a non-resonant Gaussian
laser beam above a critical mass ratio. A Bogoliubov analysis of the homogeneously pumped system reveals that mass anisotropy leaves the modulational-instability criteria unchanged but reshapes the unstable-mode dispersion by reducing the most unstable wave- length along the direction of larger effective mass with increasing mass ratio. This introduces an anisotropy-controlled length scale for pattern selection. When the pump width becomes comparable to the most unstable wavelength, the condensate becomes modulationally unstable and develops stripe patterns along the direction of larger effective mass, accompanied by particle-number fluctua- tions and center-of-mass oscillations along the same direction. As the pump width increases further, the stripes become distorted and develop spatial irregularities during the time
evolution, indicative of modulational instability. Nevertheless, the anisotropic mass distribution preserves a pronounced directional preference, in contrast to the fully disordered patterns observed in the isotropic-mass case. Our results identify mass anisotropy as a key control parameter for directional modulational instability and pattern formation in nonequilibrium polariton condensates.
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All authors Hari Sadhan Ghosh, Soumyadeep Halder, Subrata Das, Sonjoy Majumder
Strongly Correlated Electrons
Fate of the non-Abelian Moore-Read manifold under the non-Hermitian skin effect
Jiaxuan Guo, Simin Nie, Xiting Zhang et al. (+1 more)
We study a non-Abelian Moore-Read fractional Chern
insulator under a translation-preserving, nonreciprocal deformation that generates the non-Hermitian skin effect under open boundaries. The model combines the imaginary-gauge Hatano-Nelson deformation with a kagome-
lattice three-body interaction designed to stabilize Moore-Read order at $\nu=1/2$. Our primary diagnostic is the biorthogonal $(2,4)$-admissible particle-
entanglement counting of the sixfold Moore-Read
manifold, the standard Moore-Read fingerprint. Across three sizes ($N=16,20,24$), the counting locks to the clean references 1308, 3965, and 9282 over finite nonreciprocity windows through $\gamma\le0.55$, $0.65$, and $0.74$, respectively, with positive reference-rank
entanglement gaps. Within every reported window the count is unchanged by the spectral readings tested; at $N=16$ it is also unchanged across three reduced density operators, with all 15 combinations returning 1308. The sixfold pattern for even $N_f$ and the adiabatically tracked Ising-odd doublet remain separated over the tested range $\gamma\le0.6$. Beyond a geometry-dependent threshold the instantaneous-lowest-six reference-rank gap drops sharply and its counting destabilizes. At $N=24$ a sector-0 branch pair becomes complex conjugate over a narrow interval inside the delocking bracket; both continuations through the interval are delocked at the tested PES points $\gamma=0.76$, $0.77$, and $0.80$. A same-
lattice Abelian $\nu=1/3$ Laughlin realization retains its counting to $\gamma=1.0$, so its counting is the more robust. On the
torus the eigenstates remain extended; under open boundaries the right and left states skin-localize at opposite edges while the biorthogonal particle-
entanglement spectrum is invariant under the imaginary-gauge similarity, so the
torus and the open cylinder probe the same deformation under periodic and open boundaries.
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All authors Jiaxuan Guo, Simin Nie, Xiting Zhang, Fritz B. Prinz
Disordered Systems and Neural Networks
Semi-localized ground state in a 1D system with long-range hopping
Murod S. Bahovadinov, Faridun N. Jalolov, Vladimir E. Kravtsov et al. (+2 more)
We study the localization of a
quantum particle in a one-dimensional disordered system with long-range hopping amplitudes $t(r)\propto r^{-a}$. In contrast to the standard one-dimensional Anderson model ($a\to\infty$), in which all states are localized and the localization length is minimal at the band edge, the long-range model with $1<a<3/2$ exhibits a disorder-driven transition at the band edge, while high-energy states remain localized at arbitrary disorder strength. We investigate this transition for the ground state in momentum space. In the weak-disorder regime, we derive perturbative expressions for the characteristic functions and moments of the momentum-space wave function, as well as for its fractal dimensions. Our results demonstrate that the ground state exhibits $\it semilocalization$ rather than conventional localization, thereby extending the class of models displaying the unusual $\it semifractality$ of wave functions.
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All authors Murod S. Bahovadinov, Faridun N. Jalolov, Vladimir E. Kravtsov, Boris L. Altshuler, Georgy V. Shlyapnikov
Strongly Correlated Electrons
Quasi two dimensional magnetic structure of the triclinic double perovskite Ca$_2$CuWO$_6$
Bangye Qin, Dmitry D. Khalyavin, Xuan Liang et al. (+3 more)
We present the antiferromagnetic ground state of the triclinic double perovskite Ca$_2$CuWO$_6$solved by
neutron powder diffraction, and analyze it in direct comparison with tetragonal Sr$_2$CuWO$_6$. Below $T_\mathrm{N} \simeq 32$ K, the
magnetic Bragg reflections of Ca$_2$CuWO$_6$ are indexed by the commensurate propagation vector $\mathbf{k}=(\tfrac{1}{2},\tfrac{1}{2},0)$ in its native $P\bar{1}$
cell. Rietveld refinement yields a collinear structure with equal-magnitude, antiparallel moments on the crystallographically inequivalent Cu1 and Cu2 sites and an ordered moment of $0.66(3)~\mu_{\mathrm B}$ per Cu at 1.5 K. A direct comparison with Sr$_2$CuWO$_6$ is obscured by different crystallographic settings and orientations of the cooperative Jahn-Teller elongation axes. Hence, we introduce a common crystallographic supercell through which effects of
symmetry lowering from tetragonal to triclinic in the double perovskite are explored: Apparently different
magnetic propagation vectors map onto the same supercell wave vector, revealing a common
magnetic structure stabilized by tungsten-mediated, second-neighbor interactions. Mean field calculations further show that tetragonal
symmetry preserves the degeneracy of four
magnetic $\mathbf{k}$-domains in Sr$_2$CuWO$_6$, whereas the triclinic splitting of
symmetry-related exchange pathways in Ca$_2$CuWO$_6$, most strongly within the Cu2 network, selects a single $\mathbf{k}$-domain. These results establish the
magnetic ground state of Ca$_2$CuWO$_6$ and show how
symmetry breaking selects a given ordered state without changing the underlying
magnetic motif of the Sr analogue.
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All authors Bangye Qin, Dmitry D. Khalyavin, Xuan Liang, Kazunari Yamaura, Alexei A. Belik, Roger D. Johnson
Soft Condensed Matter
Lipid Hydrocarbon Tail Structure Governs Interfacial Anchoring and Stripe Morphology in Cholesteric Liquid Crystals
Mengwei Li, Stefanie D. Pritzl, Martin F. Haase et al. (+1 more)
Liquid crystal-based biosensors exploit the sensitivity of interfacial anchoring to molecular adsorption. Cholesteric
liquid crystals are especially useful because their helical structure supports multiple optically distinct textures that evolve with anchoring strength. Here, we compare saturated 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC) and unsaturated 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) monolayers to determine how lipid acyl chain structure governs interfacial organization and director
alignment. Mapping stripe spacing across lipid concentration, mixing ratio, cholesteric pitch, and confinement shows that the transition from fingerprint textures toward homeotropic
alignment depends on both lipid structure and collective interfacial organization. DLPC produces comparatively regular textures and more readily promotes helix unwinding at high coverage, consistent with more spatially uniform collective anchoring. DOPC-containing interfaces show greater morphological heterogeneity, consistent with strong local anchoring from longer tails together with less uniform organization arising from cis-unsaturation. FRAP measurements provide complementary information on fluorescent-probe mobility, which becomes strongly restricted at high lipid concentration for both systems. Variations in pitch and film thickness further modulate the response, producing coexisting regular, distorted, and lipid-enriched textures. Together, these results show that lipid acyl chain structure regulates cholesteric anchoring through its effects on local interactions, collective interfacial organization, and mobility, providing design principles for responsive
liquid-
crystal interfaces.
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All authors Mengwei Li, Stefanie D. Pritzl, Martin F. Haase, Lisa Tran
Other Condensed Matter
PCB-Integrated CoPt Micromagnets for Magnetophoresis
Melissa Mitchell, Henrique Mira, Simon Bending et al. (+2 more)
Integration of
magnetic material with scalable microfluidic platforms can significantly improve the throughput and precision in biotechnology processes. In this work we have developed a new
magnetic platform based on printed
circuit board (PCB) technology. Cobalt-Platinum (CoPt) micromagnets are electroplated on copper pads with an arbitrary footprint on a Kapton substrate to enable generation of different
magnetic field gradients. The magnets are characterized by XRD and VSM, before and after thermal annealing. The ordered L10 phase appear in XRD results after annealing at 600 {\deg}C, and VSM results show around six times increase for in-plane
magnetic remanence from 0.24T to 1.4T. The near equiatomic ratios of Co:Pt is confirmed by EDX observations. The performance of these magnets is experimentally validated by trapping
magnetic nanoparticles in microfluidic channels. These results are in excellent agreement with FEA models presented in COMSOL Multiphysics.
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All authors Melissa Mitchell, Henrique Mira, Simon Bending, Chris Bell, Ali Mohammadi
Materials Science
Observation of thermal Hall effect in diamond
Marcin Matusiak, Andrzej Ptok, Maria Szlawska et al. (+1 more)
Numerous
insulators, including non-
magnetic ones, have been unexpectedly found to display a finite thermal Hall signal, which has stimulated debate about its origin. Here, we report on a study of the thermal Hall effect in two diamond single
crystals. The transverse thermal conductivity (kappa_xy) was found to peak at a temperature close to that at which the longitudinal thermal conductivity (kappa_xx) reaches its maximum. The measured kappa_xy, with an amplitude of 340 W/(m K) at B = 10 T, is the largest ever observed, while the kappa_xy/kappa_xx ratio follows the phenomenological trend identified in other
insulators. Our observation implies the existence of an intrinsic thermal Hall effect in a generic
phonon gas. We argue that the rough amplitude of both the thermal Hall angle and the thermal Hall resistivity can be accounted for by simple arguments invoking fundamental constants and
quantum-mechanical constraints on solid state cohesion.
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All authors Marcin Matusiak, Andrzej Ptok, Maria Szlawska, Kamran Behnia
Materials Science
Muonium dynamics as a probe for depth-resolved properties of 4H-SiC
Maria Mendes Martins, Piyush Kumar, Marianne E. Bathen et al. (+5 more)
This study establishes a baseline for muonium (Mu) charge-exchange dynamics in n-type 4H-SiC through a detailed low-energy
muon spin rotation (LE-uSR) investigation. Epitaxially grown and ion-implanted samples with nitrogen and phosphorus donors were characterized to assess the effect of carrier concentration and doping method on defect formation. LE-uSR enabled nanometer scale depth profiling of near-surface and implanted regions, revealing variations in charge carrier concentration due to fixed surface charges. The temperature dependence of the diamagnetic fraction and phase provided direct evidence of the Mu0 to Mu- transition, with extracted activation energies consistent with known donor ionization energies. Additionally, high-field uSR was used to analyze the Mu dynamics, and Monte-Carlo simulations to model the Mu0 electron capture process. The simulation results offer a quantitative method to extract free electron concentrations from LE-uSR data, enhancing its capability to characterize the activation of dopants and carrier depth profiles. We demonstrate that LE-uSR is a powerful depth-resolved tool that can provide insights for optimizing the fabrication of reliable SiC devices for power electronics.
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All authors Maria Mendes Martins, Piyush Kumar, Marianne E. Bathen, Robert J. Scheuermann, Zurab Guguchia, Lasse Vines, Ulrike Grossner, Thomas Prokscha
Mesoscale and Nanoscale Physics
Chirality-Selective Phonon Pumping by Ferroelectric Dynamics
Dapeng Yao and Ping Tang
The discovery of chiral
phonons has expanded the conventional view of
lattice vibrations as passive heat carriers, opening new opportunities for phononic spintronic devices. However, their realization has been largely limited to chiral
crystals or to specific regions of momentum space in certain achiral materials. Here, we propose a generic mechanism for generating propagating chiral
phonons in an ordinary dielectric through the precession of the electric polarization in an adjacent ferroelectric. The polarization dynamics transfers its intrinsic angular momentum to the
lattice via electrostrictive coupling, thereby pumping chirality-selective
phonons whose handedness is dictated by that of the polarization precession. For a typical LiNbO$_{3}$$|$Y$_{3}$Al$_{5}$O$_{12}$ bilayer, we find that the pumping efficiency quantified by an interfacial convertance substantially exceeds those of thermally induced chiral-
phonon generation in chiral
crystals, owing to the strong electrostrictive coupling in ferroelectrics. Our work establishes ferroelectric dynamics as a versatile electrical source of chiral
phonons and provides a general route toward electrically programmable chiral-phononic and spintronic functionalities.
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Strongly Correlated Electrons
Phase calibration of quantum oscillations in the magnetostrictive coefficient using the topological antiferromagnet YbMnBi$_2$
Qin Deng, Long Zhang, Zeyu Li et al. (+6 more)
The Berry phase accumulated along a cyclotron orbit encodes important information about electronic band
topology and is commonly inferred from the phase of
quantum oscillations. Measurements of the ac magnetostrictive coefficient have recently emerged as a sensitive thermodynamic probe of
quantum oscillations, but the phase offset has not been experimentally calibrated. Here, using the topological antiferromagnet YbMnBi$_2$, we calibrate this offset by directly comparing
quantum oscillations in magnetization with those in the ac magnetostrictive coefficient. Measurements of both responses on the same single
crystal reveal a single fundamental frequency of approximately 160 T in fields up to 14 T, enabling a direct phase comparison free from ambiguities associated with multiple frequencies. We observe an approximately $\pi/2$ relative phase shift between the two oscillatory responses, consistent with the Maxwell relation linking the magnetostrictive coefficient to the stress derivative of magnetization. Our results establish the appropriate phase needed to extract cyclotron-orbit phase information from
quantum oscillations in the ac magnetostrictive coefficient.
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All authors Qin Deng, Long Zhang, Zeyu Li, Ying Zhu, Shuai Wu, Yan Liu, Aifeng Wang, Yu Pan, Yisheng Chai
Superconductivity · Cross-listed from quant-ph
Phase-sensitive cascade quantum amplifier with nearly noiseless operation
Ilari Lilja, Ekaterina Mukhanova, Michael Perelshtein et al. (+5 more)
Phase-sensitive parametric devices enable quadrature-selective amplification with the potential for sub-
quantum-limited noise performance. In this work, we investigate the operation of a SQUID-based Josephson Parametric Amplifier (JPA), comparing its performance in the phase-preserving and phase-sensitive regimes. The device, fabricated using VTT SWAPS technology, is driven in a three-wave mixing configuration and characterized in a reflection-based measurement setup at millikelvin temperatures. To directly probe the noise performance at low JPA gains, we employ a cascaded amplification scheme in which a Traveling-Wave Parametric Amplifier (TWPA) provides low-noise pre-amplification of the JPA output. In a phase-preserving operation, the JPA exhibits near-
quantum-limited performance with a system noise temperature of $351\pm53$ mK at 6 GHz. In contrast, phase-sensitive operation yields a minimum system noise temperature of $94\pm12$ mK, well below the standard
quantum limit of 288 mK. Our results demonstrate that a JPA-TWPA amplifier cascade opens the door to direct, high-fidelity probing of
quantum devices without the need for background noise subtraction.
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All authors Ilari Lilja, Ekaterina Mukhanova, Michael Perelshtein, Kirill Petrovnin, Stanislav Khaldeev, Visa Vesterinen, Gheorghe Sorin Paraoanu, Pertti Hakonen
Materials Science
Nuclearity of Copper Clusters on hBN/SiC Heterostructure Modulates Molecular Adsorption
Reza Khakpour, Arsalan Hashemi, Xiaoya Chang et al. (+3 more)
Defect engineering can transform inert two-dimensional (2D) materials into chemically active and electronically tunable platforms by creating anchoring sites for metal atoms and clusters. Nevertheless, precise control over the formation, thermodynamic and kinetic stability, electronic structure, and chemical reactivity of metal species confined at these defect sites remains a challenge. Here, we use density functional theory (DFT) calculations assisted by machine-learning molecular dynamics (MLMD) simulations to elucidate the stability, electronic structure, and reactivity of Cu clusters anchored at boron vacancies (VB) in hBN/SiC
heterostructures. Systematic variation of the Cu-to-vacancy ratio reveals a transition from isolated Cu atoms to multiatom Cu clusters at VB sites, with cluster growth reshaping the stability, electronic structure, and surface reactivity. Our results show that a single VB defect can be passivated by three Cu atoms, which compensate the local charge deficiency and stabilize the defect through Cu-N coordination. Capturing further Cu introduces localized midgap states that could influence the reactivity of the Cu-decorated defect sites. We probe the response of the Cu-decorated surface to chemically relevant gases CO, H2, O2, N2, H2S, and CO2, revealing implications for surface reactivity and stability. The calculations show pronounced cluster-size-dependent reactivity of Cu clusters at VB sites, with CO forming strong Cu-C bonds and O2 undergoing enhanced adsorption and molecular activation. Overall, this work identifies defect-engineered hBN/SiC as a versatile 2D platform for stabilizing Cu clusters and tuning gas-surface reactivity. By correlating Cu nuclearity at VB sites with electronic structure, molecular activation, and environmental robustness, our findings provide design guidelines for nuclearity-dependent metal functionalization of 2D
heterostructures.
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All authors Reza Khakpour, Arsalan Hashemi, Xiaoya Chang, Nima Ghafari Cherati, Mikko Karttunen, Tapio Ala-Nissila
Statistical Mechanics
Exact chemo–thermal Metropolis Brownian engine: chemical leverage, temperature-neutral stall, power optimization, and multicyclic dissipation
Mesfin Taye
We develop an exactly solvable chemo–thermal extension of the three-state Metropolis Brownian heat engine. The particle moves through the periodic energy sequence $0\to E\to 2E\to0$, performs mechanical work against a load $f$ on every forward step, interacts with two cold links and one hot link, and consumes one fuel molecule of free-energy drop $\muu$ on the hot transition. Local detailed balance gives an exact cycle affinity \begin{equation*} \mathcal A=E\left(\Tc^{-1}-\Th^{-1}\right)+\muu/\Th-f\left(2/\Tc+1/\Th\right), \end{equation*} and the full stationary probabilities and current are obtained without linear-response, weak-driving, or high-barrier approximations. Several results follow. First, the exact stall force is \begin{equation*} \fs=\frac{E(\Th-\Tc)+\Tc\muu}{2\Th+\Tc}. \end{equation*} Second, there is a temperature-neutral chemical compensation point $\muu_*=3E/2$ at which $\fs=E/2$ for every $\Th>\Tc$ and the hot and cold heats both vanish at reversible stall. Third, in both Metropolis branches the stationary current is a strictly increasing function of $\muu$ at fixed mechanical parameters, but approac
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Disordered Systems and Neural Networks · Cross-listed from q-bio.QM
Propensity Straight-Through Gradients for Discrete Stochastic Systems
Jose M. G. Vilar and Leonor Saiz
Continuous-time Markov chains (CTMCs) provide the backbone for modeling discrete
stochastic dynamics across applied, physical, and biological sciences. Their integration with modern gradient-based machine learning, however, is limited by the hard categorical event selection intrinsic to Gillespie-type simulation
algorithms. We exploit the affine state update to obtain the exact one-step conditional-mean sensitivity by differentiating normalized reaction propensities. We pair this backward rule with exact forward trajectories to define the propensity straight-through (PST)
estimator. At the trajectory level, we show that one-step sensitivities composed across events can depart from the exact multistep sensitivity. We derive the resulting per-step discrepancy in closed form and prove that it vanishes identically for affine downstream dependence. PST matches the accuracy of Gumbel-Softmax straight-through across all
benchmarks: reversible dimerization (0.06% error), a genetic oscillator (1.7% error), a 50-task repressilator suite (0.17% median error), and patch-clamp ion-channel recordings ($R^2$ = 0.988). Under matched settings, PST converges 3.0-fold faster on the oscillator and 2.1-fold faster on the ion channel. At deep-learning scale, PST trains a 203,796-parameter
stochastic reaction network with hard sampling, reaching 98.22% MNIST digit classification accuracy. By differentiating an exact conditional mean rather than a relaxed sample, PST offers a temperature- and Gumbel-free path to scalable gradient-based learning through exact
stochastic trajectories.
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Soft Condensed Matter
Closed-form hard-sphere thermodynamics under nanoscale confinement: from equations of state to unmixing forces
Jose M. G. Vilar and Leonor Saiz
Equations of state accurately describe hard-sphere thermodynamics but are generally considered to fail under nanoscale confinement. We show that this failure is
geometric rather than thermodynamic: a closed-form, parameter-free mapping from apparent to effective packing fraction restores the accuracy of the Carnahan-Starling equation of state and, with it, the entire analytical thermodynamic framework, including free energies, wall pressures, chemical potentials, and the large-cavity surface response. Applied to overlapping anchored hard-sphere droplets, a geometry inherent to biomolecular force generation, it yields unmixing free energies and full distance-dependent force profiles in quantitative agreement with simulations from the dilute regime to above the bulk freezing transition.
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Materials Science
Magnetic-configuration design for reliable Heisenberg exchange parameters
Ben Li, Stephan von Malottki and Gian-Marco Rignanese
The determination of
magnetic exchange interactions is essential for the quantitative description and predictive modeling of
magnetic materials. In this work, we present a neighbor-shell-based screening method for selecting
magnetic configurations suitable for extracting Heisenberg exchange parameters beyond nearest-neighbor from density functional theory (DFT) calculations. Using only the structure, the proposed approach identifies the linear independence of neighbor-shell contributions before any first-principles calculations instead of relying on trial-and-error generation of
magnetic configurations. We apply the proposed approach to two representative classes of
magnetic configurations: random
spin states and
spin spirals, and validate its predictions against direct DFT fitting for Fe and MnF$_2$. We show that only parameters obtained when all relevant neighbor-shell contributions are linearly independent remain transferable to other
magnetic configurations. The proposed method provides practical guidance for selecting
magnetic configurations for reliable exchange-parameter extraction and may also benefit other neighbor-shell-based models.
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Superconductivity
Nearly Isotropic Quantum-Critical Transport in Single-Crystal CeNiC2
Hanming Ma, Jun Gouchi, Dilip Bhoi et al. (+4 more)
Pressure-induced superconductivity and $T$-linear resistivity have been reported in polycrystalline CeNiC$_2$, but orientational averaging has left the directional character of the critical scattering unresolved. We report pressure-dependent resistivity of high-quality single
crystals for current along each crystallographic axis. These
crystals have substantially lower residual resistivity and a slightly higher maximum onset $T_c$ than the polycrystalline sample, placing superconductivity in a cleaner transport regime. Near $P_c \approx 9.5-10$ GPa, the normal-state resistivity becomes nearly $T$-linear along every axis, the fitted residual resistivity is strongly enhanced, and superconductivity forms a narrow dome. For $I \parallel b$, the $T$-linear normal state remains nearly unchanged in
magnetic fields up to 9 T applied along $a$ and $c$; the upper critical field is large and only moderately anisotropic. The common
evolution along all three axes establishes a nearly isotropic
quantum-critical transport regime, inconsistent with a simple low-dimensional
spin-fluctuation picture and implicates valence fluctuations as the leading source of critical scattering associated with the superconducting dome.
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All authors Hanming Ma, Jun Gouchi, Dilip Bhoi, Toru Shigeoka, Bosen Wang, J.-G. Cheng, Yoshiya Uwatoko
Materials Science
Substitution effects in RuO$_2$ single crystals
Shubhankar Paul, Kunihiko Yamauchi, Shogo Yamashita et al. (+7 more)
RuO$_2$ has emerged as one of the leading candidates for investigating altermagnetism. Recent
quantum oscillation and angle-resolved photoemission spectroscopy measurements found the absence of altermagnetism or antiferromagnetism in pure RuO$_2$
crystals. The continuing debate over intrinsic
magnetic order in RuO$_2$ may reflect its proximity to an altermagnetic instability. In this work, we grow single
crystals of Ru$_{0.9}$V$_{0.1}$O$_2$ and investigate their structural, transport, and
magnetic properties. X-ray photoelectron spectroscopy reveals an average V oxidation state near $+4$. The paramagnetic susceptibility remains nearly unchanged up to room temperature, with no evidence of
magnetic ordering. Thus, the 10% V-substitution in RuO$_2$ does not induce altermagnetism. Electronic structure calculations for the V-substituted systems using two methods suggest that a higher level of V-substitution leads to a significant change in the density of states. These findings underscore the potential of nonmagnetic substitution in RuO$_2$ as an attractive candidate for probing altermagnetic transitions and their experimental signatures.
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All authors Shubhankar Paul, Kunihiko Yamauchi, Shogo Yamashita, Hisakazu Matsuki, Shuhei Iwashita, Mitsuhiko Maesato, Hiroshi Kitagawa, Chanchal Sow, Shingo Yonezawa, Yoshiteru Maeno
Statistical Mechanics
Nonequilibrium Dynamics of Simple Exclusion Processes Across Dimensions
Zhimao Liu, Jing Liu, Pan Zhang et al. (+1 more)
The simple exclusion process (SEP) is a paradigmatic model for nonequilibrium transport, yet its rich dynamics over an exponentially large configuration space remain notoriously intractable. Here, we leverage variational autoregressive networks to characterize the nonequilibrium dynamics of the symmetric (SSEP), asymmetric (ASEP), and totally asymmetric (TASEP) cases in one to three dimensions at any time. We validate the approach against established finite-time 1D and long-time 2D results for the SSEP, and further provide new results on dynamical activity, density fields and nonequilibrium phase transitions for 2D and 3D cases. In 2D, we give a directional-density criterion connecting the bulk-density organization to the 1D TASEP phase diagram, and reveal how boundary and bulk rates separately control the activity and susceptibility. In 3D, we provide the first finite-time characterization of the SSEP active-inactive phase transition, and uncover scaling relations over time. Across dimensions, the critical field follows a trend $s_c\sim L^{-2}$, suggesting tuning strategies by the characteristic diffusive length scale. Overall, this work establishes a unified neural-network framework for characterizing nonequilibrium dynamics of representative transport systems.
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All authors Zhimao Liu, Jing Liu, Pan Zhang, Ying Tang
Materials Science
Optical and magneto-optical interactions in Co-doped CeO$_2$ thin films prepared by pulsed laser deposition
Martin Zahradník, Miroslav Kučera, Roman Antoš et al. (+5 more)
Magnetically doped CeO$_2$ is a dilute
magnetic semiconductor, promising for various applications in photonics, but the origin of its ferromagnetic properties is not fully understood. Here, thin films of Ce$_{1-x}$Co$_x$O$_{2-\delta}$ prepared by pulsed
laser deposition on MgO ($x=0.05$ and $0.10$) and oxidized Si ($x=0.20$) substrates were systematically studied by spectroscopic ellipsometry and magneto-optical spectroscopy. Both diagonal and off-diagonal permittivity-tensor elements were obtained. Diagonal spectra revealed two optical transitions between oxygen and cerium states. Off-diagonal spectra revealed two paramagnetic transitions involving cobalt ions, from which an essential influence of cobalt doping on resulting ferromagnetic properties of CeO$_2$ was inferred. The full permittivity-tensor spectra are provided for further use in prospective modelling of magneto-optical device concepts.
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All authors Martin Zahradník, Miroslav Kučera, Roman Antoš, Martin Veis, Jan Mistrík, Lei Bi, Hyun-Suk Kim, Caroline A. Ross
Materials Science
A Hierarchical Synergistic Deep Learning Framework Integrating Composition, Structure, and Ionic Transport for Solid-State Electrolyte Discovery
Hongwei Du, Dingyang Lv, Baole Wei et al. (+5 more)
Inorganic solid-state electrolytes must combine high room-temperature ionic conductivity, a wide electrochemical window, excellent electronic insulation, and favorable mechanical compliance. Single models struggle to support reliable multi-objective screening across vast chemical spaces because of training-data distribution mismatch, cross-property
dataset heterogeneity, and scarce kinetic transport data. To overcome these limitations, we develop a hierarchical synergistic deep-learning framework that sequentially coordinates efficiency, accuracy, and reliability through four complementary modules. The in-house-developed L-G-DCNN and a multi-fidelity implementation built on DenseGNN serve as compositional and structural experts for thermodynamic coarse screening and multi-property evaluation, respectively; MatterSim and system-specific DeePMD models provide transport pre-assessment and kinetic validation. Systematic
benchmarks show that each module outperforms mainstream counterparts in its task, while retrospective validation establishes dual closed-loop verification of module-level accuracy and end-to-end workflow reliability. Applied to 30,364,908 Alex/ICSD-derived candidates, the framework identifies 97 high-performance candidates with room-temperature ionic conductivities of 0.109–59.0 mS/cm, including 94 halides, one borohydride, and two oxides. Consistency with independent experimental data confirms that 76 of the 94 halides fall within reported high-conductivity structural regions. Analysis reveals that Li$^{+}$ jump-network connectivity, rather than the number of
geometric Li sites, is the core determinant of room-temperature ionic conductivity. Li-defect engineering effectively enhances oxide transport, whereas the inherent rigidity of the O$^{2-}$ framework suggests a potential upper limit on oxide electrolyte performance.
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All authors Hongwei Du, Dingyang Lv, Baole Wei, Yongheng Li, Feng Yu, Ziheng Lu, Siqi Shi, Hong Wang
Materials Science
Exchange splitting as a descriptor for giant anomalous Hall and Nernst effects in ferromagnets
Ivan Kurniawan, Guangzong Xing, Yoshio Miura et al. (+1 more)
The anomalous Hall effect (AHE) and anomalous Nernst effect (ANE), which describe transverse electrical and thermoelectric responses in
magnetic materials, respectively, are promising for spintronic and energy-harvesting applications. Here, we employ high-throughput first-principles calculations to investigate 2251 chemically substituted tetragonal $L1_0$
alloys. Among ferromagnets, enhanced responses emerge preferentially in
alloys derived from parent compounds with small exchange splitting: no
alloy derived from FePt, the archetypal $L1_0$ ferromagnet, reaches the high-response regime, whereas NiPt- and CoIr-derived
alloys occupy it in large numbers. Small exchange splitting keeps majority- and minority-
spin bands near the Fermi level, giving chemical substitution more opportunity to modify near-Fermi-level band crossings and amplify the Berry
curvature. We predict a giant anomalous Hall conductivity of $2809\,\mathrm{S\,cm^{-1}}$ in (Co$_{0.8}$Fe$_{0.2}$)(Ir$_{0.7}$Pt$_{0.3}$) and a giant anomalous Nernst conductivity of $7.72\,\mathrm{A\,m^{-1}\,K^{-1}}$ in (Ni$_{0.8}$Co$_{0.2}$)(Pt$_{0.7}$Ir$_{0.3}$). Our results identify the exchange splitting of the parent compound as a descriptor for chemical tunability toward giant Berry-
curvature-driven transport responses.
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All authors Ivan Kurniawan, Guangzong Xing, Yoshio Miura, Keisuke Masuda
Disordered Systems and Neural Networks · Cross-listed from physics.soc-ph
$(k,n)$-core percolation on hypergraphs with anchor nodes
Hoseung Jang, Byungjoon Min and Ginestra Bianconi
Hypergraphs describe higher-order interactions that involve more than a pair of nodes. A characteristic feature of hypergraphs is that their robustness can be strongly affected by the different roles of the nodes. Indeed, some nodes might be essential for a hyperedge's function, while others might not be. The loss of a single essential node completely destroys the hyperedge it belongs to, while the loss of a non-essential node has a buffering effect, inducing the hyperedge to simply reduce its size. In order to capture this phenomenology, we formulate a comprehensive theoretical framework for $(k,n)$-core percolation models on hypergraphs, where each node of a hyperedge is an anchor with probability $\theta$, and a hyperedge fails if an anchor node fails. Hypergraph $(k,n)$-core percolation problems can be classified as first-neighbor and second-neighbor problems, indicating that in the
pruning process the connectivity is ensured only by the state of the first neighbors or the second neighbors, respectively. We derive self-consistency equations for first-neighbor and second-neighbor (node- and hyperedge-based)
pruning processes, and obtain the size of the giant $(k,n)$-core. We obtain the phase diagram, including continuous and discontinuous transitions, and confirm our theory on random hypergraphs using numerical simulations. The results show how the heterogeneity of the nodes' functional roles and the extended range of the interactions affect the robustness of higher-order networks.
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