Materials Science
Boron-assisted stabilization of low-resistivity mixed-valence Cu-O thin films prepared by reactive magnetron sputtering
Nirmal Kumar, Jemal Yimer Damte, Michal Procházka et al. (+5 more)
This study systematically investigated the influence of boron incorporation in Cu-O thin films and the effect of oxygen partial pressure ($p_{\rm ox}$) on the phase
evolution, chemical bonding, and electrical characteristics of the prepared films. A phase transition from Cu$_2$O to Cu$_2$O/Cu$_4$O$_3$ to CuO was observed as oxygen partial pressure increased. Boron incorporation significantly broadened the stability window of the Cu$_2$O and Cu$_4$O$_3$ phases and delayed the transition to CuO at higher oxygen partial pressure. In the highly B-doped Cu-O films, Cu$_4$O$_3$ was stabilized even under oxygen-rich conditions along with the CuO phase, suggesting that boron significantly altered the oxidation pathway. The formation of B-O and possible B-O-Cu configurations altered the local oxygen chemistry and promoted mixed-valence copper
oxide phases. Electrical measurements revealed that highly B-doped Cu-O films exhibited a delayed transition from a high-resistivity low-$p_{\rm ox}$ regime to a low-resistivity mixed-valence regime, ultimately reaching approximately 0.06 $\Omega$ cm, among the lowest reported resistivities for a CuO-like material. These findings demonstrate that boron doping is an effective approach for tailoring the phase stability, defect chemistry, and electrical characteristics of Cu-O thin films for optoelectronic and photovoltaic applications.
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All authors Nirmal Kumar, Jemal Yimer Damte, Michal Procházka, Radomír Čerstvý, Jiří Houška, Pavel Baroch, Stanislav Haviar, Jiří Rezek
Mesoscale and Nanoscale Physics
Rolling Two-Dimensional Collinear Magnets into Chiral Nanotubes with $p$-Wave Magnetism
Zhejunyu Jin, Robin R. Neumann, Rodrigo Jaeschke-Ubiergo et al. (+2 more)
$p$-wave magnets are noncollinear compensated
magnetic systems that exhibit nonrelativistic antisymmetric
spin splitting in momentum space. Their odd-parity
spin symmetry enables unconventional spintronic functionalities, including highly efficient charge-to-
spin conversion via the Edelstein effect. An outstanding question is whether such
magnetic phases can emerge from simple and broadly accessible
magnetic building blocks rather than from intrinsically noncollinear
magnetic orders. Here, we show that rolling two-dimensional collinear magnets – ferromagnets, antiferromagnets, and altermagnets – into nanotubes generates a rich
spin-
symmetry landscape controlled by
curvature, chirality, and
magnetic order. Remarkably,
chiral nanotubes hosting radial or tangential coplanar
spin textures generically realize $p$-wave magnetism irrespective of the underlying collinear parent phase. The emergent odd-parity
spin symmetry manifests itself in both electronic and magnonic spectra through antisymmetric $p$-wave
spin splitting. Our results establish
magnetic nanotubes as a versatile platform for engineering unconventional $p$-wave magnetism and predict a nonrelativistic Edelstein response that exceeds conventional
spin-orbit-driven charge-to-
spin conversion by more than an order of magnitude.
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All authors Zhejunyu Jin, Robin R. Neumann, Rodrigo Jaeschke-Ubiergo, Jairo Sinova, Alexander Mook
Quantum Gases
Spin-orbit coupling induced geometric squeezing in rotating Bose-Einstein condensates
Fei Zhu, Chunxia Guo, Rui Zhang et al. (+3 more)
Squeezed states play a key role in diverse frontiers of
quantum physics. Geometrically squeezed states, a squeezed state in the orbital phase space of rotating Bose-Einstein condensates (BEC), have been conventionally generated by anisotropic trapping potentials. In this work, we propose a different route to generate
geometric squeezing via
spin-orbit coupling (SOC) in a pseudospin-1/2 BEC. We show that the SOC enables effective two-
phonon transitions within the lowest Landau level via virtual
spin-flip processes, leading to exponential squeezing dynamics in both
spin components. Furthermore, by applying a $\pi/2$
spin rotation, the two
spin channels can be coherently coupled to produce two-mode
geometric squeezing. We also investigate the influence of interatomic interactions on squeezing performance and identify parameters where robust squeezing can be achieved. Our work provides a viable pathway to realize and manipulate
geometric squeezing in spinor
quantum gases.
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All authors Fei Zhu, Chunxia Guo, Rui Zhang, Lianghui Huang, Ren Zhang, Li Chen
Strongly Correlated Electrons
Trimers in the Extended Hubbard Model
R. R. Montenegro-Filho, D. R. B. Silva, D. Cogollo et al. (+1 more)
The Lieb
theorem is a cornerstone of
quantum magnetism theory in condensed matter. In this work, we investigate the instability of the Lieb insulating ferrimagnetic phase in the extended Hubbard model on a trimer chain at half-filling, with one electron per site, under increasing the nearest-neighbor Coulomb coupling $V$. Our results show that despite a noticeable increase in doublon density with $V$, the ferrimagnetic insulating phase remains robust up to the phase separation (PS) line, which is observed at $V \gtrsim U/4$, where $U$ is the local Coulomb repulsion. Above the PS line, one of the coexisting phases is primarily populated by doublons on one of the two sublattices of the chain. This phase coexists with a metallic, unsaturated
ferromagnetic phase for $U \gtrsim t$, and with a singlet phase for $U \lesssim t$, where $t$ is the intra-trimer hopping amplitude. We estimate the PS and the crossover lines with the help of density
matrix renormalization group calculations.
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All authors R. R. Montenegro-Filho, D. R. B. Silva, D. Cogollo, M. D. Coutinho-Filho
Mesoscale and Nanoscale Physics · Cross-listed from cs.LG
Beyond Drug Discovery: The Nanotechnology Molecular Optimization (NMO) Benchmark
Matthias Blaschke, Daniel Kienzle, Zsuzsanna Koczor-Benda et al. (+3 more)
Generative molecular design is shaped by simple proxy
benchmarks for drug-like properties and models pretrained on large pharmaceutical
datasets. This combination yields strong
benchmark metrics but limits transferability to domains structurally distinct from drug discovery. To overcome this limitation and drive discovery toward real, scientifically grounded targets, we introduce the Nanotechnology Molecular Optimization (NMO)
Benchmark, which bridges machine learning (ML) and
quantum materials science. NMO acts simultaneously as a rigorous testbed for the ML community and a discovery engine for nanotechnology research. The suite replaces proxy oracles with
quantum simulations and introduces strict protocols that prioritize scientific utility over leaderboard-oriented overfitting. The physics-based NMO tasks impose hard structural constraints and rugged fitness landscapes, posing fundamentally new requirements on generative models. Notably, advanced molecular optimization methods underperform much simpler approaches on the NMO tasks. We develop a new baseline method identifying the critical components to solve the NMO tasks, including a novel representation for modeling structural constraints and a domain-agnostic pretraining strategy to eliminate pharmaceutical
dataset bias. Our results surpass state-of-the-art physical properties and reveal previously unknown structural motifs, offering new insights for the nanotechnology community and demonstrating that ML can drive genuine scientific discovery.
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All authors Matthias Blaschke, Daniel Kienzle, Zsuzsanna Koczor-Benda, Julian Lorenz, Rainer Lienhart, Fabian Pauly
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Spin bath mediated long-lived coherent oscillations of NV centers in diamond
Akshat Rana, Pooja Lamba, Basanta Mistri et al. (+3 more)
Decoherence is the biggest bottleneck in all
quantum technologies. For nitrogen-vacancy (NV) centers in diamond, the loss of coherence is caused by the electron and
nuclear spin bath of the diamond
lattice. Here, we demonstrate that the
spin bath - that typically causes decoherence - entangles the
spin states of the NV electron and the host $^{14}$N
nucleus. The many-body interaction between the $^{14}$N
nucleus - electron - bath
spins at an energy level anti-crossing occurring for an applied
magnetic field orientation perpendicular to the NV axis is responsible for this effect. This is observed experimentally in NV ensembles via electron
spin-echo measurements, where the echo envelope is modulated at the frequency of a $^{14}$N
nuclear spin transition. Using numerical simulations, we show that the
spin bath coupling to the NV centers is essential for observing this modulation. Due to the zero first-order Zeeman effect at the anti-crossing, the observed oscillations have long
spin-echo coherence times, 2–3 times those at the parallel
magnetic field orientation. The oscillation frequency is highly stable and robust against environmental fluctuations. These findings provide new opportunities for fundamental studies of many-body physics and
quantum sensing.
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All authors Akshat Rana, Pooja Lamba, Basanta Mistri, Dieter Suter, Siddharth Dhomkar, Rama K. Kamineni
Materials Science
Ferroelastic domain wall motion and collective domain switching in RbSCN
V. Soprunyuk, A. Tröster, J. Pils et al. (+4 more)
Low frequency (0.05 - 40 Hz) dynamic elastic measurements and resonant ultrasound spectroscopy measurements (100-600 kHz) of RbSCN have been performed in the temperature region of the order-disorder improper ferroelastic phase transition at T$_c \approx$ 435~K. Quite similar to KSCN, the low frequency data show - in addition to the intrinsic phase transition anomalies - superelastic softening in a- and b-directions, resulting from movements of ferroelastic domain walls under dynamic stress. However, in contrast to KSCN, a sudden discontinuous increase of Young's modulus appears in RbSCN at { T$^{\ast} < T_c $}, which is accompanied by a frequency dependent damping peak. This behaviour is reminiscent of a first order phase transition.\\ Heating RbSCN slightly above T$^{\ast}$, followed by subseqent cooling, removes all {signs of domain wall dynamics}. The results demonstrate, that the anomalies in RbSCN around $T^{\ast}$ result from collective domain switching events that are induced when the {temperature dependent critical pinning stress, $\sigma_c(T)$ falls below the applied external stress $\sigma$, implying that $T^{\ast}(\sigma=\sigma_c)$. This interpretation is supported by calculations of the temperature dependences of twin boundary widths $w$ and energies $F_w$, as well as the Peierls potential $V_0$ using a compressible pseudospin model, which leads to a critical pinning stress, $\sigma_c(T)$ that is in excellent agreement with experimental values of $T^{\ast}(\sigma_c)$. }
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All authors V. Soprunyuk, A. Tröster, J. Pils, W. Schranz, I. Rychetsky, A. Klic, M.A. Carpenter
Quantum Gases · Cross-listed from physics.plasm-ph
Kinetic energy from the cubic sum rule of the dynamic structure factor
Fotios Kalkavouras, Panagiotis Tolias, Sebastian Schwalbe et al. (+6 more)
The third frequency moment sum rule of the dynamic structure factor $S(\mathbf{q},\omega)$ is explored for the first time as an alternative
estimator of the kinetic energy $K$ of
quantum many-body systems. As a practical example, the uniform electron gas at warm dense matter conditions is considered. First, $K$ is extracted from quasi-exact ab initio path integral Monte Carlo results for the imaginary-time density–density correlation function $F(\mathbf{q},\tau)$ and the expected excellent self-consistency with the thermodynamic differentiation route is confirmed. Second, $K$ is extracted from approximate dielectric formalism results for $S(\mathbf{q},\omega)$ and it is observed that common semi-classical approximations lead to a wave-number dependent $K$ with an incorrect short-wavelength limit. Our results are expected to be of broad interest for a great variety of applications, including time-dependent density functional theory, dielectric formalism schemes and warm dense matter models, as well as for the design of dedicated x-ray Thomson scattering experiments with the potential to provide model-free access to the full electronic equation of state.
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All authors Fotios Kalkavouras, Panagiotis Tolias, Sebastian Schwalbe, Thomas Gawne, Alexander Benedix Robles, Jan Vorberger, Zhandos Moldabekov, Maximilian Böhme, Tobias Dornheim
Mesoscale and Nanoscale Physics
Anomalous Duffing mechanics of a suspended carbon nanotube quantum dot at ultrastrong coupling
Akong N. Loh, Furkan R. Özyiğit, Fabian Stadler et al. (+3 more)
At cryogenic temperatures, suspended single-wall carbon nanotube
quantum dots act both as prototypical
quantum dots as well as high-quality factor mechanical resonators. Single-electron tunneling enables reaching an ultrastrong electron-vibron coupling regime, where the coupling parameter exceeds the vibration frequency. Due to the high quality factors, a strongly nonlinear Duffing response is easily reached. Here, we quantitatively study the Duffing response parameters of such a device and their relation to Coulomb blockade oscillation. At the edges of single-electron tunneling regions, a local increase of the Duffing parameter corresponding to a stiffening spring is observed. Size and approximate scaling of the effect agree with single-electron tunneling phenomena, which however should lead to softening spring behaviour. Possible causes of these puzzling results are discussed.
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All authors Akong N. Loh, Furkan R. Özyiğit, Fabian Stadler, Katrin Burkert, Niklas Hüttner, Andreas K. Hüttel
Materials Science
A parsimonious structure model for the icosahedral quasicrystal Cd5.7Yb
Michael Feuerbacher
A compact structure model for the icosahedral phase Cd5.7Yb is presented. The model is based on a higher-dimensional description and a cut-and-projection procedure to generate the atom distribution in three-dimensional physical space. It strictly employs only spherical or elliptical occupation domains, ensuring a low number of parameters and low calculation cost. In the presented form the model has seven adjustable parameters. Despite its minimalistic setting, the model reproduces available experimental data, such as chemical composition, mass density and electron density distribution, as well as the cluster structure in physical space very well. Nevertheless, the approximation of the occupation domains by spheres and ellipses evidently implies limitations in accuracy and universality. The model can be adapted for the description of other Tsai-type icosahedral phases.
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Materials Science
Phonon-driven Floquet engineering for electronic states
Yu-Chan Tai, Chih-Wei Luo, Noriaki Takagi et al. (+3 more)
Controlling material excitations offers access to novel fundamental and technological properties. The paradigm of Floquet engineering, the manipulation of the electronic structure using a coherent and time-periodic driving source, has attracted significant
attention. While most realizations rely on strong optical fields, coherent
phonons provide an alternative route to realizing Floquet-Bloch states and are expected to enable substantially longer-lived Floquet-Bloch states. We show that
laser-excited coherent
phonons drive Floquet-Bloch states. Using time-resolved multiphoton photoemission combined with
quantum beat spectroscopy on
graphene-covered Ir(111), we track the coherent electronic dynamics of the image-potential states dressed by coherent
phonons. The beat signal indicates the presence of sideband structure with the coherent-
phonon frequency as its fundamental period, consistent with Floquet theory. Furthermore, an independent oscillation in intensity at the same frequency was observed, confirming excitation of the coherent
phonon mode. Compared with conventional light-driven Floquet-Bloch states, the observed
phonon-driven Floquet-Bloch states persist for one to two orders of magnitude longer. These results establish coherent
phonons as a material-driven route to Floquet engineering and demonstrate the long-lived dressing of electronic states beyond the optical excitation window.
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All authors Yu-Chan Tai, Chih-Wei Luo, Noriaki Takagi, Hiroshi Ishida, Chun-Liang Lin, Ryuichi Arafune
Mesoscale and Nanoscale Physics
Perfect elliptic dichroism: Probing the metric of anisotropic quantum Hall droplets
Bruno Mera, Alberto Nardin, Anaïs Defossez et al. (+3 more)
Understanding the geometry of
quantum Hall systems is a central challenge in modern condensed matter physics. We introduce a framework for probing the
geometric structure of
quantum Hall droplets by engineering the geometry of a dichroic probe and identifying the onset of "perfect
elliptic dichroism", a regime in which the system responds exclusively to an elliptically polarized drive of a given chirality. This phenomenon provides a direct diagnostic of the droplet's intrinsic metric, and we show that it extends naturally to ideal Chern bands, where holomorphicity of the occupied states guarantees the vanishing of one
chiral absorption rate with a quantized response for the other. In
lattice realizations, such as the Harper-Hofstadter model, finite
lattice-spacing corrections break the exact continuum metric description and give rise to a renormalized, emergent Landau-orbit metric; the probe ellipticity at which perfect dichroism is achieved then shifts accordingly, offering a direct spectroscopic window onto this
lattice-induced
geometric renormalization. Our results illuminate the rich
geometric structure of
quantum Hall phases and offer concrete pathways for observing these effects in
quantum-engineered platforms.
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All authors Bruno Mera, Alberto Nardin, Anaïs Defossez, Baptiste Bermond, Tomoki Ozawa, Nathan Goldman
Mesoscale and Nanoscale Physics
Hall viscosity from metric-sensitive dichroic probes
Alberto Nardin, Bruno Mera, Anaïs Defossez et al. (+3 more)
Hall viscosity characterizes the
geometric response of a
quantum Hall droplet to deformations of the underlying metric, yet it has remained difficult to measure directly. We propose a spectroscopic probe based on circular dichroism, using
chiral metric-sensitive drives – implemented as rotating quadrupolar ("saddle") perturbations – that effectively modulate the metric and couple to the generators of area-preserving deformations. The resulting dichroic signal directly measures the
Hall viscosity, while frequency-resolved spectroscopy disentangles it from other excitations. A local formulation further enables spatially resolved markers of
Hall viscosity applicable to both continuum and
lattice systems. Our results open a direct route to measuring
Hall viscosity in
quantum-engineered platforms such as cold atoms in optical
lattices.
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All authors Alberto Nardin, Bruno Mera, Anaïs Defossez, Baptiste Bermond, Tomoki Ozawa, Nathan Goldman
Soft Condensed Matter
A phase-field model for viscoelastic compressible tumor growth
Luise Zieger, Min Wu, Chaozhen Wei et al. (+2 more)
It is well known that growing tumors generate and respond to stress in their local microenvironment. Tissue re-arrangements can relax these mechanical stresses and make the tissue more fluid-like. Further, intricate coupling between mechanotransduction and biochemical signaling leads to complex patterns of growth. To predict the outcomes of these nonlinear interactions, we develop a phase-field model to simulate tumors growing into a surrounding medium taking into account their elastic and viscous properties as well as their compressibilities. We couple continuum modeling of the viscoelastic mechanics to the concentration of a diffusible growth-promoting nutrient in a mass conservative way. The phase-field method is a stable and flexible way to describe the dynamics of arbitrarily shaped tumors. We demonstrate convergence of the phase-field model to a sharp interface model in radially symmetric geometries and can observe progression to stationary tumors. However, our results show that these stationary symmetric tumors are subject to
symmetry-breaking instabilities in 2D and 3D driven by two primary mechanisms: (i) elastic buckling instabiliies due to differential growth induced by the nutrient gradient and (ii) instabilities generated by apoptosis-related volumetric loss. Further, tissue fluidity and compressibility can lead to changes in tumor
topologies. Our modeling framework provides a robust methodology for investigating how tissue mechanics and growth factor signaling influence the progression and invasive potential of solid tumors.
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All authors Luise Zieger, Min Wu, Chaozhen Wei, John Lowengrub, Sebastian Aland
Materials Science
Analytical approximations of dispersion laws and ultra-complex conductivity diagrams
A.Ya. Maltsev
We study the probability of the emergence of ultra-complex conductivity diagrams in conductors that satisfy the tight-binding approximation and have the simple or body-centered cubic
lattice. The presence of ultra-complex conductivity diagrams allows us to observe a number of highly nontrivial effects in strong
magnetic fields, however, the probability of their emergence in a given substance is quite low. In the case of the simple or body-centered cubic
lattice, the leading tight-binding approximation does not allow us to estimate this probability due to the peculiarities of the spectra in this situation. To estimate this probability, we use higher-order corrections to the leading approximation, which yield more accurate analytical expressions for the electron spectra.
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Materials Science · Cross-listed from physics.optics
Dynamic Topological Light Control in Reconfigurable Non-Hermitian Metastacks
Ryan Hogan, Zihan Lu, Han Peng et al. (+4 more)
Metasurfaces often require complex lithography for dynamic optical control. To overcome this, we utilize a lithography-free, non-Hermitian planar metastack comprising a distributed Bragg reflector and a vanadium dioxide (VO2) thin film. By virtue of temperature and thermal hysteresis as an active synthetic dimension and exploiting the VO2
insulator-to-metal transition, we actively tune topological interface states to achieve polarization-sensitive spectral control. Notably, our system hosts path-dependent exceptional points (EPs); the intermediate hysteretic states generate a continuum of hot and cold EP pairs that ultimately converge into a single, degenerate EP. Furthermore, we experimentally observe wide-range dynamic optical control, comprising reversible 8% spectral shifts with near-unity reflectance modulation, alongside potential for ultrafast dynamics. Ultimately, our CMOS-compatible design provides a scalable, simple platform for active and topological photonics.
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All authors Ryan Hogan, Zihan Lu, Han Peng, Jie Zhou, Yanling Xiao, Shining Zhu, Hui Liu
Materials Science · Cross-listed from cs.LG
Atompack: A Storage and Distribution Layer for Read-Heavy Atomistic ML Training Datasets
Ali Ramlaoui, Daniel T. Speckhard, Sagar Pal et al. (+3 more)
Atomistic machine learning
datasets are increasingly used for training: large immutable snapshots are read repeatedly, shuffled across epochs, staged across clusters' storage systems, and republished as reusable scientific artifacts. This workload differs from interactive scientific curation, where mutable records and ad hoc inspection are often more important than random indexed throughput. We present Atompack, an append-oriented storage format and distribution layer designed around a simple workload: training pipelines usually consume complete molecular records, while the order of records is randomized by the learning
algorithm. Atompack appends records efficiently during
dataset construction, then commits an immutable index and serves records through a
memory-mapped read path optimized for training. We compare Atompack with HDF5, LMDB, and ASE baselines representing array stores, key-value records, serialized records, and object-oriented databases. The
benchmarks measure sequential reads, shuffled reads, shared-filesystem behavior, write throughput, and artifact size. On a representative 64-atom workload, Atompack is 96x faster than ASE LMDB on shuffled training-style reads while producing artifacts about 79% smaller. The results indicate that serving complete molecule records, rather than field chunks or reconstructed objects, improves shuffled training throughput while keeping artifacts compact enough for public distribution.
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All authors Ali Ramlaoui, Daniel T. Speckhard, Sagar Pal, Fragkiskos D. Malliaros, Alexandre Duval, Victor Schmidt
Materials Science
Consistent transition model for Bi0.5Na0.5TiO3 from temperature-dependent structural and electrical properties
Thomas Fourgassie, Omar Ibder, Cosme Milesi-Brault et al. (+5 more)
BNT based solid solutions are promising parent materials for lead free dielectric capacitors, thanks to their high recoverable energy densities and breakdown strengths. However, the ambient temperature
symmetry and high temperature phase
evolution of BNT remain unclear. Crucially, structural transformations and electrical ordering are most often considered independently, hindering a coherent understanding of the BNT phase transition. In this work, we combine X ray diffraction, transmission electron microscopy, Raman spectroscopy, impedance spectroscopy, and high field polarization cycling to establish a unified picture of the structural and dielectric response of BNT. Based on these results, we propose a consistent transition model for BNT that reconciles previously conflicting interpretations. This integrated structure property study provides a rationale for developing high performance, lead free energy storage materials.
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All authors Thomas Fourgassie, Omar Ibder, Cosme Milesi-Brault, Anna Katharina Ott, Eric Bourhis, Pascal Andreazza, Pierre-Eymeric Janolin, Cécile Autret-Lambert
Soft Condensed Matter · Cross-listed from physics.flu-dyn
Gappy Reconstruction of Bubbly Flows by Guided Diffusion Models
Hridey Narula, Tianyi Li, Michele Buzzicotti et al. (+2 more)
Experiments in multiphase flows are often limited in their ability to simultaneously obtain velocity measurements in different phases. At the same time, flow reconstruction from phase-limited measurements is a challenging problem due to the substantially different velocity statistics across the phases. We address this problem for buoyancy-driven bubbly flows in the pseudo-
turbulence regime by using a guided
diffusion model. We train the model using two-dimensional slices of the velocity field extracted from fully resolved three-dimensional direct numerical simulations. The model generates physically realistic velocity fields both unconditionally and when conditioned on the surrounding
liquid flow. The reconstructed bubble-phase velocity field accurately reproduces key statistical features of the flow. We further show that a simple patching procedure for adjacent two-dimensional slices enables a reasonable reconstruction of the three-dimensional flow inside a bubble. These results establish the potential of
diffusion models to serve as generative priors for three-dimensional turbulent multiphase flows, opening a route toward the reconstruction of unobserved or experimentally inaccessible velocity fields from sparse, partial, or phase-limited measurements.
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All authors Hridey Narula, Tianyi Li, Michele Buzzicotti, Luca Biferale, Prasad Perlekar
Statistical Mechanics
Poisson-shot-noise hybrid machines: efficiency and quasistatic divergence
Rita Majumdar, Costantino Di Bello, Ralf Metzler et al. (+2 more)
We study
stochastic models of a microscopic active heat engine, comprised of an overdamped Brownian particle trapped in a harmonic potential, and in simultaneous contact with thermal (passive) and athermal (active) baths. The interaction with the active bath is modeled as a
stochastic force described by Poisson shot-noise (PSN) having a specified amplitude distribution. With analytical calculations and numerical simulations, we study the thermodynamic performance of the machine to quasistatic cyclic protocols analogous to those running two-stroke and Stirling-like engines. For specific parameter ranges, the thermodynamic behavior is that of a $\textit{hybrid machine}$, simultaneously operating as a heat engine with respect to the passive/active baths and as a refrigerator with respect to the passive/active baths. Focusing on the parameter region where the overall performance is such of an engine, we show that the average total extracted work per cycle divided by average total heat intake from the cold baths per cycle may surpass the Carnot efficiency associated with the temperature of the passive baths. Applying the second law for active heat engines, we focus on a bona fide efficiency (bounded by Carnot's efficiency) that incorporates an information-theoretic metric $\mathcal{I}-$ which we call $\textit{quasistatic divergence}-$ quantifying how distinguishable are the engine's statistics in the quasistatic limit with respect to a continually changing
equilibrium distribution. We analyze, with theory and numerical simulations, how the PSN shot rate and the degree of non-Gaussianity in the particle position distribution influence the efficiency of the engine, and explore the correlation between non-Gaussianity and efficiency. Our findings reveal optimal PSN shot rates maximizing the engine's efficiency and an intriguing non-bijective relation between efficiency and kurtosis
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All authors Rita Majumdar, Costantino Di Bello, Ralf Metzler, Rahul Marathe, Édgar Roldán
Mesoscale and Nanoscale Physics
Spin-1 Dirac dispersion and Chern insulating phases in 2D honeycomb Sierpiński fractal
Shneha Biswas, Shouya Yoshida, Katsunori Wakabayashi et al. (+1 more)
Graphene-based Sierpiński fractals host a zero-energy
chiral mode and
spin-1 Dirac dispersions within the nearest-neighbor tight-binding model. However, the presence of complex next-nearest neighbor hopping arising from the local flux and the staggered Semenoff mass terms, modeled within the Haldane
Hamiltonian, breaks the time-reversal and spatial inversion
symmetries, respectively, and makes these flat bands dispersive. Moreover, they introduce rich topological phases in this class of systems that can be characterized by Chern numbers up to $\pm 3$, i.e., beyond the conventional honeycomb
lattice. These observations pave the way for the exploration of 2D periodic fractals beyond
graphene, where topological phase transitions can be realized through externally applied fields.
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All authors Shneha Biswas, Shouya Yoshida, Katsunori Wakabayashi, Sudipta Dutta
Materials Science
Field-induced topological Hall effect and butterfly-shaped magnetoresistance in the centrosymmetric antiferromagnet EuAuAs
Yu Zhang, Junfa Lin, Huan Wang et al. (+6 more)
The coupling between
magnetic and electronic degrees of freedom gives rise to a variety of intriguing transport phenomena. Among them, the topological
Hall effect, originating from the real-space Berry phase associated with nontrivial
magnetic textures, has attracted considerable
attention. Here, we systematically investigate the
magnetic and transport properties of antiferromagnet EuAuAs.
Magnetic characterizations reveal
antiferromagnetic transition at 5.7 K and 6.3 K for $H \parallel ab$ and $H \parallel c$, accompanied by metamagnetic transition and small hysteresis for $H \parallel ab$. Electrical transport measurements reveal a pronounced topological
Hall effct in the
antiferromagnetic state with $H \parallel ab$ and $I \parallel c$, which may be attributed to finite scalar
spin chirality. Furthermore, the magnetoresistance exhibits butterfly-shaped hysteresis and strong angular dependence, which are likely associated with
spin-dependent electron scattering,
magnetic-domain
evolution, and domain-wall pinning. Our results suggest that field-induced
spin textures play an important role in the magnetotransport properties and provide insights into the interplay between
magnetic textures and electronic transport in centrosymmetric antiferromagnets.
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All authors Yu Zhang, Junfa Lin, Huan Wang, Kun Han, Yiting Wang, Xue Dong, Zhenfeng Guan, Shengdi Xi, Tian-Long Xia
Superconductivity
Unconventional Superconductivity in the Chiral Topological Semimetal Ag2Pd3S
Roshan Kumar Kushwaha, Dibyendu Samanta, Sudarshan Sharma et al. (+15 more)
Chiral crystals provide a unique setting where broken inversion
symmetry, strong
spin-orbit coupling, and electronic
topology intertwine, yet superconductivity in intrinsically
chiral materials remains rare. Here, we report unconventional superconductivity in the
chiral topological semimetal Ag$_2$Pd$_3$S, an enantiomorphic analog of natural mineral coldwellite, crystallizing in the right-handed space group $P4_132$. Bulk superconductivity with a transition temperature $T_C = 1.1(2)$ K is confirmed by electrical resistivity, magnetization, and specific-heat measurements.
Muon spin rotation and relaxation ($\mu$SR) experiments reveal a fully gapped superconducting state that spontaneously time-reversal
symmetry (TRS) breaking establishing Ag$_2$Pd$_3$S as the first
chiral topological semimetal
superconductor exhibiting intrinsic TRS breaking. First-principles calculations uncover multiple multifold band crossings near the
Fermi level, hosting Kramers-Weyl, double
spin-1, and
spin-3/2 quasiparticles with large topological charges. These unconventional
fermions generate
symmetry-protected topological surface states and underscore the nontrivial
topology of the normal state.
Symmetry analysis based on the Ginzburg-Landau theory suggests a loop-supercurrent-ordered superconducting state, yielding a full gap alongside spontaneous TRS breaking. The coexistence of TRS-breaking superconductivity and
chiral multifold
fermions identifies Ag$_2$Pd$_3$S as a platform for realizing intrinsic superconducting diode effects and chirality-induced
spin selectivity, offering a transformative pathway toward dissipationless topological
quantum technologies.
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All authors Roshan Kumar Kushwaha, Dibyendu Samanta, Sudarshan Sharma, Mathew Pula, Shashank Srivastava, Poulami Manna, Arushi, Sajilesh K. P., Suhani Sharma, Priya Mishra, Prabin Kumar Naik, James Beare, Yipeng Cai, Kenji M. Kojima, Amit Kanigel, Graeme M. Luke, Sudeep Kumar Ghosh, Ravi Prakash Singh
Materials Science
Ferron Hall effect: Transverse accumulation of polarization driven by thermal gradients in ferroelectrics
Daniel A. Bustamante Lopez, Verena Brehm and Dominik M. Juraschek
The
phonon Hall effect describes the generation of a transverse heat current in response to a longitudinal thermal gradient in a
magnetic field. Here, we theoretically demonstrate that, when the
lattice excitations deflected by the
Hall effect carry electric dipole moments, their transverse motion produces an accumulation of electric polarization in ferroelectric materials. This accumulation is driven by
lattice excitations that carry polarization, known as ferrons, and we therefore call the mechanism the ferron
Hall effect. Using atomistic
lattice dynamics with parameters obtained from density functional theory, we illustrate the effect in the prototypical ferroelectric BaTiO3. Our results identify ferrons as the electric-polarization analogues of
magnons in transverse transport and provide a route toward thermal and
magnetic manipulation of ferroic order.
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Statistical Mechanics
Finite-resolution exhaustive traversal of thermodynamic state spaces has divergent thermodynamic length
Satori Tsuzuki
Mapping an entire multidimensional thermodynamic control region is fundamentally different from driving a system between prescribed endpoints. We formulate such mapping as a finite-resolution coverage problem: a rectifiable protocol must come within thermodynamic distance $\varepsilon$ of every point in a regular $d$-dimensional state-space window. A covering argument shows that the required thermodynamic length grows at least as $\varepsilon^{(1-d)}$.
Hilbert- and Peano-type finite traversals attain the same exponent, demonstrating that it is fixed by the codimension of a curve rather than by a particular scanning construction. When the coverage metric is a physical friction tensor, or is uniformly dominated by one, this
geometric law implies a slow-driving resource constraint: at fixed duration, the quadratic excess-work cost grows at least as $\varepsilon^{(2(1-d))}$, whereas at fixed excess-work budget the required duration grows with the same power. We derive microscopic friction metrics for a detailed-balance three-state Markov jump process and an overdamped harmonic trap. Raster scans of the trap illustrate how refinement costs can appear either as excess work or as acquisition time, depending on the allocation of time along the protocol. Finite experimental or numerical resolution cuts off the continuum divergence, while singular thermodynamic response can additionally modify the prefactor according to a directional-integrability criterion. Morton/Z-order traversal preserves the universal exponent but increases locality-dependent amplitudes. These results establish finite-resolution state-space coverage as a resource problem distinct from endpoint-to-endpoint thermodynamic control.
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Superconductivity
Electronic inhomogeneity in Cs- and Sb-terminated surfaces of CsV$_3$Sb$_5$ probed by scanning photoemission spectromicroscopy
T. Mizokawa, G. Tomassucci, M. Hattori et al. (+6 more)
Electronic structures of Cs- and Sb-terminated surfaces of a kagome
superconductor CsV$_3$Sb$_5$ have been elucidated by means of scanning photoemission microscopy (SPEM). The observed band structure of the Cs-terminated surface is rather close to that of the bulk while that of the Sb-terminated one is substantially modified around K/H point of the Brillouin zone. While the contrast between the Cs- and Sb-terminated regions is reduced below the charge density wave transition temperature, the Sb 5$p$ band of Cs-terminated region exhibits electronic inhomogeneity which slightly increases below it. The inhomogeneity of the Sb 5$p$ band would be related to disorders of the out-of-plane Sb and relevant for the band folding along $\Gamma$-A with the charge density wave. The SPEM results suggest that the less inhomogeneous Cs termination is more suitable for interface of kagome
superconductors. However, the inhomogeneity of Cs termination, which is significant at $\Gamma$/A, noticeable at K/H, and negligible at M/L, is expected to affect the Sb 5$p$-V 3$d$ hybridization at the interface.
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All authors T. Mizokawa, G. Tomassucci, M. Hattori, F. Minati, L. Tortora, A. Barinov, Z. Wang, J.-X. Yin, N. L. Saini
Materials Science
The substitutional atomic distance model for predicting lattice thermal conductivity in alloys
Zhicheng Zong, Tianhao Li, Shixian Liu et al. (+2 more)
Understanding
phonon transport in
alloys is crucial for the design of high-performance electronic and thermoelectric devices. However, conventional theoretical models fail to provide a clear physical picture of
phonon scattering caused by atomic disorder in
alloys, and their prediction accuracy is limited. In this work, a new substitutional atomic distance model for
alloys is proposed, providing an intuitive physical picture. SiGe and InGaAs
alloys are taken as representative systems, and their thermal conductivities are calculated, showing good agreement with previous experimental measurements. The results indicate that
alloy scattering plays a dominant role in reducing thermal conductivity. This study provides new insights into
phonon transport in
alloys and offers guidance for tailoring thermal properties through compositional engineering.
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All authors Zhicheng Zong, Tianhao Li, Shixian Liu, Haisheng Fang, Nuo Yang
Materials Science
Atomically Thin Amorphous Carbon with an Ultralow Dielectric Constant
Chee-Tat Toh, Artem K. Grebenko, Ugur Karadeniz et al. (+17 more)
Two-dimensional (2D) materials exhibit excellent properties at monolayer thickness and are viable replacements for various microelectronic components as scaling gradually approaches the atomic limit. Despite significant advancements in the ongoing 2D revolution of integrated
circuits, one crucial building block, namely a 2D ultralow-k (ULK) dielectric, remains unreported. The challenge lies in achieving a dielectric constant less than 3, as traditional low-k dielectrics are inherently unstable at the 2D limit due to their amorphous or porous nature. The realisation of ultrathin dielectrics with low-k is also needed to address current bottlenecks in integrated
circuits scaling. Specifically, low-k materials are necessary to minimise parasitic capacitances as the distance between conductive elements shrinks below 10 nm. Moreover, advanced architectures like gate-all-around field effect transistors (GAA FET) require even lower dielectric constants (k<2) at sub-3nm thickness. Here, we show that layer-by-layer grown multilayer amorphous carbon (ML-AC), as thin as 0.8 nm, is a mechanically robust 2D ULK dielectric with k of 1.35 and dielectric strength of 28-31 MV cm-1. The lack of any long-range order, its intrinsic 2D nature, sp2 carbon character and low density are all essential for minimising dielectric permittivity. Moreover, ML-AC overcomes the vulnerability of existing dielectrics to ion
diffusion degradation with a record metal ion
diffusion time to failure (TTF) of 10^10 s for even a single layer. Therefore, otherwise necessary additional layers occupying up to 3 nm can be eliminated, which is especially significant as metal line widths approach 10 nm. Combined with its low-temperature, direct and conformal growth even on a dielectric, these critical features enable substantial improvements in silicon-based
semiconductor electronics and ensure compatibility with future 2D electronics.
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All authors Chee-Tat Toh, Artem K. Grebenko, Ugur Karadeniz, Usha Bhat, Ya He, Hongji Zhang, Denis V. Vyalikh, Anna Makarova, Alexander Fedorov, Alena A. Alekseeva, Kostya Iakoubovskii, Lu Shi, Andrei Starkov, Chuan Chu Tee, Lucas M. Sassi, Michel Bosman, Naoto Kamiuchi, Yuta Sato, Kazutomo Suenaga, Barbaros Oezyilmaz
Materials Science
Optimizing Expert-Designed Crystal Graph Networks for Band-Gap Prediction with an Autonomous LLM Research Loop
Chenmu Zhang and Boris I. Yakobson
Predicting a material's properties from its structure is a central, fast-advancing problem in computational materials science. A decade of work has produced standard public
benchmarks and many published machine-learning models for the task (Dunn et al., 2020). The task's fixed metric and these baselines make it a natural setting for autonomous
agent research (Karpathy, 2026). On the MatBench band-gap
benchmark ($>$100k
crystals), a general-purpose coding
agent autonomously built the most accurate model trained without external pretraining, ahead of all seventeen expert-designed models reported for the task. A closer analysis shows it reached this by implementing known methods: either already standard in
crystal neural-network models, or borrowed from other areas of machine learning. The contributing implementations include element-pair features on each message-passing edge and a
crystal space-group
embedding. The work not only demonstrates that LLM-
agent autonomous research can optimize an expert-designed machine learning model for material property prediction, but also investigates the limitations of such autonomous research.
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Materials Science · Cross-listed from physics.chem-ph
Thermal Fundamental Gap Predictions in DFT via Optimally Tuned Hybrids
Tim Gould, Leeor Kronik, Gil Amoyal et al. (+1 more)
Predicting electronic fundamental gaps at finite temperature has remained conceptually and practically challenging. We address this in three connected steps. First, we extend generalized Kohn–Sham hybrid density functional theory to thermal ensembles, deriving a Mermin generalized Kohn–Sham framework from a thermal one-particle auxiliary system and an exact density-functional remainder. Second, via an extension of Janak's
theorem that holds rigorously in this framework, we recast Hirata's thermal-quasiparticle picture as a thermal orbital gap
estimator and derive a closed low-temperature form, the error of which is controlled by the derivative discontinuity. Third, because optimal tuning eliminates this error, the auxiliary orbital gap matches the interacting gap at low temperature, upgrading optimal tuning from a ground-state strategy to the governing principle – mandatory, not optional – for accurate finite-temperature gap predictions obtained from gaps of orbital
eigenvalues within a hybrid functional framework. We present applications that validate the theory and demonstrate its consequences.
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All authors Tim Gould, Leeor Kronik, Gil Amoyal, Stefano Pittalis