Mesoscale and Nanoscale Physics
Quantum geometry-driven photogalvanic responses in semi-Dirac systems
Bristi Ghosh, Malay Bandyopadhyay and Snehasish Nandy
The photogalvanic effect (PGE), a fundamental nonlinear optical phenomenon in non-centrosymmetric materials, generates direct photocurrent under polarized light. Using
quantum kinetic theory within the relaxation-time approximation, we theoretically investigate the PGE as a probe of
quantum geometry in anisotropic type-I and type-II semi-Dirac (SD) systems, characterized by distinct electronic structures. We systematically analyse various microscopic contributions to the PGE conductivity, including injection, shift, resonance, higher-order pole, and anomalous terms, and emphasize their connections to different
quantum geometric quantities, namely, Berry
curvature,
quantum metric, and metric connection. By studying the frequency and chemical-potential dependence of the PGE conductivity in SD systems, we find that the optical conductivities in the type-II case are significantly enhanced relative to those in type-I. For the circular PGE (CPGE), Berry-
curvature-driven contributions remain qualitatively similar in both phases, whereas the linear PGE (LPGE) displays clear qualitative differences. In particular, the $xxx$ component of the shift conductivity in the type-II phase reverses sign upon tuning the perturbation parameter $\delta$, providing a direct signature of the Lifshitz transition. In contrast, other components remain sign-invariant, as in type-I SD systems. These combined CPGE and LPGE signatures provide an unambiguous distinction between the two SD phases. The predicted effects, realizable in TiO$_2$/VO$_2$
heterostructures, establish PGE as a sensitive probe of
quantum geometry with potential applications in polarization-selective photodetection, optical rectification, and next-generation optoelectronic devices.
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Materials Science
Seamlessly joining length scales: From atomistic thermal graphs to anisotropic continuum conductivity
C. Ugwumadu, D. A. Drabold and R. M. Tutchton
Thermal transport in complex solids is governed by local structure, defects, and anisotropy, yet most continuum models still rely on oversimplified, homogenized conductivities. Here, we bridge atomistic and continuum descriptions by building finite element (FE) models directly from the site-projected thermal conductivity (SPTC), an atomic-level decomposition of the Green-Kubo thermal conductivity. We introduce a new toolkit, the Simulator Collection for Atomic-to-Continuum Scales (SCACS), which uses a graph neural network to predict SPTC on large atomic structures, coarse-grain these fields into anisotropic conductivity tensors, and embeds them into the heat-flow FE equation with a customized, anisotropy-aware adaptive mesh refinement scheme. Applied to silicon nanostructures, the resulting FE models act as representative volume elements, reproduce bulk conductivities, and capture interfacial and defect-driven anisotropy while maintaining thermodynamic consistency. Additionally, SCACS predicts experimental conductance trends and fields. This innovation demonstrates a novel and general route for transferring atomistic transport information into device-scale thermal simulations with physics-based approximations.
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Materials Science · Cross-listed from cs.LG
Zatom-1: Towards a Multimodal Foundation Model for 3D Molecules and Materials
Alex Morehead, Miruna Cretu, Antonia Panescu et al. (+14 more)
General-purpose 3D modeling in chemistry encompasses molecules and materials, requiring both generative and predictive capabilities. However, most existing AI approaches are optimized for a single domain (molecules or materials) and a single task (generation or prediction), which limits representation sharing and transfer. We introduce Zatom-1, a cross-domain, general-purpose model architecture that unifies generative and predictive learning of 3D molecules and materials. Zatom-1 is a deliberately simplified
Transformer trained with a
multimodal flow matching objective that jointly models discrete atom types and continuous 3D geometries. This approach supports scalable pretraining with predictable gains as model capacity increases, while enabling fast and stable sampling. We use cross-domain generative pretraining as a universal initialization for downstream multi-task prediction of properties, energies, and forces. Empirically, Zatom-1 outperforms or competes with specialized baselines on both multi-task generative and predictive
benchmarks in data-controlled settings, while improving generative inference speed by more than an order of magnitude. Our experiments demonstrate positive predictive transfer between data domains from joint generative pretraining: modeling materials during generative pretraining improves molecular property prediction accuracy. Open-source code and model weights are freely available at https://github.com/Zatom-AI/zatom.
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All authors Alex Morehead, Miruna Cretu, Antonia Panescu, Rishabh Anand, Maurice Weiler, Tynan Perez, Samuel Blau, Steven Farrell, Wahid Bhimji, Anubhav Jain, Hrushikesh Sahasrabuddhe, Pietro Lio, Tommi Jaakkola, Rafael Gomez-Bombarelli, Rex Ying, N. Benjamin Erichson, Michael W. Mahoney
Strongly Correlated Electrons
Rotational Phonons Drive Low-Energy Kinks in Cuprate Superconductors
Yanyong Wang, Manuel Engel, Christopher Lane et al. (+9 more)
Angle-resolved photoemission spectroscopy (ARPES) reveals ubiquitous quasiparticle “kinks” near $\sim$70 meV and $\sim$40 meV across cuprate
superconductors, often accompanied by peak–dip–hump (PDH) structures. These features point to strong coupling between electrons and low-energy bosonic excitations, but the microscopic origin has remained elusive due to the limitations of conventional density-functional theory (DFT) and the high cost of beyond-DFT methods. Here, we systematically study the electron–
phonon coupling (EPC) in hole-doped infinite-layer CaCuO$_2$ using the Strongly Constrained and Appropriately Normed (SCAN) density functional, explicitly including
magnetic effects. We find a substantial EPC strength $\lambda$ of $\sim$0.5 in the
magnetic phase, producing kinks and PDH structures in the 40-80~meV window in excellent agreement with experiments. The dominant contribution arises from rotational oxygen
phonons, while breathing modes contribute little. Our results establish strong EPC in cuprates, highlight the key role of rotational
phonons, and provide a framework for understanding spectral anomalies in cuprates and beyond.
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All authors Yanyong Wang, Manuel Engel, Christopher Lane, Henrique Miranda, Lin Hou, Bernardo Barbiellini, Adrienn Ruzsinszky, John P. Perdew, Robert S. Markiewicz, Arun Bansil, Jianwei Sun, Ruiqi Zhang
Quantum Gases · Cross-listed from physics.atom-ph
Efimov Effect in Ultracold Microwave-Shielded Polar Molecules
Shayamal Singh and Chris H. Greene
A
quantum-mechanical description is presented for the three-body physics of shielded dipolar molecules, including a prediction of observable Efimov physics. Despite the anisotropic and long-range nature of the interaction, shielding enables a regime in which universality emerges already at the two-body level and extends to the three-body sector, where Efimov physics emerges. On the negative side of the scattering-length resonance, computed trimer binding energies display the characteristic scaling expected for Efimov resonances. Finally, the sudden approximation can be used to create trimer bound states, starting from positive energy trap states as a way to create or detect these molecular trimers. Moreover, the three-body parameter expressed in dipolar units is found to be universal.
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Materials Science
Electrostatic Gating of Ionic Conductance Through Heterogeneous van der Waals Nanopores
Aaron H. Barajas-Aguilar, Matthew Schiel, Ethan Cao et al. (+6 more)
Nanofluidic ionic transistors typically require gate voltages above 1 V and operate only at sub millimolar ionic strengths, limiting their biocompatible applications. We demonstrate ionic transistors consisting of single sub 10 nm nanopores drilled in van der Waals (vdW)
heterostructures with internal gate electrodes made of few layer
graphene. These devices deliver up to 10fold current modulation at gate voltages as low as 0.3 V in 10 mM KCl, and 2fold modulation at near physiological 100 mM KCl. Baseline conductance with no gate shows surface charge dominated transport below 100 mM KCl consistent with negatively charged hBN walls and 5 nm opening of the pores. The surface charge and the electrochemical asymmetry introduced by the three electrode configuration govern the device behavior: negative gate voltage (VG) enriches ionic concentrations and enhances current, whereas positive VG induces a local depletion zone that suppresses transport. The current modulation by VG is dependent on the polarity of the transmembrane potential and leads to ion current rectification. Molecular dynamics simulations of a nanopore in a hBN
graphene hBN stack reveal confinement and surface charge dependent suppression of relative permittivity of interfacial water. Continuum modeling with radially varying interfacial water permittivity reproduces the asymmetric IV characteristics and explains how the embedded gate sculpts local potential and ion concentrations. By enabling sub 0.5 V control of ionic transport at up to 100 mM salt concentrations, these devices address a key barrier in nanofluidics and open the pathway to low power ionic
circuits and biosensing.
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All authors Aaron H. Barajas-Aguilar, Matthew Schiel, Ethan Cao, DaVante Cain, Margaret L. Berrens, Fikret Aydin, Tuan Anh Pham, Javier Sanchez-Yamagishi, Zuzanna S. Siwy
Materials Science
Ambient-Pressure Organic Dirac Electron State in $\alpha$-(BETS)$_2$AuCl$_2$
Takuya Kobayashi, Kazuyoshi Yoshimi, Aoto Nishimoto et al. (+2 more)
We report an ambient-pressure Dirac electron (DE) state in a new organic conductor, $\alpha$-(BETS)$_2$AuCl$_2$ (BETS = bis(ethylenedithio)tetraselenafulvalene). This salt exhibits characteristic transport properties, including large positive in-plane and anomalous negative interlayer magnetoresistance. These signatures closely resemble the high-pressure DE states of $\alpha$-(ET)$_2$I$_3$ (ET = bis(ethylenedithio)tetrathiafulvalene). First-principles calculations including
spin-orbit coupling identify the electronic state as a quasi-three-dimensional massive Dirac semimetal with residual
Fermi pockets. This discovery provides a valuable platform for exploring bulk Dirac
fermions without the complexity of high-pressure measurements.
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All authors Takuya Kobayashi, Kazuyoshi Yoshimi, Aoto Nishimoto, Shinji Michimura, Hiromi Taniguchi
Statistical Mechanics
Yet another look at narrow escape through a tube
Victorya Richardson, Yick Hin Ling and Sean D Lawley
The narrow escape problem concerns the time needed for a diffusing particle to exit a confining domain through a small hole in the boundary. While this problem is now well-understood, determining the escape time for a particle that must exit through a narrow tube has proven challenging. Indeed, relying on analogies with electrodynamics, parameter fits to simulations, and heuristics, a variety of conflicting estimates for this escape time have been offered over the last three decades, some of which are counterintuitive and arguably non-physical. In this paper, we combine matched asymptotic analysis and probabilistic methods to determine the exact asymptotics of the narrow escape time through a tube. We obtain a new escape time formula which reduces to the various prior estimates in certain special cases. If the diffusivity in the tube differs from the diffusivity in the rest of the domain, our results reveal the importance of the form of the multiplicative noise inherent to any diffusivity that varies in space. We discuss our results in the context of asymmetric
cell division.
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Mesoscale and Nanoscale Physics
Phonon decoherence produced by two-level tunneling states
Ryan O. Behunin, Taylor Ray, Dylan Chapman et al. (+3 more)
Phonon modes within pristine crystalline resonators now routinely reach the
quantum ground state. Such systems are attractive for
quantum information science applications, as advanced fabrication and processing can enable relatively long
quantum coherence times, and precision control can be realized through optical, electrical, or
qubit coupling. In many state-of-the-art systems, the
phonon lifetime is limited by disorder. In particular, native
oxides or damaged `dead layers' at surfaces can host two-level tunneling states that lead to a particularly problematic form of dissipation that increases at lower temperatures. As mechanical losses are driven down in systems such as micro-fabricated bulk acoustic wave resonators, tunneling states are expected to emerge as the dominant mechanism for
phonon decoherence. A quantitative description of these mesoscopic systems therefore requires a framework that captures interactions between a selected
phonon mode and a large ensemble of TLS. Here, we derive a
quantum master equation for this coupled system, permitting the
phonon decoherence produced by two-level tunneling states to be calculated. As an example, we estimate the lifetime of a variety of
quantum states within quartz micro-resonators hosting a thin surface layer of tunneling states. We find that the
phonon coherence time is maximized at low temperatures, in spite of increased mechanical dissipation, and that
phonon-TLS coupling can be reduced for modes with strain nodes at the surfaces.
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All authors Ryan O. Behunin, Taylor Ray, Dylan Chapman, Andrew J. Shepherd, Yizhi Luo, Peter T. Rakich
Quantum Gases
Finite-temperature superfluid depletion of disordered Bose gases
Cord A. Müller
At zero temperature, homogeneous interacting Bose-condensed fluids are entirely superfluid, with remarkable transport properties. A non-superfluid, normal component is induced by finite temperatures and spatial inhomogeneity, the combined effects of which are rather intriguing, and difficult to describe quantitatively. By inhomogeneous Bogoliubov theory, applicable to weakly interacting condensed Bose gases in static external potentials with arbitrary spatial correlations, we calculate the normal fluid density via the transverse current-current correlation. We obtain finite-temperature disorder corrections to the normal fraction known since Laudau's seminal two-fluid theory, using diagrammatic perturbation theory for systems of any dimensionality, with closed analytical expressions to leading, quadratic order in disorder strength.
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Soft Condensed Matter
Chapman-Enskog expansion for chirally colliding disks
Ruben Lier and Paweł Matus
We study a two-dimensional gas of hard disks undergoing
chiral, energy- and momentum-conserving collisions. We propose a simple
chiral collision rule and show that it can effectively capture collisions of spinning noncircular particles without retaining
spin or orientation as kinetic variables. Despite the microscopic breaking of time-reversal
symmetry, the H-
theorem is obeyed, guaranteeing relaxation towards
equilibrium in the absence of external forces. A Chapman-Enskog expansion yields analytical expressions for the shear and odd viscosity and the thermal conductivity. Theoretical predictions are confirmed by nonequilibrium molecular dynamics simulations
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Mesoscale and Nanoscale Physics
Granular aluminum induced superconductivity in germanium for hole spin-based hybrid devices
Giorgio Fabris, Paul Falthansl-Scheinecker, Devashish Shah et al. (+19 more)
In
superconductor-
semiconductor hybrid structures, superconductivity and
spin polarization are competing effects as
magnetic fields break Cooper pairs. They can be combined using thin films and in-plane
magnetic fields, an approach that enabled the pursuit of Majorana zero modes, Kitaev chains, and Andreev
spin qubits (ASQs), but remains challenging for materials with small in-plane $g$-factors or when out-of-plane fields are required. We demonstrate that granular aluminium (grAl), composed of nanometre-scale aluminium grains embedded in an amorphous
oxide matrix, can overcome this limitation. By depositing grAl on Ge/SiGe
heterostructures, we induce a hard superconducting gap with BCS peaks at $305~\mu\mathrm{eV}$ and
magnetic-field resilience for both the in-plane and out-of-plane directions, allowing Zeeman splitting of Yu-Shiba-Rusinov (YSR) states beyond $50~\mu\mathrm{eV}$ (12 GHz). Leveraging this robustness, we reveal signatures of hole physics and discuss a driving mechanism for ASQs regardless of the strength of the Rashba
spin-orbit coupling in planar germanium.
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All authors Giorgio Fabris, Paul Falthansl-Scheinecker, Devashish Shah, Daniel Michel Pino, Maksim Borovkov, Anton Bubis, Kevin Roux, Dina Sokolova, Alejandro Andres Juanes, Tommaso Costanzo, Inas Taha, Aziz Genç, Jordi Arbiol, Stefano Calcaterra, Afonso De Cerdeira Oliveira, Daniel Chrastina, Giovanni Isella, Ruben Seoane Souto, Maria Jose Calderon, Ramon Aguado, Jose Carlos Abadillo-Uriel, Georgios Katsaros
Mesoscale and Nanoscale Physics
Low-Noise Quantum Dots in Ultra-Shallow Ge/SiGe Heterostructures for Prototyping Hybrid Semiconducting-Superconducting Devices
M. Borovkov, Y. Schell, D. Sokolova et al. (+15 more)
Planar germanium is currently the only semiconducting platform where high-coherence
spin qubits and proximity-induced superconductivity have each been demonstrated. Recent research into
spin qubits in Ge/SiGe
heterostructures has focused on increasing the thickness of the SiGe capping layer, reporting improvements in the electrostatic noise levels. Meanwhile,
heterostructures with thinner capping layers remain rather unexplored, despite the potential advantages for proximity-induced superconductivity. Here, we study a Ge/SiGe
heterostructure with a thin SiGe cap $d \approx 4\ \mathrm{nm}$ and investigate its viability to host low-noise
quantum dots. To keep the thermal budget compatible with superconducting layers, low-temperature
oxide deposition processes were developed and implemented for the gate dielectrics. The charge-noise level of fabricated devices is estimated to be $1.8 \pm 1.0\ \mu\mathrm{eV}/\sqrt{\mathrm{Hz}}$, comparable to devices fabricated on shallow
heterostructures $\left(d \sim 20\ \mathrm{nm}\right)$ with high-temperature deposited
oxides. Low charge-noise levels, together with the straightforward integration of
superconductors, make this
heterostructure an attractive platform for prototyping hybrid semiconducting-superconducting devices.
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All authors M. Borovkov, Y. Schell, D. Sokolova, K. Roux, P. Falthansl-Scheinecker, G. Fabris, D. Shah, J. Saez-Mollejo, R. Previdi, I. Taha, Aziz Genç, J. Arbiol, S. Calcaterra, A. D. C. Oliveira, D. Chrastina, G. Isella, A. Bubis, G. Katsaros
Other Condensed Matter · Cross-listed from quant-ph
Identifying quantum coherence in quantum annealers
Connor Aronoff, Travis Howard, David Nicholaeff et al. (+2 more)
Demonstrating genuine many-body
quantum coherence in large-scale
quantum processors remains a central challenge for near-term
quantum technologies. Recent experiments on D-Wave
quantum annealers have investigated quenches of Ising chains and observed defect densities that show Kibble-Zurek scaling, consistent with coherent
quantum dynamics. However, identical scaling can arise from classical or thermal processes. Here we propose the use of many-body coherent oscillations (MBCO) as a diagnostic for the identification of system-wide coherence in analog
quantum simulators. Solving the time-dependent Schrodinger equation, we show that quenches of a staggered one-dimensional Ising chain across a
quantum critical point produce oscillatory signatures in defect observables. We implement this model on the D-Wave Advantage
quantum annealer. Using fast-anneal protocols, we find that, although defect densities follow Kibble-Zurek scaling, the expected oscillatory behavior is absent. We demonstrate that static disorder associated with individual
qubits is not likely responsible for the absence of MBCO. Modest modifications to annealing schedules can dramatically enhance oscillation visibility. This work gives a general roadmap for the search for
quantum coherence in noisy, large-scale
quantum platforms.
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All authors Connor Aronoff, Travis Howard, David Nicholaeff, Alejandro Lopez-Bezanilla, Wade DeGottardi
Soft Condensed Matter
From Global Flocking to Local Clustering: Interplay between Velocity Alignment and Visual Perception of Active Particles
Mohit Gaur, Arnab Saha and Subhajit Paul
Collective behavior in biological systems was first captured by the Vicsek model, in which particles align their velocities in the average direction of neighbors, leading to coherent motion and showing an order-disorder transition. However, in many complex environments, the interactions are non-reciprocal, lacking an action-reaction
symmetry. Using framework of the Vicsek model, we implement non-reciprocity by restricting interactions to neighbors located inside a finite
vision cone, for a particle by limiting its set of interacting neighbors which fall within a
vision-cone, providing a minimal description for cognitive perception. Using detailed numerical simulations, we explore the clustering and flocking behavior due to competition between noise and limited visual perception in the presence of
alignment interaction. For low noise, with reduction in the
vision angle the system shows transition from a global coherent motion to locally ordered small-sized clusters. This behavior is confirmed through the steady-state distributions of velocity components and their fluctuation relative to the global mean. This is also characterized using a polar order-parameter and a two-point velocity correlation function. Interestingly, at small
vision angles, particles exhibit strong short-range correlations within clusters even in the absence of any global coherence. Time-
evolution of the related correlation functions illustrate the pathways towards the emergence of such structures. The time dependence of the average cluster size and the length-scale calculated from the two-point velocity correlation show scaling behavior and indicate that the emergence of density field clustering is a consequence of the velocity-field coherence. Any kind of ordering and clustering disappear in the limit of high noise and low
vision-angle regime.
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