Materials Science
CHIPS-TB: Evaluating Tight-Binding Models For Metals, Semiconductors, and Insulators
In Jun Park and Kamal Choudhary
As
semiconductor technologies continue to scale down to the nanoscale, the efficient prediction of material properties becomes increasingly critical. The tight-binding (TB) method is a widely used semi-empirical approach that offers a computationally tractable alternative to Density Functional Theory (DFT) for large-scale electronic structure calculations. However, conventional TB models often suffer from limited transferability and lack standardized benchmarking protocols. In this study, we introduce a computational framework (CHIPS-TB) for evaluating and comparing tight-binding parameterizations across diverse material systems relevant to
semiconductor design, focusing on properties such as electronic bandgaps, band structures, and bulk modulus. We assess model parameterizations including Density Functional Tight-Binding (DFTB)-based MatSci, PBC, PTBP, SlaKoNet and TB3PY against OptB88vdW, TBmBJ-DFT and experimental reference data from the JARVIS-DFT database for 50+ materials pertinent to
semiconductor applications. The CHIPS-TB code will be made publicly available on GitHub and
benchmarks will be available on JARVIS-Leaderboard.
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Statistical Mechanics · Cross-listed from astro-ph.CO
Game Theory in Cosmology
Oem Trivedi and Venkat Venkatsubramanian
We present a game-theoretic statistical framework for cosmology, which we term Cosmological Teleodynamics. We recast the dark sector,
cosmic acceleration, large-scale structure, and
cosmic tensions as emergent consequences of nonlocal
memory and intrinsically persistent organization in a self-gravitating Universe. By introducing a maximum-caliber weight on
cosmic histories and a bias functional encoding structural
memory, we derive modified Friedmann, Boltzmann, and Poisson equations that naturally generate dark energy-like acceleration, dark matter-like clustering, and scale-dependent growth suppression. We also show how this approach can naturally help alleviate the $H_0$ and $S_8$ tensions, can produce anisotropic velocity fields, and predict environment-dependent
halo signatures that cannot arise from particle dark matter or scalar-field dark energy. We also derive a generalized horizon
entropy and temperature, revealing a nonequilibrium statistical origin for
cosmic acceleration and formulating a Law of Universal Arbitrage
Equilibrium that governs the
evolution of the Universe, showing that it is expanding towards a continuous form of Nash
equilibrium. Cosmological Teleodynamics therefore offers a unified, emergent, and testable alternative to the conventional dark sector, rooted not in new particles but in the intrinsic statistical and systemic structure of
cosmic memory, and shows that the universe itself operates like a
giant potential game.
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Materials Science
Towards superior van der Waals density functionals for molecular crystals
Dmitry V. Fedorov, Nikita E. Rybin, Mikhail A. Averyanov et al. (+3 more)
Ubiquitous van der Waals (vdW) interactions play a subtle yet crucial role in determining the precise atomic arrangements in solids, particularly in molecular
crystals where these weak forces are the primary link between constituent building blocks. Within density functional (DF) theory, the most natural approach for addressing vdW forces is the use of vdW-inclusive density functionals. Through a detailed analysis of the underlying formalism, we have developed a computational scheme that combines vdW functionals of type DF1 and DF2 and serves as a well optimizable tool to improve the theoretical description and prediction of molecular
crystals and other sparse materials. The proof of principle is demonstrated by our consideration of the molecular
crystals from the X23
dataset.
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All authors Dmitry V. Fedorov, Nikita E. Rybin, Mikhail A. Averyanov, Alexander V. Shapeev, Artem R. Oganov, Carlo Nervi
Materials Science
Carrier transport and electrical bandgaps in epitaxial CrN layers
Duc V. Dinh, Jens Herfort, Andreas Fiedler et al. (+1 more)
The transport properties and electrical bandgap of nominally undoped ~75-nm-thick CrN layers simultaneously grown on AlN(0001) and AlN(11\bar{2}2) templates using
plasma-assisted molecular beam epitaxy are investigated. The layers grown on AlN(0001) and AlN(11\bar{2}2) exhibit (111) and (113) surface orientations, respectively. All layers exhibit antiferromagnetism with a Néel temperature of ~280 K, observed by temperature-dependent
magnetic and electrical measurements.
Hall-effect measurements demonstrate n-type semiconducting behavior across a wide temperature range from 4 to 920 K. At low temperatures (4 - 260 K), the data show parallel conduction channels from a metallic
impurity band and the conduction band. The carrier mobility exhibits a temperature dependence consistent with a nondegenerate
semiconductor, governed by ionized-
impurity scattering below 400 K and
phonon scattering above 400 K. An analysis of the temperature-dependent carrier density between 300 and 920 K yields two activation energies associated with intrinsic conduction: 0.15 eV (with an uncertainty of -0.02/+0.10 eV), which we attribute to the fundamental bandgap, and 0.50 eV (with an uncertainty of -0.05/+0.15 eV) representing a higher energy transition.
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All authors Duc V. Dinh, Jens Herfort, Andreas Fiedler, Oliver Brandt
Statistical Mechanics · Cross-listed from quant-ph
Extracting conserved operators from a projected entangled pair state
Wen-Tao Xu, Miguel Frías Pérez and Mingru Yang
Given a tensor network state, how can we determine conserved operators (including
Hamiltonians) for which the state is an eigenstate? We answer this question by presenting a method to extract geometrically $k$-local conserved operators that have the given infinite projected entangled pair state (iPEPS) in 2D as an (approximate) eigenstate. The key ingredient is the evaluation of the static structure factors of multi-site operators through differentiating the generating function. These generating functions define a
manifold of the given tensor network state deformed by some parameters, endowed with a
quantum geometry, where conserved operators correspond to vanishing fidelity susceptibility. Despite the approximation errors, we show that our method is still able to extract from exact or variational iPEPS to good precision both frustration-free and non-frustration-free parent
Hamiltonians that are beyond the standard construction and obtain better locality. In particular, we find a 4-site-plaquette local
Hamiltonian that approximately has the short-range RVB state as the ground state. Moreover, we find a
Hamiltonian for which the deformed toric code state at arbitrary string tension is an excited eigenstate with the same energy, thereby potentially realizing
quantum many-body scars.
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Mesoscale and Nanoscale Physics
From quantum geometry to non-linear optics and gerbes: Recent advances in topological band theory
Tomáš Bzdušek
Topological principles constitute at present an integral component of condensed matter physics, permeating the modern characterization of electronic states while also guiding materials design. In this brief Perspective, I highlight three research threads in single-particle topological band theory that have recently gained momentum: (i) the rise of the
quantum geometric tensor, whose components can at present be directly accessed with optical probes; (ii) the notions of delicate and multigap
topology, which fall outside the scope of tenfold way and
symmetry-based indicators yet leave robust physical fingerprints; and (iii) the consideration of bundle gerbes, which capture formerly overlooked higher-form topological aspects of energy bands. These distinct directions have been elegantly woven together: delicate and multigap topological
insulators have peculiar features in
quantum geometry that can be conveniently captured by bundle gerbes. This viewpoint exposes the recently identified quantization of a non-linear optical response, and it invites deeper and systematic investigations into
geometric and topological aspects of band structures beyond conventional Berryology.
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Quantum Gases
Precision thermodynamics of the strongly interacting Fermi gas in two dimensions
S. Ramachandran, S. Jensen and Y. Alhassid
The two-species cold atomic
Fermi gas with attractive short-range interactions in two spatial dimensions undergoes a Bardeen-Cooper-Schrieffer (BCS) to a Bose-Einstein Condensate (BEC) crossover as a function of $\ln (k_F a)$, where $a$ is the scattering length. However, the nature of this crossover in the strong coupling regime $\ln(k_F a) \sim 1$ remains poorly understood. In this work we use canonical-ensemble auxiliary-field
quantum Monte Carlo methods on discrete
lattices to calculate several thermodynamical quantities in the strongly interacting regime, and eliminate systematic errors by extrapolating to continuous time and taking the continuum limit. In particular, we present results for the condensate fraction,
spin susceptibility, contact, energy equation of state, and the free energy staggering gap. We identify signatures of a pseudogap regime, in which pairing correlations survive above the critical temperature for superfluidity, in the
spin susceptibility and in the free energy staggering gap. These results can be used as a
benchmark for future experiments.
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Materials Science
Emergent Superfluidity of Hard-Core Excitons in Single-Layer Breathing-Kagome Nb$_3$Te$_x$Cl$_{8-x}$
Mahtab A. Khan and Michael N. Leuenberger
We develop a microscopic theory of superfluidity for hard-core dark
excitons on the triangular
lattice by mapping the large-$U$ Bose–Hubbard model to an effective XXZ
spin-$\frac{1}{2}$
Hamiltonian including virtual hopping processes. Within this framework, we identify the superfluid phase that emerges between the two Mott-insulating endpoints at fillings 0 and 1, and derive its mean-field structure via a canted-
spin solution. We then construct the corresponding continuum Landau-Ginzburg (LG) functional and analyze phase fluctuations and
vortex dynamics. In two dimensions, the superfluid–normal transition is shown to be governed by a Berezinskii–Kosterlitz–Thouless (BKT) mechanism with a stiffness determined by microscopic parameters. Our results provide a unified description connecting
lattice-scale
exciton dynamics to continuum critical behavior in triangular geometries.
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Quantum Gases · Cross-listed from physics.atom-ph
atomSmltr: a modular Python package to simulate laser cooling setups
Mateo Weill, Andrea Bertoldi and Alexandre Dareau
We introduce atomSmltr, a Python package for simulating
laser cooling in complex
magnetic field and
laser beams geometries. The package features a modular design that enables users to easily construct experimental setups, including
magnetic fields,
laser beams and other environment components, and to perform a range of simulations within these configurations. We present the overall architecture of atomSmltr and illustrate its capabilities through a series of examples, including
benchmarks against standard textbook cases in
laser cooling.
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Soft Condensed Matter
X-ray Microscopy Study of Freezing Sessile Droplets
Jae Kwan Im, Hyeonjun An, Seob-Gu Kim et al. (+2 more)
A sessile water droplet on a cold substrate freezes into a shape with a sharp apex because of water's expansion upon freezing, yielding a universal tip angle across various conditions. Using in situ X-ray imaging, we report that this angle changes with substrate temperature, and the deviation originates from bubble formation during freezing. Three-dimensional
tomography enables direct quantification of the effective ice-water density ratio, accounting for trapped bubbles. Incorporating this effective density ratio reconciles the temperature-dependent tip angles. We also confirm that a bubble-free frozen droplet in a
vacuum chamber exhibits the universal tip angle. Furthermore, X-ray imaging allows us to measure the three-phase boundary angles in situ, thereby validating the
geometric theory behind tip formation. These findings advance our understanding of the freezing dynamics associated with multiphase systems and highlight the capabilities of high-resolution X-ray imaging in ice research.
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All authors Jae Kwan Im, Hyeonjun An, Seob-Gu Kim, Jae-Hong Lim, Joonwoo Jeong
Strongly Correlated Electrons
Tuning entanglement phases and topological memory in the measurement-only Kitaev model with single and multi-qubit checks
Tushya Kalpada, Aayush Vijayvargia, Ezra Day-Roberts et al. (+1 more)
Quantum circuits provide an emerging controllable platform to realize novel dynamical non-
equilibrium phases including topologically ordered states. The Kitaev model has become a cornerstone of
quantum magnetism due to its
quantum spin liquid ground state and rich phase diagram. The Kitaev model has also been treated in the monitored
circuit setting, giving rise to topological area-law and critical-law
entanglement entropy phases. In this article, we study the
evolution of its phase diagram under the addition of new terms, motivated by their effects in the Kitaev model. We find that a single-
qubit term, analogous to a
magnetic field, leads to a trivial state in the high field limit, but with an additional intermediate volume-law phase. A three-
qubit operator that commutes with the flux operators has the opposite effect: it stabilizes the critical-law phase against the short ranged area-law
entanglement. We also employ a four-
qubit plaquette commuting operator that simultaneously measures two opposite identical-type bonds on a plaquette. This generates a distinct volume-law phase and preserves the plaquette fluxes and associated topological order, yielding extensive
entanglement while coexisting with the topological
memory characteristic of the area-law phase. We quantitatively locate phase boundaries using stabilizer (Clifford) simulations together with tripartite mutual information and
entanglement entropy measures. Our results highlight the rich phase diagram accessible from the measurement-only Kitaev model as well as suggesting rules relating the newly added operators to the phases they promote.
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All authors Tushya Kalpada, Aayush Vijayvargia, Ezra Day-Roberts, Onur Erten
Statistical Mechanics · Cross-listed from hep-th
Scaling limit of $Q$-functions for the ${\cal Z}_r$ invariant inhomogeneous XXZ spin-$\frac{1}{2}$ chain near free fermion point
Gleb A. Kotousov, Sergei L. Lukyanov and Daria A. Shabetnik
At the beginning of the 70's, Baxter introduced a multiparametric generalization of the six-vertex model. This integrable system has been found to exhibit a remarkable variety of critical behaviors. The work is part of a series of papers devoted to their systematic study. We focus on the case when the
lattice model possesses an additional ${\cal Z}_r$
symmetry and consider the critical behavior near the so-called free
fermion point. Among other things, discussed is the
algebra of extended conformal
symmetry underlying the universal behavior. The main result of the paper is the class of differential equations that describe the scaling limit of the solutions to the Bethe Ansatz equations. This is an instance of the correspondence between Ordinary Differential Equations and Integrable
Quantum Field Theory (ODE/IQFT correspondence).
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Disordered Systems and Neural Networks · Cross-listed from quant-ph
Magnetic Control of the Non-Hermitian Skin Effect in Two-Dimensional Lattices
Stefano Longhi
The non-Hermitian skin effect (NHSE) – the anomalous boundary accumulation of an extensive number of bulk modes – has emerged as a hallmark of non-Hermitian physics, with broad implications for transport, sensing, and topological classification. A central open question is how
magnetic or synthetic gauge fields influence this boundary phenomenon. Here, we develop a theoretical framework for
magnetic control of the NHSE along line boundaries in two-dimensional single-band
lattices. Using a non-Hermitian extension of the anisotropic Harper–Hofstadter model as a representative example, we show that
magnetic fields suppress the
geometric skin effect in reciprocal models, whereas skin localization can persist in nonreciprocal systems. The analysis disentangles the interplay of flux, nonreciprocity, and boundary geometry, revealing that
magnetic fields mitigate or suppress the NHSE through distinct physical mechanisms – such as bulk localization via Landau or Anderson physics, or the restoration of effective reciprocity. In particular, the geometry-dependent skin effect in reciprocal systems is found to be fragile against even weak
magnetic fields.
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Mesoscale and Nanoscale Physics
Orbital Longitudinal Magnetoelectricity in Quasi-2D Parity-Violating Antiferromagnets: Interplay of Berry Phase and Stacking Order
Jin-Xin Hu
In this work, we propose an intrinsic mechanism for longitudinal magnetoelectric (ME) coupling in quasi-2D antiferromagnets that lack spatial inversion
symmetry. We demonstrate that in such parity-violating antiferromagnets, the stacking order, when coupled with Berry
curvature and orbital
magnetic moment, generates a stacking Berry
curvature dipole (SBCD) and a stacking orbital
magnetic moment dipole (SOMD). The SBCD and SOMD act as the fundamental ingredients of the longitudinal ME response. As concrete examples, we apply our framework to typical parity-violating antiferromagnets with stacking
magnetic orders. Furthermore, the SBCD is also identified as the origin of electric-field-induced
Hall effects. Our results reveal the microscopic orbital origin of the ME effect in
antiferromagnetic systems with vanishing net Berry
curvature and orbital magnetization, governed by the interplay between Berry phase effects and layer stacking orders.
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Materials Science
Physically Interpretable Interatomic Potentials via Symbolic Regression and Reinforcement Learning
Bilvin Varughese, Troy D. Loeffler, Suvo Banik et al. (+9 more)
The development of next-generation molecular simulation models requires moving beyond pre-defined functional forms toward machine learning (ML) techniques that directly capture multiscale physics. Here, we demonstrate such an approach using symbolic regression (SR) with equation learner networks and a reinforcement learning search engine to derive interpretable equations for interatomic interactions. Training data were generated through nested ensemble sampling with density functional theory (DFT) energetics, spanning crystalline to highly disordered states. The optimization of the learner network employed continuous-action Monte Carlo Tree Search (MCTS) combined with gradient descent, enabling efficient exploration of function space. For copper as a representative transition metal, an unconstrained search produced models that outperformed fixed-form Sutton-Chen EAM potentials. The SR-derived models (SR1 and SR2) reproduced key material properties -
lattice constants, cohesive energies, equations of state, elastic constants,
phonon dispersion, defect formation energies, surface/bulk energetics, and phase transformation with significantly improved accuracy. Furthermore, stringent melting simulations using two-phase solid-amorphous interfaces confirmed that SR models accurately capture the interplay of vibrational
entropy, cohesive energy, and structural dynamics, surpassing SC-EAM in both qualitative and quantitative predictions. This highlights the potential of SR to deliver fast, accurate, flexible, and physically meaningful potentials, advancing predictive modeling across scales.
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All authors Bilvin Varughese, Troy D. Loeffler, Suvo Banik, Aditya Koneru, Sukriti Manna, Karthik Balasubramanian, Rohit Batra, Mathew J. Cherukara, Orcun Yildiz, Tom Peterka, Bobby G. Sumpter, Subramanian K.R.S. Sankaranarayanan
Mesoscale and Nanoscale Physics
Yuncheng Mao and Claudio Attaccalite
We investigate the shift-current response of inversion-broken AB-stacked
bilayer graphene under in-plane and perpendicular
magnetic fields, from the perturbative regime to strong orbital quantization, in both two-dimensional bulk systems and finite nanoribbons. An in-plane field enters through opposite momentum shifts in the two layers and leaves the bulk band dispersion essentially unchanged, producing only a modest, frequency-dependent redistribution of the shift-current spectrum. A weak perpendicular field is treated using a gauge-covariant Peierls expansion. The resulting band corrections are concentrated near Berry-
curvature hot spots, although the dominant shift-current transitions occur elsewhere, and the valley-summed response is even in the field with a leading quadratic correction. At strong perpendicular field, a rational-flux
magnetic supercell reveals nearly flat Landau-level-like bulk bands and a greatly enhanced density of states, yet the bulk shift current is almost completely quenched because the relevant optical
matrix elements and shift-vector contributions are suppressed or cancel. Finite ribbons retain optically active boundary channels: in zigzag ribbons,
magnetic reconstruction turns edge-derived states from dark states into bright photovoltaic channels, with the associated peak scaling inversely with ribbon width. These results show that
magnetic control of the nonlinear photovoltaic response is governed by wave-function reconstruction and
quantum-
geometric matrix elements rather than by the density of states alone.
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Superconductivity · Cross-listed from hep-ph
Chiral phonons in metal-organic frameworks as quantum sensors for the direct detection of dark matter
Marek Matas, Filip Krizek and Carl P. Romao
We investigate a new
quantum sensor for dark matter direct detection with sub-eV sensitivity, focusing on several candidate materials that potentially host
chiral phonons with large
magnetic moments that can be directly read out with an external magnetometer. We focus on metal-organic frameworks (MOFs) as possible candidate materials for single
chiral phonon detection due to their noncentrosymmetric structure, tunability, and the ability to host these excitations in stable acoustic bands. We identify several promising candidates and compare their projected dark matter detection sensitivity for all possible interactions identified within effective field theory. We establish that the expected sensitivity does not depend heavily on the specific choice of the MOF, enabling us to tailor the final material composition to facilitate the
magnetic readout. We then propose a prototype setup able to test the direct readout of a
chiral phonon sensor with a surface-integrated magnetometer.
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Strongly Correlated Electrons
Single-hole spectral functions in one-dimensional quantum magnets with different ground states
Sibin Yang, Gabe Schumm, Bowen Zhao et al. (+1 more)
Recent advances in numerical analytic continuation with physics-motivated constraints allow sharp spectral features to be extracted from imaginary-time
quantum Monte Carlo (QMC) data. We apply these methods to one-dimensional $S=1/2$
spin systems with a single ejected
fermion, computing the momentum- and energy-dependent single-hole spectral function $A(k,\omega)$. The real-space Green's function $G(r,\tau)$ is evaluated using Angelucci's canonical transformation [Phys. Rev. B 51, 11580 (1995)] implemented within
stochastic series expansion QMC, and $A(k,\omega)$ is obtained by constrained
stochastic analytic continuation. We contrast systems exhibiting
spin-charge separation with those forming a
spin polaron through effective
spin-charge attraction. For the conventional $t$-$J$ chain, we recover the established signatures of
spin-charge separation. Adding a multispin interaction $Q$ drives the system into a spontaneously dimerized valence-bond-solid (VBS) state;
spin-charge-separation features persist up to the transition. Although the spectra generally agree with the conventional analytical ansatz, we find a gap between two holon bands that the ansatz predicts to be degenerate at $k=0$ and $k=\pi$. Deep in the VBS phase, the spectra provide evidence for spinon-holon binding at large $Q/J$. In a statically dimerized $t$-$J$ chain, we observe equally spaced
spin-polaron bands associated with increasingly large bound states and two internal modes, even and odd under parton permutation. These results demonstrate the power of constrained analytic continuation combined with large-scale QMC for resolving sharp spectral features and distinguishing fractionalized from bound excitations.
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All authors Sibin Yang, Gabe Schumm, Bowen Zhao, Anders W. Sandvik
Mesoscale and Nanoscale Physics
Impact of the valence band on Rydberg excitons in cuprous oxide quantum wells
Niklas Scheuler, Jörg Main, Patric Rommel et al. (+3 more)
The complex valence band structure of bulk cuprous
oxide necessitates going beyond the
parabolic approximation to precisely estimate
exciton binding energies. The same is true for
excitons in cuprous
oxide quantum wells, for which many effects have been obtained so far only qualitatively within a hydrogenlike two-band model. Here, we derive the complete
Hamiltonian for
excitons in cuprous
oxide quantum wells based on the Luttinger-Kohn model, taking into account the full complex valence band structure.
Symmetry properties of the system are discussed. Numerical results based on the diagonalization of the
Hamiltonian using B-spline functions reveal the energy shifts and the lifting of degeneracies due to the nondiagonal coupling terms of the complex valence band. The relative oscillator strengths of the excitonic transitions induced by circularly polarized light are also calculated.
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All authors Niklas Scheuler, Jörg Main, Patric Rommel, Frieder Pfeiffer, Stefan Scheel, Pavel A. Belov
Superconductivity
Planar Josephson junctions for sensors and electronics:Different geometry, new functionality
Vladimir M. Krasnov
Josephson junctions are key elements in superconducting electronics. The most common type is the overlap (sandwich-type) junction, formed by vertically stacking two superconducting layers. In contrast, planar junctions are fabricated without overlap, at the edge of two superconducting films within a single plane. This
geometric distinction has a significant impact on their physical properties. The planar geometry greatly enhances sensitivity to
magnetic fields and improves impedance matching for terahertz (THz) devices. Its two-dimensional structure allows for simple and flexible electronic component design, enabling drastic miniaturization. Here I highlight recent advances in the application of planar junctions for novel technologies, including junction-on-cantilever sensors for super-resolution
magnetic imaging,
vortex-based
memory cells, and programmable superconducting diodes. I will also discuss the general requirements, future perspectives, and key challenges in the evolving field of superconducting electronics.
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Materials Science
Tuning Yttrium {\Sigma}7(0001) Twist Grain Boundary Properties through Segregation and Co-segregation of Low Neutron Absorption Elements: First-Principles Insights
Guanlin Lyu, Yuguo Sun, Panpan Gao et al. (+1 more)
Elements with low thermal
neutron absorption cross-sections are ideal for enhancing structural materials in
nuclear systems. In this study, We systematically investigate the segregation and co-segregation behaviors of eleven elements at the {\Sigma}7(0001) twist grain boundary in yttrium and their effects on stability and strength. The {\Sigma}7(0001) grain boundary exhibits weakening, with fracture occurring preferentially along path I. Segregation energy calculations show that Si, Cu, Cr, Mo and Fe prefer interstitial sites, while others occupy substitutional ones. Si, Al, Zn, Cu, Mg and Fe stabilize the boundary, while Mo, Fe, Si, Cr, Cu, Nb and Ti strengthen it, with Si offering the most balanced improvement. Co-segregation studies reveal that Si induces the enrichment of other solutes at the boundary, promoting synergistic stabilization and turning embrittling elements (Al, Mg, Zn, Zr) into strengthening
agents. Electronic structure analysis shows that Si-Y covalent bonds enhance electron localization, and Si+Mg co-segregation optimizes electronic distribution through metallic-covalent cooperation, significantly improving fracture resistance. The density of states analysis indicates new low-energy deep states in the Si, and Si+Al, Si+Mg systems, which lower grain boundary energy and improve stability. This study provides guidance for designing high-performance, low-
neutron-absorption Y-based
alloys.
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All authors Guanlin Lyu, Yuguo Sun, Panpan Gao, Ping Qian
Mesoscale and Nanoscale Physics
Real-Space Imaging of Moiré-Confined Excitons in Twisted Bilayer MoS$_2$
Laurens J.M. Westenberg, Lumen Eek, Jort D. Verbakel et al. (+8 more)
Twisted two-dimensional
semiconductors generate a moiré landscape that confines
excitons (bound electron-hole pairs) into programmable
lattices, offering routes to efficient light sources, sensing, and room-temperature information processing. However, direct real-space imaging of confined excitonic species within a moiré unit
cell remains challenging; existing claims are inferred from spatially averaged far-field signals that are intrinsically insufficient to resolve nanometre-scale variations. Here, we imaged
excitons across the moiré of a 2$^{\circ}$ twisted
bilayer MoS$_2$ with nanometre resolution using room-temperature photocurrent atomic force microscopy. We directly resolved site-selective confinement: direct and indirect
excitons localize at different stacking registries of the moiré, with contrast governed by
alignment between site-selective generation and confinement minima. A Wannier-based moiré-
exciton model reproduces the measured energies and the moiré-induced localization of the
exciton wavefunction. These species-specific, unit-
cell-resolved measurements constrain microscopic models of moiré
excitons, provide
benchmarks for excitonic order, and establish a device-compatible route to engineering excitonic
lattices in van der Waals
heterostructures.
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All authors Laurens J.M. Westenberg, Lumen Eek, Jort D. Verbakel, Kevin Vonk, Stijn J.H. Borggreve, Kenji Watanabe, Takashi Taniguchi, Paul de Boeij, Rodrigo Arouca, Cristiane Morais Smith, Pantelis Bampoulis
Strongly Correlated Electrons · Cross-listed from quant-ph
Resource assessment of classical and quantum hardware for post-quench dynamics
Joseph Vovrosh, Tiago Mendes-Santos, Hadriel Mamann et al. (+6 more)
We estimate the run-time and energy consumption of simulating non-
equilibrium dynamics on neutral atom
quantum computers in analog mode, directly comparing their performance to state-of-the-art classical methods, namely
Matrix Product States and Neural
Quantum States. By collecting both experimental data from a
quantum processing unit (QPU) in analog mode and numerical
benchmarks, we enable accurate predictions of run-time and energy consumption for large-scale simulations on both QPUs and classical systems through fitting of theoretical scaling laws. Our analysis shows that neutral atom devices are already operating in a competitive regime, achieving comparable or superior performance to classical approaches while consuming significantly less energy. These results demonstrate the potential of analog neutral atom
quantum computing for energy-efficient simulation and highlight a viable path toward sustainable computational strategies.
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All authors Joseph Vovrosh, Tiago Mendes-Santos, Hadriel Mamann, Kemal Bidzhiev, Fergus Hayes, Bruno Ximenez, Lucas Béguin, Constantin Dalyac, Alexandre Dauphin
Mesoscale and Nanoscale Physics
Spin current symmetries generated by GdFeCo ferrimagnet across its magnetisation compensation temperature
Héloïse Damas, Michel Hehn, Juan-Carlos Rojás-Sanchez et al. (+1 more)
Ferrimagnets, composed of antiferromagnetically coupled
magnetic sublattices whose net magnetisation can be tuned by temperature, offer a unique platform for probing the
symmetry of the
spin currents they generate and for identifying the sublattice contributions to these currents. Here, we investigate the
spin current
symmetries produced by GdFeCo ferrimagnet at a fixed concentration and across a broad temperature range, including the magnetisation compensation point. Using complementary techniques based on
spin-torque
ferromagnetic resonance spectroscopy, we separate the contributions of the
spin Hall effect (SHE) and the
spin anomalous
Hall effect (SAHE). We show that the torques arising from both mechanisms retain their sign across the magnetisation compensation temperature, and that the SAHE-driven damping-like torque has the opposite sign to the SHE-driven term. We suggest that both effects originates from distinct electronic subsystems: the SHE emerging from Gd 5d electrons, and the SAHE from FeCo 3d electrons. Consequently, the SHE sign remains insensitive to the magnetisation state, whereas the SAHE sign does not invert at compensation, reproducing our observations. Together, these insights clarify the interplay between sublattices in ferrimagnetic
spin transport and highlight the potential of ferrimagnetic
spin currents to generate
spin torques in adjacent layers or within the ferrimagnet itself.
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All authors Héloïse Damas, Michel Hehn, Juan-Carlos Rojás-Sanchez, Sébastien Petit-Watelot
Mesoscale and Nanoscale Physics
Stretching helical molecular springs: the peculiar evolution of electron transport in helicene junctions
Anil Kumar Singh, Yuta Ito, León Martin et al. (+10 more)
Single-molecule junctions represent electromechanical systems at the edge of device miniaturization. Despite extensive studies on the interplay between mechanical manipulation and electron transport in molecular junctions, a thorough understanding of conducting molecular springs remains elusive. Here, we investigate the impact of mechanical elongation and compression on the electron transport and electronic structure of helicene-based spring-like single-molecule junctions, utilizing 2,2'-dithiol-[6]helicene and thioacetyl-[13]helicene molecules bridging two gold electrodes. We observe robust, reversible U-shaped conductance variations with interelectrode distance. Ab-initio electronic structure and
quantum transport calculations reveal that this behavior stems from destructive
quantum interference, induced mainly by modifications of the coupling at the metal-molecule interface as a peculiar outcome of the helical backbone deformation. These findings highlight the central role of the helical geometry in combination with contact properties in the electromechanical response of conducting molecular springs, offering insights for designing functional electromechanical devices that leverage similar mechanisms.
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All authors Anil Kumar Singh, Yuta Ito, León Martin, Lukas Krieger, Matea Sršen, Stephan Korsager Pedersen, Axel Houssin, Satyaki Kundu, Carlos Sabater, Narcis Avarvari, Michael Pittelkow, Fabian Pauly, Oren Tal
Materials Science · Cross-listed from cs.LG
PRISM: Periodic Representation with multIscale and Similarity graph Modelling for enhanced crystal structure property prediction
Àlex Solé, Albert Mosella-Montoro, Joan Cardona et al. (+4 more)
Crystal structures are characterised by repeating atomic patterns within unit
cells across three-dimensional space, posing unique challenges for graph-based representation learning. Current methods often overlook essential periodic boundary conditions and multiscale interactions inherent to crystalline structures. In this paper, we introduce PRISM, a graph neural network framework that explicitly integrates multiscale representations and periodic feature encoding by employing a set of expert modules, each specialised in encoding distinct structural and chemical aspects of periodic systems. Extensive experiments across
crystal structure-based
benchmarks demonstrate that PRISM improves state-of-the-art predictive accuracy, significantly enhancing
crystal property prediction.
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All authors Àlex Solé, Albert Mosella-Montoro, Joan Cardona, Daniel Aravena, Silvia Gómez-Coca, Eliseo Ruiz, Javier Ruiz-Hidalgo
Materials Science
Signatures of coherent phonon transport in frequency dependent lattice thermal conductivity
{\DJ}or{\dj}e Dangić
Thermal transport in highly anharmonic, amorphous, or alloyed materials often deviates from the predictions of conventional
phonon-based models. First-principles approaches have introduced a coherent contribution to account for these deviations and to explain ultra-low
lattice thermal conductivity, but direct experimental evidence for this mechanism remains elusive. Here, we propose that the frequency-dependent
lattice thermal conductivity, $\kappa(\nu)$, provides a direct signature of coherent transport. Specifically, we show that peaks in $\kappa(\nu)$ arise from the frequency nesting of modes with identical wave vectors. Applying this approach to CuCl, we identify clear signatures of coherent transport in its dynamical
lattice thermal conductivity. We revisit the interpretation of thermoreflectance experiments and argue that the conventional understanding breaks down in strongly anharmonic
crystals,
alloys, and amorphous materials. Finally, we discuss experimental pathways to measure $\kappa(\nu)$, offering a new route to verify coherent contributions in thermal transport.
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Materials Science
Influence of temperature, initial grain-boundary bubble density and grain structure on fission gas behaviour in UO$_2$: a 3D hybrid multiscale study
Sourav Chatterjee, Md. Ali Muntaha, Sophie Blondel et al. (+3 more)
Fission gas swelling and release in UO$_2$ are governed by the coupled
evolution of intragranular clusters and bubbles, migrating grain boundaries (GBs), triple junctions (TJs), and their eventual connection to a free surface (FS). We extend a hybrid multiscale framework that couples cluster dynamics (Xolotl) with a phase-field model (MARMOT) to large 3D polycrystals with heterogeneous GB and surface
diffusion and evolving GB networks. We simulate 10- and 100-grain UO$_2$ microstructures at 1200 and 1600 K, with and without a FS, to interrogate bubble growth, coalescence, GB/TJ coverage, gas arrival at interfaces, and fission gas release (FGR). At 1200 K, both GB mobility and gas transport are low, yielding negligible bubble and GB
evolution. At 1600 K, intergranular bubbles rapidly become lenticular and coalesce into networks while unpinned GBs migrate; fewer initial bubbles reduce coalescence but enhance GB migration due to less pinning and produce spikes in interfacial gas arrival rate due to GB sweeping. Bubble density versus mean projected area agrees with White's (2004) coalescence trend and remains on the left side of the analytical curve, in contrast to several prior simulations, likely due to the inclusion of GB migration. In domains with a FS, early release is rapid and bubbles near the FS collapse to form a denuded zone, suppressing local network connectivity; GB coverage rises and approaches but does not exceed 50%. TJ coverage remains low without preferential nucleation at TJs. To our knowledge, these are the first large-scale 3D mesoscale simulations of intergranular fission gas behavior that provide mechanistic insight and quantitative metrics to inform engineering-scale FGR models.
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All authors Sourav Chatterjee, Md. Ali Muntaha, Sophie Blondel, David Andersson, Brian D. Wirth, Michael R. Tonks
Materials Science
Predicting Friction under Vastly Different Lubrication Scenarios
Yulong Li, Peter Gumbsch and Christian Greiner
Friction is ubiquitous in daily life, from nanoscale machines to large engineering components. By probing the intricate interplay between system parameters and frictional behavior, scientists seek to unveil the underlying mechanisms that enable prediction and control of friction – an essential step toward carbon neutrality. Yet, reproducing frictional behavior in experiments is notoriously difficult. Here, we show that this challenge stems from the extreme sensitivity of tribological systems to tiny variations, e.g. in surface topography, typically presumed well-controlled. Even after meticulous surface preparation to
semiconductor-industry standards and curtailing misalignment-induced oscillations, subtle variations remain and interact. In turn, such minute initial differences lead to statistically significant variations in friction and wear, giving rise to system-level chaotic behavior. Yet, by leveraging mid-scale features of surface topography and misalignment-induced oscillations – information often filtered out or overlooked – we established a model that accurately predicts high-friction regions under vastly different lubrication scenarios, with its performance further enhanced by machine learning.
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Quantum Gases
Bloch oscillations of a mobile impurity in a one-dimensional Bose gas
Saptarshi Majumdar and Aleksandra Petković
We study the motion of an
impurity under the action of a constant force through a one-dimensional system of weakly-interacting
bosons. The interplay of the
impurity-
boson interaction, the
boson-
boson interaction, and the driving force gives rise to a rich dynamics. We focus on the influence of a finite external force. Under these far-from-
equilibrium conditions, we show that in a wide range of forces, one part of the momentum transferred to the system is periodically channeled into the Bose gas through the emission of dispersive density shock waves,
solitons, density waves and the creation of additional phase gradients. As a result, the
impurity velocity does not increase indefinitely, but periodically oscillates in time around the drift velocity. We uncover and characterize different dynamical regimes in a wide range of the
impurity-
boson coupling, the
impurity mass and the external force. At a sufficiently large force, the Bloch oscillations cease and the
impurity exhibits an unlimited acceleration.
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