Materials Science
Evaluating Blended Refrigerants for Thermochemical Energy Storage and Circular Refrigerant Recovery using Activated Carbons
H. Lucassen, A. Luna-Triguero and J. M. Vicent-Luna
The
climate crisis demands a rapid shift to sustainable energy technologies and higher efficiency in existing energy systems. Adsorption-based thermochemical energy storage is a promising alternative due to its high energy density and compatibility with renewable heat sources. In this work, we investigate the adsorption behavior of pure refrigerants (R32, R125, R134a, and R600) and their commercial blends (R410A, R407F, R417A, and R417C) in six activated carbons for thermochemical energy storage and circular refrigerant recovery. A multiscale computational workflow combining Monte Carlo simulations, thermodynamic modeling, and breakthrough simulations is developed to predict adsorption, storage, and separation behavior from pure-component adsorption data. The methodology integrates adsorption potential theory (APT), ideal adsorbed solution theory (IAST), and models for the isosteric heat of adsorption. In addition, an in-house computational framework is developed to calculate heats of adsorption and energy storage densities for both pure refrigerants and multicomponent mixtures. Although developed using molecular simulations as a
benchmark, the methodology is directly applicable to experimental studies, since it only requires adsorption isotherms of the pure components as input to evaluate the performance of refrigerant blends. The results show that refrigerant blends can achieve higher storage densities than their pure counterparts due to cooperative adsorption and more efficient molecular packing. Furthermore, the activated carbons selectively separate key refrigerant components, highlighting their potential for sustainable refrigerant recovery. Overall, this work provides a general framework for the rational design and screening of next-generation refrigerant blends for adsorption-driven energy storage and separation applications.
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Superconductivity
Superconducting PdTe Thin Film Via Topotactic Transformation, Toward Topological Superconductors
Hee Taek Yi, Min Ge, Renjie Xie et al. (+5 more)
Topological
superconductors (TSCs) hosting Majorana zero modes (MZMs) offer a pathway to fault-tolerant
quantum computation. PdTe is a promising TSC candidate due to its topological surface states and a reasonable superconducting critical temperature of ~4.5 K. However, it has been challenging to grow PdTe thin films with bulk-like superconducting properties. Here, we show that high-quality, superconducting PdTe thin films can be grown using molecular beam epitaxy (MBE). The films exhibit a sharp superconducting transition (T_onset = 4.43 K with transition width of 0.06 K), comparable to that of bulk
crystals. This was made possible via a topotactic transformation from a PdTe_2 buffer layer to a PdTe phase by growing Pd on top under Te-deficient conditions. Structural and transport analyses confirm the NiAs-type structure of PdTe, as well as its two-dimensional superconducting behavior and excellent air stability. These findings suggest that the MBE-grown PdTe films and their
heterostructures are a promising platform for topological superconductivity and Majorana physics.
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All authors Hee Taek Yi, Min Ge, Renjie Xie, Colby J. Stoddard, David H. Yi, Xiaoyu Yuan, Xiong Yao, Seongshik Oh
Mesoscale and Nanoscale Physics
Excitation-Energy-Selective Control of Hot-Carrier Cooling via a Resonant Optical-Phonon Bottleneck in Graphene
Sachin Sharm, Elliott Walker, Rachael Myers-Ward et al. (+4 more)
Understanding and controlling hot-carrier relaxation in
graphene is crucial for advancing ultrafast optoelectronic and terahertz technologies. Here, we investigate carrier cooling dynamics in monolayer and
bilayer graphene using mid-infrared pump pulses (0.22-0.73 eV) and terahertz probe pulses. We uncover a pronounced, reproducible, and non-monotonic dependence of the carrier relaxation time on excitation
photon energy. Remarkably, within a narrow spectral window (0.42 to 0.48 eV), the carrier lifetime increases by an order of magnitude compared to a few picosecond-scale cooling observed at other energies. We show that this anomalous slowdown originates from a resonant enhancement of the optical-
phonon lifetime, causing accumulation and reabsorption of hot optical
phonons that suppress energy transfer to the
lattice. All observed behaviors are captured within a unified carrier-
phonon energy-balance framework, where excitation-energy-dependent variations of the effective optical-
phonon decay pathway govern the cooling dynamics. These findings demonstrate excitation-energy-selective control of hot-carrier relaxation in
graphene and provide new insight into non-
equilibrium carrier-
phonon interactions near the optical-
phonon bottleneck.
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All authors Sachin Sharm, Elliott Walker, Rachael Myers-Ward, Jenifer Hajzus, Yijing Liu, Paola Barbara, Ioannis Chatzakis
Mesoscale and Nanoscale Physics
Fröhlich-type Polarons in Isotopically Enriched Hexagonal Boron Nitride
Ioannis Chatzakis, Timur Abdilov, Elliot Walker et al. (+3 more)
Exciton-
phonon interactions play a central role in defining the optical response of hexagonal boron nitride (hBN), yet their quantitative determination has remained incomplete. Here, we reveal the Fröhlich-type
exciton-
phonon coupling in boron-10-enriched hBN using low-temperature cathodoluminescence. We resolve the indirect
exciton 5.95$\pm$0.02 eV together with its longitudinal optical (LO)
phonon replica detuned by 184$\pm$56 meV, enabling the extraction of a Fröhlich coupling constant $\alpha$=0.159 and a larger
exciton binding energy of 161 meV, larger than previously reported values for natural-abundance hBN, which is attributed to isotope enrichment. The inferred polaron radius exceeds the
lattice constant, indicating large-polaron behavior. We deduced an
exciton scattering time ~of 97 fs, corresponding to a homogeneous linewidth of ~6.76 meV. We further obtain a polaron binding energy of ~48 meV and an effective mass of 1.045 $m_0$. These results provide a direct quantitative characterization of
exciton-
phonon coupling in isotopically engineered hBN and establish a foundation for tailoring its
phonon-polaritonic and
quantum-optical properties.
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All authors Ioannis Chatzakis, Timur Abdilov, Elliot Walker, Jaime Freitas, Song Liu, James H. Edgar
Mesoscale and Nanoscale Physics
An AI-driven robotic system for two-dimensional hetero-assemblies
Xiaoxi Li, Jinkun He, Haojie Liu et al. (+28 more)
Nanomaterials stacked on-demand, such as rotationally assembled two-dimensional (2D) van der Waals (vdW) layered compounds, provides a versatile platform for
quantum simulation and the exploration of exotic electronic phases. Currently, however, such nanoassemblies remain largely confined to inefficiency, manually operated process, limiting their potential for probing emergent physical phenomena. There is a pressing need in the field for high-precision, automated assembling techniques, especially for the scalable fabrication of 2D twistronic
heterostructures. Here, we present an intelligent automation system dedicated to the fabrication of van der Waals stacks, following the state-of-the-art protocol for dry transfer of exfoliated 2D materials. The system further employs metadata generated from each automated stacking procedure to perform reinforcement learning, thereby continuously bettering its performances. As a concrete demonstration, we fabricate twisted
bilayer graphene (TBLG) – known for its challenging preparation – and exhibit its unconventional superconductivity near the magic angle. Our work may pave the way for high-throughput fabrication of low-dimensional nanomaterials including twistronic
heterostructures, where integrating data mining and artificial intelligence can accelerate the discovery of novel physical phenomena.
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All authors Xiaoxi Li, Jinkun He, Haojie Liu, Xipeng Liu, Zewen Wu, Jing Li, Kai Zhao, Shan Li, Xingdan Sun, Xiaoxue Fan, Zhiren Xiong, Xingguang Wu, Xuanzhe Sha, Zhili Lin, Caixia Yang, Luosha Han, Jie Xu, Woye Pei, Kaining Yang, Jing Zhang, Xiaolong Feng, Tongyao Zhang, Zhu Liang, Kenji Watanabe, Takashi Taniguchi, Ming Tian, Neng Wan, Jing Zhang, Jianming Lu, Wenjing Hong, Zheng Vitto Han
Mesoscale and Nanoscale Physics · Cross-listed from hep-th
The dual Ginzburg-Landau theory for a holographic superfluid/superconductor: Critical dynamics
Makoto Natsuume
Holographic superfluids/
superconductors are one of the most studied systems in the AdS/CFT duality. In the low-energy, in the long-wavelength limit, they should be described by a Ginzburg-Landau theory. For critical dynamics, one expects that they belong to "model F" universality class. We consider a bulk 5-dimensional
holographic superfluid/
superconductor in the probe limit. For the
holographic superconductor, we impose the boundary Maxwell equation to make the boundary Maxwell field dynamical. We identify the dual model F equations where numerical coefficients are obtained exactly.
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Materials Science
Dataset-aware entropy-maximized active learning for machine-learned interatomic potentials
Meiyan Wang, Rishi Rao and Li Zhu
We present an active learning framework for efficiently generating training data for machine-learned interatomic potentials (MLIPs). The method combines local
entropy-driven molecular dynamics with global
dataset-aware filtering: a per-configuration
entropy term biases MD trajectories toward structurally diverse snapshots, while a global
entropy measure, the log-determinant of the fingerprint covariance
matrix of the entire
dataset, selects only those configurations that provide genuinely new information. We employ dual covariance modes (per-atom for disordered structures and per-config for ordered phases) to achieve broad coverage of configuration space. Combined with a pre-trained foundation model (Allegro-OAM-L) and analytical fingerprint gradients from Gaussian overlap
matrix eigenvalues, the framework produces high-quality domain-specific potentials with near- or sub-meV/atom accuracy on test data drawn from the same distribution at training-set sizes of order $10^{2}$ to $10^{3}$
entropy-selected DFT-labeled structures. We demonstrate the method on three systems spanning diverse bonding types and pressure-driven phase transitions: carbon (covalent), silicon (covalent/metallic), and NaCl (ionic). In learning curve comparisons against random molecular dynamics sampling at matched training set sizes ($N = 100$ to $800$), evaluated over three independent training-set draws per condition,
entropy-driven sampling achieves a factor of approximately $3$ to $10$ lower energy MAE at $N = 800$ on in-distribution holdouts across the three systems, with the magnitude of the gain depending on the bonding type and the size at which the random-MD baseline saturates.
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Strongly Correlated Electrons · Cross-listed from quant-ph
Sampling Noise and Optimized Measurement Distribution in Imaginary-Time Quantum Dynamics Simulations
Feng Zhang, Niladri Gomes, Joshua Aftergood et al. (+3 more)
Variational
quantum dynamics simulations (VQDS) provide a promising route to simulate real- and imaginary-time
quantum dynamics on noisy intermediate-scale
quantum devices using fixed-depth
circuits. However, their practical performance is strongly limited by sampling noise arising from a finite number of
circuit measurements. In this work, we systematically investigate the impact of sampling noise on VQDS, with a focus on ground-state preparation in one-dimensional Ising
spin models using imaginary time
evolution. We compare different regularization strategies for stabilizing the equations of motion and show that Tikhonov regularization provides robust performance in noisy imaginary-time
evolution. We then
benchmark measurement-distribution strategies that allocate shots by minimizing a cost function that characterizes the error in solving the equation of motion. Using noisy
circuit simulations, we demonstrate that such optimized shot allocation can significantly improve state fidelity and reduce the total measurement cost by more than a factor of two compared to uniform shot distributions. We observe that the best results are found if a sufficiently large number of measurements is guaranteed for all
circuits, suggesting that a finite fraction of shots should be distributed evenly. Our results provide practical guidelines for implementing measurement-efficient variational
quantum dynamics and ground-state preparation on near-term
quantum hardware.
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All authors Feng Zhang, Niladri Gomes, Joshua Aftergood, Thomas Iadecola, Yong-Xin Yao, Peter P. Orth
Materials Science · Cross-listed from physics.optics
2D GaSe-Based Single-Pixel Spectrometer via Electro-Optical Barrier Co-Modulation
Shibesh Pramanik, Rishabh Sahoo, Arnab Mondal et al. (+4 more)
Driven by the growing demand for miniaturized spectrometers for in-situ analysis, and point-of-care diagnostics, conventional spectrometers are often constrained by bulky architectures and pathlength-limited spectral resolution. Achieving high-resolution, single-pixel computational spectrometers is therefore critical for the realization of compact, on-chip systems. Here, we report a single-pixel spectrometer enabled by a single 2D material; few-layer GaSe-based photodetector, in which the Schottky barrier height modulation, governed jointly by applied bias and optical excitation, provides an efficient mechanism for spectral encoding without the need for bulky dispersive elements. The device exhibits a high peak-wavelength accuracy of ~0.78 nm across a broad operational bandwidth (300-700 nm) within a compact footprint of ~100 um^2 and resolves closely spaced spectral features with separations down to ~5 nm. The device operates at low bias (+/- 4V) with an ultralow dark current density ~0.3 pA/um^2 at 4V bias. These results establish a simple, scalable route toward compact, cost-effective spectroscopic systems for on-chip spectral sensing and portable hyperspectral imaging applications.
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All authors Shibesh Pramanik, Rishabh Sahoo, Arnab Mondal, Tithi Saha, Ankush Bag, Vibhav Bharadwaj Shivakumar, Rishi Maiti
Materials Science
Modeling phase separation in polymer-derived silicon carbonitride ceramics through extended machine learning molecular dynamics
Fabien Mortier, Sylvian Cadars, Olivier Masson et al. (+5 more)
Polymer-derived ceramics combine the thermal stability of ceramics with the versatile properties of carbon domains, but modeling their atomic-scale
evolution during processing remains elusive due to the limitations of traditional computational methods. To address this issue, here we develop and apply a machine learning interatomic potential for silicon carbonitride-based (Si-C-N-H) systems, trained on a diversified database of over 9000 configurations – including amorphous models, high-temperature states, surfaces, and
crystal structure predictions – to capture the full complexity of these materials. This potential enables large-scale molecular dynamics simulations of 8000-atom systems revealing the atomic-scale
evolution of the
polymer-derived ceramic during thermal treatment. A key result of this work is the occurrence of a phase separation where carbon domains progressively nucleate from the amorphous SiCN
matrix during thermal processing, forming distinct
graphene-like sheets while preserving the integrity of the ceramic network. The resulting models reproduce the experimental atomic pair distribution functions with exceptional fidelity, validating our approach and providing microscopic explanations for the material unique combination of ceramic and graphitic properties. In this process, defective 5- and/or 7-member carbon rings, mediate the transformation to stable 6-member aromatic structures. These findings offer new atomic-scale insights into the thermal stability and structural transformation pathways of
polymer-derived ceramics, while our methodology opens avenues for studying complex amorphous systems with first-principles accuracy at experimentally relevant scales.
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All authors Fabien Mortier, Sylvian Cadars, Olivier Masson, Mauro Boero, Guido Ori, Yun Wang, Samuel Bernard, Assil Bouzid
Strongly Correlated Electrons
Velocity collapse and non-conformal spiral phase in the sawtooth spin chain
Nai Chao Hu
Recent
matrix-product-state calculations show that the spiral phase in the sawtooth chain has numerical signatures that are difficult to reconcile with an ordinary conformal critical point: a large apparent central charge, slow dynamical scaling, nearly flat excitations, and no detectable dimerization. We develop a bosonization theory for this phenomenology by
embedding the sawtooth limit in a zigzag ladder described by two coupled SU(2)$_1$ conformal field theories characterized by an extreme velocity ratio. We show that the sawtooth geometry cancels the leading staggered interaction, leaving a marginal twist interaction that selectively collapses the slow apical
spin velocity. Crucially, as this velocity vanishes, the generated apical backscattering interaction diverges only in dimensionless units, causing the energy scale to collapse independently of the spatial correlation length. This mechanism naturally accounts for many of the numerical anomalies and we interpret the perturbative flow as an entrance to local
quantum criticality in the strong-coupling regime.
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Strongly Correlated Electrons
Textured phase diagrams of featureless insulators
Sashank Singam, Nick G. Jones and Abhishodh Prakash
We study phase diagrams of charge-conserving `class A' non-interacting
fermions, focusing on the trivial phase in various dimensions. Such phases are usually termed `featureless' to distinguish them from those others with either
symmetry-broken or topological order. We show that the presence of non-trivial topological families of states, including charge pumps and their generalizations, results in phase diagrams being endowed with non-trivial topological textures that can be visualized through Berry phases and their higher-dimensional generalizations. We show that for non-interacting
fermion systems with translation invariance, these `higher' Berry phases can be computed using integrals of non-abelian Chern-Simons forms of the Berry-Bloch connection over momentum and parameter spaces. Singularities in these textures correspond to gap-closing loci of `diabolical points', which represent the obstruction to contracting topologically non-trivial families of states, and bulk-boundary correspondence results in a locus of robust boundary modes that terminate at the bulk diabolical points. In the presence of finite chemical potential, we argue that the edge modes are generically robust without any need for fine-tuning for two and higher dimensions, whereas in one dimension they are `estranged' in the phase diagram, i.e. appearing at different parameter values for different edges. We demonstrate our results by constructing several microscopic models of non-interacting
fermions. We argue stability to interactions and explore proximate phase diagrams by mapping to continuum field theories.
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Superconductivity · Cross-listed from quant-ph
Orbital-Angular-Momentum Entangled Photon Emission from Circular Currents in Semiconductor-Superconductor Structures
Avi Koriat, Ankit Kumar and Alex Hayat
We theoretically demonstrate that a superconducting circular current induced in a
semiconductor results in emission of orbital-angular-momentum (OAM) entangled
photon pairs upon carrier recombination. Combining the macroscopic Ginzburg-Landau theory and the microscopic Bardeen-Cooper-Schrieffer (BCS) theory, we investigate the emission of a superconducting light-emitting diode (SLED) with a spatially varying phase profile in the superconducting order parameter. We show that in the active region of the SLED with a circular supercurrent, radiative recombination processes inherit the order parameter phase and result in
photon pairs emitted into modes of different OAM
quantum numbers. We demonstrate that coherent superposition of superconducting
qubit eigenstates can also be mapped onto a coherent superposition of emitted
photon states. We also show that other recombination processes due to thermally excited quasi particles do not significantly degrade the state purity. Our results introduce an original scheme for generating OAM-entangled
photons enabling a new method of transmitting superconducting
qubit information to photonic channels thereby bridging the gap between solid-state and
photon-based platforms for
quantum communications and information processing.
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Statistical Mechanics
Targeting Clause Type Distributions: a Picklock for Random Satisfiability Problems
J. Schwardt and J. C. Budich
Optimization problems such as the NP-complete 3-SAT provide an important
benchmark for the difficult task of finding ground-states in strongly correlated many-body systems with rugged energy landscapes. The study of random 3-SAT problems as Ising
spin Hamiltonians in statistical physics has yielded major insights including the existence of a satisfiability phase transition, and the prediction of a critical parameter line of particularly hard instances. Yet, progress on solving those instances has been scarce for several decades. Here, introducing the Target-SAT (TSAT)
algorithm, we roughly triple the tractable problem sizes in the hardest regime, with an even greater improvement in a vast range of neighboring regions. By leveraging statistical information hidden in the combinatorial constraints of the problem, TSAT is actively guided in its
stochastic local search toward a target within the relevant parameter space. Our analysis also explains why established local search
algorithms are limited to relatively small system sizes due to a vast low-energy trap. Furthermore, we characterize the aforementioned critical line in terms of a dominant additional complexity barrier, whose exponential scaling is quickly overcome by TSAT only in the surrounding parameter space. With TSAT, the lead in solving the hardest known random satisfiability problems returns to the realm of
stochastic local search
algorithms.
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Strongly Correlated Electrons
Representability-Aware Neural Networks for Reduced Density Matrices: Application to Fractional Chern Insulators
Justin B. Hart, Awwab A. Azam, Thomas Li et al. (+4 more)
We develop a representability-aware and interpolable neural network (NN) framework for predicting two-particle reduced density
matrices (2-RDMs). The NN incorporates a subset of representability conditions through its architecture and loss function, and can operate on different momentum meshes, enabling evaluating the representability conditions across multiple meshes, which we call interpolated representability condition. The framework can be used either to predict 2-RDMs on large momentum meshes by interpolating exact results from small meshes, or as a variational 2-RDM ansatz optimized by energy minimization on arbitrary meshes. We apply this approach to the fractional Chern
insulator in the one-band projected model of twisted
bilayer MoTe$_2$ at twist angle $3.89^\circ$ and hole filling $2/3$. Trained on exact-diagonalization (ED) 2-RDMs from meshes with $12$ or $18$ momentum points using six different NN architectures, the best NN is the residual multilayer perceptron, which predicts the $6\times6$ 2-RDM with $97.07\%-98.18\%$ accuracy relative to the ED 2-RDM but predicts an energy $77.353$ meV above ED ground-state energy. We then variationally optimize the NN on several meshes including $6\times6$, predicting a $6\times 6$ energy of just $0.104$ meV below ED while maintaining $98.94\%-98.96\%$ accuracy. Compared with the conventional boundary-point semidefinite programming, which gives an energy $5.560$ meV below ED with $96.40\%-98.94\%$ accuracy, the NN achieves a more accurate energy and similar accuracy while using only less than 1/20 as many parameters. Eventually, we add a symmetric mesh of $48$ momentum points to the variational optimization of the NN, and provide a prediction of the many-body ground-state energy and the many-body
quantum metric on that mesh.
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All authors Justin B. Hart, Awwab A. Azam, Thomas Li, Yunxuan Li, Ye Bi, Haining Pan, Jiabin Yu
Strongly Correlated Electrons · Cross-listed from hep-th
Thomas Kögel, Alessio Caddeo, Amelie Pitters et al. (+5 more)
Inspired by the poles-zeros duality of Green's functions that appears in transitions into Mott-insulating phases in strongly correlated condensed matter systems, we propose a semi-
holographic approach to Mott
insulators. In this model, a fundamental
fermion is coupled to a large-$N$, strongly interacting sector that generates a self-energy for the fundamental
fermion's Green's function. This coupling amounts to a hybridization of the fundamental
fermion with a strongly correlated fermionic composite. Within the
holographic framework, at large $N$, the Green's function of the composite
fermion naturally exhibits a poles-zeros duality. Zeros of the Green's function are caused by the poles of the self-energy that correspond to collective many-body excitations of the
holographic strongly interacting sector. We calculate the spectral function of the fundamental
fermion, from which we characterize the semi-
holographic metallic and the Mott-insulating phases. In addition to the new physical interpretation of the zeros, our analysis yields a well-defined picture of the poles-zeros duality in terms of the freedom to choose between standard and alternative quantization in the strongly coupled sector.
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All authors Thomas Kögel, Alessio Caddeo, Amelie Pitters, Francesca Paoletti, Lorenzo Crippa, Giorgio Sangiovanni, René Meyer, Johanna Erdmenger
Strongly Correlated Electrons
Band Structure and topology of a periodically deformed Kitaev honeycomb model
Abdullah AlJishi, Ali AlSwaid, Moayad Ekhwan et al. (+3 more)
Motivated by the growing interest in
spin liquids and topological phases, as well as the rise of deformation engineering, we study the combined effects of deformation and
magnetic fields on the honeycomb Kitaev model. The Kitaev model, as one of the prototypical and exactly solvable
spin liquid-hosting models, serves as a simple platform that demonstrates the rich physics one can expect at the intersection of deformation physics and
quantum spin liquids. Our work builds on a simplified solution to the undeformed base model that we present. This simplified solution allows for a straightforward extension of our analysis to the deformed case. After incorporating periodic deformations into the Kitaev model (chosen for its similarity to moiré physics), we investigate the effects of a hexagonally symmetric deformation on the band structure. We find that deformation leads to a smaller Brillouin zone with new band gaps at the edges, indicating the potential for topological transitions. Finally, we introduce a
magnetic field to break time-reversal
symmetry and thereby allow for non-trivial
topology. We find that, under specific parameter conditions, the
magnetic field leads to multiple band-gap closings and openings. An investigation into topological properties reveals nontrivial Chern numbers and a plethora of topological transitions. Our results suggest possible thermal
Hall or Nernst-type responses. We also suggest a potential bulk measurement approach for he Chern numbers and possible path to physical realization. Most importantly, our results serve as a demonstration of the rich phenomenology that can arise due to the interplay between deformation and
spin-
liquid physics.
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All authors Abdullah AlJishi, Ali AlSwaid, Moayad Ekhwan, Hocine Bahlouli, Raditya Weda Bomantara, Michael Vogl
Strongly Correlated Electrons
Controlled expansion for correlated electrons with concentrated kinematics
Pavel A Nosov, Eslam Khalaf and Patrick Ledwith
We introduce a systematic expansion tailored to systems with strong local interactions and capable of computing response functions, including finite DC transport, analytically. The expansion is controlled by a small parameter $s^2$ that measures the area of the momentum space region where kinematics of the theory is concentrated. In real space, this corresponds to single-particle or correlated hopping terms with amplitudes that decay over a length scale $1/s$ and scale in magnitude as $s^2$ in two dimensions. In the limit $s^2\ll 1$, long, self-avoiding tunneling paths dominate over paths revisiting the same site. This enables systematic controlled calculations of various physical quantities. We illustrate the method with three applications. (i) A Hubbard model with concentrated dispersion: we analytically obtain spectral broadening which scales as $s^2$ and identify a high-temperature bad metal with $T$-linear resistivity coexisting with parametrically long-lived quasiparticles, as well as an intermediate-temperature "thermal FL*" with a small hole pocket that coexists with thermally disordered fluctuating local moments, all within a single controlled framework. (ii) A correlated-hopping model with interesting electron-trion dynamics. (iii) A model of Chern bands with concentrated Berry
curvature, motivated by twisted
bilayer graphene, which realizes a Mott semimetal where we compute the broadening for the electron and trion spectral functions. At the end, we discuss how our approach paves the way to addressing various challenging questions in strongly correlated systems and outline its various generalizations.
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Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Stochastic trajectories and excursions in a double quantum dot system
Guilherme Fiusa, Pedro E. Harunari, Alberto J. B. Rosal et al. (+2 more)
We investigate the trajectory-level
stochastic dynamics of a double
quantum dot system using the formalism of
stochastic excursions. An excursion is a sub-trajectory that begins when the system leaves a chosen reference state (or more generally, a set of states)—here, the empty double dot—and ends upon its first return to it. Filtering trajectories into excursions extends full counting statistics and gives access to the correlations between thermodynamic currents and excursion durations. The main objects of study are counting observables, defined as weighted sums of transition counts within a single excursion. For three main counting observables—charge current, dynamical activity, and
entropy production—we compute averages and noise contributions and show how they provide insights into the operation of the double
quantum dot system. At the trajectory level, we analyze outcome distributions for transport and connect the results with trade-offs between successful and unsuccessful events that shape the overall performance of the double
quantum dot as a transport device. We then discuss the populations of the two dots, as well as their correlations. Finally, we illustrate how the framework provides insights into the thermodynamics of precision through the Fano factor and thermo-kinetic uncertainty relations, where different regimes are fundamentally constrained either by
entropy production or by dynamical activity. Altogether, our work is a case study that highlights the utility of the excursion framework as a toolkit to analyze many quantities of interest and to uncover the structure of nonequilibrium fluctuations. Moreover, it also suggests new avenues for refining uncertainty relations and understanding transport in mesoscopic systems.
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All authors Guilherme Fiusa, Pedro E. Harunari, Alberto J. B. Rosal, John M. Nichol, Gabriel T. Landi
Statistical Mechanics
Towards a Matrix Product Ansatz in Two Dimensions
Chandraniva Guha Ray, Aikya Banerjee and P. K. Mohanty
Matrix product ansatz (MPA) is a powerful framework for constructing exact steady state weights of one dimensional non-
equilibrium stochastic processes; but its generalization to higher dimensions is limited. Here, we introduce the MPA formalism for two dimensions (2D). As a concrete application, we introduce and exactly solve a non-conserved assisted exclusion model (NAEM) in one and two dimensions with constrained hopping and local birth-death dynamics: a particle can hop to a neighbouring site only when exactly one of its neighbouring sites is vacant, while creation and annihilation occur exclusively at sites whose neighbours are all occupied. The MPA yields exact steady-state weights and provides a systematic method to compute observables such as density moments and particle currents. In the particle-conserving limit, the system undergoes an absorbing phase transition at the critical density $\rho_c=\frac12$ with order-parameter exponent $\beta=3$. We further show that the steady state of the NAEM maps exactly onto the well-studied hard-square
lattice gas with nearest-neighbour exclusion, thereby providing a nonequilibrium dynamical route to realizing
equilibrium states of constrained
lattice gases. Our work generalizes
matrix-product methods beyond one dimension, establishing a systematic approach to exact solutions of interacting
stochastic systems in 2D.
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Materials Science · Cross-listed from cs.CV
Interpretable Computer Vision for Defect Detection in X-ray Tomography of Aerospace SiC/SiC Composites
Antonio Peña Corredor, Julien Lesseur, Romain Nunez et al. (+2 more)
Non-destructive testing of aerospace SiC/SiC composites via X-ray computed
tomography (XCT) relies on expert visual assessment, with current workflows offering limited traceability for accept/reject decisions. Deep convolutional networks can automate defect detection, yet their black-box nature conflicts with the transparency that industrial inspection practice demands. To close this gap, we introduce p-ResNet-50, a convolutional framework extended with a prototype layer that couples high detection accuracy with case-based explanations. Six learned prototypes are explicitly aligned with expert-defined semantic categories-healthy
matrix,
matrix–air interfaces, pores, line-like defects, and mixed morphologies-so that every classification is traceable to a physically meaningful reference. Two novel regularisation terms, anchor-based and medoid-based, tether prototypes to expert-selected patches and prevent prototype collapse, addressing a known limitation of prototype networks. Latent-space analysis via UMAP delineates semantically coherent sub-domains and maps zones of uncertainty where misclassifications concentrate, giving inspectors an explicit picture of where the model is-and is not-reliable. The framework is validated on an XCT patch
dataset of approximately 12,000 patches extracted from four defect-rich SiC/SiC laboratory specimens. Taking a black-box ResNet-50 as a baseline (ROC-AUC = 0.991), the prototype extension achieves comparable performance (accuracy 0.957 vs. 0.959; ROC-AUC 0.994 vs. 0.993) while trading a slight reduction in sensitivity for higher precision and specificity. Each decision is backed by representative evidence patches, and the model explicitly flags its uncertainty regions. Beyond defect mapping, the framework establishes a reusable methodology for
embedding domain-expert knowledge into prototype networks, applicable to other XCT inspection scenarios requiring traceable, auditable decisions.
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All authors Antonio Peña Corredor, Julien Lesseur, Romain Nunez, Paul Rivalland, Thomas Philippe
Mesoscale and Nanoscale Physics
Probing tunable Kerr nonlinearity in graphene Josephson junctions
Priyanka Samanta, Joydip Sarkar, Ashish Abhraham Samuel et al. (+4 more)
Josephson junction (JJ) is a key nonlinear element in superconducting devices such as
qubits, amplifiers, and bolometers. Recently, gate-tunable JJs based on
graphene and
semiconductors have gained interest due to their rich Andreev physics and wide applications in
circuit quantum electrodynamics devices. In addition to gate tunability, it offers many advantages over conventional JJs, such as exceptional thermal properties for bolometric sensors,
magnetic-field compatibility, and operability at elevated temperatures above 1 K. Like conventional Al-AlOx-Al JJs,
graphene JJs also act as nonlinear inductors, and at their heart lies the Kerr nonlinearity. Additionally, in
graphene JJs, the nonlinearity is tunable via external knobs in a single device. However, a detailed exploration of the tunable Kerr nonlinearity in
graphene JJs has never been performed. In this work, we study the dependence of the Kerr nonlinearity on gate voltage, temperature, and DC bias - an interesting knob that has been less explored. Using these parameters, we show that the magnitude of the Kerr coefficient can be tuned over a wide range, from 300 kHz to 1.2 MHz. Our work will be a valuable resource for further understanding of the nonlinearity in
graphene JJs and for the design of next-generation amplifiers and sensors, with enhanced performance.
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All authors Priyanka Samanta, Joydip Sarkar, Ashish Abhraham Samuel, Madhavi Chand, Kenji Watanabe, Takashi Taniguchi, Mandar M. Deshmukh
Strongly Correlated Electrons
Itinerant Nature of Spin-Density-Wave Order in Ruddlesden-Popper Nickelates
Jiong Mei, Tianyang Xie and Kun Jiang
The nature of magnetism in layered Ruddlesden-Popper nickelates remains a central open question, particularly in light of recent observations of
spin-wave-like
magnetic excitations in metallic multilayer compounds. Here, we develop a unified itinerant description of
spin-density-wave (SDW) order and
magnetic excitations in La$_3$Ni$_2$O$_7$ and La$_4$Ni$_3$O$_{10}$. The essential ingredient is the multilayer mirror structure of the NiO$_2$ blocks, which organizes the low-energy electronic states into mirror-even and mirror-odd sectors. We show that dominant interband nesting between mirror-opposite bands drives a mirror-selective itinerant SDW instability, whose collective modes naturally reproduce the experimentally observed
spin-wave-like spectra. In La$_4$Ni$_3$O$_{10}$, the SDW further induces a secondary mirror-even charge density wave, yielding intertwined
spin and charge textures. Our results demonstrate that magnetism in multilayer nickelates is fundamentally itinerant rather than local-moment in origin, and establish mirror-selective interband SDW order as a unifying organizing principle for
magnetic correlations in these systems.
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Disordered Systems and Neural Networks
Relativistic saturation of Coulomb-induced electron decoherence: from eikonal phase noise to Bethe–Salpeter kinetic theory
Yury A. Budkov
We develop a microscopic theory of the mutual coherence and small-angle scattering of relativistic electron matter waves propagating through a Coulomb-fluctuating medium. Starting from the Dirac equation, we derive a relativistic paraxial wave equation and then obtain, rather than assume, the Bethe–Salpeter and Wigner–Boltzmann kinetic equations for the disorder-averaged two-point coherence. The Coulomb environment enters through the eikonal phase-coupling factor $A_{\rm rel}=1/(\hbar v)$, which saturates at $1/(\hbar c)$ for ultra-relativistic particles. This saturation is the central physical result: increasing the beam voltage suppresses Coulomb phase noise only up to a finite relativistic floor. We first formulate the eikonal approximation, in which the transmitted electron wave accumulates a random longitudinal phase. For a one-component Coulomb medium the electrostatic potential correlator retains a Coulomb tail, producing a logarithmic phase structure function and an algebraic decay of the transverse mutual coherence. We then go beyond the eikonal construction by deriving the Bethe–Salpeter equation for the Cooperon-like two-point coherence propagator directly from the paraxial wave equation. After a longitudinal Markov projection this equation reduces, after a Wigner transform, to a kinetic equation with a Coulomb small-angle scattering kernel. The coordinate-space solution of the same Bethe–Salpeter equation recovers the eikonal mutual coherence function, while the Wigner form additionally describes angular
diffusion and transverse broadening caused by multiple small-angle scattering. The resulting theory separates three effects which are often conflated in charged-particle wave propagation: attenuation of the coherent amplitude, decay of mutual coherence, and conservative redistribution of intensity in transverse phase space.
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Quantum Gases
Finite-temperature spin diffusion in the two-dimensional XY model
Erik Fitzner, Byungjin Lee, Junhyeok Hur et al. (+4 more)
We present a combined theory-experiment study to quantify
spin diffusion in the square
lattice quantum spin-1/2 XY model at finite temperature. On the theory side, we leverage a recently developed dynamical high-temperature expansion method to faithfully capture the long spatiotemporal scales of the hydrodynamic regime. Experimental results are obtained from an optical
lattice hard-core
boson quantum simulator. The excellent agreement of
spin diffusion constants marks a breakthrough in
spin-transport beyond one dimension and for the quantitative validation of state-of-the-art
quantum simulation platforms. We also provide theory predictions for future experiments on dynamic
spin conductivity or anisotropy-induced integrability breaking.
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All authors Erik Fitzner, Byungjin Lee, Junhyeok Hur, Minseok Kim, Benedikt Schneider, Jae-yoon Choi, Björn Sbierski
Statistical Mechanics
Diffusive-to-Ballistic transition in a Persistent Random Walk
Amit Pradhan, Reshmi Roy and Purusattam Ray
We study persistent random walk with time dependent velocity reversal probabilities and identify a criterion for a non-
equilibrium dynamical transition. As a representative example, we consider a power law reversal probability $p(t)\sim t^{-\alpha}$ and show that the system undergoes a transition at $\alpha=1$, separating a super-diffusive regime for $\alpha<1$ from ballistic regime for $\alpha \geq 1$. Using the results for velocity correlations and persistence statistics, together with finite time scaling of the Binder cumulant and displacement fluctuations, we characterize the transition and its properties in detail. We further argue that the transition is not limited to the power law form, but can also arise for several other time dependent reversal probabilities satisfying the same criterion. The transition persists in arbitrary spatial dimensions provided isotropy of the velocity space is preserved.
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Materials Science
Lattice thermal conductivity decomposition: Peierls vs. non-Peierls contributions
Andrey Pereverzev
The Green-Kubo
lattice thermal conductivity computed using the full classical heat current of a crystalline solid is compared with results obtained from the quadratic component of the heat current and from the commonly used Peierls heat current. In addition, thermal conductivity within the relaxation time approximation is evaluated. Three crystalline systems are investigated: solid argon, a model of solid argon with alternating masses, and $\alpha$-quartz. For all materials considered, the thermal conductivities calculated using the quadratic and Peierls heat currents differ only slightly. In the case of $\alpha$-quartz, the optical
phonon contribution to the thermal conductivity is found to exceed that of the acoustic modes. The relaxation time approximation systematically underestimates the thermal conductivity in all three systems.
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Materials Science
Spin polarization enhancement in a single-layer Bi(1-x)Sb(x) alloy on Ag(111) via isovalent substitution
Javier D. Fuhr, Polina M. Sheverdyaeva, Paolo Moras et al. (+2 more)
Co-adsorption of Bi and Sb on Ag(111) at room temperature yields a single-layer Bi(1-x)Sb(x)
alloy with a rectangular 3xsqrt(3) structure containing four atoms per unit
cell (2/3 ML total coverage) and lacking long-range chemical order. We present an electronic structure study of this system combining angle-resolved photoemission spectroscopy (ARPES) and density functional theory (DFT) calculations. To investigate the effect of inversion
symmetry breaking induced by substituting a heavier atom (Bi) with a lighter isoelectronic one (Sb) within a fixed crystallographic framework, we focused on a Bi-rich composition. ARPES measurements reveal four surface-state bands, in good agreement with DFT calculations based on a rectangular four-atom overlayer unit
cell. DFT calculations further show that Sb incorporation induces both in-plane and out-of-plane asymmetries in the electronic potential, leading to sizable
spin splitting and
spin polarization of the overlayer bands. Although these effects are partially reduced by interaction with the substrate, they remain significant. Our work illustrates, through a concrete model system, a general principle: incorporating a lighter isovalent element can significantly enhance
spin polarization, potentially offering a useful design guideline for understanding and engineering Rashba-related systems.
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All authors Javier D. Fuhr, Polina M. Sheverdyaeva, Paolo Moras, J. Esteban Gayone, Hugo Ascolani
Mesoscale and Nanoscale Physics
Spectral and transmission properties of multiple correlated quantum dots made simple
Nahual Sobrino and Stefan Kurth
Steady-state density functional theory, called i-DFT, is employed to compute spectral and transmission properties of general interacting nanoscale regions coupled to electronic reservoirs. Exchange-correlation functionals are constructed for different interactions and coupling geometries. The potential of the method is illustrated by applications to various multiple
quantum dots from the Coulomb blockade to the Kondo regime. The results are in reasonable agreement with many-body approaches at a fraction of the computational cost.
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Materials Science
Coherent terahertz magnon-phonon three-wave mixing in a layered antiferromagnet
Liangyue Li, Na Wu, Zhengwang Lin et al. (+9 more)
The coherent nonlinear dynamics between collective excitations, such as
magnons and
phonons, drive emergent phenomena in
quantum materials, yet their direct observation remains a central challenge. Here, using double-terahertz-pump optical-probe spectroscopy, we report the direct observation of coherent
magnon-
phonon three-wave mixing in the layered
antiferromagnetic insulator FePS$_{3}$. We resolve both second- and third-order nonlinear responses of
antiferromagnetic magnons and identify a suite of nonlinear couplings in two-dimensional (2D) coherent spectra, including definitive sum- and difference-frequency generation between
magnons and
phonons. These results lay the groundwork for exploiting coherent nonlinearities to entangle
magnetic and vibrational excitations, opening avenues for
quantum control and hybrid
quantum technologies in the terahertz regime.
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All authors Liangyue Li, Na Wu, Zhengwang Lin, Zefen Li, Lixin Liu, Emil Vinas Boström, Yuan Wan, Xinbo Wang, Jianlin Luo, Fucai Liu, Angel Rubio, Qi Zhang