Statistical Mechanics · Cross-listed from math-ph
Two-Species Boltzmann–Kac Kinetics with Matsumoto–Yor Nonlinear Collisions: Conserved Energy and Conic Equilibria
Yoshiaki Itoh
We extend Mark Kac's kinetic framework from single-species Euclidean spaces to a two-species, non-linear interaction space on the open cone $(0, \infty)^2$ governed by the Matsumoto–Yor rational collision involution. We identify a non-linear conserved energy $E(x,y) = x + y + 1/x$ and an invariant conic metric measure $d\mu = \frac{dx \, dy}{x(x+y)}$. By establishing a two-species $H$-
theorem, we prove that
entropy production vanishes if and only if post-collision velocities are statistically independent ($I(U;V)=0$). In contrast to the transform-domain proof of Letac and Wesołowski~\cite{letac2000}, which relies on joint Laplace transforms of general measures, our approach yields a direct physical derivation in state space via the transformation law for logarithmic gradients and separation of variables. This uncouples the functional-differential system to uniquely characterize the Generalized Inverse Gaussian (GIG) and Gamma distributions as the non-
equilibrium thermodynamic
equilibria.
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Statistical Mechanics · Cross-listed from hep-th
TheoPhysEval: Assessing AI agents at autonomous theoretical physics problem solving
A. Ramesh Chandra, Aaghaz Mahajan, Ainesh Sanyal et al. (+32 more)
We present a suite of 50 unpublished research-level theoretical physics problems with verifiable answers. Without AI assistance, a typical problem in our collection could be solved by a world expert in about a day or less but would take considerably longer for experts in adjacent specialties. We test the ability of off-the-shelf AI
agents to tackle these problems autonomously, without human hints. When given access to tools available in a realistic setting, including the ability to search the literature and write scripts for numerical and symbolic work, the best-performing
agent, GPT-6-Astra harnessed in Codex, obtains the final answers with a near-perfect accuracy of 98% at an average cost under USD 3 per problem. On average,
agents show only small changes in accuracy when denied web search and access to background research papers, suggesting significant memorization of the literature. These results suggest that state-of-the-art
agents can accurately perform concrete calculations required across theoretical physics research. We comment on the broader implications of these findings and discuss possible explanations for the current lack of
agent-led breakthroughs in theoretical physics despite their outstanding problem-solving abilities.
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All authors A. Ramesh Chandra, Aaghaz Mahajan, Ainesh Sanyal, Mianqi Wang, Shubhadeep Chakraborty, Sudip Chakraborty, Shailesh Chandrasekharan, Rama Govindarajan, Akshit Goyal, Jonathan J. Heckman, Yasir Iqbal, Divya Jaganathan, Saumav Kapoor, Andreas Karch, Pushkar Khandare, Sandeep Krishna, Anupam Kundu, Alok Laddha, Tongyan Lin, Swarnendu Maity, Nilmani Mathur, Shani Nadir Meynet, Alessandro Mininno, Abhijeet Mishra, Vidur Niranjan, Abhishodh Prakash, Pratik Rath, Durbar Roy, Debargha Sarkar, Srikanth Sastry, Gary Shiu, Aninda Sinha, Thomas Van Riet, Praneeth Netrapalli, Suvrat Raju
Superconductivity
Pre-pairing and polarization of doped charge carriers in unconventional superconductors
Lixin Zhang, Mengyan Nie, Yan Cheng et al. (+1 more)
Based on first principles calculations, we show in hole-doped La2-xSrxCuO4, the Sr dopants prefer to form dimers, rather than be isolated as generally believed. Same trend applies to other
superconductors such as Na-doped Ca2CuO2Cl2, and electron type Nd2-xCexCuO4. The dimer structure makes the two doped holes (electrons) bound up and form a singlet which is also polarized. Another type of dopant in cuprates is oxygen which behaves similarly. So, we propose that, for all oxide high TC
superconductors, the holes (electrons) are pre-paired (Z-pairs) during the preparation of the
superconductor. The spontaneously formed Z-pairs are conceptually different from not only the Cooper pairs, but also the Zhang-Rice singlets. The attraction force in a Z-pair originates basically from the strong antiferromagnetic exchange energy. We also found that the on-site Coulomb repulsion (U) is no longer a constant due to doping. Around a doping site, U can reduce its value discontinuously, which plays a key role in stabilizing the Z-pairs against isolated holes (electrons). A Z-pair is a p-wave like localized state which breaks the
symmetry of the CuO2 plain and attracts each other along the direction perpendicular to the polarization. The Z-pairs may be popular in all of the unconventional
superconductors and the periodic assembly can result in the emergence of coherence states and superconductivity.
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All authors Lixin Zhang, Mengyan Nie, Yan Cheng, Ran Zhao
Soft Condensed Matter
Biomolecular condensates and their pathologies: A colloidal, interfacial, and transport perspective
Vineeth Godavarti and Vinny Chandran Suja
Biomolecular condensates are micron-scale, membraneless compartments that concentrate
proteins and nucleic acids by
liquid-
liquid phase separation (LLPS). Condensates play critical roles in transcription, mRNA metabolism, stress responses, and signaling across the
cell, with their dysregulation increasingly correlated with several pathologies spanning neurodegeneration, cancer, cardiometabolic disease, and viral infections. The emergent biology of condensates can be cohesively viewed through the framework of colloidal, interfacial, and transport phenomena. Here we review the condensate literature through this joint lens, treating each condensate as a biological colloid whose behavior is captured by four measurable physical quantities: a Flory–Huggins interaction parameter that determines whether the dense phase forms at all, a partition coefficient that dictates the degree of client molecule accumulation, a viscoelastic relaxation time that sets whether the dense phase responds as a
liquid or a solid, and an interfacial tension that governs droplet shape and interfacial dynamics. Each quantity is traced to its physical origin, its measured range in biological condensates, and the techniques that quantify it, for both three-dimensional droplets and two-dimensional membrane-tethered condensates. Interpreting disease as the displacement of these physical quantities from their functional ranges, we reorganize condensate pathologies into a small set of physical failure modes — saturation concentration dysregulation, aberrant aging and
liquid-to-solid transitions, disrupted partitioning, interfacial aggregation, and pathogen hijacking — and show how the same parameters become design variables for condensate-targeted drugs and engineered coacervate delivery vehicles. The review concludes with open questions at the interface of condensate biology and colloidal and interfacial science.
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Materials Science
Atoms that Matter: Largest Materials Datasets Are 99% Redundant, and Local Chemistry Can Guide the Required 1%
Evgeny Moerman, Igor Poltavsky, Anton Charkin-Gorbulin et al. (+1 more)
General-purpose machine-learning force fields (MLFFs) for materials are now trained on the order of $100$ million structures, assuming transferability requires such scale. We test this premise on OMat24, the largest available materials
dataset, by training MACE models on subsets of $6.5$ million atoms, less than $1\%$ of OMat24, selected in three complementary ways: at random, by latent-space clustering of a pretrained MLFF (DIRECT), and by a new model-free method maximizing the diversity of discrete, interpretable local environments (EnvTok). All three models approach the full-data reference MACE-OMAT-0 model to within a few tens of $\mathrm{meV}/\mathring{\mathrm{A}}$ in forces, and remain close to or exceed it on formation energies, elastic moduli, heat capacities, Li$^{+}$ migration barriers, and molecular-dynamics stability up to $3000\,$K and $500\,$GPa. This near-independence from the selection strategy shows that chemical environment diversity, not size, defines OMat24's information content: the remaining $99\%$ of structures are largely redundant. Broad sampling of chemical space thus remains essential, but reference labels are needed only for structurally and chemically distinct configurations. Using atomic positions and species, optionally augmented by
magnetic moments, EnvTok identifies these before any labelling or training, yielding compact, architecture-independent
datasets. This hundredfold reduction makes hybrid-DFT or higher-level relabelling of general-purpose training sets feasible, and frees computational budget for extending environmental coverage and multi-fidelity learning.
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All authors Evgeny Moerman, Igor Poltavsky, Anton Charkin-Gorbulin, Alexandre Tkatchenko
Mesoscale and Nanoscale Physics
Direct Observation of Chirality-Dependent Berry Curvature Dipole via Cross-Axial Nonlinear Hall Effect in Trigonal Te
Jaehyun Lee, Junhee Shin, Daryll J. C. Dalayoan et al. (+8 more)
Quantum geometric quantities, such as Berry
curvature (BC) and
quantum metric, are known to govern the physical and topological properties of materials, making access to these quantities critically important for the comprehensive understanding of the materials. Chiral
crystals offer a natural platform in which structural handedness can control
quantum geometry and nonlinear transport, but direct experimental access to the
quantum geometric quantities has remained elusive. Here, we show that trigonal tellurium (Te) hosts an enantiomer-dependent Berry
curvature dipole (BCD) that can be accessed through the measurement of cross-axial nonlinear Hall effect (NHE), unlike previously studied in-plane configurations where the BCD contribution vanishes. Angle-resolved measurements on left- and right-handed Te devices reveal a second-order transverse response whose sign reverses with
crystal chirality. The extracted cross-axial nonlinear susceptibility, $\chi_{yxz}$, exceeds the in-plane susceptibility, $\chi_{xxx}$, by more than two-folds, indicating a strong BCD-driven contribution. First-principles calculations attribute this behavior to a topologically nontrivial hedgehog-like BC texture near the H points and predict a BCD that reverses sign between opposite enantiomers, consistent with experiment. These results establish cross-axial nonlinear Hall transport as a
symmetry-selective probe of chirality-controlled
quantum geometry in tellurium and related chiral materials.
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All authors Jaehyun Lee, Junhee Shin, Daryll J. C. Dalayoan, Miju Park, Changhee Sohn, Gang Qiu, Noejung Park, Binghai Yan, Tony Low, Hosub Jin, Seon Namgung
Soft Condensed Matter
Explicit Solvents Reverse Temperature Dependence of Phase Behavior in Charged Fluids
Pierre J. Walker and Zhen-Gang Wang
In most theories of electrolyte and polyelectrolyte solutions, the solvent is treated implicitly as a dielectric continuum. While this approximation has enabled major advances, it neglects coupling between ionic and dipolar degrees of freedom. Using molecular dynamics simulations and the mean-spherical approximation, we show that this coupling qualitatively alters electrostatically driven phase behaviour. At finite ion concentrations, many-body ion-dipole correlations reverse the temperature dependence of effective electrostatic interactions, leading to upper-critical solution temperature (UCST) behaviour in direct contrast to the lower-critical solution temperature (LCST) behaviour predicted by implicit-solvent electrostatic theories. This phase reversal arises from ion-induced suppression of local dipolar screening, a collective effect inaccessible to pairwise implicit-solvent descriptions.
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Statistical Mechanics
Competitive scaling of small-subsystem-optimization heuristics for LABS
Ginger E. Lau and Adil A. Gangat
The low autocorrelation binary sequences (LABS) problem, often formulated as a
spin-
lattice energy-minimization problem, is a combinatorial optimization problem with a very rugged energy landscape. We demonstrate that iterative optimization of very small subsystems of n
spins that are decoupled from the rest of the system achieves global optimization of LABS with a time-to-solution scaling that is competitive with heuristics that optimize the global system of N
spins directly. Our isolated-subsystem heuristic with n = 4 achieves a time scaling of O(1.333^N ) on the interval N = [27, 60], while the current state-of-the-art classical and
quantum scalings are respectively O(1.34^N ) and O(1.21^N ). Our results suggest that specialized optimization hardware with only small numbers of logical
spins may be of practical relevance.
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Materials Science
A Solution-Processed Ti/Pt/NiOx/Ag RRAM Device with Multiple Forming-Free Non-Volatile Intermediate States
Abhrajit Roy, Chopali Chanchal Sahu, Rudraksh Sangore et al. (+5 more)
Artificial neural networks (ANN) implemented on crossbar arrays of non-volatile synaptic devices are known to consume much less energy compared to that implemented on conventional computing units. Solution-processed resistive random-access
memory (RRAM) devices based on transition-metal oxides are suitable as such synaptic devices because of their cheap and easy fabrication method, stability, and suitable memristive properties. Here, in NiO-based RRAM devices with Ti/Pt as the bottom electrode and Ag as the top electrode (NiO layer deposited through solution processing), we experimentally report forming-free binary switching between a high resistance state (HRS) and a low resistance state (LRS) as well as forming-free pulse-driven modulation (long-term potentiation (LTP), long-term depression (LTD)) through 30 intermediate synaptic states between HRS and LRS (around 5-bit synaptic weight resolution). Many of these states are measured to be stable at least up to 1000 seconds confirming their non-
volatility and their utility in storage of synaptic weights for ANN crossbar arrays. On the contrary, most prior experimental reports (including reports both on solution-processing-based and sputtering-based RRAM devices) require forming to exhibit non-
volatility. Avoiding forming reduces variability, eliminates the need for high voltage pulses, and makes the crossbar array design simpler. Further, we confirm the presence of oxygen vacancies in our materials stack using X-ray photo-electron spectroscopy (XPS). Finally, we show successful data classification on MNIST and CIFAR-10 data sets using a multi-layer perceptron (MLP) model and a convolution neural network (CNN) model respectively, where the synaptic weight updates of these ANN models are calibrated against the experimentally measured LTP-LTD characteristics of the NiO RRAM devices.
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All authors Abhrajit Roy, Chopali Chanchal Sahu, Rudraksh Sangore, Raman Hissariya, Poulomi Chakrabarty, Harsh Roniyar, Merlyne De Souza, Debanjan Bhowmik
Other Condensed Matter
Revealing New Leakage Paths in GAAFETs using Predictive First-Principles Simulations
Denis Mamaluy, Juan P. Mendez, Coleman Cariker et al. (+2 more)
Gate-All-Around Field-Effect Transistors (GAAFETs) are emerging as successors to Fin Field-Effect Transistors (FinFETs) and are central to continued scaling at advanced
semiconductor nodes. Despite their improved electrostatic control, recent measurements show that the drain current in GAAFETs deviates strongly from thermionic behavior at negative gate voltages, increasing as the gate voltage becomes more negative. This leakage has been attributed to direct gate-drain tunneling through the high-$k$ dielectric, enhanced by drain-induced dielectric barrier lowering (DIDBL). Here, we use predictive, charge-self-consistent Non-
Equilibrium Green Function (NEGF) simulations based on the Contact Block Reduction (CBR) method to spatially resolve this leakage pathway in GAAFETs. Unlike approaches based primarily on phenomenological leakage models, our first-principles, multi-terminal
quantum-transport framework treats the source, drain, and gate as current-carrying
quantum-mechanical contacts and resolves the local current density throughout the device. The spatially resolved current density shows that gate-injected carriers tunnel through the high-$k$ dielectric preferentially near the drain side of the gate, where the dielectric barrier is most strongly lowered by the drain bias, and are collected by the drain. This provides a direct real-space picture of the DIDBL-driven gate-drain leakage mechanism.
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All authors Denis Mamaluy, Juan P. Mendez, Coleman Cariker, Michael Titze, Alex A. Belianinov
Mesoscale and Nanoscale Physics
Establishing the role of thickness in LaOBr; an alternative gate dielectric for vdW heterostructures
Isaac Antoine Lagaud, Justin Boddison-Chouinard, Antoine Labbé et al. (+9 more)
In electronic devices, the quality of the dielectric material is determined by figures of merit such as the band gap, leakage onset field, breakdown field and the number of built-in defects, which can all limit device performance. An additional and important metric to consider is the strength of the dielectric constant. Hexagonal boron nitride (hBN) is the
benchmark gate dielectric for two-dimensional van der Waals
heterostructures, owing to its wide bandgap, and atomically flat interface. At the same time, its dielectric constant (2–4) highlights the opportunity to explore alternative higher-permittivity van der Waals dielectrics that provide stronger electrostatic control. Previous work established lanthanum oxybromide (LaOBr), a layered dielectric with a predicted dielectric constant of 12.5, as a potential dielectric for van der Waals
heterostructures. Using
graphene field-effect devices with LaOBr, we show that the leakage-onset and breakdown fields decrease systematically with thickness. Dual-gate capacitance measurements combined with a dead-layer model reveal a bulk dielectric constant of $\varepsilon_{\mathrm{bulk}} = 12.2$, in agreement with theory, while interfacial dead-layers cause the effective dielectric constant to vary from 6 to 11 across multiple thicknesses. Benchmarked against established gate dielectrics, LaOBr combines breakdown fields comparable to hBN with dielectric constants 2 to 3 times larger. By establishing the operating regime of devices with various thicknesses, we further confirm the advantage of LaOBr over hBN for high-capacitance gate-dielectric operation. These results validate LaOBr as a promising dielectric for integration into two-dimensional
heterostructures, and establish thickness-dependent benchmarking as essential for evaluating emerging layered dielectric materials.
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All authors Isaac Antoine Lagaud, Justin Boddison-Chouinard, Antoine Labbé, Ayse Melis Aygar, Alex Bogan, Li-Lin Tay, Takashi Taniguchi, Kenji Watanabe, Aljoscha Söll, Zdeněk Sofer, Adina Luican-Mayer, Louis Gaudreau
Materials Science
Mn–Cr dopant association in dilute co-doped $\mathrm{ZnAl_2O_4}$ revealed by combined EPR and optical spectroscopy
Apoko S. Omondi, Mátyás M. Rudolf, Nikoletta Jegenyés et al. (+5 more)
Efficient and durable phosphors made from abundant elements underpin energy-saving solid-state lighting, near-infrared light sources for sensing, and X-ray and biomedical imaging. Co-doping is a standard route to brighter phosphors, yet the fate of the co-dopants is rarely established. We combine quantitative electron paramagnetic resonance (EPR)
spin counting with photoluminescence, photoluminescence excitation, and X-ray-excited spectroscopy across two dilute Mn/Cr co-doping series of hydrothermally grown $\mathrm{ZnAl_2O_4}$ nanoparticles and show that the two ions can form an exchange-coupled, edge-sharing Cr–Mn defect complex, with $\mathrm{Mn^{2+/4+}}$ entering an octahedral site next to $\mathrm{Cr^{3+}}$. The octahedral Mn lifts the inversion
symmetry of the $\mathrm{Cr^{3+}}$ site and strengthens its parity-forbidden absorption, enhancing the $\mathrm{Cr^{3+}}$ emission without energy transfer. The population of the defect complex follows the law of mass action, and above a threshold Mn concentration, Mn re-partitions into EPR-silent octahedral configurations that quench both emissions. Concentration optima in co-doped phosphors can thus reflect defect speciation, not only energy-transfer efficiency, which opens a structural design handle for brighter emitters.
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All authors Apoko S. Omondi, Mátyás M. Rudolf, Nikoletta Jegenyés, Árpád Jakab, Gábor Bortel, Bence G. Márkus, Adam Gali, Dávid Beke
Soft Condensed Matter
Explicit Solutions in a Probabilistic Cellular Automaton Model for Self-Assembled Monolayer Degradation
Wes Caldwell, Ryan Evans, Jacob Majikes et al. (+1 more)
Self-assembled monolayers (SAMs), formed by the adsorption of a monomolecular layer of adsorbate onto a surface, have emerged as leading candidates for plat- forms for electrochemical biosensors. In order to characterize the working age of a SAM-based biosensor, it is necessary to understand the long-term degradation of the monolayer, with particular emphasis on the intermolecular forces present in the self-assembly process. In this work, discrete- and continuous-time proba- bilistic cellular automaton (PCA) models for the degradation of SAMs involving adsorbate-adsorbate interactions are proposed in which adsorbate molecules desorb at a rate dependent only on the number of adsorbed neighbors. Impor- tantly, we make no assumptions on the relationship between degradation rate and adsorbed neighbors. Using techniques from generating function theory and complex analysis, the expected degradation curve is solved for explicitly in one dimension and shown to be a sigmoid curve related to the Gompertz function.
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All authors Wes Caldwell, Ryan Evans, Jacob Majikes, Anthony Kearsley
Soft Condensed Matter
Partitioning the magnetization raises the stability limit of ferromagnetic colloids
Paramita Modak, Priyadharshini M, Ankur Jaiswar et al. (+1 more)
Magnetic actuation scales with a particle's
magnetic moment, yet practical colloidal suspensions remain superparamagnetic or weakly magnetized, a permanent dipole drives a near contact attraction growing as the square of the moment, binding particles irreversibly. Here we show that this constraint depends not only on how much
magnetic material a particle carries, but on where it sits. Partitioning a fixed moment M into N internal elements leaves the far field interaction, and every actuation force, unchanged while suppressing the near-field pair energy by 1/N. As we show in our experiments across 57 samples and three geometries, stability collapses onto a single $\sim M^{2}/N$ boundary, raising the accessible dipolar energy scale nearly 150-fold. A
liquid-phase analogue of
magnetic force microscopy images the engineered energy landscape directly. The resulting colloids outrun size-matched superparamagnetic beads in weak fields far from a
magnetic source, suggesting their applicability in hard to reach places. Together, these results open a new operating regime for colloidal manipulation, with impactful implications in microfluidics and drug delivery.
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All authors Paramita Modak, Priyadharshini M, Ankur Jaiswar, Ambarish Ghosh
Materials Science
Benchmarking machine-learning interatomic potentials using classical force fields
Johannes Sandberg, Geneviève Dusson and Julien Lam
We propose a rational comparison between several well-known machine-learning interatomic potentials (linear atomic cluster expansion, the Behler-Parrinello high-dimensional neural network potential, and the graph neural network-based MACE potential) by testing their performance for fitting classical potentials such as the Lennard-Jones and Stillinger-Weber potential. With this we assess their advantages and limitations regarding several aspects: varying training
dataset size, robustness to noise, carbon footprint, as well as the ability to reproduce the radial distribution function as an example observable. Overall the MACE models are shown to most accurately reproduce the potential energy surface, with little sign of overfitting, but at a significant computational cost, highlighting important questions regarding the choice of models in computational materials science.
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Materials Science
Emergence of quantum transport in SnTe films upon structural refinement
Shrinkhala Sharma, Rabindra Basnet, Thomas Parker et al. (+4 more)
Topological crystalline
insulators are distinguished from the conventional Z2 topological
insulators by crystalline
symmetry protection of the surface states. Quantitative characterization of these states requires magneto-transport measurements from which the phase coherence length and number of independent coherent channels can be extracted. Here we report such measurements on textured thin films of SnTe grown on Bi2Te3 buffered c-plane sapphire (Al2O3) by pulsed
laser ablation. A post deposition annealing protocol was implemented to control the crystallographic texture, which reveals improved crystallinity and enhanced epitaxial
alignment along the [111] direction in films annealed at elevated temperatures. The higher carrier density and lower resistivity seen in films annealed at 100 oC are suggestive of Sn vacancies which act as native acceptor defects, while films annealed at 200 oC approach the 1:1 stoichiometry. The magnetoresistance of all samples at T < 10 K characterized by a cusp centered around zero-field is suggestive of weak antilocalization and interpreted in the framework of the Hikami-Larkin-Nagaoka theory in the strong
spin-orbit coupling limit. At T > 20 K, the MR is small and positive, and deviates from conventional Kohler scaling. An approximate collapse of the MR curves between 50 and 250 K is obtained using an empirical temperature-dependent scaling factor, indicating that changes in the Hall-derived carrier density alone cannot account for the observed scaling behavior. These results demonstrate that post growth annealing strongly influences the interplay between stoichiometry, crystallinity, and coherent transport in SnTe thin films.
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All authors Shrinkhala Sharma, Rabindra Basnet, Thomas Parker, Afolabi Akinfaderin, Alexander Samokhvalov, Rajeswari Kolagani, Ramesh C. Budhani
Materials Science
Anisotropic pressure response of thermal conductivity in crystalline polytetrafluoroethylene
Maissa Adi, Jamal Abou Haibeh and Samuel Huberman
Compression can change thermal conductivity differently along
polymer chains and across them by altering
phonon velocities and lifetimes. We examine this directional response in orthorhombic Form III polytetrafluoroethylene (PTFE) at calculated pressures of 1.503, 3.452, and 5.056 GPa, using first-principles harmonic and cubic force constants within the single-mode relaxation-time approximation (SMRTA). At 100, 200, and 300 K, the chain-axis conductivity decreases at every pressure step. Between 3.452 and 5.056 GPa, both transverse components recover: at 300 K they increase by 23.7% and 13.7%, while the longitudinal conductivity decreases by 14.5%. An exact factorization separates the conductivity into a heat-capacity–velocity factor and a weighted effective lifetime. The transverse recovery follows from larger heat-capacity-weighted squared velocities, consistent with stiffer interchain restoring forces. Along the chains, shorter effective lifetimes dominate, and both conductivity-weighted Normal and Umklapp rates increase at 300 K. Comparing the same cubic force-constant blocks at all three pressures, we find that interchain coupling is already substantial at 1.503 GPa and increases under compression.
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Materials Science
Precursor stoichiometry controls dopant structure, defect chemistry, and valence in Mn-doped ZnGa$_2$O$_4$ nanocrystals
Mátyás M. Rudolf, Gábor Bortel, Nikoletta Jegenyés et al. (+5 more)
The luminescence of doped nanocrystals is usually optimised through the activator; here we show that the host cation ratio is an equally decisive, and largely overlooked, design variable. Mn-doped ZnGa$_2$O$_4$ nanocrystals (Mn:Zn = $4\times10^{-4}$) were grown hydrothermally at nominal Zn/Ga ratios between 0.30 and 0.75 (stoichiometric: 0.50) and post-annealed at 400–1100$^\circ$C, and the resulting composition–temperature
matrix was mapped by X-ray- and UV-excited luminescence, EPR, Rietveld-refined X-ray diffraction, Raman spectroscopy and SEM. The as-grown
crystals are phase-pure spinel at every composition and accommodate their off-stoichiometry internally as a point-defect inventory, reflected in a 0.4% variation of the
lattice parameter; on annealing, the excess gallium is exsolved as $\beta$-Ga$_2$O$_3$ in amounts set by the solution composition. The Mn$^{2+}$ emission separates into two optima, near-stoichiometric
crystals annealed at 400–600$^\circ$C and Zn-excess
crystals annealed at 1100$^\circ$C, the latter being twice as bright under X-ray excitation. Under X-ray and 365~nm excitation the two optima are separated by a minimum at 800$^\circ$C that coincides with a collapse of the Mn$^{2+}$ EPR population and has no counterpart in the Raman linewidths, identifying transient, defect-compensated oxidation of the dopant rather than
lattice degradation as its origin. The most Zn-rich composition shows neither Mn$^{2+}$ nor Mn$^{4+}$ emission at any annealing stage, whereas its trace Cr$^{3+}$ emission is strong, indicating that Mn is rejected already during growth. Solution stoichiometry therefore acts on two levels, dopant capture and native-defect inventory, while annealing controls dopant valence and
lattice order. The brightest high-temperature phosphor is thus not the nominally stoichiometric one, but the composition whose excess is consumed on its way to stoichiometry.
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All authors Mátyás M. Rudolf, Gábor Bortel, Nikoletta Jegenyés, Árpád Jakab, László Bencs, Ferenc Simon, Adam Gali, Dávid Beke
Strongly Correlated Electrons
Exact SU($N$) symmetry resolution of bosonic Hubbard models: general boson-fermion mappings and flat-band singlet-cluster states
Loïc Herviou
We show how to perform exact diagonalization of SU($N$)-symmetric Bose-Hubbard models separately in each irreducible representation of SU($N$), by exploiting the Howe duality between U($L$) and U($N$). Three structural consequences follow for any
lattice and any
Hamiltonian built from the U($L$) generators: (i) the spectrum in a given orbital sector is independent of $N$ and of the particle statistics, (ii) the canonical partition functions for
bosons and
fermions obey the exact identity $Z_{\mathrm{b}}(-N)=(-1)^{N_\mathrm{b}}Z_{\mathrm{f}}(N)$, (iii) with unfrustrated hopping the groundstate is always a color ferromagnet, so that the color-resolved method we introduce is useful to study excited sectors, frustrated
lattices and finite temperatures. As applications, we first derive the finite-temperature phase diagram of attractive SU($N$)
bosons on few-site rings at large $N$ for arbitrary filling. We then show the emergence of singlet-cluster states from frustrated hopping, the counterpart of fermionic ferromagnetism, with the example of the sawtooth and kagome
lattice.
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Quantum Gases
Experimental observation of Higgs oscillations and their power-law decay across pairing regimes in a cavity QED quantum simulator
Chitose Maruko, Haoqing Zhang, Eliot A. Bohr et al. (+6 more)
Understanding how pairing correlations in
superconductors evolve out of
equilibrium is a central challenge in
quantum many-body physics. In systems with $s$-wave pairing, the character of Cooper pairing evolves continuously from a BCS regime of weakly bound, overlapping pairs to a BEC regime of tightly bound molecules, each with distinct excitation spectra. Here we realize and probe pairing dynamics across these regimes using cold, non-degenerate $^{87}$Rb atoms coupled to an optical cavity with Floquet dressing. Our cavity-QED platform emulates fermionic superfluids through a mapping onto Anderson pseudospins, while optical and microwave control tunes the ratio of interactions to single-particle energies, providing a flexible approach complementary to ultracold Feshbach and ultrafast solid-state platforms. Following a quench, we observe persistent pairing and transient oscillations of the order parameter associated with a collective amplitude (
Higgs) mode. We find that the decay of these oscillations sharply distinguishes weak- and strong-pairing regimes: in the weak-pairing regime, oscillations decay with a power-law exponent $|\alpha|=0.65(8)$, whereas in the strong-pairing regime the decay is substantially faster, with $|\alpha|>1$. The oscillation frequency is set by the minimum quasiparticle excitation energy, directly linking nonequilibrium dynamics to the underlying excitation spectrum. Our results establish nonequilibrium dynamics as a direct probe of pairing character and collective excitations in interacting
quantum systems.
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All authors Chitose Maruko, Haoqing Zhang, Eliot A. Bohr, Leah Huzjak, Anjun Chu, Victor Gurarie, Chengyi Luo, Ana Maria Rey, James K. Thompson
Strongly Correlated Electrons · Cross-listed from math-ph
Categorifying Quantum Spin Systems
Matthew Yu
We develop a homotopical framework for understanding the space of
quantum spin systems based on topological $n$-nets, which assign associative unital
algebras to local regions in an $n$-dimensional space in a manner that captures the locality structure of the underlying
lattice theories. The net-theoretic perspective admits a natural categorification, in which the category of topological $n$-nets carries the structure of a higher Morita category. Moreover, the nets of greatest physical interest form a Karoubi-complete subcategory that shares many of the characteristic structural features of the category of finite TQFTs. Our main result identifies the group of locality-preserving
symmetries of (3+1)-dimensional
quantum spin systems (i.e.
quantum cellular automata modulo stabilization, finite-depth
quantum circuits, and translations) with the full Witt group of nondegenerate braided fusion categories, thereby answering a question posed by Haah.
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Materials Science
In-Situ TEM Observation of Solid-State Phase Evolution in High-Entropy Alloy Nanoparticles
Nirmal Kumar Katiyar, Noorbasha Bhavani Sai, Guilherme Gurian Dariani et al. (+5 more)
The emergence of new materials has gone beyond conventional design principles. Among them are high
entropy alloys (HEAs), in which multiple metallic elements coexist within a single unit
cell. In this case, each atomic position in a solid material has a different chemical environment, leading to configurational
entropy as high as that in the fully random or melted state, which has been frozen to a solid solution. However, the behaviour of such
alloy systems at pre-melting temperatures is largely unknown, where atoms gain sufficient mobility and time to rearrange, leading to an enthalpic rather than an entropic interplay. This study demonstrated the phase transformation of HEA nanoclusters (CoCrFeMnNi) under high-resolution transmission electron microscopy (HRTEM) at different temperatures, including room temperature (RT), 550 {\deg}C, and 850 {\deg}C. The clustered nanoparticles coarsen into larger clusters, accompanied by compositional heterogeneity due to surface and
lattice diffusion. This experimental finding of atomic mobility was further corroborated using molecular dynamics, which provides a detailed mechanistic description.
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All authors Nirmal Kumar Katiyar, Noorbasha Bhavani Sai, Guilherme Gurian Dariani, Douglas S. Galvao, Pulickel M. Ajayan, Pedro Alves da Silva Autreto, Sriram Vijayan, Chandra Sekhar Tiwary
Mesoscale and Nanoscale Physics
Electric-dipole-induced nuclear electric resonance in silicon
Jiyun Su, Shihang Zhang and Peihao Huang
The nuclear
spin of a phosphorus atom in silicon is considered as a promising
quantum information carrier for
quantum computing due to its long coherence time. Coherent control of the nuclear
spin is typically realized using nuclear
magnetic resonance (NMR). In this work, we theoretically propose that with the aid of hyperfine interactions and
magnetic field gradients, fast electric-dipole-induced nuclear electric resonance (EDNER) can be achieved. The stronger EDNER (compared with NMR) arises from the combined effects of hyperfine interaction between the nuclear and electron
spins and coupling between the electron
spin and charge degrees of freedom mediated by
magnetic field gradients in this scheme. By operating at specific working points, the nuclear-
spin splitting becomes less sensitive to electrical noise, enabling long coherence times and high-fidelity
quantum operations. All elctrical, addressable control of nuclear
spins paves the way for scalable silicon-based
quantum computing.
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