Statistical Mechanics
Dynamic structure factor of a monatomic cubic crystal
Arsene Yerle, Pierre Gaspard and Joel Mabillard
The spectral function of density fluctuations, also known as the dynamic structure factor, of a monatomic cubic
crystal with vacancies is derived from the macroscopic equations describing transport in crystalline solids. The resonances of the spectral function are identified as a Brillouin doublet of sound propagation, a central Rayleigh peak of heat
diffusion, as for perfect
crystals, and another central sharp peak associated with vacancy
diffusion. Analytical expressions for the heat and vacancy diffusivities, speeds of sound, and sound damping coefficients are obtained. The theoretical results are compared to molecular dynamics simulations of a face-centered cubic
crystal of hard spheres.
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Strongly Correlated Electrons
Infinite-component $BF$ field theory: Connection of fracton order, Toeplitz braiding, and non-Hermitian amplification
Bo-Xi Li and Peng Ye
Building on the infinite-component Chern–Simons theory of three-dimensional fracton phases by Ma et al. [Phys. Rev. B 105, 195124 (2022)] and the Toeplitz braiding of anyons by Li et al.~[Phys. Rev B 110, 205108 (2024)], we show that stacking $(3+1)$D $BF$ topological field theories, which serve as low-energy effective descriptions of a class of three-dimensional topological orders, along a fourth spatial direction gives rise to an exotic class of four-dimensional fracton phases. Their low-energy physics is governed by a new field-theoretic framework, namely \textit{infinite-component $BF$} (i$BF$) theories, characterized by asymmetric integer Toeplitz $K$
matrices. Under open boundary conditions along the stacking direction, i$BF$ theories with properly chosen $K$
matrices exhibit a striking phenomenon termed Toeplitz particle–loop braiding, where a particle and a loop placed on opposite three-dimensional boundaries acquire a strongly oscillating yet robustly nonvanishing braiding phase even at infinite separation. This nonlocal braiding admits a
geometric interpretation: adiabatically transporting the particle induces a winding boundary trajectory on the opposite boundary that encircles the loop. We show that this robustness originates from boundary zero singular modes (ZSMs) of Toeplitz $K$
matrices revealed by singular value decomposition, rather than from boundary zero eigenmodes responsible for previously known Toeplitz braiding of anyons, and that the same ZSM mechanism also underlies directional amplification in the rapidly developing field of non-Hermitian physics. We analytically and numerically study representative i$BF$ theories with Hatano–Nelson–type and non-Hermitian Su–Schrieffer–Heeger–type $K$
matrices, establishing a universal correspondence between ZSMs and Toeplitz particle–loop braiding.
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Statistical Mechanics · Cross-listed from math.PR
Random Walk conditioned to stay above a non-flat floor: curvature effects
Sébastien Ott and Yvan Velenik
Let $h:[0,1]\to\mathbb{R}$ be $C^2$ and such that $\sup_{[0,1]} h''<0$. For a (large) positive integer $n$, set $h_n(k) = n h(k/n)$ for any $k\in\{0,\dots,n\}$. We consider a random walk $(S_k)_{k\geq 0}$ with i.i.d.\ centred increments having some finite exponential moments. We are interested in the event $\{S\geq h_n\} = \{S_k\geq h_n(k)\;\forall k\in\{0,\dots,n\}\}$. It is well known that $P(S\geq h_n \,|\, S_0=0,\, S_n=\lceil h_n(n) \rceil) = e^{n\int_0^1 I(h'(s)) \,ds + o(n)}$, where $I$ is the Legendre-Fenchel transform of the log-moment generating function associated to the increments. We first prove that the leading correction is of order $e^{-\Theta(n^{1/3})}$. We then turn our
attention to the conditional random walk measure $P^h_n = P(\cdot \,|\, S\geq h_n, S_0=0, S_n=\lceil h_n(n) \rceil)$. We prove that the one-point tails are of the form $\mathbb{P}_n^h (S_k \geq h_n(k) + t n^{1/3} ) = e^{-\Theta(t^{3/2})}$ for all $t<n^\beta$ for any $\beta\in (0,1/6)$. Moreover, we prove that, for any $r\geq 1$, $E_n^h((S_k-h_n(k))^r) = \Theta(n^{r/3})$ and $\mathrm{Var}_{P_n^h}(S_k) = \Theta(n^{2/3})$, for all $k$ far enough from $0$ and $n$. In addition, we show that $\mathrm{Cov}_{P_n^h}(S_k,S_\ell) \leq e^{-O(|\ell-k|/n^{2/3})}$ for all $k,\ell$ not too close to $0$ and $n$.
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Quantum Gases
Quantum-droplet interferometry
Sriganapathy Raghav, Boris Malomed and Utpal Roy
We propose atom interferometers based on
quantum droplet (QD), which is also being reported as a superior platform for interferometry. The emphasis has been given to harmonic-oscillator (HO) or ring-shaped potentials. In the HO trap, a Gaussian barrier induces coherent splitting; in the ring, one or two barriers guide the splitting and subsequent recombination. The atom number and relative mean-field interaction strength critically affect the interferometric performance. The transmission-coefficient analysis identifies values of the barrier parameters for the balanced $50:50$ splitting. The post-recombination atom-number imbalance serves as a sensitive indicator of the relative phase between merging daughter QDs. We demonstrate that the HO-based setup may serve as a tilt-meter and target detector, and the ring geometry may be used as a compact QD Sagnac interferometer for rotation sensing.
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Statistical Mechanics · Cross-listed from math.PR
Finite-time trajectorial estimates for inhomogeneous random walks
Sébastien Ott and Yvan Velenik
We consider integer-valued random walks with independent but not identically distributed increments, and extend to this context several classical estimates, including a local limit
theorem, precise small-ball estimates (both conditional on the final point and unconditional), and bounds on the probability that the random walk trajectory remains positive up to a given time (again, both conditional on the final point and unconditional). Two key features of this work are that the bounds are non-asymptotic, holding true for finite time horizons, and, crucially, that the latter hold uniformly over an entire class of admissible increment sequences. This provides a robust framework for applications. These results are, in particular, tailored for the analysis of processes derived through a time-dependent tilting of the increments of a time-homogeneous random walk.
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Mesoscale and Nanoscale Physics
Dynamical Orbital Angular Momentum Induced by Circularly Polarized Phonons
Dapeng Yao, Dongwook Go, Yuriy Mokrousov et al. (+1 more)
We show that the orbital angular momentum (OAM) of electrons is dynamically induced by circularly polarized
phonons. The induced OAM originates from the adiabatic
evolution in which electrons acquire Berry phase formulated in terms of the Berry
curvature encoded in
phonon displacement space. By introducing a tight-binding model with $p$ orbitals on a honeycomb
lattice, we show a microscopic picture that ionic rotations modulate orbital overlaps of electrons, and calculate the generated OAM, whose sign depends on
phonon chirality. We then construct an effective model for valley
phonons with different
phonon pseudoangular momenta (PAM) and identity their distinct intervalley-scattering channels. Our model obeys the selection rule between
phonons and electrons with the orbital degree of freedom. Extending this framework to $d$-orbital electrons, our model is applied to describe the induced OAM in monolayer transition metal dichalcogenides. Our results reveal a direct orbital generation mechanism that emerges even in materials with weak
spin-orbital coupling, opening a new promising way for orbitronics applications.
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All authors Dapeng Yao, Dongwook Go, Yuriy Mokrousov, Shuichi Murakami
Materials Science
Hydrogen permeability prediction in palladium alloys and virtual screening of B2-phase stabilized Pd(100-x-y)CuxMy ternary alloys using machine learning
Eric Kolor, Edoardo Magnone, Muhammad Harussani Moklis et al. (+4 more)
We present a forward prediction material screening framework designed to discover Pd-Cu
alloys with improved B2 phase stability, thereby unlocking simultaneous $H_2$ generation and utilization. First, we trained CatBoost models with literature-derived Pd
alloy data to predict $H_2$ permeability from composition and testing conditions. We evaluated fractional, composition-based, and physics-informed descriptors, individually and in combination, and showed that sequential Pearson filtering and fold-wise SHAP-based recursive feature elimination with cross-fold aggregation reduced errors while controlling complexity. Guided by the one-SE rule, a narrower domain-informed set of 13 features provided the best accuracy parsimony trade-off ($R^2=0.81$), only 0.01 below the max. $R^2$ achievable with 3x the number of features. SHAP analysis indicated that high permeability is promoted by elevated temperature,
lattice expansion relative to Pd, atomic size mismatch, and favorable mixing tendencies. Second, the selected model was applied to screen $Pd_{(100-x-y)}Cu_{x}M_{y}$ spanning 16 co-dopants M for B2 stabilization. For each M system, we obtained the Pareto set of compositions that minimize Pd content and Miedema heat of formation and maximize the permeability, then picked three compounds, including that with the highest predicted permeability, the lowest Miedema heat of formation, and the lowest Pd content. With a final filter considering M concentration for single-phase Pd-M solution formation, we recommend Pd48.48Cu43.00Y8.52, Pd49.08Cu42.45Sc8.47, Pd56.09Cu33.70La10.21, and Pd52.68Cu40.44Mg6.88 for experimental validation. We predict those
alloys to exhibit permeabilities 1.7 to 1.9 higher than B2 Pd60Cu40. Our framework provides plausible experimental targets and a scalable pathway for designing stable, high-temperature, H2-selective Pd-
alloy membranes.
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All authors Eric Kolor, Edoardo Magnone, Muhammad Harussani Moklis, Md. Rubel, Sasipa Boonyubol, Koichi Mikami, Jeffrey S. Cross
Materials Science
Phase transformations in metastable $\beta$ Zr15Nb alloy revealed by in-situ methods
Anna Veverková, Kristína Bartha, Jozef Veselý et al. (+6 more)
This study examines the phase transitions occurring during linear heating of the Zr15Nb
alloy through a comprehensive, multi-technique methodology comprising in-situ high-energy synchrotron X-ray diffraction (HEXRD), electrical resistance measurements, differential scanning calorimetry (DSC), and thermal expansion analysis, supplemented by ex-situ transmission electron microscopy (TEM). The findings reveal a complex sequence of phase transformations and corresponding structural changes over a broad temperature range (from room temperature up to 800 ${\deg}$C). Two distinct body-centered cubic (bcc) $\beta$ phases - $\beta_{Zr}$ and $\beta_{Nb}$ - with closely related
lattice parameters are identified. At room temperature, the microstructure is characterized by a mixture of the metastable $\beta_{Zr}$ + $\omega_{ath}$ phase. Upon heating, $\beta_{Zr}$ progressively decomposes, giving rise to the formation of $\beta_{Nb}$. TEM observation revealed the cuboidal shape of the $\omega_{iso}$ particles resulting from the high
lattice misfit between $\beta$ and $\omega$ phase. The $\omega$ solvus temperature is determined to be approximately 555 ${\deg}$C, as evidenced by in situ HEXRD and abrupt changes in the
alloy's thermal and electrical properties. The growth of the $\alpha$ phase occurs after the dissolution of the $\omega$ phase, resulting in a pronounced increase in thermal expansion.
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All authors Anna Veverková, Kristína Bartha, Jozef Veselý, Pere Barriobero-Vila, Jiří Kozlík, Petr Doležal, Jiří Pospíšil, Jana Šmilauerová, Josef Stráský
Materials Science
Assessing Band Gap Stability of Organic Semiconductor Thin Films for Flexible Electronic Applications
Mahya Ghorab, Ayush K. Ranga, Arnulf Materny et al. (+2 more)
Integration of organic
semiconductors into flexible electronics requires that their optoelectronic properties remain stable under mechanical deformation. Among these, the optical band gap governs
exciton generation and limits photovoltaic voltage, making it a key parameter for strain-resilient design. In this work, we investigate band gap shifts in poly(3-hexylthiophene-2,5-diyl) (P3HT) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/P3HT thin films deposited on flexible poly(ethylene terephthalate) (PET) substrates under uniaxial tensile strain ranging from 1% to 10%. Samples were subjected to mechanical deformation and then characterized by ultraviolet–visible (UV–Vis) absorption spectroscopy. The optical band gaps extracted using a standardized Tauc analysis and statistically validated through equivalence testing and robust regression models. We find that up to 7% strain, the band gap shift ($\Delta E_g$) remains effectively invariant, independent of annealing condition or stack configuration, demonstrating electronic stability. However, at 10% strain, all groups exhibit a reproducible widening of $\sim$4–5~meV. This threshold-like behavior marks a transition from mechanical accommodation to electronic perturbation. These findings confirm that the optical band gap in semicrystalline P3HT-based thin films is robust under practical deformation, which provides clear strain thresholds to inform mechanical modeling and device-level simulation of flexible organic optoelectronic systems.
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All authors Mahya Ghorab, Ayush K. Ranga, Arnulf Materny, Veit Wagner, Mojtaba Joodaki
Statistical Mechanics
Discontinuous transition in explosive percolation via local suppression
Young Sul Cho
We study an explosive percolation model in which a link is randomly added and neighboring nodes sequentially rewire their links to suppress the growth of large clusters. In this manner, the rewiring nodes spread outward starting from the initial node closest to the added link. We show that a discontinuous transition emerges even when the total number of rewiring nodes after each link addition is finite. This finding implies that adding a link using the information of the cluster sizes attached to a finite set of link candidates (local information) can lead to a discontinuous transition if link rewiring is allowed. This result thus extends the previous result that a discontinuous transition arises only when a link is added using the information of the cluster sizes attached to an infinite number of link candidates (global information) in the absence of rewiring.
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Superconductivity
First-principles evidence for conventional superconductivity in a quasicrystal approximant
Pedro N. Ferreira, Roman Lucrezi, Sangmin Lee et al. (+7 more)
Quasicrystals (QCs) host long-range order without translational
symmetry, a regime in which the very foundations of BCS theory are not straightforwardly applicable, yet experiments on QCs and their approximant
crystals (ACs) point to conventional, $s$-wave, electron-
phonon coupled superconductivity. Here we test the predictive power of the electron-
phonon framework in a representative decagonal AC from first principles. Using state-of-the-art ab initio methods, we compute the superconducting properties of the recently discovered AC Al$_{13}$Os$_4$ and quantitatively reproduce its bulk $T_\text{c}$. This constitutes, to our knowledge, the first ab initio determination of $T_\text{c}$ for an AC and establishes that the electron-
phonon framework is predictive in these systems as well. Using the generalized quasichemical approximation for
alloy modeling in the decagonal Al–Os family, we predict tunable superconductivity in Al$_{13}$Os$_{4-x}$Re$_x$ and Al$_{13}$Os$_{4-x}$Ir$_x$; in particular, Al$_{13}$Re$_4$ is dynamically stable and estimated to have a $T_\text{c}$ about 30% above Al$_{13}$Os$_4$. Finally, we discuss the role of ACs as high-fidelity proxies for their parent QCs. Although long-range quasiperiodicity may introduce subtle electronic features, our findings indicate that the key ingredients for superconductivity are already encoded in the local structural motifs preserved by the AC. This places the Al–Os and Al–Re families among the most promising candidates for the highest-$T_\text{c}$ quasicrystalline superconductivity.
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All authors Pedro N. Ferreira, Roman Lucrezi, Sangmin Lee, Lucy Nathwani, Matthew Julian, Rohit P. Prasankumar, Warren E. Pickett, Chris J. Pickard, Philip Kim, Christoph Heil
Statistical Mechanics
Determining extended Markov parameterizations for vector-valued generalized Langevin Equations
Niklas Bockius, Maximilian Braun, Kay Hofmann et al. (+2 more)
The generalized Langevin equation is used as a model for various coarse-grained physical processes, e.g., the time
evolution of the velocity of a given larger particle in an implicitly represented solvent, when the relevant time scales of the dynamics of the larger particle and the solvent particles are not strictly separated. Since this equation involves an integrated history of past velocities, considerable efforts have been made to approximate this dynamics by data-driven Markov models, where auxiliary variables are used to compensate for the
memory term. In recent works we have developed two
algorithms which can be used for this purpose, provided the dynamics in question are scalar processes. Here we extend these
algorithms to vector-valued processes. As a physical test bed we consider an S-shaped particle sliding on a planar substrate, which gives rise to a truly two-dimensional velocity process. The two
algorithms provide Markov approximations of this process with 10-20 auxiliary variables and a very accurate fit of the given autocorrelation data over the entire time interval where these data are non-negligible.
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All authors Niklas Bockius, Maximilian Braun, Kay Hofmann, Friederike Schmid, Martin Hanke
Statistical Mechanics
Mean-field theory of the DNLS equation at positive and negative absolute temperatures
Michele Giusfredi, Stefano Iubini, Antonio Politi et al. (+1 more)
The Discrete Non Linear Schrödinger (DNLS) model, due to the existence of two conserved quantities, displays an
equilibrium transition between a homogeneous phase at positive absolute temperature and a localized phase at negative absolute temperature. Here, we provide a mean-field theory of DNLS through a suitable approximation of the grandcanonical partition function which makes it factorizable and can be used to describe the
equilibrium state at positive temperatures as well as the metastable state at negative temperatures. By comparing our mean-field results with numerically exact ones, we show that this approximation is good-to-excellent in the whole grandcanonical phase diagram. Explicit approximate expressions for
equilibrium observables are provided in the high-temperature limit. Our theory represents a clear advancement over the model that neglects the interaction between sites.
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All authors Michele Giusfredi, Stefano Iubini, Antonio Politi, Paolo Politi
Statistical Mechanics · Cross-listed from math.PR
Moderate-to-large deviation asymptotics for real eigenvalues of the elliptic Ginibre matrices
Sung-Soo Byun, Jonas Jalowy, Yong-Woo Lee et al. (+1 more)
We study the statistics of the number of real
eigenvalues in the
elliptic deformation of the real Ginibre ensemble. As the
matrix dimension grows, the law of large numbers and the central limit
theorem for the number of real
eigenvalues are well understood, but the probabilities of rare events remain largely unexplored. Large deviation type results have been obtained only in extreme cases, when either a vanishingly small proportion of
eigenvalues are real or almost all
eigenvalues are real. Here, in both the strong and weak asymmetry regimes, we derive the probabilities of rare events in the moderate-to-large deviation regime, thereby providing a natural connection between the previously known regime of Gaussian fluctuations and the large deviation regime. Our results are new even for the classical real Ginibre ensemble.
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All authors Sung-Soo Byun, Jonas Jalowy, Yong-Woo Lee, Grégory Schehr
Quantum Gases · Cross-listed from physics.optics
Direct observation of room-temperature exciton condensation
Jiaxin Yu, Guangyu Dai, Shuai Xing et al. (+5 more)
Exciton condensation–an interaction-driven, macroscopically coherent paired-
fermion state–offers the prospect for dissipationless energy transport in solids, akin to that in superconductivity. Although their light effective mass and strong Coulomb binding favour high transition temperatures, convincing demonstrations of pure-
exciton condensation have hitherto been limited to cryogenic conditions. Here, we report the direct observation of quasi-
equilibrium condensation of dark
excitons in monolayer tungsten diselenide at 300 K and ambient pressure. We achieve this by creating nanoscale spacing-graded Stark traps to confine free
excitons, setting the finite-size scale, non-resonant off-axis optical injection to control the local density-temperature trajectory, and employing surface plasmon polariton-enhanced microsphere-assisted microscopy to boost dark-
exciton emission and directly image first-order spatial coherence with sub-diffraction resolution. We observe a sharp degeneracy threshold and a clear phase transition, evidenced by extended first-order spatial coherence with algebraic decay and a critical exponent consistent with the universal Berezinskii-Kosterlitz-Thouless criterion. Identical condensation signatures are observed in over 30 independent samples. Our work establishes a room-temperature excitonic platform for exploring strongly correlated many-body physics and advancing near-dissipationless, coherent
quantum technologies.
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All authors Jiaxin Yu, Guangyu Dai, Shuai Xing, Weiwei Zhang, Lin Dou, Tianci Shen, Xinyu Zhang, Xialian Feng Fuxing Gu
Statistical Mechanics
Experimentally accessible measurement of irreversibility in stochastic systems by categorizing single-molecule displacements
Alvaro Lanza, Inés Martínez-Martín, Rafael Tapia-Rojo et al. (+1 more)
Quantifying the irreversibility and dissipation of non-
equilibrium processes is crucial to understanding their behavior, assessing their possible capabilities, and characterizing their efficiency. We introduce a physical quantity that quantifies the irreversibility of
stochastic Langevin systems from the observation of individual molecules' displacements. Categorizing these displacements into a few groups based on their initial and final position allows us to measure irreversibility precisely without the need to know the forces and magnitude of the fluctuations acting on the system. For short times, our model-free estimate of irreversibility is related to
entropy production by a conditional fluctuation
theorem. For short times and in general for stationary protocols, our estimate provides a lower bound to the average
entropy production. We validate the method on single-molecule force spectroscopy experiments of
proteins subject to force ramps. We show that irreversibility is sensitive to detailed features of the energy landscape underlying the
protein folding dynamics and suggest how our methods can be employed to unveil key properties of
protein folding processes.
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All authors Alvaro Lanza, Inés Martínez-Martín, Rafael Tapia-Rojo, Stefano Bo
Materials Science
Enhanced spectral range of strain-induced tuning of quantum dots in circular Bragg grating cavities
Ivan Gamov, Matthias Sauter, Samuel Huber et al. (+5 more)
Tunable sources of entangled and single
photons are essential for implementing
entanglement-based
quantum information protocols, as
quantum teleportation and
entanglement swapping depend on
photon indistinguishability. Tunable devices are fabricated from indium arsenide (InAs)
quantum dots (QDs) embedded in gallium arsenide (GaAs) nanomembranes placed on monolithic piezoelectric substrates. Circular Bragg grating (CBG) resonators enhance emission brightness and exploit the Purcell effect; however, the inclusion of CBGs reduces strain-mediated tunability compared to planar nanomembranes. A simple and effective solution is introduced: filling the CBG trenches with a stiff dielectric (aluminum
oxide) via atomic layer deposition (ALD) restores up to 95% of the tunability of planar structures. Finite element analysis (FEA) confirms that the tunability loss originates from bending in the device layers due to strain relief in the CBG geometry. Lowering the stiffness of intermediate layers between the QDs and the piezoelectric actuator, such as in bonding or reflector layers, further increases strain losses in uncoated CBGs. Coated devices maintain 98-99% strain-tuning efficiency across all simulated underlayer stiffnesses. The results demonstrate that advantageous optical cavity properties can be effectively combined with piezoelectric strain tuning, enabling scalable, bright, and tunable
quantum light sources.
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All authors Ivan Gamov, Matthias Sauter, Samuel Huber, Quirin Buchinger, Peter Gschwandtner, Ulrike Wallrabe, Sven Höfling, Tobias Huber-Loyola
Statistical Mechanics · Cross-listed from physics.soc-ph
Threshold model of language competition including the bilingual state
Mikhail V. Tamm, Els Heinsalu, Stefano Scialla et al. (+1 more)
We propose a threshold model of
language competition which includes intermediate bilingual state. The model is based on the Minett-Wang model but through the introduction of thresholds in the
language shift rates it incorporates the effects of
memory and learning. The model is piecewise-linear, allowing the exact analytical treatment. We study the symmetric case where two competing
languages are equivalent in terms of status and social pressure and provide a complete list of the various dynamical regimes. We also study several limiting regimes corresponding to asymmetric systems and characterize the full spectrum of possible asymptotic behaviors. Unlike the Minett-Wang model, which always predicts the extinction of one of the
languages, the proposed new model exhibits a wide range of possible
equilibrium scenarios, including
equilibrium states of coexistence. Most commonly, in such coexistence regimes the minority
language speakers are either completely monolingual or completely bilingual.
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All authors Mikhail V. Tamm, Els Heinsalu, Stefano Scialla, Marco Patriarca
Materials Science
Discovery of a new magnesium iron boride Mg4Fe1.1B13.9 in the Mg-Fe-B-N system
N.D. Zhigadlo
A new boron-rich ternary phase, Mg4Fe1.1B13.9, was discovered in the Mg-Fe-B-N quaternary system. This novel phase appears in the form of plate-like shaped
crystals formed on the surface of Fe-substituted MgB2 during high-pressure, high-temperature (HPHT) solution growth at 3 GPa and 1960 C. Mg4Fe1.1B13.9 crystallizes in an orthorhombic structure with space group Pnam (No. 62) and
lattice parameters a = 10.95(2) A, b = 7.07(1) A, and c = 8.72(1) A. Structural refinement reveals a layered architecture composed of alternating layers of Mg-Fe and boron, with boron atoms forming 5-, 6-, and 7-membered ring motifs. A structural comparison indicates that Mg4Fe1.1B13.9 is closely related to the Y2ReB6-type borides. This discovery highlights the effectiveness of the HPHT synthesis in accessing new, complex boron-rich phases. As research in the binary Mg-B system approaches saturation, the identification of Mg4Fe1.1B13.9 offers new insights into the formation of phases in the Mg-Fe-B-N system. This paves the way for the guided synthesis of novel borides with unique properties in other multicomponent systems.
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Strongly Correlated Electrons
Stability Frontiers and Mixed-dimensional physics in the Kagome Intermetallics Ln3ScBi5 (Ln = La-Nd, Sm)
Zhongchen Xu, Wenbo Ma, Shijun Guo et al. (+5 more)
Low-dimensional physics provides profound insights into strongly correlated interactions, leading to enhanced
quantum effects and the emergence of exotic
quantum states. The Ln3ScBi5 family stands out as a chemically versatile kagome platform with mixed low-dimensional structural framework and tunable physical properties. Our research initiates with a comprehensive evaluation of the currently known Ln3ScBi5 (Ln = La-Nd, Sm) materials, providing a robust methodology for assessing their stability frontiers within this system. Focusing on Pr3ScBi5, we investigate the influence of the zigzag chains of quasi-one-dimensional (Q1D) motifs and the distorted kagome layers of quasi-two-dimensional (Q2D) networks in the mixed-dimensional structure on the intricate
magnetic ground states and unique
spin fluctuations. Our study reveals that the noncollinear
antiferromagnetic (AFM) moments of Pr3+ ions are confined within the Q2D kagome planes, displaying minimal in-plane anisotropy. In contrast, a strong AFM coupling is observed within the Q1D zigzag chains, significantly constraining
spin motion. Notably, the
magnetic frustration is partially the consequence of coupling to conduction electrons via the Ruderman-Kittel-Kasuya Yosida (RKKY) interaction, highlighting a promising framework for future investigations into mixed-dimensional frustration in Ln3ScBi5 systems.
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All authors Zhongchen Xu, Wenbo Ma, Shijun Guo, Ziyi Zhang, Quansheng Wu, Xianmin Zhang, Xiuliang Yuan, Youguo Shi
Statistical Mechanics
Spontaneous breaking of a continuous symmetry at a non-conformal quantum critical point in one dimension
R. Flores-Calderón and M. Zündel
In this work, we present numerical evidence for the spontaneous breaking of a continuous $U(1)$
symmetry in a nearest-neighbor interacting
spin-1 chain at a
quantum critical point separating two XY quasi-long-range ordered phases distinguished by a spontaneously broken $\mathbb{Z}_2$
symmetry. Remarkably, the continuous
symmetry breaking emerges precisely at the critical point of the discrete order parameter, suggesting a novel mechanism beyond currently established scenarios. At criticality, the XY correlations develop true long-range order, accompanied by a finite perpendicular magnetization, a zero-frequency Bragg peak in the transverse dynamical structure factor, and sharp gapless collective excitations. From complementary static and dynamical observables, we quantitatively determine the critical exponents, obtaining a dynamical exponent $z=1.50\pm0.04$ and an anomalous dimension $\eta=1.04\pm0.03$. We further show that the non-interacting continuum limit is equivalent to the recently introduced transverse
quantum fluid, displaying their off-diagonal long-ranged order in one dimension. Complementing the numerical study, we derive the renormalization-group flow equations of the continuum theory to second order in the $\varepsilon$ expansion. We identify an interacting fixed point whose critical behavior differs from the Ising universality class already at two-loop order, although the perturbative exponents remain far from the numerical values.
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Strongly Correlated Electrons
Magnetization plateau and anisotropic magnetoresistance in the frustrated Kondo-lattice compound Ce3ScBi5
Zhongchen Xu, Yaxian Wang, Cuiwei Zhang et al. (+6 more)
Kondo metals with
geometric frustration offer fertile ground for exploring exotic states of matter with a field-induced fractional magnetization platform and nonsaturating magnetoresistance. Herein, a Ce3ScBi5 single
crystal with anti-Hf5Sn3Cu hexagonal structure was successfully synthesized via the bismuth self-flux method, leading to the formation of cerium cations arranged in a frustrated structure within a distorted kagome
lattice.
Magnetic measurements exhibit two distinct
antiferromagnetic transitions at 4.1 and 5.9 K. Specifically, the occurrence of multiple metamagnetic transitions between magnetization plateaus is evidenced upon applying
magnetic fields perpendicular to the c axis. Transport measurements highlight remarkable Kondo-
lattice characteristics and anisotropic magnetoresistance in Ce3ScBi5. The anomalous
Hall contributions are observed at low temperatures under critical fields, suggesting
Fermi surface reconstruction in a subset of the metamagnetic transitions. We have constructed a temperature-field phase diagram to provide comprehensive information on the complex
magnetic structures arising from competitive interactions. Our work establishes Ce3ScBi5 and related materials as a unique platform for exploring low-dimensional
quantum fluctuations in bulk
crystals, and analyzes the critical role of
geometric frustration in Kondo and Ruderman-Kittel-Kasuya-Yosida physical frameworks.
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All authors Zhongchen Xu, Yaxian Wang, Cuiwei Zhang, Hongxiong Liu, Xin Han, Liusuo Wu, Xianmin Zhang, Quansheng Wu, Youguo Shi
Superconductivity
Stability, electronic disruption, and anisotropic superconductivity of hydrogenated trilayer metal tetraborides (MB$_{4}$H; M=Be, Mg, Ca, Al)
Jakkapat Seeyangnok, Udomsilp Pinsook and Graeme J. Ackland
The discovery of superconductivity in MgB$_2$ (\(T_c = 39\) K) \cite{nagamatsu2001superconductivity} established metal diborides (MB$_2$) as a promising class of conventional
superconductors. Recent advances in fabrication techniques have enabled the synthesis of 2D MgB$_2$ with a \(T_c\) of 36 K \cite{cheng2018fabrication}, reigniting interest in layered metal borides. This has led to predictions of superconductivity in various 2D metal borides, including MB$_4$ (M = Be, Mg, Ca, Al), with CaB$_4$ exhibiting the highest estimated \(T_c\) of 36.1 K. To explore the impact of hydrogenation on superconductivity, we systematically investigate two-dimensional hydrogenated trilayer metal borides (MB$_4$H; M = Be, Mg, Ca, Al). Our results reveal that these materials retain a metallic nature dominated by boron \(p\)-orbitals, while hydrogenation significantly alters their band dispersion and
Fermi surface
topology.
Phonon calculations confirm their dynamical stability and reveal strong electron-
phonon interactions, leading to multi-gap superconductivity. Among the studied compounds, MgB$_4$H, AlB$_4$H, and CaB$_4$H exhibit possible two superconducting gaps, with CaB$_4$H showing the strongest electron-
phonon coupling, resulting in an intrinsic superconducting transition temperature of 64 K. In contrast, AlB$_4$H shows the weakest coupling, with \(T_c = 22\) K. The calculated electron-
phonon coupling constants (\(\lambda\)) range from 0.62 to 0.99, demonstrating the tunability of superconducting properties through elemental substitution. These findings provide valuable insights into superconductivity in hydrogenated metal borides and highlight their potential for high-\(T_c\) applications.
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Statistical Mechanics
Control and optimisation of irreversible processes in non-equilibrium systems
Antonio Patrón Castro
This thesis is devoted to the study of physical systems embedded within the field of non-
equilibrium statistical mechanics. Specifically, the state of the systems of interest constitutes a
stochastic process that can be externally driven by a set of controllable parameters. On the one hand, for systems in contact with a thermal bath, we have studied the emergence of strong
memory effects and glassy behaviour upon varying the bath temperature, and how these are related to the existence of non-
equilibrium attractors governing the dynamics. On the other hand, for overdamped harmonic systems, we have studied the problem of minimising the connection time between arbitrary stationary (either
equilibrium or non-
equilibrium) states, by suitably varying either the bath temperature or the stiffnesses of the potential.
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Materials Science
High-throughput, Non-Destructive, Three-Dimensional Imaging of GaN Threading Dislocations with in-Plane Burgers Vector Component via Phase-Contrast Microscopy
Yukari Ishiakwa, Ryo Hattori, Yongzhao Yao et al. (+2 more)
We demonstrate a nondestructive, high-throughput method for observing dislocations in GaN (0001) using phase-contrast microscopy (PCM). The PCM images (359x300 $\mu$m$^2$) analyzed in this study were acquired with an exposure time of 3 ms per image. The one-to-one correspondence between threading dislocation (TD) contrasts in PCM images and the corresponding contrasts in multiphoton excitation photoluminescence (MPPL) images provides clear evidence that PCM can detect TDs with in-plane Burgers vector components. The contrast shape in PCM reflects the inclination of dislocations with respect to the surface normal: dot contrasts correspond to vertical dislocations, whereas line contrasts correspond to inclined dislocations. By shifting the focal plane from the top surface to the back surface, the three-dimensional propagation paths of dislocations can be visualized. The PCM image obtained represents a projection of threading dislocations within a thickness of approximately 43 $\mu$m. Dislocations spaced as close as 1.3 $\mu$m can be individually resolved. In addition, the capability of PCM to detect scratches, subsurface scratches, facet boundaries, and voids was demonstrated. This study establishes PCM as a versatile and laboratory-accessible technique for three-dimensional, nondestructive characterization of dislocations and other defects in wide-bandgap
semiconductors.
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All authors Yukari Ishiakwa, Ryo Hattori, Yongzhao Yao, Daiki Katsube, Koji Sato
Materials Science
High-speed, High-Resolution, Three-Dimensional Imaging of Threading Dislocations in beta-$Ga_{2}O_{3}$ via Phase-Contrast Microscopy
Yukari Ishiakwa, Daiki Katsube, Yongzhao Yao et al. (+2 more)
This study presents a nondestructive, high-resolution method for three-dimensional imaging of threading dislocations in beta-$Ga_{2}O_{3}$ (010) using phase-contrast microscopy (PCM). A one-to-one correspondence between dislocation contrasts in PCM images and synchrotron X-ray topography (SR-XRT) images confirms the detection capability of PCM. Compared to SR-XRT, PCM provides enhanced spatial resolution, enabling the distinction of closely spaced dislocations with sub-10-micrometer separation. PCM facilitates direct visualization of dislocation propagation paths along the depth (z) direction by systematically shifting the focal plane into the
crystal. In addition, the projection of stacked PCM images enables in-plane (XY) tracing of dislocation lines, providing insight into the preferred slip systems in beta-$Ga_{2}O_{3}$. This work establishes PCM as a versatile and laboratory-accessible technique for three-dimensional, nondestructive characterization of dislocations across entire wide-bandgap
semiconductor wafers within a practically acceptable time frame.
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All authors Yukari Ishiakwa, Daiki Katsube, Yongzhao Yao, Koji Sato, Kohei Sasaki
Superconductivity
Higher-order topological superconductivity in type-II time-reversal-symmetric Weyl semimetals with a hybrid pairing
Junkang Huang, Z. D. Wang and Tao Zhou
We employed the self-consistent method on a two-orbital type-II time-reversal-symmetric Weyl semimetal, revealing a hybrid pairing of singlet $s$-wave and triplet $p$-wave. We present a detailed analysis of the normal-state electronic structure and the self-consistent results. Our findings indicate that the selection of hybrid pairings is governed by distinct surface
Fermi-arc configurations: specifically, $s$-wave pairing dominates on the bottom surface, while $p$-wave pairing prevails on the top. Furthermore, the emergent superconducting state is a second-order topological
superconductors with hinge states in the system. Our results identify type-II time-reversal-invariant Weyl semimetals as a promising intrinsic platform for realizing unconventional and topological superconductivity.
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Materials Science
AC magnetometry of van der Waals magnets using ultrasensitive Graphene Hall sensors
Eugene Park, Jihoon Keum, Ji-Hwan Baek et al. (+5 more)
Probing the dynamical
magnetic properties of two-dimensional (2D) materials requires sensitive techniques capable of detecting small
magnetic fields from nanoscale samples. We demonstrate quantitative AC and DC magnetometry of a
ferromagnetic Fe3-xGeTe2 nanoflakes using ultrasensitive
graphene Hall sensors. These devices achieve record-low
magnetic field detection noise at both cryogenic and room temperature, enabled by hBN encapsulation, low-resistance fluorographene contacts, and a novel fabrication process. We perform quantitative AC susceptibility measurements up to 1 kHz, resolving both real and imaginary components with nanotesla-scale sensitivity and milliradian phase accuracy, the first such measurement in a van der Waals magnet. Our results establish
graphene Hall sensors as a powerful and broadly applicable platform for studying
magnetic and superconducting phases near the 2D limit.
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All authors Eugene Park, Jihoon Keum, Ji-Hwan Baek, Hyuncheol Kim, Kenji Watanabe, Takashi Taniguchi, Gwan-Hyoung Lee, Je-Geun Park
Materials Science
MicroEvoEval: A Systematic Evaluation Framework for Image-Based Microstructure Evolution Prediction
Qinyi Zhang, Duanyu Feng, Ronghui Han et al. (+2 more)
Simulating microstructure
evolution (MicroEvo) is vital for materials design but demands high numerical accuracy, efficiency, and physical fidelity. Although recent studies on deep learning (DL) offer a promising alternative to traditional solvers, the field lacks standardized
benchmarks. Existing studies are flawed due to a lack of comparing specialized MicroEvo DL models with state-of-the-art spatio-temporal architectures, an overemphasis on numerical accuracy over physical fidelity, and a failure to analyze error propagation over time. To address these gaps, we introduce MicroEvoEval, the first comprehensive
benchmark for image-based microstructure
evolution prediction. We evaluate 14 models, encompassing both domain-specific and general-purpose architectures, across four representative MicroEvo tasks with
datasets specifically structured for both short- and long-term assessment. Our multi-faceted evaluation framework goes beyond numerical accuracy and computational cost, incorporating a curated set of structure-preserving metrics to assess physical fidelity. Our extensive evaluations yield several key insights. Notably, we find that modern architectures (e.g., VMamba), not only achieve superior long-term stability and physical fidelity but also operate with an order-of-magnitude greater computational efficiency. The results highlight the necessity of holistic evaluation and identify these modern architectures as a highly promising direction for developing efficient and reliable surrogate models in data-driven materials science.
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All authors Qinyi Zhang, Duanyu Feng, Ronghui Han, Yangshuai Wang, Hao Wang
Statistical Mechanics
Introduction to the Modern Theory of Bose-Einstein Condensation, Superfluidity, and Superconductivity
Phil Attard
The modern theory of Bose-Einstein condensation, superfluidity, and superconductivity is reviewed. The thermodynamic principle for superfluid flow and the equation of motion for condensed
bosons are given. Computer simulations of Lennard-Jones $^4$He give the $\lambda$-transition and the superfluid viscosity. The statistical mechanical theory of high-temperature superconductivity is presented. Critical comparison is made with older approaches, such as ground energy state condensation, irrotational superfluid flow, and the macroscopic wavefunction.
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