Materials Science
Pressure induced structural transitions, coordination crossover, and optoelectronic response in divalent metavanadate CaV$_2$O$_6$
Bhagyashri Giri, Asish Kumar Mishra, Bidisha Mukherjee et al. (+3 more)
High-pressure synchrotron X-ray diffraction, Raman spectroscopy, photoluminescence (PL), and UV-Vis absorption measurements were carried out on the divalent metavanadate CaV$_2$O$_6$ up to 31 GPa at room temperature. Ambient CaV$_2$O$_6$ crystallizes in a centrosymmetric pseudo-brannerite monoclinic structure ($C2/m$), where vanadium atoms reside in fivefold-coordinated VO$_5$ trigonal bipyramids. Under hydrostatic compression, the system undergoes a structural phase transition starting at $\sim$1 GPa to a lower-
symmetry, non-centrosymmetric monoclinic phase ($C2$), which becomes the single stable phase above 5.2 GPa. This transition involves an increase in vanadium coordination from VO$_5$ bipyramids to edge-sharing distorted VO$_6$ octahedra. High-pressure Raman scattering corroborates the structural phase boundaries, exhibiting mode softening ($\gamma_3 = -0.42$, $\gamma_9 = -0.46$) within the mixed-phase regime (1.0 - 4.4 GPa) and sharp anomalies in mode frequencies and linewidths across 5.2 GPa. The optical measurements show complete PL quenching near 1 GPa due to non-radiative recombination pathways introduced by local polyhedral distortions, alongside a non-monotonic
evolution of the indirect optical band gap. Above 20 GPa, an anomaly in polyhedral distortion and internal strain drives an isosymmetric structural modification within the $C2$ phase, marked by an alteration in bulk compressibility and stabilization of the optical gap. Comparative high-pressure band-gap measurements on the sister compound MgV$_2$O$_6$ validate the explicit coupling between cation coordination changes and optoelectronic response in divalent metavanadates.
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All authors Bhagyashri Giri, Asish Kumar Mishra, Bidisha Mukherjee, Debabrata Samanta, Nico Giordano, Goutam Dev Mukherjee
Soft Condensed Matter
Ideal gas of active particles in a box
Siran Li, Ralf Eichhorn and Lennart Dabelow
Extending a fundamental concept of thermodynamics to the nonequilibrium realm of active matter, we derive an ideal gas law for a suspension of noninteracting active particles confined to a finite rectangular box. The law is exact for run-and-tumble particles (RTPs) in one dimension and established by a systematic analytical expansion of the steady-state probability density for active Ornstein-Uhlenbeck particles in any dimension. It also agrees well with numerical results for active Brownian particles and RTPs in higher dimensions and recovers previously known relations for the limit of large system sizes. Together, these results demonstrate the applicability of the ideal active gas law to the three most widely studied theoretical models of colloidal active matter. As an application, we analyze thermodynamic processes involving active matter on a macroscopic level, without recourse to microscopic particle trajectories or self-propulsion fluctuations.
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Soft Condensed Matter
Inclined surfaces bias bacterial swarming expansion and edge organization
Pengxi Gu, Zixiang Lin, Hui Ren et al. (+5 more)
Bacterial swarming is the collective expansion of dense populations of motile
cells across hydrated soft surfaces, yet
gravity is usually treated as a fixed background condition in standard horizontal assays. We used surface inclination to examine how agar-surface orientation relative to
gravity affects the expansion of Enterobacter sp. SM3 swarms. Colony expansion depended non-monotonically on inclination, with the strongest spreading at intermediate inclinations and weaker expansion under shallow or near-inverted conditions. Paired up-facing acute and down-facing obtuse configurations with the same tilt magnitude showed different expansion responses, suggesting that swarm expansion depended on both tilt magnitude and which side of the agar surface faced upward relative to
gravity. Inclination also produced downhill-biased colony morphologies. PIV analysis showed generally lower mean activity under inclination than in the flat references, with a non-monotonic angular response and inward increases in speed and spatial velocity-correlation length. The downhill tip showed slower motion, shorter spatial correlations and smaller
vortex cores than the upper region. To interpret the macroscopic trends, we extended a two-phase thin-film model by introducing an effective
gravity coupling projected normal and tangential to the agar surface. Simulations suggest that the surface-tangential component mainly drives lateral redistribution, whereas the surface-normal component modifies film pressure and thereby pressure-dependent water replenishment, helping distinguish up-facing from down-facing configurations.
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All authors Pengxi Gu, Zixiang Lin, Hui Ren, Jin Zhu, Anqi Li, Omar Said, Weijie Chen, Zijie Qu
Statistical Mechanics
Work fluctuation speed limit in boundary conformal field theories
Shihao Xia, Ahsan Nazir and Harry J. D. Miller
We explore the fundamental limits on finite-time driving in
quantum critical systems described by boundary conformal field theory. We show that
stochastic work fluctuations arising from external driving are a resource for speedy control, and derive an exact, saturable fluctuation-based speed limit in weakly driven boundary conformal field theories at finite temperature. The bound and saturating protocol can be expressed entirely in terms of the universal scaling dimension, and the result interpolates between the Kibble–Zurek regime,where temporal correlations are strongly nonlocal, and an adiabatic regime where linear driving becomes optimal. For small scaling dimension, the enhanced temporal correlations produce pronounced departures from linear protocols and a larger optimization advantage. These results establish a universal work precision–time tradeoff for boundary-critical control, applicable to
quantum impurity, fractional
quantum Hall, and superconducting-
circuit platforms.
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Mesoscale and Nanoscale Physics
Composite fermions in ideal Chern bands
Songyang Pu, Liangtao Peng and Shaffique Adam
The composite-
fermion framework maps the strongly correlated fractional
quantum Hall state onto a weakly interacting integer
quantum Hall state in a reduced effective
magnetic field. We ask how this framework is modified for fractional Chern
insulators, where the role of a uniform
magnetic field is replaced by the nonuniform Berry
curvature of a Chern band. Specifically, we construct composite-
fermion wave functions for Jain states and their quasiparticles and quasiholes in Aharonov-Casher bands, a widely used model for ideal Chern bands. We find that these states overlap closely with exact eigenstates over a broad range of field modulation. Using these wave functions, we demonstrate that the emergent composite-
fermion band structure goes beyond the conventional picture of effective Landau levels, correctly capturing the quasiparticle dispersion. Remarkably, we find that an isolated quasiparticle band carries a total Berry flux that is different from a Landau level. These results establish a composite-
fermion description for mobile fractional Chern
insulator anyons and provide a framework to understand their stability.
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Quantum Gases · Cross-listed from quant-ph
Fermionic Gaussian Scrooge Ensembles in Deep Thermalization
Ning Sun and Pengfei Zhang
Measuring part of a many-body wave function generates a projected ensemble of pure
quantum states on the unmeasured subsystem. Recent advances in deep thermalization have shown that, in chaotic systems, this ensemble universally converges to the maximally random ensemble compatible with its average density
matrix, known as the Scrooge ensemble. By contrast, free-
fermion systems are nonchaotic, and their
quantum states are constrained to remain Gaussian. Motivated by this distinction, we introduce the fermionic Gaussian Scrooge ensemble to describe deep thermalization in generic free-
fermion systems. This ensemble is defined as a distortion of the Gaussian Haar ensemble by the average density
matrix, and its moments reveal an enlarged
symmetry of Gaussian states in the replicated
Hilbert space. We demonstrate the emergence of the fermionic Gaussian Scrooge ensemble in two complementary settings: (1) we analytically prove that the projected ensemble of the SYK$_2$ model follows the fermionic Gaussian Scrooge ensemble at arbitrary
evolution times; (2) we provide numerical evidence that it emerges at sufficiently long times in random Gaussian
circuits with charge conservation. Our results establish the fermionic Gaussian Scrooge ensemble as a universal description of deep thermalization in free-
fermion systems.
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Mesoscale and Nanoscale Physics
Phonon interference induced by defect pairs
Ran-Bo Yang, Ming-Hao Li, Chun-Yu Cai et al. (+4 more)
The coherent dynamics of
lattice waves is of significant importance for exploring the nonadiabatic phenomena of the electron-
phonon coupling under nonequilibrium conditions. Here, we propose a theoretical model for
phonon interference induced by a defect pair, in which
lattice waves with the selective modes are launched independently by each of defects due to the strongly local electron-
phonon coupling. We find that the intensities of
phonon interference fringes could be directly evaluated by a measurable quantity in experiments–Huang-Rhys factor, and the geometry of interference patterns could be modified by the internal parameters of defect pair, including the charge states, spatial distance, energy-level depth and localization strength. In particular, several novel
quantum states, such as the Dirac-like and nodal-line topological states are emerged for the appropriate internal parameters. Furthermore, using Huang-Rhys model, we simulate the ultrafast optical spectroscopy in the
phonon interference duration when defect pairs are excited as the color centers, where interference fringes are perfectly matched by intensities of spectrum, similar to the $\textit{lock-key}$ pattern. These results show that defect pair, serving as the driven force for the coherent dynamical processes for multidegrees of freedom, offers an ideal platform to explore fundamental
quantum phenomena in nonequilibrium and ultrafast physics.
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All authors Ran-Bo Yang, Ming-Hao Li, Chun-Yu Cai, Yue-Wen Wang, Zhi-Qing Li, Li-Xia Zhao, Zi-Wu Wang
Mesoscale and Nanoscale Physics
Synthesis of Metal-Semiconductor Heterojunctions in Single Graphene Nanoribbons
Ziyi Wang, Kaitlin Slicker, Weichen Tang et al. (+9 more)
Graphene nanoribbons (GNRs) are a highly tunable class of one-dimensional (1D)
quantum materials that can be fabricated through bottom-up synthesis. Precise control over GNR band gaps and band-edge
alignments has established them as a promising nanoelectronics platform, but forming high-quality electronic interfaces remains challenging. Here we combine sequential on-surface synthesis and scanning tunneling microscopy (STM)-induced dehydrogenation to directly write metallic 7-iGNR segments into otherwise semiconducting H$_2$-7-iGNRs without changing the GNR width or carbon backbone connectivity. The resulting metallic segments exhibit nonzero spectral weight at the Fermi level ($E_\mathrm{F}$) and spatially extended electronic states, consistent with two dispersive bands crossing $E_\mathrm{F}$. The new metallic states are well described by an extended Su–Schrieffer–Heeger zigzag-ladder
Hamiltonian. Scanning tunnelling spectroscopy (STS) and first-principles calculations show that the valence band edge of adjacent, connected semiconducting GNR segments lies close to $E_\mathrm{F}$ for the metallic segments. STS spectra recover bulk GNR properties within $\sim$1 nm on either side of the metal-
semiconductor GNR interface, with no discernible depletion region. The observed GNR band edge
alignment is consistent with a small energy barrier for hole injection, thus suggesting a possible route towards atomically precise, low-barrier p-type contacts for future GNR-based electronic devices.
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All authors Ziyi Wang, Kaitlin Slicker, Weichen Tang, Boyu Qie, Rafal Zuzak, Haowen Pang, Yudi Huang, Xinheng Li, Peter H. Jacobse, Steven G. Louie, Felix R. Fischer, Michael F. Crommie
Statistical Mechanics · Cross-listed from quant-ph
Rapid mixing of quantum spin chains at any finite temperature
Leeseok Kim
We prove that a quasi-local
quantum Gibbs sampler rapidly mixes to the Gibbs state of any 1D finite-range
Hamiltonian at all finite temperatures in $\mathcal{O}\left(\log (n/\varepsilon)\right)$ time. Each update traces out a contiguous block of constant length and reconstructs it using the Petz recovery map, following early proposals for
quantum heat-bath Gibbs samplers by Kastoryano and Brandão~\cite{kastoryano2016
quantum}. Our proof directly bounds the distance between the updated state and the target Gibbs state using
quantum Wasserstein distance of order $1$. We further provide $\mathcal{O}(\text{polylog}(n/\varepsilon))$ depth of
quantum circuits to prepare these Gibbs states. We hope these techniques will facilitate the analysis and design of other Gibbs samplers.
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Materials Science
Additive solid immersion lenses for enhanced collection efficiency of shallow NV centers by pulsed laser deposition and structurization of high-k amorphous oxides
Michael S. Bar, Nicole Raatz, Max Kneiss et al. (+3 more)
The negatively charged nitrogen-vacancy ($\mathrm{NV}^-$) defect in diamond can be used for
quantum information processing via the readout of the radiative decay of the excited state into the ground state. The large refractive index mismatch of diamond and air causes low
photon extraction efficiency due to total internal reflection losses. Here, we investigate the
photon extraction numerically and report additive solid immersion lenses (SILs) consisting of the high-k dielectric yttria-stabilized-zirconia (YSZ) for surface modification and enhanced light extraction of shallow implanted nitrogen-vacancy centers. We demonstrate an average increase of 63% in saturation intensity using a scalable bottum up room temperature pulsed
laser deposition and photolithography structurization process. The average necessary
laser intensity for saturation is reduced by 33% by the SILs.
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All authors Michael S. Bar, Nicole Raatz, Max Kneiss, Andreas Koenig, Marius Grundmann, Holger von Wenckstern
Statistical Mechanics
Dynamical Critical Properties of the Random-Bond three-state Potts Model
Zeynep Demir Vatansever, Ulvi Kanbur, Mohammed Sadra Najafi et al. (+2 more)
We study the dynamic critical behavior of the two-dimensional random-bond three-state Potts model using large-scale Monte Carlo simulations with the Wolff and Swendsen–Wang cluster
algorithms. At the disorder-dependent critical temperature, we compute integrated and exponential autocorrelation times and extract the dynamic critical exponent $z$ via finite-size scaling. Critical slowing down is significantly weakened by bond randomness, with the dynamic exponent decreasing from $z \approx 0.54$ in the pure system to $z \approx 0.24$ at strong disorder. From the finite-size scaling of the Wolff cluster size, we obtain $\gamma/\nu \approx 1.73$, where $\gamma$ and $\nu$ are the susceptibility and correlation-length exponents, respectively, consistent with the universality class of the two-dimensional three-state Potts model. These results indicate that bond randomness strongly affects the critical dynamics but leaves the underlying static universality class unchanged. Furthermore, both static and dynamic observables, including the specific heat and the autocorrelation times, show a lack of self-averaging.
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All authors Zeynep Demir Vatansever, Ulvi Kanbur, Mohammed Sadra Najafi, Muktish Acharyya, Erol Vatansever
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Vector chiral order and dynamical quantum phase transitions in an Ising chain with dimerized anisotropic Gamma interaction
Yu-Hong Yan, Shi-Qiao Wu and Kun-Liang Zhang
We investigate a transverse-field Ising chain with dimerized anisotropic Gamma interactions and demonstrate that, both in the absence and presence of Ising interactions, the competition between Gamma anisotropy and the transverse field gives rise to vector chiral order and dynamical
quantum phase transitions. The phase diagram comprises positive and negative vector chiral phases and a paramagnetic phase, characterized by the vector
spin chirality and the vector chiral order parameter. In the absence of Ising interactions, we identify a gapless critical line that exhibits no finite-size drift, along which the
spin-
spin correlations and subsystem
entanglement entropy display behavior distinct from that of Ising criticality. Furthermore, we find that the critical times of dynamical
quantum phase transitions form periodic or aperiodic sequences, depending on the quench path. Our findings highlight how dimerized off-diagonal exchange enriches both
equilibrium ordering and dynamical critical behavior in a
quantum Ising chain.
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Mesoscale and Nanoscale Physics
Nutational Spin Pumping and Dissipation
Hans Gløckner Giil and Arne Brataas
At terahertz drive frequencies, magnetization dynamics enter an inertial regime beyond the scope of standard Landau-Lifshitz-Gilbert (LLG) theory. We reveal a nutational damping torque comprising a bulk term and an interfacial contribution that describes
spin emission into adjacent metals. The interfacial term generates nutational
spin pumping: a dc
spin current that scales quadratically with the drive frequency. Using a scattering approach, we relate this effect to microscopic material parameters and predict pronounced enhancements in ultrathin films and low-Fermi-energy conductors. Nutational
spin pumping can be detected directly via the inverse
spin Hall effect or indirectly via thickness-dependent renormalization of nutational damping.
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Quantum Gases · Cross-listed from nucl-th
Microscopic Insights into the Quarkyonic Hadron–Quark Crossover: Lessons from Ultracold Fermi Gases
Hiroyuki Tajima
In
neutron-
star and dense
quantum chromodynamics (QCD) physics, it is important to understand how baryonic matter evolves into
quark matter at high density. A continuous
hadron–
quark crossover is one of the most attractive candidates because it can reconcile the comparatively soft equation of state around nuclear density with the rapid stiffening required to support massive
neutron stars. Recent
neutron-
star observations motivate equations of state that stiffen rapidly across the intermediate-density regime, while quarkyonic-matter descriptions feature a shell-like baryon momentum distribution there. In this paper, we review our recent work on the microscopic description and interpretation of these phenomena by drawing an analogy with the Bose–Einstein condensate (BEC) to Bardeen–Cooper–Schrieffer (BCS) crossover in ultracold Fermi gases and two-color QCD. As pairing fluctuations play a crucial role in the BEC–BCS crossover, we discuss the role of its three-body counterpart, that is, tripling fluctuations associated with baryon formation in the
hadron–
quark crossover. In terms of a phase-shift representation of tripling fluctuations, the interplay between a three-body bound-state pole and the scattering continuum suppresses low-momentum baryonic occupation, generates a baryonic momentum shell, and reduces the density susceptibility, thereby producing a peak in the speed of sound. We review the demonstration of this mechanism in a one-dimensional three-component Fermi gas, its relativistic extension, and its connection to phenomenological quarkyonic equations of state.
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Statistical Mechanics · Cross-listed from quant-ph
Dissipation-Sensitivity Trade-Off in Dissipative Bosonic Systems
Kohei Yoshimura and Ryusuke Hamazaki
We discover a universal trade-off between the dissipation required to maintain a
quantum state more sensitive than a thermal one and the sensitivity gain for a driven single-mode bosonic system under a thermal environment. Specifically, for Gaussian states, we rigorously derive a lower bound on the
entropy production rate in the steady state in terms of the
quantum Fisher information gain relative to a thermal reference state. Numerical investigations of Kerr nonlinearities further support that these bounds can hold beyond the Gaussian regime. Our results establish a new connection between steady-state thermodynamics and
quantum metrological performance.
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Mesoscale and Nanoscale Physics
Gate Dispersive Charge Detection in Ge/SiGe Quantum Dots
M.R. Tanvir, E. Sajadi, M. Veldhorst et al. (+2 more)
Spin qubits are an attractive platform for scalable
quantum information processing, and recently, laterally gated
quantum dots (QDs) in Ge
heterostructures have emerged as a leading implementation of
spin qubits. To date, RF single-hole transistors (SHT) and integrated superconducting resonators have been used for
spin and charge readout, but their size can pose challenges. Here we demonstrate compact RF gate-dispersive charge readout of a Ge double QD (DQD), and a single hole box (SHB)-DQD system. We resolve QD loading and interdot transitions with both techniques. We find that the SHB enhances the interdot signal-to-noise ratio (SNR) of our 540 MHz
circuit by a factor of 20 for a DQD coupling $t_c \approx 5$ GHz, providing a unity-SNR at 135 microseconds, c.f. for 2.7 miliseconds for the direct detection. Power- and temperature-dependent measurements verify that SNR is limited by dielectric loss which compromises impedance matching. These results establish a compact readout approach based on gate-dispersive detection for Ge/SiGe
heterostructure QDs.
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All authors M.R. Tanvir, E. Sajadi, M. Veldhorst, G. Scappucci, J. Salfi
Statistical Mechanics
Effects of on-site Gaussian disorder in the ferromagnetic Blume Capel model
Kimberly J. Silverman, Daria Lhommedieu, Alykhan Rajan et al. (+3 more)
We conduct a numerical study of a generalization of the Blume-Capel model in which the
crystal field $D_i$, which controls the local vacancy density, is site dependent rather than uniform. We employ Markov Chain Monte Carlo to compute the shifted phase transition line $T_c$ as a function of the width $\sigma$ of a gaussian distribution $P(D_i) \sim \exp( -(D_i - \bar{D})^2/2 \sigma^2)$ at fixed $\bar{D}$. We characterize how the presence of this on-site Gaussian disorder reduces $T_c$ across the second order transition line, and discuss how our results suggest that $T_c$ remains finite even at large values of $\sigma$. We also determine the effects of disorder on the tricritical point of the conventional, uniform, Blume-Capel model, finding that it significantly suppresses the first-order phase transition, eliminating it entirely at large values of $\sigma$.
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All authors Kimberly J. Silverman, Daria Lhommedieu, Alykhan Rajan, Kathryn A. Cooper, Richard T. Scalettar, Eduardo Ibarra-García-Padilla
Mesoscale and Nanoscale Physics
Charge and spin dynamics in spintronic THz emitters from Time-Dependent Density Functional Theory
Ali Kefayati
Spintronic terahertz (THz) emitters based on ferromagnet/heavy-metal
heterostructures provide efficient broadband sources of THz radiation, yet the microscopic relation between ultrafast
spin transport and charge redistribution remains incompletely understood. Here, we employ time-dependent density functional theory to resolve the coupled charge,
spin, and magnetization dynamics of Co/Pt and Co/W bilayers in real time and space. Despite qualitatively similar interlayer
spin-current dynamics, the two
heterostructures exhibit markedly different interlayer charge transfer: Co/Pt shows a relatively small and partially reversed transfer from Pt to Co, whereas Co/W exhibits a larger and persistent transfer from Co to W. We trace these differences to the material-dependent ground-state electronic structure and the
spin- and orbital-resolved phase space accessible to photoexcited carriers.
Spin-resolved dynamics further reveal coexisting
spin-orbit-mediated redistribution and optically induced intersite
spin transfer, including a delayed minority-
spin transfer from the heavy metal to Co common to both systems. While net electronic
spin angular momentum is transferred between the layers, we find no corresponding net transfer of electronic orbital angular momentum. In Co/W, the persistent redistribution of electronic density from interstitial to atom-centered states additionally provides strong evidence for light-induced electronic localization. These results demonstrate that ultrafast
spin transport does not uniquely determine charge or angular-momentum redistribution in spintronic THz emitters, which instead depends critically on the material-specific electronic phase space.
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Materials Science
Topo-Spectral Percolation Descriptors for Mechanistic Ion Transport Pathways from Static Crystal Structures
Diptendu Roy, Chiku Parida, Juan María García-Lastra et al. (+1 more)
Ion transport controls the macroscopic performance of solid electrolytes, battery electrodes, ion-selective membranes, electrolysis ceramics, mixed conductors, porous sorbents, and biological channels. In each case, ion transport is determined by structural characteristics, namely the available
diffusion pathways and the specific bottleneck atoms that limit the ionic jumps. These are intrinsic properties of the crystalline framework, whereas temperature, carrier concentration, and correlated motion govern the transport rate. Ab initio molecular dynamics (AIMD) resolves the mechanism directly but is too costly for materials screening, and most surrogate models give only a single transport number. Here we present a calibration-free method for determining the mechanism, based on Topo-Spectral Percolation Descriptors (TSPD). TSPD obtains the transport mechanism from a single static structure in seconds. It constructs a periodic migration network whose edge barriers are computed from physics-based energetics. We then analyze the barrier-threshold
topology of this network and the spectrum of its barrier-weighted graph
Laplacian. To establish its validity for computational solid-state ionics, we test TSPD against AIMD ion densities and
neutron diffraction data for eight materials, including cathodes and solid electrolytes, whose transport ranges from one- to three-dimensional. TSPD reproduces the established mechanism in every case and correctly identifies structures in which
geometric openness does not imply viable ion percolation. The method is most informative for pathway-limited, direction-dependent transport, and it complements full dynamical simulations for strongly cooperative or nearly isotropic transport.
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All authors Diptendu Roy, Chiku Parida, Juan María García-Lastra, Arghya Bhowmik
Materials Science · Cross-listed from physics.optics
Parallax Depth Sectioning and 3D Reconstruction in 4D-STEM
Desheng Ma, Chia-Hao Lee, Zixiao Shi et al. (+2 more)
Three-dimensional (3D) information is encoded in four-dimensional scanning transmission electron microscopy (4D-STEM) through parallax between the virtual images formed at each detector pixel. In this paper we connect the encoding and
retrieval of depth-dependent information in 4D-STEM to two other widely-used 3D imaging methods,
tomography and light-field photography, and derive its 3D phase contrast transfer function. Viewing the 4D data as a collection of angular slices yields a collection of sinograms, providing an intuitive visual representation of the 3D information transfer. Within the small-angle approximation, tilt-corrected bright-field (tcBF) depth sectioning is equivalent to non-iterative tomographic reconstruction. Alternatively, the 4D data also can be mapped to light-field (or plenoptic) imaging, which acquires spatially resolved diffraction data in parallel using an array of lenslets. Adapting a light-field imaging
algorithm, we show that tcBF depth sections can be obtained by extracting two-dimensional slices from a single four-dimensional fast
Fourier transform (4D FFT) of the
dataset, yielding a substantial speedup when reconstructing a large number of depth slices. These differing perspectives distinguish the
geometric aspects of depth resolution from wave-optical effects that are present in phase-contrast imaging. Depth-resolved aberration-corrected bright-field (acBF) imaging yields improved 3D reconstructions compared to tcBF, removing contrast oscillations and reducing the variation in response with depth. We demonstrate acBF depth sectioning using simulated and experimental data and resolve distinct layers in stacked oxide films and nanoparticle assemblies. These non-iterative volumetric reconstructions from a single 4D-STEM
dataset show promise for improved imaging of thick, weakly-scattering samples and for reconstructing low-dose acquisitions.
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All authors Desheng Ma, Chia-Hao Lee, Zixiao Shi, David A. Muller, Steven E. Zeltmann
Materials Science
Landau-like formalism for the thermal-runaway and filamentation instabilities in switching Mott devices
Aniket Bajaj, Anudeep Tullibilli, Arup Basak et al. (+2 more)
Correlated oxides can switch to a low-resistance state when exposed to a voltage, making these
insulator-to-metal transition materials promising candidates for memristor technology. Switching in materials such as VO2 occurs because of a thermal-runaway instability that leads to the abrupt formation of a hot current-carrying metallic filament within the
insulator. We study, theoretically and experimentally, this bias-induced switching as a non-linear dynamics stability problem. We construct Landau free energy-like Lyapunov functions to show that both the on-state ("set") and the off-state ("reset") transitions can be described as separate saddle-node bifurcations. Starting from the reaction-
diffusion equation for the heat transport, the abrupt snap-back (reset) to the insulating state is systematically formulated as a mean field Landau-like dynamics with the filament width playing the role of the order parameter. The formulation predicts an abrupt first-order phase transition with a break-off of a finite width filament across the current-controlled reset transition. The formulation is quantitatively compared against our electrical and optical microscopy experiments on VO2 thin film devices. Multi-cycle switching dynamics experiments further reveal the emergence of a stable
stochastic regime following an initial electro-spatial forming phase. Beyond establishing a cross-disciplinary dynamical framework that may be readily compared to instabilities in various reaction-
diffusion scenarios, the work also provides a predictive foundation for the rational design and optimization of Mott-transition-based technologies.
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All authors Aniket Bajaj, Anudeep Tullibilli, Arup Basak, Pavan Nukala, Bhavtosh Bansal
Soft Condensed Matter
Anisotropic medium-range order uncovers dynamic crossovers in glass-forming liquids
Kamlesh Mishra, Rajesh Ganapathy and Walter Kob
On cooling
liquids towards their glass-transition temperature, the dramatic increase of their relaxation times is accompanied by changes in particle dynamics at two distinct temperatures: A high-T crossover, where particles become temporarily caged by their neighbors, and a low-T crossover, where the cage escape mechanism changes. While there is some evidence that the former is associated with a change in local particle arrangement, no structural modification has so far been detected across the low-T crossover, fueling scepticism about the relevance of structure for glassy dynamics. Here, we introduce a novel four-point correlation function which allows to determine a structural length scale characterizing cage anisotropy. Extensive molecular dynamics simulations reveal that this scale, as well as the mean structural length scale of the glass-former, extends into the medium range, i.e., significantly exceeds the particle size. Strikingly, the difference between these two scales - a measure of the degree of cage anisotropy - peaks at both crossover temperatures. We discuss how the presence of these peaks enables understanding the nature of the change in the microscopic transport mechanism at the two temperatures, thereby linking both dynamical crossovers to a single structural observable, the anisotropic medium-range order. This fundamental insight demonstrates that structure, extending well-beyond the local cage, is an essential ingredient for understanding the relaxation dynamics of deeply supercooled
liquids.
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Materials Science
Train for Accuracy, Execute at Scale: Architecture-Preserving Inference for Equivariant Atomistic Foundation Models
Lei Fu, Zihui Feng, Yongheng Li et al. (+8 more)
Equivariant atomistic foundation models provide broadly transferable interatomic potentials trained against
quantum-mechanical reference data, but their repeated execution at simulation scale remains computationally and
memory intensive. We present Symmetrix-XL, an inference engine that scales pretrained MACE checkpoints without retraining,
distillation, or modification of their learned weights. It combines streamed-edge execution to avoid graph-wide materialization of expanded edge intermediates, model-specialized code generation to compile checkpoint-specific operators, and tiled execution to reuse a bounded device-
memory workspace. On complete LAMMPS-step
benchmarks, Symmetrix-XL reduces inference time by 3.1-5.0 times relative to ML-IAP + cuEquivariance across tested A100 and RTX 5090 workloads. On a single A100 80 GB GPU, the tested MACE-OMAT-0 capacity boundary increases from 24,565 atoms to 11.24 million atoms. This substantially lowers the hardware threshold for simulations that would otherwise require spatial decomposition across many GPUs and compute nodes. The same backend weak-scales to 703 million atoms on 64 A800 GPUs at 93.8 percent efficiency. Energy, force, stress, molecular-dynamics stability, and Matbench Discovery evaluations reproduce reference MACE behavior within measured tolerances. Case studies spanning solid-state, interfacial, and reactive systems demonstrate the increased capacity in realistic workflows. These results establish post-training execution as a scaling axis complementary to model redesign, compression, and distributed scale-out, and show that the practical accuracy-cost frontier depends on both model architecture and inference execution.
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All authors Lei Fu, Zihui Feng, Yongheng Li, Hongwei Du, Xin He, Junyi Wu, Kejie Bao, Yueyu Zhang, Zeyu Deng, Ziheng Lu, Bonan Zhu
Superconductivity
Highly anisotropic collective modes of altermagnetic superconductors with Bogoliubov Fermi surfaces
Huaisong Zhao, Peng Zou, Xia-Ji Liu et al. (+1 more)
We investigate collective modes in charge-neutral altermagnetic
superconductors with $d$-wave
spin-split bands, focusing on the impact of emergent Bogoliubov Fermi surfaces. In the absence of a
magnetic field, the BCS state supports collective modes that inherit the underlying $d$-wave
symmetry, resulting in pronounced momentum-space anisotropy. The broken time-reversal
symmetry further couples these modes to
spin-density fluctuations, allowing their signatures to emerge in the
spin dynamical structure factor. Upon applying a
magnetic field, Bogoliubov Fermi surfaces emerge and qualitatively reshape the collective-mode dynamics through gapless particle-hole excitations and strongly anisotropic Landau damping. The damping is strongest along the momentum-space diagonal, where it can suppress the low-energy
phonon mode at small momenta. Remarkably, the suppressed
phonon is accompanied by the emergence of an in-gap structure in the
Higgs mode and an associated pronounced enhancement of the
spin response. These results establish Bogoliubov Fermi surfaces as a mechanism for generating highly anisotropic collective-mode dynamics and identify
spin response as a sensitive probe of in-gap
Higgs excitations in altermagnetic
superconductors.
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All authors Huaisong Zhao, Peng Zou, Xia-Ji Liu, Hui Hu
Materials Science
HVPE Homoepitaxy of $\beta$-Ga$_2$O$_3$: High-Temperature Growth and Orientation-Dependent Surface Evolution
Sourav Sarker, Saleh Ahmed Khan, Ahmed Ibreljic et al. (+2 more)
In this work, we systematically investigate homoepitaxial $\beta$-Ga$_2$O$_3$ growth by halide vapor phase epitaxy (HVPE) on (010), (001), and ($\bar{2}$01) native substrates over a broad growth parameter space, extending the growth temperature as high as 1150 $^\circ$C. The growth kinetics exhibit strong dependence on precursor supply, temperature, reactor pressure, and Ga-source-to-substrate distance. Increasing the HCl flow from 80 to 300 sccm enhances the growth rate by up to seven-fold, while increasing the temperature from 1050 to 1150 $^\circ$C nearly doubles the deposition rate. At 1150 $^\circ$C, atmospheric-pressure growth yields rates more than 2.5 times higher than those at 100 Torr, while reducing the O$_2$ flow to 5 sccm further increases the growth rate to 14.3 $\mu$m/h, producing films up to 42.9 $\mu$m thick in 3 h. Notably, phase-pure homoepitaxial layers with good crystalline quality are obtained across all three orientations, with low rocking-curve full width at half maximum (FWHM) values of 63.4, 66.6, and 42.8 arcsec for the (010), (001), and ($\bar{2}$01) epilayers, respectively. The surface morphology exhibits a pronounced crystallographic dependence and evolves strongly with the HVPE growth conditions. In particular, the ($\bar{2}$01) surface develops well-defined step-and-terrace morphology with local RMS roughness as low as 0.17 nm. These results extend $\beta$-Ga$_2$O$_3$ HVPE homoepitaxy into a higher-temperature regime and demonstrate a broad process window for high-rate growth of thick, high-quality epilayers with strongly orientation-dependent surface
evolution.
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All authors Sourav Sarker, Saleh Ahmed Khan, Ahmed Ibreljic, Pronoy Kanti Das, Anhar Bhuiyan
Materials Science
Layer-by-layer growth of highly aligned MoS$_2$ nanoribbon arrays
Kaichi Yamamoto, Pablo Solís-Fernández, Haiming Sun et al. (+10 more)
One-dimensional transition metal dichalcogenides (TMD) nanoribbons (NRs) offer a promising route to aggressive channel-width scaling in nanoscale transistors. However, controlling their layer number, a key determinant of device performance, has remained elusive. Here, we demonstrate a chemical vapor deposition (CVD) approach for layer-by-layer growth of MoS$_2$ NRs on a low-
symmetry sapphire surface. This approach enables the oriented growth of single-crystalline bilayer NRs with a 2H stacking configuration, while maintaining widths below 20 nm. Increasing the MoO$_3$ precursor supply was found to be crucial for promoting the growth of the second and subsequent layers. By controlling the growth time and precursor supply, the layer number of MoS$_2$ NRs can be increased up to four layers. This method can also be extended to the growth of vertical MoS$_2$/WS$_2$ hetero-NRs. The average carrier mobility and current density of bilayer NR field-effect transistors (FETs) are two- and three-times higher than those of monolayer counterparts, respectively, and a maximum mobility of 86.7 cm$^2$V$^{-1}$s$^{-1}$ was attained with a bilayer NR-FET. These results highlight layer number as a key parameter for optimizing NR device performance. Our thickness-controlled growth strategy provides a general route towards TMD NR-based transistors with enhanced scalability and performance.
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All authors Kaichi Yamamoto, Pablo Solís-Fernández, Haiming Sun, Yanlin Gao, Yeri Lee, Yushan Tseng, Aika Uchida, Masahiro Hara, Sunmin Ryu, Yung-Chang Lin, Susumu Okada, Kazu Suenaga, Hiroki Ago
Materials Science
Topological robustness of thermally disordered lattices: From average structures to ensemble electronic properties
Oleg Rubel and Karekin Sadikian
Band
topology is usually assigned to a single
crystal structure, yet at finite temperature a
crystal is an ensemble of thermally disordered configurations with a fluctuating band gap. We ask whether the thermally averaged structure is a faithful proxy for this ensemble, taking Bi$_2$Se$_3$ as a representative topological
insulator and classifying band ordering in each ab initio molecular dynamics snapshot by scaling the
spin-orbit coupling. The averaged structure fails in two ways: it misses the Rashba-like
spin splitting that instantaneous
symmetry breaking produces in individual configurations, and it substantially underestimates the band-gap renormalization, whereas a small ensemble of harmonic Monte Carlo configurations reproduces both the mean and the spread of the gap. Using a band-inversion survival probability, we find that the band inversion of Bi$_2$Se$_3$ holds in every sampled configuration up to 600 K, above which individual configurations cross into normal band ordering well before the average gap closes. Topological robustness at finite temperature is thus a property of the distribution over configurations rather than of any single structure.
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Mesoscale and Nanoscale Physics
Hydrogen plasma-assisted atomic layer epitaxy of superconducting titanium nitride
Yi-Hsun Chen, Yin-Chun Huang, Zachary Degnan et al. (+10 more)
Atomic layer deposition (ALD) offers precise, conformal control of thin-film growth and is a workhorse for
semiconductor manufacturing, but its use in superconducting
quantum circuits is constrained by the need to simultaneously control crystallinity, stoichiometry and interfacial disorder at cryogenic temperatures. Here we develop hydrogen
plasma assisted ALD to epitaxially grow superconducting titanium nitride (TiN) thin films, using a hydrogen
plasma step to modify the surface chemistry to suppress precursor-derived impurities during each deposition cycle. Synchrotron X-ray scattering reveals semi-coherent epitaxy of TiN on c-plane sapphire, with discrete crystallographic domains and minimal long-range structural disorder. Complementary X-ray spectroscopy and
neutron reflectometry show negligible oxygen-related disorder throughout the film and no substantial hydrogen incorporation. The resulting TiN films exhibit a superconducting transition at 2.2 K, a kinetic inductance of 15 pH/sq and a superconducting coherence length of 14.6 nm, comparable to the measured
crystal coherence length. These results establish hydrogen
plasma assisted ALD as a route to structurally ordered superconducting TiN thin film epitaxy and demonstrate that the nanoscale control of ALD can be extended to materials suitable for cryogenic
quantum technologies.
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All authors Yi-Hsun Chen, Yin-Chun Huang, Zachary Degnan, David Sommers, Kaijian Xing, Manjith Bose, Eduardo Solano, David Cortie, Michael Fuhrer, Julian A. Steele, Peter Jacobson, Miin-Jang Chen, Arkady Fedorov
Soft Condensed Matter
Nucleation and phase transition of spherical crystals and quasicrystals
Tiejun Zhou, Aibei Xie, Gang Cui et al. (+3 more)
We investigated the nucleation, growth, and solid-to-solid phase transition processes of spherical six-fold symmetric
crystals (C6) and ten-fold symmetric quasicrystals (DQC) using the Lifshitz-Petrich model. By combining the spherical-harmonic pseudospectral method with a nullspace-preserving saddle-point search technique, we resolved the critical
nucleus structures and phase transition pathways. Although both transitions from the homogeneous state to the ordered state involve the formation of localized critical
nuclei, their subsequent growth processes exhibit distinct modes of accommodating
geometric mismatch: C6 forms branched domain structures and persistent line defects associated with orientation and phase mismatches, whereas DQC relaxes collision-induced defects through local coordination rearrangements. The resolved DQC-to-C6 pathway proceeds through a series of metastable intermediates that progressively connect these distinct modes of mismatch accommodation. Its multi-step character reflects the coupled adjustment of local coordination and compatibility between the emerging C6 domains. These results reveal the intrinsic link between the multi-step nature of the phase transition and the distinct structural requirements for accommodating
geometric mismatch.
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All authors Tiejun Zhou, Aibei Xie, Gang Cui, Xianbo Huang, Li Peng, Kai Jiang
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Telecom-Band Optical Transitions of Erbium Atoms in Rare-Gas Solids
Evgenii Zaitsev, Alec Dinerstein, Shan Zou et al. (+6 more)
Rare-earth (RE) atoms, such as erbium (Er), have inner-shell optical transitions in the near-infrared, some of which are in the telecom bands. These transitions are largely insensitive to the host environment due to effective shielding by the filled outer shells. Cryogenic rare-gas (RG) solids, such as solid neon (Ne) and argon (Ar), combine high chemical purity with a nearly nuclear-
spin-free environment, making them attractive solid hosts for preserving optical and
spin coherence. In this work, we isolate neutral Er atoms in solid Ne and Ar at 6 K and characterize their emission by steady-state and time-resolved photoluminescence (PL) spectroscopy. In both hosts, we observe several near-infrared transitions between 1000–1500 nm, including inner-shell emission in the telecom O and E bands. The $4f \rightarrow 5d$ transition near 1299 nm forms a multiplet of narrow components, consistent with
crystal-field splitting, and decays on a microsecond timescale. The $4f \rightarrow 4f$ transition near 1437 nm shows a
matrix shift below 1 cm$^{-1}$ in both hosts. In solid Ne, its inhomogeneous linewidth is bounded by the spectrometer resolution to < 22 GHz, and its PL lifetime reaches up to 78.9 ms, close to the estimated radiative limit. Thermal annealing extends the 1437 nm lifetime in Ne and suppresses the
phonon sidebands relative to the zero-
phonon lines in Ar. These results identify RG solids as promising hosts for long-lived telecom-band Er emission and provide a foundation for future
spin-
photon interfaces and hybrid
quantum architectures.
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All authors Evgenii Zaitsev, Alec Dinerstein, Shan Zou, Charles Peretti, Yutian Wen, Wei Guo, Gregory V. Hartland, Yizhong Huang, Dafei Jin