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Physics Condensed Matter

cond-mat Watch Condensed Matter

Wednesday 5 November

Soft Condensed Matter

Microscopic model for a granular solid-liquid-like phase transition

Sébastien Aumaître and Nicolas Mujica

Forced granular matter in confined geometries presents phase transitions and coexistence. Depending on the system and forcing parameters, liquid-vapor and liquid-solid co-existing states are possible. For the solid-liquid coexistence that is observed in quasi-two-dimensional vibrated systems, both first- and second-order transitions have been reported. Experiments show that particles in the solid cluster move collectively, synchronized with the cell's vibration, in a similar way to the collect-and-collide regime observed in granular dampers. Here, we present a model that proposes a microscopic origin of this granular phase transition and co-existence. Imposing synchronicity, we model the solid cluster as an effective particle of zero restitution coefficient. In addition, we use the mechanical equilibrium between the two phases, with an equation of state validated for hard spheres relating the horizontal velocities in each phase. Balancing energy input and dissipation per unit time we obtain a global power equation, which relates the characteristic vertical and horizontal velocities to the microscopic relevant parameters (geometric and dissipation coefficients) as well as to the vibration amplitude and solid cluster's size. The predictions of the model compare quite well with our experimental results and with the experimental and dynamic simulation results reported elsewhere.
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Strongly Correlated Electrons

Competitive Orders in Altermagnetic Chiral Magnons

Congzhe Yan Zhijun Jiang Jinyang Ni and Guoqing Chang

The magnons in altermagnets exhibit chiral splitting even in the absence of spin-orbit coupling and external magnetic fields. Typically, this chiral splitting behavior can be well described by alternating isotropic spin exchanges (ISE) near the zero temperature. However, its finite-temperature dynamics, particularly when incorporating spin-orbit coupling effects, remains elusive. In this study, we reveal that, when including magnon-magnon interactions, long-range anisotropic spin exchange (ASE) can also induce chiral splitting of magnons at a finite temperature. Crucially, the chiral splitting induced by ASE competes with that arising from ISE, leading to a pronounced temperature-dependent modulation of the altermagnetic chiral splitting. Moreover, this competition is intimately connected to spin fluctuations, and can reverse the spin current driven by the band splitting as temperature increases. Our work uncovers the intrinsic competition governing collective spin excitations in altermagnets, providing new insights into their finite-temperature dynamical behavior.
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Materials Science · Cross-listed from quant-ph

Controlled growth of rare-earth-doped TiO$_{2}$ thin films on III-V semiconductors for hybrid quantum photonic interfaces

Henry C. Hammer, Caleb Whittier, Nathan A. Helvy et al. (+3 more)

Quantum photonic networks require two distinct functionalities: bright single-photon sources and long-lived quantum memories. III-V semiconductor quantum dots excel as deterministic and coherent photon emitters, while rare-earth ions such as erbium (Er$^{3+}$) in crystalline oxides offer exceptional spin and optical coherence at telecom wavelengths. Combining these systems and their functionalities via direct epitaxy is challenging due to lattice mismatch and incompatible growth conditions. Here we demonstrate low-temperature pulsed laser deposition of Er$^{3+}$-doped TiO$_{2}$ thin films directly on GaAs and GaSb substrates. Controlled surface preparation with an arsenic cap and an oxygen-deficient buffer layer enables the growth of epitaxial anatase TiO$_{2}$ (001) at 390$^{o}$C with sub-300 pm surface roughness, while avoiding interface degradation. In contrast, high-temperature oxide desorption or growth temperatures drive the transition to rough, polycrystalline rutile film, as confirmed by transmission electron microscopy. Minimal coincident interface area (MCIA) modeling explains the orientation-selective growth on GaAs and GaSb. Raman and cryogenic photoluminescence excitation spectroscopy verify the crystal phase and optical activation of Er$^{3+}$ ions. This multi-parameter growth strategy helps preserve III-V quantum dot functionality and yields smooth surfaces suitable for low-loss nanophotonic structures. Our results establish a materials platform for monolithically integrating rare-earth quantum memories with semiconductor photon sources, paving the way toward scalable hybrid quantum photonic chips.
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All authors Henry C. Hammer, Caleb Whittier, Nathan A. Helvy, Christopher Rouleau, Nabil D. Bassim, Ravitej Uppu

Materials Science

Unconventional cross sections in zinc phosphide nanowires grown using exclusively earth-abundant components

Simon Escobar Steinvall, Hampus Thulin, Nico Kawashima et al. (+8 more)

To enable lightweight and flexible solar cell applications it is imperative to develop direct bandgap absorber materials. Moreover, to enhance the potential sustainability impact of the technologies there is a drive to base the devices on earth-abundant and readily available elements. Herein, we report on the epitaxial growth of Zn3P2 nanowires using exclusively earth-abundant components, using Sn as the nanowire catalyst and Si (111) as the substrate. We observe that the nanowires exhibit a triangular cross section at lower temperatures, a pseudo-pentagonal cross section at intermediate temperatures, and a hexagonal cross section in a twin plane superlattice configuration at high temperatures and high V/II ratios. At low temperatures, the surface facets are constricted into a metastable configuration, yielding the triangular morphology due to the symmetry of the substrate, while intermediate temperatures facilitate the formation of a pseudo-pentagonal morphology with lower surface to volume ratio. The twin plane superlattice structure can only be observed at conditions that facilitate the incorporation of Sn into Zn3P2, which is needed to form heterotwins in the tetragonal structure, namely at high temperatures and high phosphine partial pressures. These findings show a clear pathway to use Zn3P2 nanowires in sustainable solar energy harvesting using exclusively earth-abundant components, as well as opening up a novel route of fabricating quantum wells inside nanowires using heterotwins.
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All authors Simon Escobar Steinvall, Hampus Thulin, Nico Kawashima, Francesco Salutari, Jonas Johansson, Aidas Urbonavicius, Sebastian Lehmann, Maria Chiara Spadaro, Jordi Arbiol, Silvana Botti, Kimberly A. Dick

Mesoscale and Nanoscale Physics

Orbital Hall effect from orbital magnetic moments of Bloch states: the role of a new correction term

Tarik P. Cysne, Ivo Souza and Tatiana G. Rappoport

We present a rigorous derivation of the matrix elements of the orbital magnetic moment (OMM) of Bloch states. Our calculations include the Berry connection term in the k-derivatives of Bloch states, which was omitted in previous works. The resulting formula for the OMM matrix elements applies to any non-degenerate Bloch states within Hilbert space. We identify two new contributions: the first restores gauge covariance for non-degenerate states, while the second, being itself gauge covariant, can provide significant quantitative corrections depending on the system under study. We examine their impact on the orbital Hall effect in two bilayer systems: a 2H transition metal dichalcogenide bilayer and a biased bilayer graphene. In both cases, these new terms reduce the orbital Hall conductivity plateau compared with results that neglect them, suggesting that multi-layered van der Waals materials may be particularly susceptible to the derived OMM corrections. Our findings may contribute to the formal understanding of electronic OMM transport and to the conceptual foundations of the emerging field of orbitronics.
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Materials Science

Learning to shine: Neuroevolution enables optical control of phase transitions

Sraddha Agrawal, Stephen Whitelam and Pierre Darancet

We address active optical steering of structural phase transitions in solids. We demonstrate that existing evolutionary reinforcement learning approaches can derive optimal time-dependent electric fields in driven dissipative classical systems far beyond the harmonic regime, enabling the stabilization of non-thermal structural phases. Our approach relies on experimentally-extractable metrics of the phase-space evolution and interpretable Fourier Neural Network surrogates of the electric field. Using this method on first-principles models, we obtain protocols stabilizing a symmetric phase in bismuth through impulsive Raman and displacive excitations with continuous and pulsed light sources in the presence of dissipation and thermal disorder. The method is gradient-free, enabling optimization loops based solely on experimental data and providing a practical route for controlling light-induced structural dynamics independently of the microscopic model of light-matter interactions.
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Mesoscale and Nanoscale Physics

Measuring non-Abelian quantum geometry and topology in a multi-gap photonic lattice

Martin Guillot, Cédric Blanchard, Martina Morassi et al. (+8 more)

Recent discoveries in semi-metallic multi-gap systems featuring band singularities have galvanized enormous interest in particular due to the emergence of non-Abelian braiding properties of band nodes. This previously uncharted set of topological phases necessitates novel approaches to probe them in laboratories, a pursuit that intricately relates to evaluating non-Abelian generalizations of the Abelian quantum geometric tensor (QGT) that characterizes geometric responses. Here, we pioneer the direct measurement of the non-Abelian QGT. We achieve this by implementing a novel orbital-resolved polarimetry technique to probe the full Bloch Hamiltonian of a six-band two-dimensional (2D) synthetic lattice, which grants direct experimental access to non-Abelian quaternion charges, the Euler curvature, and the non-Abelian quantum metric associated with all bands. Quantum geometry has been highlighted to play a key role on macroscopic phenomena ranging from superconductivity in flat-bands, to optical responses, transport, metrology, and quantum Hall physics. Therefore, our work unlocks the experimental probing of a wide phenomenology of multi-gap systems, at the confluence of topology, geometry and non-Abelian physics.
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All authors Martin Guillot, Cédric Blanchard, Martina Morassi, Aristide Lemaître, Luc Le Gratiet, Abdelmounaim Harouri, Isabelle Sagnes, Robert-Jan Slager, F. Nur Ünal, Jacqueline Bloch, Sylvain Ravets

Materials Science

Scalable Autoregressive Deep Surrogates for Dendritic Microstructure Dynamics

Kaihua Ji, Luning Sun, Shusen Liu et al. (+2 more)

Microstructural pattern formation, such as dendrite growth, occurs widely in materials and energy systems, significantly influencing material properties and functional performance. While the phase-field method has emerged as a powerful computational tool for modeling microstructure dynamics, its high computational cost limits its integration into practical materials design workflows. Here, we introduce a machine-learning framework using autoregressive deep surrogates trained on short trajectories from quantitative phase-field simulations of alloy solidification in limited spatial domains. Once trained, these surrogates accurately predict dendritic evolution at scalable length and time scales, achieving a speed-up of more than two orders of magnitude. Demonstrations in isothermal growth and in directional solidification of a dilute Al-Cu alloy validate their ability to predict microstructure evolution. Quantitative comparisons with phase-field benchmarks further show excellent agreement in the tip-selection constant, morphological symmetry, and primary spacing evolution.
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All authors Kaihua Ji, Luning Sun, Shusen Liu, Fei Zhou, Tae Wook Heo

Strongly Correlated Electrons

AI-Driven Discovery of High-Temperature Superconductors via Materials Genome Initiative and High-Throughput Screening

H. Gashmard, H. Shakeripour and M. Alaei

Inspired by nature, this study employs the Materials Genome Initiative to identify key components of HTSC superconductors. Integrating AI with high-throughput screening, we uncover crucial superconducting "genes". Through HTS techniques and advanced machine learning models, we demonstrate that Functional Convolutional Neural Networks (CNNs) ensure accurate extrapolation of potential compounds. Leveraging extensive datasets from the ICSD, the Materials Project and COD, our implemented HTS pipeline classifies superconductors, with CNN and long short-term memory (LSTM) models predicting Tc and their foundational elements. We address the scarcity of non-superconducting material data by compiling a dataset of 53,196 non-superconducting materials (DataG Non-Sc) and introduce a novel neural network architecture using Functional API for improved prediction, offering a powerful tool for future superconductor discovery. Our findings underscore the transformative potential of combining HTS with AI-driven models in advancing HTSC materials, highlighting Pu and H elements (with Tc nearly 100 K) as significant predictors of high-temperature superconductivity, suggesting their role as a crucial gene in these materials.
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Mesoscale and Nanoscale Physics

Modeling Memristor-Based Neural Networks with Manhattan Update: Trade-offs in Learning Performance and Energy Consumption

Walter Quiñonez, María José Sánchez and Diego Rubi

We present a systematic study of memristor based neural networks trained with the hardware-friendly Manhattan update rule, focusing on the trade offs between learning performance and energy consumption. Using realistic models of potentiation/depression (P/D) curves, we evaluate the impact of nonlinearity (NLI), conductance range, and number of accessible levels on both a single perceptron (SP) and a deep neural network (DNN) trained on the MNIST dataset. Our results show that SPs tolerate P/D nonlinearity up to NLI $\leq 0.01$, while DNNs require stricter conditions of NLI $\leq$ 0.001 to preserve accuracy. Increasing the number of discrete conductance states improves convergence, effectively acting as a finer learning rate. We further propose a strategy where one memristor of each differential pair is fixed, reducing redundant memristor conductance updates. This approach lowers training energy by nearly 50% in DNN with little to no loss in accuracy. Our findings highlight the importance of device algorithm codesign in enabling scalable, low power neuromorphic hardware for edge AI applications.
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Superconductivity

Vortex-Controlled Quasiparticle Multiplication and Self-Growth Dynamics in Superconducting Resonators

Joong M. Park, Martin Mootz, Richard H. J. Kim et al. (+11 more)

Even in the quantum limit, non-equilibrium quasiparticle (QP) populations induce QP poisoning that irreversibly relaxes the quantum state and significantly degrades the coherence of transmon qubits. A particularly detrimental yet previously unexplored mechanism arises from QP multiplication facilitated by vortex trapping in superconducting quantum circuits, where a high-energy QP relaxes by breaking additional Cooper pairs and amplifying the QP population due to the locally reduced excitation gap and enhanced quantum confinement within the vortex core. Here we directly resolve this elusive QP multiplication process by revealing vortex-controlled QP self-generation in a highly nonequilibrium regime preceding the phonon bottleneck of QP relaxation. At sufficiently low fluence, femtosecond-resolved magneto-reflection spectroscopy directly reveals a continuously increasing QP population that is strongly dependent on magnetic-field-tuned vortex density and absent at higher excitation fluences. Quantitative analysis of the emergent QP pre-bottleneck dynamics further reveals that, although the phonon population saturates within $\simeq$10~ps, both free and trapped QPs continue to grow in a self-sustained manner–hallmarks of the long-anticipated QP-vortex interactions in nonequilibrium superconductivity. We estimate a substantial increase of $\sim$34% in QP density at vortex densities of $\sim$ 100 magnetic flux quanta per $\mathrm{\mu m^{2}}$. Our findings establish a powerful spectroscopic tool for uncovering QP multiplication and reveal vortex-assisted QP relaxation as a critical materials bottleneck whose mitigation will be essential for resolving QP poisoning and enhancing coherence in superconducting qubits.
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All authors Joong M. Park, Martin Mootz, Richard H. J. Kim, Zhixiang Chong, Samuel Haeuser, Randall K. Chan, Liang Luo, Dominic P. Goronzy, Mark C. Hersam, Ilias E. Perakis, Akshay A Murthy, Alexander Romanenko, Anna Grassellino, Jigang Wang

Statistical Mechanics · Cross-listed from quant-ph

Temporal entanglement transition in chaotic quantum many-body dynamics

Ilya Vilkoviskiy, Michael Sonner, Qi Camm Huang et al. (+3 more)

Temporal entanglement (TE) of an influence matrix (IM) has been proposed as a measure of complexity of simulating dynamics of local observables in a many-body system. Foligno et al. [Phys. Rev. X 13, 041008 (2023)] recently argued that the TE in chaotic 1d quantum circuits obeys linear (volume-law) scaling with evolution time. To reconcile this apparent high complexity of IM with the rapid thermalization of local observables, here we study the relation between TE, non-Markovianity, and local temporal correlations for chaotic quantum baths. By exactly solving a random-unitary bath model, and bounding distillable entanglement between future and past degrees of freedom, we identify a regime where TE is extensive and reflects genuine non-Markovianity. This memory, however, is entirely contained in highly complex temporal correlations, and its effect on few-point temporal correlators is negligible. An IM coarse-graining procedure, reducing the allowed frequency of measurements of the probe system, results in a transition from volume- to {subvolume- (area or logarithmic)} law TE scaling. We demonstrate the generality of this TE transition in 1d circuits by analyzing the kicked Ising model analytically at dual-unitary points, as well as numerically away from them. This finding indicates that dynamics of local observables are fully captured by a subvolume-law IM. We provide evidence that the compact IM MPS obtained via standard compression algorithms accurately describes local~evolution.
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All authors Ilya Vilkoviskiy, Michael Sonner, Qi Camm Huang, Wen Wei Ho, Alessio Lerose, Dmitry A. Abanin

Statistical Mechanics

Quantum Inaccessibility

Ira Wolfson

Loschmidt's paradox asks why macroscopic irreversibility is universal despite the time-reversal symmetry of microscopic dynamics. We argue that irreversibility is not a property of the dynamics but of accessibility: chaotic evolution drives phase-space structure below the quantum resolution scale $\ell_\hbar$, at a critical time $t_c = \lambda^{-1}\ln(\delta_0/\ell_\hbar)$, after which the time-reversed microstate exists as a valid solution of Hamilton's equations but cannot be selected by any physically admissible operation. The mechanism operates entirely within the semiclassical regime $t_c \leq t_E$, where classical geometry is exact. This provides a dynamical resolution of the Loschmidt paradox. The quantum foundation is established using a Krylov-complexity framework: we prove that for any $H(t)=H(-t)$, the quantum Lyapunov exponent satisfies $\lambda_L^{\rm forward} = \lambda_L^{\rm backward}$. The arrow of time is not in the dynamics. The mechanism predicts sigmoid fidelity decay, logarithmic scaling of $t_c$ with $\lambda^{-1}$, and ensemble-size independence of the inaccessibility threshold – all consistent with three decades of Loschmidt echo experiments and confirmed in a stadium-billiard simulation reported here. Underlying everything: quantum mechanics conserves information exactly. Entropy, defined as the logarithm of the multiplicity $\Omega$ – the number of possibilities consistent with the available information – can only increase when information becomes operationally inaccessible. The second law reflects not a breakdown of microscopic reversibility, but the dynamical inaccessibility of the information required to reverse it.
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Mesoscale and Nanoscale Physics

Unconventional quantization of 2D plasmons in cavities formed by gate slots

Ilia Moiseenko, Zhanna Devizorova, Olga Polischuk et al. (+2 more)

We demonstrate that the slot between parallel metal gates placed above two-dimensional electron system (2DES) forms a plasmonic cavity with unconventional mode quantization. The resonant plasmon modes are excited when the slot width $L$ and the plasmon wavelength $\lambda$ satisfy the condition $L = \lambda/8 +n \times \lambda/2$, where $n=0, 1, 2 \ldots$. The lowest resonance occurs at a surprisingly small cavity size, specifically one eighth of the plasmon wavelength, which contrasts with the conventional half-wavelength Fabry-Perot cavities in optics. This unique quantization rule arises from a non-trivial phase shift of $-\pi/4$ acquired by the 2D plasmon upon reflection from the edge of the gate. The slot plasmon modes exhibit weak decay into the gated 2DES region, with the decay rate being proportional to the square root of the separation between the gate and the 2DES. Absorption cross-section by such slots reaches $\sim 50$ % of the fundamental dipole limit without any matching strategies, and is facilitated by field enhancement at the metal edges.
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All authors Ilia Moiseenko, Zhanna Devizorova, Olga Polischuk, Viacheslav Muravev, Dmitry Svintsov

Materials Science

Crystallization Behavior of ZBLAN Glass Under Combined Thermal and Vibrational Effects: Part II - COMSOL Simulation and Apparatus Redesign

Ayush Subedi, Anthony Torres and Jeff Ganley

In Part I of this study, vibration assisted heat treatments of ZBLAN glass revealed irregular crystallization at higher vibration levels, attributed to intermittent loss of thermal contact between the sample and the inner silica ampoule wall. The present work (Part II) investigates this mechanism through finite element modeling (FEM) and experimental validation.COMSOL Multiphysics simulations incorporating conduction, radiation, and contact resistance confirm that intermittent contact markedly reduces heat transfer efficiency, lowering the sampletemperature. To mitigate this effect, the experimental setup was redesigned with a four-degree inclination to maintain stable contact during vibration. Subsequent experiments at vibration levels H3-H5 demonstrated uniform heating and consistent crystallization behavior.Comprehensive microscopic, Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS), and Atomic Force Microscopy (AFM) analyses revealed that even at subtle vibration levels (~50 Hz), partially crystallized ZBLAN transformed into well-developed crystalline structures near 360C. With increasing vibration amplitude, amorphous ZBLAN began forming incipient crystalline phases around 330C, and at higher frequencies (~100 Hz), partial crystallization initiated at approximately 350C. These results indicate that higher vibration frequencies accelerate nucleation, enhance heat transfer, and reduce the effective fiber-drawing temperature window by about 30C. Prolonged exposure above 330C under vibration promotes unwanted phase transitions, emphasizing the need for precise thermal and vibrational control. This study establishes a predictive framework for vibration-resistant ZBLAN processing applicable to both terrestrial and microgravity environments.
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Materials Science

A data-driven quest for room-temperature bulk plastically deformable ceramics

Iwo Słodczyk, Alexander Frisch, Xufei Fang et al. (+2 more)

The growing number of ceramics exhibiting bulk plasticity at room temperature has renewed interest in revisiting plastic deformation and dislocation-mediated mechanical and functional properties in these materials. In this work, a data-driven approach is employed to identify the key parameters governing room-temperature bulk plasticity in ceramics. The model integrates an existing dataset of 55 ceramic materials, 38 plastically deformable and 17 brittle, and achieves accurate classification of bulk plasticity. The analysis reveals several key parameters essential for predicting bulk plasticity: i) Poisson's ratio and Pugh's ratio as macroscopic indicators reflecting the balance between shear and volumetric deformation resistance, and ii) Burgers vector, crystal structure and melting temperature as crystallographic descriptors associated with lattice geometry, slip resistance and thermal stability, and iii) Bader charge as a microscopic measure of bonding character. Together, these parameters define a multiscale descriptor space linking intrinsic materials properties to bulk room-temperature plasticity in ceramics, bridging the gap between empirical ductility criteria and atomistic mechanisms of dislocation-mediated plasticity. While preliminary, this study provides the first systematic, data-driven mapping of the governing factors of ceramic plasticity. The resulting framework establishes a foundation for unifying experimental and computational studies through shared datasets and descriptors, fostering collective progress toward understanding and designing intrinsically ductile ceramics.
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All authors Iwo Słodczyk, Alexander Frisch, Xufei Fang, Inna Gitman, Fengxian Liu

Mesoscale and Nanoscale Physics

Dynamics of Josephson junctions beyond the tunneling limit

Jacob F. Steiner, Larissa Melischek and Felix von Oppen

The dynamics of the superconducting phase difference across a Josephson junction can be described within the resistively and capacitively shunted Josephson junction (RCSJ) model. Microscopic derivations of this model traditionally rely on the tunneling limit. Here, we present a derivation of a generalized version of the RCSJ model, which accounts for dissipative currents with nonlinear current-voltage characteristics as well as supercurrents with arbitrary current-phase relations. This requires a generalized fluctuation-dissipation theorem to describe the Langevin current, which we deduce along the lines of fluctuation theorems for mesoscopic conductors. Our work is motivated in particular by recent theories of the Josephson diode effect, which is not captured within the RCSJ model in the tunneling limit.
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Other Condensed Matter · Cross-listed from physics.optics

A quasi-bound band in the continuum in a photonic slab

Stanislav Tsoi, Nicholas Proscia, Marc Christophersen et al. (+6 more)

Bound states in the continuum (BIC) are localized waves in electronic, photonic and acoustic systems, which remain decoupled from surrounding propagating waves and hence maintain their oscillation for extraordinary long time [Nat Rev Mater 1, 16048 (2016)]. In photonic crystals, symmetry-protected quasi-BICs (SP-qBIC) have been realized at high symmetry points of the Brillouin zone and utilized in photonic crystal and distributed feedback lasers. In the present work, we measure wavevector-resolved photoluminescence (PL) of monolayer WSe2 weakly coupled to a photonic slab, consisting of a square array of aluminum nanodisks. The results show that the slab supports a continuous band of symmetry-protected quasi-bound states along the Gamma-X direction, extending from the previously reported SP-qBIC at the Gamma point. The spectral width of this quasi-bound band in the continuum remains narrow through at least a half of the Brillouin zone, indicating its long lifetime.
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All authors Stanislav Tsoi, Nicholas Proscia, Marc Christophersen, Joseph Christodoulides, Hsun-Jen Chuang, Michael Povolotskyi, Kathleen McCreary, Paul Cunningham, Igor Vurgaftman

Statistical Mechanics · Cross-listed from quant-ph

Boltzmann Sampling of Frustrated J1 - J2 Ising Models with Programmable Quantum Annealers

Elijah Pelofske

One of the surprising, and potentially very useful, capabilities of analog quantum computers, such as D-Wave quantum annealers, is sampling from the Boltzmann, or Gibbs, distribution defined by a classical Hamiltonian. In this study, we thoroughly examine the ability of D-Wave quantum annealers to sample from the Boltzmann distribution defined by a canonical type of competing magnetic frustration $J_1$-$J_2$ model; the 1-dimensional ANNNI (axial next-nearest-neighbor Ising) model. Boltzmann sampling error rate is quantified for standard linear-ramp anneals ranging from $5$ nanosecond annealing times up to $2000$ microseconds on two different D-Wave quantum annealing processors. Interestingly, we find some analog hardware parameters which result in a very high accuracy (down to a TVD of $0.0003$) and low temperature sampling (down to $\beta=32.2$) in a frustrated region of the ANNNI model magnetic phase diagram. This bolsters the viability of current analog quantum computers for thermodynamic sampling applications of highly frustrated magnetic spin systems.
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Strongly Correlated Electrons

Fermionic spinon theory of the hourglass spin excitation spectrum of the cuprates

Alexander Nikolaenko, Pietro M. Bonetti and Subir Sachdev

We present a theory for the spin fluctuation spectrum of the hole-doped cuprates in a ground state with period 4 unidirectional charge density wave (`stripe') order. Motivated by recent experimental evidence for a fractionalized Fermi liquid (FL*) description of the intermediate temperature pseudogap metal, we employ a theory of fermionic spinons which are confined with the onset of stripe order at low temperatures. The theory produces the `hourglass' spectrum near stripe-ordering wavevector observed by neutron scattering. Additional scattering from spinon continua and bound states appears at higher energies and elsewhere in the Brillouin zone, and could be observed by neutron or X-ray scattering.
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Superconductivity

Dynamics of the Schmid-Higgs Mode in $d$-wave superconductors

Samuel Awelewa and Maxim Dzero

We study the dynamics of the longitudinal collective mode in an unconventional superconductor. For concreteness, we assume that the superconductor is described by a $d$-wave order parameter with $d_{x^2-y^2}$ symmetry. After the superconductor has been suddenly subjected to a perturbation at time $t=0$, the order parameter exhibits a peculiar oscillatory behavior, with the amplitude of the oscillations slowly decaying with time in a power-law fashion. Assuming that the initial perturbation is weak, we use a formalism based on quasi-classical approach to superconductivity to determine both the frequency of the oscillations as well as how fast these oscillations decay with time by evaluating the time dependence of the pairing susceptibility. We find that the frequency of the oscillations is given by twice the value of the pairing amplitude in the anti-nodal direction and its amplitude decays as $1/t^2$. The results are also verified by a direct calculation of the order parameter dynamics by numerically solving the equations of motion for the Anderson pseudospins.
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Statistical Mechanics

Krylov Complexity Meets Confinement

Xuhao Jiang, Jad C. Halimeh and N. S. Srivatsa

In high-energy physics, confinement denotes the tendency of fundamental particles to remain bound together, preventing their observation as free, isolated entities. Interestingly, analogous confinement behavior emerges in certain condensed matter systems, for instance, in the Ising model with both transverse and longitudinal fields, where domain walls become confined into meson-like bound states as a result of a longitudinal field-induced linear potential. In this work, we employ the Ising model to demonstrate that Krylov state complexity–a measure quantifying the spread of quantum information under the repeated action of the Hamiltonian on a quantum state–serves as a sensitive and quantitative probe of confinement. We show that confinement manifests as a pronounced suppression of Krylov complexity growth following quenches within the ferromagnetic phase in the presence of a longitudinal field, reflecting slow correlation dynamics. In contrast, while quenches within the paramagnetic phase exhibit enhanced complexity with increasing longitudinal field, reflecting the absence of confinement, those crossing the critical point to the ferromagnetic phase reveal a distinct regime characterized by orders-of-magnitude larger complexity and display trends of weak confinement. Notably, in the confining regime, the complexity oscillates at frequencies corresponding to the meson masses, with its power-spectrum peaks closely matching the semiclassical predictions.
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Superconductivity

Expert Evaluation of LLM World Models: A High-$T_c$ Superconductivity Case Study

Haoyu Guo, Maria Tikhanovskaya, Paul Raccuglia et al. (+20 more)

Large Language Models (LLMs) show great promise as a powerful tool for scientific literature exploration. However, their effectiveness in providing scientifically accurate and comprehensive answers to complex questions within specialized domains remains an active area of research. Using the field of high-temperature cuprates as an exemplar, we evaluate the ability of LLM systems to understand the literature at the level of an expert. We construct an expert-curated database of 1,726 scientific papers that covers the history of the field, and a set of 67 expert-formulated questions that probe deep understanding of the literature. We then evaluate six different LLM-based systems for answering these questions, including both commercially available closed models and a custom retrieval-augmented generation (RAG) system capable of retrieving images alongside text. Experts then evaluate the answers of these systems against a rubric that assesses balanced perspectives, factual comprehensiveness, succinctness, and evidentiary support. Among the six systems two using RAG on curated literature outperformed existing closed models across key metrics, particularly in providing comprehensive and well-supported answers. We discuss promising aspects of LLM performances as well as critical short-comings of all the models. The set of expert-formulated questions and the rubric will be valuable for assessing expert level performance of LLM based reasoning systems.
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All authors Haoyu Guo, Maria Tikhanovskaya, Paul Raccuglia, Alexey Vlaskin, Chris Co, Daniel J. Liebling, Scott Ellsworth, Matthew Abraham, Elizabeth Dorfman, N. P. Armitage, Chunhan Feng, Antoine Georges, Olivier Gingras, Dominik Kiese, Steven A. Kivelson, Vadim Oganesyan, B. J. Ramshaw, Subir Sachdev, T. Senthil, J. M. Tranquada, Michael P. Brenner, Subhashini Venugopalan, Eun-Ah Kim

Statistical Mechanics · Cross-listed from hep-th

Variations on a Theme of Krylov

Vijay Balasubramanian, Pawel Caputa and Joan Simón

Spread complexity uses the distribution of support of a time-evolving state in the Krylov basis to quantify dispersal across accessible dimensions of a Hilbert space. Here, we describe how variations in initial conditions, the Hamiltonian, and the dimension of the Hilbert space affect spread complexity and Krylov basis structure. We introduce Koherence, the entropy of coherence between perturbed and unperturbed Krylov bases, which can, e.g., quantify dynamical amplification of differences in initial conditions in chaos. To illustrate, we show that dynamics on SL(2,R), SU(2), and Heisenberg-Weyl group manifolds, often used as paradigmatic settings for contrasting chaotic and integrable (semi-)classical behavior, display distinctively different responses to variations of the initial state or Hamiltonian. We then describe a lattice model that displays linear growth of spread complexity, saturating for bounded lattices and continuing forever in a thermodynamic limit. The latter example illustrates a breakdown of continuum/classical effective descriptions of complexity growth in bounded quantum systems.
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Superconductivity

Ultrasmall (3,0) carbon nanotube: a superconducting unit with strong electron-phonon coupling

Zhenfeng Ouyang, Jing Jiang, Jian-Feng Zhang et al. (+3 more)

Based on density-functional first-principles calculations, we study the electronic structures, lattice dynamics, and electron-phonon coupling (EPC) properties of the ultrasmall one-dimensional (3,0) carbon nanotube (CNT). Our studies reveal that the (3,0) CNT hosts characteristic collective phonon modes, in which the corresponding atomic vibrations can significantly modulate the electronic self-consistent potential and induce strong EPC. Our results further show that the (3,0) CNT exhibits robust phonon-mediated superconductivity under ambient pressure, with a superconducting transition temperature reaching $\sim$ 33 K ($\mu^*$ = 0.10). We also find that although hole doping enhances the density of states (DOS) near the Fermi level, it simultaneously hardens the strongly coupled phonon modes and suppresses the total EPC. This result indicates that phonons play a more crucial role in the superconductivity of ultrasmall CNTs rather than the DOS alone. Therefore, we suggest that the ultrasmall (3,0) CNT can serve as a superconducting unit hosting phonon modes with strong EPC, and propose a strategy for discovering new phonon-mediated superconductors by identifying superconducting units.
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All authors Zhenfeng Ouyang, Jing Jiang, Jian-Feng Zhang, Miao Gao, Kai Liu, Zhong-Yi Lu

Materials Science

Peierls Transition and Magnetism in a Dirac Semimetal: CaMnBi$_2$

Aashish Sapkota, Niraj Aryal, Xiao Hu et al. (+9 more)

Dirac semimetals of the form $A$Mn$X_2$ ($A =$ alkaline-earth or divalent rare earth; $X =$ Bi, Sb) host conducting square-net Dirac-electron layers of $X$ atoms interleaved with antiferromagnetic Mn$X$ layers. Hypervalent pnictogen square nets have long been predicted to host an electronically driven Peierls instability, whereas low-temperature anomalies in CaMnBi$_2$ near $T^{*}\sim 50$~K have previously been discussed in terms of possible magnetic canting, TRS breaking, and a resulting Weyl-semimetal (WSM) state. Here we use polarized and unpolarized neutron diffraction, x-ray diffraction, and density functional theory (DFT) to investigate this transition in single-crystal CaMnBi$_2$. We observe a coupled structural/magnetic symmetry-lowering transition at $T^{*}=46(2)$ K from a tetragonal lattice with C-type antiferromagnetism to an orthorhombic phase with unit-cell doubling along the $c$ axis, minimal impact on magnetism, and no measurable uniform spin canting ($\lesssim 2^\circ$). Superlattice peak intensities and the lattice distortion reveal a continuous second-order transition governed by a single primary order parameter. The refined displacement pattern corresponds to a zigzag bond-order-wave (BOW) modulation of in-plane Bi–Bi bonds, providing direct diffraction evidence for a Peierls-type instability of the Dirac-electron Bi layer anticipated by Hoffmann and co-workers [W. Tremel and R. Hoffmann, J. Am. Chem. Soc. 109, 124 (1987); G. A. Papoian and R. Hoffmann, Angew. Chem. Int. Ed. 39, 2408 (2000)]. These results identify the $T^{*}$ anomaly as an intrinsic Dirac-electron-driven Peierls/BOW transition of the Bi square net.
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All authors Aashish Sapkota, Niraj Aryal, Xiao Hu, Masaaki Matsuda, Yan Wu, Guangyong Xu, John M. Wilde, Andreas Kreyssig, Paul C. Canfield, Cedomir Petrovic, John M. Tranquada, Igor A. Zaliznyak

Quantum Gases

Control of dynamical phase transitions and non-ergodic relaxation via spinor phases

J. O. Austin-Harris, P. Sigdel, C. Binegar et al. (+3 more)

Utilizing ultracold spinor gases as large-scale, many-body quantum simulation platforms, we establish a toolbox for the precise control, characterization, and detection of nonequilibrium dynamics via internal spinor phases. We develop a method to extract the phase evolution from the observed spin population dynamics, allowing us to define an order parameter that sharply identifies dynamical phase transitions over a wide range of conditions. This work also demonstrates a technique for inferring spin-dependent interactions from a single experimental time trace, in contrast to the standard approach that requires mapping a cross section of the phase diagram, with immediate applications to systems experiencing complex time-dependent interactions. Additionally, we demonstrate experimental access to and control over non-ergodic relaxation dynamics, where states of similar energy in the (nominally) thermal region of the energy spectrum retain a dependence on the initial state, via the manipulation of spinor phases, enabling the study of non-ergodic thermalization dynamics connected to quantum scarring.
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All authors J. O. Austin-Harris, P. Sigdel, C. Binegar, S. E. Begg, T. Bilitewski, Y. Liu

Materials Science

Intercalation induced quasi-freestanding layer in TiSe$_2$

Turgut Yilmaz, Yi Sheng Ng, Anil Rajapitamahuni et al. (+4 more)

Angle-resolved photoemission spectroscopy is employed to study the electronic structure of bulk TiSe2 before and after doping with potassium impurities. A splitting in the conduction band into two branches is observed after room-temperature deposition. The splitting energy increases to approximately 130 meV when the sample is cooled to 40 K. One branch exhibits a non-dispersive two-dimensional feature, while other one shows the characteristics of three dimensional bulk band dispersion. Core level spectroscopy suggests that the K impurities predominantly occupy the intercalated sites within the van derWaals gap. The results indicate the formation of a quasi-freestandingTiSe2 layer. Additionally, doping completely suppresses the periodic lattice distortion in the surface region. These findings are further supported by density functional theory calculations, which compare the band structure of monolayer and bulk TiSe2 with experimental data. Thus, the dimensional and intrinsic electronic properties of 1T-TiSe2 can be controlled through the intercalation procedure used in this work.
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All authors Turgut Yilmaz, Yi Sheng Ng, Anil Rajapitamahuni, Asish Kundu, Hui-Qiong Wang, Jin-Cheng Zheng, Elio Vescovo

Other Condensed Matter

An Extensible Julia Toolkit for Symmetry-Aware Dual Space Phasing in Arbitrary Dimensions

Pavel Kalugin

We present an open-source Julia-based software toolkit for solving the phase problem using dual-space iterative algorithms. The toolkit is specifically designed for aperiodic crystals and quasicrystals, supporting general space group symmetries in arbitrary dimensions. A key feature is the symmetry-breaking anti-aliasing sampling scheme, optimized for computational efficiency when working with strongly anisotropic diffraction data, common for quasicrystals. This scheme avoids sampling redundancy caused by symmetry constraints, imposed during phasing iterations. The toolkit includes a reference implementation of the charge flipping algorithm and also allows users to implement custom phasing algorithms with fine-grained control over the iterative process.
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Materials Science

Efficient GPU Parallelization of Electronic Transport and Nonequilibrium Dynamics from Electron-Phonon Interactions in the Perturbo Code

Shiyu Peng, Donnie Pinkston, Jia Yao et al. (+3 more)

The Boltzmann transport equation (BTE) with electron-phonon (e-ph) interactions computed from first principles is widely used to study electronic transport and nonequilibrium dynamics in materials. Calculating the e-ph collision integral is the most important step in the BTE, but it remains computationally costly, even with current MPI+OpenMP parallelization. This challenge makes it difficult to study materials with large unit cells and to achieve high resolution in momentum space. Here, we show acceleration of BTE calculations of electronic transport and ultrafast dynamics using graphical processing units (GPUs). We implement a novel data structure and algorithm, optimized for GPU hardware and developed using OpenACC, to process scattering channels and efficiently compute the collision integral. This approach significantly reduces the overhead for data referencing, movement, and synchronization. Relative to the efficient CPU implementation in the open-source package Perturbo (v2.2.0), used as a baseline, this approach achieves a speed-up of 40 times for both transport and nonequilibrium dynamics on GPU hardware, and achieves nearly linear scaling up to 100 GPUs. The novel data structure can be generalized to other electron interactions and scattering processes. We released this GPU implementation in the latest public version (v3.0.0) of Perturbo. The new MPI+OpenMP+GPU parallelization enables sweeping studies of e-ph physics and electron dynamics in conventional and quantum materials, and prepares Perturbo for exascale supercomputing platforms.
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All authors Shiyu Peng, Donnie Pinkston, Jia Yao, Sergei Kliavinek, Ivan Maliyov, Marco Bernardi