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Physics Condensed Matter

cond-mat Watch Condensed Matter

Thursday 8 January

Superconductivity

Condensation mechanism of high-$T_c$ cuprates: the key role of pairon excitations

Yves Noat, Alain Mauger and William Sacks

In this article we show that the condensation mechanism in cuprates involves the strong coupling of the condensate to pairon excited states. We present an accessible formalism that significantly extends our previous work, providing a theoretical basis for the energy-dependent gap function $\Delta(E)$. The latter is proportional to the effective spin exchange energy, $J_{eff}$, with no retardation effects, such as the case of spin-fluctuation or phonon mediated couplings. The fundamental parameters of the superconducting (SC) state are the condensation energy per pair, $\beta_c$, and the antinodal energy gap, $\Delta_p$, which are quantitatively extracted by fitting the cuprate quasiparticle spectrum from tunneling experiments. An explicit formula for the critical temperature is also derived in the model. Valid for any doping, we find $T_c$ to be proportional to $\beta_c$, and not the gap $\Delta_p$, in sharp contrast to conventional SC. The numerical factor $\beta_c/k_BT_c\simeq 2.24$ originates from pair excitations of the condensate, following Bose statistics, with a mini-gap $\delta_M \simeq 1\,$meV in the excitation spectrum. These results strongly suggest that the same `all-electron' mechanism is at work all along the $T_c$-dome.
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Statistical Mechanics

Construction of asymptotic quantum many-body scar states in the SU($N$) Hubbard model

Daiki Hashimoto, Masaya Kunimi and Tetsuro Nikuni

We construct asymptotic quantum many-body scars (AQMBS) in one-dimensional SU($N$) Hubbard chains ($N\geq 3$) by embedding the scar subspace into an auxiliary Hilbert subspace $\mathcal{H}_P$ and identifying a parent Hamiltonian within it, together with a corresponding extension of the restricted spectrum-generating algebra to the multi-ladder case. Unlike previous applications of the parent-Hamiltonian scheme, we show that the parent Hamiltonian becomes the SU($N$) ferromagnetic Heisenberg model rather than the spin-1/2 case, so that its gapless magnons realize explicit AQMBS of the original model. Working in the doublon-holon subspace, we derive this mapping, obtain the one-magnon dispersion for periodic and open boundaries, and prove (i) orthogonality to the scar states, (ii) vanishing energy variance in the thermodynamic limit, and (iii) subvolume entanglement entropy with rigorous MPS/MPO bounds. Our results broaden the parent-Hamiltonian family for AQMBS beyond spin-1/2 and provide analytic, low-entanglement excitations in SU($N$)-symmetric systems.
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Mesoscale and Nanoscale Physics

Optical Signatures and Quantum Geometry in Proximity-Induced Topological Superconductors

Myungjun Kang, Yogeshwar Prasad, Nikhil Danny Babu et al. (+3 more)

Topological-insulator-superconductor (TI-SC) heterostructures provide a promising platform for proximity-induced topological superconductivity, but diagnosing superconductivity at a buried interface remains challenging for conventional surface-sensitive probes. Here, we develop a quantitative theory of the longitudinal optical response of a TI-SC heterostructure and show that the complex sheet conductance provides an interface-selective route to isolating and diagnosing the buried proximitized interface state. Starting from a minimal model, we derive a low-energy description of the heterointerface in which the induced gap emerges directly from the TI-SC coupling. Combined with a slab-based thickness-extrapolation procedure, this framework yields a practical protocol for separating the buried interfacial sheet conductance from bulk and exposed-surface optical contributions. The extracted interface response exhibits a robust, thickness-independent coherence peak at an energy set by the proximity-induced gap, clearly distinguishable from both the pair-breaking scale of the parent superconductor and the Dirac cone on the exposed TI surface. At low energies, the heterointerface is described by an effective time-reversal-invariant topological-superconducting theory, while the associated low-frequency optical spectral weight admits a quantum-geometric interpretation through the optical sum rule. Our results establish terahertz/infrared spectroscopy of thickness-extracted sheet conductance as a noninvasive route to identifying and quantifying proximity-induced superconductivity at buried TI-SC interfaces.
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All authors Myungjun Kang, Yogeshwar Prasad, Nikhil Danny Babu, Rasoul Ghadimi, Jae Hoon Kim, Sangmo Cheon

Strongly Correlated Electrons · Cross-listed from physics.chem-ph

Classical computational simulation of the FeMo-cofactor model to chemical accuracy and its implications

Huanchen Zhai, Chenghan Li, Xing Zhang et al. (+3 more)

We use classical computational methods to estimate the ground-state energy to chemical accuracy in a model of the FeMo-cofactor of nitrogenase which is widely studied as a target of quantum computing. Our result relies on the insight that the ground-state problem can be characterized as one of ranking many competing, but largely simple, states. This allows a combination of systematic high-order coupled cluster and density matrix renormalization group calculations together with an extrapolation protocol to obtain an accurate energy. Within the model we identify several spin isomer candidates for the ground-state that are degenerate to chemical accuracy. Beyond this model, we characterize the impact of additional electronic excitations and the cluster and protein geometric fluctuations on the low-lying electronic landscape. We find that many features of the landscape are retained in more detailed representations of nitrogenase, which points to the complexity of spectroscopic interpretations of the electronic structure of the FeMo-cofactor.
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All authors Huanchen Zhai, Chenghan Li, Xing Zhang, Zhendong Li, Seunghoon Lee, Garnet Kin-Lic Chan

Materials Science

High mobility holes at germanane/Ge(111) allotropic cross-dimensional heterointerface

Yumiko Katayama, Daiki Kobayashi, Hikaru Okuma et al. (+3 more)

Germanane (GeH) is essentially a hydrogen-terminated Ge analog of graphene with a direct gap (~1.6 eV). Record hole mobility mu_h~67,000 cm2/Vs is found at 15 K for a single allotropic cross-dimensional(D) heterointerface. This is enabled by making topotactically-transformed 2D GeH layers meet the 3D bulk Ge(111). Temperature dependence of mu_h implies metallic conduction without ionized impurity scattering between 20 K and 250 K. Sheet hole density for a Fermi sphere n_S=2.8x10^11 /cm2 agrees well with 3.0x10^11 /cm2 of Hall measurements. A 6,500% magnetoresistance at 7 T accompanies Shubnikov-de Haas oscillations visible even at 15 K. These imply single-band conduction of holes with small effective mass in the in-plane directions, invoking a 2D hole gas (2DHG) picture that allotropic cross-D heterointerface between 2D GeH and 3D Ge harbors 2D-confined high-mobility holes. Even without elaborate heteroepitaxy and modulation doping, allotropic cross-D heterostructures pave the way toward facile 2DHG creation.
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All authors Yumiko Katayama, Daiki Kobayashi, Hikaru Okuma, Yuhsuke Yasutake, Susumu Fukatsu, Kazunori Ueno

Soft Condensed Matter

Power-law molecular-weight distributions dictate universal behaviors in highly polydisperse polymer solutions

Naoya Yanagisawa, Daisuke S. Shimamoto and Miho Yanagisawa

Polydispersity is a universal feature of synthetic polymers and biological molecules in the cytoplasm. However, its quantitative impact on collective behavior remains poorly understood because conventional metrics, such as the polydispersity index, fail to capture broad, non-Gaussian size distributions. Here, we develop an experimental platform in which polyethylene glycol (PEG) solutions are engineered to follow tunable power-law molecular-weight distributions spanning an extensive range, from $M = 1$ kg/mol to $10^{4}$ kg/mol. By systematically varying the $M$ distribution exponent $a$, we identify a robust regime ($1 < a \lesssim 2.5$) in which the viscosity scaling exponent in the entangled regime, the overlap concentration $c^{\ast}$, and the entanglement concentration ${c_{\mathrm{e}}}$ all exhibit pronounced maxima that exceed monodisperse limits. This amplification minimizes as the upper cutoff $M_{\max}$ is reduced, with the system approaching monodisperse behavior. The enhanced rheology arises from a competition between long-chain-dominated entanglement and short-chain-mediated void filling, demonstrating that the whole shape of the molecular-weight distribution plays a decisive role. Consequently, these collective behaviors cannot be reproduced by simply tuning the average molecular weight. Together, our results establish the power-law exponent $a$ as a quantitative control parameter that links polymer entanglement, soft packing, and molecular crowding in highly polydisperse systems.
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Materials Science

Crystal Generation using the Fully Differentiable Pipeline and Latent Space Optimization

Osman Goni Ridwan, Gilles Frapper, Hongfei Xue et al. (+1 more)

We present a materials generation framework that couples a symmetry-conditioned variational autoencoder (CVAE) with a differentiable SO(3) power spectrum objective to steer candidates toward a specified local environment under the crystallographic constraints. In particular, we implement a fully differentiable pipeline to enable batch-wise optimization on both direct and latent crystallographic representations. Using the GPU acceleration, this implementation achieves about fivefold speed compared to our previous CPU workflow, while yielding comparable outcomes. In addition, we introduce the optimization strategy that alternatively performs optimization on the direct and latent crystal representations. This dual-level relaxation approach can effectively escape local minima defined by different objective gradients, thus increasing the success rate of generating complex structures satisfying the target local environments. This framework can be extended to systems consisting of multi-components and multi-environments, providing a scalable route to generate material structures with the target local environment.
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All authors Osman Goni Ridwan, Gilles Frapper, Hongfei Xue, Qiang Zhu

Superconductivity

Direct Observation of the Spillover of High Magnetic Field-induced SC3 Superconductivity Outside the Spin-Polarized State in UTe2

Zheyu Wu, Hanyi Chen, Theodore I. Weinberger et al. (+8 more)

In our recent study of the high magnetic field phase landscape of UTe$_2$ [Phys. Rev. X 15, 021019 (2025)] we found indirect evidence that the SC3 superconducting phase spills out beyond the first-order phase boundary of the spin-polarized state. This prior study was limited to a maximal field strength of 41.5 T, and mapped the $b-ac$ rotation plane. Here we measure a high quality sample with residual resistivity ratio RRR = 605 under rotations in the $b-c$ plane up to 45 T. This extended field range helps to unambiguously demonstrate the spillover of SC3 outside the polarized paramagnetic state. This is identified by the observation of zero resistance at low temperatures, for magnetic field strengths lower than the metamagnetic transition field resolved at higher temperatures. This observation is consistent with the scenario that electronic pairing of the SC3 phase is mediated by quantum critical fluctuations.
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All authors Zheyu Wu, Hanyi Chen, Theodore I. Weinberger, Mengmeng Long, David Graf, Andrej Cabala, Vladimir Sechovsky, Michal Valiska, Gilbert G. Lonzarich, F. Malte Grosche, Alexander G. Eaton

Materials Science

Spatial resolution(s) in atom probe tomography

Baptiste Gault, Frédéric De Geuser, Christoph Freysoldt et al. (+2 more)

Atom probe tomography (APT) is often quoted to provide "atomic-scale" analysis of materials in three dimensions. Despite efforts to quantify APT's spatial resolution, misunderstanding remain regarding its true spatial performance. If the depth resolution was once reported to be 20 pm, quoting this value outside of its specific context is misleading and should be avoided. The resolution achievable in pure metals, at one specific location within one reconstructed dataset, does not generally apply across materials or analysis conditions, or even throughout a single tomographic reconstruction. Here, we review various efforts at defining and measuring the spatial resolution in the study of single phase and single element materials - i.e. pure metals - in field-ion microscopy (FIM) and APT. We also report on the degradation of the resolution arising from ion optical devices used to improve the mass-resolution. We aim to offer some perspective as to how reported resolutions may be or may not be of any relevance to most of the materials characterisation efforts by APT, including cases of precipitates in a matrix that emphasise the need to consider an effective resolution. Finally, we discuss concepts to improve the spatial accuracy of the technique in a relatively distant future.
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All authors Baptiste Gault, Frédéric De Geuser, Christoph Freysoldt, Benjamin Klaes, François Vurpillot

Mesoscale and Nanoscale Physics

Anisotropic magnon transport in an antiferromagnetic trilayer heterostructure: is BiFeO$_3$ an altermagnet?

Sajid Husain, Maya Ramesh, Qian Song et al. (+18 more)

Magnons provide a route to ultra-fast transport and non-destructive readout of spin-based information transfer. Here, we report magnon transport and its emergent anisotropic nature in BiFeO$_3$ layers confined between ultrathin layers of the antiferromagnet LaFeO$_3$. Due to the confined state, BiFeO$_3$ serves as an efficient magnon transmission channel as well as a magnetoelectric knob by which to control the stack by means of an electric field. We discuss the mechanism of the anisotropic spin transport based on the interaction between the antiferromagnetic order and the electric field. This allows us to manipulate and amplify the spin transport in such a confined geometry. Furthermore, lower crystal symmetric and suppression of the spin cycloid in ultrathin BiFeO$_3$ stabilizes a non-trivial antiferromagnetic state exhibiting symmetry-protected spin-split bands that provide the non-trivial sign inversion of the spin current, which is a characteristic of an altermagnet. This work provides an understanding of the anisotropic spin transport in complex antiferromagnetic heterostructures where ferroelectricity and altermagnetism coexist, paving the way for a new route to realize electric-field control of a novel state of magnetism.
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All authors Sajid Husain, Maya Ramesh, Qian Song, Sergei Prokhorenko, Shashank Kumar Ojha, Surya Narayan Panda, Xinyan Li, Yousra Nahas, Yogesh Kumar, Pushpendra Gupta, Tenzin Chang, Alan Ji-in Jung, Rogério de Sousa, James G. Analytis, Lane W. Martin, Zhi Yao, Sang-Wook Cheong, Laurent Bellaiche, Manuel Bibes, Darrell G. Schlom, Ramamoorthy Ramesh

Materials Science

Breaking Four-Point and Three-Point Bending Tests

Subhrangsu Saha, Jeffery R. Roesler and Oscar Lopez-Pamies

Since their initial standardizations in the 1930s and 1950s, the so-called four-point and three-point bending tests on unnotched beams have been embraced by practitioners as two popular methods to indirectly measure the tensile strength of concrete, ceramics, and other materials with a large compressive strength relative to their tensile strength. This is because of the ease that the tests afford in both the preparation of the specimen (a beam of rectangular cross section) and the application of the loads (simple supports pressing on the specimen). Yet, this practical advantage has to be tempered by the fact that the observations from both of these tests – being indirect experiments in the sense that they involve not uniform uniaxial tension but non-uniform triaxial stress states throughout the specimen – have to be appropriately interpreted to be useful. By making use of the phase-field fracture theory initiated by Kumar, Francfort, and Lopez-Pamies (2018), which has been recently established as a complete theory of fracture capable of accurately describing the nucleation and propagation of cracks in elastic brittle materials under arbitrary quasistatic loading conditions, the main objective of this paper is to carry out a thorough 3D quantitative analysis of when and where fracture nucleates and propagates in four-point and three-point bending tests and thereby establish how to appropriately interpret their results. As a corollary, the analysis provides an explanation for why four-point bending tests typically yield smaller flexural strengths than three-point bending tests, a source of constant headaches for practitioners who have been left to wonder which test – if any – would be more appropriate for their purposes.
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Strongly Correlated Electrons

Artificial Gauge Field Engineered Excited-State Topology: Control of Dynamical Evolution of Localized Spinons

Jie Ren, Yi-Ran Xue, Run-Jia Luo et al. (+2 more)

Spinons are elementary excitations at the core of frustrated quantum magnets. Although it is well-established that a pair of spinons can emerge from a magnon via deconfinement, controlled manipulation of individual spinons and direct observation of their deconfinement remain elusive. We propose an artificial gauge field scenario that enables the engineering of specific excited states in quantum spin models. This generates spatially localized individual spinons with high controllability. By applying time-dependent gauge fields, we realize adiabatic braiding of these spinons, as well as their dynamical evolution in a controllable manner. These results not only provide the first direct visualization of individual spinons localized in the bulk, but also point to new possibilities to simulate their confinement process. Finally, we demonstrate the feasibility of our scenario in Rydberg atoms, which suggests an experimentally viable direction–gauge field engineering of correlated phenomena in excited states.
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All authors Jie Ren, Yi-Ran Xue, Run-Jia Luo, Rui Wang, Baigeng Wang

Superconductivity

Studies of superconductivity of Fe chalcogenides in films grown by PLD technique

Atsutaka Maeda, Tomoki Kobayashi and Fuyuki Nabeshima

Studies on Fe chalcogenide superconductor using thin films grown by the PLD technique are reviewed in terms of electronic phase diagram, properties in the normal state, properties in the superconducting state, together with the comparison with properties in bulk crystals, MBE grown films and exfoliated crystals. Challenges to increase superconducting Tc will also be introduced.
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Quantum Gases · Cross-listed from quant-ph

Maximal Entanglement and Frozen Information: A Unified Framework for Dynamical Quantum Phase Transitions

Kaiyuan Cao, Mingzhi Li, Xiang-Ping Jiang et al. (+2 more)

Dynamical quantum phase transitions (DQPTs) are temporal singularities marked by zeros of the Loschmidt echo, yet their underlying quantum-information structure remains elusive. Here, we introduce a momentum-resolved entanglement entropy as a direct probe of DQPTs in translation-invariant free systems. We analytically establish that every critical momentum mode $k^{*}$ associated with a DQPT saturates its entanglement to the maximal value $\ln{2}$, coinciding with the vanishing of the Loschmidt echo. Crucially, we demonstrate that this maximal entanglement universally suppresses information scrambling: a momentum-resolved out-of-time-ordered correlator (OTOC) vanishes identically for all times at $k^{*}$. These three signatures – Fisher zeros, maximal entanglement, and vanished OTOC – are proved to be equivalent in both the transverse-field Ising and Su-Schrieffer-Heeger models, despite their distinct bipartitions (momentum-pair vs. sublattice). Our results establish a unified, information-theoretic framework for DQPTs, revealing them a points where quantum correlations saturate and information flow halts. This work elevates entanglement and scrambling to central dynamical order parameters, offering a universal perspective on nonequilibrium quantum critically.
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All authors Kaiyuan Cao, Mingzhi Li, Xiang-Ping Jiang, Shu Chen, Jian Wang

Materials Science · Cross-listed from math-ph

Mixed-mode loading of a straight crack with surface strain-gradient elasticity

C. Rodriguez and A. Zemlyanova

This work models brittle fracture using a linearized surface-substrate theory in which the crack faces possess surface stresses derived from a surface strain-gradient elastic energy. The model incorporates surface stretching, curvature, and surface gradients of stretching into the surface energy, thereby capturing small-length-scale effects absent from earlier surface elasticity formulations. The theory, supplemented with physically motivated tip conditions, is applied to the mixed mode-I/mode-II loading of a finite straight crack in an infinite isotropic plate. Using complex-analytic techniques, it is shown that the resulting stress and strain fields remain bounded up to the crack tips for nearly all admissible parameter values. Combined with previous results for mode-III loading, the analysis demonstrates that linearized surface-substrate models incorporating surface strain-gradient elasticity eliminate crack-tip singularities across all principal modes of far-field loading.
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Soft Condensed Matter

Anomalous Dynamical Heterogeneity in Active Glasses as a Signature of Violation of Mermin-Wagner-Hohenberg Theorem

Subhodeep Dey and Smarajit Karmakar

Two-dimensional (2D) systems have attracted renewed interest within the scientific community due to their anomalous dynamical behaviors, which arise from long-wavelength density fluctuations as predicted by the Mermin-Wagner-Hohenberg (MWH) theorem. In equilibrium, it is well established that continuous spontaneous symmetry breaking (SSB) in 2D is prohibited at any finite temperature ($T > 0$), resulting in the absence of true long-range positional order and establishing $d_l = 2$ as the lower critical dimension. Recent studies have demonstrated that, in active systems, the lower critical dimension can shift from $d_l = 2$ to $3$. This study examines the impact of MWH theorem violation in active systems on dynamical heterogeneity (DH). As a minimal model, glassy systems of active particles undergoing run-and-tumble (RT) motion are considered. Glass-like dynamical behavior, including anomalously enhanced DH, is observed in various biological systems such as collective cell migration, bacterial cytoplasm, and ant colonies. Furthermore, the study investigates the influence of local positional order, or medium-range crystalline order (MRCO), on DH in the presence of activity. The results indicate that the growth of DH with increasing activity differs significantly between systems with and without MRCO. These findings may have important implications, as many biological systems exhibit local structural ordering, and DH could serve as a useful indicator for quantifying the degree of ordering.
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Materials Science

A Structural Map of Potential Correlated Electron Molecular Orbital Materials

Md. Rajbanul Akhond and Alexandru B. Georgescu

Correlated electron molecular orbital (CEMO) materials host emergent electronic states built from molecular orbitals localized over clusters of transition metal ions in a solid, yet have historically been discovered sporadically and generally been treated as isolated case studies. Here, we present criteria and tools to classify and analyze these materials, provide a database of identified materials with cluster-specific symmetry analysis, including cluster point groups, effective cluster sublattice dimensionality. Our electronic structure analysis shows that narrow bands in cluster materials can arise either from relatively isolated cluster molecular orbitals or from a mixed mechanism in which cluster localization coexists with frustrated-lattice flat-band topology. We discuss how CEMO properties do not arise from metal clusters in a solid alone: rather they depend on electron count, symmetry, frustration and correlation strength. By integrating cluster classification with flat-band lattice topology and electrochemistry-relevant information, we provide further relevant information to multiple scientific communities. Applying this approach in a high-throughput screen of 34,548 compounds yields potential 2,627 stable or metastable CEMO compounds with isolated cluster motifs. The accompanying open dataset, Cluster Finder software, and interactive web platform enable systematic exploration of cluster-containing electronic solid state materials and establish a starting point for discovering a new class of correlated quantum materials with a wide array of properties.
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Wednesday 7 January

Materials Science · Cross-listed from physics.plasm-ph

Autonomous Sampling and SHAP Interpretation of Deposition-Rates in Bipolar HiPIMS

Alexander Wieczorek, Nathan Rodkey, Jan Sommerhäuser et al. (+2 more)

High-power impulse magnetron sputtering (HiPIMS) offers considerable control over ion energy and flux, making it invaluable for tailoring the microstructure and properties of advanced functional coatings. However, compared to conventional sputtering techniques, HiPIMS suffers from reduced deposition rates. Many groups have begun to evaluate complex pulsing schemes to improve upon this, leveraging multi-pulse schemes (e.g. pre-ionization or bipolar pulses). Unfortunately, the increased complexity of these pulsing schemes has led to high-dimensionality parameter spaces that are prohibitive to classic design of experi-ments. In this work we evaluate bipolar HiPIMS pulses for improving deposition rates of Al and Ti sputter tar-gets. Over 3000 process conditions were collected via autonomous Bayesian sampling over a 6-dimensional parameter space. These process conditions were then interpreted using Shapley Additive Explanations (SHAP), to deconvolute complex process influences on deposition rates. This allows us to link observed var-iations in deposition rate to physical mechanisms such as back-attraction and plasma ignition. Insights gained from this approach were then used to target specific processes where the positive pulse components were expected to have the highest impact on deposition rates. However, in practice, only minimal improve-ments in deposition rate were achieved. In most cases, the positive pulse appears to be detrimental when placed immediately after the neg. pulse which we hypothesize relates to quenching of the afterglow plasma. The proposed workflow combining autonomous experimentation and interpretable machine learning is broad-ly applicable to the discovery and optimization of complex plasma processes, paving the way for physics-informed, data-driven advancements in coating technologies.
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All authors Alexander Wieczorek, Nathan Rodkey, Jan Sommerhäuser, Jason Hattrick-Simpers, Sebastian Siol

Materials Science · Cross-listed from physics.optics

Processing-Dependent Near-Field Radiative Heat Transfer at Au/SiC Interfaces

A. Márquez and R. Esquivel-Sirvent

Thermal annealing is a widely used thin-film processing technique for modifying interfacial optical losses and electronic scattering in plasmonic materials. Here, we investigate how thermal annealing of gold thin films deposited on silicon carbide substrates influences interfacial near-field radiative heat transfer across nanoscale vacuum gaps. Using experimentally measured dielectric functions for annealed and unannealed Au films, we evaluate the spectral and total radiative heat flux between Au/SiC interfaces within a fluctuational electrodynamics framework. We show that annealing-induced changes in the low-frequency dielectric losses of Au significantly alter evanescent electromagnetic coupling at the interface, leading to enhancements of up to ~40% in the total near-field radiative heat transfer at separations of tens of nanometers. Mode-resolved analysis reveals that this enhancement originates from strengthened coupling of overdamped plasmonic surface modes, which are highly sensitive to thin-film processing and interfacial microstructure. These results demonstrate that standard thermal annealing provides a practical route for tuning interfacial radiative heat transfer in metallic thin-film systems without modifying material composition or geometry, offering guidance for the design and interpretation of nanoscale thermal and plasmonic interfaces.
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Strongly Correlated Electrons

Dynamical instability in a Floquet-Driven Dissipative System

Takuya Okugawa, Jens Paaske, Martin Eckstein et al. (+3 more)

We analyse the magnon spectrum and distribution function of the antiferromagnetic phase of the Floquet-driven Hubbard model. Above a critical drive strength, we find a dynamical instability, resulting from a change in sign of the magnon damping at a non-zero wavevector. The change in sign means that infinitesimal fluctuations grow with time, corresponding to an instability of the driven state. Implications for the nonequilibrium distribution function and the strong drive nonlinear dynamics are discussed.
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All authors Takuya Okugawa, Jens Paaske, Martin Eckstein, Michael A. Sentef, Angel Rubio, Andrew J. Millis

Materials Science

SpectraFormer: an Attention-Based Raman Unmixing Tool for Accessing the Graphene Buffer-Layer Signature on SiC

Dmitriy Poteryayev, Pietro Novelli, Annalisa Coriolano et al. (+7 more)

Raman spectroscopy is a key tool for graphene characterization, yet its application to graphene grown on silicon carbide (SiC) is strongly limited by the intense and variable second-order Raman response of the substrate. This limitation is critical for buffer layer graphene, a semiconducting interfacial phase, whose vibrational signatures are overlapped with the SiC background and challenging to be reliably accessed using conventional reference-based subtraction, due to strong spatial and experimental variability of the substrate signal. Here we present SpectraFormer, a transformer-based deep learning model that reconstructs the SiC Raman substrate contribution directly from post-growth partially masked spectroscopic data without relying on explicit reference measurements. By learning global correlations across the entire Raman shift range, the model captures the statistical structure of the SiC background and enables accurate reconstruction of its contribution in mixed spectra. Subtraction of the reconstructed substrate signal reveals weak vibrational features associated with ZLG that are inaccessible through conventional analysis methods. The extracted spectra are validated by ab initio vibrational calculations, allowing assignment of the resolved features to specific modes and confirming their physical consistency. By leveraging a state-of-the-art attention-based deep learning architecture, this approach establishes a robust, reference-free framework for Raman analysis of graphene on SiC and provides a foundation, compatible with real-time data acquisition, to its integration into automated, closed-loop AI-assisted growth optimization.
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All authors Dmitriy Poteryayev, Pietro Novelli, Annalisa Coriolano, Riccardo Dettori, Valentina Tozzini, Fabio Beltram, Massimiliano Pontil, Antonio Rossi, Stiven Forti, Camilla Coletti

Mesoscale and Nanoscale Physics

Quantum Geometric Origin of Orbital Magnetization

Xiao-Bin Qiang, Tianyu Liu, Hai-Zhou Lu et al. (+1 more)

The exploration of the Riemannian structure of the Hilbert space has led to the concept of quantum geometry, comprising geometric quantities exemplified by Berry curvature and quantum metric. While this framework has profoundly advanced the understanding of various electronic phenomena, its potential for illuminating magnetic phenomena has remained less explored. In this Perspective, we highlight how quantum geometry paves a new way for understanding magnetization within a single-particle framework. We first elucidate the geometric origin of equilibrium magnetization in the modern theory of magnetization, then discuss the role of quantum geometry in kinetic magnetization, and finally outline promising future directions at the frontier of quantum geometric magnetization.
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All authors Xiao-Bin Qiang, Tianyu Liu, Hai-Zhou Lu, X. C. Xie

Soft Condensed Matter

Mesoscale flows in active baths dictate the dynamics of semi-flexible filaments

Bipul Biswas, Devadyouti Das, Manasa Kandula et al. (+1 more)

Semi-flexible filaments in living systems are constantly driven by active forces that often organize into mesoscale coherent flows. Although theory and simulations predict rich filament dynamics, experimental studies of passive filaments in collective active baths remain scarce. Here we present an experimental study on passive colloidal filaments confined to the air-liquid interface beneath a free-standing, quasi-two-dimensional bacterial film featuring jet-like mesoscale flows. By varying filament contour length and bacterial activity, we demonstrate that filament dynamics are governed by its length relative to the characteristic size of the bath. Filaments shorter than the jet width exhibit greatly enhanced translation and rotation with minimal deformation, while long filaments show dramatic deformation but less enhanced transport. We explain our findings through the competition between the active viscous drag of the bath and passive elastic resistance of the filaments, using a modified elastoviscous number that considers the mesoscale flows.
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All authors Bipul Biswas, Devadyouti Das, Manasa Kandula, Shuang Zhou

Mesoscale and Nanoscale Physics

Hidden Information in Force Curves: Transient- and Brownian-Driven Dynamics

Sergio Santos and Roger Proksch

Force distance curves (FCs) are direct probes of tip sample interactions in atomic force microscopy, but their dynamic content is often suppressed by filtering, averaging and quasistatic analysis. Indeed, in the forty years since the invention of the AFM, this hidden dynamic signal has been largely ignored, with exceptions restricted to the large oscillations associated with relatively large adhesive separations (snap from contact) or to time averaged approaches that carry their own challenges. Using high bandwidth interferometric detection, we directly measure fast FCs, including short lived cantilever oscillations during snap in, contact and pull off. Two excitation mechanisms coexist: thermal fluctuations and transients generated by rapid changes in the tip sample boundary condition. Cycle resolved frequency and amplitude estimators provide time local observables of the evolving cantilever and sample system within single FCs, creating a pixel by pixel mechanical contrast channel that requires no external broadband excitation, resonant tracking or multi pass imaging. A state dependent harmonic oscillator model incorporating van der Waals attraction, hysteretic capillary bridge formation and rupture, hydration mediated damping and repulsive contact stiffness partitions each FC into five interaction regimes and reproduces the observed responses. In repulsive contact, frequency shifts yield stiffness maps consistent with contact-mechanics estimates, enabling high throughput stiffness mapping and localization of transient tip sample events from individual pixels. More broadly, this hitherto hidden signal may pave the way for new ways of studying and exploiting Brownian motion in a variety of systems, providing the capability to follow time resolved (non) Markovian and (non) ergodic dynamics mediated by the tip sample interaction, including single event dynamics.
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Materials Science

Oxygen in diamond: thermal stability of ST1 spin centres and creation of oxygen-pair complexes

Paul Neugebauer, Xinxi Huang, Chloe Newsom et al. (+11 more)

Little is known about oxygen-related defects in diamond. Recently, the promising room-temperature spin centre named ST1 was identified as an oxygen centre, but of still unknown atomic structure and thermal stability. In this work, we report on the optically active oxygen-related centres and the conditions for their formation, using ion implantation of oxygen in various conditions of depth and fluence. More specifically, we establish the temperature formation/stability range of the ST1 centre, which has a maximum at about 1100{\deg}C and is narrower than for NV centres. In these conditions, optically detected magnetic resonance (ODMR) on small ST1 ensembles was measured with a spin readout contrast of > 20% at 300K. In cathodoluminescence, the 535 nm ST1 peak is not observed. Besides, a broad peak centred at 460 nm is measured for implantation of O$_2$ molecular ions. For an annealing temperature of 1500{\deg}C, a different centre is formed (with ZPL at 584.5 nm) with an intensity increasing with a power law 1.5 < p < 1.9 dependence from the implantation fluence. This suggests that this centre contains two oxygen atoms. Besides, a new spectral feature associated to an intrinsic defect was also observed, with four prominent lines (especially at 594nm). Finally, the thermal formation and stability of oxygen centres in diamond presented here are important for the identification of the atomic structure of defects such as the ST1 and possible O$_2$V$_x$ complex by means of ab initio calculations. Indeed, the formation energies and charge states of defect centres are easier to compute than the full energy level scheme, which to date still remains unsuccessful regarding the ST1 centre.
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All authors Paul Neugebauer, Xinxi Huang, Chloe Newsom, Christophe Arnold, Hjørdis Martelock, Séverine Diziain, Edoardo Monnetti, Jocelyn Achard, Tobias Lühmann, Paolo Olivero, Jan Meijer, Julien Barjon, Alexandre Tallaire, Sébastien Pezzagna

Materials Science

Interactive Analysis of Static, Dynamic, and Crystalline SDTrimSP Simulations: Application to Nitrogen Ion Implantation into Vanadium

Miroslav Lebeda, Jan Drahokoupil, Vojtěch Smola et al. (+1 more)

SDTrimSP is a widely used Monte Carlo simulation code based on the Binary Collision Approximation (BCA) for modeling ion implantation and ion-solid interaction processes. While an established graphical user interface (GUI) exists for simulation setup and execution, efficient post-processing, comparison of multiple simulations, and preparation of specific input file parameters remain limited. In this work, we present a web-based interface (sdtrimsp.streamlit.app) that complements existing SDTrimSP tools by focusing on interactive visualization and analysis of depth distribution profiles. The platform enables direct upload and comparison of static and fluence-dependent dynamic profiles, supports unit conversion, and provides an integrated calculator for determining the adjustable atomic density parameter of implanted ions required in dynamic simulations. In addition, the interface offers automated conversion of standard crystallographic file formats into the SDTrimSP-specific crystal structure input format for simulations into crystalline targets. The capabilities of the interface are demonstrated for nitrogen ion implantation into vanadium, including amorphous static and dynamic simulations and static crystalline simulations for different surface orientations. The results illustrate fluence-dependent saturation effects as well as orientation-dependent ion channeling behavior. Overall, the presented web-based tool provides a convenient and flexible extension to existing SDTrimSP workflows.
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All authors Miroslav Lebeda, Jan Drahokoupil, Vojtěch Smola, Petr Vlčák

Mesoscale and Nanoscale Physics · Cross-listed from quant-ph

Exact Multimode Quantization of Superconducting Circuits via Boundary Admittance and Continued Fractions

Mustafa Bakr and Robin Wopalenski

Accurate extraction of linearized quantum circuit models from electromagnetic simulations is essential for the design of superconducting circuits. We present a quantization framework based on the driving-point admittance $Y_{\mathrm{in}}(s)$ seen by a Josephson junction embedded in an arbitrary passive linear environment. By taking the Schur complement of the nodal admittance matrix, we show that the linearized coupled system obeys an eigenvalue-dependent boundary condition, $s Y_{\mathrm{in}}(s) + 1/L_J = 0$, whose roots determine the dressed linear mode frequencies. This boundary condition admits an exact continued fraction representation: any positive-real admittance can be realized as a canonical Cauer ladder, yielding a tridiagonal (Jacobi) structure that enables certified convergence bounds via interlacing theorems.For the full nonlinear Hamiltonian, we treat Josephson junctions in the charge basis, where each cosine potential is exactly tridiagonal, and couple them to cavity modes in the Fock basis; in the general multi-junction case this yields a block-tridiagonal structure solvable by matrix continued fractions, enabling systematic diagonalization across all coupling regimes from dispersive through ultrastrong and deep strong coupling. The resulting quantization procedure is: (i)~compute or measure $Y_{\mathrm{in}}(s)$, (ii)~solve the boundary condition to obtain dressed eigenfrequencies, (iii)~synthesize an equivalent passive network, and (iv)~quantize while retaining the full cosine nonlinearity of the Josephson junction. We prove that junction participation decays as $\mathcal{O}(\omega_n^{-1})$ at high frequencies for any circuit with finite shunt capacitance, ensuring ultraviolet convergence of perturbative corrections without imposed cutoffs.
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Statistical Mechanics · Cross-listed from quant-ph

Quantum sensing with critical systems: impact of symmetry, imperfections, and decoherence

Yinan Chen, Sara Murciano, Pablo Sala et al. (+1 more)

Entangled many-body states enable high-precision quantum sensing beyond the standard quantum limit. We develop interferometric sensing protocols based on quantum critical wavefunctions and compare their performance with Greenberger-Horne-Zeilinger (GHZ) and spin-squeezed states. Building on the idea of symmetries as a metrological resource, we introduce a symmetry-based algorithm to identify optimal measurement strategies. We illustrate this algorithm both for magnetic systems with internal symmetries and Rydberg-atom arrays with spatial symmetries. We study the robustness of criticality for quantum sensing under non-unitary deformations, symmetry-preserving and symmetry-breaking decoherence, and qubit loss – identifying regimes where critical systems outperform GHZ states and showing that non-unitary deformation can even enhance sensing precision. Combined with recent results on log-depth preparation of critical wavefunctions, interferometric sensing in this setting appears increasingly promising.
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All authors Yinan Chen, Sara Murciano, Pablo Sala, Jason Alicea

Superconductivity

Inductorless Fast Phase Logic: Enabling Two-Order-of-Magnitude Density Scaling for Superconductor VLSI

Sasan Razmkhah, Douglas Scott Holmes and Massoud Pedram

Fast phase logic (FPL) is a novel digital superconductor electronic (SCE) logic family that employs multiple junction types, including switching 0-Josephson junctions (0-JJs), non-switching 0-JJ stacks, and $\pi$-JJs. FPL enables flexible, automatable cell layouts, faster pulse propagation, reduced bias current via phase-shifting $\pi$-JJs, and minimized inductive loops, thereby reducing susceptibility to trapped flux and crosstalk. A fabrication process to support FPL is proposed. NbTiN superconductors offer small grain sizes, smooth surfaces, and thermal stability up to 400~$^\circ$C, while high-$J_c$, self-shunted JJs enable compact devices. AlN dielectrics provide good crystal matching to NbTiN, improving superconducting properties. Projections indicate that FPL, combined with the proposed process, can achieve a two-order-of-magnitude increase in integration density over conventional RSFQ logic and a five-fold reduction in supply current. The increased density reduces latency and improves computational throughput, while NbTiN-based devices provide higher output voltage and impedance, improving compatibility with CMOS circuits. Further fabrication advancements, such as higher-$J_c$ NbTiN-based JJs, higher processing temperatures, and stacked JJ structures, could enhance FPL implementation and scalability toward very large-scale integration (VLSI). FPL has the potential to significantly advance SCE technology, with near-term applications in accelerator cores for signal processing and artificial intelligence, and long-term potential in supercomputing. Its advantages are evaluated through an architectural study of a fast Fourier transform (FFT) circuit, with comparisons to CMOS and SFQ technologies.
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Statistical Mechanics

Energy-Time-Accuracy Tradeoffs in Thermodynamic Computing

Alberto Rolandi, Paolo Abiuso, Patryk Lipka-Bartosik et al. (+3 more)

In the paradigm of thermodynamic computing, instead of behaving deterministically, hardware undergoes a stochastic process in order to sample from a distribution of interest. While it has been hypothesized that thermodynamic computers may achieve better energy efficiency and performance, a theoretical characterization of the resource cost of thermodynamic computations is still lacking. Here, we analyze the fundamental trade-offs between computational accuracy, energy dissipation, and time in thermodynamic computing. Using geometric bounds on entropy production, we derive general limits on the energy-delay-deficiency product (EDDP), a stochastic generalization of the traditional energy-delay product (EDP). While these limits can in principle be saturated, the corresponding optimal driving protocols require full knowledge of the final equilibrium distribution, i.e., the solution itself. To overcome this limitation, we develop quasi-optimal control schemes that require no prior information of the solution and demonstrate their performance for matrix inversion in overdamped quadratic systems. The derived bounds extend beyond this setting to more general potentials, being directly relevant to recent proposals based on non-equilibrium Langevin dynamics.
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All authors Alberto Rolandi, Paolo Abiuso, Patryk Lipka-Bartosik, Maxwell Aifer, Patrick J. Coles, Martí Perarnau-Llobet