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Physics Condensed Matter

cond-mat Watch Condensed Matter

Tuesday 4 November

Strongly Correlated Electrons

Role of on-site Coulomb energy and negative-charge transfer in a Dirac semi-metal NiTe$_2$

A. R. Shelke, C.-W. Chuang, S. Hamamoto et al. (+7 more)

Angle-resolved photoemission spectroscopy (ARPES) combined with band structure calculations have shown that the layered transition metal dichalcogenide(TMD) NiTe$_2$ is a type-II Dirac semimetal. However, conflicting conclusions were reported regarding the role of electron correlations in NiTe$_2$. We study core-levels and valence band electronic structure of single crystal NiTe$_2$ using soft and hard x-ray photoemission spectroscopy(SXPES, HAXPES), X-ray absorption spectroscopy(XAS) and Ni $2p-3d$ Resonant-PES to quantify electronic parameters in NiTe$_2$. The Ni $3d$ on-site Coulomb energy ($U_{dd}$) is quantified from measurements of the Ni $3d$ single particle density of states(DOS) and the two-hole correlation satellite. The Ni $2p$ core level and $L$-edge XAS spectra are analyzed by charge-transfer (CT) cluster model calculations using the experimental $U_{dd}$, and it shows that NiTe$_2$ exhibits a negative CT energy $\Delta$. A comparative analysis of NiO $L$-edge XAS confirms its well-known strongly correlated CT insulator character, with a larger $U_{dd}$ and positive $\Delta$. The $d$-$p$ hybridization strength $T_{eg}$ for NiTe$_2$$<$NiO, and shows that $T_{eg}$ is not responsible for reducing $U_{dd}$ in NiTe\textsubscript{2} compared to NiO. The negative-$\Delta$ and a reduced $U_{dd}$ leads to the increase in $d^n$ count on the Ni site in NiTe$_{2}$ by nearly one electron. However, importantly, since $U_{dd}$$>$$|\Delta|$, a finite repulsive $U_{dd}$ results in pushing $d$-states away from Fermi level and this is required to make NiTe$_{2}$ a moderately correlated Dirac semi-metal with band inversion in the $p$-$p$ type lowest energy excitations.
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All authors A. R. Shelke, C.-W. Chuang, S. Hamamoto, M. Oura, M. Yoshimura, N. Hiraoka, C.-N. Kuo, C.-S. Lue, A. Fujimori, A. Chainani

Mesoscale and Nanoscale Physics

Embedding independent length scale of flat bands

Seokju Lee, Seung Hun Lee and Bohm-Jung Yang

In flat-band systems with quenched kinetic energy, most of the conventional length scales related to the band dispersion become ineffectual. Although a few geometric length scales, such as the quantum metric length, can still be defined, because of their embedding dependence, i.e., the dependence on the choice of orbital positions used to construct the tight-binding model, they cannot serve as a universal length scale of the flat-band systems. Here, we introduce an embedding independent length scale $\xi_\text{flat}$ of a flat band that is defined as the localization length of an in-gap state proximate to the flat band. Because $\xi_\text{flat}$ is derived from the intrinsic localization of compact localized states, it is solely determined by the Hamiltonian and provides a robust foundation for embedding independent observables. We show analytically that the superconducting coherence length in a flat-band superconductor is given by $\xi_\text{flat}$ in the weak-coupling limit, thereby identifying $\xi_\text{flat}$ as the relevant length scale for many-body phenomena. Numerical simulations on various lattice models confirm all theoretical predictions, including the correspondence between $\xi_\text{flat}$ and the superconducting coherence length. Our results highlight $\xi_\text{flat}$ as a universal length scale for flat bands and open a pathway to embedding independent characterization of interacting flat-band materials.
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Superconductivity

Origin of sublattice particle-hole asymmetry in monolayer FeSe superconductors

Mercè Roig, Kazi Ranjibul Islam, Basu Dev Oli et al. (+7 more)

In iron-based superconductors, the two Fe atoms in the unit cell are typically related by crystal symmetries; therefore, we expect no intra-unit cell variations in the superconducting gap. However, recent experiments have challenged this expectation, reporting intra-unit cell variations in the gap with an unusual particle-hole asymmetry. Here, we examine the origin of this asymmetry between the two Fe sublattices in monolayer FeSe grown on SrTiO$_3$. We reveal that, in addition to the substrate-induced broken inversion symmetry, substrate nematic symmetry breaking is key to observing this asymmetry. We further identify two possible mechanisms through which this can occur. The first is through an odd-parity gap function that coexists with an extended $s$-wave function. The second is via a nodeless $d$-wave gap function that develops in the presence of a symmetry-breaking substrate. We argue that the latter mechanism is more physical. To test our theory, we performed scanning tunneling spectroscopy measurements across the nematic domain walls, which exhibit a clear enhancement of the asymmetry between the two Fe sublattices. In addition, we reveal that the observed sublattice particle-hole asymmetry is associated with odd-frequency pairing correlations, providing an experimental realization of this unusual pairing correlation.
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All authors Mercè Roig, Kazi Ranjibul Islam, Basu Dev Oli, Huimin Zhang, P. M. R. Brydon, Aline Ramires, Yue Yu, Michael Weinert, Lian Li, Daniel F. Agterberg

Quantum Gases

Interaction-Induced Quasicrystalline Order: Emergence of Quasi-Solid and Quasi-Supersolid Phases

Chao Zhang

Deterministic quasiperiodicity in quantum systems has long been associated with localization, criticality, or glassy behavior, and has therefore been believed to suppress long-range order rather than stabilize it. Here we demonstrate the opposite: quasiperiodicity in interactions–without any quasiperiodic potential, disorder, or geometric modulation–can generate coherent, ordered quantum phases. We study hard-core bosons in one dimension with quasiperiodic long-range interactions, V_{ij}=V_0 \cos(\pi \alpha i)\cos(\pi \alpha j), where n=\alpha=(\sqrt{5}-1)/2 is the inverse golden ratio. Using large-scale path-integral quantum Monte Carlo simulations, we uncover thermodynamically stable incompressible plateaus at irrational densities tied to Fibonacci ratios. These plateaus exhibit sharp incommensurate Bragg peaks, signaling an emergent quasi-solid with long-range quasicrystalline density order. More strikingly, at nearby fillings and interaction strengths, we identify a quasi-supersolid phase that supports both Fibonacci density ordering and finite superfluid density–demonstrating that interaction-induced quasiperiodicity can stabilize supersolid coherence. Our results establish a new mechanism for realizing ordered quasicrystalline quantum matter, and provide realistic guidance for implementation in Rydberg atom arrays, multimode cavity-QED systems, and trapped-ion quantum simulators.
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Mesoscale and Nanoscale Physics

Nanofluidic logic based on chiral skyrmion flows

Xichao Zhang, Jing Xia, Yan Zhou et al. (+4 more)

Particle-like chiral magnetic skyrmions can flow in nanotracks and behave like chiral fluids. Using interacting flows to perform logical operations is an important topic in microfluidics and nanofluidics. Here, we report a basic nanofluidic logic computing system based on chiral magnetic skyrmions flowing in parallel pipelines connected by an H-shaped junction. The flow behaviors could be manipulated by adjusting the spin polarization angle, which controls the intrinsic skyrmion Hall angle. We demonstrate that within certain range of the spin polarization angle, fully developed skyrmion flows could lead to fluidic logical operations, which significantly reduce the complexity of skyrmion logic as there is no need for deterministic creation, precise control, and detection of a single isolated skyrmion. Our results suggest that the chiral flow behaviors of magnetic quasiparticles may offer possibilities for spintronic and nanofluidic functions.
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All authors Xichao Zhang, Jing Xia, Yan Zhou, Guoping Zhao, Xiaoxi Liu, Yongbing Xu, Masahito Mochizuki

Materials Science · Cross-listed from physics.optics

Extending Reflectometry Range, A Zero-Crossing Algorithm for Thick Film Metrology

Zimu Zhou, Enrique Lopez-Guerra, Iulica Zana et al. (+7 more)

Accurate and high-efficiency film metrology remains a key challenge in High-Volume Manufacturing (HVM), where conventional spectroscopic reflectometry and white light interferometry (WLI) are either limited by model dependence or throughput. In this work, we extend the measurable film-thickness range of reflectometry to at least 50 um through a new model-free algorithm, the Linearized Reflectance Zero-Crossing (LRZ) method. The approach builds upon the previously reported Linearized Reflectance Extrema (LRE) technique but eliminates the sensitivity to spectral sampling and fringe attenuation that degrade performance in the thick-film regime. By linearizing phase response and extracting zero-crossing positions in wavenumber space, LRZ provides robust and repeatable thickness estimation without iterative fitting, achieving comparable accuracy with much higher computational efficiency than conventional model-based methods. Validation using more than 80 measurements on alumina films over NiFe substrates shows excellent correlation with WLI (r = 0.97) and low gauge repeatability and reproducibility (GR&R < 3%). Moreover, LRZ achieves an average Move-Acquire-Measure (MAM) time of approximately 2 s, which is about 7 times faster than WLI. The proposed method enables fast, accurate, and model-independent optical metrology for thick films, offering a practical solution for advanced HVM process control.
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All authors Zimu Zhou, Enrique Lopez-Guerra, Iulica Zana, Vu Nguyen, Nguyen Quoc Huy Tran, Bojun Zhou, Gary Qian, Michael Kwan, Peter Wilkens, Chester Chien

Materials Science

Homogeneous All-Inorganic Perovskite Films via High-Pressure Recrystallization

Asma Miled, Trong Tam Nguyen, Anh Vui Nguyen et al. (+13 more)

Metal halide perovskites are promising materials for optoelectronic applications owing to their outstanding optical and electronic properties. Among them, all-inorganic perovskites such as CsPbBr$_3$ offer superior thermal and chemical stability. However, obtaining high-quality CsPbBr$_3$ thin films via solution processing remains challenging due to the precursor's low solubility, and current additive or solvent engineering strategies are often complex and poorly reproducible. High-pressure recrystallization has recently emerged as a promising route to improve film quality, yet its impact on film properties remains insufficiently explored. Here, we systematically investigate the morphological, structural, and optical properties of CsPbBr$_3$ thin films prepared by high-pressure recrystallization, in comparison with standard non-recrystallized films. Optimized recrystallization at 300 bar produces smooth, pinhole-free, single-phase 3D perovskite layers with sub-nanometer roughness, while the film thickness is precisely tunable via precursor concentration. The process enhances both grain and crystallite sizes, leading to amplified spontaneous emission with a reduced excitation threshold and improved photostability. Temperature-dependent X-ray diffraction further reveals the orthorhombic–tetragonal–cubic phase transition, consistent with single-crystal behavior. This study provides fundamental insights into pressure-driven recrystallization and establishes a reproducible, scalable approach for fabricating high-quality CsPbBr$_3$ films for optoelectronic devices.
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All authors Asma Miled, Trong Tam Nguyen, Anh Vui Nguyen, José Penuelas, Aziz Benamrouche, Céline Chevalier, Thi Kim Anh Hoang, Gaëlle Trippé-Allard, Elsa Cassette, Brice Devif, Emmanuel Drouard, Emmanuelle Deleporte, Hong Hanh Mai, Abdelaziz Bouazizi, Christian Seassal, Hai Son Nguyen

Mesoscale and Nanoscale Physics

Fabrication and characterization of high-Q silicon nitride membrane resonators

Atkin D. Hyatt, Oscar A. Flores, Aman R. Agrawal et al. (+2 more)

Silicon nitride membranes are a powerful and ubiquitous optomechanical resonator technology, enabling high mechanical Q, low optical loss, and enhanced optomechanical coupling via a panoply of strain-, phononic-, and photonic-crystal engineering techniques. Fabrication and characterization of silicon nitride membranes has become a form of tacit knowledge in optomechanics research groups. Here we present a video run-through of the design, fabrication, and characterization of a contemporary silicon nitride membrane resonator (specifically, a centimeter-scale Si3N4 nanoribbon supporting $Q>10^8$ torsion modes). Our tutorial can serve as a starting point or refresher for practitioners in the field.
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All authors Atkin D. Hyatt, Oscar A. Flores, Aman R. Agrawal, Charles A. Condos, Dalziel J. Wilson

Materials Science

Equivalence of charged and neutral density functional formulations for correcting the many-body self-interaction of polarons

Stefano Falletta, Jennifer Coulter, Joel B. Varley et al. (+4 more)

The electron self-interaction problem in density functional theory affects the accurate modeling of polarons, particularly their localization and formation energy. Charged and neutral density functional formulations have been developed to address this issue, yet their relationship remains unclear. Here, we demonstrate their equivalence in treating the many-body self-interaction of the polaron state. In particular, we connect with each other piecewise-linear functionals based on adding an extra charge to the supercell, the pSIC approach derived from the energetics of the neutral defect with polaronic distortions in a supercell, and the unit-cell method for polarons based on electron-phonon couplings. We show that these approaches lead to the same formal expression of the self-interaction corrected energy, which is fully defined by the energetics of the neutral charge state of the charged polaronic structure. Residual differences between these methods solely arise from the achieved polaronic structure, which is affected by different treatments of electron-screening and finite-size effects. We apply these methods to a set of prototypical small hole and electron polarons, including the hole polaron in MgO, the hole polaron in $\beta$-Ga$_2$O$_3$, the $V_\text{k}$ center in NaI, the electron polaron in BiVO$_4$, and the electron polaron in TiO$_2$. We show that the ground-state properties of polarons obtained using charged and neutral density functional formulations are in excellent agreement.
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All authors Stefano Falletta, Jennifer Coulter, Joel B. Varley, Daniel Aberg, Babak Sadigh, Boris Kozinsky, Alfredo Pasquarello

Monday 3 November

Soft Condensed Matter

AI-assisted design of chemically recyclable polymers for food packaging

Brandon K. Phan, Chiho Kim, Janhavi Nistane et al. (+9 more)

Polymer packaging plays a crucial role in food preservation but poses major challenges in recycling and environmental persistence. To address the need for sustainable, high-performance alternatives, we employed a polymer informatics workflow to identify single- and multi-layer drop-in replacements for polymer-based packaging materials. Machine learning (ML) models, trained on carefully curated polymer datasets, predicted eight key properties across a library of approximately 7.4 million ring-opening polymerization (ROP) polymers generated by virtual forward synthesis (VFS). Candidates were prioritized by the enthalpy of polymerization, a critical metric for chemical recyclability. This screening yielded thousands of promising candidates, demonstrating the feasibility of replacing diverse packaging architectures. We then experimentally validated poly(p-dioxanone) (poly-PDO), an existing ROP polymer whose barrier performance had not been previously reported. Validation showed that poly-PDO exhibits strong water barrier performance, mechanical and thermal properties consistent with predictions, and excellent chemical recyclability (95% monomer recovery), thereby meeting the design targets and underscoring its potential for sustainable packaging. These findings highlight the power of informatics-driven approaches to accelerate the discovery of sustainable polymers by uncovering opportunities in both existing and novel chemistries.
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All authors Brandon K. Phan, Chiho Kim, Janhavi Nistane, Wei Xiong, Haoyu Chen, Woo Jin Jang, Farzad Gholami, Yongliang Su, Jerry Qi, Ryan Lively, Will Gutekunst, Rampi Ramprasad

Statistical Mechanics

Exact Mapping of Nonequilibrium to Equilibrium Phase Transitions for Systems in Contact with Two Thermal Baths

Iago N. Mamede, Carlos E. Fiore, Gustavo A. L. Forão et al. (+2 more)

We show that a large class of nonequilibrium many-body systems in contact with two thermal baths admit an exact mapping onto equivalent equilibrium systems. This mapping provides direct access to nonequilibrium phase transition points from known equilibrium results, irrespective of the model, interaction topology, or distance from equilibrium. We verify the universality of this correspondence using paradigmatic models (Ising, Potts, and Blume-Capel), and highlight distinctive features in entropy production close to critical and tricritical points. Our findings connect equilibrium and nonequilibrium statistical mechanics, with implications for microscopic thermal machines and stochastic thermodynamics.
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All authors Iago N. Mamede, Carlos E. Fiore, Gustavo A. L. Forão, Karel Proesmans, André P. Vieira

Strongly Correlated Electrons · Cross-listed from quant-ph

Superconducting pairing correlations on a trapped-ion quantum computer

Etienne Granet, Sheng-Hsuan Lin, Kevin Hémery et al. (+31 more)

The Fermi-Hubbard model is the starting point for the simulation of many strongly correlated materials, including high-temperature superconductors, whose modelling is a key motivation for the construction of quantum simulation and computing devices. However, the detection of superconducting pairing correlations has so far remained out of reach, both because of their off-diagonal character - which makes them inaccessible to local density measurements - and because of the difficulty of preparing superconducting states. Here, we report measurement of significant pairing correlations in three different regimes of Fermi-Hubbard models simulated on Quantinuum's Helios trapped-ion quantum computer. Specifically, we measure non-equilibrium pairing induced by an electromagnetic field in the half-filled square lattice model, d-wave pairing in an approximate ground state of the checkerboard Hubbard model at $1/6$-doping, and s-wave pairing in a bilayer model relevant to nickelate superconductors. These results show that a quantum computer can reliably create and probe physically relevant states with superconducting pairing correlations, opening a path to the exploration of superconductivity with quantum computers.
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All authors Etienne Granet, Sheng-Hsuan Lin, Kevin Hémery, Reza Haghshenas, Pablo Andres-Martinez, David T. Stephen, Anthony Ransford, Jake Arkinstall, M.S. Allman, Pete Campora, Samuel F. Cooper, Robert D. Delaney, Joan M. Dreiling, Brian Estey, Caroline Figgatt, Cameron Foltz, John P. Gaebler, Alex Hall, Ali Husain, Akhil Isanaka, Colin J. Kennedy, Nikhil Kotibhaskar, Ivaylo S. Madjarov, Michael Mills, Alistair R. Milne, Annie J. Park, Adam P. Reed, Brian Neyenhuis, Justin G. Bohnet, Michael Foss-Feig, Andrew C. Potter, Ramil Nigmatullin, Mohsin Iqbal, Henrik Dreyer

Other Condensed Matter · Cross-listed from hep-th

Euler-Heisenberg actions for gauge-axial background vectors: Hessian diagonalization, sector classification, and applications

Lucas Pereira de Souza

We derive the closed-form one-loop Euler-Heisenberg effective actions for Dirac fermions coupled simultaneously to classical electromagnetic vector and massive pseudo-vector backgrounds within a controlled quasi-static approximation. Through complete diagonalization of the functional Hessian, we systematically delineate the parameter space into distinct sectors characterized by stability properties and spectral structure. We identify subspaces that encompass and extend results from previous studies into a broader class, admitting propagating axial fields as physically viable regimes; strikingly, we note sectors presenting chirality-asymmetric instability. This addresses long-standing questions regarding the well-defined nature, diagonalizability, and stability of these models. From the effective actions, we derive novel nonperturbative pair-production rates for simultaneously propagating electromagnetic and axial vector backgrounds; remarkably, we find pronounced vacuum stabilization compared to previous results. Furthermore, we derive the non-perturbative contributions to the chiral current divergence, which enables dynamical chiral symmetry breaking and show that the electromagnetic coupling induces instanton-like configurations for the axial field, even when it is not a fundamental gauge field. As a proof-of-concept, we analyze a cosmological toy model of baryogenesis driven by an axial vector, providing numerical estimates that support the viability of this hypothesis. Additionally, we outline qualitative predictions for Weyl/Dirac semi-metals and briefly discuss potential applications in related phenomena, such as Quark-Gluon plasma, Electroweak scenarios and the Strong-CP problem.
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Mesoscale and Nanoscale Physics

Current cross-correlation spectroscopy of Majorana bound states

Michael Ridley, Eliahu Cohen, Christian Flindt et al. (+1 more)

The clock speed of topological quantum computers based on Majorana zero mode (MZM)-supporting nanoscale devices is limited by the time taken for electrons to traverse the device. We employ the time-dependent Landauer-Büttiker transport theory for current cross-lead correlations in a superconducting nanowire junction hosting MZMs. From the time-dependent quantum noise, we are able to extract traversal times for electrons crossing the system. After demonstrating a linear scaling of traversal times with nanowire length, we present a heuristic formula for the traversal times which accurately captures their behaviour. We then connect our framework to a proposed experimental verification of this discriminant between spurious and genuine MZMs utilizing time-resolved transport measurements.
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All authors Michael Ridley, Eliahu Cohen, Christian Flindt, Riku Tuovinen

Statistical Mechanics

Nonequilibrium Macroscopic Response Relations for Counting Statistics

Jiming Zheng and Zhiyue Lu

Understanding how macroscopic nonequilibrium systems respond to changes in external or internal parameters remains a fundamental challenge in physics. In this work, we report a parameter transitional symmetry valid for macroscopic dynamics arbitrarily far from equilibrium. The symmetry leads to exact response relations and gives meaningful expansions in both linear and short-time regimes. This framework provides a universal description of macroscopic response phenomena arbitrarily far from equilibrium - including non-stationary processes and time-dependent attractors. The theory is validated and demonstrated numerically using the Willamowski-Rossler model, which exhibits rich dynamical behaviors including limit cycles and chaos.
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Strongly Correlated Electrons

Marginal Fermi liquids from Fermi surfaces coupled via matrix boson gas

Vibhu Mishra

We propose a model of metallic critical point which we study at $T=0$ in the large-$N$ limit. We start with two species of fermions $u_i, d_i$, each with $N$ flavors and a gas of matrix bosons $b_{ij}$ with $N^2$ components. The fermions interact with each other via the intermediate boson as $\int b_{ij}^{\dagger} \, u_i^{\dagger}d_j$. The bosons have a bare dispersion $\varepsilon_{\textbf{q}}^b = \lambda_z |\textbf{q}|^z$ and we study the problem in $d$ spatial dimensions. We show that for $d = z+1,$ the electronic self energy shows marginal Fermi liquid behavior. We first evaluate the fermionic self energy $\Sigma(i\omega)$ using the standard approximate boson self energy $\Pi(\textbf{q}, i\nu) \propto |\nu|/|\textbf{q}|$ and find that $\Sigma(i\omega) \sim \omega \ln(N/|\omega|)$ which shows a much weaker dependence on $N$ when compared with similar results from non-SYK large-$N$ Ising-nematic models. Then we evaluate $\Sigma(i\omega)$ again using a more precise form of $\Pi(\textbf{q}, i\nu)$ which allows us to study the interplay between $N \rightarrow \infty$ limit for which $\Sigma(i\omega) \sim \omega \ln(1/|\omega|)$, and the $\omega \rightarrow 0$ limit where we recover $\Sigma(i\omega) \sim \omega \ln(N/|\omega|)$. We also use the full bosonic self energy to obtain the correction to the bosonic specific heat as $\frac{T}{N} \ln(1/T)$. Since there are $N^2$ bosons and $N$ fermions, the bulk heat capacity for both fermions and bosons shows nearly identical functional form $NVT \ln(N/T)$ and $NVT \ln(1/T)$ respectively for $T \rightarrow 0$. This suggests that coupling the hybridization operator $u^{\dagger}d$ to non-relativistic bosons for $d=3$ and relativistic bosons for $d=2$ provides a simple route to marginal Fermi liquid scaling.
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Superconductivity

Collective excitations and divergent spin currents in non-centrosymmetric superconductors

Markus Lysne, Philipp Werner and Nikolaj Bittner

We study the collective modes in a non-centrosymmetric superconductor with Rashba spin-orbit coupling under laser irradiation. The concept of Anderson Pseudospin Resonance allows to reveal how laser driving gives rise not only to the established resonant enhancement of the third harmonic response, but also to a resonant enhancement in the second harmonic response of the spin current. We propose a theory which explains the phenomenon without including interband transitions. The theory is corroborated by numerical simulations which incorporate interband effects and allow us to clarify the signatures of the collective modes in the long-time dynamics of the superconductor.
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Materials Science · Cross-listed from physics.chem-ph

Non-adiabatic perturbation theory of the exact factorisation

Matisse Wei-Yuan Tu and E.K.U. Gross

We present a novel nonadiabatic perturbation theory (NAPT) for correlated systems of electrons and nuclei beyond the Born-Oppenheimer (BO) approximation. The essence of the method is to exploit the smallness of the electronic-to-nuclear mass ratio by treating the electron-nuclear correlation terms in the electronic equation of motion of the exact factorisation (EF) framework as perturbation. We prove that any finite-order truncation of the NAPT preserves the normalisation of the conditional electronic factor as well as the gauge covariance of the resulting perturbative equations of motion. We illustrate the usefulness of NAPT by obtaining nonadiabatic corrections to the BO Berry phase in Jahn–Teller systems with a conical intersection. It well captures the departure of the exact Berry phase from being topological via the lowest-order NAPT. By removing the conical intersection with a constant gap, it further yields the correct scaling of the Berry phase toward zero.
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Disordered Systems and Neural Networks · Cross-listed from cs.LG

Bulk-boundary decomposition of neural networks

Donghee Lee, Hye-Sung Lee and Jaeok Yi

We present the bulk–boundary decomposition as a new framework for understanding the training dynamics of deep neural networks. Starting from the stochastic gradient descent formulation, we show that the Lagrangian can be reorganized into a data-independent bulk term and a data-dependent boundary term. The bulk captures the intrinsic dynamics set by network architecture and activation functions, while the boundary reflects stochastic interactions from training samples at the input and output layers. This decomposition exposes the local and homogeneous structure underlying deep networks. As a physical consequence of locality and homogeneity, we derive the energy continuity equation within a deep neural network.
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Mesoscale and Nanoscale Physics

Dynamical Phase Transitions Across Slow and Fast Regimes in a Two-Tone Driven Duffing Resonator

Soumya S. Kumar, Javier del Pino, Letizia Catalini et al. (+2 more)

The response of nonlinear resonators to multifrequency driving reveals rich dynamics beyond conventional single-tone theory. We study a Duffing resonator under bichromatic excitation and identify a competition between the two drives, governed by their detuning and relative amplitudes. In the slow-beating regime, where the tones are closely spaced, the secondary drive acts as a modulation that induces dynamical phase transitions between coexisting stationary states. We introduce the cycle-averaged amplitude as an order parameter and map the resulting phase diagram as a function of the drive detuning and amplitude ratio, capturing the pronounced asymmetry observed for blue versus red detuning in experiment. We devise a model to link the onset of these transitions to the resonance properties around the nonlinear stationary mode of the system. Our results provide a framework for controlling driven nonlinear systems, enabling state manipulation, and sensing in nanomechanical, optical, and superconducting circuit platforms.
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All authors Soumya S. Kumar, Javier del Pino, Letizia Catalini, Alexander Eichler, Oded Zilberberg

Statistical Mechanics · Cross-listed from quant-ph

Stability of mixed-state phases under weak decoherence

Yifan F. Zhang and Sarang Gopalakrishnan

We prove that the Gibbs states of classical, and commuting-Pauli, Hamiltonians are stable under weak local decoherence: i.e., we show that the effect of the decoherence can be locally reversed. In particular, our conclusions apply to finite-temperature equilibrium critical points and ordered low-temperature phases. In these systems the unconditional spatio-temporal correlations are long-range, and local (e.g., Metropolis) dynamics exhibits critical slowing down. Nevertheless, our results imply the existence of local "decoders" that undo the decoherence, when the decoherence strength is below a critical value. An implication of these results is that thermally stable quantum memories have a threshold against decoherence that remains nonzero as one approaches the critical temperature. Analogously, in diffusion models, stability of data distributions implies the existence of computationally-efficent local denoisers in the late-time generation dynamics.
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Statistical Mechanics · Cross-listed from hep-th

Gradient RG Flow in Scalar-Fermion QFTs

William H. Pannell, William Patrick Ronayne and Andreas Stergiou

The gradient property of the renormalisation group (RG) is examined to four-loop order in scalar-fermion systems in $d=4$ and $d=4-\varepsilon$ dimensions. The crucial role played by the beta shift, which is a modification of the standard dim-reg beta function, is elucidated, and specific conditions that it needs to satisfy for the RG flow to be gradient are derived. Over a thousand gradient-flow conditions are found, all of which are scheme-independent and satisfied whenever the full set of results needed to check them is available. It is shown, in the framework of the $\varepsilon=4-d$ expansion, that the space of conformal field theories (CFTs) is dominated by those with non-zero beta shift as the number of fields grows. Physical properties of CFTs obtained as solutions where the beta functions are not zero in the $\varepsilon$ expansion are discussed.
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Statistical Mechanics · Cross-listed from hep-th

Entanglement asymmetry in gauge theories: chiral anomaly in the finite temperature massless Schwinger model

Adrien Florio and Sara Murciano

The entanglement asymmetry has emerged in recent years as a practical quantity to study phases of matter. We present the first study of entanglement asymmetry in gauge theories by considering the chiral anomaly of the analytically solvable massless Schwinger model at both zero and finite temperatures. At zero temperature, we find the asymmetry exhibits logarithmic growth with system size. At finite temperature, we show that it is parametrically more sensitive to chiral symmetry-breaking than the corresponding local order parameter: while the chiral condensate decays exponentially, the asymmetry decreases only logarithmically. This establishes the entanglement asymmetry as a promising tool to probe (finite-temperature) phase transitions in gauge theories.
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Strongly Correlated Electrons · Cross-listed from hep-th

Intrinsic NISPT Phases, igNISPT Phases, and Mixed Anomalies of Non-Invertible Symmetries

Da-Chuan Lu and Zhengdi Sun

A bosonic non-invertible Symmetry Protected Topological (NISPT) phase in (1+1)-dim is referred to as $\textit{intrinsic}$ if it cannot be mapped, under discrete gauging, to a gapped phase with any invertible symmetry, that is, if it is protected by a non-group-theoretical fusion category symmetry. We construct the intrinsic NISPT phases by performing discrete gauging in a partial SSB phase with a fusion category symmetry that has a certain mixed anomaly. Sometimes, the anomaly of that symmetry category can be alternatively understood as a self-anomaly of a proper categorical sub-symmetry; when this is the case, the same gauging provides an anomaly resolution of this anomalous categorical sub-symmetry. This allows us to construct intrinsic gapless SPT (igSPT) phases, where the anomalous faithfully acting symmetry is non-invertible; and we refer to such igSPT phases as igNISPT phases. We provide two concrete lattice models realizing an intrinsic NISPT phase and an igNISPT phase, respectively. We also generalize the construction of intrinsic NISPT phases to (3+1)-dim.
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Materials Science · Cross-listed from physics.chem-ph

Edge Irregularity Strength: A Complementary Descriptor to Topological Indices in QSPR and QSAR Studies

U. Vijaya Chandra Kumar, H.M. Nagesh and Narahari N

In chemical graph theory, topological indices are widely used as numerical descriptors for establishing quantitative structure-property relationships (QSPR) and quantitative structure-activity relationships (QSAR). These indices successfully correlate molecular structure with various physicochemical and biological properties. In addition to these methods, the concept of edge irregularity strength, a graph labeling measure, offers another perspective for representing structural characteristics. In this context, the edge irregularity strength concept provides a systematic way of assigning numerical labels to atoms based on specific rules. In this work, we explore the chemical applicability of the edge irregularity strength and demonstrate that it can also serve as a predictive tool for physicochemical properties, similar to topological indices. The findings show that the edge irregularity strength captures molecular features and complements existing approaches to structure-property analysis in chemical graph theory.
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Materials Science · Cross-listed from cs.LG

COFAP: A Universal Framework for COFs Adsorption Prediction through Designed Multi-Modal Extraction and Cross-Modal Synergy

Zihan Li, Mingyang Wan, Mingyu Gao et al. (+4 more)

Covalent organic frameworks (COFs) are promising adsorbents for gas adsorption and separation, while identifying the optimal structures among their vast design space requires efficient high-throughput screening. Conventional machine-learning predictors rely heavily on specific gas-related features. However, these features are time-consuming and limit scalability, leading to inefficiency and labor-intensive processes. Herein, a universal COFs adsorption prediction framework (COFAP) is proposed, which can extract multi-modal structural and chemical features through deep learning, and fuse these complementary features via cross-modal attention mechanism. Without relying on explicit gas-specific thermodynamic descriptors, COFAP achieves state-of-the-art prediction performance on the hypoCOFs dataset under the conditions investigated in this study, outperforming existing approaches. Based on COFAP, we also found that high-performing COFs for gas separation concentrate within a narrow range of pore size and surface area. A weight-adjustable prioritization scheme is also developed to enable flexible, application-specific ranking of candidate COFs for researchers. Superior efficiency and accuracy render COFAP directly deployable in crystalline porous materials.
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All authors Zihan Li, Mingyang Wan, Mingyu Gao, Xishi Tai, Zhongshan Chen, Xiangke Wang, Feifan Zhang

Materials Science · Cross-listed from cs.DB

Towards Defect Phase Diagrams: From Research Data Management to Automated Workflows

Khalil Rejiba, Sang-Hyeok Lee, Christina Gasper et al. (+3 more)

Defect phase diagrams provide a unified description of crystal defect states for materials design and are central to the scientific objectives of the Collaborative Research Centre (CRC) 1394. Their construction requires the systematic integration of heterogeneous experimental and simulation data across research groups and locations. In this setting, research data management (RDM) is a key enabler of new scientific insight by linking distributed research activities and making complex data reproducible and reusable. To address the challenge of heterogeneous data sources and formats, a comprehensive RDM infrastructure has been established that links experiment, data, and analysis in a seamless workflow. The system combines: (1) a joint electronic laboratory notebook and laboratory information management system, (2) easy-to-use large-object data storage, (3) automatic metadata extraction from heterogeneous and proprietary file formats, (4) interactive provenance graphs for data exploration and reuse, and (5) automated reporting and analysis workflows. The two key technological elements are the openBIS electronic laboratory notebook and laboratory information management system, and a newly developed companion application that extends openBIS with large-scale data handling, automated metadata capture, and federated access to distributed research data. This integrated approach reduces friction in data capture and curation, enabling traceable and reusable datasets that accelerate the construction of defect phase diagrams across institutions.
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All authors Khalil Rejiba, Sang-Hyeok Lee, Christina Gasper, Martina Freund, Sandra Korte-Kerzel, Ulrich Kerzel

Materials Science

Posterior corrections for systematic distortions in atomic-resolution images from hexagonal crystals

Tyler Bortel and Peter Moeck

Digital images from crystals, as projected from the third spatial dimension and recorded in atomic resolution with any kind of real-world microscope, feature necessarily broken symmetries of the translation-periodicity-restricted Euclidean plane. The symmetry breakings are due to both the imaging process and the real structure of the imaged crystal, with the former cause typically dominating. A posterior algorithmic reduction of the symmetry breaking in such images constitutes, thus, often a correction for many of the distortions that were introduced by the imaging processes. Numerically quantified restorations of such symmetries can, therefore, be used to demonstrate the efficacy of a newly implemented posterior correction method for atomic-resolution images from hexagonal crystals. Recently developed information theory based methods are here shown to be suitable for this purpose. Thirteen experimental atomic-resolution images from graphite and monolayer molybdenite (MoS2), as respectively obtained by scanning tunneling microscopy, atomic force microscopy in the torsional resonance mode, and aberration-corrected parallel illumination transmission electron microscopy served as test cases in our larger (in its totality so far unpublished) study, from which we quote here. The source code of the software that was used for our distortion corrections and the whole report on that study are freely available on GitHub.
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Strongly Correlated Electrons

Quantum Acoustics Demystifies the Strange Metals

Eric J. Heller, Alhun Aydin, Anton M. Graf et al. (+11 more)

Phonons have long been thought to be incapable of explaining key phenomena in strange metals, including linear-in-T Planckian resistivity from high to very low temperatures. We argue that these conclusions were based on static, perturbative approaches that overlooked essential time-dependent and nonperturbative electron-lattice physics. In fact “phonons” are not the best target for discussion, just like “photons” are not the best way to think about Maxwell's equations. Quantum optics connects photons and electromagnetism, as developed 60 years ago by Glauber and others. We have been developing the parallel world of quantum acoustics. Far from being only of academic interest, the new tools are rapidly exposing the secrets of the strange metals, revealing strong vibronic (vibration-electronic) interactions playing a crucial role forming polarons and charge density waves, linear-in-$T$ resistivity at the Planckian rate over thousands of degrees, resolution of the Drude peak infrared anomaly, and the absence of a $T^4$ low-temperature resistivity rise in 2D systems, and of a Mott-Ioffe-Regel resistivity saturation. We derive Planckian transport, polarons, CDWs, and pseudogaps from the Fröhlich model. The “new physics” has been hiding in this model all along, in the right parameter regime, if it is treated nonperturbatively. In the course of this work we have uncovered the generalization of Anderson localization to dynamic media: a universal Planckian diffusion emerges, a “ghost” of Anderson localization. Planckian diffusion is clearly defined and is more fundamental than the popular but elusive, model dependent concept of “Planckian speed limit”.
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All authors Eric J. Heller, Alhun Aydin, Anton M. Graf, Joost de Nijs, Yoel Zimmermann, Xiaoyu Ouyang, Shaobing Yuan, Zixuan Chai, Siyuan Chen, Jasper Jain, Mingxuan Xiao, Chenzheng Yu, Zhongling Lu, Joonas Keski-Rahkonen

Materials Science

Directional atomic layer etching of MgO-doped lithium niobate using Br-based plasma

Ivy I. Chen, Mariya Ezzy, Emily Hsue-Chi Shi et al. (+8 more)

Lithium niobate (LiNbO$_3$, LN) is a nonlinear optical material of high interest for integrated photonics with applications ranging from optical communications to quantum information processing. The performance of on-chip devices based on thin-film lithium niobate (TFLN) is presently limited by fabrication imperfections such as sidewall surface roughness and geometry inhomogeneities over the chip. Atomic layer etching (ALE) could potentially be used to overcome these difficulties. Although an isotropic ALE process for LN has been reported, performing LN fabrication completely with ALE faces several challenges, including the lack of a directional ALE process for pattern transfer and the redeposition of involatile compounds. Here, we report a directional ALE process for LN consisting of sequential exposures of HBr/BCl$_3$/Ar plasma for surface modification and Ar plasma for removal. The HBr chemistry is found to decrease redeposition compared to F- and Cl-based plasmas, which we attribute to the higher vapor pressures of Br-based products. A grating pattern etched entirely by the process (total etch depth of 220 nm) exhibits no aspect ratio dependent etching (ARDE) down to the smallest tested gap of 150 nm, in contrast to ion milling in which ARDE manifests even at 300 nm gaps for the same etch depth. The HBr plasma chemistry is also found to support an isotropic process consisting of sequential exposures of H$_2$ plasma and HBr/BCl$_3$/Ar plasma. These processes could be used together to perform the complete fabrication process for TFLN devices, eliminating imperfections arising from ion milling.
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All authors Ivy I. Chen, Mariya Ezzy, Emily Hsue-Chi Shi, Clifford F. Frez, Suraj, Lin Yi, Mahmood Bagheri, James R. Renzas, Alireza Marandi, Frank Greer, Austin J. Minnich