Statistical Mechanics · Cross-listed from q-bio.BM
Polyformer: a generative framework for thermodynamic modeling of polymeric molecules
Alessio Valentini, David Pekker, Chungwen Liang et al. (+2 more)
The classic paradigm of structural biology is that the sequence of a biomolecule (
protein, nucleic acid, lipid, etc) determines its conformation (shape) which determines its biological function.
Protein folding programs like AlphaFold address this paradigm by predicting the single best conformation given a sequence that defines the molecule. However, biomolecules are not static structures, and their conformational ensemble determines their function. We present the Polyformer – a generative framework for thermodynamic modeling of polymeric molecules. Given the sequence and temperature (or another thermodynamic variable), the Polyformer generates conformations faithful to the molecule's thermodynamic conformational ensemble. It is the first generative model that solves three problems simultaneously: how does a molecule fold, what is its conformational ensemble, and how does the conformational ensemble change as we change physical temperature. As a concrete test case, we apply Polyformer to
protein domains with 50-111 residues and report good agreement of model predictions to Molecular Dynamics (MD) trajectories.
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All authors Alessio Valentini, David Pekker, Chungwen Liang, Todd Martinez, Swagatam Mukhopadhyay
Mesoscale and Nanoscale Physics
Thermodynamic signatures of spectral compression in weakly non-Hermitian Dirac fermions
Juan Pablo Esparza, Francisco J. Peña, Patricio Vargas et al. (+1 more)
Non-Hermitian band descriptions capture how loss, gain, and environmental coupling reshape
quantum matter, yet most experimental probes remain wave based or dynamical. Here we develop an
equilibrium charge-response route to spectral compression in Dirac materials. In the real-spectrum regime, invariance of the particle-number operator under the similarity transformation makes the
quantum capacitance exactly that of the Hermitian partner, so the whole non-Hermitian content is carried by the Petermann factor. In a minimal nonreciprocal
graphene model, hopping imbalance suppresses the Dirac velocity, enhancing the low-energy density of states and the capacitance as an exceptional point is approached. At charge neutrality the capacitance stays linear in temperature, with its slope enhanced relative to the Hermitian value. A perpendicular
magnetic field recasts the same compression as a collapse of the Landau-level ladder, drawing more levels into the thermal window. In two dimensions, the capacitance enhancement relative to the Hermitian partner coincides exactly with the Petermann factor, even though the two have entirely different origins. This relation provides a controlled starting point for extending
equilibrium thermodynamic probes to non-Hermitian electronic systems with interactions, disorder, and reservoir coupling.
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All authors Juan Pablo Esparza, Francisco J. Peña, Patricio Vargas, Vladimir Juričić
Strongly Correlated Electrons
Topological anisotropic non-Fermi liquid from a Berry-dipole semimetal
Konstantinos Ladovrechis
The interplay among
topology and interactions has been a promising path towards identifying novel phases of condensed matter beyond these predicted by the established classification paradigms. In the present work, we propose such a novel phase of matter by studying the fate of a three-dimensional Berry-dipole semimetal, lying at the topological
quantum critical point separating a
Hopf insulator from a trivial
insulator, in the presence of long-range Coulomb interactions. Utilizing large-$N_f$ analysis and an $\epsilon$-expansion within the renormalization-group scheme, we predict the emergence of a spatially anisotropic non-
Fermi liquid with enhanced Berry-dipole moment. The corresponding scaling relations of certain physical observables are derived as functions of the probed energy and temperature scale, and we conclude by providing an observational test for probing the enhanced topological features of the anisotropic non-
Fermi liquid.
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Statistical Mechanics
Quantum matter is weakly entangled at low energies
Samuel J. Garratt and Dmitry A. Abanin
We construct upper bounds on
entanglement entropies of many-body
quantum states that have fixed energy expectation values with respect to local
Hamiltonians. Our focus is on
entanglement entropies of subsystems that make up approximately half of the full system. The upper bound on the von Neumann
entanglement entropy is half the sum of the thermal
entropies of two fictitious systems at the same temperature as one another, with an additional area-law contribution in some systems. The effective temperature is chosen such that the sum of the thermal energies of the two fictitious systems matches the constraint on the energy of the state in the original problem; at subextensive energies, this temperature decreases with increasing system size. Our upper bounds on Rényi
entanglement entropies take an analogous form. These inequalities show that, in systems that are frustration-free (FF) and whose zero-temperature subsystem thermal
entropies scale with surface areas (rather than subsystem volumes), ground states are area-law entangled. For physical models of
quantum matter, which have well-defined specific heat capacities (and are not necessarily FF), our bounds provide a way to convert this thermodynamic data into constraints on pure-state
entanglement at both subextensive and extensive energies. We also show that our general upper bounds on half-system
entanglement entropies are optimal, up to subleading corrections, in systems with reflection
symmetry and above a subextensive energy threshold. A key application of our results is to constrain the
entanglement of
quantum states relevant to simulations of zero-temperature response functions, which have energies of order unity. We prove that, in wide varieties of FF systems in two dimensions and higher, the contributions of excitations to von Neumann
entanglement entropy are subleading compared with the contribution from the ground state.
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Strongly Correlated Electrons · Cross-listed from physics.chem-ph
Configuration interaction extension of AGP for incorporating inter-geminal correlations
Airi Kawasaki, Fei Gao and Gustavo E. Scuseria
In this paper, we develop a class of antisymmetrized geminal power configuration interaction (AGP-CI) wave functions that extend the AGP framework by incorporating inter-geminal correlations through a CI expansion. To make these wavefunctions computationally tractable, we evaluate them by rewriting the AGP-CI ansatz as a linear combination of AGPs (LC-AGP), for which overlaps and
Hamiltonian matrix elements can be computed with standard AGP machinery. Motivated by border-rank decompositions, we further reorganize this ansatz into a compact linear combination of AGPs depending on a small deformation parameter $\tau$, which controls how closely the truncated expansion approximates the full AGP-CI state.
Benchmark applications to the Hubbard model and to the small molecules H$_2$O and N$_2$ demonstrate that the proposed wavefunctions achieve consistently high accuracy and outperform the LC-AGP, particularly for systems with more electrons and in strongly correlated regimes.
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Statistical Mechanics · Cross-listed from nucl-th
Non-Gaussian fluctuations in relativistic hydrodynamics: Confluent equations for three-point correlations
Xin An, Gokce Basar and Mikhail Stephanov
We derive deterministic equations for the
evolution of non-Gaussian fluctuations in relativistic
stochastic hydrodynamics. This is achieved by defining the average local Landau frame and corresponding fluctuating hydrodynamic variables. Fully nonlinear
stochastic hydrodynamics is expressed in a unified multi-component
matrix form. A novel relativistic formalism, also manifestly covariant under SO(3) rotations of the local spatial basis in the average local Landau frame, is introduced. The equations describe correlators of all hydrodynamic variables, including fluctuating velocity (or momentum density) – a nontrivial problem in relativistic hydrodynamics.
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Materials Science · Cross-listed from physics.comp-ph
Distributional Inverse Homogenization
Arnaud Vadeboncoeur, Mark Girolami, Kaushik Bhattacharya et al. (+1 more)
For many materials, macroscopic mechanical behavior is determined by an intricate microstructure. Understanding the relation between these two scales helps scientists and engineers design better materials. The relation which maps microstructure to bulk material properties can be understood via the well-established theory of homogenization. However inverting the homogenization process, to recover microstructural information from measured macroscopic properties, is fraught with difficulties because of the averaging processes that underlie homogenization. Therefore, scientists and engineers usually need recourse to more invasive, often highly localized, investigations to estimate the microstructure. In this work, we develop a noninvasive methodology by which one can leverage large collections of measured bulk material properties to infer information about the statistics of microstructure at a global level. We call this, distributional inverse homogenization. We study this problem in one and two dimensions, considering both periodic and
stochastic homogenization. We demonstrate the methodology in the context of 2D Voronoi constructions and underpin the observed empirical success with theory in 1D. We also show how the natural spatial variability of microstructure can be exploited to gather data that enables distributional inversion. And we concurrently learn a surrogate model, approximating the homogenization map, that accelerates the resulting computations in this setting. The work formulates a new class of inverse problems, bridging ideas from probability and homogenization to facilitate the inference of microstructural material variability from macroscopic measurements.
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All authors Arnaud Vadeboncoeur, Mark Girolami, Kaushik Bhattacharya, Andrew M. Stuart
Materials Science
Generative design of inorganic materials
Jose Recatala-Gomez, Haiwen Dai, Zhu Ruiming et al. (+9 more)
Materials discovery is fundamental to advance next-generation technologies as well as for sustainable and circular economy. Beyond computational screening, generative models are efficient at finding materials with desired properties, via multi-modal learning using multiscale data. This perspective examines the landscape of generative design for inorganic materials and discusses the integration of multi-modal learning with high-throughput experimental validation. We contextualize these challenges through the lens of a generative design framework as a unified approach to address the data-driven inverse design of functional materials. The central idea of the framework is constructed around a foundation AI model for inorganic materials interlinked deeply with various property databases and high-throughput experiments via a machine learning driven closed loop, which enables the framework to solve key challenges in functional materials. We argue that domain-specific implementations of such integrated workflows represent a promising pathway toward the unresolved challenge of data-driven inverse design for atom-engineered inorganic functional materials.
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All authors Jose Recatala-Gomez, Haiwen Dai, Zhu Ruiming, Nikita Kazeev, Nong Wei, Gang Wu, Maciej Koperski, Tan Teck Leong, Andrey Ustyuzhanin, Gerbrand Ceder, Kostya Novoselov, Kedar Hippalgaonkar
Materials Science
Natural Language Embeddings of Synthesis and Testing conditions Enhance Glass Dissolution Prediction
Sajid Mannan, K. Sidharth Nambudiripad, Indrajeet Mandal et al. (+2 more)
Long-term chemical durability of glass, crucial for immobilizing
nuclear waste, is governed by glass properties such as composition, surface geometry, as well as external factors like thermodynamic conditions and surrounding medium. Despite decades of research, there are no models that account for these intrinsic and extrinsic factors to predict the dissolution rates of glass compositions. To address this challenge, we evaluate the role of natural
language embeddings capturing the synthesis and testing conditions in enhancing the predictability of glass dissolution. Evaluating the approach on hand-curated ~700 datapoints extracted from the literature, we reveal that the machine learning (ML) model including natural
language embeddings (NLP-ML) outperforms classical ML model in predicting glass dissolution rate. Furthermore, we developed a generalizable ML model by transforming the compositional features to structural descriptors of glass alongside NLP-derived features, enabling extrapolation capability to glass compositions with completely new elements absent in the training data. Evaluating this model on a completely new
dataset of glass compositions 34 chemical components in contrast to the training
dataset that had only 28 components, we demonstrate that the model indeed exhibits generalizability to glass compositions that are out-of-distribution. Altogether, this integrated approach offers a pathway towards high-fidelity glass dissolution prediction and accelerate the discovery of novel glass compositions with tailored durability for sustainable
nuclear waste management.
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All authors Sajid Mannan, K. Sidharth Nambudiripad, Indrajeet Mandal, Nitya Nand Gosvami, N. M. Anoop Krishnan
Statistical Mechanics
Specific heat of thermally driven chains
Michiel Gautama, Faezeh Khodabandehlou, Christian Maes et al. (+1 more)
We investigate the thermal responses of a harmonic oscillator chain coupled at its boundaries to heat baths held at different temperatures. This setup sustains a steady energy flux, continuously dissipating heat into both reservoirs. By introducing slow variations in the bath temperatures, we quantify the resulting excess heat currents and thereby obtain the nonequilibrium heat capacity
matrix at fixed but arbitrary temperature differences. We demonstrate the existence of a well-defined thermodynamic limit for long chains. The specific heat associated with energy exchanges with a single bath depends on the difference in friction coefficients governing the system-bath couplings. That thermokinetic effect is typical for nonequilibrium response. When the couplings with the thermal baths acquire temperature dependence, the specific heat correspondingly inherits a nontrivial temperature dependence, in sharp contrast with
equilibrium. Our results provide the first explicit determination of specific heat(s) in a locally interacting, spatially extended driven system. Beyond its exact solvability, the model may offer a natural nonequilibrium extension of the Dulong-Petit law, capturing the high-temperature behavior of driven molecules.
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All authors Michiel Gautama, Faezeh Khodabandehlou, Christian Maes, Ion Santra
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
From coupled $\mathbb{Z}_3$ Rabi models to the $\mathbb{Z}_3$ Potts model
Anatoliy I. Lotkov, Valerii K. Kozin, Denis V. Kurlov et al. (+2 more)
We study $\mathbb{Z}_3$-symmetric Rabi model that describes a three-level system coupled to two bosonic modes. We derive a mapping of the two-mode $\mathbb{Z}_3$ Rabi model onto a
qubit-
boson ring. This mapping allows us to formulate a realistic implementation of the $\mathbb{Z}_3$ Rabi model based on superconducting
qubits. It also provides context for the previously proposed optomechanical implementation of the $\mathbb{Z}_3$ Rabi model. In addition, we propose a physical implementation of the $\mathbb{Z}_3$ Potts model via a coupled chain of $\mathbb{Z}_3$ Rabi models.
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All authors Anatoliy I. Lotkov, Valerii K. Kozin, Denis V. Kurlov, Jelena Klinovaja, Daniel Loss
Superconductivity
Strong Correlation Drives Zero-Field Josephson Diode Effect
Yiheng Sun, Zhenyu Zhang and James Jun He
The supercurrent diode effect (SDE), characterized by unequal critical currents in opposite directions, has been observed with or without
magnetic fields, yet mechanisms enabling zero-field SDE without explicit
symmetry breaking remain underexplored. Here we investigate a Josephson junction with strong electron-electron interaction modeled by a Hubbard $U$ term and an odd number of electrons. We find that strong correlations induce spontaneous breaking of time-reversal and mirror
symmetries, forming a $\varphi$-junction with degenerate energy minima at $\pm\varphi$, resulting in zero-field Josephson diode effect (JDE) without
magnetic order.
Spin-orbit coupling breaks SU(2)
symmetry but does not determine diode polarity, contrasting with magneto-
chiral mechanisms. We further show that applying a tiny Zeeman field enables controllable JDE with sizable efficiency due to the enhancement by the strong
magnetic correlation, and the JDE strength peaks when the field induces a level-crossing transition. These findings establish strong electron correlation as a distinct mechanism for nonreciprocal superconducting transport, broadening the understanding of SDE origins.
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Quantum Gases
Hole and spin dynamics in an anti-ferromagnet close to half filling
Magnus Callsen, Jens H. Nyhegn, Kristian Knakkergaard Nielsen et al. (+1 more)
The interplay between charge and
spin dynamics is at the heart of strongly correlated materials. Inspired by recent
quantum simulation experiments, we develop a conserving diagrammatic method to describe the
Fermi-Hubbard model for strong repulsion and small hole doping away from the half-filled anti-
ferromagnetic ground state. We show that doping leads to four hole pockets in the Brillouin zone formed by
magnetic polarons, which become increasingly damped with hole concentration. Likewise, the
magnon spectrum of the anti-ferromagnet softens and dampens with doping due to hole-induced
magnetic frustration. This gives rise to a suppression of the anti-
ferromagnetic correlations in agreement with recent experiments. We then calculate the response of the system to a
lattice modulation and recover the qualitative difference between in-phase and out-of-phase modulations seen in experiments, which was interpreted as signs of pseudogap physics. Our results indicate that the complex competition between
spin and charge degrees of freedom and the emergence of the pseudogap phase may be usefully analyzed for small dopings, where systematic theories can be developed.
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All authors Magnus Callsen, Jens H. Nyhegn, Kristian Knakkergaard Nielsen, Georg M. Bruun
Superconductivity
Crystal structure effects on vortex dynamics in superconducting MgB$_2$ thin films
Clemens Schmid, Anton Pokusinskyi, Markus Gruber et al. (+7 more)
The current-driven resistive transition is central to superconducting single-
photon detectors, transition-edge sensors, and fluxonic devices. Depending on sample uniformity, dimensions, and heat removal, it can be driven by phase-slip events, flux-flow instabilities (FFI), or normal-domain formation. Here, we investigate the influence of two types of microstructural defects on
vortex dynamics in MgB$_2$ films: columnar growth in textured films and buffer-layer roughness in single-
crystal films. The current-voltage ($I$-$V$) curves measured at $T \approx 0.25 T_\mathrm{c}$ for both films exhibit multiple steps. Time-dependent Ginzburg-Landau simulations reproduce the major features of the experimental $I$-$V$ curves and suggest that the resistive transitions for both films are mediated by the formation and growth of normal domains rather than FFI. The single-
crystal film with buffer-layer roughness exhibits superconductivity breakdown at higher currents and pinning activation energies approximately twice those of the textured film, along with more pronounced multi-step features in the $I$-$V$ curves. These features are attributed to the combination of stronger pinning induced by lateral variations of the superconducting order parameter along the MgO buffer layer and its lower thermal boundary resistance. Our results show that both the film microstructure and the film-buffer interface are critical for the resistive transition, offering insights for superconducting devices requiring controlled dissipation at high transport currents.
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All authors Clemens Schmid, Anton Pokusinskyi, Markus Gruber, Corentin Pfaff, Theo Courtois, Alexander Kasatkin, Karine Dumesnil, Stephane Mangin, Thomas Hauet, Oleksandr Dobrovolskiy
Strongly Correlated Electrons
Tunable bifurcation of magnetic anisotropy and bi-oriented antiferromagnetic order in kagome metal GdTi3Bi4
Jianfeng Guo, Shiyu Zhu, Runnong Zhou et al. (+9 more)
The novel kagome family RTi3Bi4 (R: rare-earth) offers a unique platform for exploring distinctive physical phenomena such as anisotropy,
spin density wave, and anomalous
Hall effect. In particular, the
magnetic frustration and behavior of
magnetic anisotropy in
antiferromagnetic (AFM) kagome materials are of great interest for the fundamental studies and hold promise for next-generation device applications. Here, we report a tunable bifurcation of
magnetic anisotropic and bi-oriented AFM order observed in the quasi-1D kagome antiferromagnet GdTi3Bi4. The
magnetic domain evolutions during two plateau transition processes are directly visualized, unveiling a pronounced in-plane anisotropy along the a-axis. Temperature-dependent characterization reveals a bifurcation transition of anisotropy at approximately 2 K, where the a-axis anisotropy splits into two special orientations, revealing a hidden bi-oriented in-plane AFM order deviating from the high-
symmetry direction by 7 degree. More intriguingly, the characteristics of the bifurcated anisotropy are clearly illustrated through vector
magnetic field modulation, revealing three distinct in-plane domain phases in the transverse
magnetic field phase diagram. Our results not only provide valuable insights into the tunable bifurcation of
magnetic anisotropic in GdTi3Bi4, but also pave a novel pathway for AFM spintronics development.
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All authors Jianfeng Guo, Shiyu Zhu, Runnong Zhou, Ruwen Wang, Yunhao Wang, Jianping Sun, Zhen Zhao, Xiaoli Dong, Jinguang Cheng, Haitao Yang, Jiang Xiao, Hong-Jun Gao
Strongly Correlated Electrons
Spin-mediated hysteretic switching of unidirectional charge density waves by rotating magnetic fields
Zichao Chen, Shiyu Zhu, Kailin Xu et al. (+12 more)
Charge density waves (CDWs) are a widespread collective electronic order in
quantum materials, furnishing key insights into
symmetry breaking and competing phases. However, their dynamic control with external fields remains a pivotal challenge. Here, we report deterministic and hysteretic switching of unidirectional CDW orientation via in-plane
magnetic field rotation in
magnetic kagome metal GdTi3Bi4. Atomically resolved spectroscopy shows two types of 3a0*1a0 CDW domains, Q1 and Q2 oriented 60 degree apart along two distinct crystallographic directions and separated by atomically sharp domain walls. Rotating the
magnetic field drives reversible transitions between these CDW configurations, exhibiting a robust C2-symmetric phase diagram with pronounced hysteresis. This hysteretic switching is mediated by a field-dependent reorientation of underlying
antiferromagnetic spins, revealing a tunable energy landscape with stable and metastable states and modulates the electronic charge order via
spin-
lattice coupling. Our findings not only demonstrate the switching of CDW configurations by in-plane
magnetic field but also reveal the mechanism of coupling between CDW and
magnetic fields, offering new insights into CDW manipulation and versatile platform for developing a
spin-mediated multistate
spin-charge coupling
memory and programmable
quantum devices.
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All authors Zichao Chen, Shiyu Zhu, Kailin Xu, Ruwen Wang, Ningning Wang, Jianfeng Guo, Yunhao Wang, Xianghe Han, Zhongyi Cao, Jianping Sun, Hui Chen, Haitao Yang, Jinguang Cheng, Ziqiang Wang, Hong-Jun Gao
Materials Science
Twist-engineering of a robust Quantum Spin Hall phase in $\beta$-/flat bismuthene bilayer from first principles
Umberto Pelliccia, Alberto M. Ruiz, Diego López-Alcalá et al. (+3 more)
Twist-engineering of topological phases in two-dimensional materials offers a powerful route to modulate electronic structure beyond conventional strain or chemical control. In particular, group 15 (pnictogens) monolayers such as bismuthene provide an ideal platform due to their strong intrinsic
spin-orbit coupling (SOC) and robust topological character. Here, we investigate a previously unexplored
heterostructure consisting of a $\beta$-bismuthene monolayer rotated by 30$^\circ$ on a planar bismuthene layer stabilized on a SiC(0001) substrate. Using first-principles calculations, we demonstrate that this specific rotational
alignment induces a unique interlayer orbital hybridization which, combined with the strong SOC and the naturally broken inversion
symmetry, gives rise to a pronounced Rashba
spin-splitting, absent in the isolated monolayers. The topological nature of the system is confirmed through the calculation of the Z2 topological invariant and
Spin Hall Conductivity (SHC), revealing a robust
Quantum Spin Hall (QSH) phase with an enhanced topological response compared to the individual layers. Furthermore, we explore the chemical tunability of this system via Sb substitution, showing that the gradual reduction of SOC systematically narrows the band gap while preserving the non-trivial
topology. Our results establish large-angle twisted group 15
heterostructures as a versatile platform for engineering
spin-orbit-driven phenomena and advancing topological spintronics.
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All authors Umberto Pelliccia, Alberto M. Ruiz, Diego López-Alcalá, Gonzalo Abellán, Rafael Gonzalez-Hernandez, José J. Baldoví
Strongly Correlated Electrons
Continuous correlated states and dual-flatness in a moiré heterostructure
Mohammed M. Al Ezzi, Na Xin, Yanmeng Shi et al. (+13 more)
Many-body effects in condensed matter yield novel
quantum states when the electronic density of states is enhanced. A vivid example is flat bands, which suppress kinetic energy and let interactions dominate, when they are filled with an integer number of electrons in moire systems. Yet flat bands and commensurate fillings are not the only conditions for correlated phenomena. Situations may occur where the band structure develops locally enhanced density of states, leading to strong correlations even at non-integer fillings, although such cases often yield pseudogaps that make detection elusive. Here we demonstrate that small-angle twisted monolayer-
bilayer graphene combines moire-induced global flat band and additional local band flattening. Their coexistence allows direct comparison of correlated effects. The global route stabilizes commensurate states, while the local mechanism produces nearly flat bands, lifting degeneracy and generating
symmetry breaking at non-integer fillings, yet without opening a global gap. Because there is no global gapped signature, the system remains metallic, but the effect reveals itself in anomalous
Hall responses, signaling time-reversal
symmetry breaking and valley polarization. Our results demonstrate dual-flatness as a guiding principle, extending moire physics beyond commensurate fillings and identifying topological transport as a probe of gapless correlated metals.
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All authors Mohammed M. Al Ezzi, Na Xin, Yanmeng Shi, Shuigang Xu, Julien Barrier, Alexey Berdyugin, Shubhadeep Bhattacharjee, Angelika Knothe, Kenji Watanabe, Takashi Taniguchi, Vladimir Falko, Giovanni Vignale, Andre K. Geim, Shaffique Adam, Kostya S. Novoselov, Minsoo Kim
Materials Science
Symmetry-protected coexistence of a nodal surface and multiple types of Weyl fermions in $P6_3$-$\text{B}_{30}$
Xiao-Jing Gao, Yanfeng Ge and Yan Gao
The coexistence of topological states with different dimensionalities in a single crystalline system offers a unique platform to study the interplay of distinct fermionic excitations. Here, integrating first-principles calculations with
symmetry analysis, we propose the three-dimensional boron allotrope $P6_3$-$\text{B}_{30}$ as an ideal, structurally stable candidate for exploring multidimensional topological physics. Benefiting from the practically negligible
spin-orbit coupling of the light-element framework, $P6_3$-$\text{B}_{30}$ operates as a pristine spinless topological semimetal. We show that the combined time-reversal and twofold screw
symmetry ($\mathcal{T}S_{2z}$) enforces a robust two-dimensional nodal surface on the $k_z = \pi$ plane via a Kramers-like degeneracy. Concurrently, the system hosts a diverse set of zero-dimensional Weyl
fermions – including an unconventional double-Weyl point ($\mathcal{C} = -2$), conventional Type-I WPs ($\mathcal{C} = -1$), and completely tilted Type-II WPs ($\mathcal{C} = +1$) – emerging at the high-
symmetry points $\Gamma$ and K, as well as along the H-K path, protected by $C_6$ and $C_3$ crystalline rotational
symmetries. Crucially, the substantial momentum-space separation between the nodal surface and Weyl points allows for their unambiguous independent resolution. Calculations of the (100) surface states reveal distinct, nontrivial
Fermi arcs connecting Weyl nodes of opposite chirality. This work establishes $P6_3$-$\text{B}_{30}$ as a compelling material platform for investigating the physics of multidimensional hybrid topological
fermions and their interplay.
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Mesoscale and Nanoscale Physics
Optimal Majoranas in Mesoscopic Kitaev Chains
M. Alvarado, R. Seoane Souto, María José Calderón et al. (+1 more)
Kitaev chains realized in
quantum dots coupled via superconducting segments provide a controllable platform for engineering Majorana zero modes (MZMs). In these systems, subgap states in the hybrid region mediate the effective coupling between
quantum dots and determine the emergence of sweet-spots where MZMs are strongly localized. However, existing minimal treatments often oversimplify the mesoscopic hybrid region. We perform a full microscopic treatment of this hybrid segment, capturing the quasiparticle continuum and
spin-split Andreev bound states (ABSs), and show that it fundamentally alters the minimal picture. We derive analytical expressions for the renormalized couplings and sweet-spot conditions, establishing a direct link between microscopic chain parameters and Majorana optimization and identifying experimentally relevant regimes for improved device performance. Critically, we find that parity-crossings of the ABS, marking the onset of an odd-parity
spin-polarized regime in the segment, identify the optimal operating windows where MZMs are simultaneously well localized with a large gap to excited states.
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All authors M. Alvarado, R. Seoane Souto, María José Calderón, Ramón Aguado
Mesoscale and Nanoscale Physics
Fermionic many-body topology in cavity-coupled Su-Schrieffer-Heeger chains
Anna Ritz-Zwilling and Olesia Dmytruk
We study the effects of cavity-mediated interactions on the
symmetries and topological properties of a Su-Schrieffer-Heeger chain coupled to a single mode photonic cavity. Considering an off-resonant regime we use the high-frequency expansion in order to obtain an effective fermionic
Hamiltonian with cavity-mediated interactions. We characterize the effects of the cavity on
topology in a finite size chain by studying three different fermionic many-body topological markers using exact diagonalization: correlation functions between edges in a chain with open boundary conditions, and a winding number based on the single-particle Green's function and bulk electric polarization via the many-body formula by Resta for a chain with periodic boundary conditions. Importantly, we show that
chiral symmetry is not broken by the cavity in the many-body ground state in the high-frequency limit. Our work highlights the importance of the cavity-mediated many-body interactions in understanding the
symmetry and
topology of the system.
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Materials Science
Magnetic Microscopy of Skyrmions in Magnetic Thin Films with Chiral Overlayers
Buddhika Hondamuni, Théo Balland, Fabian Kammerbauer et al. (+15 more)
Topologically nontrivial
magnetic textures such as skyrmions offer promising opportunities for spintronic applications. In recent years, it has been shown that the
magnetic properties of layered materials can be affected by depositing
chiral molecules on the surface, while the influence of
chiral overlayers on skyrmion properties such as their stability and interactions remains largely unexplored. To address this challenge, we employ wide-field nitrogen-vacancy (NV) magnetometry to directly image skyrmions in
chiral-molecule-functionalized
magnetic thin films, enabling quantitative mapping of
magnetic stray fields over extended areas under ambient conditions. Using pixel-resolved optically detected
magnetic resonance (ODMR) combined with controlled
magnetic fields, we reproducibly nucleate and probe skyrmion states in CoFeB
ferromagnetic samples, enabling quantitative investigation of their properties. We find evidence for enantioselective and
magnetic-field-polarity-dependent modifications of skyrmion diameter, spacing, and shape, pointing to a possibility of molecular control of topological
spin textures via magneto-
chiral coupling.
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All authors Buddhika Hondamuni, Théo Balland, Fabian Kammerbauer, Ashish Moharana, Bindu, Amandeep Singh, Meital Ozeri, Shira Yochelis, Yossi Paltiel, Omkar Dhungel, Zeeshawn Kazi, Kai-Mei C. Fu, Hideyuki Watanabe, Mathias Kläui, Arne Wickenbrock, Nir Bar-Gill, Angela Wittmann, Dmitry Budker
Soft Condensed Matter · Cross-listed from physics.optics
Three-dimensional photon transport in spinodal photocatalytic aerogels: how bicontinuous morphology controls kinetic rate constants
Renaud A.L. Vallée
Anatase TiO2 dispersed in a silica aerogel
matrix forms porous monolithic photocatalysts promising for indoor air purification and VOC photo-degradation. Their bicontinuous spinodal architecture provides high surface area, structural integrity, and intense UV multiple scattering. Extracting kinetic descriptors from apparent rate constants requires an optical model for the
photon fluence, and current practice replaces the 3D pore network by a homogeneous 1D slab with effective optical coefficients – an approximation never quantified for spinodal geometries. We combine realistic 3D spinodal pore masks from Cahn-Hilliard spectral integration with 3D GPU-accelerated Monte Carlo (MC)
photon-migration simulations, introducing the solid-phase-weighted
estimator $\Phi_{3D}$ and comparing it with the conventional volume average $\Phi_{1D}$ and the
diffusion-approximation (DA) prediction $\Phi_{DA}$. The ratio $\Phi_{3D}/\Phi_{1D}$ equals 1.515 at porosity $\phi=0.70$ and 1.774 at $\phi=0.90$: the solid phase is preferentially illuminated, traced to optical phase contrast. Since pores neither absorb nor scatter,
photons cross quasi-ballistically, and the void phase sustains only $r=0.514$ of the solid-phase fluence, diluting the volume average with dark voxels. This ratio is porosity-independent, so the concentration ratio obeys the exact relation $1/[\phi r+(1-\phi)]$, reproducing both simulated values. The kinetic descriptor $k_{surf}\cdot K_{ads}$ is underestimated by 20% via the DA route and overestimated by 51.5% via the volume-averaged route. Homogeneous-slab MC simulations at matched optical thickness show that 84% of the fluence-weighted RMS discrepancy between MC and DA is intrinsic to the bicontinuous architecture and beyond any effective-medium DA. These results give a quantitative correction for kinetic extraction and design rules linking porosity, pore size and
photon utilisation.
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Statistical Mechanics · Cross-listed from quant-ph
Quantum information spreading in inhomogeneous spin ensembles
Rahul Gupta, Florian Mintert and Himadri Shekhar Dhar
We present a Krylov space based theoretical framework for modeling inhomogeneous
spin ensembles with arbitrary distributions of
spin frequencies and couplings. The framework is then used to asymptotically large
spin ensemble. In the single-excitation subspace, the Krylov construction allows for to derive exact expressions for the Lieb-Robinson velocity and
quantum speed limit, and figure of merit such as Krylov complexity. Our work reveals a strong dependence of the speed of information flow on the statistical distribution of resonance frequencies in the
spin ensemble with immediate implications for the design of components for
quantum technologies, realized for example with nitrogen vacancy centers,
nuclear spins or ultracold atoms.
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Mesoscale and Nanoscale Physics
Experimental Quantification of Nonlinear Mode Coupling in Nanomechanical Resonators using Multi-tone Excitation
Chris F. D. Wattjes, Zichao Li, Minxing Xu et al. (+3 more)
Nonlinear modal interactions in resonant systems govern a wide range of phenomena, with broad relevance across modern physics and engineering. Yet, experimentally determining the strength of nonlinear coupling in multimode resonators remains highly challenging. Here, we introduce a multi-tone spectroscopy method for identifying nonlinear coupling coefficients directly from experimental data. Our approach employs dual-tone excitation near selected resonances which, in combination with additional probing tones at higher-order modes, generates sideband responses associated with specific modal couplings. These spectral signatures are analyzed using an inverse reconstruction procedure to quantitatively determine the corresponding nonlinear coupling strengths in the frequency domain. Using this method, we determine ten pairwise nonlinear coupling parameters across five modes of highly tensioned nanostrings, enabling the reconstruction of fully experimental, device-specific nonlinear reduced-order models. Our experimentally derived models show excellent agreement with values obtained numerically using finite element based nonlinear reduced-order models. Our method is generic and can be used for the characterization of diverse modal and intermodal couplings in mechanical and hybrid resonant systems.
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All authors Chris F. D. Wattjes, Zichao Li, Minxing Xu, Richard A. Norte, Peter G. Steeneken, Farbod Alijani
Materials Science · Cross-listed from physics.optics
Twistoptics in Planar Heterostructures with an Arbitrary Number of Rotated 3D Thin Layers and 2D Conductive Sheets
Christian Lanza, José Álvarez-Cuervo, Kirill V. Voronin et al. (+5 more)
Twistoptics has recently emerged as a branch of nano-optics that explores light propagation in stacks of thin anisotropic layers rotated relative to one another. The concept is particularly relevant for polaritons – hybrid light-matter quasiparticles – in van der Waals (vdW) materials, where strong in-plane anisotropy and deep subwavelength confinement make the polaritonic dispersion highly sensitive to interlayer twist angles. This sensitivity enables exotic phenomena such as canalization, i.e., diffraction-free propagation, with potential applications ranging from thermal management to super-resolution imaging. Despite rapid progress, a general analytical framework to describe polariton propagation in twisted planar
heterostructures has been missing. Here we present an analytical model for planar stacks comprising an arbitrary number of finite-thickness anisotropic (biaxial) layers and infinitesimally thin anisotropic conductive sheets. The formalism and its high-momentum and thin-film approximations predict key polaritonic observables, such as wavelength, propagation length, and electromagnetic field distributions. We also provide open-access numerical scripts implementing the model to support their practical use. Together, these results provide a general theoretical foundation for twistoptics and should facilitate the discovery and accelerate the implementation of twist-engineered polaritonic phenomena across the electromagnetic spectrum.
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All authors Christian Lanza, José Álvarez-Cuervo, Kirill V. Voronin, Gonzalo Álvarez-Pérez, Aitana Tarazaga Martín-Luengo, Javier Martín-Sánchez, Alexey Y. Nikitin, Pablo Alonso-González
Mesoscale and Nanoscale Physics
Giant Room-Temperature Third-Order Electrical Transport in a Thin-Film Altermagnet Candidate
Hongyu Chen, Peixin Qin, Ziang Meng et al. (+14 more)
Quantum geometry, a
quantum mechanical quantity comprised of Berry
curvature and
quantum metric, describes the
geometric structure of the electronic bands in solids. The correlation between nontrivial
quantum geometry and
quantum materials leads to new findings in condensed matter systems. Here we demonstrate that altermagnets, with spontaneously broken time-reversal (T)- half-
lattice-translation and parity-time
symmetry, host both T-odd and T-even
quantum geometric quantities that simultaneously manifest themselves despite the vanishing net magnetization. Consequently,
giant room-temperature third-order electrical transport responses with sizable
quantum geometric contributions are observed in (101)-oriented RuO2 thin films, an altermagnetic candidate; in particular, the third-order
Hall effect is intimately correlated with altermagnetic order and can serve as a promising tool for detecting the Neel vector. Our work not only supports the existence of altermagnetism in 8-nm-thick RuO2 thin films, but also shows altermagnets as a versatile platform for exploring
quantum geometry and constructing
quantum electronic and spintronic devices.
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All authors Hongyu Chen, Peixin Qin, Ziang Meng, Guojian Zhao, Kai Chen, Chuanying Xi, Xiaoning Wang, Li Liu, Zhiyuan Duan, Sixu Jiang, Jingyu Li, Xiaoyang Tan, Jinghua Liu, Jianfeng Wang, Huiying Liu, Chengbao Jiang, Zhiqi Liu
Other Condensed Matter · Cross-listed from physics.optics
Time-resolved SNOM via phase-domain sampling
Philipp Schwendke, Julia Stähler and Samuel Palato
Time-resolved scanning near-field optical microscopy (tr-SNOM) enables the measurement of the dynamic optical response of functional surfaces beyond the diffraction limit. Experimental challenges are imposed both by the use of a pulsed light source, and by the need for interferometric signal modulation to isolate the near-field contribution. We present a novel experimental approach to retrieve the tr-SNOM signal using a 200 kHz
laser system and pseudo-heterodyne modulation. We circumvent the Nyquist limit for spectral demodulation by sampling modulation phases, pump intensity and SNOM signal for every
laser shot. A general time-resolved SNOM signal is derived, independent of detection scheme or physical assumptions about the near-field enhancement, and is successfully measured and isolated on WS$_2$ monolayer and multilayer regions. We confirm localization by signal-distance curves, spatial confinement at material boundaries, and by identifying signal contributions at individual modulation harmonics. Disentangling the dynamic contributions enables us to extract the dynamic dielectric function of the sample. Showing the capability of phase-domain sampling paves the way to integration of more diverse and specialized light sources, growing the potential of optical ultrafast near-field measurements.
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Statistical Mechanics
Role of volatility mixing in wealth condensation transition
Jaeseok Hur, Meesoon Ha and Hawoong Jeong
We study the role of heterogeneous
volatility in a networked wealth dynamics model and its impact on the wealth condensation transition. Extending the Bouchaud-Mézard framework, we introduce binary
volatility in networks and investigate how its configuration affects the effective power-law tail exponent of the wealth distribution. Using a
stochastic block model, we control the mixing between
volatility groups and show that the effective exponent is governed not only by the global parameter $\Lambda=2J/\beta^2$ but also by the
volatility configuration in the network. We find that local interactions between nodes with different
volatility induce the neutralization of group-wise exponents, which lowers the aggregate tail exponent and yields a condensation transition across $\gamma_{\rm c}=2$. Our results identify
volatility mixing as another control mechanism for wealth condensation and highlight the importance of noise heterogeneity in nonequilibrium systems on networks.
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Superconductivity
Controlling the Band Filling and the Band Width in Nickelate Superconductors
M. Kriener, C. Terakura, A. Kikkawa et al. (+9 more)
The new family of superconducting nickelates centered around La$_{3}$Ni$_{2}$O$_{7}$ possesses attractive features, such as the high transition temperature and the presence of an
antiferromagnetic ground state at ambient pressure, suggesting an unconventional pairing mechanism. In the nonsuperconducting state, the possibility of different density-wave orders with opposite pressure dependencies is discussed, whose relationships and microscopic origins are largely unknown. However, sample-quality issues, such as
impurity-phase formation or oxygen vacancies, impede the progress in the field. Here, we employ high-pressure synthesis and hydrostatic high-pressure transport techniques to investigate
bilayer nickelates with controlled band width and filling, and perform a systematic study on their impact on the superconductivity and other characteristic properties. While increasing the tilting of the NiO$_6$ octahedra shifts the superconducting phase to higher pressure, simultaneous hole doping reverts this trend. We also observe up to three distinct anomalies in the nonsuperconducting state which are possibly related to density-wave formation.
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All authors M. Kriener, C. Terakura, A. Kikkawa, Z. Liu, H. Murayama, M. Nakajima, Y. Fujishiro, S. Sasano, R. Ishikawa, N. Shibata, Y. Tokura, Y. Taguchi