Superconductivity
Gauge invariance, collective modes, and the justification of normal-state subtraction in Dirac superconductors
Hiroshi Hayasaka
In Dirac
superconductors, the unbounded spectrum of low-energy Dirac models is known to give rise to unphysical interband contributions from deep-lying states to the electromagnetic response. To eliminate these contributions, normal-state subtraction (NSS), in which the normal-state response is subtracted from the superconducting-state response, has been widely employed. However, the relation between NSS and a gauge-invariant electromagnetic response, particularly the role of the vertex correction required by the Ward identity, has remained unclear. In this work, we consider a massive-Dirac model with $s$-wave pairing and analytically investigate the electromagnetic response at zero temperature by solving the Bethe–Salpeter equation and incorporating the collective-mode contribution to the electromagnetic vertex. We show that, in the static long-wavelength limit, the vertex correction exactly cancels the bare longitudinal response with NSS, yielding the vanishing longitudinal response required by gauge invariance. In contrast, the transverse component of the vertex correction vanishes in the long-wavelength limit, so that the gauge-invariant Meissner weight coincides with that obtained from the bare transverse response with NSS. Moreover, within the class of isotropic and analytic UV regularization terms, we show that gauge invariance uniquely fixes the regularization term in the static long-wavelength limit to the value prescribed by NSS. Our results thus provide a microscopic justification for NSS.
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Mesoscale and Nanoscale Physics
ScatterWorks: A Python package for building and solving scattering network models
R. Johanna Zijderveld, Hélène Spring and Anton R. Akhmerov
Network models provide an efficient framework for studying non-interacting transport and wave-propagation phenomena in disordered and topological systems. We introduce ScatterWorks, an open-source Python package for building and solving network models. The package uses a compact network representation with composable transformation operations (tile, cut, relink, and union) to enable flexible construction of periodic and finite networks. Local scattering
matrices on nodes can be assigned by node labels or explicit indexing, assembled into global scattering equations, and used to compute quasienergies and transport observables. The package supports sparse scattering
matrices, allowing transport observables to be evaluated with Schur-based solvers. We demonstrate the package workflow on a symbolic Fabry-Perot interferometer and a numerical Chalker-Coddington model, recovering analytical expressions and the expected near-critical transport behavior of the
quantum Hall transition. Plotting utilities with label-aware rendering are included to streamline debugging and reproducible setup for larger, custom network geometries.
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Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Fabrication-free assessment of microwave losses in germanium-based dielectrics and superconductors
Haoran Lu, Kushagra Aggarwal, Xiangqin Wang et al. (+10 more)
We present a flip-chip-based sensing scheme to measure effective microwave losses associated with target materials for
quantum technologies, without requiring any device fabrication on the material under test. Using this approach, we quantify the microwave losses of a strain-engineered Ge/SiGe
quantum well
heterostructure and investigate losses arising from its Ge substrate and intermediate layers. The quality factors of the fabricated microwave resonators agree with the losses of dielectric materials independently extracted from flip-chip sensing measurements. We further study the
superconductor platinum silicon germanide (PtSiGe) prepared by thermal reaction with a deposited Pt film, finding high microwave losses that limit the suitability of the films studied here as the sole
superconductor for high-quality resonator applications. By coating Pt with Nb prior to the reaction, we observe a substantial reduction in microwave loss and a nearly three-fold enhancement of the transport critical temperature. The temperature dependence of the microwave loss is consistent with gap inhomogeneity in both superconducting films. These results identify constraints on material choices, provide design guidance for microwave
circuits on planar Ge
heterostructures, and demonstrate a fast-turnaround testing method for new materials for superconducting
quantum circuits.
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All authors Haoran Lu, Kushagra Aggarwal, Xiangqin Wang, Pauline Drexler, Daniel Tong, Maciej W. Olszewski, Anand Ithepalli, Lingda Kong, Debdeep Jena, Peter L. McMahon, David A. Muller, Dominique Bougeard, Valla Fatemi
Other Condensed Matter
Magnonic Combinatorial Memory based on a network of coupled active ring circuits
Mykhaylo Balinskiy, Paulo Julio, Jeffrey Vargas et al. (+3 more)
Magnonic Combinatorial
Memory (MCM) is a type of
memory where the bits of information are encoded in the signal propagation paths in the network. In this work, we consider MCM based on the network of a coupled active ring
circuit (ARC). Each
circuit includes a broadband amplifier, a magnonic delay line, an adjustable frequency filter, an adjustable phase shifter, and a power detector. The coupling between the
circuits is via
spin waves propagating in the common delay line - ferrite film. There may or may not be auto-oscillations in the active ring
circuits, depending on the combination of
circuit parameters and
circuit coupling. The address of MCM is defined as the combination of the states of the phase shifters and frequency filters, while the MCM state is defined as the presence/absence of the auto-oscillations. The coupling between the
circuits is achieved by placing micromagnets on top of the ferrite film. The number of bits that can be encoded in the network increases quadratically with the number of coupled
circuits. This scaling provides a fundamental advantage over conventional
memory. We present experimental data obtained for three magnonic ARCs connected via a single-
crystal yttrium iron garnet Y3Fe2(FeO4)3 (YIG) film. The data illustrate an example of encoding a 27-bit binary response pattern, corresponding to the 27 experimentally accessible phase combinations. The results demonstrate a robust operation of MCM with an On/Off ratio exceeding 30 dB at room temperature. The advantages and shortcomings of the proposed approach are discussed.
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All authors Mykhaylo Balinskiy, Paulo Julio, Jeffrey Vargas, Diana Bisono Balaguer, Jacob Greenstein, Alexander Khitun
Materials Science · Cross-listed from cs.LG
Euclidean Fourier Neural Operators
Nathanael Bosch, Niklas Frederik Schmitz and Michael F. Herbst
Fourier neural operators (FNOs) provide an efficient framework for learning mappings between function spaces as they are, by construction, independent of the grid resolution at which they are trained and evaluated. However, FNOs are not independent of the periodic domain they are applied to: their discrete spectral weights are indexed by integer
Fourier mode numbers, which correspond to physical wavevectors. When applied to a different domain, the same trained weights act at different wavevectors, and the FNO silently represents a different operator. This makes FNOs unsuitable for tasks where transfer across domains is crucial. We propose Euclidean
Fourier neural operators~(EFNOs) as a domain-independent alternative to FNOs. By parameterizing the spectral kernel as a continuous function of the physical wavevector, the EFNO can learn operators that act consistently across periodic domains of varying shape and size. We evaluate the EFNO on a simple heat equation and on a practically relevant materials science task of learning exchange-correlation potentials across different
crystal structures, and demonstrate that the EFNO is able to generalize to unseen grid sizes and domains.
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Mesoscale and Nanoscale Physics
Quantum transport and unified scaling law in graphene with polyadic Cantor electrostatic barriers
Sudhanshu Shekhar, Mohammad Umar and Bhabani Prasad Mandal
We study the
quantum transport of Dirac electrons in
graphene subjected to a polyadic Cantor-structured electrostatic potential. Using the superperiodic potential formalism, we obtain a closed-form expression for the transmission probability. As the Cantor stage increases, the transmission spectrum evolves from a sparse set of superlattice resonances to a near-transparent regime, with the polyadic order setting the rate of this
evolution. The angular response depends on the doping configuration, showing distinct behavior in the $n$–$n$–$n$, $n$–$p$–$n$, and Dirac-point cases. In the near-transparent regime, the transmission follows double-logarithmic scaling laws with respect to four independent control parameters: the Cantor stage, the potential height, the initiator length, and the angle of incidence. By combining these individual scaling relations, we establish a unified scaling law governing
quantum transport. These results show that the hierarchical self-similarity of the potential governs the transport properties of such systems.
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Mesoscale and Nanoscale Physics
Electrically Tunable Two-Component Exciton Condensate in a Coulomb-Coupled Graphene Trilayer
Bo Zou, A. Okounkova, Shuaiqing Zhang et al. (+5 more)
Multicomponent condensates possess internal phase degrees of freedom unavailable to a single-component condensate, yet their components are rarely controllable in solids. Here we realize a
graphene trilayer with negligible interlayer tunnelling in which the layer-specific carrier densities are continuously tuned by electrostatic gating.
Quantum-capacitance measurements demonstrate that charge-incompressible
quantum Hall states at total filling factors 1 and 2 persist across the full range of layer-filling configurations and continuously connect the three bilayer
exciton-condensate limits. This persistence provides evidence for a trilayer excitonic state. Static Hartree-Fock and time-dependent Hartree-Fock calculations yield two independent finite phase-stiffness eigenmodes and two linearly dispersing Goldstone modes, respectively, when all three layers are partially filled, whereas only one phase-stiffness eigenmode and one linear Goldstone mode remain when one layer is unfilled. The stiffness eigenmodes rotate continuously between the two adjacent-layer
exciton bases as charge is transferred among the layers, revealing electrical control of the condensate-mode composition. Together, the experimental and theoretical results support the identification of a two-component
exciton condensate with a continuously tunable internal structure.
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All authors Bo Zou, A. Okounkova, Shuaiqing Zhang, Jian Liao, J. Pack, K. Watanabe, T. Taniguchi, Yihang Zeng
Soft Condensed Matter
Nonholonomic collective flows: velocity–orientation locking in a continuum with microstructure
Gaetano Napoli
We develop a continuum theory for a fluid of elongated particles that advance along their own axes. The same kinematics is ideally shared by flocks of sheep, self-propelled rods, vehicular traffic, and turning flocks of birds. Within the framework of continua with vectorial microstructure, in which each point also carries an orientation, we impose the no-side-slip (skate) condition $\vv=u\,\nn$ as an ideal, non-integrable internal constraint. We derive the pure equations of motion and the equation governing the constraint reaction from the principle of virtual power. Using a constitutive closure provided by the Ericksen-Leslie theory of nematic
liquid crystals, we show how the constraint also shapes collective effects. It turns parabolic orientational
diffusion into
hyperbolic orientation-density waves and forbids any steady simple shear. It fixes the empirical Toner-Tu convective coefficient to the flow-
alignment ratio measured in colloidal rollers, thereby providing a mechanical foundation for angular sound in micropolar active hydrodynamics. It also recovers the inertial
spin model of bird flocks, with the addition of a banking force and a turn-density coupling. Finally, it recovers the classical macroscopic models of one-dimensional traffic flow, while describing steering, lateral tyre forces, and road geometry in two dimensions.
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Materials Science
Topological Signatures of Hardness and Structural Order in Network-Forming Materials
Yair Augusto Gutiérrez Fosado, Ayobami Daramola, Davide Marenduzzo et al. (+1 more)
Understanding how the
topology of network forming materials influences their physical properties remains a longstanding challenge. Here, we investigate the
topology of experimentally compatible atomistic models of amorphous silica together with the crystalline polymorphs cristobalite and quartz. By comparing multiple atomistic models of amorphous silica that equally reproduce
neutron-scattering data, we show that different microscopic descriptions can imply different topological interpretations of glass stability. To characterize the network beyond conventional
geometric descriptors, we introduce the linking valence, which quantifies the average number of topological links per network loop. This topological descriptor separates silica into two distinct classes: the mechanically harder quartz exhibit values more than an order of magnitude larger than those of amorphous silica and cristobalite, despite their common tetrahedral building blocks. Spectral analysis of the loop-linking networks provides a complementary distinction, separating amorphous from crystalline phases and revealing differences in the long-range organization of topological constraints. These results establish topological linking as a new framework for connecting the structure and physical properties of network-forming materials.
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All authors Yair Augusto Gutiérrez Fosado, Ayobami Daramola, Davide Marenduzzo, Ciprian G. Pruteanu
Mesoscale and Nanoscale Physics
Crystal-phase quantum dots in AlGaAs nanowires
Rohan Radhakrishnan, Rodion Reznik, Gilles Patriarche et al. (+6 more)
Crystal-phase
quantum dots (CPQDs)$\unicode{x2014}$
quantum dots in nanowires defined by
crystal structure rather than material composition$\unicode{x2014}$constitute the only platform capable of fabricating
quantum-dot arrays with the ultimate precision of a single atomic layer. This intrinsic control yields perfectly aligned
quantum dots with atomically sharp interfaces, providing a unique pathway toward scalable
quantum-dot-based photonic
quantum technologies. To date, CPQDs have been studied primarily in binary
semiconductors, such as InP and GaAs, where their emission linewidths are typically in the meV range, thereby limiting their technological potential. Here, we report, for the first time, CPQDs in AlGaAs nanowires and show bright single-
photon emission with linewidths as narrow as 61 $\mu eV$ and low background emission, demonstrating optical quality well beyond typical CPQDs. We attribute this performance to a type-I band
alignment, as suggested by an
exciton lifetime of 1 ns, significantly shorter than that typically observed in type-II CPQDs. Additionally, we observe an
exciton fine-structure splitting and a Zeeman splitting, as commonly observed in standard type-I self-assembled
quantum dots.
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All authors Rohan Radhakrishnan, Rodion Reznik, Gilles Patriarche, Lorenzo Leandro, Igor Ilkiv, Anna Andreeva, Artem Khrebtov, George Cirlin, Nika Akopian
Materials Science
Work Function and High-Coverage Adsorption Energy as Hydrogen-Evolution Descriptors on Ag-Au-Pd-Pt Alloys
Zacharias Liasi, Ridha Zerdoumi, Felix Thelen et al. (+8 more)
Hydrogen-
evolution activity is commonly rationalized through hydrogen adsorption energies and the Sabatier principle, yet this descriptor picture becomes ambiguous on multimetallic surfaces, where each composition exposes a distribution of local adsorption environments. Here we investigate whether the bare-surface work function, previously shown to add predictive information for monometallic surfaces, remains an activity descriptor for compositionally complex surfaces. We test this on three combinatorial Ag-Au-Pd-Pt thin-film materials libraries screened for acidic hydrogen
evolution by scanning electrochemical
cell microscopy. Graph neural networks provide adsorption-energy distributions and work functions for each measured composition. A work-function-only model explained most of the activity variation (mean $R^2_\mathrm{log}$ = 0.903), as did a coverage-corrected adsorption model (mean $R^2_\mathrm{log}$ = 0.955), outperforming dilute adsorption (mean $R^2_\mathrm{log}$ = 0.758). Combining work function and coverage-corrected adsorption yielded the highest fit quality (mean $R^2_\mathrm{log}$ = 0.969), but only a small gain over coverage-corrected adsorption alone. For these four metals the coverage-corrected adsorption energy and work function follow a similar trend, producing similar activity rankings, hence including both adds little beyond either one individually, although both are strong predictors.
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All authors Zacharias Liasi, Ridha Zerdoumi, Felix Thelen, Geovane Arruda de Oliveira, Rico Zehl, Natalia Pukhareva, Leonardo H. Morais, Henrik H. Kristoffersen, Alfred Ludwig, Wolfgang Schuhmann, Jan Rossmeisl
Mesoscale and Nanoscale Physics
Evidence for Three-component Interlayer Coherent Exciton Condensation
Subi Du, Xiaohan Zhang, Hongxi Song et al. (+8 more)
Increasing the number of internal components in a
quantum many-body system can host collective orders inaccessible to simpler settings.
Quantum Hall bilayers provide a canonical realization of interlayer
exciton condensation, yet extending such coherence across three independently addressable electronic fluids has remained elusive. Here we report evidence for three-component interlayer coherent
exciton condensation in triple-layer
graphene system. Using Rydberg
excitons in an adjacent WSe2 monolayer as a layer-sensitive optical probe, we resolve interaction-induced incompressibility at zeroth-Landau-level crossings for all three pairwise layer combinations, establishing top-middle, middle-bottom and top-bottom
exciton condensate channels within the same device. Independent control of displacement field and interlayer bias continuously tunes these pairwise states towards a regime where Landau levels from all three layers approach simultaneous degeneracy. At their convergence, incompressibility persists while the
exciton energy and spectral weight evolve smoothly between the pairwise limits, suggesting coherent participation of all three layers in a single three-component state. More broadly, the ability to independently control layer potentials and engineer interlayer interactions establishes multilayer
graphene as a programmable synthetic dimension for exploring higher-component
quantum Hall order and simulating strongly correlated
quantum matter.
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All authors Subi Du, Xiaohan Zhang, Hongxi Song, Siyu Fan, Yiduo Wang, Zhenyu Wang, Song Liu, Kenji Watanabe, Takashi Taniguchi, Jiangping Hu, Yang Xu
Statistical Mechanics
A Generalized Model for Disordered Random Sequential Adsorption with Charge-Dependent Deposition
G. Palacios and A. M. S. Macêdo
We generalize a one-dimensional random sequential adsorption model (RSA) of charged unit segments in which the deposition position follows a beta kernel determined by the charges bounding the available gap and those of the incoming particle. The interaction parameter \(0\leq\lambda<1\) interpolates between uniform car parking and strongly localized deposition. We derive a four component generating function equation that provides exact recursions for the complete occupation statistics, although only the mean and variance are analyzed in detail here. Exact finite-shell solutions serve as
benchmarks for the Gauss–Jacobi quadrature and Monte Carlo simulations. We prove that, although boundary charges affect finite size behavior, the four boundary states have the same asymptotic mean and variance densities, consequently, we prove that the jammed density is self-averaging. Numerical results show that charge selectivity increases the coverage, especially for mixtures dominated by opposite endpoint charges, which also exhibit strongly reduced fluctuations near \(\lambda=1\). The model provides a tractable connection between uniform RSA, dynamically generated disorder, and interaction-driven deposition.
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Materials Science · Cross-listed from physics.ins-det
Full-field fluorescence computed tomography (F3CT) using a calibrated virtual cone-beam pinhole geometry
Thomas Zillhardt, Yunhui Chen, Alexander Rack et al. (+4 more)
We present F3CT, a synchrotron-based hyperspectral full-field fluorescence computed
tomography technique that avoids raster scanning by combining a pinhole aperture with an energy-resolving 2D detector. A virtual cone-beam model and two-stage calibration-reconstruction workflow enable 3D elemental mapping under full-field illumination. The method is demonstrated on biological and geological specimens, resolving silver-stain distributions in zebrafish tissue and high-energy fluorescence signatures in rock cores. Phase-contrast tomograms acquired sequentially under the same experimental geometry provide co-registered structural context. F3CT provides a high-throughput route to 3D XRF imaging and establishes a foundation for correlated structural and chemical
tomography, with potential for future in-situ and operando implementations.
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All authors Thomas Zillhardt, Yunhui Chen, Alexander Rack, Matthew Veale, Matt Wilson, Philip J. Withers, Nicola Viganò
Materials Science
Phenomenological Growth Regimes in Liquid-Precursor CVD of MoS$_2$ on Functional Substrates
Osamah Kharsah, Kilian Mouchel, Yossarian Liebsch et al. (+8 more)
The integration of two-dimensional transition-metal dichalcogenides (TMDCs) onto functional substrates remains constrained by
stochastic vapor-phase growth dynamics. Here, we show that
liquid-phase precursor chemical vapor deposition (CVD) of MoS$_2$ introduces growth conditions that are consistent with a substrate-influenced reaction-
diffusion process. By utilizing pre-growth
spin-coated MoO$_3$ intermediates across a diverse crystalline library (sapphire, SrTiO$_3$, rutile TiO$_2$, MgO, and 6H-SiC), we find that substrate-dependent variations in precursor wetting, surface chemistry, and inferred mass-transport constraints correlate with distinct growth morphologies. These substrate-dependent growth regimes are interpreted in terms of reduced effective lateral growth length on SrTiO$_3$, possible precursor anchoring on TiO$_2$, likely chemical surface restructuring on MgO, and possible step-edge growth on SiC. Raman and photoluminescence spectroscopy reveal substrate-dependent variations in vibrational and optical response that correlate with differences in strain, charge environment, and dielectric screening. Ultimately, this work highlights a substrate-dependent reaction-
diffusion framework as a potentially useful route for tuning the structural and optical properties of large-area 2D materials.
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All authors Osamah Kharsah, Kilian Mouchel, Yossarian Liebsch, Cathy Sulaiman, Joel Verlande, Anke Hierzenberger, Abdallah Alghazali, Clara Grygiel, Stéphane Guillous, Henning Lebius, Marika Schleberger
Materials Science
Nanolamellar Hybrid High-Entropy Alloys with Superior Micromechanical Properties
Shivam Dangwal, Yoji Mine, Shohei Ueki et al. (+5 more)
Metallic materials with nanolamellar structures, such as pearlitic steels, exhibit high strength with appropriate ductility. Considering the potential ability of such nanolamellar structures to break the traditional strength-ductility trade-off in metallic
alloys, this study aims at developing a unique nanolamellar structure with superior micromechanical properties by combining two different high-
entropy alloys (HEAs). Al0.1CoCrFeNi with the face-centered cubic (FCC) structure is combined with TiZrHfNbTa with the body-centered cubic (BCC) structure using high-pressure torsion (HPT) of half discs of each
alloy. That way, a layered hybrid structure was formed, with layer thickness down to about 61 nm. The BCC/FCC nanolamellar hybrid structure exhibits an exceptional combination of properties with an ultimate tensile strength of 2.4 GPa, a maximum bending strength of 4.0 GPa, and a hardness of 740 Hv, while retaining some ductility/plasticity under both tensile and bending loads. Detailed analyses by synchrotron diffraction, electron microscopy and atom probe
tomography suggests that these high strength and hardness, which are superior to those of nanostructured HEAs, result from: (i) extreme grain boundary strengthening from nanograins with a mean size of 22 nm, (ii) presence of defects such as dislocations in FCC and BCC, stacking faults in FCC and twins in FCC, and (iii) interphase hardening from BCC/FCC nanolamellar boundaries with about 30% contribution to the total hardness. This work demonstrates that combining two HEAs using HPT into a defect-rich hybrid nanolamellar composite forms a promising synergy of ultrahigh strength and reasonable ductility/plasticity.
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All authors Shivam Dangwal, Yoji Mine, Shohei Ueki, Xavier Sauvage, Fabien Cuvilly, Liliana Romero Resendiz, Muhammad Naeem, Kaveh Edalati
Mesoscale and Nanoscale Physics
Rapid Charge Stability Diagram Generation from Device-level Modeling of Semiconductor Quantum Dots
Ron Nodel, David W. Kanaar, Connor Nasseraddin et al. (+5 more)
Self-consistent Schrödinger-Poisson calculations are a powerful tool for predicting the behavior of layered
semiconductor quantum dot devices. However, characterization of charge stability diagrams through fully simulated gate-voltage sweeps is computationally expensive. Combining a Multi-Domain Multi-Model (MDMM) approach with an automated tuning routine, we identify gate voltages associated with selected charge configurations. This small set of self-consistent simulations can be augmented with Full Configuration Interaction (FCI) energy calculations to extract charging energies, lever arms, and interdot Coulomb interactions to directly parameterize a Hubbard model for rapid charge stability diagram generation. For an Intel Tunnel Falls Si/SiGe device, we demonstrate the Hubbard model's ability to reproduce charge stability diagrams at a fraction of the computational cost in comparison to voltage bias sweeps. We further compare the simulated diagrams to experimental data and demonstrate qualitative agreement. Our result represents a step towards predictive digital twin models for
semiconductor quantum dot devices. Finally, we apply this workflow towards lever arm engineering in a second device, demonstrating that the method extends to multiple architectures.
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All authors Ron Nodel, David W. Kanaar, Connor Nasseraddin, Tim J. Wilson, Hong-Wen Jiang, Jason R. Petta, Chris Anderson, Mark F. Gyure
Materials Science
QUBO-Compatible Active Learning for Inverse Design of High-Entropy Alloys
Giorgio Silvi, Kirsten Bark, Rolando Reiner et al. (+5 more)
Machine-learned forward models can rapidly predict
alloy properties, but their use for inverse design remains challenging when the search should also retain compatibility with quadratic unconstrained binary optimization (QUBO). Here, we develop a QUBO-compatible active-learning framework for inverse design of high-
entropy alloys using a pretrained graph-neural-network predictor as a fixed property oracle. A property-guided binary variational autoencoder provides a binary latent representation, while an ensemble of quadratic factorization machines guides candidate selection. We systematically
benchmark the framework through controlled latent-space ablations and comparison with direct composition-space optimization. The results show that candidate generation is a major determinant of search performance: local perturbations around previously high-performing latent codes provide the largest workflow-specific improvement, while surrogate-based selection further prioritizes candidates within the enriched search pool. The resulting QUBO-compatible workflow remains competitive with strong classical optimization strategies, although a composition-space genetic
algorithm achieves the highest mean score. Finally, the learned quadratic surrogate can be exported directly as a QUBO. These results show that effective data acquisition can be separated from the final QUBO optimization endpoint, providing a benchmarked route for QUBO-compatible data-driven materials inverse design.
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All authors Giorgio Silvi, Kirsten Bark, Rolando Reiner, Nicolas Vogt, Thomas Plehn, Daniel Barragan-Yani, Marc Landmann, David Melching
Materials Science
Interplay between crystal structure and magnetism in CeCrB$_4$
Mirosław Werwiński, Andrzej Szajek and Andrzej Kowalczyk
CeCrB$_4$ belongs to the family of MTB$_4$ ternary metal borides, some of whose
magnetic phases have recently been identified as
quantum spin dimers. Employing density functional theory within the GGA+$U$ framework, this work investigates the key ground-state properties of this system, including its ferromagnetic ground state, the mixed-valence nature of cerium, and the charge transfer from the cationic cerium–chromium layers to the anionic boron layers. In particular, we focus on elucidating the bonding mechanism within the structurally embedded Cr-Cr dimers. Specifically, we evaluate a previously proposed interpretation that the localized Cr $3d_{z^2}$ states are molecular-like bonding and antibonding states. The calculated dependence of the $3d_{z^2}$ electronic structure on the intra-dimer distance correlates with the level-splitting characteristics known for classical homonuclear diatomic molecules.
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Mesoscale and Nanoscale Physics
Quantum Geometric Origin of Nonlinear Current Induced Orbital Magnetization
Xue-Jin Zhang, Yue-Xin Huang, Wei Du et al. (+5 more)
Electric generation of magnetization is a focus of condensed matter research, and has recently been advanced into the nonlinear regime. However, due to the nonlocal nature of orbital magnetism, how to properly formulate nonlinear current-induced orbital magnetization remains a fundamental challenge. Here, we develop the proper theory for this effect. This is based on the microscopic derivation of field-corrected orbital
magnetic moment of a Bloch electron, a critical missing piece in the present theory. We show that the
quantum geometric origin of this phenomenon lies in both the anomalous orbital polarizability and the Berry-connection polarizability, which often provide competing contributions. Combining our theory with first-principles calculations, we predict significant, experimentally accessible nonlinear orbital magnetization generated in strained bilayer
graphene, monolayer 1T' $\mathrm{MoS_2}$ and $\mathrm{MoTe_2}$. Remarkably, nonlinear orbital magnetization can dominate over its
spin counterpart in materials with topological band features, irrespective of the
spin-orbit coupling strength.
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All authors Xue-Jin Zhang, Yue-Xin Huang, Wei Du, Xiaolong Feng, Shen Lai, Cong Xiao, Qian Niu, Shengyuan A. Yang
Soft Condensed Matter · Cross-listed from physics.flu-dyn
Inclination-Induced Crossover in the Velocity Scaling of Lubrication-Mediated Droplet Motion
Haruka Hitomi and Ko Okumura
We experimentally investigate the creeping motion of water droplets sliding along an inclined surface immersed in a viscous oil. The droplet velocity, width, and height are measured over a broad range of droplet sizes and inclination angles. The velocity increases with droplet radius according to a power law, but the corresponding exponent depends strongly on the inclination angle. At small inclinations, the exponent is close to 3/2, whereas at larger inclinations it progressively approaches 9/4. The results therefore reveal a continuous inclination-induced crossover in the velocity-size scaling of lubrication-mediated droplet motion. A scaling analysis based on Landau-Levich-Derjaguin film formation and viscous dissipation in the dynamic meniscus reproduces these limiting behaviors, which correspond to the quasi-spherical and pancake scaling regimes, respectively. Remarkably, the
evolution of the velocity scaling is substantially more pronounced than the corresponding
evolution of the macroscopic droplet shape. While the velocity data progressively approach the pancake scaling law at large inclinations, the global droplet dimensions evolve in a more complex manner than expected from a simple pancake-shape picture. In particular, the approach to pancake-like velocity scaling occurs even when the measured droplet dimensions remain far from the corresponding pancake-limit geometry. These observations suggest a crossover in the dominant lubrication-dissipation mechanism beneath the droplet that is not directly reflected in the global droplet morphology. The results identify inclination angle as a key control parameter governing lubrication-mediated droplet motion and highlight the distinction between global shape
evolution and local dissipation dynamics in
liquid-
liquid systems.
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Quantum Gases · Cross-listed from physics.optics
Three-dimensional optical vortices in nonlinear Bessel waveguides
Carlos F. Sánchez, Humberto Michinel, Boris Malomed et al. (+2 more)
We explore the formation, stability, and propagation dynamics of light bullets carrying orbital angular momentum (vorticity) in Bessel-structured nonlinear graded-index waveguides. While these waves are prone to the collapse in uniform three-dimensional media, we demonstrate that their stabilization is provided by a squared-Bessel index profile in the plane orthogonal to the propagation direction, which may play the role of the waveguiding or antiwaveguiding potential. Different solution families are obtained, revealing a variety of power-vs.-propagation-constant diagrams, characterizing the coexistence of multiple families. We analyze the propagation dynamics in a wide experimentally accessible parameter range. Our results contribute to the understanding of nonlinear light localization in multidimensional settings and suggest new possibilities for using structured light in advanced photonic applications.
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All authors Carlos F. Sánchez, Humberto Michinel, Boris Malomed, Ángel Paredes, José R. Salgueiro
Superconductivity
Two-dimensional quantum Griffith singularity in three-dimensional ZrN$_x$ superconducting films
Zi-Yan Han, Li-Min Yu, Yu-Cheng Cong et al. (+3 more)
We report the experimental observation of two-dimensional (2D)
quantum Griffiths singularity (QGS) in $\sim$200-nm-thick epitaxial ZrN$_x$ superconducting films. The films possess a rock-salt structure and are three-dimensional (3D) with respect to superconductivity. For each film with $x \gtrsim 1.30$, the low-temperature magnetoresistance isotherms under fields perpendicular and parallel to the film plane cross over at a broad
magnetic field range independently rather than at a single crossing point. Despite the macroscopic 3D nature of the superconductivity, the magnetoresistance isotherms at selected adjacent temperatures follow the theoretical prediction of power-law scaling for 2D superconducting systems, rather than that for 3D systems. The effective critical exponent $z\nu$, obtained by analyzing the magnetoresistance isotherms using the 2D power-law scaling, increases with decreasing temperature and diverges as the
quantum phase transition is approached. In addition, the resistivity data near the
superconductor-
insulator or
superconductor-metal transitions obey an activated scaling form that describes the
quantum phase transition of 2D superconducting systems governed by an infinite-randomness critical point. The QGS in the ZrN$_x$ films is attributed to quenched disorder induced by intrinsic defects, such as Zr vacancies and N interstitials, which creates spatially inhomogeneous superconducting rare regions. The dynamics of these rare regions, which may exhibit effective 2D characteristics near the
quantum critical point, dominate the transport properties of the system near the
quantum phase transition. Our results provide compelling evidence for the existence of QGS in 3D
superconductors and highlight the crucial role of disorder-induced inhomogeneity in determining the critical behavior of
quantum phase transitions.
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All authors Zi-Yan Han, Li-Min Yu, Yu-Cheng Cong, Yang Yang, Zhi-Xiang Sun, Zhi-Qing Li
Quantum Gases
Quantum thermodynamics near the border of a one-dimensional Bose gas
Carsten Henkel
We consider an ultracold Bose gas in a half-open potential well, otherwise confined to a quasi-one-dimensional geometry. The Bogoliubov equations for its elementary excitations are solved in the continuous spectrum to explore the particle and energy content near the edge of the gas, beyond the often applied local density approximation. In particular, gradients in the condensate density enhance density-dominated excitations in the border region. We discuss excess (missing) particles and their energy by comparing to suitable reference solutions for quasi-homogeneous systems. The density profile near the edge shows no Friedel oscillations, but a dipolar feature from the spill-out of thermally excited particles. The calculations are performed in the grand-canonical ensemble and in the thermodynamic limit.
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Soft Condensed Matter
Proximity to Jamming Governs Acoustic Attenuation in Damped Packings
Colton Kawamura, Derek R. Olson, Anthony P. Austin et al. (+3 more)
We use particle-based numerical simulations to address a longstanding question regarding the origins of the linear frequency dependence of attenuation in fluid-saturated granular media. We study both the acoustic modes and wave propagation in damped, disordered particle packings. We calculate the damped vibrational modes of packings as a function of frequency, pressure, and grain-contact dissipation. The spatial structure and dissipation of these modes show a clear transition at a pressure-dependent critical frequency from viscous-like continuum behavior to more localized, scattering modes. We also measure how wavespeed and spatial attenuation rate depend on these same parameters. At the same critical frequency, wave propagation also shifts from coherent motion, where attenuation scales quadratically with frequency and linearly with contact damping, to much more incoherent particle-scale motion, where attenuation scales linearly with frequency and sublinearly with contact damping. All of these features, including the transition frequency, are consistent with a large collection of experimental data, which has not been explained by any framework based on grain-scale physics. We refer to this approach as “Jammed-Network Scattering” (JNS), and propose it as a grain-scale framework for understanding the acoustics of fluid-saturated granular media.
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All authors Colton Kawamura, Derek R. Olson, Anthony P. Austin, Joshua A. Dijksman, Brian P. Tighe, Abram H. Clark
Mesoscale and Nanoscale Physics
Topological signatures in the curvature-induced energy response
Jaehyeok Lee, Iuegyun Hong and Jinhong Park
Relativistic effective field theory predicts a topological energy response to a gravitational field that appears at third order in spatial gradients. Here, we investigate how this response emerges in the nonrelativistic Haldane model using a microscopic
lattice formulation of
curvature-induced deformations. We find that the leading first-order energy response is nonuniversal and depends on the bond-resolved structure of the deformation; in particular, it vanishes for a symmetric modulation of the three nearest-neighbor hoppings. At third order, the
curvature-induced energy response contains a bond-symmetric component together with nonuniversal bond-dependent contributions. The bond-symmetric component, which is isolated by a uniform modulation of the three hoppings, exhibits a universal discontinuity across the topological transition whose magnitude agrees with the relativistic gravitational Chern–Simons prediction. Thus, although the full
curvature-induced energy response generally contains nonuniversal
lattice contributions, its third-order response retains a universal topological component beyond the relativistic limit.
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Materials Science
Light-induced atomic motion in ionic crystals
Jacob C. Warming, Simon P. S. Jessen, Emma A. Husted et al. (+5 more)
Atomic motion in solids is conventionally driven by elastic collisions between ionizing particles and atoms, which transfer momentum and induce
lattice displacements. In this work, we demonstrate a different mechanism for atomic displacement based on optical excitation of scintillating ionic
crystals. Ionic
crystals are unique systems because of the closed-shell electronic configuration of their constituent ions. In these materials, excitation above the band gap generates a hole that strongly distorts the
lattice, resulting in the formation of a self-trapped hole (STH). The STH is Coulomb-attracted to the electron, thereby forming a self-trapped
exciton (STE). Here, we demonstrate that in BaF2 - one of the fastest scintillators - the STE structure promotes the formation of long-lived electron and hole traps that persist in the
lattice at room temperature. Such trapped electron-hole pairs occupy vacancy-interstitial fluorine pair positions, and can be created indiscernibly using optical or ionizing radiation excitation, as long as the STH is formed. Further, we demonstrate that it is possible to control the defect
evolution with light. Selective optical stimulation of the trapped electrons or holes enables the regeneration of the STE at later times. This light-controlled defect engineering allows us to increase the yield of the STE signal appearing as optically stimulated luminescence (OSL) and to image the spatial distribution of the initial energy deposition, holding strong potential for ionizing-radiation detection. These findings provide a common framework underlying scintillation and OSL in ionic
crystals of the fluorite structure, allowing for optical manipulation of atomic vacancies-interstitial pairs in similar systems.
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All authors Jacob C. Warming, Simon P. S. Jessen, Emma A. Husted, Jan Thøgersen, Stefan Gundacker, Brian Julsgaard, Peter Balling, Rosana M. Turtos
Statistical Mechanics · Cross-listed from math-ph
Lattice Green's function of the hyperkagome lattice: modular uniformization at level 30 from an orthogonal differential Galois group
Bryan Nasr and Jean-Marie Maillard
The
lattice Green's functions of the cubic
lattices are classical: each is a symmetric square of a second-order operator, with a closed form in complete elliptic integrals. The hyperkagome
lattice, realized by the iridium sublattice of the
spin-
liquid candidate Na4Ir3O8, has resisted such a treatment: Varma and Monien reduced its density of states to a threefold integral they found no way to solve exactly. From exact
lattice moments we obtain an irreducible third-order linear differential (Picard-Fuchs) operator annihilating the Green's function. It is not a literal symmetric square, yet its symmetric square carries a rational solution: the differential Galois group is orthogonal, and an order-two differential intertwiner makes the operator projectively a symmetric square. Our main result is that the underlying second-order operator is the uniformizing equation of the genus-zero modular curve of Gamma_0(30)+, the level-thirty group generated by Gamma_0(30) and all its Atkin-Lehner involutions, an explicit eta quotient parametrizing the natural variable. That uniformizing equation is itself not new - it is a row of the Lian-Yau table of genus-zero groups - so what is new here is the identification of a
lattice Green's function with it, together with a proof: the Schwarzian identity is established by an a priori pole-degree bound rather than checked numerically, which also proves the tabulated entry. The hyperkagome Green's function is therefore modular at level thirty, supplying the closed form Varma and Monien sought. Its weight-two period is obtained explicitly: a depth-one quasimodular form which we prove is not a modular form times an algebraic function at any weight.
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Mesoscale and Nanoscale Physics · Cross-listed from physics.optics
Self-partitioned Interfacial Time Crystals
Joseph Huang and Yi Yang
Nonequilibrium many-body systems can spontaneously break
symmetry in time, as in time
crystals, or in space, through self-organized domains and interfaces. Whether these two forms of
symmetry breaking can intertwine so that an emergent interface alone hosts time-crystalline order remains unknown. In this work, by introducing the Rabi-Hatano-Nelson model, we unveil the existence and mechanism of a self-partitioned interfacial time
crystal (SPITC), where a homogeneous system generates its own internal and tunable interface, at which the time-translation
symmetry is also spontaneously broken. Such a SPITC phase is intrinsically induced by nonreciprocity and open boundary conditions, without external pumping or long-range interaction. The periodic and open boundary phase diagrams of the system are both mapped out;
vacuum and Dicke-like superradiance with static or active orders are identified, with analytical phase boundaries in the weak coupling limit. The frequency of the SPITC is found to scale quadratically with the
spin-
photon coupling strength, as we derive analytically for the slow dynamics of the
spins. The position of the SPITC boundary scales with a critical exponent of $-1$ as a function of the degree of nonreciprocity, in stark contrast to $-1/2$ for an otherwise stationary boundary. Our construction of SPITC establishes a route to spatiotemporal order in non-Hermitian many-body systems.
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Strongly Correlated Electrons
Field-tuned quasiparticles and electronic structure in heavy-fermion YbNi4P2
Will Broad, Owen Moulding, Takaki Muramatsu et al. (+7 more)
We study the Fermi surface
topology and quasiparticle properties in the heavy
fermion compound YbNi4P2 at high
magnetic fields using
quantum oscillation measurements. We observe a large decrease of the quasiparticle mass with increasing field and demonstrate good qualitative agreement with the single-ion Kondo model. At the putative Lifshitz transition at 17 T, we observe a sudden change of
quantum oscillation frequencies suggesting an abrupt change of the electronic structure and/or quasiparticle characteristics. Our results demonstrate the ability to tune the electronic structure and provide input for theoretical models of YbNi4P2 and correlated electron systems in high
magnetic fields.
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All authors Will Broad, Owen Moulding, Takaki Muramatsu, Manuel Brando, Alix McCollam, Femke Bangman, Gertrud Zwicknagl, Kristin Kliemt, Cornelius Krellner, Sven Friedemann