Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Low-loss frequency-tunable Josephson junction array cavities on Ge/SiGe heterostructures with a tapered etching approach
Franco De Palma, Elena Acinapura, Wonjin Jang et al. (+5 more)
Ge/SiGe
heterostructures represent a promising platform for hosting various
quantum devices such as hole
spin qubits and Andreev
spin qubits. However, the compatibility of such
heterostructures with high-quality-factor microwave superconducting cavities remains a challenge due to defects in the material stack. In this work, we present an approach to enhance the coherence of cavity modes on a reverse-graded Ge/SiGe
heterostructure, which consists of etching the full $\sim 1.6~\mathrm{\mu m}$-thick Ge/SiGe stack down to its starting high-resistivity Si substrate, in order to pattern superconducting cavities directly on it. We engineer the mesa step to be tapered, so that it can be easily climbed by the superconducting cavities to reach the
quantum devices potentially hosted in the Ge
quantum well. Using this approach, we observe internal quality factors of $Q_\mathrm{i} \approx 10000-20000$ for high-impedance frequency-tunable Josephson junction array resonators, limited by the junctions' fabrication, and $Q_\mathrm{i} \approx 100000$ for $50~\mathrm{\Omega}$ coplanar waveguide Nb lift-off resonators. These $Q_\mathrm{i}$ are preserved despite the overlap with the mesa structure in the climbing region, and are comparable to the ones obtained for identical resonators fabricated on a high-resistivity Si wafer reference. Thereby, this work paves a practical path toward
superconductor-
semiconductor hybrid devices, immediately applicable to emerging technologies on planar Ge.
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All authors Franco De Palma, Elena Acinapura, Wonjin Jang, Fabian Oppliger, Radha Krishnan, Arianna Nigro, Ilaria Zardo, Pasquale Scarlino
Statistical Mechanics · Cross-listed from physics.soc-ph
Biswas-Chatterjee-Sen (BChS) kinetic exchange opinion model on modular networks
Hrishidev Unni, Soumyajyoti Biswas and Anirban Chakraborti
We study opinion formation in a society where
agents interact on a modular network generated using a
stochastic block model (SBM). Opinion dynamics is modeled through the Biswas-Chatterjee-Sen (BChS) kinetic exchange model, in which
agents undergo pairwise interactions that could be positive or negative. By tuning the relative strength of intra- and inter-group connectivity inherent to the SBM, as well as the disagreement probability, we identify distinct collective phases. In particular, we observe a robust regime with strong intragroup ordering but no global consensus, in addition to fully ordered and disordered states. In the particular case of two modules, we observe an anti-
ferromagnetic type ordering with the increase of negative interaction between the groups. We show approximate analytical calculations and numerical results of it. These results demonstrate how modular interaction structure can qualitatively alter collective opinion dynamics and hinder consensus formation.
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Quantum Gases
Momentum correlations of the Hawking effect in a quantum fluid
Marcos Gil de Olivera, Malo Joly, Antonio Z. Khoury et al. (+2 more)
The Hawking effect – the amplification of fluctuations at the horizon – has been detected in
quantum fluids through real-space density correlations. However, real-space observables integrate over frequency, mixing distinct scattering channels into a single interference pattern and obscuring the spectral and
entanglement structure of the emission. Here, we numerically compute momentum-space two-point correlations in a transcritical
quantum fluid, using the truncated Wigner approximation applied to a realistic, driven-dissipative polariton system. We spectrally resolve the Hawking–partner as well as greybody factor channels and find that both carry comparable correlation strength, demonstrating that the well-known real-space “moustache” is an interference between these spectrally distinct contributions. The Hawking–partner channel is dominated by negative correlations, a direct signature of
quantum-
vacuum pair creation. All features reach amplitudes detectable in state-of-the-art experiments. Our results establish that the full three-mode output state must be considered for
entanglement characterization, and provide a general framework applicable to any
quantum fluid.
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All authors Marcos Gil de Olivera, Malo Joly, Antonio Z. Khoury, Alberto Bramati, Maxime J. Jacquet
Strongly Correlated Electrons
Quantum Monte Carlo studies of U(1) lattice gauge models of Kondo breakdown
Gaopei Pan and Fakher F. Assaad
In the local-moment regime, heavy
fermions are most economically described by a compact U(1) gauge theory. Motivated by this perspective, we study a minimal compact U(1)
lattice gauge model describing a
spin chain coupled to two-dimensional Dirac conduction electrons. The
spin chain is described by fermionic partons carrying
spin and U(1) gauge charge. The heavy-
fermion quasiparticle is a bound state of a U(1) matter field carrying unit electric charge and U(1) gauge charge, and the fermionic parton. Using sign-problem-free determinant
quantum Monte Carlo simulations, we identify two
symmetry-equivalent regimes: a heavy-
fermion metal with a sharp composite-
fermion resonance and robust low-frequency transport, and a Kondo-breakdown metal with an incoherent resonance and vanishing low-frequency transport. For any finite
lattice extent in the direction perpendicular to the chain, the Luttinger volume of the heavy-
fermion phase counts both composite and conduction electrons, while in the Kondo-breakdown phase it counts only the conduction electrons. The
evolution of the composite-
fermion spectrum, dynamical
spin structure factor, and optical conductivity provides a nonperturbative demonstration of gauge-mediated Kondo breakdown and establishes transport fingerprints of an orbital-selective Mott transition in the context of U(1) gauge theories of heavy
fermions.
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Materials Science
Bayesian Methods for the Investigation of Temperature-Dependence in Conductivity
Andrew R. McCluskey, Samuel W. Coles and Benjamin J. Morgan
Temperature-dependent transport data, including
diffusion coefficients and ionic conductivities, are routinely analysed by fitting empirical models such as the Arrhenius equation. These fitted models yield parameters such as the activation energy, and can be used to extrapolate to temperatures outside the measured range. Researchers frequently face challenges in this analysis: quantifying the uncertainty of fitted parameters, assessing whether the data quality is sufficient to support a particular empirical model, and using these models to predict behaviour at temperatures outside the measured range.
Bayesian methods offer a coherent framework that addresses all of these challenges. This tutorial introduces the use of
Bayesian methods for analysing temperature-dependent transport data, covering parameter estimation, model selection, and extrapolation with uncertainty propagation, with illustrative examples from molecular dynamics simulations of superionic materials.
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Materials Science
Mechanistic Origin of Charge Separation and Enhanced Photocatalytic Activity in D-$\pi$-A-Functionalized UiO-66-NH$_2$ MOFs
Anastasiia Kultaeva, Volodymyr Vasylkovskyi, Andreas Sperlich et al. (+4 more)
Donor-$\pi$-acceptor (D-$\pi$-A) functionalization of MOF linkers can enhance visible-light photocatalytic activity, yet the mechanisms responsible for these effects remain unclear. Here we combine EPR spectroscopy, transient photoluminescence, and first-principles calculations to examine how diazo-coupled anisole, diphenylamine (DPA), and N,N-dimethylaniline (NNDMA) groups modify the photophysics of UiO-66-NH$_2$. All donor units introduce new occupied states near the valence-band edge, enabling charge separation through dye-to-framework electron transfer. Among them, the anisole-modified material stands out for facilitating efficient intersystem crossing into a triplet charge-transfer configuration that suppresses fast recombination and yields long-lived charge carriers detectable by photo-EPR. Meanwhile, bulkier donors such as DPA and NNDMA - despite their stronger electron-donating character - also tend to introduce defect-associated trap states. These results underscore the interplay between donor-induced electronic-structure changes, triplet pathways, and defect-mediated recombination, offering a mechanistic basis for tuning photocatalytic response in D-$\pi$-A-modified MOFs.
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All authors Anastasiia Kultaeva, Volodymyr Vasylkovskyi, Andreas Sperlich, Eugenio Otal, Katsuya Teshima, Wolf Gero Schmidt, Timur Biktagirov
Superconductivity
Proximity effect in gap-asymmetric superconducting bilayers and regularization of transition rates
G. Marchegiani and G. Catelani
The standard mean-field treatment of low-temperature
superconductors leads to a square-root divergent density of states at the gap value. This feature can lead to unphysical logarithmic divergences in various quantities, such as currents and
qubit transition rates. We revisit their possible regularization based on the proximity effect between two superconducting films with different gaps. We derive analytical approximations for the density of states in each superconducting film. We find that the smearing of the density of states grows with the gap asymmetry. As a concrete example, we discuss the regularization of transition rates in
qubits with frequency close to resonance with the gap asymmetry between the two films, and the consequent smoothening of the jump discontinuity in the
qubit frequency shift. Our results could also aid the development of superconducting detectors and related devices based on superconducting
bilayers.
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Soft Condensed Matter
Condensation dynamics of sticky and anchored flexible biopolymers
Adam R. Lamson, Mohammadhossein Firouznia and Michael J. Shelley
Cells regulate gene expression in part by forming DNA-
protein condensates in the
nucleus. While existing theories describe the
equilibrium size and stability of such condensates, their dynamics remain less understood. Here, we use coarse-grained 3D Brownian-dynamics simulations to study how long, end-anchored biopolymers condense over time due to transient crosslinking. By tracking how clusters nucleate, merge, and disappear, we identify two dominant dynamical pathways, ripening and merging, that govern the progression from an uncompacted chain to a single condensate. We show how microscopic kinetic parameters,
protein density, and mechanical constraints shape these pathways. Using insights from the simulations, we construct a minimal mechanistic free-energy model that captures the observed scaling behavior. Together, these results clarify the dynamical determinants of DNA and chromatin reorganization on timescales relevant to gene regulation.
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Mesoscale and Nanoscale Physics
MOF-derived Fe-doped $\delta$-MnO$_2$ nanoflowers as oxidase mimics: Chromogenic sensing of Hg$^{2+}$ and hydroquinone in aqueous media
Udisha Duhan, Arnab Pan, Ritesh Dubey et al. (+3 more)
Structure and morphology play a crucial role in enhancing the biomimetic oxidase activity of nanozymes. In this study, a facile in situ chemical oxidation strategy was employed to synthesize MOF-derived MnO$_x$, utilizing the structural features of the parent MOF to enhance oxidase-mimicking activity. We systematically investigated the effects of phase
evolution, structural modulation, and morphology on the oxidase activity of MnO$_x$ with Fe substitution. The oxidase-like activity was evaluated using the chromogenic substrate 3,3$'$,5,5$'$-tetramethylbenzidine (TMB), which produced a blue-colored oxidized TMB (ox-TMB) with an absorption peak at 652~nm upon oxidation. While all Fe-doped MnO$_x$ nanostructures exhibited oxidase-like activity, the 10% Fe-doped sample (10Fe-MnO$_x$) demonstrated the highest performance, likely due to a synergistic effect of structure, morphology, and the presence of oxygen vacancies. The underlying oxidase mechanism was investigated using steady-state kinetics and electron paramagnetic resonance (EPR) analysis. In addition, a colorimetric assay was developed for the detection of Hg$^{2+}$ and hydroquinone (HQ) in real water samples collected from industrial and natural sources. The calculated detection limits of the 10Fe-MnO$_x$ colorimetric probe for HQ (1.74~$\mu$M) and Hg$^{2+}$ (0.47~$\mu$M) outperformed those of conventional metal
oxide-based nanozymes. These findings pave the way for the development of easily synthesizable, scalable, and highly sensitive oxidase-based MOF-derived metal
oxide nanomaterials with significant potential in biological and environmental applications.
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All authors Udisha Duhan, Arnab Pan, Ritesh Dubey, Samar Layek, Sushil Kumar, Tapas Goswami
Strongly Correlated Electrons
Fractionalized topological d+id superconductivity in the Yao-Lee-Kondo model
Chengzhi Tang and Hong Yao
A conclusive experimental realization of 2D
chiral topological superconductivity remains elusive. Here we present a theoretical demonstration that a topological $d+id$ fractionalized superconducting phase (SC*) can emerge in the weak-coupling limit of a Kondo
lattice model, where conduction electrons interact with a Yao-Lee
spin liquid on the honeycomb
lattice (the Yao-Lee-Kondo model). Using a renormalization-group analysis, we show that exchanging Majorana spinons from the Yao-Lee
spin liquid generates effective interactions among the conduction electrons and drives a Cooper instability even for arbitrarily weak Kondo coupling. We further find that the induced leading inter-orbital
antiferromagnetic interaction selects topological $d+id$
spin-singlet pairing with Chern number $C=\pm 2$. Meanwhile, the Majorana
fermions in the Yao-Lee
spin liquid remain gapless and deconfined in this regime, so the resulting state is a fractionalized topological $d+id$
superconductor (SC*). For sufficiently strong Kondo coupling, the system instead enters a heavy
Fermi liquid phase with fractionalization (HFL*).
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Materials Science
Corrosion-resistant and conductive Ti-Nb-O coatings tailored for ultra-low Pt-loaded BPPs and PTLs in PEM electrolyzers
David Kolenatý, Jiří Čapek, Stanislav Haviar et al. (+6 more)
We develop highly corrosion-resistant and conductive Ti-Nb-O coatings for metallic components – bipolar plates (BPPs) and porous transport layers (PTLs) – in PEM water electrolyzers. Using reactive high-power impulse magnetron sputtering (HiPIMS), we deposit compact 200 nm
bilayer coatings onto SS316L substrates, systematically tailoring their composition. By precisely controlling oxygen partial pressure and Nb/Ti ratio, we adjust stoichiometry and structure, directly affecting electrical resistivity and corrosion resistance. We examine interfacial contact resistance (ICR) and electrochemical parameters before and after accelerated corrosion testing. Optimized coatings exhibit resistivity on the order of 10^-4 Ohmcm and extremely low corrosion current densities (J_corr = 0.01-0.08 uA/cm^2), well below the U.S. DOE 2026 target. Most importantly, these coatings enable the ICR target after accelerated corrosion testing with a Pt overlayer as thin as 5 nm, reducing Pt loading by up to two orders of magnitude compared to conventional approaches.
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All authors David Kolenatý, Jiří Čapek, Stanislav Haviar, Jiří Rezek, Radomír Čerstvý, Akash Kumar, Kalyani Shaji, Mariia Zhadko, Petr Zeman
Materials Science
Design principles for metal-organic receptors targeting optical recognition of Pd(II) in environmental matrices
Sudhanshu Naithani, Pramod Kumar, Ritesh Dubey et al. (+4 more)
A precise detection of palladium (Pd) ions is a critical challenge with significant socio-economic implications across various industrial and chemical sectors. Due to its widespread use and poor biodegradability, Pd2+ accumulates in environmental ecosystems, posing severe risks to both the environment and living organisms. Consequently, there is a strong demand for selective, sensitive, and user-friendly detection methods. Among emerging strategies, optical detection techniques (both luminescent and colorimetric) using metal-based receptors have gained considerable
attention. These sensors offer distinct advantages over traditional organic probes, including large Stokes shifts, long emission lifetimes, exceptional photostability, enhanced water solubility, recyclability, and remarkable chemical versatility. These attributes make them highly suitable for diverse applications in sensing and bioanalytical fields. This review provides a comprehensive overview of recent advancements in luminescent and colorimetric metal-based probes, including metal complexes and metal-organic frameworks (MOFs), for the selective detection of Pd2+. It discusses key design strategies, critical performance factors, and future prospects, offering valuable insights for researchers working on next-generation sensing platform.
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All authors Sudhanshu Naithani, Pramod Kumar, Ritesh Dubey, Franck Thetiot, Samar Layek, Tapas Goswami, Sushil Kumar
Strongly Correlated Electrons
Non-perturbative effects of short-range spatial correlations at the two-particle level
Michael Meixner, Matthias Reitner, Thomas Schäfer et al. (+1 more)
By means of cellular dynamical mean-field theory (CDMFT) we study how short-range correlations drive the breakdown of the self-consistent perturbation theory in two-dimensional systems and the most relevant physical consequences associated to it. To this aim, we first derive in a structured and consistent way the Bethe-Salpeter equation (BSE) formalism at the CDMFT level in all physical channels, explicitly addressing the important aspect of the related Ward identities. In this context, we perform systematic calculations of the BSE for the two-dimensional Hubbard model at half-filling at intermediate coupling. Our study illustrates how the divergence of a fundamental building block of the BSE in the charge channel, the two-particle irreducible vertex, systematically occurs at lower interactions than in the (purely local) DMFT case, due to short-range
antiferromagnetic fluctuations. Further, the change of sign of the
eigenvalues of the generalized charge susceptibility associated to the vertex divergences is identified as the essential prerequisite to drive, at larger interaction values, the physics of the Mott transition in two dimensions, as well as of the adjacent phase-separation instabilities.
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All authors Michael Meixner, Matthias Reitner, Thomas Schäfer, Alessandro Toschi
Materials Science
Lanthanide Ion Electronic Structure Controls Magnetic Excitations in Topological Quantum Ferrimagnets $LnMn_{6}Sn_{6}$ (Ln = Tb, Dy, Ho)
Kelsey A. Collins, Jacob Pfund, Michael R. Page et al. (+3 more)
The $LnMn_{6}Sn_{6}$ family of topological magnets is a promising platform for next-generation spintronic and magnonic technologies. However, the influence of the lanthanide ion ($Ln^{3+}$) on the excited-state
spin dynamics, or
magnons, remains a critical knowledge gap. Here, we present the first comparative study of the
magnetic dynamics in $LnMn_{6}Sn_{6}$ materials (Ln = Tb, Dy, Ho) using Brillouin light scattering. Our findings reveal a direct correlation between the lanthanide ion's intrinsic properties and the
magnon behavior. We demonstrate that the
magnon frequency in the absence of an applied
magnetic field is primarily dictated by the strength of the lanthanide exchange coupling, as modeled by its relationship with the de Gennes factor. The response of the
magnon to an applied field is influenced by material's gyromagnetic ratio and the overall anisotropy of the material, which are dictated by total angular momentum and the anisotropy of the lanthanide sublattice, respectively. These results establish that simple lanthanide substitution provides a powerful and predictable method for tuning
magnon properties, enabling the rational design of materials for advanced technological applications.
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All authors Kelsey A. Collins, Jacob Pfund, Michael R. Page, Menka Jain, Michael A. Susner, Michael J. Newburger
Strongly Correlated Electrons
Revisiting the Broken Symmetry Phase of Solid Hydrogen: A Neural Network Variational Monte Carlo Study
Shengdu Chai, Chen Lin, Xinyang Dong et al. (+4 more)
The
crystal structure of high-pressure solid hydrogen remains a fundamental open problem. Although the research frontier has mostly shifted toward ultra-high pressure phases above 400 GPa, we show that even the broken
symmetry phase observed around 130~GPa requires revisiting due to its intricate coupling of electronic and
nuclear degrees of freedom. Here, we develop a first principle
quantum Monte Carlo framework based on a deep neural network wave function that treats both electrons and
nuclei quantum mechanically within the constant pressure ensemble. Our calculations reveal an unreported ground-state structure candidate for the broken
symmetry phase with $Cmcm$ space group
symmetry, and we test its stability up to 96 atoms. The predicted structure quantitatively matches the experimental equation of state and gives the closest x-ray diffraction peak-position match among the tested candidates. Furthermore, our group-theoretical analysis provides a
symmetry-counting compatibility check between the $Cmcm$ structure and existing Raman and infrared spectroscopic data. Crucially, static density functional theory calculation reveals the $Cmcm$ structure as a dynamically unstable saddle point on the Born-Oppenheimer potential energy surface, demonstrating that a full
quantum many-body treatment of the problem is necessary. These results shed new light on the phase diagram of high-pressure hydrogen and call for further experimental verifications.
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All authors Shengdu Chai, Chen Lin, Xinyang Dong, Yuqiang Li, Wanli Ouyang, Lei Wang, X.C. Xie
Mesoscale and Nanoscale Physics
Higher-Order Topological Systems and Their Sub-Symmetry-Protected Topology
Myungjun Kang, Wonjun Sung, Sonu Verma et al. (+1 more)
Symmetry and
topology are essential principles in topological physics. Recently, the idea of sub-
symmetry-protected
topology – where some of the original
symmetries are broken while a remaining subset, called sub-
symmetries, continues to protect specific boundary states – has been developed. Here, we extend sub-
symmetry-protected
topology to higher-order topological systems from second-order topological
insulators to semimetals. By introducing a sub-
symmetry-protecting perturbation that acts on a single sublattice and selectively preserves specific topological boundary states, we track the
evolution of these states and their topological features using numerical and analytical methods, and we show that state-resolved quadrupole moments diagnose which corner or hinge modes remain topological. As a representative example of a second-order topological
insulator, we begin with the Benalcazar-Bernevig-Hughes model. We demonstrate that, under a sub-
symmetry-protecting perturbation, sub-
symmetry-protected corner states remain pinned at zero energy and maintain quantized state-resolved quadrupole moments. In contrast, corner states on sub-
symmetry-broken boundaries shift away from zero energy and lose their quantized character. We further extend this framework to a three-dimensional second-order topological semimetal, constructed by stacking second-order topological
insulator layers, and analyze how second-order
Fermi arc states – hinge-localized modes that link the projections of bulk Dirac points, in contrast to conventional surface
Fermi arcs – evolve under a sub-
symmetry-protecting perturbation. While one second-order
Fermi arc becomes dispersive and loses its quadrupolar character under a sub-
symmetry-breaking perturbation, the remaining second-order
Fermi arcs retain
chiral symmetry and preserve quantized quadrupolar characters.
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All authors Myungjun Kang, Wonjun Sung, Sonu Verma, Sangmo Cheon
Superconductivity
Bulk signatures of re-entrant superconductivity in UTe$_2$ from ultrasound measurements
N. Marquardt, C. Duffy, C. Proust et al. (+7 more)
We report bulk ultrasound measurements up to 80 T and down to 0.5 K of the field re-entrant superconducting phase of the unconventional
superconductor UTe$_2$. Clear bulk signatures of superconductivity are observed in the longitudinal elastic mode $c_{11}$ for fields applied at a tilt angle of $\theta_{b-c} =30^\circ$ from $b$-axis. We confirm an upper critical field of $H_{\rm c2}\approx65$ T at 0.5 K and bulk superconductivity which survives up to $T\approx 2$ K for fields above the metamagnetic transition. The $c_{11}$ mode has propagation and displacement vectors along the $a$-axis, and for fields applied at a tilt angle of $\theta_{b-c} =30^\circ$, this mode is sensitive to the elasticity of the
vortex lattice. The anomalies observed in $c_{11}$ are in part reminiscent of superconducting
vortices pinned to
lattice defects. Nonetheless, an excess attenuation, with respect to the normal state, is observed throughout the entire superconducting phase, suggesting unusual
vortex dynamics and pinning in the field re-entrant superconducting phase of UTe$_2$.
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All authors N. Marquardt, C. Duffy, C. Proust, S. Badoux, M. Amano Patino, G. Lapertot, D. Aoki, J.-P. Brison, G. Knebel, D. LeBoeuf
Soft Condensed Matter
Internal Waves Control Bulk Flow in Silos
David Luce, Adrien Gans, Nicolas Vandewalle et al. (+1 more)
We experimentally measure paticle acceleration within the bulk during the discharge of a granular silo. We highlight the existence of a deceleration wave emerging at the outlet level near the dead zone and propagates toward the top of the medium. The wave emission frequency is extracted from spatiotemporal diagrams of the Eulerian instantaneous acceleration profiles. Surprisingly, we find that this frequency decreases with the cohesion of the medium and is independent of the outlet size.
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All authors David Luce, Adrien Gans, Nicolas Vandewalle, Sébastien Kiesgen de Richter
Statistical Mechanics · Cross-listed from gr-qc
Networks as the fundamental constituents of the universe
Carlo A. Trugenberger
We review an approach that uses binary relations as the fundamental constituents of the universe, utilizing them as building blocks for both space and matter. The model is defined by an ultraviolet continuous fixed point of a statistical model on random networks, governed by the combinatorial Ollivier-
Ricci curvature, which acts as a network analogue of the Einstein-
Hilbert action. The model exhibits two distinct phases separated by this fixed point, a
geometric and a random phase, representing space and matter, respectively. At weak coupling and on large scales, the network organizes into a
holographic surface whose collective state encodes both an emergent 3D space and the matter distributed in it. The Einstein equations emerge as constitutive relations expressing matter in terms of fundamental network degrees of freedom while dynamics in a comoving frame is governed by relativistic
quantum mechanics.
Quantum mechanics, however is an effective theory breaking down at the scale of the radius of
curvature of the
holographic network. On smaller scales, not only relativistic invariance is lost but also the Lorentzian signature of space-time. Finally, the
manifold nature of space-time breaks down on the Planck length, where the random character of the fundamental network on the smallest scales becomes apparent. The network model seems to naturally encode several of the large-distance features of cosmology, albeit still at a qualitative level. The
holographic property of black holes arises intrinsically from the expander nature of random regular graphs. There is a natural mechanism to resolve the cosmological constant problem and dark matter appears naturally as a metastable allotrope in the network fabric of space-time. In this model, both
gravity and
quantum mechanics are macroscopic statistical effects reflecting the free energy minimization of fundamental binary degrees of freedom.
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Materials Science · Cross-listed from quant-ph
Quantum heat current in Terahertz-driven phonon systems
Yulong Qiao and Richard. Matthias Geilhufe
The advent of high-intensity ultrafast
laser pulses has opened new opportunities for controlling and designing
quantum materials. In particular, terahertz (THz) pulses can resonantly drive optical
phonon modes, enabling dynamic manipulation of
lattice degrees of freedom. In this work, we investigate the ultrafast
quantum thermodynamics of optical
phonon mode driven by a THz pulse by treating the
phonon as an open
quantum system coupled to a thermal environment within a Caldeira-Leggett-type framework. We derive the
quantum heat current between the
phonon and the bath and analyze its behavior under realistic pulse protocols. Our results demonstrate that ultrafast
laser driving can reveal and even induce significant deviations from the commonly adopted Markovian approximation, thereby providing a pathway to probe and control non-Markovian dissipation in driven solid-state systems.
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Materials Science · Cross-listed from stat.ML
Generative Multi-Objective Bayesian Optimization with Scalable Batch Evaluations for Sample-Efficient De Novo Molecular Design
Madhav R. Muthyala, Farshud Sorourifar, Tianhong Tan et al. (+2 more)
Designing molecules that must satisfy multiple, often conflicting objectives is a central challenge in molecular discovery. The enormous size of chemical space and the cost of high-fidelity simulations have driven the development of machine learning-guided strategies for accelerating design with limited data. Among these,
Bayesian optimization (BO) offers a principled framework for sample-efficient search, while generative models provide a mechanism to propose novel, diverse candidates beyond fixed libraries. However, existing methods that couple the two often rely on continuous latent spaces, which introduces both architectural
entanglement and scalability challenges. This work introduces an alternative, modular "generate-then-optimize" framework for de novo multi-objective molecular design/discovery. At each iteration, a generative model is used to construct a large, diverse pool of candidate molecules, after which a novel acquisition function, qPMHI (multi-point Probability of Maximum Hypervolume Improvement), is used to optimally select a batch of candidates most likely to induce the largest Pareto front expansion. The key insight is that qPMHI decomposes additively, enabling exact, scalable batch selection via only simple ranking of probabilities that can be easily estimated with Monte Carlo sampling. We
benchmark the framework against state-of-the-art latent-space and discrete molecular optimization methods, demonstrating significant improvements across synthetic
benchmarks and application-driven tasks. Specifically, in a case study related to sustainable energy storage, we show that our approach quickly uncovers novel, diverse, and high-performing organic (quinone-based) cathode materials for aqueous redox flow battery applications.
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All authors Madhav R. Muthyala, Farshud Sorourifar, Tianhong Tan, You Peng, Joel A. Paulson
Materials Science
Thermal Control of Size Distribution and Optical Properties in Gallium Nanoparticles
S. Catalan-Gomez, M. Ibanez, J. Rico et al. (+5 more)
Gallium nanoparticles (Ga-NPs) exhibit promising plasmonic properties spanning ultraviolet to infrared spectral regions, making them suitable for diverse nanophotonic applications. However, the synthesis of uniform and ordered Ga-NP arrays remains challenging due to size heterogeneity arising from coarsening during physical deposition. Here, we systematically investigate the influence of substrate temperature on the nucleation, growth, and homogenization dynamics of Ga-NPs formed via Joule-effect thermal evaporation on GaAs substrates. Atomic force microscopy and scanning electron microscopy reveal temperature-dependent transitions from broad, bimodal size distributions to narrow dispersed arrays within an optimal substrate temperature range of 300-350{\deg}C. Above this window, increased
diffusion and desorption induce size increase, decreased density, and morphological relaxation manifested as NP shape flattening. Optical reflectance measurements identify distinct localized surface plasmon resonance (LSPR) modes whose energies are closely correlated with NP dimensions and aspect ratios. A figure of merit combining NP density and size uniformity quantifies optimal conditions at intermediate substrate temperatures, consistent with enhanced plasmonic quality factors derived from spectral LSPRs. In-situ post-deposition annealing experiments confirm Ostwald ripening as the dominant coarsening mechanism at elevated temperatures and highlight the necessity of rapid cooling and
oxide shell formation to stabilize homogeneous arrays. Cross-sectional transmission electron microscopy with electron energy-loss spectroscopy validates the core-shell structure of individual Ga-NPs, quantifies temperature-dependent
oxide shell thickening, and confirms the
liquid metal character of the Ga within the core...
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All authors S. Catalan-Gomez, M. Ibanez, J. Rico, V. Braza, D. F. Reyes, M. Villanueva-Blanco, E. Squiccimarro, J. M. Ulloa
Mesoscale and Nanoscale Physics · Cross-listed from physics.optics
Hyperbolic-enhanced Raman scattering in van der Waals MoOCl2: from Fano resonances to picomolar detection
Anton Minnekhanov, Gleb Tikhonowski, Georgy Ermolaev et al. (+13 more)
Natural van der Waals (vdW)
crystals with
hyperbolic dispersion challenge artificial metamaterials but remain confined to the mid-infrared. The emergence of MoOCl2, a quasi-one-dimensional metal with in-plane hyperbolicity, overcomes this spectral limit, shifting the focus to the practical visible range. Here, using angle-resolved polarized Raman spectroscopy, we uncover pronounced polarization-dependent Fano lineshapes that reveal coupling between
phonons and the anisotropic metallic continuum, together with strong wavelength-dependent reshaping of the Raman polarization patterns governed by the anisotropic optical response of MoOCl2. Harnessing this optical anisotropy, we demonstrate "
Hyperbolic-Enhanced Raman" (HypER) scattering, where MoOCl2 provides polarization-tunable analytical enhancement factors exceeding 10^7 and picomolar-level detection of Rhodamine 6G down to 100 pM, without deliberate surface nanostructuring. These results establish air-stable MoOCl2 as a simple, wafer-compatible platform for visible-range
hyperbolic nanophotonics and lithography-free sensing.
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All authors Anton Minnekhanov, Gleb Tikhonowski, Georgy Ermolaev, Konstantin V. Kravtsov, Gleb Tselikov, Adilet Toksumakov, Aleksandr Slavich, Ivan Kazantsev, Ilia Fradkin, Andrey Vyshnevyy, Ivan Kruglov, Ilya Radko, Zdenek Sofer, Aleksey Arsenin, Kostya S. Novoselov, Valentyn Volkov
Mesoscale and Nanoscale Physics
Picosecond localization dynamics following ultrafast nanoscale magnetic switching
Daniel Metternich, Michael Schneider, Giuseppe Mercurio et al. (+28 more)
Ultrashort
laser pulses provide the fastest known way to switch
magnetic order. Such excitation commonly creates nanometer-scale domains, even after homogeneous illumination when the position of nucleated domains is not externally defined. However, the physics of domain localization during such ultrafast phase transitions remains unresolved. Here, we use shot-resolved pump-probe resonant x-ray scattering together with a material featuring a periodically modulated
magnetic anisotropy landscape to track, in real time, the
laser-driven nucleation and localization of nanometer-scale
spin textures. We find that nucleation and localization are two distinct processes. Nucleation occurs homogeneously via fluctuations at early times, whereas spatially periodic structures emerge only later and, under suitable conditions, localize in less than one nanosecond. Real-space simulations show that this localization is governed by strong lateral variations in
spin-texture lifetimes. Our results demonstrate that ultrafast phase-transition dynamics fundamentally differ from conventional transitions, yet still can be controlled through moderate nanometer-scale tailoring of the energy landscape.
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All authors Daniel Metternich, Michael Schneider, Giuseppe Mercurio, Torstein Hegstad, Marcel Möller, Riccardo Battistelli, Christopher Klose, Steffen Wittrock, Manas R. Patra, Krishnanjana Puzhekadavil Joy, Victor Deinhart, Sascha Petz, Karel Prokes, Sebastian Wintz, Markus Weigand, Wolfgang-Dietrich Engel, Themistoklis Sidiropoulos, Ingo Will, Stefan Eisebitt, Robert E. Carley, Laurent Mercadier, Justine Schlappa, Martin Teichmann, Andreas Scherz, Sergey Zayko, Boris V. Sorokin, Kai Bagschik, Claus Ropers, Johan H. Mentink, Bastian Pfau, Felix Büttner
Superconductivity
Theoretical study on the electronic properties and multiorbital models of La$_3$Ni$_2$O$_7$ thin films on SrLaAlO$_4$ (001)
Guanlin Li, Cui-Qun Chen, Haoliang Shi et al. (+5 more)
The realization of ambient-pressure superconductivity in La$_3$Ni$_2$O$_7$ thin films raises a fundamental question: is the metallic ground state driven by
lattice strain or interfacial charge reconstruction? Using fully self-consistent DFT+$U$ calculations on La$_3$Ni$_2$O$_7$/SrLaAlO$_4$
heterostructures, we identify that intrinsic hole doping via interfacial Sr interdiffusion is the decisive factor in stabilizing the metallic state. Our 1-unit-
cell model accurately reproduces the ARPES-observed
Fermi surface, particularly the critical Ni-$d_{z^2}$ derived $\gamma$ hole pocket, which originates exclusively from the interface-proximal
bilayer. Furthermore, comparative tight-binding analysis suggests that the reduced superconducting transition temperature ($T_c$) in thin films stems from the synergistic suppression of the electronic density of states (DOS) and vertical superexchange coupling ($J \perp Z$). These findings highlight that interface engineering plays a critical role beyond simple strain imposition in modulating nickelate orbital physics.
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All authors Guanlin Li, Cui-Qun Chen, Haoliang Shi, Zhengtao Liu, Hao Ma, Fubo Tian, Dao-Xin Yao, Defang Duan
Mesoscale and Nanoscale Physics
Synergy and Competition of Dual Chirality in the Chirality-Induced Spin Selectivity of Supramolecular Helices
Song Chen, Kai-Yuan Zhang, Xi Sun et al. (+2 more)
Recent progress in constructing supramolecular assemblies with hierarchical chirality offers new opportunities to investigate the chirality-induced
spin selectivity (CISS) effect and its potential applications. In this work, we systematically examine the CISS effect in such multichiral systems by designing a class of multilayer helical architectures constructed of stacked and interfaced individual helical rings, each possessing well-defined local chirality. Through controlled interlayer twisting, a global helical handedness is further imposed, forming a multichiral tubular helix. Theoretical calculations reveal that these two distinct
chiral hierarchies lead to several unprecedented CISS phenomena, such as enhanced
spin polarization arising from cooperative dual chirality, along with the simultaneous emergence of transverse and longitudinal CISS signals. Moreover, interlayer torsional competition modulates the system's response to external fields. The dual-
chiral geometry breaks the conventional
symmetry of single helices, inducing an anomalous angular phase shift in magnetoresistance. Furthermore, Floquet analysis reveals that the interplay between local and global chirality enables controlled
spin polarization switching under circularly polarized light. These findings provide a basic theoretical framework for studying the CISS in multichiral superstructures and establish design principles for coupled optical,
magnetic, and
spin manipulations, thereby facilitating the development of multichiral spintronic devices.
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All authors Song Chen, Kai-Yuan Zhang, Xi Sun, Shu-Zheng Zhou, Hua-Hua Fu
Statistical Mechanics
Earthquake Dynamics as a Benchmark for Scale-Invariant Behavior
Kilian Duplat, German Varas and Osvanny Ramos
We analyze regional earthquake energy statistics from the Southern California and Japan seismic catalogs and find scale-invariant energy distributions characterized by an exponent $\tau \simeq 1.67$. To quantify how closely scale-invariant dynamics with different exponent values resemble real earthquakes, we generate synthetic energy distributions over a wide range of $\tau$ under conditions of constant activity. Earthquake-like behavior, in a broad sense, is obtained for $1.5 \leqslant \tau < 2.0$. When energy variations are further restricted to be within a factor of ten relative to real earthquakes, the admissible range narrows to $1.58 \leqslant \tau \leqslant 1.76$. We identify the physical mechanisms governing the dynamics in the different regimes: fault dynamics characterized by a balance between slow energy accumulation and release through scale-free events in the earthquake-like regime; externally supplied energy relative to a slowly driven fault for $\tau < 1.5$; and dominance of small events in the energy budget for $\tau > 2$
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Soft Condensed Matter · Cross-listed from q-bio.MN
Design of a minimal, allosteric, and ATPase-like machine using mechanical linkages
Tosan Omabegho
ATPases cyclically convert chemical energy in the form of ATP gradients into directed motion inside
cells. To function, ATPases rely on allosteric communication between at least two binding sites, an internal signaling mechanism that is not well understood. Here, we model an ATPase-like machine by using a system of mechanical linkages to recreate negative allosteric coupling between two binding sites and generate cycles in which the sites alternate occupancy. The ATPase analog has two mechanical degrees of freedom and two discretized binding sites: one for the ATP, Pi and ADP analogs, and one for an allosteric effector analog. The geometry of the ATPase analog allows stepwise binding reactions at each site to capture the two degrees of freedom in a mutually exclusive way. Consequently, the enzyme interconverts between multiple rigid and partially rigid forms, such that neither site can be fully bound when both sites are occupied. Two mechanisms work together to generate an enzymatic cycle: one, in which the tighter-binding ATP analog can bind and displace the effector from the enzyme; and a second, in which flexibility introduced by splitting the ATP analog into two pieces (catalysis) allows the effector to rebind and displace the products (ADP analog). We show that cleavage (forward catalysis) and ligation (reverse catalysis) alter the
rigidity of the enzyme complex equivalently to binding and dissociation, respectively, but must do so more slowly for effective cycling to take place. Simple designs for synthetic systems that mimic ATPase monomers can be derived from this work.
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Strongly Correlated Electrons
Charge fluctuations and topological phases in Kitaev-Heisenberg ladders
M. G. Sousa, O. Ávalos-Ovando, E. Vernek et al. (+1 more)
We investigate the stability of topological phases in doped Kitaev-Heisenberg ladders by studying the competition with itinerant electrons and the associated charge fluctuations in a Hubbard model on a honeycomb ribbon geometry. We analyze the
evolution of string order parameters,
spin correlations, and charge fluctuations as functions of hopping amplitude and interaction strength in a half-filled band. Our results from density
matrix renormalization group (DMRG) calculations show that increasing electron bandwidth progressively suppresses the topological phases, shifting and narrowing their stability regions in the phase diagram. We identify the critical values of hopping where string order vanishes and characterize the interplay between
magnetic order and charge fluctuations. These findings provide insight into the robustness of topological phases against doping and charge dynamics, with implications for candidate Kitaev materials and engineered
quantum systems.
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All authors M. G. Sousa, O. Ávalos-Ovando, E. Vernek, S. E. Ulloa
Materials Science
Multipoles as quantitative order parameters for altermagnetic spin splitting
Francesco Martinelli, Anouk Droux and Claude Ederer
We establish a quantitative relation between the altermagnetic
spin-splitting and different higher order multipoles of the charge and magnetization density around the
magnetic atoms.
Magnetic multipoles such as octupoles or triakontadipoles have been suggested as potential ferroic order parameters for d- and g-wave altermagnetism, respectively, based mainly on qualitative
symmetry arguments. We use first-principles-based electronic structure calculations to establish a clear quantitative relation between the strength of the altermagnetic
spin splitting and the magnitude of certain local multipoles. We vary the magnitude of these multipoles either by applying an appropriate constraint on the charge density or by varying a corresponding structural distortion mode, using two simple perovskite materials, SrCrO3 and LaVO3, as model systems. Our analysis indicates that in general the altermagnetic
spin splitting is not exclusively determined by the lowest order nonzero
magnetic multipole, but results from a superposition of contributions from different multipoles with comparable strength, suggesting the need for a multi-component order parameter to describe altermagnetism. We also discuss different measures to quantify the overall
spin-splitting of a material, without relying on features that might be specific to only individual bands.
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