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Physics Condensed Matter

cond-mat Watch Condensed Matter

Wednesday 8 October

Superconductivity

Quasiparticle Description of Angle-Resolved Photoemission Spectroscopy for SrCuO2

Dimitar Pashov, Casey Eichstaedt, Swagata Acharya et al. (+1 more)

SrCuO2 has long been considered a near-archetypal realization of a quasi one dimensional (1D) system of interacting electrons with short-range interactions. Within this framework, experimental observations - interpreted through the lens of the 1D Hubbard model-suggest that electron and hole excitations decay into two types of (unphysical) collective bosonic modes: spinons, which carry the spin degree of freedom, and holons, which carry the charge degree of freedom. This model, known as spin-charge separation, is most directly evidenced by angle-resolved photoemission spectroscopy (ARPES), where a photo-induced hole decays into a continuum of these excitations. Here we present an alternative perspective grounded in first-principles, self-consistent, and parameter-free many-body perturbation theory. In this revised quasiparticle framework, ARPES can be understood as a one-body effect arising from mild disorder in a long-range antiferromagnetic ground state. the emergence of the so-called spinon branch arises naturally from spin disorder, the anomalous line widths are accurately captured, and we provide a compelling explanation for the spectral weight observed at the non-magnetic zone boundary. This reinterpretation provides a unified explanation for key experimental signatures previously attributed to spin-charge separation, including features observed in optical conductivity. Additionally, we show that SrCuO2 exhibits a nontrivial interchain coupling that significantly influences both its one-particle and two-particle spectral functions. By comparing the spectral features of SrCuO2 with those of La2CuO4, we argue that SrCuO2 shares notable similarities with the two-dimensional cuprates - both being rooted in a common CuO4 plaquette-based molecular orbital framework.
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All authors Dimitar Pashov, Casey Eichstaedt, Swagata Acharya, Mark van Schilfgaarde

Superconductivity

Berezinskii-Kosterlitz-Thouless quantum transition in 2 dimensions

M. C. Diamantini, C. A. Trugenberger and V. M. Vinokur

The Berezinskii-Kosterlitz-Thouless (BKT) transition is the prototype of a phase transition driven by the formation and interaction of topological defects in two-dimensional (2D) systems. In typical models these are vortices: above a transition temperature $T_{\rm BKT}$ vortices are free, below this transition temperature they get confined. In this work we extend the concept of BKT transition to quantum systems in two dimensions. In particular, we demonstrate that a zero-temperature quantum BKT phase transition, driven by a coupling constant can occur in 2D models governed by an effective gauge field theory with a diverging dielectric constant. One particular example is that of a compact U(1) gauge theory with a diverging dielectric constant, where the quantum BKT transition is induced by non-relativistic, purely 2D magnetic monopoles, which can be viewed also as electric vortices. These quantum BKT transitions have the same diverging exponent $z$ as the quantum Griffiths transition but have nothing to do with disorder.
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Statistical Mechanics

Anomalous Criticality of Absorbing State Transition toward Jamming

He-Da Wang, Bo Wang, Hao-Zheng Gu et al. (+2 more)

The jamming transition has traditionally been regarded as a geometric transition governed by static contact networks. Recently, dynamic phase transitions of athermal particles under periodic shear have offered a new perspective on this problem, leading to the conjecture that the jamming transition corresponds to an absorbing-state transition belonging to the conserved directed percolation (C-DP) or Manna universality class. Here, by re-examining the biased random organization (BRO) models on which this conjecture is based, we uncover anomalous criticality at high density. In disordered packings, we find a dynamic transition from absorbing to active-glass states with continuously varying dynamic critical exponents. Near the jamming point, quenched disorder arising from heterogeneous contact networks induces Griffiths effects, smearing the critical point into a pseudo-critical regime. In close-packed crystals, C-DP-like dynamic criticality is restored. We propose a field-theoretic description incorporating dynamical slowing down and quenched disorder to account for this anomalous criticality, providing a unified framework that links glassiness, jamming, and dynamic criticality.
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All authors He-Da Wang, Bo Wang, Hao-Zheng Gu, Qun-Li Lei, Yu-Qiang Ma

Materials Science

Phase relation investigation of U-La-O system under oxidizing conditions and observation of novel meta-stable and mixed-valent uranium phase- Ln3U11O36 (Ln=La, Nd, Sm, Gd)

Shafeeq Muhammed, Geeta Patkare and Rohan Phatak

Total of twelve samples in the U-La-O system with the compositions U1-yLayO2+x (y=0.025, 0.05, 0.1, up to 0.3) were synthesized by gel combustion synthesis method followed by appropriate heat treatment in air atmosphere. Comprehensive experimental analysis using various techniques like X-ray diffraction, thermogravimetry and oxygen to uranium ratio (O/U) are used to establish the phase relation in U1-yLayO2+x system at 1173 K and 1523 K heated in air. A novel meta-stable phase with stoichiometry La3U11O36 having mixed-valent uranium is reported for the first time in U-La-O system. The thermal property of this new phase is reported along with the updated phase relations at and above 1173 K temperature for the compositions U1-yLayO2+x (y < 0.3). Further, formation and stability of this new Ln3U11O36 phase was also investigated with smaller cations like Nd3+, Sm3+, Gd3+ and the smallest Y3+ cation.
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Mesoscale and Nanoscale Physics

Intrinsic ultrafast edge photocurrent dynamics in WTe$_2$ driven by broken crystal symmetry

Subhashri Chatterjee, Katsumasa Yoshioka, Taro Wakamura et al. (+2 more)

Directional photocurrents in two-dimensional materials arise from broken crystal symmetry, offering pathways to high-speed, bias-free photodetection beyond conventional devices. Tungsten ditelluride (WTe$_2$), a type-II Weyl semimetal, exhibits robust symmetry-breaking-induced edge photocurrents from competing nonlinear optical and photothermoelectric mechanisms, whose intrinsic dynamics have remained experimentally inaccessible. Here, we directly resolve sub-picosecond edge photocurrent dynamics in WTe$_2$ through ohmic contacts over temperatures from 300 K to 4 K. We demonstrate ultrafast optical-to-electrical conversion with a 3 dB bandwidth of $\sim$250 GHz and reveal picosecond-timescale switching of the net photocurrent direction below 150 K, linked to a Lifshitz transition. This transient bipolar response arises from non-equilibrium Seebeck effects due to asymmetric cooling of hot electrons and holes. These findings reveal previously hidden ultrafast dynamics in symmetry-engineered materials, offering new strategies to disentangle competing photocurrent mechanisms and enabling the development of self-powered, ultrafast optoelectronic devices.
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All authors Subhashri Chatterjee, Katsumasa Yoshioka, Taro Wakamura, Vasili Perebeinos, Norio Kumada

Mesoscale and Nanoscale Physics

Interband optical conductivity in two-dimensional semi-Dirac bands tilting along the quadratic dispersion

Xin Chen, Jian-Tong Hou, Long Liang et al. (+4 more)

Two-dimensional (2D) semi-Dirac materials feature a unique anisotropic band structure characterized by quadratic dispersion along one spatial direction and linear dispersion along the other, effectively hybridizing ordinary and Dirac fermions. The anisotropy of energy dispersion can be further modulated through band tilting along either spatial direction of the wave vector. We propose a new definition of tilt parameter to characterize Lifshitz phases in 2D semi-Dirac bands tilting along the quadratically dispersing direction. Using linear response theory, we theoretically investigate the interband optical conductivity of 2D tilted semi-Dirac bands. Our analytical zero-temperature results reveal pronounced distinctions from Dirac and semi-Dirac systems tilting along the linearly dispersing direction. Notably, we find that spectral fixed point emerges in the optical conductivity over a specific range of the tilt parameter, a phenomenon explained by the corresponding behavior of the joint density of states. These findings provide a robust theoretical framework for identifying and characterizing 2D tilted semi-Dirac materials and establish clear spectral fingerprints that distinguish different kinds of 2D semi-Dirac bands and Dirac bands. Our predictions can guide future experimental studies of anisotropic band engineering and tilt-dependent phenomena.
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All authors Xin Chen, Jian-Tong Hou, Long Liang, Jie Lu, Hong Guo, Chang-Xu Yan, Hao-Ran Chang

Mesoscale and Nanoscale Physics

Nonlinear Optical Response in Pseudo-Hermitian Systems at Steady State

S. Sajad Dabiri and Reza Asgari

We establish a steady-state theory for nonlinear optical conductivity in pseudo-Hermitian systems. We derive compact formulas for the first and second order conductivity tensors in both the velocity and length gauges and prove their exact equivalence through generalized sum rules and Berry connection identities by formulating the nonlinear response in terms of a biorthogonal density matrix. Utilizing the formalism on parity-time symmetric two-level systems reveals nonlinear phenomena that are not present in Hermitian systems, such as extra terms in the conductivity, corrections to the velocity operator, photocurrent, and resonance structures with higher-order poles at one-photon transitions. These features yield qualitatively distinct harmonic generation responses like real second-order conductivities and nonzero DC limits. These results provide new insights into nonlinear light-matter interactions in active media characterized by balanced gain and loss, with implications for non-Hermitian photonics, dissipative topological systems, and quantum devices designed with engineered dissipation.
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Strongly Correlated Electrons

Topological Hall Effect in PrSb$_2$

Shingo Araki, Hinata Izumida, Kazuto Akiba et al. (+2 more)

PrSb$_2$ exhibits a charge-density wave (CDW) transition at $T_\mathrm{CDW} = 100$ K and antiferromagnetic (AFM) ordering at $T_\mathrm{N} = 5$ K at ambient pressure. Hall resistivity measurements revealed an anomalous feature within the AFM state, which was attributed to the topological Hall effect (THE), ruling out contributions from the ordinary and anomalous Hall effects. Significantly, the THE anomaly diminished with increasing pressure and almost vanished as the CDW transition was suppressed near the critical pressure $P_c$ = 1.0 GPa. These findings suggest a relationship between the CDW order and the appearance of the THE in PrSb$_2$.
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All authors Shingo Araki, Hinata Izumida, Kazuto Akiba, Tatsuo C. Kobayashi, Takashi Kambe

Statistical Mechanics

Recurrence in a periodically driven and weakly damped Fermi-Pasta-Ulam-Tsingou chain

Yujun Shi and Haijiang Ren

We report numerical evidence of Fermi-Pasta-Ulam-Tsingou (FPUT)-like recurrence in weakly damped, periodically driven alpha-FPUT chains. In narrow regions of driving amplitude and damping, the steady-state energy is exchanged among a few low-frequency modes in a quasi-periodic (or highly regular, near-periodic) manner over long timescales. The maximum damping allowing recurrence decreases rapidly with chain length, suggesting that in the thermodynamic limit such behavior is unlikely to persist. Unlike discrete time crystals, the recurrence period is not an integer multiple of the driving period and does not correspond to spontaneous symmetry breaking. Nevertheless, these results reveal a new type of coherent nonlinear dynamics in driven, open multimode systems and provide guidance for experimentally realizing long-lived quasi-periodic states.
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Strongly Correlated Electrons

Twisted locality-preserving automorphisms, anomaly index, and generalized Lieb-Schultz-Mattis theorems with anti-unitary symmetries

Ruizhi Liu, Jinmin Yi and Liujun Zou

Symmetries and their anomalies are powerful tools to understand quantum matter. In this work, for quantum spin chains, we define twisted locality-preserving automorphisms and their Gross-Nesme-Vogts-Werner indices, which provide a unified framework to describe both unitary and anti-unitary symmetries, on-site and non-on-site symmetries, and internal and translation symmetries. For a symmetry $G$ with actions given by twisted locality-preserving automorphisms, we give a microscopic definition of its anomaly index, which is an element in $H^3_\varphi(G; U(1))$, where the subscript $\varphi$ means that anti-unitary elements of $G$ act on $U(1)$ by complex conjugation. We show that an anomalous symmetry leads to multiple Lieb-Schultz-Matttis-type theorems. In particular, any state with an anomalous symmetry must either have long-range correlation or violate the entanglement area law. Based on this theorem, we further deduce that any state with an anomalous symmetry must have long-range entanglement, and any Hamiltonian that has an anomalous symmetry cannot have a unique gapped symmetric ground state, as long as the interactions in the Hamiltonian decay fast enough as the range of the interaction increases. For Hamiltonians with only two-spin interactions, the last theorem holds if the interactions decay faster than $1/r^2$, where $r$ is the distance between the two interacting spins. We demonstrate these general theorems in various concrete examples.
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Materials Science

Real-Space Quantification of Exciton Localization in Acene Crystals Using Wannier Function Decomposition

Zui Tao, Jonah B. Haber and Jeffrey B. Neaton

We introduce the Wannier function decomposition of excitons (WFDX) method to quantify exciton localization in solids within the ab initio Bethe-Salpeter equation framework. By decomposing each Bloch exciton wavefunction into products of single-particle electron and hole maximally localized Wannier functions, this real-space approach provides well-defined orbital- and spatial- resolved measures of both Frenkel and charge-transfer excitons at low computational cost. We apply WFDX to excitons in acene crystals, quantifying how the number of rings, the exciton spin state, and the center-of-mass momntum affect spatial localization. Additionally, we show how this real-space representation reflects structural nonsymmorphic symmetries that are hidden in standard reciprocal-space descriptions. We demonstrate how the WFDX framework can be used to efficiently interpolate exciton expansion coefficients in reciprocal-space and outline how it may facilitate evaluation of observables involving position operators, highlighting its potential as a general tool for both analyzing and computing excitonic properties in solids.
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Tuesday 7 October

Soft Condensed Matter

High Strain Rate Behavior of Liquid Crystal Elastomers

Adeline Wihardja, Juan Carlos Nieto Fuentes, Daniel Rittel et al. (+1 more)

Liquid crystal elastomers are rubbery solids that couple liquid crystalline order and deformation. This coupling leads to properties that are attractive for a number of applications in soft robotics and energy absorption. This paper is motivated by the latter application, and provides a systematic experimental study of a particular class of liquid crystal elastomers – the isotropic genesis polydomain liquid crystal elastomers – over a wide range of strain rates. An important aspect of this study is a novel tensile drop-tower that enables tensile strain rates of 100 s$^{-1}$ that are important to application but previously inaccessible. The paper also extends a recently proposed constitutive model to the high strain rate regime, and shows that it can be fit to describe the observed behavior across the spectrum of examined behavior.
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All authors Adeline Wihardja, Juan Carlos Nieto Fuentes, Daniel Rittel, Kaushik Bhattacharya

Materials Science · Cross-listed from cs.DL

Evolve with Your Research – Stepwise System Evolution from Document-driven to Fact-centric Research Data Management in Materials Science

Victor Dudarev and Alfred Ludwig

The digitalisation of research requires data management systems capable of supporting a broad spectrum of usage scenarios, ranging from document-oriented repositories to fully factographic environments. This paper introduces a methodological approach for the stepwise development of such systems, illustrated by the MatInf Research Data Management System (RDMS). The proposed framework combines a graph-based STAR paradigm-emphasising Statefulness, Traceability, Aim, and Result-with the SET methodology, which enables systematic Standardisation, Extraction, and Testing of research data. Together, these principles provide a pathway towards FAIR-compliant data infrastructures, facilitating reproducibility, re-use, and integration of heterogeneous materials science data. By demonstrating the gradual consolidation of research outputs into unified datasets, this study highlights how adaptive RDMS design can support accelerated scientific discovery and enhance collaborative research in large-scale projects.
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Materials Science · Cross-listed from cs.LG

Assessment of different loss functions for fitting equivalent circuit models to electrochemical impedance spectroscopy data

Ali Jaberi, Amin Sadeghi, Runze Zhang et al. (+5 more)

Electrochemical impedance spectroscopy (EIS) data is typically modeled using an equivalent circuit model (ECM), with parameters obtained by minimizing a loss function via nonlinear least squares fitting. This paper introduces two new loss functions, log-B and log-BW, derived from the Bode representation of EIS. Using a large dataset of generated EIS data, the performance of proposed loss functions was evaluated alongside existing ones in terms of R2 scores, chi-squared, computational efficiency, and the mean absolute percentage error (MAPE) between the predicted component values and the original values. Statistical comparisons revealed that the choice of loss function impacts convergence, computational efficiency, quality of fit, and MAPE. Our analysis showed that X2 loss function (squared sum of residuals with proportional weighting) achieved the highest performance across multiple quality of fit metrics, making it the preferred choice when the quality of fit is the primary goal. On the other hand, log-B offered a slightly lower quality of fit while being approximately 1.4 times faster and producing lower MAPE for most circuit components, making log-B as a strong alternative. This is a critical factor for large-scale least squares fitting in data-driven applications, such as training machine learning models on extensive datasets or iterations.
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All authors Ali Jaberi, Amin Sadeghi, Runze Zhang, Zhaoyang Zhao, Qiuyu Shi, Robert Black, Zoya Sadighi, Jason Hattrick-Simpers

Materials Science · Cross-listed from eess.SY

Techno-economic analysis of self-sustainable thermophotovoltaic systems for grid-scale energy generation

Jihun Lim and Sungwon Lee

To facilitate the widespread adoption of renewable energy, dispatchable, zero-emission power sources are essential for grid stability. This work performs a comprehensive techno-economic analysis of a self-sustainable thermophotovoltaic (TPV) system, an architecture that integrates solar charging to function as a standalone power generation asset. Using theory-based models for conventional air-bridge InGaAs and Si diode cells, our analysis reveals that while the system is not currently competitive from a pure levelized of storage cost (LCOS) perspective due to the high capital expenditure for thermal battery materials, its primary value lies in its competitive levelized cost of electricity (LCOE), which is comparable to that of conventional dispatchable generators such as gas turbines. Furthermore, we show that a full Si-based TPV system, utilizing a 50-{\mu}m-thick air-bridge cell for enhanced photon utilization, can also achieve an LCOE that is competitive with such conventional power sources at scales exceeding the gigawatt-hour level, despite its lower conversion efficiency relative to its InGaAs counterpart. This highlights a practical engineering pathway for leveraging the immense manufacturing scalability of Si, offering a lower-risk route to deployment compared to III-V materials. Ultimately, this work establishes the self-sustainable TPV architecture as a compelling pathway toward providing grid-scale, on-demand, zero-emission power.
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Disordered Systems and Neural Networks

Application of deep neural networks for computing the renormalization group flow of the two-dimensional phi^4 field theory

Yueqi Zhao, Michael M. Fogler and Yi-Zhuang You

We introduce RGFlow, a deep neural network-based real-space renormalization group (RG) framework tailored for continuum scalar field theories. Leveraging generative capabilities of flow-based neural networks, RGFlow autonomously learns real-space RG transformations from data without prior knowledge of the underlying model. In contrast to conventional approaches, RGFlow is bijective (information-preserving) and is optimized based on the principle of minimal mutual information. We demonstrate the method on two examples. The first one is a one-dimensional Gaussian model, where RGFlow is shown to learn the classical decimation rule. The second is the two-dimensional phi^4 theory, where the network successfully identifies a Wilson-Fisher-like critical point and provides an estimate of the correlation-length critical exponent.
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Soft Condensed Matter

Frenkel's entropy-exchange mechanism in monodisperse, nearly hard-sphere colloids: minimal perturbations to access fluid-crystal coexistence

J. Galen Wang, Umesh Dhumal, Monica E. A. Zakhari et al. (+1 more)

Entropically driven fluid-solid transitions in monodisperse, purely repulsive hard spheres (MPRHS) are well established in theory, simulation, and experiment for atomic and colloidal systems. For MPRHS, however, coexistence is usually located via bulk free-energy calculations; the underlying microscopic balance between configurational and vibrational entropy is left implicit. Frenkel clarified this mechanism explicitly as an exchange of long-range configurational entropy for short-range vibrational entropy, but in the pristine MPRHS limit the nucleation barrier near coexistence is so high that phase separation is predicted only on astronomical time scales. Consistent with this, even unbiased simulations do not show spontaneous, equilibrium fluid-crystal coexistence; transient mixtures are mostly overtaken by a single phase; observed coexistence is still algorithmically-driven. Nearly hard-sphere colloid experiments do observe fluid-crystal coexistence, but always in the presence of unavoidable triggers such as gravity, walls, and polydispersity. We treat the hard-sphere phase diagram as settled and ask how the entropic exchange mechanism can be revealed in nearly hard-sphere colloidal simulations. We probe the mechanism on finite time scales by introducing minimal perturbations that trigger phase separation: small reductions in hardness that increase locally accessible free volume (and thus gently increase vibrational entropy), and 2-4% distributed crystal seeds. These perturbations produce coexisting fluid and crystal domains with crystal fraction, phase envelope and osmotic pressure that, with systematically increasing particle hardness, approach the hard-sphere limit. These results demonstrate that slight enhancements to vibrational entropy provide a dynamically accessible route to realizing the long-range/short-range entropy exchange required for phase separation.
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All authors J. Galen Wang, Umesh Dhumal, Monica E. A. Zakhari, Roseanna N. Zia

Materials Science

High temperature Neel skyrmions in simple ferromagnets

Peng Wang, Rana Saha, Holger L. Meyerheim et al. (+10 more)

A wide variety of chiral non-collinear spin textures have been discovered and have unique properties that make them highly interesting for technological applications. However, many of these are found in complex materials and only in a narrow window of temperature. Here, we show the formation of Neel-type skyrmions in thin layers of simple ferromagnetic alloys, namely Co-Al and Co-Ni-Al, over a wide range of temperature up to 770 K, by imposing a vertical strain gradient via epitaxy with an Ir-Al underlayer. The Neel skyrmions are directly observed using Lorentz transmission electron microscopy in freestanding membranes at high temperatures and the strain gradient is directly measured from x-ray diffraction anomalous peak profiles. Our concept allows simple centrosymmetric ferromagnets with high magnetic ordering temperatures to exhibit hot skyrmions, thereby, bringing closer skyrmionic electronics.
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All authors Peng Wang, Rana Saha, Holger L. Meyerheim, Ke Gu, Hakan Deniz, David Eilmsteiner, Andrea Migliorini, Juan Rubio Zuazo, Engenia Sebastiani-Tofano, Ilya Kostanovski, Abhay Kant Srivastava, Arthur Ernst, Stuart S. P. Parkin

Materials Science

Multimode magnon-phonon cavity driven by symmetry-locked strain fields

Chunli Tang, Yujie Zhu, Dayne Sasaki et al. (+13 more)

Hybrid magnon-phonon cavities with precise control knobs are highly sought after for coherent energy and signal transduction in solid-state platforms. While strain offers a powerful means to tune magnonic characteristics, extending strain engineering into magnon-phonon hybridization has remained elusive. Moreover, implementing controllable strain at the meso- or nanoscale poses a formidable challenge, as spatial inhomogeneity of strain fields often leads to enhanced damping and reduced coherence, thereby hindering device integration and scalability. Here, we present an epitaxial La0.7Sr0.3MnO3/SrTiO3 (LSMO/STO) heterostructure that exhibits strong coupling between the Kittel magnon and acoustic phonon. Leveraging the emergence of structural domains when STO undergoes a cubic-to-tetragonal phase transition, we create anisotropic local strains at the interface. Remarkably, the anisotropic local strain of less than 0.1 % drives the pronounced splitting of the magnon into three branches. Each branch independently hybridizes with acoustic phonons, forming a matrix of magnon-phonon avoided crossings that underpins multimode transduction and programmable networks in frequency and magnetic field space. An analytical model reveals that the split magnon branches are deterministically locked to the three main crystalline axes, enabling robust, orientation-selective control of the hybridized magnon-phonon spectrum against spatial inhomogeneity. Our results establish designed local strain as an exceptionally sensitive trigger for multimode magnon-phonon hybridization in magnetoelastic oxide heterostructures, and highlight local strain engineering as a viable strategy for designing tunable hybrid magnonic and phononic devices.
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All authors Chunli Tang, Yujie Zhu, Dayne Sasaki, Jiaxuan Wu, Yuzan Xiong, Harshil Goyal, Masoud Mahjouri-Samani, Mark Adams, Xiang Meng, Bethany E. Matthews, Le Wang, Yingge Du, Jia-Mian Hu, Yayoi Takamura, Wei Zhang, Wencan Jin

Materials Science

Local Order Average-Atom Interatomic Potentials

Chloe A. Zeller, Ronald E. Miller and Ellad B. Tadmor

This article describes an extension to the effective Average-Atom (AA) method for random alloys to account for local ordering (short-range order) effects by utilizing information from partial radial distribution functions. The new Local Order Average-Atom (LOAA) method is rigorously derived based on statistical mechanics arguments and validated for non-stoichiometric binary 2D hexagonal crystals and 3D FeNiCr and NiAl alloys whose ground state is obtained through Monte Carlo sampling. Material properties for these alloys computed from atomistic simulations using standard interatomic potentials (IPs) exhibit a strong dependence on local ordering that is captured by simulations with effective LOAA IPs, but not the original AA method. The advantage of LOAA is that it requires smaller system sizes to achieve statistically converged results and therefore enables the simulation of complex materials, such as high-entropy alloys, at a fraction of the computational cost of standard IPs.
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Materials Science

Mechanistic insights into hydrogen reduction of multicomponent oxides via in-situ high-energy X-ray diffraction

Shiv Shankar, Barak Ratzker, Claudio Pistidda et al. (+2 more)

Co-reduction of multicomponent oxides with hydrogen provides a carbon-neutral approach toward sustainable alloy design. Herein, we investigate the hydrogen-based direct reduction, using in-situ high-energy X-ray diffraction of two precursor variants: mechanically mixed powders and pre-sintered oxide mixtures, targeting an equiatomic CoFeMnNi alloy. We find distinct reduction pathways and microstructure evolution depending on initial precursors. Mixed powders at 700 {\deg}C are reduced to body-centered-cubic, face-centered-cubic, and MnO phases via halite, spinel, and Mn3O4 intermediates, whereas the pre-sintered material directly transforms into a mixture of metallic and oxide phases. The post-reduction microstructures are also different: mixed oxides show loosely packed morphology, whereas pre-sintered material reveals metallic nanoparticles supported on nanoporous MnO. The formation of nanoporous metallic networks is strongly governed by the precursor state, highlighting the role of initial precursors on the final microstructure. This precursor design strategy offers a single-step route to nanoporous alloys with potential applications in catalysis and energy technologies.
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All authors Shiv Shankar, Barak Ratzker, Claudio Pistidda, Dierk Raabe, Yan Ma

Superconductivity

Kekulé Superconductivity in Twisted Magic Angle Bilayer Graphene

Ke Wang and K. Levin

While it has been one of the most important new physics discoveries in the last decade, the nature of superconductivity in the twisted graphene family remains an unsolved problem. Motivated by recent scanning tunneling experiments that report Kekulé ordering in moiré graphene superconductors, we develop a microscopic theory of this superconductivity for the twisted bilayer system. The pairing we find is an intra-valley, finite-momentum pair-density wave (PDW) that intrinsically carries a Kekulé modulation. This state exhibits four salient features: (i) spontaneous breaking of $C_3$ rotation symmetry, producing nematic order (ii)with triplet pairing; and (iii) a quasiparticle density of states that evolves from a V-shaped profile to a fully gapped, U-shaped spectrum as the attraction increases which is accompanied by (iv) systematic behavior of the temperature dependent zero bias conductance. These features align with key experimental signatures. We find, as well, that with only modest interaction strengths, the state is near to a BEC-like phase, consistent with the observed extremely short coherence lengths. Taken together, these results identify a microscopic intra-valley Kekulé PDW as a compelling candidate for unconventional superconductivity in the twisted graphene family.
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Materials Science

Synthesis and Characterization of Ultrasonically Atomized Al-Based Alloy Powders for Tunable Thermal Reactivity

Chetan Singh, Ava Goglia, Peter Mastracco et al. (+4 more)

Reactive aluminum (Al) alloy powders are promising for advanced manufacturing, joining, and energetic applications, yet scalable routes that couple controlled reactivity with safe handling remain limited. While nanoscale Al powders ignite readily, their agglomeration, handling, and safety limit broad deployment. Here, we manufacture micron-sized Al-based powders produced by ultrasonic atomization (UA), targeting a balance of enhanced reactivity and process robustness. Binary systems (AlCu, AlSi, AlMg) and pure Al were synthesized, and their morphology, phases present, thermal stability, and oxidation behavior were characterized using XRD, SEM, and DTA/TGA in an Ar/O2 environment. We show that alloy selection and UA-controlled microstructure can modify the native Al2O3 passivation, alter oxidation pathways, and shift thermal onsets/exotherms. The results establish a manufacturing-forward framework for designing micron-sized powders with tunable ignition/oxidation behavior.
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All authors Chetan Singh, Ava Goglia, Peter Mastracco, Michael Flickinger, Laszlo J. Kecskes, Paulette Clancy, Timothy P. Weihs

Strongly Correlated Electrons

Phonon Hall Viscosity and the Intrinsic Thermal Hall Effect of $\alpha$-RuCl$_3$

Avi Shragai, Ezekiel Horsley, Subin Kim et al. (+2 more)

The thermal Hall effect has been observed in a wide variety of magnetic insulators, yet its origins remains controversial. While some studies attribute the effect to intrinsic mechanism, such as heat carriers with Berry curvature, others propose extrinsic mechanisms, such as heat carriers scattering off crystal defects. Even the nature of the heat carriers is unknown: magnons, phonons, and fractionalized spin excitations have all been proposed. Resolving these issues is essential for the study of quantum spin liquids, and particularly for $\alpha$-RuCl$_3$, where a quantized thermal Hall effect has been attributed to Majorana edge modes. Here, we use ultrasonic measurements of the acoustic Faraday effect to demonstrate that the phonons in $\alpha$-RuCl$_3$ have Hall viscosity – a non-dissipative viscosity that rotates phonon polarizations and deflects phonon heat currents. We show that phonon Hall viscosity produces an intrinsic thermal Hall effect that quantitatively accounts for a significant fraction of the measured thermal Hall effect in $\alpha$-RuCl$_3$: the thermal Hall effect in $\alpha$-RuCl$_3$ is due to phonons and it is intrinsic. More broadly, we demonstrate that the acoustic Faraday effect is a powerful tool for detecting phonon Hall viscosity and the associated phonon Berry curvature, offering a new way to uncover and study exotic states of matter that elude conventional experiments.
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All authors Avi Shragai, Ezekiel Horsley, Subin Kim, Young-June Kim, B.J. Ramshaw

Mesoscale and Nanoscale Physics

Many-Body Effects in a Molecular Quantum NAND Tree

Justin P. Bergfield

Molecules provide the smallest possible circuits in which quantum interference and electron correlation can be engineered to perform logical operations, including the universal NAND gate. We investigate a chemically encoded quantum NAND tree based on alkynyl-extended iso-polyacetylene backbones, where inputs are set by end-group substitution and outputs are read from the presence or absence of transmission nodes. Using quantum many-body transport theory, we show that NAND behavior persists in the presence of dynamic correlations, but that the nodal positions and their chemical shifts depend sensitively on electron-electron interactions. This sensitivity highlights the potential of these systems not only to probe the strength of electronic correlations but also to harness them in shaping logical response. The thermopower is identified as a chemically robust readout of gate logic, providing discrimination margins that greatly exceed typical experimental uncertainties, in an observable governed primarily by the variation of transport rather than its absolute magnitude.
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Superconductivity

Hund's coupling assisted orbital-selective superconductivity in Ba1-xKxFe2As2

Elena Corbae, Rong Zhang, Cong Li et al. (+10 more)

While the superconducting transition temperature of hole-doped Ba_{1-x}K_{x}Fe_{2}As_{2} decreases past optimal doping, superconductivity does not completely disappear even for the fully doped KFe_{2}As_{2} compound. In fact, superconductivity is robust through a Lifshitz transition where electron bands become hole-like around the zone corner at around x=0.7, thus challenging the conventional understanding of superconductivity in iron-based systems. High-resolution angle-resolved photoemission spectroscopy is used to investigate the superconducting gap structure, as well as the normal state electronic structure, around optimal doping and across the Lifshitz transition. Our findings reveal a largely orbital-dependent superconducting gap structure, where the more strongly correlated d_{xy} band has a vanishing superconducting gap at higher doping, aligning with the Hund's metal behavior observed in the normal state. Notably, the superconducting gap on the d_{xy} band disappears before the Lifshitz transition, suggesting that the Fermi surface topology may play a secondary role. We discuss how these results point to orbital-selective superconducting pairing and how strong correlations via Hund's coupling may shape superconducting gap structures in iron-based and other multiorbital superconductors.
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All authors Elena Corbae, Rong Zhang, Cong Li, Kunihiro Kihou, Chul-Ho Lee, Makoto Hashimoto, Thomas Devereaux, Oscar Tjernberg, Egor Babaev, Dung-Hai Lee, Vadim Grinenko, Donghui Lu, Zhi-Xun Shen

Disordered Systems and Neural Networks

Fully Parallel Multi-Agent Photonic Optimizer

Ghazi Sarwat Syed, Philipp Schmidt, Frank Brückerhoff-Plückelmann et al. (+3 more)

Optimization problems are central to many important cross-disciplinary applications.In their conventional implementations, the sequential nature of operations imposes strict limitations on the computational efficiency. Here, we discuss how analog optical computing can overcome this fundamental bottleneck. We propose a photonic optimizer unit, together with supporting algorithms that uses in memory computation within a nature inspired, multi agent cooperative framework. The system performs a sequence of reconfigurable parallel matrix vector operations, enabled by the high bandwidth and multiplexing capabilities inherent to photonic circuits. This approach provides a pathway toward fast paced and high quality solutions for difficult optimization and search problems.
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All authors Ghazi Sarwat Syed, Philipp Schmidt, Frank Brückerhoff-Plückelmann, Jelle Dijkstra, Wolfram H.P Pernice, Abu Sebastian

Statistical Mechanics · Cross-listed from quant-ph

Stochastic interpretation of quantum mechanics

Mário J. de Oliveira

We express the probabilistic character associated to the wave function by treating it as a stochastic variable. This is accomplished by means of a stochastic equation for the wave function whose noise changes the phase of the wave function but not its absolute value, so that the norm of the wave function is strictly conserved along a stochastic trajectory. We show that the density matrix that obeys the quantum Liouville equation is the covariance matrix associated to the stochastic wave function.
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Materials Science

Emergence of multiple relaxation processes during low to high density transition in Au49Cu26.9Si16.3Ag5.5Pd2.3 metallic glass

Alberto Ronca, Antoine Cornet, Jie Shen et al. (+8 more)

The existence of multiple amorphous states, or polyamorphism, remains one of the most debated phenomena in disordered matter, particularly regarding its microscopic origin and impact on glassy dynamics. Profiting of the enhanced data quality provided by brilliant synchrotrons, we combined high pressure X-ray photon correlation spectroscopy and X-ray diffraction to investigate the atomic dynamics-structure relationship in a Au49Cu26.9Si16.3Ag5.5Pd2.3 metallic glass at room temperature. We identify a structural and dynamical crossover near 3 GPa, marked by avalanches-like massive atomic rearrangements that promote the system toward increasingly compact atomic cluster connections. This crossover superimposes to a pressure-induced acceleration of the atomic motion recently reported, and signals the onset of a transitional state, potentially linked to the nucleation of a new phase within the glass, characterized by the coexistence of two amorphous states with distinct relaxation processes. These results provide evidence for a sluggish, continuous polyamorphic transformation, even in absence of marked structural discontinuities.
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All authors Alberto Ronca, Antoine Cornet, Jie Shen, Thierry Deschamps, Eloi Pineda, Yuriy Chushkin, Federico Zontone, Mohamed Mezouar, Isabella Gallino, Gaston Garbarino, Beatrice Ruta

Materials Science · Cross-listed from quant-ph

Prediction of Molecular Single-Photon Emitters: A Materials-Modelling Approach

Erik Karlsson Öhman, Daqing Wang, R. Matthias Geilhufe et al. (+1 more)

Interfacing light with quantum systems is an integral part of quantum technology, with the most essential building block being single-photon emitters. Although various platforms exist, each with its individual strengths, molecular emitters boast a unique advantage – namely the flexibility to tailor their design to fit the requirements of a specific task. However, the characteristics of the vast space of possible molecular configurations are challenging to understand and explore. Here, we present a theoretical and computational framework to initiate exploration of this vast potential by integrating database analysis with microscopic predictions. Using a model system of dibenzoterrylene in an anthracene host as benchmark, our approach identifies promising new candidates, among them a chiral molecular emitter. Future extensions of our approach integrated with machine learning routines hold the promise of ultimately unlocking the full potential of molecular quantum light-matter interfaces.
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All authors Erik Karlsson Öhman, Daqing Wang, R. Matthias Geilhufe, Christian Schäfer