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Physics Condensed Matter

cond-mat Watch Condensed Matter

Saturday 8 November

Strongly Correlated Electrons

Effects of crystal field and momentum-based frustrated exchange interactions on multiorbital square skyrmion lattice

Yan S. Zha and Satoru Hayami

Motivated by recent theoretical predictions of a square-shaped skyrmion lattice (S-SkL) in centrosymmetric tetragonal Ce-based magnets [Yan Zha and Satoru Hayami, Phys. Rev. B 111, 165155 (2025)], we perform a comprehensive theoretical investigation into the role of multiorbital effects and momentum-based frustrated exchange interactions in stabilizing such topologically nontrivial magnetic textures. By employing self-consistent mean-field calculations over a broad range of model parameters, we demonstrate that the cooperative interplay among interorbital coupling, frustrated exchange interactions at higher-harmonic wave vectors, and crystal-field-induced anisotropy is crucial for the stabilization of the S-SkL. Furthermore, the competition between the easy-plane intraorbital anisotropy and the easy-axis interorbital anisotropy leads to a significant enhancement of the S-SkL stability region. We also identify a rich variety of multi-$Q$ states, including a topologically nontrivial S-SkL state with a slight breaking of fourfold rotational symmetry (S-SkL$'$), magnetic bubble lattices (MBLs), and double-$Q$ phases with a local/net scalar chirality. Our findings elucidate the microscopic mechanism responsible for the emergence of S-SkLs in prototypical Ce-based magnets and provide a route toward realizing skyrmion lattices in a broader class of $f$-electron materials beyond conventional Gd- and Eu-based systems lacking orbital angular momentum.
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Mesoscale and Nanoscale Physics

Crossover from quantum correlation to hot-carrier transport in scattering-tolerant 2D transistors

Debottam Daw, Houcine Bouzid, Sung-Gyu Lee et al. (+6 more)

Quantum correlation and hot-carrier transport represent two fundamentally distinct regimes of electronic conduction, rarely accessible within the same device. Here, we report a state-of-the-art monolayer transition metal dichalcogenides transistor architecture on a ferroelectric substrate that enables this crossover by leveraging the strong dielectric screening and in-plane gate control. At cryogenic temperatures, the devices exhibit reproducible quasi-periodic current fluctuations, consistent with an emergent potential landscape driven by electron-electron interactions at low carrier densities. As the temperature increases, this correlated potential profile thermally dissolves and transport is dominated by the lateral gate-field that drives the carriers with high kinetic energy. These hot-carriers can efficiently surmount the scattering events, exhibiting a record-high room-temperature electron mobility of ~4,800 cm^2/Vs and a maximum on-current ~0.5 mA/{\mu}m, surpassing traditional FETs in key performance metrics. These findings establish a unified approach for probing intermediate mesoscopic orders, while advancing the transistor performance limits in scalable 2D transistors.
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All authors Debottam Daw, Houcine Bouzid, Sung-Gyu Lee, Wujoon Cha, Ki Kang Kim, Min-kyu Joo, Yan Wang, Manish Chhowalla, Young Hee Lee

Mesoscale and Nanoscale Physics

An Unusual Dresselhaus Spin-Orbit Contribution of Even Order in Momentum

Hao Yang, Wei Wang, Gerson J. Ferreira et al. (+3 more)

The spin-orbit (SO) coupling is conventionally known to manifest as odd functions of momentum. Here, through both model calculations and symmetry analysis along with the method of invariants, we reveal that, in ordinary semiconductor heterostructures, a quadratic Dresselhaus SO term – inheriting from its bulk crystal form – emerges via the interband effect, while complying with time-reversal and spatial symmetries. Furthermore, we observe that this unusual SO term gives rise to a range of striking quantum phenomena, including hybridized swirling texture, anisotropic energy dispersion, avoided band crossing, longitudinal Zitterbewegung, and opposite spin evolution between different bands in quantum dynamics. These stand in stark contrast to those associated with the usual linear SO terms. Our findings uncover a previously overlooked route for exploiting interband effects and open new avenues for spintronic functionalities that leverage unusual SO terms of even orders in momentum.
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All authors Hao Yang, Wei Wang, Gerson J. Ferreira, Ning Hao, Ping Zhang, Jiyong Fu

Strongly Correlated Electrons · Cross-listed from hep-th

Dual holography as functional renormalization group

Ki-Seok Kim, Arpita Mitra, Debangshu Mukherjee et al. (+1 more)

We investigate the relationship between the functional renormalization group (RG) and the dual holography framework in the path integral formulation, highlighting how each can be understood as a manifestation of the other. Rather than employing the conventional functional RG formalism, we consider a functional RG equation for the probability distribution function, where the RG flow is governed by a Fokker-Planck-type equation. The central idea is to reformulate the solution of Fokker-Planck type functional RG equation in a path integral representation. Within the semiclassical approximation, this leads to a Hamilton-Jacobi equation for an effective renormalized on-shell action. We then examine our framework for an Einstein-Hilbert action coupled to a scalar field. Applying standard techniques, we derive a corresponding functional RG equation for the distribution function, where the dual holographic path integral serves as its formal solution. By synthesizing these two perspectives, we propose a generalized dual holography framework in which the RG flow is explicitly incorporated into the bulk effective action. This generalization naturally introduces RG $\beta$-functions and reveals that the RG flow of the distribution function is essentially identical to that of the functional RG equation.
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All authors Ki-Seok Kim, Arpita Mitra, Debangshu Mukherjee, Seung-Jong Yoo

Materials Science

Impact of electron-phonon interaction on the electronic structure of interfaces between organic molecules and a MoS$_2$ monolayer

Ignacio Gonzalez Oliva, Sebastian Tillack, Fabio Caruso et al. (+2 more)

By means of first-principles calculations, we investigate the role of electron-phonon interaction in the electronic structure of hybrid interfaces, formed by MoS$_2$ and monolayers of the organic molecules pyrene and pyridine, respectively. Quasiparticle energies are initially obtained within the $G_0W_0$ approximation and subsequently used to evaluate the electron-phonon self-energy and momentum-resolved spectral functions to assess the temperature renormalization of the band structure. We find that the band-gap renormalization by zero-point vibrations of both hybrid systems is comparable to that of pristine MoS$_2$, with a value of approximately 80 meV. Pronounced features of molecular origin emerge in the spectral function of the valence region, which we attribute to satellites arising from out-of-plane vibrational modes of the organic monolayers. For pyrene, this satellite exhibits a predominantly molecular character, while for pyridine, it has a hybrid nature, originating from the coupling of molecular vibrations to the MoS$_2$ valence band.
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All authors Ignacio Gonzalez Oliva, Sebastian Tillack, Fabio Caruso, Pasquale Pavone, Claudia Draxl

Friday 7 November

Materials Science · Cross-listed from cs.LG

Predicting Grain Growth in Polycrystalline Materials Using Deep Learning Time Series Models

Eliane Younes, Elie Hachem and Marc Bernacki

Grain Growth strongly influences the mechanical behavior of materials, making its prediction a key objective in microstructural engineering. In this study, several deep learning approaches were evaluated, including recurrent neural networks (RNN), long short-term memory (LSTM), temporal convolutional networks (TCN), and transformers, to forecast grain size distributions during grain growth. Unlike full-field simulations, which are computationally demanding, the present work relies on mean-field statistical descriptors extracted from high-fidelity simulations. A dataset of 120 grain growth sequences was processed into normalized grain size distributions as a function of time. The models were trained to predict future distributions from a short temporal history using a recursive forecasting strategy. Among the tested models, the LSTM network achieved the highest accuracy (above 90%) and the most stable performance, maintaining physically consistent predictions over extended horizons while reducing computation time from about 20 minutes per sequence to only a few seconds, whereas the other architectures tended to diverge when forecasting further in time. These results highlight the potential of low-dimensional descriptors and LSTM-based forecasting for efficient and accurate microstructure prediction, with direct implications for digital twin development and process optimization.
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Materials Science · Cross-listed from physics.chem-ph

Omics-scale polymer computational database transferable to real-world artificial intelligence applications

Ryo Yoshida, Yoshihiro Hayashi, Hidemine Furuya et al. (+103 more)

Developing large-scale foundational datasets is a critical milestone in advancing artificial intelligence (AI)-driven scientific innovation. However, unlike AI-mature fields such as natural language processing, materials science, particularly polymer research, has significantly lagged in developing extensive open datasets. This lag is primarily due to the high costs of polymer synthesis and property measurements, along with the vastness and complexity of the chemical space. This study presents PolyOmics, an omics-scale computational database generated through fully automated molecular dynamics simulation pipelines that provide diverse physical properties for over $10^5$ polymeric materials. The PolyOmics database is collaboratively developed by approximately 260 researchers from 48 institutions to bridge the gap between academia and industry. Machine learning models pretrained on PolyOmics can be efficiently fine-tuned for a wide range of real-world downstream tasks, even when only limited experimental data are available. Notably, the generalisation capability of these simulation-to-real transfer models improve significantly as the size of the PolyOmics database increases, exhibiting power-law scaling. The emergence of scaling laws supports the "more is better" principle, highlighting the significance of ultralarge-scale computational materials data for improving real-world prediction performance. This unprecedented omics-scale database reveals vast unexplored regions of polymer materials, providing a foundation for AI-driven polymer science.
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All authors Ryo Yoshida, Yoshihiro Hayashi, Hidemine Furuya, Ryohei Hosoya, Kazuyoshi Kaneko, Hiroki Sugisawa, Yu Kaneko, Aiko Takahashi, Yoh Noguchi, Shun Nanjo, Keiko Shinoda, Tomu Hamakawa, Mitsuru Ohno, Takuya Kitamura, Misaki Yonekawa, Stephen Wu, Masato Ohnishi, Chang Liu, Teruki Tsurimoto, Arifin, Araki Wakiuchi, Kohei Noda, Junko Morikawa, Teruaki Hayakawa, Junichiro Shiomi, Masanobu Naito, Kazuya Shiratori, Tomoki Nagai, Norio Tomotsu, Hiroto Inoue, Ryuichi Sakashita, Masashi Ishii, Isao Kuwajima, Kenji Furuichi, Norihiko Hiroi, Yuki Takemoto, Takahiro Ohkuma, Keita Yamamoto, Naoya Kowatari, Masato Suzuki, Naoya Matsumoto, Seiryu Umetani, Hisaki Ikebata, Yasuyuki Shudo, Mayu Nagao, Shinya Kamada, Kazunori Kamio, Taichi Shomura, Kensaku Nakamura, Yudai Iwamizu, Atsutoshi Abe, Koki Yoshitomi, Yuki Horie, Katsuhiko Koike, Koichi Iwakabe, Shinya Gima, Kota Usui, Gikyo Usuki, Takuro Tsutsumi, Keitaro Matsuoka, Kazuki Sada, Masahiro Kitabata, Takuma Kikutsuji, Akitaka Kamauchi, Yusuke Iijima, Tsubasa Suzuki, Takenori Goda, Yuki Takabayashi, Kazuko Imai, Yuji Mochizuki, Hideo Doi, Koji Okuwaki, Hiroya Nitta, Taku Ozawa, Hitoshi Kamijima, Toshiaki Shintani, Takuma Mitamura, Massimiliano Zamengo, Yuitsu Sugami, Seiji Akiyama, Yoshinari Murakami, Atsushi Betto, Naoya Matsuo, Satoru Kagao, Tetsuya Kobayashi, Norie Matsubara, Shosei Kubo, Yuki Ishiyama, Yuri Ichioka, Mamoru Usami, Satoru Yoshizaki, Seigo Mizutani, Yosuke Hanawa, Shogo Kunieda, Mitsuru Yambe, Takeru Nakamura, Hiromori Murashima, Kenji Takahashi, Naoki Wada, Masahiro Kawano, Yosuke Harada, Takehiro Fujita, Erina Fujita, Ryoji Himeno, Hiori Kino, Kenji Fukumizu

Superconductivity

Controllable Superconductivity in Suspended van der Waals Materials

Ruihuan Fang, Cuiju Yu, Youqiang Huang et al. (+12 more)

Tunable superconductors provide a versatile platform for advancing next-generation quantum technologies. Here, we demonstrate controllable superconductivity in suspended NbSe2 thin layers, achieved through local strain and thermal modulation of the superconducting state. Our results show that suspended NbSe2 structures enable strain modulation of the critical temperature by up to approximately 0.92 K (about 12.5% of the critical temperature) and allow the realization of gate-tunable superconducting critical currents. We further demonstrate configurable hysteretic transport characteristics exhibiting multistability and negative differential resistance, providing easily reconfigurable, spatially dependent superconducting states. These phenomena are well explained by calculations of electron-phonon coupling using density functional theory, together with time-dependent Ginzburg-Landau dynamics coupled to the thermal diffusion equation. Our work provides profound insight into strain and thermal modulation of van der Waals superconductors and opens new opportunities for tunable on-chip superconductor devices, integrated superconducting circuits, and quantum simulators.
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All authors Ruihuan Fang, Cuiju Yu, Youqiang Huang, Tosson Elalaily, Yuvraj Chaudhry, Yaoqiang Zhou, Andres Castellanos-Gomez, Sanshui Xiao, Jiwon Park, Hyunyong Choi, Fida Ali, Hanlin Fang, Jose Lado, Pertti Hakonen, Zhipei Sun

Materials Science

Novel Transformations of PbTiO3 with Pressure and Temperature

Husam Farraj, Stefano Racioppi, Gaston Garbarino et al. (+8 more)

We investigated the behavior of lead titanate (PbTiO3) up to 100 GPa, both at room temperature and upon laser heating, using synchrotron X ray diffraction combined with density functional theory (DFT) computations. At the high pressure temperature (PT) conditions produced in laser heated diamond anvil cells, PbTiO3 dissociates into PbO and TiO2, consistent with our DFT computations showing that decomposition becomes enthalpically favored above 65 GPa. In contrast, on room temperature compression, PbTiO3 persists in the tetragonal I4mcm phase up to at least 100 GPa. Laser heating produces distinct PbO phases: a compressed form of alpha PbO and a previously unreported delta PbO polymorph, both of which transform to beta PbO on decompression. The calculations predict that alpha PbO undergoes pressure-induced band gap closure, metallizing above 70 GPa, whereas the delta and beta phases remain semiconducting with a band gap above 1 eV even at megabar pressures. The experimental and confirming theoretical results reveal an unanticipated dimension of the behavior of PbTiO3, showing that distinct equilibrium and metastable phases can be stabilized along different PT synthesis paths.
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All authors Husam Farraj, Stefano Racioppi, Gaston Garbarino, Muhtar Ahart, Anshuman Mondal, Samuel G. Parra, Jesse S. Smith, R. E. Cohen, Eva Zurek, Jordi Cabana, Russell J. Hemley

Strongly Correlated Electrons

Chiral Cavity Control of the Interlayer Exciton Energy Spectrum

Jonathan Sanchez-Lopez, Ze-Xun Lin, Di Luo et al. (+1 more)

Heterostructures of two-dimensional materials offer a versatile platform to study light-matter interactions of electron and hole gases. By separating electron and hole layers with an insulator long-lived electron-hole bound states known as interlayer excitons can form. We predict that by placing an interlayer exciton in a time-reversal-symmetry-breaking chiral cavity the energy spectrum of an interlayer exciton can be reordered. As a consequence of this reordering the ground state of the interlayer exciton can be driven from an s-orbital to a p-orbital, effectively changing the symmetry of the electron-hole pair. We present a phase diagram showing the couplings and separations required for a p-orbital excitonic ground state where we predict that larger interlayer separations require higher cavity couplings. We expect these results to be relevant for angular-momentum-tunable, single photon emission physics.
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All authors Jonathan Sanchez-Lopez, Ze-Xun Lin, Di Luo, Prineha narang

Materials Science

From Quantum Annealing to Alloy Discovery: Towards Accelerated Design of High-Entropy Alloys

Diego Ibarra-Hoyos, Peter Connors, Ho Jang et al. (+6 more)

Data scarcity remains a central challenge in materials discovery, where finding meaningful descriptors and tuning models for generalization is critical but inherently a discrete optimization problem prone to multiple local minima confounding the true optimal state. Classical methods often get trapped in these minima, while quantum annealing can escape them via quantum fluctuations, including tunneling, that overcome narrow energy barriers. We present a quantum-assisted machine-learning (QaML) framework that employs quantum annealing to address these combinatorial optimization challenges through feature selection, support-vector training formulated in QUBO form for classification and regression, and a new QUBO-based neural-network pruning formulation. Recursive batching enables quantum annealing to handle large feature spaces beyond current qubit limits, while quantum-pruned networks exhibit superior generalization over classical methods, suggesting that quantum annealing preferentially samples flatter, more stable regions of the loss landscape. Applied to high-entropy alloys (HEAs), a data-limited but compositionally complex testbed, the framework integrates models for fracture-strain classification and yield-strength regression under physics-based constraints. The framework identified and experimentally validated Al8Cr38Fe50Mn2Ti2 (at.%), a single-phase BCC alloy exhibiting a 0.2 % yield strength of 568 MPa, greater than 40 % compressive strain without fracture, and a critical current density in reducing acid nearly an order of magnitude lower than 304 stainless steel. These results establish QA as a practical route to overcome classical optimization limits and accelerate materials discovery.
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All authors Diego Ibarra-Hoyos, Peter Connors, Ho Jang, Nathan Grain, Israel Klich, Gia-Wei Chern, Peter K. Liaw, John R. Scully, Joseph Poon

Strongly Correlated Electrons

Excitation spectrum and low-temperature magnetism in disordered defect-fluorite Ho2Zr2O7

P. L. Oliveira Silva, J.G.A. Ramon, Viviane Peçanha-Antonio et al. (+4 more)

In this work, we report on the thermomagnetic characterization and crystalline-electric field (CEF) energy scheme of the disordered defect-fluorite Ho2Zr2O7. This structural phase is distinguished by the coexistence of magnetic frustration and extensive disorder, with Ho3+ and Zr4+ sharing randomly the same 4a site with even 50% occupancy, and an average 1/8 oxygen vacancy per unit cell. AC magnetic susceptibility measurements performed on powder samples down to 0.5 K revealed signs of slowing spin dynamics without glassy behavior, including a frequency dependent peak at 1 K. Yet, no evidence for long-range magnetic order is found down to 150 mK in specific heat. Inelastic neutron scattering measurements show a weak, low-lying CEF excitation around 2 meV, accompanied by a broad level centered at 60 meV. To fit our observations, we propose an approach to account for structural disorder in the crystal-field splitting of the non-Kramers Ho3+. Our model provides an explanation to the broadening of the high-energy, single-ion excitations and suggests that the zirconate ground-state wave function has zero magnetic moment. However, structural disorder acts as guarantor of the magnetism in Ho2Zr2O7, allowing the mixing of low lying states at finite temperatures. Finally, we show that this scenario is in good agreement with the bulk properties reported in this work.
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All authors P. L. Oliveira Silva, J.G.A. Ramon, Viviane Peçanha-Antonio, Tatiana Guidi, J. S. Gardner, Chun Sheng Fang, R. S. Freitas

Disordered Systems and Neural Networks

Cluster percolation in the three-dimensional $\pm J$ random-bond Ising model

Lambert Münster and Martin Weigel

Based on extensive parallel-tempering Monte Carlo simulations, we investigate the relationship between cluster percolation and equilibrium ordering phenomena in the three-dimensional $\pm J$ random-bond Ising model as one varies the fraction of antiferromagnetic bonds. We consider a range of cluster definitions, most of which are constructed in the space of overlaps between two independent real replicas of the system. In the pure ferromagnet that is contained as a limiting case in the class of problems considered, the relevant percolation point coincides with the thermodynamic ordering transition. For the disordered ferromagnet encountered first on introducing antiferromagnetic bonds and the adjacent spin-glass phase of strong disorder this connection is altered, and one finds a percolation transition above the thermodynamic ordering point that is accompanied by the appearance of /two/ percolating clusters of equal density. Only at the lower (disordered) ferromagnetic or spin-glass transition points the densities of these two clusters start to diverge, thus providing a percolation signature of these thermodynamic transitions. We compare the scaling behavior at this secondary percolation transition with the thermodynamic behavior at the corresponding ferromagnetic and spin-glass phase transitions.
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Materials Science

Exchange field induced symmetry breaking in quantum hexaborides

D. Rivera, Fernando P. Sabino, H. Raebiger et al. (+3 more)

Symmetry breaking (SB) has proven to be a powerful approach for describing quantum materials: strong correlation, mass renormalization, and complex phase transitions are among the phenomena that SB can capture, even when coupled to a mean-field-like theory. Traditionally, corrective schemes were required to account for these effects; however, SB has emerged as an alternative that can also successfully describe the intricate physics of quantum materials. Here, we explore spin SB on EuB6 and SmB6 and how its relation to the exchange field can determine onsite properties, depending on the type of symmetry breaking. Using spin-polarized Density Functional Theory (DFT) calculations with the r2SCAN functional, we systematically compare four magnetic configurations, one totally symmetric - non-magnetic (NM) configuration - and three with different types of symmetry breaking: ferromagnetic (FM), antiferromagnetic (AFM) and a paramagnetic (PM) configuration - modeled through a Special Quasirandom Structure (SQS) method - to capture local symmetry-breaking effects. Our results show that the PM configuration produces distinct magnetic environments for the rare-earth atoms, leading to different exchange fields. These, in turn, induce symmetry breaking in the electronic and magnetic properties of Eu and Sm. Those results provide an alternative explanation for the experimental results on both materials, EuB6 and SmB6, where X-ray Absorption Spectroscopy (XAS) and X-ray Absorption Near Edge Structure (XANES) measurements suggest the presence of multiple atomic environments, previously attributed to a mixed-valence configuration.
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All authors D. Rivera, Fernando P. Sabino, H. Raebiger, A. Ruzsinszky, J. P. Perdew, G. M. Dalpian

Statistical Mechanics

Weakly universal dynamical correlations between eigenvalues of large random matrices

Kirone Mallick, Gabriel Téllez and Frédéric van Wijland

It was shown roughly thirty years ago that the density correlations of eigenvalues of large random matrices display a universal form, independent of most of the details of the distribution of the random matrix itself. We show that when the matrix elements evolve according to a Dyson Brownian motion, dynamical correlations retain a large degree of the universality found at equal times when expressed in terms of the characteristics of some partial differential equation in the complex plane.
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Materials Science

Surface acoustic wave enabled all-optical determination of the interlayer elastic constants of van der Waals interface

N.Yu. Frolov, A.Yu. Klokov, A. I. Sharkov et al. (+2 more)

Understanding the properties of two-dimensional materials interfaces with the substrate is necessary for device applications. Surface acoustic wave propagation through the layered material flake on a substrate could provide unique information on the transverse rigidity of the flake-to-substrate interaction. We generate ultrasonic waves by a focused femtosecond laser pulse at the surface of the model system – fused silica with h-BN flake transferred above. Using an all-optical spatially resolved pump-probe interferometric technique, we measure the spatial dependencies of the surface vertical velocity profiles. Our measurements reveal the appearance of the surface acoustic wave dispersion in the hBN flake region compared to fused silica surface. Multilayer modeling allows us to gain access to longitudinal and shear elastic coupling constants $c^*_{33}$ and $c^*_{44}$ between hexagonal BN and substrate.
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All authors N.Yu. Frolov, A.Yu. Klokov, A. I. Sharkov, M.V. Pugachev, A.Yu. Kuntsevich

Materials Science · Cross-listed from nlin.PS

Stability theory of flat band solitons in nonlinear wave systems

Cheng Shi, Ross Parker, Panayotis G. Kevrekides et al. (+1 more)

We establish a sharp criterion for the stability of a class of compactly supported, homogeneous density“minimal compact solitons” or MCS states, of the time-dependent discrete nonlinear Schrödinger equation on a multi-lattice, $\mathbb L$ ($\mathbb L$-DNLS). MCS states arise for multi-lattices where a nearest neighbor Laplace-type operator on $\mathbb L$ has a flat band. Our stability criterion is in terms of the explicit form of the nonlinearity and the projection of distinguished vectors onto the flat band eigenspace. We apply our general results to MCS states of DNLS for the diamond, Kagomé and checkerboard lattices. In lattices where MCS states are unstable, we demonstrate how to engineer the nonlinearity to stabilize small amplitude MCS states. Finally, via systematic numerical computations, we put our analytical results in the context of global bifurcation diagrams.
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All authors Cheng Shi, Ross Parker, Panayotis G. Kevrekides, Michael I. Weinstein

Materials Science

Single-Atom Photocatalysts on TiO2 : Insights from X-ray Absorption Spectroscopy

Yingying Li, David Morris and Peng Zhang

Surface modification of TiO2 with single-atom catalysts (SACs) is an effective strategy for enhancing photocatalytic efficiency. However, thorough characterization of SACs at the atomic scale remains challenging. X-ray absorption spectroscopy (XAS) offers unique advantages for the in-depth analysis of TiO2-supported SACs. By employing XAS, the local atomic structure, oxidation state, and electronic properties of the SACs, as well as the underlying photocatalytic mechanism, can be revealed. Herein, we present a short review on the application of XAS in studying TiO2-supported SACs. We first elucidate the key role of XAS in simultaneously probing the structure and electronic properties of monometallic SACs across different periods. Next, we discuss XAS studies of bimetallic SACs from the perspective of each constituent element and highlight the element-specific capabilities of XAS for analyzing multi-element SACs. Finally, we demonstrate how in situ XAS can effectively monitor structural and electronic property changes in SACs under real photocatalytic reaction conditions. Additionally, we provide practical suggestions for utilizing XAS more efficiently in the analysis of various SAC systems.
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Strongly Correlated Electrons

Reconfigurable flat bands from cooperative moiré and charge order

B.K. Saika, S. Buchberger, S. Mo et al. (+9 more)

The formation of flat electronic bands from long-wavelength superperiodic moiré potentials in van der Waals heterostructures underpins the creation and control of a host of highly-tunable correlated and topological phases. While the underlying moiré periodicity is typically a fixed property of the heterostructure, here we show how the development of a charge-density wave (CDW) in one of the constituent materials can create an emergent moiré lattice. We demonstrate this experimentally in TiSe$_2$/graphite epitaxial heterostructures, using angle-resolved photoemission and scanning-tunnelling microscopy and spectroscopy to directly image the resulting long-wavelength moiré potential and concomitant flat-band formation. We show how the intrinsically low-energy, deformable landscape of the CDW imparts significant tunability, stabilising quasi-one-dimensional moiré domains from symmetry breaking within the CDW, and allowing the complete suppression of flat-band formation by carrier doping across the CDW phase transition. Our findings thus open a new avenue for engineering moiré matter by exploiting the rich many-body states of the parent compounds of 2D heterostructures.
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All authors B.K. Saika, S. Buchberger, S. Mo, A. Rajan, D. Halliday, Y.-C. Yao, L.C. Rhodes, H. Decitre, T. Balasubramanian, C. Polley, P. Wahl, P.D.C. King

Quantum Gases

Controlled generation of 3D vortices in driven atomic Josephson junctions

Vijay Pal Singh, Ludwig Mathey, Herwig Ott et al. (+1 more)

We propose an ac-driven atomic Josephson junction as a clean and tunable source of three dimensional (3D) solitary waves in quantum fluids. Depending on the height of the junction barrier, the emitted excitations appear as vortex rings at low velocity or vorticity-free rarefaction pulses near the sound velocity, thus spanning the complete Jones-Roberts family of solitons. The Shapiro-step phenomenon renders the emission deterministic: on the first, second, third Shapiro steps, the junction ejects one, two, and three solitary excitations per drive cycle. This enables controlled generation of single- and multi-excitation configurations, allowing detailed studies of the full crossover between vortex rings and rarefaction pulses and their interaction dynamics. In particular, deterministic multi-ring emission provides insights into leapfrogging dynamics of two and three coaxial rings and their decay via boundary-assisted, sound-mediated processes. This ac-driven protocol establishes a compact and reproducible platform for generating, classifying, and controlling 3D solitonic excitations, paving the way for precision studies of nonlinear vortex dynamics, dissipation, and quantum turbulence in trapped superfluids.
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All authors Vijay Pal Singh, Ludwig Mathey, Herwig Ott, Luigi Amico

Statistical Mechanics

Exact strong zero modes in quantum circuits and spin chains with non-diagonal boundary conditions

Sascha Gehrmann and Fabian H. L. Essler

We construct exact strong zero mode operators (ESZM) in integrable quantum circuits and the spin-1/2 XXZ chain for general open boundary conditions, which break the bulk U(1) symmetry of the time evolution operators. We show that the ESZM is localized around one of the boundaries and induces infinite boundary coherence times. Finally, we prove that the ESZM becomes spatially non-local under the map that relates the spin-1/2 XXZ chain to the asymmetric simple exclusion process, which suggests that it does not play a significant role in the dynamics of the latter.
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Soft Condensed Matter · Cross-listed from physics.bio-ph

Glassy dynamics in active epithelia emerge from an interplay of mechanochemical feedback and crowding

Sindhu Muthukrishnan, Phanindra Dewan, Tanishq Tejaswi et al. (+6 more)

Glassy dynamics in active biological cells remain a subject of debate, as cellular activity rarely slows enough for true glassy features to emerge. In this study, we address this paradox of glassy dynamics in epithelial cells by integrating experimental observations with an active vertex model. We demonstrate that while crowding is essential, it is not sufficient for glassy dynamics to emerge. A mechanochemical feedback loop (MCFL), mediated by cell shape changes through the contractile actomyosin network, is required to drive glass transition in dense epithelial tissues, as revealed via a crosstalk between actin-based cell clustering and dynamic heterogeneity in experiments. Incorporating MCFL into the vertex model reveals contrasting results from those previously predicted by theories – we show that the MCFL can counteract cell division-induced fluidisation and enable glassy dynamics to emerge through active cell-to-cell communication. Furthermore, our analysis reveals, for the first time, the existence of novel collective mechanochemical oscillations that arise from the crosstalk of two MCFLs. Together, we demonstrate that an interplay between crowding and active mechanochemical feedback enables the emergence of glass-like traits and collective biochemical oscillations in epithelial tissues with active cell-cell contacts.
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All authors Sindhu Muthukrishnan, Phanindra Dewan, Tanishq Tejaswi, Michelle B Sebastian, Tanya Chhabra, Soumyadeep Mondal, Soumitra Kolya, Sumantra Sarkar, Medhavi Vishwakarma

Soft Condensed Matter

A flexible implementation of strong segregation theory for two dimensional ABC star terpolymer morphologies

Merin Joseph, Daniel J. Read and Alastair M. Rucklidge

We present a novel computational implementation of strong segregation theory, developed specifically for calculations of phase separated ABC star terpolymers. The method allows calculation of free energies of common two-dimensional morphologies for these polymers and the efficient construction of phase diagrams. The branch points of the ABC star terpolymers are localized in core regions, modeled as cylinders in three dimensions, and our framework is applicable to morphologies with single and multiple core types. Our central idea is that all the structures we wish to model can be assembled from a flexible base motif, which we call Strongly Segregated Polygons. This method is useful for exploring a wide range of complex morphologies, using a range of compositions and interaction strengths. We focus on 2D morphologies of ABC star terpolymers, but our method could be extended into three dimensions and to other molecular architectures, and in principle to large, irregular quasiperiodic two-dimensional structures.
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Materials Science

An improved reliability factor for quantitative low-energy electron diffraction

Alexander M. Imre, Lutz Hammer, Ulrike Diebold et al. (+2 more)

Quantitative low-energy electron diffraction [LEED $I(V)$ or LEED $I(E)$, the evaluation of diffraction intensities $I$ as a function of the electron energy] is a versatile technique for the study of surface structures. The technique is based on optimizing the agreement between experimental and calculated intensities. Today, the most commonly used measure of agreement is Pendry's $R$ factor $R_\mathrm{P}$. While $R_\mathrm{P}$ has many advantages, it also has severe shortcomings, as it is a noisy target function for optimization and very sensitive to small offsets of the intensity. Furthermore, $R_\mathrm{P} = 0$, which is meant to imply perfect agreement between two $I(E)$ curves can also be achieved by qualitatively very different curves. We present a modified $R$ factor $R_\mathrm{S}$, which can be used as a direct replacement for $R_\mathrm{P}$, but avoids these shortcomings. We also demonstrate that $R_\mathrm{S}$ is as good as $R_\mathrm{P}$ or better in steering the optimization to the correct result in the case of imperfections of the experimental data, while another common $R$ factor, $R_\mathrm{ZJ}$ (suggested by Zanazzi and Jona) is worse in this respect.
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All authors Alexander M. Imre, Lutz Hammer, Ulrike Diebold, Michele Riva, Michael Schmid

Materials Science

Point Defects Limited Carrier Mobility in Janus MoSSe monolayer

Nguyen Tran Gia Bao, Ton Nu Quynh Trang, Phan Bach Thang et al. (+3 more)

Point defects, often formed during the growth of Janus MoSSe, act as built-in scatterers and affect carrier transport in electronic devices based on Janus MoSSe. In this study, we employ first-principles calculations to investigate the impact of common defects, such as sulfur vacancies, selenium vacancies, and chalcogen substitutions, on electron transport, and compare their influence with that of mobility limited by phonons. Here, we define the saturation defect concentration ($C_{\mathrm{sat}}$) as the highest defect density that still allows the total mobility to remain within 90% of the phonon-limited value, providing a direct measure of how many defects a device can tolerate. Based on $C_{\mathrm{sat}}$, we find a clear ranking of defect impact: selenium substituting for sulfur is relatively tolerant, with $C_{\mathrm{sat}}\approx2.07\times10^{-4}$, while selenium vacancies are the most sensitive, with $C_{\mathrm{sat}}\approx3.65\times10^{-5}$. Our $C_{\mathrm{sat}}$ benchmarks and defect hierarchy provide quantitative, materials-specific design rules that can guide the fabrication of high-mobility field-effect transistors, electronic devices, and sensors based on Janus MoSSe.
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All authors Nguyen Tran Gia Bao, Ton Nu Quynh Trang, Phan Bach Thang, Nam Thoai, Vu Thi Hanh Thu, Nguyen Tuan Hung

Superconductivity

Anomalous Nodal Gap in a Doped Spin-1/2 Antiferromagnetic Mott Insulator

Yong Hu, Christopher Lane, Xiang Chen et al. (+10 more)

Many emergent phenomena appear in doped Mott insulators near the insulator-to-metal transition. In high-temperature cuprate superconductors, superconductivity arises when antiferromagnetic (AFM) order is gradually suppressed by carrier doping, and a $\textit{d}$-wave superconducting gap forms when an enigmatic nodal gap evolves into a point node. Here, we examine electron-doped Sr$_{2}$IrO$_{4}$, the 5$\textit{d}$-electron counterpart of cuprates, using angle-resolved photoemission spectroscopy. At low doping levels, we observe the formation of electronic states near the Fermi level, accompanied by a gap at the AFM zone boundary, mimicking the AFM gap in electron-doped cuprates. With increasing doping, a distinct gap emerges along the (0,0)-($\pi$,$\pi$) nodal direction, paralleling that observed in hole-doped cuprates. This anomalous nodal gap persists after the collapse of the AFM gap and gradually decreases with further doping. It eventually vanishes into a point node of the reported $\textit{d}$-wave gap. These observations replicate the characteristic features in both electron- and hole-doped cuprates, indicating a unified route toward nodal metallicity in doped spin-1/2 AFM Mott insulators.
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All authors Yong Hu, Christopher Lane, Xiang Chen, Shuting Peng, Zeliang Sun, Makoto Hashimoto, Donghui Lu, Tao Wu, Robert S. Markiewicz, Xianhui Chen, Arun Bansil, Stephen D. Wilson, Junfeng He

Mesoscale and Nanoscale Physics

Spin-Based True Random Number Generation Enabled by Voltage-Amplified Quantum Fluctuations

Jie Zheng, Jiyong Kang, Zheng Zhu et al. (+6 more)

We investigate spin quantum-fluctuation effects that originate from the Heisenberg uncertainty principle during the dynamical cycle of disentanglement, entanglement, and re-disentanglement between itinerant electrons and localized magnetic moments mediated by the s-d exchange interaction. Beyond conventional deterministic spin-transfer torque, we analyze an intrinsic mechanism that transfers spin quantum fluctuations to a nanomagnet. By extending the Landau-Lifshitz-Gilbert equation to incorporate both quantum and thermal stochastic fields, we identify a temperature regime in which quantum fluctuations dominate the magnetization dynamics. We further show that voltage-controlled magnetic anisotropy exponentially amplifies spin quantum fluctuations, enabling binary readout through magnetoresistance in magnetic tunnel junctions. These findings provide a microscopic framework for fluctuation-driven spin dynamics and outline a device-level pathway toward spin-based quantum true random number generation.
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All authors Jie Zheng, Jiyong Kang, Zheng Zhu, Di Wu, Yuesheng Li, Dongxing Yu, Jiayong Wang, Hongxing Xu, Chenglong Jia

Strongly Correlated Electrons

Structural modulation, physical properties, and electronic band structure of the kagome metal UCr$_6$Ge$_6$

Z. W. Riedel, P. A. E. Murgatroyd, C. S. Kengle et al. (+13 more)

The chemical flexibility of the $RM_6X_6$ stoichiometry, where an $f$-block element is intercalated in the CoSn structure type, allows for the tuning of flatbands associated with kagome lattices to the Fermi level and for emergent phenomena due to interactions between the $f$- and $d$-electron lattices. Yet, 5$f$ members of the “166" compounds are underrepresented compared with 4$f$ members. Here, we report single-crystal growth of UCr$_6$Ge$_6$, which crystallizes in a monoclinically distorted Y$_{0.5}$Co$_3$Ge$_3$-type structure. The real-space character of the modulation, which is unique within the $RM_6X_6$ family, is approximated by a 3$\times$1$\times$2 supercell of the average monoclinic cell. The compound has kagome-lattice flatbands near the Fermi level and a moderately enhanced electronic heat capacity, as evidenced by its low-temperature Sommerfeld coefficient ($\gamma=86.5$~mJ~mol$^{-1}$~K$^{-2}$) paired with band structure calculations. The small, isotropic magnetization and featureless resistivity of UCr$_6$Ge$_6$ suggest itinerant uranium 5$f$ electrons and Pauli paramagnetism. Angle-resolved photoemission spectroscopy results provide evidence for uranium 5$f$ weight at the Fermi level and for a flatband near the Fermi level associated with the chromium $3d$ kagome lattice. The isotropic magnetic behavior of the uranium 5$f$ electrons starkly contrasts with localized behavior in other uranium 166 compounds, highlighting the high tunability of the magnetic ground state across the material family.
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All authors Z. W. Riedel, P. A. E. Murgatroyd, C. S. Kengle, P. M. T. Vianez, A. Schmidt, X. Du, K. Allen, T. K. Kim, C. Lane, Ying Wai Li, Jian-Xin Zhu, J. D. Thompson, F. Ronning, S. M. Thomas, P. F. S. Rosa, E. D. Bauer

Statistical Mechanics

Coarse-graining nonequilibrium diffusions with Markov chains

Ramón Nartallo-Kaluarachchi, Renaud Lambiotte and Alain Goriely

We investigate nonequilibrium steady-state dynamics in both continuous- and discrete-state stochastic processes. Our analysis focuses on planar diffusion dynamics and their coarse-grained approximations by discrete-state Markov chains. Using finite-volume approximations, we derive an approximate master equation directly from the underlying diffusion and show that this discretisation preserves key features of the nonequilibrium steady-state. In particular, we show that the entropy production rate of the approximation converges as the number of discrete states goes to the limit. These results are illustrated with analytically solvable diffusions and numerical experiments on nonlinear processes, demonstrating how this approach can be used to explore the dependence of the entropy production rate on model parameters. Finally, we address the problem of inferring discrete-state Markov models from continuous stochastic trajectories. We show that discrete-state models significantly underestimate the true entropy production rate. However, we also show that they can provide tests to determine if a stationary planar diffusion is out of equilibrium. This property is illustrated with both simulated data and empirical trajectories from schooling fish.
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Superconductivity · Cross-listed from quant-ph

Mapping the positions of Two-Level-Systems on the surface of a superconducting transmon qubit

Jürgen Lisenfeld, Alexander K. Händel, Etienne Daum et al. (+3 more)

The coherence of superconducting quantum computers is severely limited by material defects that create parasitic two-level-systems (TLS). Progress is complicated by lacking understanding how TLS are created and in which parts of a qubit circuit they are most detrimental. Here, we present a method to determine the individual positions of TLS at the surface of a transmon qubit. We employ a set of on-chip gate electrodes near the qubit to generate local DC electric fields that are used to tune the TLS' resonance frequencies. The TLS position is inferred from the strengths at which TLS couple to different electrodes and comparing them to electric field simulations. We found that the majority of detectable surface-TLS was residing on the leads of the qubit's Josephson junction, despite the dominant contribution of its coplanar capacitor to electric field energy and surface area. This indicates that the TLS density is significantly enhanced near shadow-evaporated electrodes fabricated by lift-off techniques. Our method is useful to identify critical circuit regions where TLS contribute most to decoherence, and can guide improvements in qubit design and fabrication methods.
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All authors Jürgen Lisenfeld, Alexander K. Händel, Etienne Daum, Benedikt Berlitz, Alexander Bilmes, Alexey V. Ustinov