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Physics Condensed Matter

cond-mat Watch Condensed Matter

Wednesday 17 December

Superconductivity

Spin susceptibility in quasicrystal superconductor with spin-orbit interactions

Yasuhiro Tada

We study impacts of spin-orbit interactions on the spin susceptibility in quasicrystal superconductors, motivated by the anomolous superconducting properties in the van der Waals quasicrystal Ta$_{1.6}$Te under magnetic fields. We consider the Penrose tiling model with $s$-wave pairing as a representative system and include anisotropic spin-orbit interactions allowed for the quasicrystal structure. It is shown that the spin-momentum locking locally takes place in the quasicrystal, and electron motion and spin directions are tightly connected at each spatial position in the real space. As a result, the spin susceptibility is enhanced for both in-plane and out-of-plane magnetic fields in the presence of a Rashba-type spin-orbit interaction. For an Ising-type spin-orbit interaction, the spin susceptibility only for in-plane magnetic fields is increased, while the out-of-plane spin susceptibility is almost unchanged. When there are both kinds of the spin-orbit interactions, temperature dependence of the spin susceptibility for any field directions is suppressed.
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Strongly Correlated Electrons

Canted ferromagnetic order in a distorted triangular-lattice magnet Na$_2$SrCo(VO$_4$)$_2$

Tengfei Peng, Xiaobai Ma, Xinyang Liu et al. (+5 more)

Triangular-lattice cobaltates with glaserite-type $X_2Y$Co($T$O$_4)_2$ structure provide an ideal platform to investigate intriguing quantum magnetism. Here we report a comprehensive study of the structural and magnetic properties of a triangular-lattice cobalt vanadate $\rm Na_2SrCo(VO_4)_2$. Room-temperature x-ray and neutron powder diffraction confirm that $\rm Na_2SrCo(VO_4)_2$ crystallizes in the monoclinic $P2_1/c$ space group with slightly distorted triangular layers of $\rm Co^{2+}$ ions. Magnetization measurements reveal a ferromagnetic transition at $T\rm_C \approx 3.4~{\rm K}$, where a sharp $\lambda$-type anomaly is observed in the specific heat. The magnetic entropy recovered up to 55 K approaches 90$\%$ of $R{\rm ln}2$, supporting an effective spin-1/2 state of Co$^{2+}$ ions at low temperature. Neutron diffraction at 2.3 K (below $T_{\rm C}$) further confirms a long-range canted ferromagnetic order with the Co$^{2+}$ moments aligned in the $ac$ plane and the ordered moment size of $\sim$ 2.6 $\mu\rm_{B}$. Comparing with its sister compounds with a trigonal symmetry, $\rm Na_2BaCo(VO_4)_2$ with a collinear ferromagnetic structure and the recently discovered spin supersolid candidate $\rm Na_2BaCo(PO_4)_2$ with a distinct Y-like antiferromagnetic ground state, this study indicates the decisive role of the $T{\rm O_4}$ tetrahedra in tuning exchange interactions and contrasting magnetic behaviors of these glaserite-structure compounds.
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All authors Tengfei Peng, Xiaobai Ma, Xinyang Liu, Feiran Shen, Lunhua He, Junsen Xiang, Wenyun Yang, Wentao Jin

Mesoscale and Nanoscale Physics · Cross-listed from quant-ph

Graph-theoretical search for integrable multistate Landau-Zener models

Zixuan Li and Chen Sun

The search for exactly solvable models is an evergreen topic in theoretical physics. In the context of multistate Landau-Zener models – $N$-state quantum systems with linearly time-dependent Hamiltonians – the theory of integrability provides a framework for identifying new solvable cases. In particular, it was proved that the integrability of a specific class known as the multitime Landau-Zener (MTLZ) models guarantees their exact solvability. A key finding was that an $N$-state MTLZ model can be represented by data defined on an $N$-vertex graph. While known host graphs for MTLZ models include hypercubes, fans, and their Cartesian products, no other families have been discovered, leading to the conjecture that these are the only possibilities. In this work, we conduct a systematic graph-theoretical search for integrable models within the MTLZ class. By first identifying minimal structures that a graph must contain to host an MTLZ model, we formulate an efficient algorithm to systematically search for candidate graphs for MTLZ models. Implementing this algorithm using computational software, we enumerate all candidate graphs with up to $N = 13$ vertices and perform an in-depth analysis of those with $N \le 11$. Our results corroborate the aforementioned conjecture for graphs up to $11$ vertices. For even larger graphs, we propose a specific family, termed descendants of “$(0,2)$-graphs”, as promising candidates that may violate the conjecture above. Our work can serve as a guideline to identify new exactly solvable multistate Landau-Zener models in the future.
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Mesoscale and Nanoscale Physics

Fractional quantization by interaction of arbitrary strength in gapless flat bands with divergent quantum geometry

Wenqi Yang, Dawei Zhai and Wang Yao

Fractional quantum anomalous Hall (FQAH) effect, a lattice analogue of fractional quantum Hall effect, offers a unique pathway toward fault-tolerant quantum computation and deep insights into the interplay of topology and strong correlations. The exploration has been successfully guided by the paradigm of ideal flat Chern bands, which mimic Landau levels in both band topology and local quantum geometry. Yet, given the boundless potential for Bloch bands in lattice systems, it remains a significant open question whether FQAH states can arise in scenarios fundamentally distinct from this paradigm. Here we turn to a class of gapless flat bands, featuring (i) ill-defined band topology, (ii) non-quantized Berry flux, (iii) divergent quantum geometry at singular band touchings, (iv) highly fluctuating and far-from-ideal quantum geometry across the Brillouin zone (BZ). Our exact diagonalization and density matrix renormalization group calculations unambiguously demonstrate FQAH phase that is virtually independent of the interaction strength, persisting from the weak-interaction to the strong-interaction limit. We find the stability of the FQAH states does not uniquely correlate with the singularity strength or the BZ-averaged quantum geometric fluctuations. Instead, the many-body topological order can adapt to the singular and fluctuating quantum geometric landscape by spontaneously developing an inhomogeneous carrier distribution, while its quenching accompanies the drop in the occupation-weighted Berry flux. Our work reveals a profound interplay between local quantum geometry and many-body correlation, and significantly expands the exploration space for FQAH effect and correlated phenomena in general.
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Strongly Correlated Electrons

Pair-density-wave superconductivity and Anderson's theorem in bilayer nickelates

Hanbit Oh and Ya-Hui Zhang

The recent experimental observations of high temperature superconductivity in bilayer nickelate have attracted lots of attentions. Previous studies have assumed a mirror symmetry $\mathcal M$ between the two layers and focused on uniform and clean superconducting states. Here, we show that breaking this mirror symmetry via an applied displacement field can stabilize a pair-density-wave (PDW) superconductor, which is similar to the Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) state, but at zero magnetic field. Based on a mean-field analysis of a model of $d_{x^2-y^2}$ orbital with an effective inter-layer attraction, we demonstrate that the PDW phase is robust over a wide range of displacement field, interlayer hopping strengths, and electron fillings. Finally, we analyze disorder effects on interlayer superconductivity within the first Born approximation. Based on symmetry considerations, we show that pairing is weaken by disorders which break the mirror symmetry, even with unbroken time reversal symmetry. Our results establish bilayer nickelate as a tunable platform for realizing finite-momentum pairing and for exploring generalized disorder effects.
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Materials Science

X-ray detected ferromagnetic resonance spectrometer with an out-of-vacuum photodetector

Tetsuro Ueno, Yasuo Takeichi, Masaki Mizuguchi et al. (+10 more)

X-ray detected ferromagnetic resonance (XFMR) spectroscopy is an experimental technique for element-specific spin dynamics in the GHz regime and has been utilized to study spintronic materials. The XFMR signal is usually obtained by detecting X-ray excited optical luminescence (XEOL) emitted from a sample substrate. Here, we report the development of an XFMR spectrometer that is designed to place a photodetector for XEOL detection outside an ultra-high-vacuum chamber. This configuration allows for the easy replacement of detectors, such as photodiodes, CCD cameras, and spectrometers, depending on the experimental requirements. We demonstrated the measurement of XEOL spectra from MgO using a visible light spectrometer as well as the detection of XFMR signals originating from the spin precession of a permalloy (Ni80Fe20) thin film using a photodiode detector. The XFMR spectrometer with an out-of-vacuum photodetector expands possibilities for advanced measurements such as XFMR microscopy.
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All authors Tetsuro Ueno, Yasuo Takeichi, Masaki Mizuguchi, Hideaki Iwasawa, Yoshiyuki Ohtsubo, Kanta Ono, Hiroyuki Okazaki, Songtian Li, Seiji Sakai, Tetsuya Yamaki, Tetsu Watanuki, Yoshinori Katayama, Chiharu Mitsumata

Materials Science

Site-selective enhancement of Eu emission in delta-doped GaN

Amelia R. Klein, Hayley J. Austin, Fumikazu Murakami et al. (+7 more)

Europium-doped gallium nitride (GaN:Eu) is a promising platform for classical and quantum optoelectronic applications. When grown using organometallic vapor-phase epitaxy, the dominant red emission from Eu exhibits an inhomogeneous photoluminescence (PL) spectrum due to contributions from several non-equivalent incorporation sites that can be distinguished with combined excitation emission spectroscopy. Energy transfer from the GaN bandgap to the majority site is inefficient, limiting the performance of GaN:Eu LEDs and resulting in an inhomogeneous emission spectrum dominated by disproportionate contributions from minority sites. In this work, we use site-selective spectroscopy to characterize the photoluminescence properties of delta-doped structures with alternating doped and undoped layers of varying thicknesses and demonstrate that they selectively enhance emission from the majority site when compared to uniformly-doped samples. Samples with 2-nm and 10-nm doped layers show much greater PL intensity per Eu concentration as well as more efficient energy transfer to the majority site, which are both highly desirable for creating power-efficient LEDs. Meanwhile, a sample with 1-nm doped layers shows emission only from the majority site, resulting in a narrow, homogeneous emission spectrum that is desirable for quantum technologies. This utilization of delta-doping has the potential to be broadly applicable for engineering desirable defect properties in rare-earth doped semiconductors.
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All authors Amelia R. Klein, Hayley J. Austin, Fumikazu Murakami, Jamie Ford, Jun Tatebayashi, Masayoshi Tonouchi, Yasufumi Fujiwara, Volkmar Dierolf, Lee C. Bassett, Brandon Mitchell

Materials Science

Dependence of Radiation Induced Segregation of Cr on Sink Dimensionality and Morphology in Fe-Cr Alloys

Mohammadhossein Nahavandian, Anter El-Azab and Enrique Martinez

Radiation-induced segregation (RIS) and chemical redistribution in structural alloys can significantly degrade material performance, ultimately leading to failure. In this study, building on previous work by the authors [1], we investigate how the dimensional characteristics of sinks influence solute concentration distributions and segregation behavior. Specifically, we utilize a kinetic Monte Carlo (KMC) model to simulate atomic-scale diffusion and analyze segregation processes in an Fe-3Cr alloy. Our analysis includes three representative sink geometries: one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) planar sinks to capture the effects of sink dimensionality on Cr segregation at grain boundaries (GBs). We also found solutions of concentration and segregation profiles in these cases as well as for a 3D spherical sink. KMC simulations are performed over a range of temperatures to assess thermal effects on Cr redistribution. The results reveal distinct segregation profiles and concentration gradients, although the dependence with sink density seems to remain linear in all cases with planar sinks. The analytical results show that this is not the case in spherical domains, with a more complex dependence of segregation on sink density. Our finite difference solutions for domains including 2D and 3D planer sinks show agreement with corresponding KMC results.
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Materials Science

Efficient Nudged Elastic Band Method using Neural Network Bayesian Algorithm Execution

Pranav Kakhandiki, Sathya Chitturi, Daniel Ratner et al. (+1 more)

The discovery of a minimum energy pathway (MEP) between metastable states is crucial for scientific tasks including catalyst and biomolecular design. However, the standard nudged elastic band (NEB) algorithm requires hundreds to tens of thousands of compute-intensive simulations, making applications to complex systems prohibitively expensive. We introduce Neural Network Bayesian Algorithm Execution (NN-BAX), a framework that jointly learns the energy landscape and the MEP. NN-BAX sequentially fine-tunes a foundation model by actively selecting samples targeted at improving the MEP. Tested on Lennard-Jones and Embedded Atom Method systems, our approach achieves a one to two order of magnitude reduction in energy and force evaluations with negligible loss in MEP accuracy and demonstrates scalability to >100-dimensional systems. This work is therefore a promising step towards removing the computational barrier for MEP discovery in scientifically relevant systems, suggesting that weeks-long calculations may be achieved in hours or days with minimal loss in accuracy.
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All authors Pranav Kakhandiki, Sathya Chitturi, Daniel Ratner, Sean Gasiorowski

Tuesday 16 December

Other Condensed Matter

On the comparison of models and experiments in the study of DNA open states: the problem of degrees of freedom

Alexey S. Shigaev and Victor D. Lakhno

Simple mechanical models of DNA play an important role in studying the dynamics of its open states. The main requirement when developing a DNA model is the correct selection of its effective potentials and parameters based on experimental data. At the same time, various experiments allow us to "see" different types of DNA open states. Consideration of this feature is one of the most important conditions in the development, optimization, and parameterization of any mechanical model. Violation of this condition, i.e., the comparison of incomparable characteristics, leads to critical errors. The present investigation is devoted to the problem of degrees of freedom of DNA bases taken into account in mechanical models. Using the Peyrard-Bishop-Dauxois model as an example, two types of errors in interpreting experimental data when compared with the model are examined. The first one is a mismatch between the open state types in the model and experiment. The second one is an incorrect specification of the "threshold coordinate" of the open state. The concept of the effective total threshold coordinate of the radial separation of DNA strands for registration of opening is introduced. It is shown that correct interpretation of experimental data can actually eliminate discrepancies with theory.
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Soft Condensed Matter

Composition-agnostic prediction of self-assembly in multicomponent amphiphile mixtures from molecular structure

Yuuki Ishiwatari, Takahiro Yokoyama, Tomoya Kojima et al. (+2 more)

Predicting self-assembly in multi-component amphiphilic systems is challenging due to the complexity of intercomponent interactions and the combinatorial growth of possible formulations. In this study, we develop a unified machine-learning framework that directly predicts self-assembly behavior from the molecular structures of constituent components, independent of the number or identity of those components. We extend the critical packing parameter (CPP) to multi-component systems and generate a large dataset of self-assembled morphologies using dissipative particle dynamics (DPD) simulations. By systematically evaluating twelve combinations of feature extraction methods and model architectures, we find that models incorporating a fully connected graph convolutional network (GCN) layer achieve superior performance, with the GCN-GCN architecture accurately capturing both intramolecular relationships and intercomponent interactions. Notably, this model exhibits strong extrapolative capability: it accurately predicts CPP values for five-component mixtures even when trained only on systems with fewer components, and it maintains high accuracy for mixtures composed of molecular species that are entirely absent from the training data. These results demonstrate that a composition-agnostic predictive framework can enable efficient virtual screening and provide a foundation for the rational design of complex amphiphilic materials.
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All authors Yuuki Ishiwatari, Takahiro Yokoyama, Tomoya Kojima, Taisuke Banno, Noriyoshi Arai

Mesoscale and Nanoscale Physics

Topological-Insulator and Spintronic Boundary Electrodynamics for MRI RF Coils: A Theoretical Framework for Loss, Noise, and Reciprocity

Zoran Milosavljevic

MRI radiofrequency (RF) coils are ultimately limited by conductor loss, thermal noise, and reciprocity constraints associated with conventional metallic boundary conditions. These limitations become more severe at higher static fields, where operating frequencies increase and current distributions are governed by surface impedance and electromagnetic coupling in the near field. In this work we develop a theoretical framework that incorporates topological-insulator (TI) surface transport and spintronic interface physics into RF coil electrodynamics. Starting from the Dirac surface Hamiltonian and linear-response (Kubo/Drude) transport, we derive an effective complex surface impedance for TI-coated conductors and establish modified boundary conditions for tangential fields in the presence of spin–momentum locking and spin–charge coupling. We then analyze time-reversal-symmetry-breaking TI/ferromagnet interfaces, where an anomalous Hall surface conductivity produces antisymmetric admittance and enables nonreciprocal RF response. Finally, we connect these results to MRI metrics including coil quality factor, thermal noise, and receive sensitivity through reciprocity-based formulations. The framework identifies parameter regimes in which topological and spintronic surface transport could reduce RF dissipation, modify noise mechanisms, and enable coil-level nonreciprocity without conventional ferrites.
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Superconductivity

Machine Learning-Guided Discovery of Kagome Superconductors YRu3B2 and LuRu3B2

Rose Albu Mustaf, Sajilesh K. P., Sanu Mishra et al. (+9 more)

We report the experimental discovery of bulk superconductivity in two kagome lattice compounds, YRu$_3$B$_2$ and LuRu$_3$B$_2$, which were predicted through machine learning-accelerated high-throughput screening combined with first principles calculations. These materials crystallize in the hexagonal CeCo$_3$B$_2$-type structure with planar kagome networks formed by Ru atoms. We observe superconducting critical temperatures of $T_{c} = 0.81$~K for YRu$_3$B$_2$ and $T_{c} = 0.95$~K for LuRu$_3$B$_2$, confirmed through magnetization and specific heat measurements. Both compounds exhibit nearly 100% superconducting volume fractions, demonstrating bulk superconductivity. Compared with LaRu$_3$Si$_2$, YRu$_3$B$_2$ and LuRu$_3$B$_2$ show a more dispersive Ru local $d_{x^2-y^2}$ quasi-flat band (and thus a reduced DOS at $E_F$) together with an overall hardening of the phonon spectrum, both of which lower the electron-phonon coupling (EPC) constant $\lambda$. Meanwhile, the dominant real-space EPC between Ru local $d_{x^2-y^2}$ states and the low-frequency Ru in-plane local $x$ branch remains nearly unchanged, indicating that the reduction of $\lambda$ originates from the $d_{x^2-y^2}$ DOS reduction and the overall phonon hardening. Superfluid weight calculations show that conventional contributions dominate over quantum geometric effects due to the dispersive nature of bands near the Fermi level. This work demonstrates the effectiveness of integrating machine learning screening, first principles theory, and experimental synthesis for accelerating the discovery of new superconducting materials.
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All authors Rose Albu Mustaf, Sajilesh K. P., Sanu Mishra, Junze Deng, Yi Jiang, Kaja H. Hiorth, Eeli O. Lamponen, Martin Gutierrez-Amigo, Päivi Törmä, Miguel A.L. Marques, B. Andrei Bernevig, Emilia Morosan

Quantum Gases

Localization from Infinitesimal Kinetic Grading: Finite-size Scaling, Kibble-Zurek Dynamics and Applications in Sensing

Argha Debnath, Ayan Sahoo and Debraj Rakshit

We study a one-dimensional lattice model with site-dependent nearest-neighbor hopping amplitudes that follow a power-law profile. The hopping variation is controlled by a grading exponent, $|alpha|$, which serves as the tuning parameter of the system. In the thermodynamic limit, the ground state becomes localized in the limit $|alpha| \to 0$, signaling the presence of a critical point characterized by a diverging localization length. Using exact diagonalization methods, we perform finite-size scaling analysis, and extract the associated critical exponent governing the near-critical behavior. To further characterize the criticality, we analyze inverse participation ratio (IPR), energy gap between the ground and first excited state, and fidelity-susceptibility. We also investigate the nonequilibrium dynamics by linearly ramping the hopping profile at various rates and tracking the evolution of the localization length and the IPR. The Kibble-Zurek mechanism successfully explains the resulting dynamics of the system via the critical exponents obtained from static scaling analysis. Beyond its fundamental significance, the kinetic-grading-induced localization transition provides a natural platform for quantum sensing. Using the critical enhancement of the quantum Fisher information (QFI), we demonstrate that the system enables quantum-enhanced parameter estimation of the grading exponent. We propose both adiabatic and dynamical quantum critical sensors and demonstrate that they exhibit enhanced scaling of the QFI. Our results therefore establish graded kinetic systems not only as a new setting for localization physics, but also as a potential resource for designing quantum-enhanced sensing devices.
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Materials Science

A High-Flux and High-Efficiency Setup for Magneto-Infrared Spectroscopy

Zeping Shi, Wenbin Wu, Zhiwei Zhang et al. (+14 more)

We report the design and implementation of a high-flux, high-efficiency magneto-infrared spectroscopy system optimized for broadband measurements in high magnetic fields. The setup integrates a Fourier transform infrared spectrometer, a 12 T cryogen-free superconducting magnet, precision-polished and gold-plated light tubes, custom-designed reflective focusing modules for Faraday and Voigt geometries, and an external multi-detector chamber with motorized selection. Optical throughput is maximized by reducing light tube loss from 65.5%/m to 22.0%/m via abrasive flow and mechanical polishing followed by gold electroplating, and by adopting a single-on-axis parabolic-mirror Faraday module that increases the effective numerical aperture from 0.14 to 0.36, enhancing collection efficiency by nearly an order of magnitude. An eight-position motorized sample stage and fully automated control over magnetic field, temperature, optical path, and detector choice enable high-throughput measurements without repeated warm-ups. The optimized configuration achieves a root-mean-square noise level of 0.0061% in a 2-minute integration for a 40% reflectivity sample, corresponding to a signal-to-noise ratio exceeding 16000. System capabilities are demonstrated by resolving weak replica bands in EuCd2As2 and faint Landau level transitions in LaAlSi.
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All authors Zeping Shi, Wenbin Wu, Zhiwei Zhang, Yuhan Du, Chenyao Xu, Guangyi Wang, Mingsen Zhou, Congming Hao, Xianghao Meng, Xiangyu Jiang, Chunhui Pan, Wei Lu, Hao Shen, Haifeng Pan, Zhenrong Sun, Junhao Chu, Xiang Yuan

Materials Science · Cross-listed from quant-ph

Roadmap: 2D Materials for Quantum Technologies

Qimin Yan, Tongcang Li, Xingyu Gao et al. (+29 more)

Two-dimensional (2D) materials have emerged as a versatile and powerful platform for quantum technologies, offering atomic-scale control, strong quantum confinement, and seamless integration into heterogeneous device architectures. Their reduced dimensionality enables unique quantum phenomena, including optically addressable spin defects, tunable single-photon emitters, low-dimensional magnetism, gate-controlled superconductivity, and correlated states in Moiré superlattices. This Roadmap provides a comprehensive overview of recent progress and future directions in exploiting 2D materials for quantum sensing, computation, communication, and simulation. We survey advances spanning spin defects and quantum sensing, quantum emitters and nonlinear photonics, computational theory and data-driven discovery of quantum defects, spintronic and magnonic devices, cavity-engineered quantum materials, superconducting and hybrid quantum circuits, quantum dots, Moiré quantum simulators, and quantum communication platforms. Across these themes, we identify common challenges in defect control, coherence preservation, interfacial engineering, and scalable integration, alongside emerging opportunities driven by machine$-$learning$-$assisted design and integrated experiment$-$theory feedback loops. By connecting microscopic quantum states to mesoscopic excitations and macroscopic device architectures, this Roadmap outlines a materials-centric framework for integrating coherent quantum functionalities and positions 2D materials as foundational building blocks for next-generation quantum technologies.
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All authors Qimin Yan, Tongcang Li, Xingyu Gao, Sumukh Vaidya, Saakshi Dikshit, Yue Luo, Stefan Strauf, Reda Moukaouine, Anton Pershin, Adam Gali, Zhenyao Fang, Harvey Stanfield, Ivan J. Vera-Marun, Michael Newburger, Simranjeet Singh, Tiancong Zhu, Mauro Brotons-Gisbert, Klaus D. Jöns, Brian D. Gerardot, Brian S. Y. Kim, John R. Schaibley, Kyle L. Seyler, Jesse Balgley, James Hone, Kin Chung Fong, Lin Wang, Guido Burkard, Yihang Zeng, Tobias Heindel, Serkan Ateş, Tobias Vogl, Igor Aharonovich

Materials Science

Quadrene: A Novel Quasi-2D Carbon Allotrope with High Carrier Mobility

Kleuton A. L. Lima, José A. dos S. Laranjeira, Neymar J. N. Cavalcante et al. (+4 more)

We present a comprehensive first-principles investigation of a novel carbon allotrope characterized by quasi-tetragonal atomic motifs and quasi-two-dimensional structural behavior. Structural analysis reveals an open framework composed of alternating diamond-like and square units, while thermodynamic assessments indicate a negative formation energy, suggesting high intrinsic stability. Phonon spectra confirm dynamical robustness, and ab initio molecular dynamics simulations at 1000~K validate its thermal resilience. Furthermore, the system exhibits an indirect bandgap of 1.58 eV at the HSE06 level, anisotropic mechanical behavior, and a broadband optical response, reinforcing its potential for nanoelectronic and optoelectronic applications. The highly anisotropic mechanical behavior is characterized by an in-plane Young's modulus ranging from 80 to 550 GPa, depending on crystallographic direction. Additionally, the electronic transport properties exhibit pronounced anisotropy, with hole mobilities reaching up to 5.83 x 10^6 cm^2/V . s and electron mobilities up to 6.40 x 10^6 cm^2/V . s along different crystallographic directions, highlighting the material's potential for directionally selective nanoelectronic device applications.
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All authors Kleuton A. L. Lima, José A. dos S. Laranjeira, Neymar J. N. Cavalcante, Nicolas F. Martins, Julio R. Sambrano, Douglas S. Galvão, Luiz A. Ribeiro Jr

Superconductivity

High efficiency superconducting diode effect in a gate-tunable double-loop SQUID

Wyatt Gibbons, Teng Zhang, Kevin Barrow et al. (+3 more)

In superconducting quantum interference devices (SQUIDs), the superconducting diode effect may be generated by interference of multiple harmonic components in the current-phase relationships (CPRs) of different branches forming SQUID loops. Through the inclusion of two gate-tunable Josephson junctions in series in each interference branch of a double-loop SQUID, we demonstrate independent control over both the harmonic content and the amplitude of three interfering CPRs, facilitating significant improvement in the maximum diode efficiency. Through optimized gate-controlled tuning of individual Josephson energies, diode efficiency exceeding 50% is demonstrated. Flux-dependent oscillations show quantitative agreement with a simple model of SQUID operation.
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All authors Wyatt Gibbons, Teng Zhang, Kevin Barrow, Tyler Lindemann, Jukka I. Väyrynen, Michael J. Manfra

Strongly Correlated Electrons

Applicability of the cumulant expansion method for the calculation of transport properties in electron-phonon systems

Petar Mitrić, Veljko Janković, Darko Tanasković et al. (+1 more)

We assess the accuracy of the cumulant expansion (CE) method, combined with the independent-particle approximation (IPA), for calculating charge mobility in electron-phonon systems. As representative testbeds, we consider the Peierls and Fröhlich models, which serve as simplified frameworks where accurate or numerically exact benchmarks are available. These are used to compare the CE results with those obtained using the Boltzmann formalism, the Migdal approximation, and its self consistent extension-approaches that are presently the most commonly employed alternatives for transport calculations. Supported by analytical arguments based on spectral sum rules and by our previous results for the Holstein model, we argue that, for weak to moderate coupling strengths and not-too-low temperatures, the CE within the IPA framework yields accurate results. In the case of the Peierls model, the role of vertex corrections is also discussed.
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All authors Petar Mitrić, Veljko Janković, Darko Tanasković, Nenad Vukmirović

Soft Condensed Matter

Memory-Induced Transport and Arrest in Flashing Ratchets: From Superdiffusion to Clustering

Karina I. Mazzitello, Daniel G. Zarlenga and Constancio M. Arizmendi

We investigate the transport properties of particles driven by colored noise in a flashing ratchet potential, focusing on both non-interacting and single-file interacting regimes. The model incorporates memory effects via a non-Markovian friction kernel, leading to superdiffusive dynamics and enhanced currents in the absence of interactions. However, when particles are constrained to single-file motion with hard-core repulsion, the same non-Markovian noise induces a dynamical transition: initial superdiffusion gives way to the formation of static clusters, ultimately suppressing net current. This transition occurs without a critical density and results from the interplay between noise persistence and the ratchet's potential. Our numerical results reveal a universal scaling behavior for the mean square displacement across densities, suggesting robustness of the clustering mechanism. These findings have potential implications for transport in crowded or confined systems such as colloidal suspensions, molecular motors in cellular environments, or microfluidic devices, where controlling noise and crowding can be used to tune transport efficiency.
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Statistical Mechanics

Large-$n$ $O(n)$ with long-range interactions: integrability and resonance dynamics

Guido Giachetti and Nicolo Defenu

We study the large-$n$ dynamics of the long-range quantum $O(n)$ model, focusing on the strong long-range regime $\alpha<d$. The dynamics of the model exhibits non-trivial features on mesoscopic timescales $t\sim\ln N$, due to the activation of parametric resonances of the nearly degenerate quantum modes. By using recent results establishing the integrability of the large-$n$ limit, we derive the exact resonance conditions and the associated phase diagram, construct the reduced Hamiltonian governing the nonlinear evolution of the resonant sector, and determine the quasiperiodic spectrum of the resulting mesoscopic dynamics. This framework offers a quantitative understanding on how quantum deviation can drive the system away from the mean-field limit. In particular, the presence of multiple resonant modes enhances the logarithmic growth of entanglement and leads to spatially modulated correlations.
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Mesoscale and Nanoscale Physics

Link of the Zitterbewegung with the spin conductivity and the spin-textures of multiband systems

F. Mireles and E. Ortiz

The Zitterbewegung phenomenon in multiband electronic systems is known to be subtly related to the charge conductivity, Berry curvature and the Chern number. Here we show that some spin-dependent properties as the optical spin conductivity, and intrinsic spin Hall conductivity are also entangled with the Zitterbewegung amplitudes. We also show that in multiband Dirac-type Hamiltonians, a direct link between the Zitterbewegung and the spin textures and spin transition amplitudes can be established. The later allow us to discern the presence or not of the Zitterbewegung oscillations by simply analyzing the spin or pseudo-spin textures. We provide examples of the applicability of our approach for Hamiltonian models that show the suppression of specific Zitterbewegung oscillations.
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Materials Science

Kagome Topology in Two-Dimensional Noble-Metal Monolayers

Carlos M. O. Bastos, Emanuel J. A. dos Santos, José A. dos S. Laranjeira et al. (+4 more)

Two-dimensional (2D) metallic lattices with kagome topology provide a unique platform for exploring the interplay between geometric frustration, reduced coordination, and lattice stability in elemental systems. Motivated by the recent experimental realization of atomically thin gold layers and kagome goldene, we present a first-principles investigation of free-standing kagome monolayers of Cu, Ag, and Au. Using density functional theory combined with lattice dynamics and ab initio molecular dynamics, we systematically assess their structural, mechanical, dynamical, and thermal stability. All kagome monolayers satisfy the 2D Born criteria and exhibit relatively low in-plane stiffness compared to graphene and hexagonal goldene, reflecting the porous nature of the kagome lattice and its metallic bonding. Among the three systems, the Au-based lattice displays the highest in-plane Young's modulus. Phonon calculations reveal that the unstrained kagome phase is dynamically unstable for all metals. However, a moderate biaxial tensile strain of 5% stabilizes the Ag and Au monolayers, while Cu retains residual unstable modes. Finite-temperature simulations further show that Cu rapidly reconstructs toward a trigonal lattice, Ag remains metastable at low temperature but collapses at room temperature, and Au exhibits competing kagome and trigonal motifs at 300 K, indicating near-degeneracy between these phases. These results establish that strain engineering and atomic size are key determinants of the stability of metallic kagome monolayers and provide guidance for future substrate-supported realizations.
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All authors Carlos M. O. Bastos, Emanuel J. A. dos Santos, José A. dos S. Laranjeira, Kleuton A. L. Lima, Alexandre C. Dias, Douglas S. Galvão, Luiz A. Ribeiro Jr

Strongly Correlated Electrons

Hearing the light: stray-field noise from the emergent photon in quantum spin ice

Gautam K. Naik, Jonathan N. Hallén, Nishan C. Jayarama et al. (+2 more)

Decisive experimental confirmation of the $U(1)$ quantum spin liquid phase in quantum spin ice remains an outstanding challenge. In this work, we propose stray-field magnetometry as a direct probe of the emergent photons – the gapless excitation of the emergent electrodynamics in quantum spin ice. The emergent photons are transverse magnetization waves, which, in a finite sample, form discrete modes governed by one of two sets of natural boundary conditions: “insulating” or “superconducting”. Considering cavity and thin film geometries, we find that the spectrum and spatial structure of the stray magnetic noise provide a sharp qualitative signature of the underlying electrodynamics. The predicted stray-field noise power lies comfortably within the detection range of present-day solid-state defect magnetometry.
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All authors Gautam K. Naik, Jonathan N. Hallén, Nishan C. Jayarama, Roderich Moessner, Chris R. Laumann

Statistical Mechanics · Cross-listed from quant-ph

Noise-Induced Thermalization in Quantum Systems

Sameer Dambal, Yu Zhang, Eric R Bittner et al. (+1 more)

In the current Noisy Intermediate-Scale Quantum era, noise is widely regarded as the primary obstacle to achieving fault-tolerant quantum computation. However, certain stages of the quantum computing pipeline can, in fact, benefit from this noise. In this work, we exploit the Eigenstate Thermalization Hypothesis to show that noise generically accelerates a fundamental task in quantum computing – the preparation of Gibbs states. We demonstrate this behavior using classical and quantum simulations with Haar-random and phase-flip noise, respectively, on a spin-1/2 chain with a local Hamiltonian. Our non-integrable model sees ~3.5x faster thermalization in the presence of noise, while our integrable model, which would not otherwise thermalize, reaches a thermal state due to noise. Since certifying a local Gibbs state is relatively easy on a quantum computer, our approach provides a new practical solution to a key problem in quantum computing. More broadly, these results establish a new paradigm in which noise can be harnessed on quantum computers, enabling practical advantages before the years of fault-tolerance.
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All authors Sameer Dambal, Yu Zhang, Eric R Bittner, Pavan Hosur

Strongly Correlated Electrons · Cross-listed from hep-lat

Sign-problem landscape of dimer, loop, and ground state sectors of a U(1) quantum link model

Pallabi Dey, Debasish Banerjee and Emilie Huffman

The fermion sign problem poses a formidable challenge to the use of Monte Carlo methods for lattice gauge theories with dynamical fermionic matter fields. A meron cluster algorithm recently formulated for gauge fields represented as spin-$\frac{1}{2}$ quantum links coupled to a single flavour of staggered fermions samples only two of the exponentially many Gauss law (GL) sectors at low temperatures, allowing the simulation of those two GL sectors at zero temperature in polynomial time. In this article, we analytically identify GL sectors which can be simulated without encountering the fermion sign problem in arbitrary spatial dimensions. Using large-scale exact diagonalization and cluster Monte Carlo methods, we explore the nature of phases in the GL sectors dominating at zero temperature. The ground state lives in a superselection sector free of the sign problem, and maps to the quantum dimer model with mobile monomers. The usual zero-charge GL sector suffers from the fermion sign problem, and maps to the fully packed loop model with mobile monomers. The role of the magnetic energy in causing transitions between GL sectors is outlined. We expect our results to be valid for truncated Kogut-Susskind gauge theories, beyond quantum link models.
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Statistical Mechanics · Cross-listed from quant-ph

Strong-to-weak symmetry breaking in monitored dipole conserving quantum circuits

Caterina Zerba, Sarang Gopalakrishnan and Michael Knap

We explore the information-theoretic phases of monitored quantum circuits subject to dynamics that conserves both charge and dipole moment, as well as measurements of the local charge density. Explicitly, both charge and dipole-moment conservation are strong symmetries, but under the dynamics they can be spontaneously broken to weak symmetries: this spontaneous symmetry breaking has an information-theoretic interpretation in terms of whether one can learn global charges from local measurements. We find a rich phase diagram: in one spatial dimension, charge is always easy to learn, while dipole moment can be either easy or hard. In two dimensions, we find three phases: for frequent measurements, both charge and dipole moment are easy to learn; as the measurement rate is decreased, first dipole moment and then charge become hard. In two dimensions, the low-measurement phase is an exotic critical phase with anisotropic spacetime scaling, analogous to a smectic liquid crystal.
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Statistical Mechanics · Cross-listed from quant-ph

Growth and spreading of quantum resources under random circuit dynamics

Sreemayee Aditya, Xhek Turkeshi and Piotr Sierant

Quantum many-body dynamics generate nonclassical correlations naturally described by quantum resource theories. Quantum magic resources (or nonstabilizerness) capture deviation from classically simulable stabilizer states, while coherence and fermionic non-Gaussianity measure departure from the computational basis and from fermionic Gaussian states, respectively. We track these resources in a subsystem of a one-dimensional qubit chain evolved by random brickwall circuits. For resource-generating gates, evolution from low-resource states exhibits a universal rise-peak-fall behavior, with the peak time scaling logarithmically with subsystem size and the resource eventually decaying as the subsystem approaches a maximally mixed state. Circuits whose gates do not create the resource but entangle neighboring qubits, give rise to a ballistic spreading of quantum resource initially confined to a region of the initial state. Our results give a unified picture of spatiotemporal resource dynamics in local circuits and a baseline for more structured quantum many-body systems.
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Materials Science

A computational study of thermoelectric conversion in the PbSe$_{x}$Te$_{1-x}$ semiconductor alloys

M. Kaid Slimane, B. N. Brahmi, M. Bouchenaki et al. (+1 more)

The present theoretical study focuses on the structural, electronic and thermoelectric properties of PbTe, PbSe and their ternary alloys PbSe$_{x}$Te$_{1-x}$, using the density functional theory (DFT) by the full potential linearised augmented plane wave (FP-LAPW) method implemented in Wien2k code. Structural properties were performed by using the generalized gradient approximation of Perdew Burke and Ernzenhof (GGA-PBE) scheme. The results show that the calculated lattice parameters are in good agreement with theoretical data previously obtained. For electronic properties, we noticed that for all the compounds of PbSe$_{x}$Te$_{1-x}$, we have a direct band gap in L point. For thermoelectric properties, we used BoltzTraP2 code and Gibbs2 code. Our results show that the PbSe$_{x}$Te$_{1-x}$ compounds have reached a value of 2.55 for the figure of merit, which indicates that our material is a good thermoelectric candidate.
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All authors M. Kaid Slimane, B. N. Brahmi, M. Bouchenaki, S. Bekhechi

Materials Science

Investigation of density of states and charge carrier mobility in amorphous semiconductors via time-of-flight photocurrent analysis

F. Serdouk, A. Boumali, M. L. Benkhedir et al. (+1 more)

The present study examines the electronic transport characteristics of amorphous semiconductors through TOF measurements and numerical simulations. The primary objective is to determine the DOS in amorphous selenium (a-Se) and to assess the temperature and electric field dependence of the hole mobility. A comprehensive investigation of localized states within the mobility gap is performed using Laplace transform analysis of ToF photocurrent transients, combined with the multiple trapping model. This approach enables accurate reconstruction of the DOS across a wide temperature range, allowing clear identification of shallow and deep trap levels and revealing thermally activated transport mechanisms. Simulated ToF currents are also used to evaluate the hole drift mobility under various thermal and field conditions. Activation energies are extracted from Arrhenius plots of the mobility data. The results support a physically consistent description of the electronic structure in a-Se and validate the applicability of Laplace-based techniques for probing charge transport in disordered semiconductors.
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All authors F. Serdouk, A. Boumali, M. L. Benkhedir, Y. Goutal