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Physics Condensed Matter

cond-mat Watch Condensed Matter

Friday 5 December

Statistical Mechanics

Dynamic hysteresis and transitions controlled by asymmetry in potential: energetic and entropic aspects

Samudro Ghosh and Moupriya Das

We aim to investigate the precise role of the asymmetry in the underlying potential on the process of dynamic hysteresis. So far, the theoretical modeling of this phenomenon of fundamental importance has been done considering symmetric bistable systems. The influence of asymmetry in the bistable potential has been explored in related contexts, such as first passage time estimates, escape dynamics, stochastic resonance, etc., highlighting the importance of the aspect of asymmetry in the systems. However, the perspective of developing a thorough theoretical understanding in this context remained overlooked in the case of dynamic hysteresis. Here, we scrutinize how the asymmetry in the potential influences this process, considering the physical model of a Brownian particle in a double-well potential subject to a periodic forcing. We analyze in detail the effect of two distinct types of asymmetry in the intrinsic potential, one corresponding to the different depths and the other subject to the separate widths of the two wells of the double-well potential representing the bistable system. Our study reveals that the hysteretic effect predominantly decreases with increasing asymmetry in both types of the system, reflected in the reduced hysteresis loop area. This observation suggests that the introduction of the appropriate asymmetry in the potential can quantitatively regulate the outputs of the dynamic hysteresis. This modulation can be beneficial for controlling devices' outputs in which dynamic hysteresis plays a role. Moreover, importantly, the implemented asymmetries in the potential can induce symmetry breaking in the response of the systems. This gives rise to asymmetric dynamic hysteresis loops, signifying the dynamic transition to an asymmetric phase, in moderate conditions, which is absent in the symmetric systems in the same scenarios.
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Mesoscale and Nanoscale Physics · Cross-listed from quant-ph

Mechanically mediated optical-microwave quantum state transfer by feedback

Max P. Foreman, Jesse J. Slim and Warwick P. Bowen

State transfer between light and microwaves is a key challenge in quantum networks. Promising transducers use a mechanical intermediary that couples to both fields via radiation pressure. Such electro-optomechanical devices have achieved high efficiencies, yet require resolved-sideband cavities, and generally compromise in scalability and noise performance. Here, we relax this constraint by extending the protocol of Navarathna et al. that transfers optical quantum information onto a mechanical resonator using a broadband, sideband-unresolved cavity and feedback. Combining this with parametric mechanical-to-microwave conversion, we show that continuous optical-to-microwave quantum state transfer is possible using measurement-based feedback, while all-optical coherent feedback enables bidirectional transfer. To assess the transfer, we introduce the quantum transfer witness $\mathcal{W}_T$, which – though similar to the input-referred added noise – also identifies whether a channel is capable of both preserving Gaussian entanglement and outperforming classical transduction schemes. Finally, we show that quantum-compatible noise performance is within reach of current experimental capabilities. Our results unlock a new design space for electro-optomechanical transducers and strengthens their candidacy as scalable quantum links between distant nodes.
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Materials Science

Compressional rate-dependent stability of ammonia hydrates crystallized from water-rich ammonia-water solutions

Anshuman Mondal, Katharina Mohrbach, Konstantin Glazyrin et al. (+2 more)

Understanding the crystallization pathways of water-rich ammonia-water (NH3-H2O) solutions and the stability of ammonia hydrates is key to unraveling the behavior of complex hydrogen-bonding networks as well as for planetary interior modelling. Yet, there are still inconsistencies in the crystallization sequence reported upon pressure-induced crystallization of H2O-rich NH3-H2O solutions at room temperature. Here, we investigate the effect of compression rates on the crystallization pathways of 25 wt% NH3 aqueous solutions at room temperature using dynamically compressed diamond anvil cells (dDAC) coupled with time-resolved X-ray diffraction. We show that compression rates exceeding 0.5 GPa/sec promote direct crystallization of a body-centered cubic (bcc) phase (DMA') with possible AMH stoichiometry coexisting with H2O ice VII, while rates below 0.2 GPa/sec stabilize monoclinic NH3-rich AHH-II and ice VII phases. Intermediate rates between 0.2-0.5 GPa/sec produce a mixture of both hydrates alongside ice VII, hence demonstrating the role of compression rate on the crystallization sequence of ammonia solutions. The compression behavior and phase stability of the distinct phase assemblies (AHH-II/DMA' + ice VII) are investigated further to place constraints on the composition of the DMA' phase, the effect of ice VII on the compressibility of ammonia hydrates, and the plausible incorporation of NH3 impurities within the lattice of high-pressure ice phases.
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All authors Anshuman Mondal, Katharina Mohrbach, Konstantin Glazyrin, Hanns-Peter Liermann, Carmen Sanchez-Valle

Mesoscale and Nanoscale Physics · Cross-listed from physics.chem-ph

Spin Polarization from Circularly Polarized Light Induced Charge Transfer

Sindhana Pannir-Sivajothi and David T. Limmer

We show how a spin polarization can be generated through the photo-induced electron transfer of an achiral donor-acceptor complex following chiral light excitation. In particular, we illustrate the basic energetic and symmetry requirements for chirality induced spin selectivity where the chirality emerges from the electronic degrees of freedom following excitation with circularly polarized light. We study this effect in a simple model of a metalloporphyrin complex with an axial acceptor ligand using quantum mechanical rate theories and numerical simulations. We find that the spin polarization emerges due to the selective excitation of a ring current within the porphryin, breaking the degeneracy of the two degenerate spin states. The resultant spin polarization increases with the spin orbit coupling between the metal in the porphyrin and the axial ligand, and is transient, with a lifetime dependent on the rate of dephasing from the Jahn-Teller distortion mode. This proposed effect should be observable in spin-resolved photoemission spectroscopy.
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Statistical Mechanics · Cross-listed from quant-ph

Concentrated Monte Carlo sampling for local observables in quantum spin chains

Wenxuan Zhang, Dingzu Wang and Dario Poletti

Monte Carlo methods are widely used to estimate observables in many-body quantum systems. However, conventional sampling schemes often require a large number of samples to achieve sufficient accuracy. In this work we propose the concentrated Monte Carlo sampling approach, which builds on the idea that in systems with only short range correlations, to obtain accurate expectation values for local observables, one would favor detailed information in the surroundings of this observable compared to far away from it. In this approach we consider all possible configurations in the surroundings of a local observable, and unique samples from the remaining of the setup drawn using Markov chain Monte Carlo. We have tested the performance of this approach for ground states of the spin-1/2 tilted Ising model in different phases, and also for thermal states in the a spin-1 bilinear-biquadratic model. Our results demonstrate that CMCS yields higher accuracy for local observables in short-range correlated states while requiring substantially fewer samples, showcasing in which regimes one can obtain acceleration for the evaluation of expectation values.
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Materials Science

Direct demonstration of electric chirality control in a helimagnetic YMn$_6$Sn$_6$ by spin-polarized neutron scattering

Hidetoshi Masuda, Yutaro Yanagisawa, Kazuki Ohishi et al. (+3 more)

The spiral handedness of magnetic moments, referred to as chirality, gives rise to emergent electromagnetic phenomena in helimagnets. In insulating helimagnets, known as multiferroics, the cycloidal spin structure induces electric polarization by utilizing the inverse Dzyaloshinskii-Moriya mechanism. Spin-polarized neutron diffraction experiments, which directly probe circular spin arrangements, clearly demonstrated that an electric field controlled the chirality in multiferroic helimagnets. On the other hand, it was unclear until recently how the chirality could be controlled in metallic helimagnets where a large electric field cannot be applied, while the chirality control technique in metallic helimagnets should enable the exploration of chirality-dependent spintronic functionalities. Recently, Jiang et al. succeeded in controlling the chirality of a spiral structure by the simultaneous application of a magnetic field and electric current in a metallic helimagnet, utilizing the nonreciprocal electronic transport as an indirect probe of chirality, highlighting the need for a neutron diffraction experiment that directly probes the chirality. Here, we directly demonstrate the chirality control in a metallic helimagnet YMn$_6$Sn$_6$ by means of spin-polarized neutron diffraction, which should give rise to a firm basis for the development of future helimagnetic spintronics.
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All authors Hidetoshi Masuda, Yutaro Yanagisawa, Kazuki Ohishi, Yusuke Nambu, Yoichi Nii, Yoshinori Onose

Superconductivity

Zero-field superconducting diode effect induced by magnetic flux in a van der Waals superconductor trigonal PtBi$_2$

Nan Jiang, Masaki Maeda, Yuhi Yamaguchi et al. (+9 more)

The superconducting diode effect is one of the nonreciprocal transport phenomena, where the critical current depends on the current direction. This effect is typically realized in superconductors with broken spatial-inversion and time-reversal symmetry. To break the time-reversal symmetry, external magnetic fields are commonly used. Here, we demonstrate a sign-controllable superconducting diode effect under zero external magnetic field in a van der Waals superconductor trigonal PtBi$_2$. The sign of the zero-field superconducting diode effect is controlled by the poling magnetic field, that is a large magnetic field applied prior to measurements. This result indicates that trapped magnetic flux are responsible for breaking the time-reversal symmetry. Our findings highlight the crucial role of trapped magnetic flux in generating the superconducting diode effect and provide a general pathway for realizing a zero-field superconducting diode effect.
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All authors Nan Jiang, Masaki Maeda, Yuhi Yamaguchi, Mori Watanabe, Masashi Tokuda, Kensuke Takaki, Sebun Masaki, Takumi Ikushima, Takayoshi Koyanagi, Masakazu Matsubara, Kazutaka Kudo, Yasuhiro Niim

Mesoscale and Nanoscale Physics

Sub Band Gap Operation Limits for Perovskite Light Emitting Diodes

Pradeep R. Nair

Ultra low voltage operation of Perovskite light emitting diodes (PeLEDs) has been demonstrated in recent years as high radiance with minimal power consumption is a desired feature. However, the light output at such conditions from PeLEDs is typically very low, and the maximum in external quantum efficiency (EQE) and energy conversion efficiency (ECE) are achieved at large biases with significant power consumption. Here, we explore the possibility of achieving maximums in EQE and ECE at sub band gap voltages for PeLEDs. Our analysis consistently interprets otherwise scattered experimental data from literature, identifies the limits for low voltage operation, and elucidates optimization routes for sub band gap high radiance operation of PeLEDs.
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Mesoscale and Nanoscale Physics

Observation of Custodial Chiral Symmetry in Memristive Topological Insulators

Wenhao Li, Junyao Wu, Ning Han et al. (+8 more)

The concept of custodial symmetry, a residual symmetry that protects physical observables from large quantum corrections, has been a cornerstone of high-energy physics, but its experimental observation has remained unexplored. Building on recent theoretical work [Phys. Rev. Lett. 128, 097701 (2022)], we report the first experimental observation of classical analog of custodial chiral symmetry in a memristive Su-Schrieffer-Heeger (SSH) circuit. We provide direct experimental evidence for custodial symmetry through the measurement of the correction to the Lagrangian. This Lagrangian correction, which mimics a mass term in field theory, vanishes smoothly as the perturbation is reduced. We also demonstrate that topological edge states in the memristive SSH circuit remain localized at the boundary, protected by custodial chiral symmetry. This work opens new avenues for emulating field-theoretic symmetries and nonlinear dynamics in memristive platforms.
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All authors Wenhao Li, Junyao Wu, Ning Han, Rui Zhao, Fujia Chen, Yuang Pan, Yudong Ren, Hongsheng Chen, Zhen Gao, Ce Shang, Yihao Yang

Materials Science

An evaluation of A15 Nb3Al superconducting thin films for application in quantum circuits

Joseph Falvo, Brooke Henry, Bernardo Langa Jr. et al. (+4 more)

A15 superconductors are distinguished by their high critical temperatures, magnetic fields, and current-carrying capabilities. Among them, Nb$_3$Al is of particular interest for superconducting quantum circuits as a means to extend device operating temperatures, provided that its electrodynamic properties are well understood. Here, we report on the synthesis of Nb$_3$Al thin films by magnetron co-sputtering followed by rapid thermal processing, yielding superconducting transition temperatures above 16~K. Microwire devices patterned from these films exhibit a coherence length of $3.2\,\mathrm{nm}$ and superfluid densities as low as $1.1\times 10^{26}\,\mathrm{m}^{-3}$, suggesting that Nb$_3$Al may enable high kinetic inductance in thinner films. Coplanar waveguide resonators fabricated on Nb$_3$Al demonstrate single-photon internal quality factors up to $2.26\times 10^{5}$. These results establish Nb$_3$Al as a promising material platform for the development of superconducting quantum circuits operating at elevated temperatures, contingent on appropriate control of interfacial chemistry and surface morphology.
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All authors Joseph Falvo, Brooke Henry, Bernardo Langa Jr., Rohit Pant, Ashish Alexander, Jason Dong, Kasra Sardashti

Strongly Correlated Electrons

Interaction-Induced Breakdown of Anderson Localization: Thermodynamic Segregation disguised as the Skin Effect

Ali Tozar

We investigate the interplay between strong disorder and repulsive interactions in the one-dimensional Fermi-Hubbard model under open boundary conditions. While uncorrelated disorder is widely accepted to localize all single-particle eigenstates, a phenomenon typically reinforced by interactions in the Many-Body Localization (MBL) regime, we report a counter-intuitive breakdown of this paradigm. We demonstrate that strong repulsive interactions can overcome disorder-induced localization, driving the system into a macroscopically segregated phase where spin species accumulate at opposite boundaries. Although this boundary accumulation phenomenologically mimics the Non-Hermitian Skin Effect (NHSE) observed in non-reciprocal systems, our comprehensive analysis reveals a fundamentally different origin. By performing a rigorous control experiment in the Hermitian limit, we prove that the segregation persists without non-reciprocity, identifying many-body energy minimization as the primary driver. This "interaction-induced segregation" manifests as a sharp thermodynamic crossover, characterized by a divergent energy susceptibility, challenging the conventional understanding of disorder-interaction competition in open quantum systems.
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Materials Science · Cross-listed from physics.optics

Spectrally-selective dynamic radiative thermoregulation via phase engineering

Qizhang Li, Yuanke Chen, Zhuang Luo et al. (+10 more)

Maintaining comfortable temperatures for buildings, humans, and devices consumes a substantial portion of global energy, underscoring the urgent need for energy-efficient thermoregulation technologies. Dynamic radiative thermal emitters that can switch between passive cooling and heating modes offer a promising solution, but most existing devices exhibit broadband optical responses, resulting in unwanted parasitic heat exchange and limited performance. Here, we introduce an elegant strategy that uses a dielectric cap to transform broadband metal-insulator transition (MIT) materials into spectrally selective dynamic emitters. This design creates a highly tunable Fabry-Perot cavity, enabling a tailored thermal emission spectrum by engineering the reflected-wave phase profile. Our Fresnel-formalism-based phasor diagram analysis reveals two key routes for realizing high spectral selectivity: a high-index dielectric cap and a low-loss metallic MIT state, which are further validated by Bayesian optimization. Following this principle, we demonstrated a wide-angle spectrally-selective thermoregulator operating in the atmospheric transparency window (8-13 um), where the thermal emittance can be electrically tuned from about 0.2 to 0.9 through reversible copper electrodeposition on a germanium cavity. Furthermore, this strategy can be extended to multispectral electrochromic windows, enabling switching between solar heating and spectrally-selective radiative cooling. Our work establishes a versatile and generalizable paradigm for spectral engineering of dynamic thermal emitters, opening opportunities in energy-efficient buildings, wearable thermal comfort, spacecraft thermoregulation, and multispectral camouflage.
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All authors Qizhang Li, Yuanke Chen, Zhuang Luo, Chenxi Sui, Xubing Wu, Ronghui Wu, Qingsong Fan, Ching-Tai Fu, Pei-Jan Hung, Gangbin Yan, Genesis Higueros, Ting-Hsuan Chen, Po-Chun Hsu

Materials Science

Awakening catalytically active surface of BaRuO3 thin film for alkaline hydrogen evolution

Jegon Lee, Dohyun Kim, Seulgi Ji et al. (+9 more)

The dynamic reconstruction of surfaces during electrochemical reactions plays a crucial role in determining the performance of electrocatalysts. However, because reconstructions occur at the atomic level, direct observation and elucidation of the underlying mechanism are challenging for conventional powder type catalysts with ill defined lattices. In this study, the catalytically active surface of 3C BaRuO3 (BRO) epitaxial thin films emerges upon the dynamic introduction of surface Ru clusters, for the alkaline hydrogen evolution reaction (HER). Based on the mass activity at overpotential 100 mV, the intrinsic HER performance increases dramatically from 0.11 to 7.72 A/mg immediately after the initial HER cycle and eventually saturates at 1.05 A/mg after continuous operation. The formation of Ru clusters on the catalyst surface, driven by selective Ba leaching under alkaline HER conditions, is observed experimentally. Density functional theory calculations demonstrate that HER activity increased with enhanced H* adsorption owing to the dynamic Ru6 cluster formation. A strategy for stabilizing the 'awakened' active surface of BRO is further proposed by validating that the atomic-scale control of the film thickness can effectively maintain the highly active state. This study offers fundamental insights into the design and stabilization of the highly active Ru-based electrocatalysts for the alkaline HER.
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All authors Jegon Lee, Dohyun Kim, Seulgi Ji, Sangmoon Yoon, Seung Hyun Nam, Jucheol Park, Jin Young Oh, Seung Gyo Jeong, Jong-Seong Bae, Sang A Lee, Heechae Choi, Woo Seok Choi

Materials Science

External-field-induced transition from altermagnetic metal to fully-compensated ferrimagnetic metal in monolayer $\mathrm{Cr_2O}$

San-Dong Guo, Qiqi Luo, Shi-Hao Zhang et al. (+1 more)

Altermagnets and fully-compensated ferrimagnets are two canonical classes of zero-net-moment magnets. An altermagnetic (AM) half-metal cannot exist due to its AM spin splitting, while a fully-compensated ferrimagnetic (FC-FIM) metal seems impossible to realize because both spin channels remain gapless. Here, we propose that an FC-FIM metal can be realized by breaking the rotational or mirror symmetry that links two spin-opposite magnetic atoms in an AM metal. We further demonstrate that charge-carrier doping is fundamentally unable to generate a net magnetic moment in an altermagnet, whereas such a net moment can be readily induced in a fully-compensated ferrimagnet. We use the AM monolayer $\mathrm{Cr_2O}$ as a concrete example to validate our proposal. Either electric field or uniaxial strain can break the $S_{4z}$ symmetry of $\mathrm{Cr_2O}$, thereby inducing a transition from an AM metal to an FC-FIM metal. Uniaxial strain plus carrier doping creates a net moment in an altermagnet, and the so-called piezomagnetism is essentially a strain-driven switch from altermagnetism to fully-compensated ferrimagnetism. By analogy, we advance the concept of electromagnetism: an electric field drives the transition from altermagnetism to fully-compensated ferrimagnetism, and subsequent charge-carrier doping stabilizes a net magnetization. Our work provides a roadmap for further exploring the connection and distinction between altermagnet and fully-compensated ferrimagnet, and confirms the feasibility of FC-FIM metal.
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All authors San-Dong Guo, Qiqi Luo, Shi-Hao Zhang, Peng Jiang

Materials Science

Platonic representation of foundation machine learning interatomic potentials

Zhenzhu Li and Aron Walsh

Foundation machine learning interatomic potentials (MLIPs) are trained on overlapping chemical spaces, yet their latent representations remain model-specific. Here, we show that independently developed MLIPs exhibit statistically consistent geometric organisation of atomic environments, which we term the Platonic representation. By projecting embeddings relative to a set of atomic anchors, we unify the latent spaces of seven MLIPs (spanning equivariant, non-equivariant, conservative, and non-conservative architectures) into a common metric space that preserves chemical periodicity and structural invariants. This unified framework enables direct cross-model optimal transport, interpretable embedding arithmetic, and the detection of representational biases. Furthermore, we demonstrate that geometric distortions in this space can indicate physical prediction failures, including symmetry breaking and incorrect phonon dispersions. Our results show that the latent spaces of diverse MLIPs present consistent statistical geometry shaped by shared physical and chemical constraints, suggesting that the Platonic representation offers a practical route toward interoperable, comparable, and interpretable foundation models for materials science.
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Materials Science

Phonon density of states of silica (SiO2) nanopore via molecular dynamics simulations

Pablo Galaviz, Dehong Yu, Nicolas de Souza et al. (+4 more)

This study presents a comprehensive computational investigation of the vibration density of states (VDOS) of a silica nanopore, systematically evaluating a range of force fields against inelastic neutron scattering results. We analyze the influence of temperature, crustal structure, and surface-adsorbed water molecules on the nanopore's structural and dynamic properties. We performed classical molecular dynamics simulations of nanopore and bulk silica, and used density functional theory (DFT) calculations for bulk silica for comparison. The resulting VDOS shows relatively good agreement with DFT and experimental data. The temperature has a relatively low effect on the dry nanopore. The inclusion of H2O molecules significantly affects the VDOS. The low-energy modes are dominated by H2O VDOS and increase with loading. This work is an essential step towards characterizing silica nanopores via molecular dynamics and provides a valuable reference for experimental comparison with X-ray and neutron scattering VDOS results.
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All authors Pablo Galaviz, Dehong Yu, Nicolas de Souza, Sho Kimura, Yoshitomo Kojima, Seiji Mori, Akira Yamaguchi

Thursday 4 December

Soft Condensed Matter

Biomolecular crystallization in microfluidic devices

Nadine Candoni, Romain Grossier and Stéphane Veesler

This chapter presents an overview of microfluidic devices reported in the literature, used to develop methodologies for nucleation of biomolecules, with crystal size control, and for collecting thermodynamic and kinetic data. Part I is dedicated to the properties of microfluidic devices through materials used for their fabrication and for crystals analysis. Part II describes the variety of microfluidic devices available and how to handle them to produce flows, droplets and/or wells of micrometer size. These devices use crystallization methods inspired by batch processes and they are mainly used for protein crystallization. Part III focuses on fundamental properties of biomolecule crystallization determined using droplet-based microfluidics: nucleation kinetics, nucleation rate and effective interfacial energy crystal/solution. Part IV explains how the kinetic effect of confinement due to micrometer size, and so nanovolumes, leads to isolation of different phases. These latter are characterized by X-Ray Diffraction (XRD) and methods to minimize manual handling of crystals for XRD are also presented, with appropriate equipment to store the crystals.
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Materials Science

From orbital analysis to active learning: an integrated strategy for the accelerated design of TADF emitters

Jean-Pierre Tchapet Njafa, Steve Cabrel Teguia Kouam, Patrick Mvoto Kongo et al. (+1 more)

Thermally Activated Delayed Fluorescence (TADF) emitters must satisfy two competing requirements: small singlet-triplet energy gaps for thermal upconversion and sufficient spin-orbit coupling for fast reverse intersystem crossing. Predicting these properties accurately demands expensive calculations. We address this using a validated semi-empirical protocol (GFN2-xTB geometries, sTDA/sTD-DFT-xTB excited states) on 747 molecules, combined with charge-transfer descriptors from Natural Transition Orbital analysis. The hole-electron spatial overlap She emerges as a key predictor, accounting for 21% of feature importance for the triplet state alone. Our best model (Support Vector Regression) reaches MAE = 0.024 eV and R2 = 0.96 for $\Delta E_{ST}$. Active learning reduces the data needed to reach target accuracy by approximately 25% compared to random sampling. Three application domains are explored: NIR-emitting probes for bioimaging, photocatalytic sensitizers, and fast-response materials for photodetection.
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All authors Jean-Pierre Tchapet Njafa, Steve Cabrel Teguia Kouam, Patrick Mvoto Kongo, Serge Guy Nana Engo

Materials Science

Mapping vacancy and bonding electron distributions around aluminium nanovoids

Philip N. H. Nakashima, Yu-Tsun Shao, Zezhong Zhang et al. (+6 more)

All materials have defects and many contain nanostructures, both of which disrupt chemical bonding - the basis of materials properties. No experimental measurements of bonding electron distributions associated with defects and nanostructures have ever been possible. We present a method enabling such measurements and interrogate nanovoids surrounded by vacancies - the most fundamental of nanostructures and defects - in aluminium. We measure the volume of a vacancy with 3% uncertainty and map vacancy concentrations surrounding nanovoids with nanometre resolution in three dimensions where previously only two-dimensional mapping was possible. We discover that radiation-damaged voids can "heal". Our bonding measurements are depth-resolved, vacancy-sensitive, and agree with density functional theory. This work opens bonding electron density measurements to inhomogeneous nanostructured multi-phased materials so that the electronic origins of phenomena such as strengthening, weakening, interface functionality, solute diffusion and phase transformations within them may be revealed.
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All authors Philip N. H. Nakashima, Yu-Tsun Shao, Zezhong Zhang, Andrew E. Smith, Tianyu Liu, Nikhil V. Medhekar, Joanne Etheridge, Laure Bourgeois, Jian-Min Zuo

Strongly Correlated Electrons · Cross-listed from hep-th

Scaling limits of complex Sachdev-Ye-Kitaev models and holographic geometry

Elena Gubankova, Subir Sachdev and Grigory Tarnopolsky

We compare different limits of the Sachdev-Ye-Kitaev model of $N$ complex fermion with $p$-fermion interactions. First, we compute the fermion Green's function and free energy in the limit of large $N$ followed subsequently by the limit of large $p$. Next, we examine the `double-scaling' limit in which the large $N,p$ limits are taken at fixed $\lambda = p^2/N$. Earlier results on the latter limit are resummed for small $\lambda$, and shown to match our results for the first limit. We also describe the holographic match of our results to two-dimensional Jackiw-Teitelboim gravity with an additional $U(1)$ gauge field.
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Mesoscale and Nanoscale Physics · Cross-listed from quant-ph

Photoelectrical detection and characterization of divacancy and PL5-PL7 spins in silicon carbide

Naoya Morioka, Tetsuri Nishikawa, Hiroshi Abe et al. (+2 more)

Photoelectrical detection of magnetic resonance (PDMR) offers a scalable alternative to optical readout of spin defects in semiconductors and is particularly promising for near-infrared (NIR) emitters, where photodetection is often challenging. Here, we demonstrate room-temperature coherent PDMR of PL3 (divacancy), PL5, PL6, and PL7 spins. PL7 and PL5 exhibit notably stronger PDMR than PL6 as opposed to optical detection, indicating higher ionization efficiency and suitability for electrical readout. Rabi oscillation and two-frequency spectroscopy reveal a previously undiscovered secondary resonance of PL7. We determine the zero-field splitting parameters of PL7 and assign the recently reported PL3a defect to PL7. The demonstrated PDMR of these NIR defects constitutes a key advancement toward quantum electronic devices. Also, the clarified spin parameters and ionization characteristics provide a solid foundation for advancing quantum technologies utilizing these defects regardless of the detection schemes.
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All authors Naoya Morioka, Tetsuri Nishikawa, Hiroshi Abe, Takeshi Ohshima, Norikazu Mizuochi

Mesoscale and Nanoscale Physics

Plasmonic enhancement of the infrared radiation absorption in an ultrathin InSb layer

Yurii M. Lyaschuk, Vadym V. Korotyeyev, Viacheslav A. Kochelap et al. (+1 more)

Indium antimonide (InSb) is a fundamental material for infrared radiation detectors based on interband transitions. Its narrow bandgap enables detection of infrared radiation within the $3-5 \mu m$ atmospheric window, while its high quantum efficiency ensures excellent sensitivity in InSb-based detectors. We propose a plasmonic structure that significantly enhances infrared absorption in an ultrathin InSb film. The resonant characteristics of this plasmonic enhancement effect could serve as a foundation for developing highly sensitive multi-color detectors.
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All authors Yurii M. Lyaschuk, Vadym V. Korotyeyev, Viacheslav A. Kochelap, Oleksandr O. Raichev

Disordered Systems and Neural Networks · Cross-listed from q-bio.NC

Competition, stability, and functionality in excitatory-inhibitory neural circuits

Simone Betteti, William Retnaraj, Alexander Davydov et al. (+2 more)

Energy-based models have become a central paradigm for understanding computation and stability in both theoretical neuroscience and machine learning. However, the energetic framework typically relies on symmetry in synaptic or weight matrices - a constraint that excludes biologically realistic systems such as excitatory-inhibitory (E-I) networks. When symmetry is relaxed, the classical notion of a global energy landscape fails, leaving the dynamics of asymmetric neural systems conceptually unanchored. In this work, we extend the energetic framework to asymmetric firing rate networks, revealing an underlying game-theoretic structure for the neural dynamics in which each neuron is an agent that seeks to minimize its own energy. In addition, we exploit rigorous stability principles from network theory to study regulation and balancing of neural activity in E-I networks. We combine the novel game-energetic interpretation and the stability results to revisit standard frameworks in theoretical neuroscience, such as the Wilson-Cowan and lateral inhibition models. These insights allow us to study cortical columns of lateral inhibition microcircuits as contrast enhancer - with the ability to selectively sharpen subtle differences in the environment through hierarchical excitation-inhibition interplay. Our results bridge energetic and game-theoretic views of neural computation, offering a pathway toward the systematic engineering of biologically grounded, dynamically stable neural architectures.
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All authors Simone Betteti, William Retnaraj, Alexander Davydov, Jorge Cortés, Francesco Bullo

Mesoscale and Nanoscale Physics

Cavity based sensing of antiferromagnetic canting and nonzero-momentum spin waves in a van der Waals cavity-magnon-polariton system

Supriya Mandal, Krishnendu Maji, Lucky N. Kapoor et al. (+6 more)

Cavity-magnon-polaritons are hybrid excitations from the interaction between cavity photons and magnons, the quanta of collective spin oscillations. Along with the tunability of the magnon-photon coupling strength, fast information transfer and conversion speed are desired in hybrid devices. This can be achieved utilizing the propagating nature of spin waves with non-zero momentum for their ultra-fast time dynamics and reduced ohmic dissipation. Antiferromagnets are particularly interesting as hosts for magnons since stray-field interactions are minimized, and they support multiple modes with distinctive magnetic-field behavior across the phase diagram. CrCl3 is a van der Waals antiferromagnet having a strong easy-plane anisotropy and a weak in-plane easy-axis anisotropy. Despite some magnetic resonance studies, the impact of magnetic reorientation of spins in CrCl3 on cavity-magnon-polariton interaction strength as a function of magnetic field remains largely unexplored. In this study, we investigate the coupling between magnons in CrCl3 and photons in a coplanar waveguide resonator as a function of magnetic field. In particular, we find that the magnon-photon coupling strength varies nonmonotonically and distinctly with the magnetic field for both acoustic and optical magnons, enabling tuning of the coupling strength with an external magnetic field as a knob. We find the signature of spin-flop transition in two harmonics of the cavity due to a stronger dispersive coupling between optical magnons and cavity photons at lower fields. Additionally, we find standing modes formed by spin waves with nonzero momentum associated with the two hybrid magnons when the external field is applied at an angle with the crystal plane. These modes do not undergo substantial coupling with the cavity mode unlike the antiferromagnetic modes and can be used as low-loss propagation channels in hybrid devices.
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All authors Supriya Mandal, Krishnendu Maji, Lucky N. Kapoor, Souvik Sasmal, Soham Manni, John Jesudasan, Pratap Raychaudhuri, Arumugam Thamizhavel, Mandar M. Deshmukh

Materials Science

Benchmarking Universal Machine Learning Interatomic Potentials for Supported Nanoparticles: Decoupling Energy Accuracy from Structural Exploration

Jiayan Xu, Abhirup Patra, Amar Deep Pathak et al. (+3 more)

Supported nanoparticle catalysts are widely used in the chemical industry. Computational modeling of supported nanoparticles based on density functional theory (DFT) often involves structural searches of stable local minimum energy configurations and molecular dynamics simulations at finite temperature. These are computationally demanding tasks that are intractable within DFT for large systems. In the last two decades, machine learning interatomic potentials (MLIPs) have been successfully used to substantially increase the size and time scales accessible to simulations approximating DFT accuracy. However, training reliable MLIPs is non-trivial as it requires many costly DFT calculations. Recently, several universal MLIPs (uMLIPs) have been developed, which are trained on large datasets that cover a wide range of molecules and materials. Here, we benchmark the accuracy and the efficiency of these uMLIPs in describing Cu nanoparticles supported on Al$_2$O$_3$ surfaces against our domain-specific DP-UniAlCu model. We find that the MACE-OMAT can reproduce reasonably well the low-energy structures found in global optimization at an energy accuracy comparable to DP-UniAlCu. Interestingly, the MatterSim-v1.0.0-1M model, which exhibits larger deviations in the binding energies, can find even more stable configurations than the other two models in some supported nanoparticle sizes, showing its capability in structure exploration. For MD simulations, MACE-OMAT and MatterSim-v1.0.0-1M can qualitatively reproduce the mean-squared displacements of Cu atoms (MSD$_\mathrm{Cu}$) predicted by DP-UniAlCu, albeit at roughly two orders of magnitude higher cost. We demonstrate that the uMLIPs can be very useful in simulating supported nanoparticles even without any fine-tuning, though their reduced efficiency remains a limiting factor for large-scale simulations.
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All authors Jiayan Xu, Abhirup Patra, Amar Deep Pathak, Sharan Shetty, Detlef Hohl, Roberto Car

Statistical Mechanics · Cross-listed from q-bio.PE

Exactly Solvable Population Model with Square-Root Growth Noise and Cell-Size Regulation

Farshid Jafarpour

Stochastic exponential growth is nearly ubiquitous across cellular life, but how its microscopic noise structure shapes population growth remains poorly understood. Here, we introduce an exactly solvable population model in which cells grow exponentially with fluctuations that scale with the square root of cell size, and divide according to general size-control mechanisms. Our first result is that the population growth rate is exactly equal to the mean single-cell growth rate, for all noise strengths and for all division and size-regulation schemes that maintain size homeostasis. Thus square-root growth noise does not affect long-term fitness, in sharp contrast to models with size-independent stochastic growth rates. Second, we derive an exact solution for the steady-state distribution of cell sizes in the population and show that it is broadened by growth fluctuations. Third, the mean-rescaled population size $N_t/\langle N_t \rangle$ converges to a stationary compound Poisson-exponential distribution that depends only on growth noise. This distribution, and hence the long-time shape of population-size fluctuations, is unchanged by division-size noise or asymmetric partitioning. These results identify Feller-type exponential growth with square-root noise as an exactly solvable benchmark for stochastic growth in size-controlled populations and provide concrete signatures that distinguish it from models with size-independent growth-rate noise.
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Strongly Correlated Electrons · Cross-listed from quant-ph

Investigating a Quantum-Inspired Method for Quantum Dynamics

Bo Xiao, Benedikt Kloss and E. Miles Stoudenmire

Building on recent advances in quantum algorithms which measure and reuse qubits and in efficient classical simulation leveraging projective measurements, we extend these frameworks to real-time dynamics of quantum many-body systems undergoing discrete-time and continuous-time Hamiltonian evolution, and find improvements that significantly reduce sampling overhead. The approach exploits causal light-cone structure by interleaving time and space evolution and applying projective measurements as soon as local subsystems reach the target physical time, suppressing entanglement growth. Comparing to time-evolving block decimation, the method reaches longer times per sample for the same resources. We also gain the ability to study dynamics of entanglement that would be occurring on quantum hardware when following similar protocols, such as the holographic quantum dynamics simulation framework. We show how to efficiently obtain local observables as well as equal-time and time-dependent correlation functions. Our findings show how optimizations for quantum hardware can benefit classical tensor network simulations and how such classical methods can yield insights into the utility of quantum simulations.
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Quantum Gases · Cross-listed from quant-ph

The deep Hilbert space of all-to-all interacting SU(3) atoms: from quantum to classical

Federico Balducci and Aleksandra A. Ziolkowska

We study the emergence of chaos in multilevel atoms with all-to-all interactions, inspired by cavity QED. Focusing on a 3-level Tavis-Cummings model in a far detuned limit, we detail its deep Hilbert space structure – i.e. we enumerate all distinct dynamical sectors, beyond the totally symmetric subspace – by using the Schur-Weyl duality, which is applicable thanks to the permutation symmetry in the all-to-all Hamiltonian. Strong Hilbert space fragmentation ensues from the non-abelian nature of the symmetry, with some sectors displaying regular dynamics and others being chaotic. We uncover that many permutation symmetry sectors contribute to the dynamics in the classical limit, in addition to the commonly studied totally symmetric subspace. To elucidate the dynamical responses in each of the symmetry sectors, we propose a semiclassical description in terms of spin coherent states, which is also able to explain the origin of chaotic or regular dynamics with a simple geometrical argument. Our work contributes to the study of the quantum-classical correspondence in chaotic systems, and uncovers a rich structure in multilevel all-to-all interacting models.
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Other Condensed Matter · Cross-listed from physics.ins-det

Development of a Modular Optically Detected Magnetic Resonance Setup for Optical Experiments in a Variable Temperature Insert

Anh Tong, Andreas Bauer, Markus Kleinhans et al. (+6 more)

We developed an optically detected magnetic resonance (ODMR) setup designed for compatibility with a widely used, commercially available helium bath cryostat equipped with a variable temperature insert. The optical path extends nearly two meters, spanning the full length of the cryostat insert, enabling excitation of the nitrogen-vacancy (NV) centers and detection of the resulting fluorescence from outside the cryostat. The setup preserves optical alignment and beam quality along this extended path allowing integration into existing cryogenic systems without significant modifications. We demonstrate the setup's performance by measuring the temperature dependence of the resonance signal and its behavior under small applied magnetic fields, as well as the magnetic transition of a SrRuO$_3$ sample, thereby showcasing the feasibility of NV magnetometry on a sample in constrained cryogenic environments.
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All authors Anh Tong, Andreas Bauer, Markus Kleinhans, James S. Schilling, Christian H. Back, Karl D. Briegel, Fabian A. Freire-Moschovitis, Dominik B. Bucher, Christian Pfleiderer

Superconductivity

Fluorine-substitution-dependent phase diagram and superconducting properties of Sm-based oxypnictides synthesized by a high-pressure growth technique

Mohammad Azam, Tatiana Zajarniuk, Ryszard Diduszko et al. (+5 more)

A series of SmFeAsO1-xFx (Sm1111) bulk samples (x = 0.05 to 0.40) are synthesized by an in-situ cubic-anvil high-pressure technique at 4 GPa and systematically characterized through structural, microstructural, Raman, transport, and magnetic measurements. Structural analysis confirms that the tetragonal Sm1111 phase remains dominant across the entire substitution range, with lattice parameters decreasing smoothly as fluorine content increases, demonstrating effective incorporation of F even in the overdoped regime (x = 0.4). Raman spectroscopy provides complementary, local-phase-sensitive evidence that supports the structural analysis and confirms fluorine substitution in the main Sm1111 phase. In the underdoped region, the superconducting transition temperature (Tc) is enhanced by 10-17 K and the critical current density (Jc) is increased by up to an order of magnitude compared with conventionally synthesized samples at the ambient pressure. The upper critical field, estimated using the WHH model, reaches values approaching 200 T, reflecting strong paramagnetic limitation and multiband effects. TAFF analysis reveals a power-law field dependence of the activation energy, consistent with collective vortex pinning in polycrystalline iron-based superconductors. The superconducting phase diagram constructed from Tc and Jc versus fluorine content reveals a dome-like trend, with a maximum Tc of 57 K and Jc of 10^4 A cm^-2 at the optimal doped region. Comparison with conventionally synthesized Sm1111 samples demonstrates that high-pressure growth significantly extends the effective fluorine substitution range and enhances the superconducting performance, particularly in the underdoped regime. These results establish high-pressure fluorine substitution as an effective materials-engineering approach for tuning the phase diagram and optimizing the superconducting properties of Sm1111.
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All authors Mohammad Azam, Tatiana Zajarniuk, Ryszard Diduszko, Taras Palasyuk, Cezariusz Jastrzebski, Andrzej Szewczyk, Hiraku Ogino, Shiv J. Singh