Soft Condensed Matter
Unambiguous characterization of in-plane dielectric response in nanoconfined liquids: water as a case study
Jon Zubeltzu
The in-plane dielectric constant of nanoconfined water has attracted growing interest in recent years. Nevertheless, assigning a bulk-like dielectric constant to a molecularly thin film is convention dependent because it requires choosing an effective water width. We propose the in-plane 2D polarizability, $\alpha_{\parallel}$, as a macroscopic characterization of the in-plane dielectric response that avoids this choice. Using classical molecular dynamics simulations, we compute $\alpha_{\parallel}$ via two independent and consistent methods: based on fluctuation-dissipation theory, and from the induced dipole moment when water is placed in a capacitor. Our results provide the framework to quantify the in-plane dielectric response of polar
liquids across simulations and experiments.
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Materials Science
A comparison of the spin-phonon behaviour of Fe$_2$P-based magnetocaloric materials
Mikael S. Andersson, Simon R. Larsen, Erna K. Delczeg-Czirjak et al. (+7 more)
Magnetic refrigeration can provide an environmentally friendly technology to reduce significantly the energy consumption of cooling devices. To retain the sustainability of the device, all parts must be made from abundant materials, excluding e.g. rare earth elements. As such, materials based on Fe$_2$P have shown great potential for magnetocaloric devices. In this study, Fe$_2$P and FeMnP$_{0.55}$Si$_{0.45}$, have been studied using magnetometry,
neutron scattering and theoretical modelling with the aim to understand the
ferromagnetic transition, related to the magnetocaloric effect. Analysis of the diffraction data of Fe$_2$P showed that it is the Fe$_{3g}$-site that drives the
magnetic transition as the Fe$_{3f}$ does not have any
magnetic contribution at the
magnetic transition temperature. For FeMnP$_{0.55}$Si$_{0.45}$, the
magnetic transition is more gradual, on both sites, with coexistence of the para- and
ferromagnetic phases close to the
magnetic transition. The temperature dependent
magnetic structure behaviour are well in agreement with our first principles calculations. Both Fe$_2$P and FeMnP$_{0.55}$Si$_{0.45}$ showed two distinct regions, at different length scales, in their S(Q,$\omega$) spectra. The two length scales can be modelled using a different set of
magnetic spin states (S), using S$\rm _{Fe}$~=~2 and S$\rm _{Mn}$~=~2.5, consistent with the ground state of the
magnetic atoms. QENS at low Q (Q~\textless{}~0.5~Å) shows similar
magnetic processes in both compounds with uncorrelated magnetism below the
magnetic transition temperature. The uncorrelated state highlights that the
magnetic anisotropy does not play a major role in the formation of the
magnetic state. Furthermore, this emphasises the existence of a two part system in FeMn(P,Si)-based compounds, that drives the
magnetic transition and in turn the magnetocaloric effect.
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All authors Mikael S. Andersson, Simon R. Larsen, Erna K. Delczeg-Czirjak, Antonio Corona, Jacques Ollivier, Wiebke Lohstroh, Helen Y. Playford, Cheng Li, Pascale P. Deen, Johan Cedervall
Mesoscale and Nanoscale Physics
Electronic transport in BN-encasulated graphene limited by remote phonon scattering
Khalid Dinar, Francesco Macheda, Alberto Guandalini et al. (+6 more)
We study the impact of BN's
phonons on the electrical resistivity of hBN-encapsulated
graphene. While encapsulation yields high-mobility devices, the surrounding BN itself introduces remote scattering from polar optical
phonons, whose role in standard resistivity measurements remains unclear. We combine high-quality transport experiments with ab initio calculations including a proper treatment of dynamically screened remote interactions. We demonstrate that hBN's out-of-plane
phonons strongly influence resistivity between 150 K and room temperature, whereas higher-energy LO modes and intrinsic
graphene phonons alone cannot explain the observed trends. The coupling between electrons and the BN's
phonons becomes more pronounced at low carrier densities due to reduced screening. Our findings establish that remote
phonon scattering fundamentally limits transport in encapsulated
graphene, solving a longstanding debate.
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All authors Khalid Dinar, Francesco Macheda, Alberto Guandalini, Matthieu Paillet, Christophe Consejo, Frederic Teppe, Benoit Jouault, Thibault Sohier, Sébastien Nanot
Materials Science
Microscopic Theory of Superionic Phase Transitions: Nonadiabatic Dynamics and Many-Body Effects
Jiaming Hu, Zhichao Guo, Jingyi Liang et al. (+1 more)
Superionic phase transitions have attracted extensive interest for decades due to their promising applications and rich underlying physics. In particular, complicated many-body effects and nonadiabatic dynamics are believed to play essential roles, limiting the explanatory power of phenomenological approaches and obscuring the microscopic mechanisms at play. In this work, we develop a unified theoretical framework for describing solid-state ionic conduction. After reviewing the conventional approximations, we construct a general
lattice model that applies to both normal ionic and superionic conductors. By incorporating the nonadiabatic concerted-hopping mechanism and the many-body Coulomb interaction within a self-consistent mean-field scheme, we identify these two effects as the fundamental driving forces behind type-I and type-II superionic phase transitions, respectively. Our model directly reproduces key experimental observations. Within this unified framework, we further provide a comprehensive comparison between the two types of transitions. Overall, our work offers microscopic insight into superionic phase transitions and provides guidance for the design and optimization of advanced solid-state ionic conductors.
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All authors Jiaming Hu, Zhichao Guo, Jingyi Liang, Bartomeu Monserrat
Statistical Mechanics · Cross-listed from physics.soc-ph
Simple spatial processes can generate heterogeneous contact distributions in face-to-face interactions
Juliette Gambaudo and Mathieu Génois
Face-to-face interactions reveal recurring patterns, suggesting the possibility of shared underlying mechanisms. More specifically, inter-contact durations, contact durations and number of contacts per edge share similar heavy-tail distributions in many empirical settings. A common intuition is that face-to-face interactions may be influenced by spatial constraints, and that the observed complex behaviors could arise from such physical limitations. Our models explore the impact of this constraint by simulating pedestrian dynamics, and studying the generated temporal network of contacts. Previous work showed that the inter-contact duration distribution is recovered with a pedestrian dynamic as simple as the two dimensional random walk, but this approach doesn't allow to recover the distribution of the number of times a pair of individuals has been in contact. One assumption is that the number of contact between individual arises from the social relationship between them, in other words a
memory of past interactions. However, we here present models that are based on solely spatial rules, by adding simple targeting mechanisms to the two-dimensional random walk. We show that these models allow to recover a broad distribution of the number of contacts, revealing the importance of two ingredients: localized phases and controlled population mixing. This suggests that the observed heterogeneity in the contact numbers within the data does not necessarily emerge from underlying social relationships between individuals, since an equivalent distribution may be reproduced using a purely spatially based model, without the need for
memory mechanisms.
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Quantum Gases · Cross-listed from quant-ph
Nonlinearity-Induced Thouless Pumping in Quasiperiodic Lattices
Xiao-Xiao Hu, Dun Zhao and Hong-Gang Luo
Nonlinear Thouless pumping has been established in periodic
lattices; its counterpart in quasiperiodic
lattices remains unexplored. Here, we show a nonlinear topological pumping of gap
solitons in quasiperiodic
lattices where the local nonlinear self-consistent potentials lead to a
lattice potential reconstruction; as a result, an emergent topological structure induced by this local reconstruction governs the dynamics of the gap
solitons. This enables
solitons to adiabatically occupy a single topological band, realizing quasi-quantized Thouless pumping. In addition, the intrinsic
lattice perturbations disrupt this band occupation, which drives
solitons into a non-quantized drifting regime. However, even in this regime, we also find that the
soliton transport is constrained by the topological properties of a critical rational approximant. Tuning nonlinearity or
lattice scaling reveals a controllable switching among topological pumping, drifting, and localization. Our work uncovers a mechanism for nonlinearity-induced topological behavior in complex
lattice potentials.
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Materials Science
Spontaneous structural reconstructions and properties of ultrathin triangular ZnSe nanoplatelets
Alexander I. Lebedev
Two-dimensional (2D) materials have revolutionized all areas of development of high-performance electronic devices. In particular, the unique electronic and optical properties of II–VI
semiconductor nanoplatelets have been found to be very promising for optoelectronics. However, not all properties of this intriguing class of materials are yet known. A new, previously unknown hexagonal 2D structure of ZnSe nanoplatelets whose energy is lower than the energies of all previously studied systems is found from first-principles calculations. This structure appears as a result of spontaneous reconstruction of the wurtzite structure and differs from it by the stacking order of the bulk and near-surface Zn atomic layers. The
phonon spectrum, electronic structure, and band gap of the obtained nanoplatelets are calculated. The
phonon spectra of the nanoplatelets are in complete agreement with the spectra observed in experiment and differ strongly from the vibrational spectra of ZnSe nanoclusters. The adsorption of ZnCl$_2$ and $L$-cysteine molecules on the surface of the nanoplatelets is studied and is shown to be accompanied by yet another spontaneous reconstruction of the hexagonal structure into a tetragonal one and a new rearrangement of Zn atoms in the near-surface layers. Calculations of the natural optical activity of nanoplatelets covered with $L$-cysteine reveal an increase in the specific (calculated per
chiral molecule) optical activity, which is especially strong for the Janus structures, as compared to the free $L$-cysteine molecule.
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Materials Science
Strain-tunable multipiezo effects in Janus monolayer Cr2SSe: Selective reversal of valley polarization and single-spin-channel anomalous valley Hall effect
Quan Shen, Jianing Tan, Tao Yao et al. (+2 more)
Altermagnetism, the third class of collinear
magnetic order, uniquely combines a zero net magnetization with
spin polarized bands in reciprocal space, opening new avenues for two dimensional valleytronics and spintronics. Here, using first principles calculations, we predict that the Janus monolayer Cr2SSe, which possesses intrinsic inversion
symmetry breaking, hosts a strain tunable multipiezo effect and exhibits distinctive valleytronic properties. The system displays pronounced
spin splitting and band inversion at the X and Y high
symmetry points in the Brillouin zone, giving rise to robust
spin-valley locking. The degeneracy of these valleys is protected by diagonal mirror
symmetry. Application of uniaxial strain breaks this
symmetry, concurrently inducing piezovalley, piezoelectric, and piezomagnetic responses, a manifestation of the multipiezo effect. Critically, strain applied along orthogonal crystallographic directions yields opposite valley polarization, while under small compressive strain, we achieve selective reversal of valley polarization, enabling independent control of valence and conduction band valleys and promoting a single-
spin-channel anomalous valley
Hall effect. These findings establish a pathway for low-power, non volatile manipulation of valley degrees of freedom and enhanced
spin transport efficiency, providing a theoretical foundation for the design of energy-efficient valleytronic devices.
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All authors Quan Shen, Jianing Tan, Tao Yao, Wenhu Liao, Jiansheng Dong
Superconductivity
Directional-dependent Berezinskii-Kosterlitz-Thouless transition at EuO/KTaO$_3$(111) interfaces
Zongyao Huang, Zhengjie Wang, Xiangyu Hua et al. (+10 more)
In two dimensions, a phase-coherent superconducting state is established via a Berezinskii-Kosterlitz-Thouless (BKT) transition, whose critical temperature $T_{\rm BKT}$ is determined by the global superfluid stiffness in uniform superconducting systems. We report that at the interface between (111)-oriented KTaO$_3$ and
ferromagnetic EuO, the two-dimensional superconducting state exhibits a BKT transition relying on the direction of in-plane bias current. The highest $T_{\rm BKT}$ occurs when current is applied along one of the [11$\bar{2}$] axes of KTaO$_3$, underscoring a spontaneous breaking of the threefold
lattice rotational
symmetry. Such directional dependence of $T_{\rm BKT}$ is consistently reflected in the nonreciprocal signals stemming from superconducting fluctuations above the transition. We attribute this phenomenon to an interfacial phase segregation; the phase with higher $T_{\rm BKT}$ self-organizes into quasi-one-dimensional textures that stretch along one of the [11$\bar{2}$] directions. Our results point toward the emergence of exotic phases of matter beyond the description of conventional BKT physics at a superconducting interface that is subjected to
ferromagnetic proximity.
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All authors Zongyao Huang, Zhengjie Wang, Xiangyu Hua, Huiyu Wang, Zhaohang Li, Shihao Liu, Zhiwei Wang, Feixiong Quan, Zhen Wang, Jing Tao, James Jun He, Ziji Xiang, Xianhui Chen
Materials Science
Contemporary Insights into Electronic Structure and Microscopic Transport in Nodal-Line Semimetals
Ashutosh S. Wadge, Pardeep K. Tanwar, Giuseppe Cuono et al. (+1 more)
Topological semimetals have emerged as an important class of
quantum materials with novel electronic responses and unconventional transport phenomena. Among them, nodal-line semimetals are distinguished by band crossings that extend along one-dimensional lines in momentum space rather than occurring at discrete points, forming closed loops, chains, or extended lines. The stability of these nodal structures is governed by crystalline
symmetries such as mirror,
spin-rotation, and nonsymmorphic operations, which give rise to characteristic topological invariants and surface states, including drumhead-like bands. In this review, we present a comprehensive overview of the theoretical framework and experimental realization of nodal-line semimetals, with particular emphasis on
symmetry protection and the consequences of
symmetry breaking. We discuss the classification of nodal-line structures, their
evolution into other topological phases, and their signatures in electronic structure measurements and transport phenomena. Special
attention is given to insights obtained from angle-resolved photoemission spectroscopy and related probes. By bringing together
symmetry analysis, band
topology, and experimental observations, this review aims to clarify the relationship between
topology, magnetism, and measurable electronic responses in nodal-line semimetals. These considerations highlight their potential as a versatile platform for next-generation topological electronic functionalities and emergent
quantum phenomena beyond conventional paradigms.
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All authors Ashutosh S. Wadge, Pardeep K. Tanwar, Giuseppe Cuono, Carmine Autieri
Quantum Gases
Nonequilibrium phase transition of dissipative fermionic superfluids: Case study of multi-terminal Josephson junctions
Soma Takemori and Kazuki Yamamoto
We investigate nonequilibrium dynamics of a triad of fermionic superfluids connected via Josephson junctions, following sudden switch-on of two-body loss in one of the three superfluids. By formulating the dissipative BCS theory for the Lindblad equation, we find that the superfluid order parameter exhibits a phase rotation, thereby giving rise to three types of dc Josephson currents corresponding to different junctions. We demonstrate that, when the tunneling amplitude $V_{31}$ between superfluids without two-body loss is weak, a two-step nonequilibrium phase transition characterized by the vanishing dc Josephson currents occurs: dissipation first induces the nonequilibrium phase transition by making one dc Josephson current finite, while further increasing dissipation makes this remaining dc Josephson current vanish. By contrast, when $V_{31}$ is strong, dissipation induces the nonequilibrium phase transition in which all dc Josephson currents simultaneously vanish. An analytical study based on a simplified model further supports this observation.
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Materials Science
Beyond Beryllium: AI-Accelerated Materials Discovery for Interstellar Spacecraft Shielding
Yue Li, Xu Pan and Kaiyuan Guo
Project Daedalus (1973–1978), the most detailed interstellar probe design study ever conducted, specified a 9 mm beryllium erosion shield to protect the spacecraft payload during its 5.9 light-year cruise to Barnard's
Star at 12% of the speed of light. This design, however, predated both the isolation of two-dimensional materials and the development of graph neural network (GNN) property predictors. Here, we systematically screen 20 candidate materials–spanning conventional aerospace metals, transition metal dichalcogenides, and ultra-high-temperature ceramics–using density functional theory (DFT) data from the JARVIS database (76,000 materials) with independent validation by the Atomistic Line Graph Neural Network (ALIGNN). We evaluate candidates across four criteria: specific mechanical stiffness (KV/rho), sputtering resistance, thermal
neutron absorption cross-section, and thermodynamic stability. Our screening identifies hexagonal boron nitride (h-BN) and boron carbide (B4C) as dual-function materials offering simultaneous mechanical protection and
neutron radiation shielding, and we propose a
graphene/h-BN/
polymer layered
heterostructure shield design that achieves an estimated 47% mass reduction relative to the original beryllium specification. These findings will become immediately actionable upon the successful development of fusion pulse propulsion, which we note remains an outstanding engineering challenge.
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Statistical Mechanics
Emergent Macroscopic Nonreciprocity from Identical Active Particles via Spontaneous Symmetry Breaking
Wei-Chen Guo, Zuo Wang, Pei-Fang Wu et al. (+3 more)
Nonreciprocity is known to generate a wide range of exotic phenomena in multi-species many-body systems, where different species influence one another through couplings that violate Newton's third law. In contrast, in the absence of explicitly imposed macroscopic nonreciprocal processes, single-species nonreciprocity – another distinct form of nonreciprocity – typically plays only a limited role in shaping macroscopic physics. Here, using a single-species Vicsek model with a
vision cone and extrinsic noise, we show that spontaneous
symmetry breaking (SSB) can dramatically enhance the macroscopic consequences of microscopic single-species nonreciprocity. In the ordered phase, this enhancement gives rise to an emergent macroscopic nonreciprocity that induces the system of identical active particles to admit an effective description with a "two-species" non-Hermitian structure. The resulting SSB-enhanced nonreciprocity substantially promotes traveling-band formation and, more strikingly, drives a novel real-space condensation of identical active particles, characterized by a "traveling line" with vanishing longitudinal width. Our findings uncover a fundamental mechanism by which microscopic single-species nonreciprocity can exert strong macroscopic influences in complex systems.
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All authors Wei-Chen Guo, Zuo Wang, Pei-Fang Wu, Li-Jun Lang, Bao-Quan Ai, Liang He
Strongly Correlated Electrons
Magnetoelectric Control of Toroidal Moment in Ferroaxial Crystal PbMn$_{2}$Ni$_{6}$Te$_{3}$O$_{18}$
Shungo Aoyagi, Shunsuke Kitou, Taka-hisa Arima et al. (+1 more)
Ferroic multipole orders break some
symmetry and often activate unique physical properties, such as nonreciprocal directional dichroism and linear magnetoelectric effects. Here, we demonstrate the control of
magnetic toroidal orientation in PbMn$_{2}$Ni$_{6}$Te$_{3}$O$_{18}$ through the application of electric and
magnetic fields in two distinct configurations. Through directional dichroism, we successfully visualize
magnetic ferrotoroidic domains, establishing the intrinsic coupling among
magnetic toroidal moment, crystallographic ferroaxial moment, and magnetoelectric monopoles. Our findings not only present an effective pathway for controlling
magnetic toroidal moment but also provide a novel approach for investigating ferroaxial ordering.
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All authors Shungo Aoyagi, Shunsuke Kitou, Taka-hisa Arima, Yusuke Tokunaga
Statistical Mechanics · Cross-listed from hep-lat
Strong-coupling expansion and two-point Padé approximation for lattice $\phi^4$ field theory
Yuanran Zhu, Efekan Kökcü and Chao Yang
Reliable approximations for correlation functions at intermediate and strong coupling remain hard to obtain for general
quantum field theories. Perturbative expansions are often asymptotic or have a finite radius of convergence, which limits their applicability beyond weak coupling. Here we combine weak- and strong-coupling expansions and propose to use two-point Padé schemes to construct approximants. For
lattice $\phi^4$ theory, we show that this two-point interpolation strategy yields accurate global approximations to the two-point correlation function across broad coupling regimes and compares favorably with standard one-point resummation methods. We also provide heuristic explanations for the observed convergence behavior and discuss the practical range of validity of the approach.
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Soft Condensed Matter
Organic Electrochemical Transistor Arrays with Integrated Lipid-Sealed Femtolitre Chambers for Simultaneous Electrical and Optical Detection of Membrane Protein Activity
S. Kojima, S. Rawat, M. Sanchez Miranda et al. (+4 more)
We report a scalable method for fabricating arrays of fifty-two ion-sensitive PEDOT:PSS organic electrochemical transistors (OECTs) on glass coverslips, each incorporating an integrated fluoropolymer microwell sealed with a lipid
bilayer for simultaneous electrical and fluorescence microscopy studies of membrane
proteins. The architecture addresses a key limitation of existing OECT arrays by providing every transistor with an independent fluid reservoir sealed by its own isolated segment of lipid
bilayer, thereby confining membrane
protein diffusion to a defined sensing region. Microwells containing a dye-labelled $50$~mM KCl solution were sealed with lipid
bilayers and overlaid with a dye-free $100$~mM KCl solution. Following addition of $\alpha$-hemolysin, formation of heptameric pores enabled K$^{+}$ ions to diffuse into the microwells and dye molecules to diffuse out, producing concurrent decreases in transistor conductance and fluorescence intensity. This integrated platform combines electrical and optical readout within independently addressable sensing sites and provides a versatile, scalable foundation for larger transistor arrays and the investigation of diverse membrane
proteins reconstituted into lipid
bilayers.
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All authors S. Kojima, S. Rawat, M. Sanchez Miranda, J.G. Gluschke, H. Noji, L.K. Lee, A.P. Micolich
Soft Condensed Matter
Braiding and exchange statistics of liquid crystalline Majorana quasiparticles
A. I. Tóth, G. Negro, A. D. Huxley et al. (+1 more)
Liquid crystalline defects in 3D can be viewed as
geometric spinors, whose emergent properties are reminiscent of those of topological excitations in
quantum condensed matter, such as Majorana quasiparticles. However, it is unclear how deep this analogy is, and whether this is a purely mathematical mapping, or it extends to key physical features, such as the exchange statistics or braiding behaviour. To address this question, here we consider a simple pattern made up of four nematic Majorana-like defect profiles, and ask how the defect profiles change as we braid them repeatedly around each other. Surprisingly, we find that in a large range of parameter space the defect profiles behave as classical analogues of non-Abelian anyons, which can be described in our case by defect bivectors moving on a Bloch-like hemisphere. Elastic interactions and dynamical effects enhance the complexity of the gates which can be performed by braiding these quasiparticles, making these
liquid crystalline spinors promising candidates as components of topological computers.
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All authors A. I. Tóth, G. Negro, A. D. Huxley, D. Marenduzzo
Mesoscale and Nanoscale Physics
Electronic Raman scattering from 2D metals with broken inversion symmetry
Mojdeh Saleh and Saurabh Maiti
Lack of inversion
symmetry in metals breaks SU(2)
symmetry which results in
spin-splitting of the electronic states at the
Fermi level due to various types of
spin-orbit coupling (SOC) such as Dresselhaus, Rashba, or Ising (also called valley-Zeeman). This splitting is known to enable both incoherent
spin-flip excitations and coherent
chiral-
spin modes. Another effect of breaking of SU(2) is the introduction of a direct
spin-
photon interaction. We use this concept to formulate a theory of inelastic scattering of
photons from the charge carriers of such a system [electronic Raman scattering (eRS)]. As a result of broken SU(2), we show that the eRS probe, unlike conventional theory of Raman scattering, couples to
spin excitations even without tuning the
laser to an internal resonance. We show that the
spin dependent excitations induced by
photon scattering are sensitive to the polarization geometries as well as to the
spin structure of the
Hilbert space of the low-energy states. As a concrete realization, we examine doped/gated
graphene on substrates with strong SOC with various compositions of Rashba and valley-Zeeman SOC and compare their spectra with those for a model 2D electron gas (2DEG). The spectra are shown to have a resonant feature in select polarization geometries near the SOC-splitting energy and, importantly, is shown to be different in the two systems. The signal in
graphene systems is shown to be stronger than that in a 2DEG by orders of magnitude owing to the large Dirac velocity. We also outline how the lineshapes from the spectra can be used to infer various components of SOC in the system.
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Materials Science
Revealing buried ferroelectric topologies by depth-resolved electron diffraction imaging
Ting-Ran Liu, Koushik Jagadish, Xiangwei Guo et al. (+10 more)
Nanoscale topological polar textures promise new functionalities for ferroelectric
memories and logic, yet their three-dimensional structure and mesoscale organization remain experimentally inaccessible. Here we introduce depth-resolved electron diffraction imaging (DREDI), a fast, non-destructive, method that maps polarization with <50 nm lateral and <10 nm depth sensitivity within fraction of a second. Its high acquisition speed enables the first continuous polarization mapping across six orders of magnitude in length scale, from nanometers to millimeters. Using epitaxial BiFeO3 films, DREDI reveals a hidden depth
evolution of polar textures: surface 71-degree stripes evolve into subsurface flux-closure
vortices that bifurcate into three-fold vertices near the bottom interface. Cross-sectional multi-slice electron ptychography and phase-field modeling confirm these buried configurations and attribute them to strain heterogeneity and ferroelastic twinning in the SrRuO3 electrode. Large-area analysis further shows that vertex-like frustration forms a mesoscale percolating network above a critical length scale of 4 um. DREDI enables real-time, volumetric studies of buried topological textures in ferroic nanomaterials.
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All authors Ting-Ran Liu, Koushik Jagadish, Xiangwei Guo, Maya Ramesh, Peter Meisenheimer, Harish Kumarasubramanian, Sajid Husain, Ann V. Ngo, Amir Avishai, Jayakanth Ravichandran, Darrell G. Schlom, Ramamoorthy Ramesh, Yu-Tsun Shao
Materials Science
Magnetoelastic instabilities in kagome antiferromagnet Mn3-xGa
Linxuan Song, Feng Zhou, Guilin Lu et al. (+5 more)
We present a systematic study of the structural,
magnetic, and transport properties of hexagonal Mn3-xGa
alloys, revealing a series of composition-controlled emergent phenomena. By tuning the Mn concentration, we uncover distinct
lattice responses, including a zero thermal expansion-like volume compensation behavior in Mn-poor compositions and a magnetoelastic-driven, field-assisted structural phase transition in Mn-rich samples. These
lattice instabilities are accompanied by correlated
magnetic and transport anomalies, including metamagnetic transitions, negative magnetoresistance, and anomalous
Hall sign reversal. First-principles calculations demonstrate that the
Hall sign reversal originates from
crystal-
symmetry breaking rather than
magnetic reorientation alone. Our results establish composition as the key control parameter governing magnetoelastic coupling in Mn3-xGa, providing a unified framework to tailor structural,
magnetic, and topological transport properties in kagome antiferromagnets and reconcile previously disparate experimental observations.
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All authors Linxuan Song, Feng Zhou, Guilin Lu, Liang Yao, Xuekui Xi, Yong-Chang Lau, Youguo Shi, Wenhong Wang
Materials Science
Radio-Frequency-Driven Reshaping of the Mesoscale Charge-Density-Wave Landscape in 1T-TaS2 Thin-Film Devices
Maedeh Taheri, Zahra Ebrahim Nataj, Nick Sesing et al. (+4 more)
Radio-frequency excitation directly reshapes the mesoscale charge-density-wave landscape in quasi-two-dimensional 1T-TaS2 thin films. Under combined RF and DC bias, the hysteretic current-voltage characteristics associated with the nearly commensurate-incommensurate transition are strongly altered, displaying RF-driven collapse, branching, and multiple step-like features that depend on frequency and drive amplitude. In-situ Raman measurements show enhanced intensity and linewidth narrowing of low-frequency CDW
phonon modes, consistent with reduced dephasing and increased coherence of the periodic
lattice distortion under RF drive. This behavior is captured by combining an overdamped time-dependent Ginzburg-Landau description of the commensurate CDW with a morphology-informed percolative resistor-capacitor transport model. The simulations indicate that oscillatory driving anneals frustrated domain configurations, reduces domain-wall density, and reorganizes the discommensuration network, while the transport model reproduces the resulting hysteresis, avalanche-like pathways, and RF-induced conductance steps. RF driving therefore provides an effective route for controlling collective electron-
phonon order and accessing metastable transport states in 1T-TaS2, with implications for reconfigurable RF electronics,
memory, and unconventional computing based on correlated materials.
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All authors Maedeh Taheri, Zahra Ebrahim Nataj, Nick Sesing, Topojit Debnath, Tina T. Salguero, Roger K. Lake, Alexander A. Balandin
Materials Science
Bipolar plates for the next generation of proton exchange membrane fuel cells (PEMFCs): A review of the latest processing methods for unconventional flow channels
Zahra Kazemi and Kamran Behdinan
The rapid, unsustainable depletion of finite fossil fuel resources and their environmental consequences demand the deployment of affordable clean and sustainable energy solutions.
Polymer electrolyte membrane fuel
cell (PEMFC) technology is an important pathway in decarbonization of modern energy systems, especially when fueled by high-purity green hydrogen. In PEMFCs, bipolar plates largely determine
cell efficiency, longevity, and affordability, which in turn depends on both material selection and design of the embedded flow channels. Conventional manufacturing processes have long been used to fabricate standard bipolar plate designs; however, they are incompatible with unconventional, intricate geometries due to their insufficient resolution and precision in fabrication of fine features, and reliance on multi-step post-processing modifications that limit their design adaptability. This lack of design flexibility impedes the translation of innovative laboratory-scale concepts to industrial-scale production and their practical adoption. In recent years, a growing body of research publications and patent disclosures has reported advanced manufacturing methods, such as additive manufacturing, capable of producing intricate bipolar plate geometries at competitive costs. However, a discussion of these manufacturing approaches, along with an assessment of their scalability and industrial readiness, remains absent in the literature. This study aims to fill this gap. It outlines recent progress and proposes future research directions toward affordable and efficient bipolar plate solutions for advanced PEMFC systems.
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Statistical Mechanics · Cross-listed from physics.bio-ph
In-vivo entropy production of A. subaru
Yu Fu, Emmy Dobson, Benjamin B. Machta et al. (+1 more)
Entropy production is often used as a proxy for energy consumption of a non-
equilibrium system. Lower bounds can be estimated from coarse-grained observations, and this has been done for various biological systems. Here, we apply these tools to a more macroscopic system whose true energy consumption is also known. We find that while
entropy production does give a lower bound, it is some 25 orders of magnitude away from being saturated. To be certain of this result, we survey different methods of estimating irreversibility, and write down a novel kNN
estimator.
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All authors Yu Fu, Emmy Dobson, Benjamin B. Machta, Michael C. Abbott
Materials Science
Robust $d$-wave altermagnetism in $\mathrm{XCr_2Y_2O}$ (X=K, Rb, Cs; Y=S, Se, Te) family
San-Dong Guo
The $\mathrm{KV_2Se_2O}$, $\mathrm{Rb_{1-\delta}V_2Te_2O}$ and $\mathrm{Cs_{1-\delta}V_2Te_2O}$ are experimentally confirmed to adopt either C-type or G-type
antiferromagnetic configuration, corresponding to apparent or hidden altermagnetism. However, their nearly degenerate energies lead to inconsistent experimental assignments between the two
antiferromagnetic configurations. Here, we predict that the experimentally synthesized $\mathrm{RbCr_2Se_2O}$ is a robust $d$-wave altermagnetic metal, since the energy difference between C-type and G-type configurations is large, which is independent of electron correlation strength and van der Waals interaction. Upon applying in-plane uniaxial strain, $\mathrm{RbCr_2Se_2O}$ can generate a net total
magnetic moment via a direct piezomagnetic effect, which is distinct from
semiconductor that typically requires carrier doping in addition to strain. This provides an experimental strategy for distinguishing the G-type
antiferromagnetic configuration, in which the total
magnetic moment remains zero under uniaxial strain. Our work presents an isostructural $d$-wave altermagnetic $\mathrm{RbCr_2Se_2O}$ analogous to $\mathrm{KV_2Se_2O}$, $\mathrm{Rb_{1-\delta}V_2Te_2O}$ and $\mathrm{Cs_{1-\delta}V_2Te_2O}$, which can facilitate further experimental verification. Furthermore, these results are universal across materials of this family $\mathrm{XCr_2Y_2O}$ (X=K, Rb, Cs; Y=S, Se, Te), thus expanding the family of altermagnets.
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Mesoscale and Nanoscale Physics
Gate-Tunable Photoresponse of Graphene Josephson Junctions at Terahertz Frequencies
X. Zhou, I. Gayduchenko, A. Kudriashov et al. (+12 more)
Graphene Josephson junctions (JJ) provide a promising platform for ultra-broadband
quantum sensing of light owing to
graphene's frequency-independent absorption, vanishing electronic heat capacity, and weak electron-
phonon coupling, which enable rapid suppression of the critical current through radiation-induced electron heating. Existing investigations have been confined to the microwave and infrared regimes, where competing detector technologies are already established; by contrast, the terahertz (THz) band - where sensitivity is most urgently lacking and no mature
quantum sensor exists - has remained largerly unexplored. Here we demonstrate a strong photoresponse of
graphene JJs at THz frequencies, establishing a first experimental step towards
graphene-based THz
quantum sensors. Under low-intensity illumination, we observe a pronounced suppression of the critical current that generates a strong photovoltage (Vph) under current bias. By tracking this Vph and independently measuring the electron temperature as a function of absorbed power, we extract a responsivity of 88 kV W^-1 and a noise-equivalent power of 45 aW Hz^-1/2 at 1.7 K. Furthermore, gate tunability of our JJ enables access to a regime where hysteretic current-voltage characteristics persist up to 0.9 K, offering a potential route toward single-
photon THz detection beyond millikelvin (mK) temperatures. These findings establish
graphene JJ as a versatile platform for broadband cryogenic radiation sensing and point towards their use as
quantum sensors at THz frequencies.
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All authors X. Zhou, I. Gayduchenko, A. Kudriashov, K. Shein, A. Kuksov, L. Elesin, M. Kravtsov, A. Shilov, O. Popova, S. Jana, T. Taniguchi, K. Watanabe, G. Goltsman, K. Novoselov, D.A. Bandurin
Materials Science
Comparative study of room temperature and quench condensed bismuth films: morphology and electronic characteristics
Yulia Kirina, Prakash Sharma, Wyatt Thomas et al. (+4 more)
A comparison between properties of bismuth thin films deposited at substrate temperatures of 296 K (room temperature) and 77 K (quench condensed) is studied across epitaxial, amorphous, and van der Waals substrates. The experiments demonstrate changes in crystallinity, morphology, and electrical transport arising from the influence of substrate temperature. Moreover, the work highlights changes in grain size, roughness, X-ray diffraction peak intensities, and preferred orientation between the two deposition temperatures. The orientation of the films deposited at 77 K is preferentially (110), compared to (111) for films deposited at room temperature. Films grown at 77 K differ from those deposited at room temperature, exhibiting lower surface roughness but smaller grain size, which leads to increased electrical resistivity in quench condensed films. The decrease of substrate temperature during the deposition appears to induce slightly more strain in depositions on the amorphous and van der Waals substrates than on the epitaxial substrates. Lastly, quench condensed films exhibit lower carrier mobility and lower carrier density compared to room temperature films. This study elucidates previously incompletely understood processes in bismuth deposition and raises new questions regarding growth on van der Waals surfaces.
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All authors Yulia Kirina, Prakash Sharma, Wyatt Thomas, Tristan Anderson, Arya G. Pour, Victoria Soghomonian, Jean J. Heremans
Mesoscale and Nanoscale Physics
Nonlinear Frequency-Momentum Topology and Doubling of Multifold Exceptional Points
Tsuneya Yoshida
Even in the linear limit, the
topology of multifold (also called higher-order) exceptional points across the Brillouin zone has lacked a general characterization, leaving the doubling
theorem essentially limited to two-fold exceptional points. Here, we establish the doubling
theorem of $n$-fold exceptional points [EP$n$s ($n=2,3,\ldots$)] for systems where nonlinearity enters through
eigenvalues. To this end, we introduce new topological invariants, termed frequency-momentum winding numbers, which characterize nonlinear EP$n$s in $m$-band systems throughout the Brillouin zone for arbitrary $n$ and $m$ ($m\geq n$). These invariants enable a unified proof of the doubling
theorem in the absence of
symmetry and under several
symmetry constraints, including parity-time ($PT$) and charge-conjugation-parity
symmetries. Furthermore, even in the linear limit, the frequency-momentum winding number indicates $\mathbb{Z}$
topology of $PT$-symmetric EP$2$s which is beyond the previously reported $\mathbb{Z}_2$
topology. The frequency-momentum winding numbers can also be extended to a class of coupled resonators in which nonlinearity enters via the eigenvectors, whereas the spectrum is determined by a nonlinear scalar equation for the frequency.
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Materials Science
AI-assisted Human-in-the-Loop Web Platform for Structural Characterization in Hard drive design
Utkarsh Pratiush, Huaixun Huyan, Maryam Zahiri Azar et al. (+4 more)
Scanning transmission electron microscopy (STEM) has become a cornerstone instrument for
semiconductor materials metrology, enabling nanoscale analysis of complex multilayer structures that define device performance. Developing effective metrology workflows for such systems requires balancing automation with flexibility; rigid pipelines are brittle to sample variability, while purely manual approaches are slow and subjective. Here, we present a tunable human-AI-assisted workflow framework that enables modular and adaptive analysis of STEM images for device characterization. As an illustrative example, we demonstrate a workflow for automated layer thickness and interface roughness quantification in multilayer thin films. The system integrates gradient-based peak detection with interactive correction modules, allowing human input at the design stage while maintaining fully automated execution across samples. Implemented as a web-based interface, it processes TEM/EMD files directly, applies noise reduction and interface tracking
algorithms, and outputs statistical roughness and thickness metrics with nanometer precision. This architecture exemplifies a general approach toward adaptive, reusable metrology workflows - bridging human insight and machine precision for scalable, standardized analysis in
semiconductor manufacturing. The code is made available at https://github.com/utkarshp1161/thickness-mapping-webapp
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All authors Utkarsh Pratiush, Huaixun Huyan, Maryam Zahiri Azar, Esmeralda Yitamben, Allen Bourez, Sergei V Kalinin, Vasfi Burak Ozdol
Statistical Mechanics
Anomalous waiting-time distributions in postselection-free quantum many-body dynamics under continuous monitoring
Kazuki Yamamoto and Ryusuke Hamazaki
We investigate waiting-time distributions (WTDs) of
quantum jumps in continuously monitored
quantum many-body systems, whose unconditional dynamics lead to the trivial infinite-temperature state. We demonstrate that the WTD of a half-chain subsystem exhibits an anomalous tail, markedly deviating from the Poissonian distribution in stark contrast to that of the whole system. By analyzing the spectral properties of the superoperator $\mathscr L_0$, which is defined by removing the jump terms associated with the half-chain subsystem from the full Liouvillian, we find that the long-time behavior with the anomalous tail of the half-chain WTD is governed by the
eigenvalue $\lambda_0\:(<0)$ with the largest real part. We further reveal a qualitative change in the system-size dependence of $\lambda_0$ as a function of the measurement strength: for sufficiently weak measurement, $\lambda_0$ decreases proportionally to the system size, while for strong measurement, $\lambda_0$ scales independently of the system size, signaling the persistence of the anomalous half-chain WTD in the thermodynamic limit. The WTD is extracted solely from the spacetime record of
quantum jumps $\{t_i,x_i\}$ and can be experimentally accessed without postselection. Our work establishes a spectral framework for understanding nontrivial WTDs in subsystems of monitored
quantum dynamics and provides a novel diagnostics to assess many-body effects on WTDs.
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Statistical Mechanics
Unified Gauge-Geometry Symmetry for Equilibrium Statistical Mechanics
Hai Pham-Van
We present a
symmetry-based framework for
equilibrium statistical mechanics that formulates a single Lie group combining conventional spacetime
symmetries with a recently identified phase-space gauge-shifting invariance [Muller et al., Phys. Rev. Lett. 133, 217101 (2024)]. Using Noether's
theorem, we obtain a set of general Ward identities together with previously unexplored cross-relations arising from the noncommutation of different
symmetry generators. The approach extends standard many-body
symmetries, such as translations, rotations, Galilean boosts, dilations, and particle exchange, by incorporating an internal gauge-shift
symmetry within a unified group structure. The resulting Lie
algebra suggests a hierarchy of exact identities that encompass established sum rules and indicate possible cross-coupling relations between distinct response and correlation functions. We also identify a Wigner-Eckart-Ward reduction that simplifies tensor-hyperforce correlators to two scalar radial spectra in isotropic fluids, and we outline an equivariant gauge-constrained DFT formulation whose Euler-Lagrange equations are constructed to satisfy the corresponding Ward and cross-Ward constraints. This framework provides a consistent organizational basis for phenomena in
liquids, mixtures, and interfaces, and may offer a
symmetry-based perspective connecting structure, mechanics, and dynamics in many-body systems.
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