Superconductivity
Soma Nagahama, Yuki Sato, Minoru Kawamura et al. (+7 more)
The superconducting diode effect (SDE) is characterized by the nonreciprocity of Cooper-pair motion with respect to current direction. In three-dimensional (3D) materials, SDE results in a critical current that varies with direction, making the effect distinctly observable: the material exhibits superconductivity in one direction while behaving as a resistive metal in the opposite direction. However, in genuinely two-dimensional (2D) materials, the critical current density is theoretically zero, leaving the manifestation of SDE in the 2D limit an intriguing challenge. Here, we present the observation of SDE in a
heterostructure composed of the topological
insulator Bi$_2$Te$_3$ and the iron based
superconductor Fe(Se,Te) $-$a candidate for topological
superconductor$-$ where superconductivity is confined to the 2D limit. The observed I-V characteristics reveal nonreciprocity in the
vortex-creep regime, where finite voltages arise due to the two-dimensional nature of superconductivity. Furthermore, our 2D film demonstrates abrupt voltage jumps, influenced by both the current flow direction and the transverse
magnetic field direction. This behavior resembles that of 3D materials but, in this case, is driven by the
vortex-flow instability, as illustrated by voltage controlled S-shaped I-V curves. These results underscore the pivotal role of
vortex dynamics in SDE and provide new insights into the interplay between
symmetry breaking and two-dimensionality in topological
insulator/
superconductor systems.
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All authors Soma Nagahama, Yuki Sato, Minoru Kawamura, Ilya Belopolski, Ryutaro Yoshimi, Atsushi Tsukazaki, Naoya Kanazawa, Kei S Takahashi, Masashi Kawasaki, Yoshinori Tokura
Soft Condensed Matter
Hydration Free Energies of Linear Alkanes: Systematic Deviations in Common Water Models and Their Correction
Yalda Ramezani and Sumit Sharma
Common force fields overestimate the hydration free energies of hydrophobic solutes, leading to an exaggerated hydrophobic effect. We compute the hydration free energies of linear alkanes from methane to eicosane (C${20}$H${42}$) using free energy perturbation with various three-site (SPC/E, OPC3) and four-site (TIP4P/2005, OPC) water models in combination with the TraPPE-UA alkane force field. All water models overestimate hydration free energies, although the four-site models perform better than the three-site ones. Using alkane cavity free energies, we reparameterize the alkane-water Lennard-Jones well depth to bring simulation results in agreement with experimental and group-contribution estimates at 300 K. The reparameterized models significantly improve agreement with experiments across temperatures (290–350 K). We also show that the General Amber Force Field (GAFF) with TIP4P/2005 water provides closer agreement with experimental hydration free energies than the original TraPPE-UA/TIP4P/2005 combination. Finally, we show that applying a shifted Lennard-Jones potential introduces systematic deviations in the hydration free energies.
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Soft Condensed Matter
Polymer Topology and the Depletion Interaction
Mauro L. Mugnai
Using a theoretical model we show that ideal ring
polymers are stronger depletants than ideal linear
polymers of equal radii of gyration, but not of equal hydrodynamic radii. The difference in the depletion-induced force profile is largely controlled by the thickness of the depletion layer. Theory suggests that this thickness is equal to the average extent of a
polymer along the direction perpendicular to the surfaces of the colloids. Within the limits of finite-size effects, Molecular Dynamics simulations support this conclusion.
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Materials Science
Predicting Crystal Structures and Ionic Conductivities in Li$_{3}$YCl$_{6-x}$Br$_{x}$ Halide Solid Electrolytes Using a Fine-Tuned Machine Learning Interatomic Potential
Jonas Böhm and Aurélie Champagne
Understanding ionic transport in halide solid electrolytes is essential for advancing next-generation solid-state batteries. This work demonstrates the effectiveness of fine-tuning the
Crystal Hamiltonian Graph Network (CHGNet) universal machine learning interatomic potential to accurately predict total energies, relaxed geometries, and lithium-ion dynamics in the ternary halide family Li$_{3}$YCl$_{6-x}$Br$_{x}$ (LYCB). Starting from experimentally refined disordered structures of Li$_{3}$YCl$_{6}$ and Li$_{3}$YBr$_{6}$, we present a strategy for generating ordered structural models through systematic enumeration and energy ranking, providing realistic structural models. These serve as initial configurations for an iterative fine-tuning workflow that integrates molecular dynamics simulations and static density functional theory calculations to achieve near-ab initio accuracy at four orders of magnitude lower computational cost. We further reveal the influence of composition (varied x) on the predicted phase stability and ionic conductivity in LYCB, demonstrating the robustness of our approach for modeling transport properties in complex solid electrolytes.
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Materials Science
Raman Digital Twin of Monolayer Janus Transition Metal Dichalcogenides
Johnathan Kowalski and Liangbo Liang
Monolayer transition metal dichalcogenides (TMDs) are a key class of two-dimensional (2D) materials with broad technological potential. Their Janus counterparts exhibit unique properties due to broken out-of-plane
symmetry and further enrich the functionalities of TMDs. However, experimental synthesis and identification of Janus TMDs remain challenging. It is thus highly desirable to have a rapid, simple, and in situ characterization technique to monitor, in real time, the conversion process from the parent to Janus structure. Raman spectroscopy stands out for such a task as it is a powerful, non-destructive, and very commonly used tool to characterize 2D materials both in situ and ex situ. To realize the full potential of Raman spectroscopy on rapid characterization of Janus TMDs, we present a computational "Raman digital twin" library for various monolayer Janus TMDs in both 2H and Td phases. We focus on group-6 TMDs: MoS$_2$, WS$_2$, MoSe$_2$, WSe$_2$, MoTe$_2$, WTe$_2$ and their Janus variants: MoSSe, MoSTe, MoSeTe, WSSe, WSTe, and WSeTe. Using first-principles density functional theory (DFT), we calculate their vibrational properties and predict distinct Raman fingerprints. These
phonon and Raman signatures reflect each material's structural
symmetry and atomic composition, enabling clear identification via Raman spectroscopy. Our theoretical work supports experimental efforts by providing
benchmarks for material identification, structural analysis, and quality control. The computational library expedites the discovery and development of Janus 2D materials, facilitating tighter integration between theoretical predictions and experimental validation.
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Materials Science
Spin Hall effect in the high-resistivity high-entropy alloy AlCrMoW
Jyoti Yadav, Felix Janus, Tiago de Oliveira Schneider et al. (+3 more)
We study thin films of the high-
entropy alloy system Al$_{x}$(CrMoW)$_{1-x}$, grown on Ta seed layers by magnetron co-sputtering. Between $x=0.2$ and $x=0.6$, a resistivity larger than 100$\mu\Omega$cm is achieved, with a peak of 180$\mu\Omega$cm at $x=0.5$. Around the stoichiometric composition AlCrMoW, the
alloy forms a bcc solid solution. The harmonic
Hall method was used to characterize the
spin Hall angle of the
alloy series, where a maximum
spin Hall angle of $\theta = -0.12 \pm 0.01$ is observed for $x=0.25$. The implied
spin Hall conductivity is $\sigma_\mathrm{SH} \approx -72\,000 \, \hbar/(2e)$\,S/m. The experimental results show excellent agreement with density functional theory calculations, which show similar trends and values. The results demonstrate that high-
entropy alloys with a main-group element component can form a simple
crystal structure and show high resistivity. This suggests that a whole new class of materials for
spin Hall device engineering is available with simple methods.
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All authors Jyoti Yadav, Felix Janus, Tiago de Oliveira Schneider, Shalini Sharma, Daniel Schröter, Markus Meinert
Quantum Gases
Stable High-Order Vortices in Spin-Orbit-Coupled Spin-1 Bose-Einstein Condensates
Xin-Feng Zhang, Huan-Bo Luo, Josep Batle et al. (+2 more)
The present contribution explores phase transitions that occur in the ground state (GS) of
spin-1 Bose-Einstein condensates (BECs) with
spin-orbit coupling (SOC) under the action of gradient
magnetic fields. By solving the corresponding linearized system in an exact fashion, we identify the conditions under which the GS phase transitions occur, thus transforming excited states into GS. The study of the full nonlinear system, including both density-density and
spin-
spin interactions, is numerically analyzed. For the case of repulsive
spin-
spin interactions, the results resemble the linear case, while attractive
spin-
spin interactions lead to the formation of mixed-states near the GS phase-transition points. Additionally, higher-order
vortex solitons are found to be stable even in the nonlinear regime. These findings demonstrate that arbitrary winding numbers can be achieved as corresponding to stable GS and thus contributing to the understanding of topological properties in SOC BECs.
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All authors Xin-Feng Zhang, Huan-Bo Luo, Josep Batle, Bin Liu, Yongyao Li
Materials Science
Rotation of crystal seed during early stages of growth reveals the anisotropy of glass matrix
R. Thapa, E. Mustermann, H. Jain et al. (+2 more)
Rotation of
crystal seed during the early stages of growth in a glass
matrix has been observed due to some torque, contradicting the expectations from the isotropic, uniform structure of the surrounding amorphous
matrix. We establish an atomistic origin of this new phenomenon from molecular dynamics simulations using LiNbO3 and LiNbO3-SiO2 glasses as model systems. Effectively, it arises due to non-uniform forces on the seed from the surrounding glass, which appears inhomogeneous and anisotropic on the scale of glass-
crystal interface. The seeded
crystal growth (SCG) at higher temperatures amplifies this effect due to enhanced atomic dynamics. Silica, when added to LiNbO3 glass, reduces the
crystal growth rate due to increased viscosity and restricted atomic mobility across the growth interface, but has minimal effect on the
crystal rotation. These findings challenge a general assumption that glass is an isotropic material, especially during the early stage of its crystallization, and provide insights for tailoring the microstructure of widely used glass-ceramics.
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All authors R. Thapa, E. Mustermann, H. Jain, V. Dierolf, M. E. McKenzie
Mesoscale and Nanoscale Physics
Jordan T. McCourt, John Chiles, Chun-Chia Chen et al. (+4 more)
The interfaces of
quantum Hall insulators with
superconductors have emerged as a promising platform to realise interesting physics that may be relevant for topologically protected
quantum computing. However, these interfaces can host other effects which obscure the detection of the desired excitations. Here we present measurements of the thermoelectric effect at the
quantum Hall-
superconductor interface. We explain the heat transport by considering the formation of a hotspot at the interface, which results in a non-
equilibrium distribution of electrons that can propagate across the
superconductor through
vortex cores. The observed thermoelectric effect results in a voltage which changes sign on
quantum Hall plateaus and responds to the rearrangement of
vortices in the wire. These observations highlight the complex interplay of thermal and charge phenomena at the
quantum Hall –
superconductor interfaces and should be considered when interpreting transport measurements in similar systems.
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All authors Jordan T. McCourt, John Chiles, Chun-Chia Chen, Kenji Watanabe, Takashi Tanaguchi, Francois Amet, Gleb Finkelstein
Materials Science
Dipole Alignment and Layered Flow Structure in Pressure-Driven Water Transport through MoS$_{2}$ Membranes
João Victor Lemos Vale, Lucas Cesena, Bruno H. S. Mendonça et al. (+1 more)
Efficient water transport through nanostructure membranes is essential for advancing filtration and desalination technologies. In this study, we investigate the flow of water through molybdenum disulfide (MoS$_{2}$) nanopores of varying diameters using molecular dynamics simulations. The results demonstrate that both pore size and atomic edge composition play crucial roles in regulating water flux, molecular organization, and dipole orientation. Larger pores facilitate the formation of layered water structures and promote edge-accelerated flow, driven by strong electrostatic interactions between water molecules and exposed molybdenum atoms. In narrower pores, confinement and asymmetric edge chemistry induce the ordered
alignment of dipoles, thereby enhancing directional transport. Velocity and density maps reveal that pore edges act as active zones, concentrating flow and reducing resistance. These findings highlight the significance of pore geometry, surface chemistry, and molecular dynamics in influencing water behavior within MoS$_{2}$ membranes, providing valuable insights for the design of advanced nanofluidic and water purification systems.
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All authors João Victor Lemos Vale, Lucas Cesena, Bruno H. S. Mendonça, Elizane E. de Moraes
Mesoscale and Nanoscale Physics
Electron-electron scattering processes in quantum wells in a quantizing magnetic field: II. Scattering in the case of two subbands
M.P. Telenkov and Yu.A. Mityagin
Electron-electron scattering processes involving Landau levels of two subband are considered. A
matrix of electron-electron scattering rates containing all tipes of transitions between Landau levels is calculated/ This
matrix is analized, and the relative rates of transitions of different types are determined. The effect of the quantizing
magnetic field orientation on electron-electron scattering processes is ectablished.
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Statistical Mechanics · Cross-listed from cs.LG
Combined Representation and Generation with Diffusive State Predictive Information Bottleneck
Richard John, Yunrui Qiu, Lukas Herron et al. (+1 more)
Generative modeling becomes increasingly data-intensive in high-dimensional spaces. In molecular science, where data collection is expensive and important events are rare, compression to lower-dimensional
manifolds is especially important for various downstream tasks, including generation. We combine a time-lagged information bottleneck designed to characterize molecular important representations and a
diffusion model in one joint training objective. The resulting protocol, which we term Diffusive State Predictive Information Bottleneck (D-SPIB), enables the balancing of representation learning and generation aims in one flexible architecture. Additionally, the model is capable of combining temperature information from different molecular simulation trajectories to learn a coherent and useful internal representation of thermodynamics. We
benchmark D-SPIB on multiple molecular tasks and showcase its potential for exploring physical conditions outside the training set.
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All authors Richard John, Yunrui Qiu, Lukas Herron, Pratyush Tiwary
Superconductivity
Emergent Network of Josephson Junctions in a Kagome Superconductor
Tycho J. Blom, Matthijs Rog, Marieke Altena et al. (+5 more)
Materials with a Kagome
lattice are intensely studied because they host exotic states that combine strong correlations and
topology. Recently, critical current oscillations were observed in an unstructured flake of CsV3Sb5 . In this work, we show that the origin of these oscillations is a network of Josephson junctions intrinsic to the flake that emerges below its critical temperature. Under
radio-frequency radiation, we observe quantized Shapiro steps. The sensitivity of the step height to the contact placement indicates a complex network of junctions. By performing interference studies along multiple field directions, we demonstrate that the interference effects are a result of small junctions and filamentary supercurrent flow. Upon nanostructuring the flake, prominent features of the interference pattern are preserved, illustrating the localized nature of these junctions and their stability to thermal cycles. These results pave the way for determining the exact nature of superconductivity in the AV3Sb5 family.
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All authors Tycho J. Blom, Matthijs Rog, Marieke Altena, Andrea Capa Salinas, Stephen D. Wilson, Milan P. Allan, Chuan Li, Kaveh Lahabi
Strongly Correlated Electrons
Conformal Data for the O(3) Wilson-Fisher Conformal Field Theory from Fuzzy Sphere Realization of the Quantum Rotor Model
Arjun Dey, Loic Herviou, Christopher Mudry et al. (+1 more)
We present a model for strongly interacting
fermions with internal O(3)
symmetry on the fuzzy-sphere that (i) preserves the rotational
symmetry of the fuzzy sphere and (ii) undergoes a
quantum phase transition in the (2+1)-dimensional O(3) Wilson-Fisher universality class. Using exact diagonalization (ED) and density
matrix renormalization group (DMRG), we locate the
quantum critical point via conformal perturbation theory and obtain scaling dimensions from finite-size spectra. We identify 24 primary operators and determine some of their operator product expansion coefficients through first-order conformal perturbation theory. The results are benchmarked against conformal bootstrap and large
quantum-number expansions and reveal a weakly irrelevant operator that plays a role in dimerized antiferromagnets. Our work establishes the fuzzy sphere as a general framework for quantitatively accessing conformal data in non-Abelian conformal field theories (CFTs).
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All authors Arjun Dey, Loic Herviou, Christopher Mudry, Andreas Martin Läuchli
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Vari-Cool: a non-unitary quantum variational protocol for simulated cooling
Jeffrey Z. Song, Gilad Kishony, Erez Berg et al. (+1 more)
We introduce a variational approach for preparing low energy states of arbitrary target
Hamiltonians. The protocol is defined in terms of a repeated cycle consisting of p layers of
unitary gates applied to the system and ancilla "bath"
qubits, followed by reset of the bath
qubits. The gate parameters within each cycle are optimized such that the steady state achieved after many cycles has a low energy expectation value with respect to the target
Hamiltonian, and that the energy converges toward the steady state value in as few cycles as possible. We illustrate the protocol for the transverse field Ising model, and study its systematic behaviors with respect to system size, model parameters, and noise using tensor network based classical simulations. We then experimentally demonstrate its operation on IBM's ibm_kingston
quantum processor for up to 28 system
qubits coupled to 14 bath sites. Classical training on small system sizes and with few
unitary layers per cycle gives robust results that transfer well to larger system sizes and to noisy hardware.
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All authors Jeffrey Z. Song, Gilad Kishony, Erez Berg, Mark S. Rudner
Materials Science
Ab initio study on photocatalytic properties of PtSSe-WXY Janus heterostructures
Shivprasad S. Shastri, Antonio Cammarata and Tomas Polcar
Semiconductor photocatalysis offers a sustainable route for converting
solar energy into chemical energy, enabling the production of clean fuels and valuable chemical products. To this aim, we explore van der Waals
heterostructures made up of Janus PtSSe and WXY (X, Y $=$ S, Se, Te and X $\neq$Y), in the context of photocatalytic applications. The redox capabilities of various
heterostructure configurations (atom facing types and stacking orders) are evaluated by aligning the absolute band edge positions with respect to redox potentials of hydrogen and oxygen
evolution reaction (HER and OER) and CO$_2$ reduction reactions. The stability of photocatalyst candidates are checked by layer binding energy calculations and ab initio molecular dynamics simulations. The optical absorption spectra suggest good light absorption in the visible range. Further, strain engineering is applied as a way to tune band edges and evaluate the possible use of the
heterostructures as photocatalysts. This study shows that van der Waals
heterostructure bilayers composed of Janus PtSSe and WSeTe in specific
geometric configurations can be potential materials as photocatalysts for HER, OER and CO$_2$ reduction reactions. Finally, we suggest that, although systems made up of PtSSe and WSTe cannot be used for photocatalytic applications, they can be explored for applications in thermoelectric energy conversion or infrared photovoltaics.
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Strongly Correlated Electrons · Cross-listed from hep-th
Unveiling dynamical quantum error correcting codes via non-invertible symmetries
Rajath Radhakrishnan, Adar Sharon and Nathanan Tantivasadakarn
Dynamical stabilizer codes (DSCs) have recently emerged as a powerful generalization of static stabilizer codes for
quantum error correction, replacing a fixed stabilizer group with a sequence of non-commuting measurements. This dynamical structure unlocks new possibilities for fault tolerance but also introduces new challenges, as errors must now be tracked across both space and time. In this work, we provide a physical and topological understanding of DSCs by establishing a correspondence between qudit Pauli measurements and non-invertible
symmetries in 4+1-dimensional 2-form gauge theories. Sequences of measurements in a DSC are mapped to a fusion of the operators implementing these non-invertible
symmetries. We show that the error detectors of a DSC correspond to endable surface operators in the gauge theory, whose endpoints define line operators, and that detectable errors are precisely those surface operators that braid non-trivially with these lines. Finally, we demonstrate how this framework naturally recovers the spacetime stabilizer code associated with a DSC.
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Materials Science
Orientational Order of Phenyl Rotors on Triangular Platforms on Ag and Au(111)
Behzad Mortezapour, Sebastian Hamer, Rainer Herges et al. (+2 more)
We investigated trioxatriangulenium functionalized with phenyl (phenyl-TOTA) on the (111) surfaces of Ag and Au using low-temperature scanning tunneling microscopy (STM) and density functional theory (DFT). On Ag(111), the molecules form hexagonal arrays, and on Au(111), honeycomb patterns are also observed. The orientations of the phenyl moieties are resolved on both substrates. On Ag(111), the orientations are parallel within a row and they differ by approximately $60^\circ$ between adjacent molecular rows, and STM images suggest dimerization of the molecules. DFT calculations for Ag(111) reveal that van der Waals interactions dominate this system. The optimized structure matches the experimental pattern, and the simulated STM images exhibit apparent dimerization. This dimerization results from an asymmetry of the phenyl wavefunction, which reflects intramolecular hydrogen bonding between the ligand and an oxygen atom within the triangulenium platform. The orientation of the phenyl moieties is explained by the interaction of each phenyl moiety with its triangulenium platform combined with the direct long-range interaction between phenyl moieties across molecules.
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All authors Behzad Mortezapour, Sebastian Hamer, Rainer Herges, Roberto Robles, Richard Berndt
Disordered Systems and Neural Networks
Disorder-Induced Anomalous Diffusion in a 3D Spin Network
Andrew Stasiuk, Garrett Heller, Lance Berkey et al. (+2 more)
Emergent hydrodynamics (EHD) bridges short-time unitarity with late-time thermodynamics, universal transport phenomena characterize the manner and speed of transport and thermalization. Typical non-integrable systems with few conserved local quantities are expected to be diffusive. In contrast, strongly disordered systems which admit phases such as many-body localization, are predicted to inhibit thermalization and thus slow dynamical transport. Disordered systems represent a uniquely poised platform to probe the
quantum-to-classical transition and the emergence of irreversible thermodynamics from the underlying
unitary structure. Here, we study a strongly disordered
nuclear spin ensemble, using local measurements enabled by the disordered-state technique. We observe an apparent phase transition into a sub-diffusive regime, which we model as a random walk on the emergent fractal structure of a percolating network in the dipolar
spin ensemble. Our novel theoretical model provides a framework for characterizing the emergence of thermalization in closed
quantum systems, even in the presence of strong disorder.
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All authors Andrew Stasiuk, Garrett Heller, Lance Berkey, Bo Xing, Paola Cappellaro
Mesoscale and Nanoscale Physics
Mapping the moiré potential in multi-layer rhombohedral graphene
Eric Seewald, Sanat Ghosh, Nishchhal Verma et al. (+11 more)
Rhombohedral
graphene (rG) aligned with hexagonal boron nitride (hBN) has been shown to host flat bands that stabilize various strongly correlated
quantum phases, including Mott
insulators, integer, and fractional
quantum anomalous
Hall phases. In this work, we use scanning tunneling microscopy/spectroscopy (STM/STS) to visualize the dispersion of flat bands with doping and applied displacement fields in a hBN-aligned rhombohedral trilayer
graphene (rtG)/hBN moiré superlattice. In addition to the intrinsic flat bands of rtG induced by the displacement field, we observe low-energy features originating from moiré potential-induced band folding. Real-space variations of the spectroscopic features allow us to quantify the spatial structure of the moiré potential at the rtG/hBN interface. Importantly, we find that accurately capturing the moiré site-dependent spectra requires incorporating a moiré potential acting on the top
graphene layer with a sign opposite to that of the bottom layer into the continuum model. Our results thus provide key experimental and theoretical insights into understanding the role of the moire superlattice in rG/hBN
heterostructures.
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All authors Eric Seewald, Sanat Ghosh, Nishchhal Verma, John Cenker, Yinan Dong, Birui Yang, Amit Basu, Takashi Taniguchi, Kenji Watanabe, Mandar M. Deshmukh, Dmitri N. Basov, Raquel Queiroz, Cory Dean, Abhay N. Pasupathy
Materials Science
Insights into the OER, ORR, and HER Activity of a New MXene-Family SnSiGeN4 Photocatalyst for Water Splitting: A First-Principles Study
Chhatra Bahadur Subba, Bhanu Chettri, Amel Laref et al. (+4 more)
The development of efficient and cost-effective catalysts for clean energy conversion remains a central challenge in materials science. Although platinum serves as the
benchmark catalyst, its scarcity and high cost hinder large-scale deployment. In this study, we propose a newly predicted SnSiGeN4 MXene-family monolayer as a promising candidate for the oxygen
evolution reaction (OER), oxygen reduction reaction (ORR), and hydrogen
evolution reaction (HER). Using first-principles calculations, we systematically investigated its electronic, vibrational, and optical properties across multiple exchange-correlation functionals, including hybrid approaches, revealing a wide and tunable band gap. Simulated infrared and Raman spectra further confirm the dynamical stability and the presence of catalytically active sites. Guided by these findings, we studied photocatalytic reaction analyses that demonstrate that the computed overpotentials for OER, ORR, and HER are comparable to those of Pt-based catalysts and outperform Ir-based systems, positioning SnSiGeN4 as a sustainable, high-performance platform for next-generation UV-visible-light-driven photocatalysis.
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All authors Chhatra Bahadur Subba, Bhanu Chettri, Amel Laref, Zeesham Abbas, Amna Parveen, Dibya Prakash Rai, Zaithanzauva Pachuau
Materials Science
Optically induced orbital polarization in bulk germanium
Francesco Scali, Marco Finazzi, Federico Bottegoni et al. (+1 more)
Optical orientation has been proven as a powerful tool to inject
spin-polarized electron and hole populations in III-V and group-IV
semiconductors. In particular, the absorption of circularly-polarized light in bulk Ge generates a
spin-oriented population of electrons in the conduction band with a
spin-polarization up to 50%, whereas the hole
spin-polarization, opposite to the electron one, can even reach values up to 83%. In this letter, we theoretically investigate the optical injection of orbital polarization by means of circularly-polarized light in bulk Ge and we show that the latter considerably exceeds 100% for holes and
photon energies close to the direct Ge gap. These results suggest that Ge is a convenient platform for future development of orbitronics and opto-orbitronic devices.
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All authors Francesco Scali, Marco Finazzi, Federico Bottegoni, Carlo Zucchetti
Materials Science · Cross-listed from physics.chem-ph
Is Platinum a Proton Blocking Catalyst?
Aparna Saksena, Yujun Zhao, J. Manoj Prabhakar et al. (+3 more)
Platinum, to date, is the most widely applied electrocatalyst for hydrogen
evolution reaction (HER) in acidic media. It is assumed to be a
proton-blocking catalyst with only surface-limited adsorption of the reaction intermediates. Here, we critically evaluate the bulk interaction of Pt with hydrogen (H), and its heavier isotope deuterium (D), by monitoring operando mass change of the Pt electrode during galvanostatic heavy/water splitting by employing an electrochemical quartz
crystal microbalance. Unexpectedly, we observe an irreversible temporal mass gain and a change in the reaction's overpotential, arising from
diffusion of H/D into Pt, confirmed by atom probe
tomography and thermal desorption spectroscopy. Sub-surface concentration of at least ca. 15 at. % of D in Pt was observed, diffusing down to a depth of more than 10 nm. Analytical description quantified the
diffusion coefficient of D in Pt to be 3.2X10^-18 cm2Xs-1. These findings challenge the existing credence of Pt-
proton interaction being limited to the surface, prompting the expansion of the catalyst design strategies to account for property-modifying bulk
diffusion of H/D in the Pt
matrix
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All authors Aparna Saksena, Yujun Zhao, J. Manoj Prabhakar, Dierk Raabe, Baptiste Gault, Yug Joshi
Strongly Correlated Electrons
A microscopic approach to nonlinear theory of spin-charge separation
Oleksandr Tsyplyatyev, Yiqing Jin, María Moreno et al. (+2 more)
The fate of
spin-charge separation beyond the low energy remains elusive up to now. Here we develop a microscopic theory of the correlation functions using the strong coupling expansion of the Hubbard model and demonstrate its validity down to the experimentally relevant $r_{\rm s}>1$. Evaluating the spectral function, we show the general stability of the nonlinear
spin-charge modes in whole energy band and investigate all the nonlinear features systematically. We confirm the general prediction experimentally in
semiconductor quantum wires. Furthermore, we observe a signal consistent with a continuum of the nonlinear excitations and with a final spectral density around the $3 k_{\rm F}$ point, indicating the robustness of the Hubbard model predictions for a finite range interaction.
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All authors Oleksandr Tsyplyatyev, Yiqing Jin, María Moreno, Wooi Kiat Tan, Christopher J.B. Ford
Soft Condensed Matter
Toggling stiffness via multistability
Hugo de Souza Oliveira, Michele Curatolo, Renate Sachse et al. (+1 more)
Variable stiffness is a key capability in biological and robotic systems, enabling adaptive interaction across tasks and environments. Mechanical metamaterials offer an alternative to conventional mechatronic solutions by encoding stiffness variation directly into monolithic structural architectures, reducing the need for discrete assemblies. Here, we introduce a multistable mechanical metamaterial that exhibits a toggleable stiffness effect in which the effective shear stiffness switches discretely between stable mechanical configurations. Mechanical analysis of surrogate beam models of the unit
cell reveals that this behavior originates from the rotation transmitted by the support beams to the curved beam, governing the balance between bending and axial deformation. Consequently, the shear stiffness ratio between the two states can be tuned by varying the slenderness of the support beams or by incorporating localized hinges that modulate rotational transfer. Experiments on 3D-printed prototypes validate the numerical predictions and confirm consistent stiffness toggling across different geometries. Finally, we demonstrate a monolithic soft clutch that leverages this effect to achieve programmable, stepwise stiffness modulation. This work establishes a design strategy for toggleable stiffness using multistable metamaterials, with potential applications in soft robotics and smart structures where adaptive compliance is of paramount importance.
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All authors Hugo de Souza Oliveira, Michele Curatolo, Renate Sachse, Edoardo Milana
Soft Condensed Matter
Acoustic transparency and absorption in dense granular suspensions
Arnaud Tourin, Yamil Abraham, Marie Palla et al. (+5 more)
We demonstrate the existence of a frequency band exhibiting acoustic transparency in 2D and 3D dense granular suspensions, enabling the transmission of a low-frequency ballistic wave excited by a high-frequency broadband ultrasound pulse. This phenomenon is attributed to spatial correlations in the structural disorder of the medium. To support this interpretation, we use an existing model that incorporates such correlations via the structure factor. Its predictions are shown to agree well with those of the Generalized Coherent Potential Approximation (GCPA) model, which is known to apply at high volume fractions, including the close packing limit, but does not explicitly account for disorder correlation. Within the transparency band, attenuation is found to be dominated by absorption rather than scattering. Measurements of the frequency dependence of the absorption coefficient reveal significant deviations from conventional models, challenging the current understanding of acoustic absorption in dense granular media.
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All authors Arnaud Tourin, Yamil Abraham, Marie Palla, Arthur Le Ber, Romain Pierrat, Nicolas Benech, Carlos Negreira, Xiaoping Jia
Statistical Mechanics · Cross-listed from hep-th
Locating the Ising CFT via the ground-state energy on the fuzzy sphere
Kay Joerg Wiese
We locate the phase-transition line for the Ising model on the fuzzy sphere from a finite-size scaling analysis of its ground-state energy. Our strategy is to write the latter as $E_{GS}(N_m)/N_m = E_{0} + E_1 /N_m + E_{3/2}/N_m^{3/2}+ ...$, and to search for a minimum of $ \chi:=E_{3/2}/E_0$ as a function of the couplings. Conformal perturbation theory predicts that around a CFT, $\chi= \chi_{\rm min} + \sum_i \lambda_i^2 N_m^{-\omega_i} + O(\lambda^3)$, where $\lambda_i$ are the couplings associated to perturbations of operators with dimension $\Delta_i$, and $\omega_i = d-\Delta_i$. This procedure finds the critical curve of [PRX 13 (2023) 021009] and their sweet spot with good precision. Varying two coupling constants allows us to extract the correction-to-scaling exponent $\omega$ associated to the two leading scalars $\epsilon$, and $\epsilon'$. We find similar results when normalizing by the gap to the stress tensor $T$ or first parity-odd operator $\sigma$ instead of $E_0$.
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Statistical Mechanics
Restoring detailed balance in non-Hermitian Markov processes
Tim Van Wesemael, Gilberto Nakamura, Jan Baetens et al. (+3 more)
Stochastic processes out-of-
equilibrium often involve asymmetric contributions that break detailed balance and lead to non-monotonic
entropy production, limiting thermodynamic interpretations and inference techniques. Here we use Dyson maps to restore monotonic
entropy growth in those processes, allowing the use of standard tools from statistical physics, providing a general and computationally tractable method applicable to a broad class of Markovian systems.
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All authors Tim Van Wesemael, Gilberto Nakamura, Jan Baetens, Odemir M. Bruno, Alexandre S. Martinez, Christophe Deroulers
Soft Condensed Matter
Self-Consistent Fourier-Tschebyshev Representations of the First Normal Stress Difference in Large Amplitude Oscillatory Shear
Nicholas King, Eugene Pashkovski, Reid Patterson et al. (+2 more)
Large Amplitude Oscillatory Shear (LAOS) is a key technique for characterizing nonlinear viscoelasticity in a wide range of materials. Most research to date has focused on the shear stress response to an oscillatory strain input. However, for highly elastic materials such as
polymer melts, the time-varying first normal stress difference $N_1(t;\omega,\gamma_0)$ can become much larger than the shear stress at sufficiently large strains, serving as a sensitive probe of the material's nonlinear characteristics. We present a
Fourier-Tschebyshev framework for decomposing the higher-order spectral content of the $N_1$ material functions generated in LAOS. This new decomposition is first illustrated through analysis of the second-order and fourth-order responses of the quasilinear Upper Convected Maxwell model and the fully nonlinear Giesekus model. We then use this new framework to analyze experimental data on a viscoelastic silicone
polymer and a thermoplastic polyurethane melt. Furthermore, we couple this decomposition with the recently developed Gaborheometry strain sweep technique to enable rapid and quantitative determination of the $N_1$ material function from experimental normal force data obtained in a single sweep from small to large strain amplitudes. We verify that asymptotic connections between the oscillatory shear stress and $N_1$ in the quasilinear limit are satisfied for the experimental data, ensuring self-consistency. This framework for analyzing the first normal stress difference is complementary to the established framework for analyzing the shear stresses in LAOS, and augments the content of material-specific data sets, hence more fully quantifying the important nonlinear viscoelastic properties of a wide range of soft materials.
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All authors Nicholas King, Eugene Pashkovski, Reid Patterson, Paige Rockwell, Gareth H. McKinley
Statistical Mechanics
Deep Learning of the Biswas-Chatterjee-Sen Model
J. F. Silva Neto, D. S. M. Alencar, L. T. Brito et al. (+5 more)
We investigate the critical properties of kinetic continuous opinion dynamics using deep learning techniques. The system consists of $N$ continuous
spin variables in the interval $[-1,1]$. Dense neural networks are trained on
spin configuration data generated via kinetic Monte Carlo simulations, accurately identifying the critical point on both square and triangular
lattices. Classical unsupervised learning with principal component analysis reproduces the magnetization and allows estimation of critical exponents. Additionally, variational autoencoders are implemented to study the phase transition through the loss function, which behaves as an order parameter. A correlation function between real and reconstructed data is defined and found to be universal at the critical point.
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All authors J. F. Silva Neto, D. S. M. Alencar, L. T. Brito, G. A. Alves, F. W. S. Lima, A. Macedo-Filho, R. S. Ferreira, T. F. A. Alves