Mesoscale and Nanoscale Physics
Anomalous metallic phase and reduced critical current in superconducting nanowires due to inverse proximity effect
G. M. Oliveira, G. O. Steffensen, I. Casal Iglesias et al. (+7 more)
Superconductor-to-metal transitions (SMTs) are key probes of mesoscopic superconductivity, but their interpretation can be complicated by device geometry and measurement conditions. Here, we study epitaxial InAs-Al nanowires and show that metallic contacts induce an inverse proximity effect (IPE), creating weak spots in the
superconductor that strongly suppress the critical current and give rise to an anomalous metallic phase. Using transport measurements supported by Usadel theory, we demonstrate that this phase originates from the contact-induced weakening of superconductivity together with Joule heating, rather than intrinsic material properties. Our findings reveal an overlooked observer effect in mesoscopic
superconductors and provide essential guidance for interpreting SMTs and for designing devices based on these systems.
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All authors G. M. Oliveira, G. O. Steffensen, I. Casal Iglesias, M. Gomez, A. Ibabe, T. Kanne, J. Nygard, R. Aguado, A. Levy Yeyati, E. J. H. Lee
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Phononic Casimir Effect in Planar Materials
Pablo Rodriguez-Lopez, Dai-Nam Le and Lilia M. Woods
The Phononic Casimir effect between planar objects is investigated by deriving a formalism from the
quantum partition function of the system following multiscattering approach. This fluctuation-induced coupling is mediated by
phonons modeled as an effective elastic medium. We find that excitations with three types of polarizations arise from the resolved boundary conditions, however the coupling is dominated by only one of these degrees of freedom due to exponential suppression effects in the other two. The obtained scaling laws and dependence on materials properties and temperature suggest effective pathways of interaction control. Scenarios of materials combinations are envisioned where the Phononic Casimir effect is of similar order as the standard Casimir interaction mediated by electromagnetic fluctuations.
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Mesoscale and Nanoscale Physics
Theory of single-photon emission from neutral and charged excitons in a polarization-selective cavity
Luca Vannucci and Niels Gregersen
Single-
photon sources based on neutral or charged
excitons in a
semiconductor quantum dot are attractive resources for photonic
quantum computers and simulators. To obtain indistinguishable
photons, the source is pumped on resonance with polarized
laser pulses, and the output is collected in orthogonal polarization. However, for sources featuring vertical emission of light, 50% of the emitted
photons are unavoidably lost in this way. Here, we theoretically study the
quantum dynamics of an
exciton embedded in an asymmetric vertical cavity that favors emission in a specific polarization. We identify the configuration for optimal state initialization and demonstrate a path toward near-unity polarized efficiency. We also derive simple analytical formulas for the
photon output in each polarization as a function of the Purcell-enhanced emission rates, which shed light on the physical mechanism behind our results.
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Materials Science
Realization of polytype heterostructures via delicate structural transitions from a doped-Mott insulator
Yanyan Geng, Manyu Wang, Shumin Meng et al. (+9 more)
Transition metal dichalcogenides (TMDs) host multiple competing structural and electronic phases, making them an ideal platform for constructing polytype
heterostructures with emergent
quantum properties. However, controlling phase transitions to form diverse
heterostructures inside a single
crystal remains challenging. Here, we realize vertical/lateral polytype
heterostructures in a hole-doped Mott
insulator via thermal-annealing-induced structural transitions. Raman spectroscopy, atomic force microscopy (AFM) and scanning Kelvin probe force microscopy (SKPM) confirm the coexistence of T-H polytype
heterostructures. Atomic-scale scanning tunneling microscopy/spectroscopy (STM/STS) measurements reveal the transparent effect in 1H/1T vertical
heterostructures, where the charge density wave (CDW) of the underlying 1T-layer superposes on the top 1H-layer under positive bias. By systematically comparing 1T/1H and 1T/1T interfaces, we demonstrate that the metallic 1H-layer imposes a Coulomb screening effect on the 1T-layer, suppressing the formation of CDW domain walls and forming more ordered electronic states. These results clarify the interfacial coupling between distinct
quantum many-body phases and establish a controllable pathway for constructing two-dimensional polytype
heterostructures with tunable electronic properties.
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All authors Yanyan Geng, Manyu Wang, Shumin Meng, Shuo Mi, Chang Li, Huiji Hu, Jianfeng Guo, Rui Xu, Fei Pang, Wei Ji, Weichang Zhou, Zhihai Cheng
Soft Condensed Matter · Cross-listed from physics.chem-ph
Enhanced particle diffusion in fluctuating binary environments
Fivos Perakis, Takeshi Kawasaki and Shinji Saito
We investigate single-particle
diffusion in a two-state Langevin model where the friction coefficient randomly switches between low-friction (
liquid-like) and high-friction (glassy-like) states. The dynamics are governed by the ratio between the friction switching time $\tau$ and the intrinsic velocity relaxation time $\tau_0$. For fast switching ($\tau/\tau_0 \lesssim 1$) the motion is homogeneous and Brownian, whereas for slow switching ($\tau/\tau_0 \gg 1$) the particle exhibits intermittent dynamics and an enhanced
diffusion coefficient. Analysis of the single-particle overlap function $Q(t)$ and the dynamic susceptibility $\chi_4(t)$ reveals decoupling of the
diffusion coefficient from the average friction upon cooling, which coincides with increasing temporal dynamic heterogeneity. This minimal model provides a transparent framework for understanding single-particle transport in media with fluctuating local mobility, including supercooled
liquids and phase-separated soft materials.
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Superconductivity
Intrinsic Second-Order Topological Superconductors with Tunable Majorana Zero Modes
Xiao-Jiao Wang, Yijie Mo, Zhi Wang et al. (+2 more)
Dirac semimetals, with their protected Dirac points, present an ideal platform for realizing intrinsic topological superconductivity. In this work, we investigate superconductivity in a two-dimensional, square-
lattice nonsymmorphic Dirac semimetal. In the normal state near half-filling, the
Fermi surface consists of two distinct pockets, each enclosing a Dirac point at a time-reversal invariant momentum ($\textbf{X}=(\pi,0)$ and $\textbf{Y}=(0,\pi)$). Considering an on-site repulsive and nearest-neighbor attractive interaction, we use self-consistent mean-field theory to determine the ground-state pairing
symmetry. We find that an even-parity,
spin-singlet $d_{x^{2}-y^{2}}$-wave pairing is favored as it gives rise to a fully gapped superconducting state. Since the pairing amplitude has opposite signs on the two Dirac
Fermi pockets, the superconducting state is identified as a second-order topological
superconductor. The hallmark of this topological phase is the emergence of Majorana zero modes at the system's boundaries. Notably, the positions of these Majorana modes are highly controllable and can be manipulated simply by tailoring the boundary sublattice terminations. Our results highlight the promise of nonsymmorphic Dirac semimetals for realizing and manipulating Majorana modes.
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All authors Xiao-Jiao Wang, Yijie Mo, Zhi Wang, Zhigang Wu, Zhongbo Yan
Mesoscale and Nanoscale Physics
Topological Pseudospin Hall Effect and Multi-frequency Corner Modes in Kagome-based Lattices
Shenglong Guo, Qinhui Jiang, Yuma Kawaguchi et al. (+2 more)
Topological phases and modes, including pseudospin-
Hall-selective edge transport and corner states, provide robust control of wave propagation and modal confinement in classical wave platforms. Under a tight-binding framework, we theoretically investigate two
lattice designs derived from the kagome
lattice. These extended kagome
lattices support a series of localized modes, including pseudospin-
Hall-like topological edge states and corner modes in different bandgaps and frequencies, which were not only achieved under lower
lattice symmetries than Wu-Hu
lattices, but also enable more degrees of freedom in topological and localized modes. By introducing two types of extended kagome
lattices with different topological properties, multiple interesting phenomena, including newly emerged multiple groups of corner states, parametric tunable pseudospin
Hall effect, and type-II corner states without long-range interactions, are found in theoretical models, which are possible and viable to achieve in artificial classical systems such as photonic, acoustic, or electrical
circuits.
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All authors Shenglong Guo, Qinhui Jiang, Yuma Kawaguchi, Bo Li, Mengyao Li
Soft Condensed Matter
X-ray photon correlation spectroscopy of hydrated lysozyme at elevated pressures
Milla Åhlfeldt, Maddalena Bin, Anita Girelli et al. (+12 more)
Pressure provides a powerful parameter to control the
protein conformation state, which at sufficiently high values can lead to unfolding. Here, we investigate the effects of increasing pressure up to $0.4$ GPa on hydrated lysozyme
proteins, by measuring the nanoscale stress relaxation induced and probed by X-rays. Structural and dynamical information at elevated pressures was obtained using X-ray
photon correlation spectroscopy (XPCS) in combination with a diamond anvil
cell (DAC). The dynamical analysis revealed a slowing down of the system up to $0.2$ GPa, followed by a re-acceleration at $0.4$ GPa. A similar non-monotonic behavior was observed both in the Porod and Kohlrausch-Williams-Watts (KWW) exponents, consistently indicating a crossover between $0.2$ and $0.4$ GPa. These findings suggest the presence of pressure-induced structural changes that impact
protein collective stress-relaxation as the system transitions from a jammed state to an elastically driven regime. These results may be relevant for a deeper understanding of
protein stability under compression as well as for practical high-pressure technologies, including food processing and pharmaceutical applications.
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All authors Milla Åhlfeldt, Maddalena Bin, Anita Girelli, Iason Andronis, Aigerim Karina, Nimmi Das Anthuparambil, Fiona Berner, Tobias Eklund, Louisa E. Kraft, Aliaksandr Leonau, Fabian Westermeier, Michael Sprung, Christian Gutt, Katrin Amann-Winkel, Fivos Perakis
Quantum Gases
Sachdev-Ye-Kitaev physics from the Hubbard model: A Floquet engineering approach
Charles Creffield, Fernando Sols, Marco Schirò et al. (+1 more)
The Sachdev-Ye-Kitaev (SYK) model has attracted widespread
attention due to its relevance to diverse areas of physics, such as high temperature superconductivity, black holes, and
quantum chaos. The model is, however, extremely challenging to realize experimentally. In this work, we show how a particular form of Floquet engineering, termed “kinetic driving”, effectively eliminates single-particle processes and creates quasi-random all-to-all interactions when applied to models of Hubbard type. For the specific case of the Bose-Hubbard model, we explicitly verify that the driven system indeed reproduces SYK physics by direct comparison of the spectral form factor and out-of-time ordered correlation functions (OTOCs). Our findings indicate that a cold-atom realization of kinetic driving – achieved through modulation of hopping amplitudes in an optical
lattice – offers a practical and accurate platform for
quantum simulation of the SYK model.
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All authors Charles Creffield, Fernando Sols, Marco Schirò, Nathan Goldman
Materials Science
Ultrasensitive Anti-Stokes Luminescence Thermometry in Transition Metal Dichalcogenide Monolayers
Sharada Nagarkar, Fahrettin Sarcan, Elanur Hut et al. (+4 more)
Accurate temperature mapping at the nanoscale is a critical challenge in modern science and technology, as conventional methods fail at these dimensions. To address this challenge, we demonstrate a highly sensitive nanothermometer using anti-Stokes photoluminescence, also known as photoluminescence upconversion (UPL), in monolayer tungsten disulfide ($\mathrm{WS_2}$). Leveraging the direct band gap and strong
exciton-
phonon coupling in the two-dimensional monolayers, we achieve an exceptional relative sensitivity above $4\%\,\mathrm{K}^{-1}$ across the 300 K to 425 K range, ranking it among the best-performing materials reported. A strong resonantly enhanced UPL is observed, confirming the central role of optical
phonons in the upconversion mechanism. Furthermore, we introduce a new analytical model to quantitatively describe the UPL process, taking into account the interplay of
phonon populations, bandgap narrowing, and substrate effects, which predicts resonant temperatures and provides a framework with broad applicability to any material exhibiting an anti-Stokes photoluminescence response. To demonstrate its use as a high-resolution optical thermometer, we map a $20\,^{\circ}\mathrm{C}$ thermal gradient across a $20\,\mu\mathrm{m}$ long monolayer with a spatial resolution of $1\,\mu\mathrm{m}$. With its high sensitivity, strong signal, and excellent reproducibility, our work establishes monolayer transition metal dichalcogenide as a leading platform for non-invasive thermal sensing in advanced microelectronic and biological systems.
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All authors Sharada Nagarkar, Fahrettin Sarcan, Elanur Hut, Emiliano R. Martins, Stuart A Cavill, Thomas F. Krauss, Yue Wang
Superconductivity
Phase-sensitive non-reciprocal transport in high-temperature superconductor
Guo-Liang Guo and Xin Liu
We propose the superconducting diode effect (SDE) in a planar s-wave/d-wave/s-wave Josephson junction as a direct phase-sensitive probe of the d-wave pairing function in high-Tc
superconductors. Asymmetric interface coupling breaks inversion
symmetry and induces a spontaneous Pi/2 phase difference, thereby breaking time-reversal
symmetry without a
magnetic field. In this TRS-broken state, the SDE emerges when single-Cooper-pair tunneling is enabled at the s-d interfaces, with its polarity and efficiency controllable by rotating the d-wave crystallographic orientation or perturbing its intrinsic C4
symmetry. Our results reveal a robust link between nonreciprocal Josephson transport and pairing
symmetry, establishing the SDE as a powerful diagnostic tool for high-Tc
superconductors and a tunable element for superconducting electronics.
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Strongly Correlated Electrons
Interplay of phonons, intertwined density waves, and induced spin density wave in trilayer nickelates Pr4-xLaxNi3O10
Sonia Deswal, Dibyata Rout, Nirmalya Jana et al. (+3 more)
Lattice degrees of freedom (DoF) play a central role in correlated electron systems, strongly influencing the dynamics of the underlying charge carriers and
spin excitations. In nickelates, understanding the role of
lattice is essential to unravel the interplay between charge, orbital, and
spin degree of freedom in giving rise to various emergent phenomena reported recently. Here, we investigate the phononic DoF in a series of trilayer nickelates, namely Pr4-xLaxNi3O10 (where x = 0, 0.4, 1, 2, 3.6, and 4) using temperature and polarization dependent Raman scattering measurements. Our in-depth analysis of the
phonon evolution with temperature and doping, gives interesting insights into the behaviour of these materials. All these systems undergo a metal-to-metal transition (TMMT), characterized by the development of intertwined
spin and charge density waves, with the
spin density wave preceding the charge density wave. These transitions manifest as pronounced anomalies in
phonon self-energy parameters i.e. peak frequency and linewidth in the vicinity of the metal-to-metal transition. Several
phonon modes show dramatic change (nearly an order of magnitude for some modes) in their softening rates across the TMMT, highlighting the sensitivity of the
lattice dynamics to
spin and charge order. These findings emphasize the crucial role of
lattice DoF in mediating correlated ground states in layered nickelates.
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All authors Sonia Deswal, Dibyata Rout, Nirmalya Jana, Koushik Pal, Surjeet Singh, Pradeep Kumar
Soft Condensed Matter
Nanoscale Protein Diffusion in Supercooled Cryoprotectant Solutions
Maddalena Bin, Anita Girelli, Mariia Filianina et al. (+15 more)
Vitrification during cryopreservation requires a quantitative understanding of
protein transport in deeply supercooled cryoprotectant solutions, yet direct measurements at molecular length scales remain scarce. Here, we combine X-ray
Photon Correlation Spectroscopy (XPCS) and small-angle X-ray scattering (SAXS) to investigate ferritin
diffusion in glycerol-water mixtures from ambient conditions down to 210 K. The measured
diffusion coefficients reveal that ferritin retains a higher mobility upon cooling than expected from hydrodynamic scaling based on measurements of larger silica reference tracers, with the difference emerging below approximately 230 K. A minimal fluctuating-friction model reproduces the observed relative enhancement in
diffusion, illustrating how local variations in the effective friction can give rise to such behavior. These measurements provide direct experimental
benchmarks for future theoretical and simulation studies aimed at understanding molecular transport in deeply supercooled
liquids approaching the glass transition.
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All authors Maddalena Bin, Anita Girelli, Mariia Filianina, Mario Reiser, Sharon Berkowicz, Milla Åhlfeldt, Michelle Dargasz, Sonja Timmermann, Jaqueline Savelkouls, Takeshi Kawasaki, Shinji Saito, Federico Zontone, Yuriy Chushkin, Fajun Zhang, Frank Schreiber, Michael Paulus, Christian Gutt, Fivos Perakis
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Dynamic Modulation of Long Range Photon Magnon Coupling
Alban Joseph, Mawgan A. Smith, Martin P. Weides et al. (+1 more)
Evidence of non-hermitian behavior has been recently demonstrated in cavity magnonics, including the emergence of mode level attraction and exceptional points in spectroscopic measurements. This work demonstrates experimental evidence of time-domain dynamics of
magnon-
photon systems that are coupled through a long-range interaction (i.e. remote coupling) exhibiting level attraction mediated by an auxiliary mode. We directly observe the temporal
evolution of dissipatively coupled cavity-
magnon modes, where heavily damped transmission line modes mediate the interaction. Our frequency-domain measurements confirm the predicted level attraction, while time-domain ring-down measurements reveal the characteristic signatures of dissipative coupling dynamics. Our approach offers in situ tunability over the dissipative coupling strength, including complete suppression, without requiring physical modifications to the experimental setup, providing a versatile platform for exploring tunable, non-Hermitian physics.
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All authors Alban Joseph, Mawgan A. Smith, Martin P. Weides, Rair Macêdo
Mesoscale and Nanoscale Physics
Emergent Quantum Valley Hall Insulator from Electron Interactions in Transition-Metal Dichalcogenide Heterobilayers
Palash Saha and Michał Zegrodnik
We explore the emergence of topological phases in moiré MoTe$_2$/WSe$_2$
bilayer, highlighting the crucial role of
spin-orbit coupling and Coulomb interactions at two holes per moiré unit
cell \(v = 2\). Our analysis uncovers robust
Quantum Valley
Hall Insulating (QVHI) phase and reveals that long-range interactions alone can mediate the interlayer electron tunneling, generating topologically nontrivial bands even in the absence of the corresponding single-particle hopping. Additionally, we show that in the case of band mixing terms originating both from the interaction and single particle physics a competition between topological states realizing $s$-$wave$ and $p\pm ip$-$wave$
symmetries can appear. Moreover, within the considered theoretical framework, we present that by introducing a small Zeeman field, one can lift the band inversion in one of the valleys. This leads to a
Quantum Anomalous
Hall Insulating (QAHI) state with the topological gap opening in a single valley and the other being topologically trivial.
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Statistical Mechanics
Detection of Mpemba effect through good observables in open quantum systems
Pitambar Bagui, Arijit Chatterjee and Bijay Kumar Agarwalla
The Mpemba effect refers to the anomalous relaxation of a
quantum state that, despite being initially farther from
equilibrium, relaxes faster than a closer counterpart. Detecting such a
quantum Mpemba effect typically requires full knowledge of the
quantum state during its time
evolution, which is an experimentally challenging task since state
tomography becomes exponentially difficult as system size increases. This poses a significant obstacle in studying Mpemba effect in complex many-body systems. In this work, we demonstrate that this limitation can be overcome by identifying suitable observables that signal rapid relaxation. Moreover, as long as the system equilibrates to a known unique steady-state, it is possible to fully detect the occurrence of
quantum Mpemba effect just by measuring the observable for known state preparations. Our approach thus significantly reduces experimental complexity and offers a practical route for observing the
quantum Mpemba effect in complex and extended multi-
qubit setups.
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Soft Condensed Matter
Adaptive hydrogels with spatiotemporal stiffening using pH-modulating enzymes
Natascha Gray, Zoe Grämiger, André R. Studart et al. (+1 more)
Biological systems achieve adaptive mechanical responses through reaction-
diffusion processes that couple chemical wave propagation to structural transitions. Although synthetic hydrogels with enzymatic reactions offer a platform for replicating such autonomous behavior, the mechanistic principles governing chemomechanical transduction remain poorly understood. Here, we present a glucose oxidase-embedded polyacrylamide-alginate hydrogel with slower transduction kinetics that enable independent resolution of chemical waves and mechanical adaptation. Enzymatic pH waves propagate at 15-44 um/min, triggering calcium-mediated alginate crosslinking through pH-responsive calcium-EDTA dissociation. Independent tracking of chemical and mechanical waves reveals that mechanical wavefronts (12 um/min) lag behind chemical propagation, establishing transduction as the rate-limiting step in this chemomechanical coupling. Remarkably, the enzymatic system must continuously supply chemical energy to both propagate the chemical wave and drive ongoing mechanical transitions, imposing energetic costs on reaction-
diffusion beyond kinetic constraints alone. Our adaptive system achieves up to 2.1-fold increase in stiffness and enables autonomous conversion of localized stimuli into system-wide mechanical responses. These mechanistic insights establish design principles for engineering adaptive materials with predictable spatiotemporal control in soft robotics and biomedical applications.
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All authors Natascha Gray, Zoe Grämiger, André R. Studart, Rafael Libanori
Mesoscale and Nanoscale Physics
Real-time imaging of quasiparticle dynamics at a topological defect in an electronic crystal
Yevhenii Vaskivskyi, Jaka Vodeb, Igor Vaskivskyi et al. (+1 more)
Defects formed during nonequilibrium self-assembly of
quantum matter can dominate its emergent properties. Their macroscopic manifestations are typically characterised as noise, but their internal dynamics remain largely experimentally inaccessible. Making significant advances into the investigation of the microscopic degrees of freedom of such defects, we use fast scanning tunnelling microscopy to resolve, in real time, both internal and global dynamics of a mesoscopic Y-junction defect in an electronic
crystal created through self-assembly after a local electromagnetic perturbation. We directly track individual electron rearrangements on millisecond timescales and map spatially localised telegraph noise characteristic of a two-level system. The phase and amplitude of these fluctuations are correlated with the observed charged particle trajectories, revealing a direct connection between collective order-parameter dynamics and microscopic charge motion. We model the dynamics as arising from the interplay of local Coulomb correlations, non-local configurational constraints and hybridised amplitude - phase collective modes bound to the junction. These constraints, together with the non-trivial broken
symmetries of the defect, protect long-lived local quasiparticle configurations against external perturbations. Our results establish fast scanning tunnelling microscopy as a means of probing the internal dynamics of metastable
quantum defects and reveal how microscopic correlations and collective modes are intertwined within topologically non-trivial structures in electronic
crystals.
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All authors Yevhenii Vaskivskyi, Jaka Vodeb, Igor Vaskivskyi, Dragan Mihailovic
Strongly Correlated Electrons
Kaganov-Lifshitz-Tanatarov theory for tilted Dirac-cone materials: anisotropic heating from uniform light
Navinder Singh Bathinda, Bharathiganesh Devanarayanan, Sruthi Sudhakaran et al. (+2 more)
We point out that in the tilted Dirac cone materials the non-
equilibrium (hot) electron relaxation with
phonons is anisotropic in the Brillouin zone. It means that there is a preferential heating of the
lattice degrees of freedom in the specific directions of the Brillouin zone, in particular, in the direction opposite to the tilt velocity in the model considered by us. This observation will have novel consequences: (1) With pump-probe spectroscopy applied to a given tilted Dirac cone material an anisotropic relaxation would lead to a transient anisotropic heating which can further lead to a transient Seebeck effect as transient thermal gradients would exist in the specific directions of the BZ, and (2) this direction of anisotropic heating can be controlled by controlling the direction of the tilt velocity which can be externally tuned by the application of an external pressure. We foresee novel applications of this effect in ultrafast sensor applications involving transient heating effects. This is equivalent to inducing a transient Seebeck effect by just shinning light on a tilted Dirac cone material!
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All authors Navinder Singh Bathinda, Bharathiganesh Devanarayanan, Sruthi Sudhakaran, Jalaja Pandya, Saptarshi Mandal
Strongly Correlated Electrons
The exchange coupling of a Wigner dimer
Daniele Lagasco and Zoran Ristivojevic
We study the exchange coupling in small Wigner
crystals confined to one-dimensional space. In particular we concentrate on the simplest nontrivial case of two electrons in a box potential and calculate analytically the energy splitting between the lowest spatially symmetric and antisymmetric states, which is a relevant energy scale for the
magnetic properties of the system. In the approximation of a fixed center of mass coordinate, the splitting decays exponentially with the square root of the distance between the electrons at the leading order. We show that the subleading exponential correction significantly increases the splitting and thus becomes crucial in order to describe correctly the exact numerical data for system sizes that are not astronomically large. Two methods of calculation of the energy splitting are developed. The first is based on the analysis of the exact solution that can be expressed in terms of the Whittaker functions. It applies at all values of the short-distance cutoff played by the width of one-dimensional wire that regularizes the Coulomb potential. The second method is based on the quasiclassical (or Wentzel-Kramers-Brillouin) approximation, which applies only for sufficiently large values of the cutoff. The two methods give identical result in the overlapping region. As a side result, our study gives the energy splitting in a triangular double well potential of inverse “M” shape.
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Materials Science
Rational regulation strategies of interstitial localized electrons in electride: A density functional theory study
L. Zhang, D. Wang, H. Wang et al. (+4 more)
As a class of electron-rich materials, electrides demonstrate promising applications in many fields. However, the required high pressure restricts the practical applications to some extent. This study reveals that the unique feature of electride, i.e., the localization of interstitial electrons, can be greatly enhanced and tuned by self-defective doping, applying tensile/compressive stress, or shear stress. Moreover, the requirement of orbital orthogonality between the valence and core electron wave functions, as well as the Pauli exclusion principle, should be the driven force for the electron interstitial localization; and the exertion of external pressure modifies the available space to accommodate the electronic wave functions, thus enhances the interstitial localization. These discoveries lay down the ground for searching for promising electrides that are practicable at ambient conditions.
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All authors L. Zhang, D. Wang, H. Wang, J. Li, Y. F. Wang, Q. Wu, Hua Y. Geng
Quantum Gases · Cross-listed from quant-ph
Efficient Simulation of the 2D Hubbard Model via Hilbert Space-Filling Curve Mapping
Ashkan Abedi, Vittorio Giovannetti and Dario De Santis
We investigate tensor network simulations of the two-dimensional Hubbard model by mapping the
lattice onto a one-dimensional chain using space-filling curves. In particular, we focus on the
Hilbert curve, whose locality-preserving structure minimizes the range of effective interactions in the mapped model. This enables a more compact
matrix product state (MPS) representation compared to conventional snake mapping. Through systematic
benchmarks, we show that the
Hilbert curve consistently yields lower ground-state energies at fixed bond dimension, with the advantage increasing for larger system sizes and in physically relevant interaction regimes. Our implementation reaches clusters up to $32\times32$ sites with open and periodic boundary conditions, delivering reliable ground-state energies and correlation functions in agreement with established results, but at significantly reduced computational cost. These findings establish space-filling curve mappings, particularly the
Hilbert curve, as a powerful tool for extending tensor-network studies of strongly correlated two-dimensional
quantum systems beyond the limits accessible with standard approaches.
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Statistical Mechanics
Using precision coefficients on recurrence times and integrated currents to lower bound the average dissipation rate
Alberto Garilli and Diego Frezzato
For continuous-time Markov jump processes on irreducible networks with time-independent rate constants, we employ a transition-based formalism to express the long-time precision of a single integrated current over an observable channel in terms of precisions of the recurrence times of the forward and backward jumps, and of an effective affinity that captures the thermodynamic driving on that channel. This leads to a general inequality that, similarly to the well-known Thermodynamic Uncertainty Relation (TUR), links the stationary
entropy production rate with the fluctuations of an integrated current, but also incorporates the statistics of the forward and backward recurrence times. Such inequality can be saturated in less restrictive conditions than the TUR, and potentially offers new opportunities for the optimization and design of biological and chemical out-of-
equilibrium systems at the nanoscale.
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Statistical Mechanics
Relationship between Heider links and Ising spins
Zdzisław Burda, Maciej Wołoszyn, Krzysztof Malarz et al. (+1 more)
We show that the Heider model with an external field is equivalent, in the limit of structural balance, to the Ising model with nearest-neighbor interactions without an external field. More precisely, we claim that the signs of the Heider relations that maintain structural
equilibrium in the system can be represented as nearest neighbor Ising
spin products. We demonstrate this explicitly for a complete graph and provide a general argument for an arbitrary graph. A consequence of the equivalence is that the system of balanced Heider states undergoes a phase transition, inherited from the Ising model, at a critical value of the social field at which the fluctuations of edge magnetization are maximal.
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All authors Zdzisław Burda, Maciej Wołoszyn, Krzysztof Malarz, Krzysztof Kułakowski
Materials Science
Competing excitonic couplings as origin of mimicked phase transitions in zinc-phthalocyanine single crystals
Lisa Schraut-May, Sebastian Hammer, Luca Nils Philipp et al. (+9 more)
The optical properties of molecular
crystals are largely determined by the excitonic coupling of neighboring molecules. This coupling is extremely sensitive to the arrangement of adjacent molecular units, as their electronic interaction is defined by the relative orientation of the individual transition dipole moments and their wave function overlap. Hence, the optical properties, such as fluorescence, are usually highly anisotropic and good indicators of structural changes during the variation of intensive thermodynamic parameters like temperature or pressure. Here, we discuss the peculiar though archetypical case of $\beta$-phase zinc-phthalocyanine: In single
crystals, we report a sudden change of spectral emission with temperature from a broad, unpolarized Frenkel-
exciton type luminescence to a narrow, highly polarized superradiance-like fluorescence below 80 K. Surprisingly, we find that there is no sign of a discrete structural phase transition in this temperature regime. To understand this apparent contradiction, we perform polarization-, temperature- and time-dependent photoluminescence measurements along different crystallographic directions to fully map the emission characteristics of the
crystal-
exciton. By means of ab-initio calculations on a density functional theory level we conclude that our observations are consistent with a dimer
exciton model when considering thermalized electronic states. As such, our study presents a representative case study on a well-established molecular material class demonstrating that caution is advised when attributing discrete changes in electronic observables to a structural phase transition. As we show for zinc-phthalocyanine in its $\beta$-phase modification, slowly varying excitonic couplings and thermal redistribution of excitations can mimic the same signatures attributed to a structural phase transition.
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All authors Lisa Schraut-May, Sebastian Hammer, Luca Nils Philipp, Krzysztof Radacki, Gabriele Tauscher, Helena Hollstein, Kilian Strauß, Martin Kamp, Heinrich Schwoerer, Holger Braunschweig, Roland Mitric, Jens Pflaum
Materials Science
Electric-Field and Doping-Induced Non collinear Magnetic Interactions in Monolayer Ti$_2$Si
Dimple Rani, Gayatri Panda, Subrata Jana et al. (+1 more)
Two-dimensional (2D) silicides are an emerging class of materials whose
magnetic and relativistic properties remain largely unexplored. Using first-principles calculations, we investigate how electric-field modulation and transition-metal doping influence the
magnetic exchange, magnetocrystalline anisotropy, and antisymmetric Dzyaloshinskii-Moriya interaction (DMI) in monolayer Ti2Si. Pristine Ti2Si is a dynamically stable
ferromagnetic metal with in-plane anisotropy and centrosymmetric bonding, which suppresses DMI even under strong perpendicular electric fields. To overcome this
symmetry constraint, we introduce Pt and Co substitution at Ti sites. Co enhances the
magnetic exchange, whereas Pt provides strong
spin orbit coupling (SOC), and the combined chemical asymmetry breaks inversion
symmetry sufficiently to induce a sizable DMI. A Wannier-based tight-binding model captures the orbital-resolved superexchange pathways and reveals a clear hierarchy between a weak Si-mediated channel and a dominant Pt-mediated interlayer channel. First-principles calculations confirm that the Pt-assisted pathway governs the magnitude and sign of the total DMI. Among all configurations, Pt0.5CoTi0.5Si exhibits the strongest
chiral interaction, with its intralayer and interlayer contributions favoring opposite rotation senses, namely counterclockwise (CCW) and clockwise (CW). Our results establish chemically engineered Ti2Si monolayers as a promising platform for realizing and tuning
chiral magnetic textures in 2D silicides.
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All authors Dimple Rani, Gayatri Panda, Subrata Jana, Prasanjit Samal
Superconductivity
Hao Chu, Haotian Zhang and Zhili Zhang
As pointed out by Nambu&Goldstone, continuous
symmetry breaking gives rise to gapless bosonic excitation. In
superconductors, continuous local U(1) gauge
symmetry is broken. The gapless excitation thus created is the collective phase mode of a
superconductor. In 1962, Anderson pointed out that Coulomb interaction lifts this gapless mode to the superconducting
plasma frequency. Therefore, in a superconducting fluid there are no bosonic excitations below the Cooper pair binding energy. Anderson mechanism also implies that the massless
photon becomes massive in a
superconductor. It provides a microscopic theory for dissipationless charge transport (with Landau criterion for superfluidity) and the Meissner effect in a
superconductor. Jumping to particle physics, to explain why the gauge
bosons for electroweak interaction are massive,
Higgs, Englert, Kibble et al. proposed the existence of the
Higgs field. This matter field couples to the massless W, Z
bosons and generates mass via the
Higgs mechanism. Due to their conceptual similarities, these two mechanisms are referred to as the Anderson-
Higgs mechanism. In 2013, the detection of the
Higgs boson provided the final proof for the
Higgs hypothesis decades after its conception. The amplitude mode of a
superconductor, which corresponds to the
Higgs boson in the above analogy, is referred to as the
Higgs mode. Its spectroscopic detection has also remained elusive for decades. In recent years, the development of ultrafast techniques enabled an effective approach for studying the mode. Here, we introduce the
Higgs mode from a perspective of why
superconductors superconduct and review the recent development in
Higgs spectroscopy, particularly in the field of nonlinear terahertz spectroscopy. We discuss the novel insights that may be learnt from these studies for future high-Tc superconductivity and correlated materials research in general.
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Soft Condensed Matter
Harnessing swarms for directed migration of interacting active particles via optimal global control
Chiara Calascibetta, Laëtitia Giraldi and Jérémie Bec
This study investigates the use of global control strategies to enhance the directed migration of swarms of interacting self-propelled particles confined in a channel. Uncontrolled dynamics naturally leads to wall accumulation, clogging, and band formation due to the interplay between self-organization and confinement. This work explores whether a uniform global control, such as
magnetic field acting on all particles, can optimize collective transport. Using a discrete Vicsek-like model, it is found that simple global
alignment controls, optimized via reinforcement learning, efficiently suppress unfavorable configurations and significantly increase the net particle flux along a prescribed channel direction. These results highlight that coarse, system-level observations are sufficient to achieve near-optimal control, even in regimes with strong fluctuations or partial ordering.
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Materials Science · Cross-listed from cs.LG
Modeling and Inverse Identification of Interfacial Heat Conduction in Finite Layer and Semi-Infinite Substrate Systems via a Physics-Guided Neural Framework
Wenhao Sha and Tienchong Chang
Heat transfer in
semiconductor devices is dominated by chip and substrate assemblies, where heat generated within a finite chip layer dissipates into a semi-infinite substrate with much higher thermophysical properties. This mismatch produces steep interfacial temperature gradients, making the transient thermal response highly sensitive to the interface. Conventional numerical solvers require excessive discretization to resolve these dynamics, while physics-informed neural networks (PINNs) often exhibit unstable convergence and loss of physical consistency near the material interface. To address these challenges, we introduce HeatTransFormer, a physics-guided
Transformer architecture for interface-dominated
diffusion problems. The framework integrates physically informed spatiotemporal sampling, a Laplace-based activation emulating analytical
diffusion solutions, and a mask-free
attention mechanism supporting bidirectional spatiotemporal coupling. These components enable the model to resolve steep gradients, maintain physical consistency, and remain stable where PINNs typically fail. HeatTransFormer produces coherent temperature fields across the interface when applied to a finite layer and semi-infinite substrate configuration. Coupled with a physics-constrained inverse strategy, it further enables reliable identification of three unknown thermal properties simultaneously using only external measurements. Overall, this work demonstrates that physics-guided
Transformer architectures provide a unified framework for forward and inverse modeling in interface-dominated thermal systems.
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Materials Science
Precise Twist Angle Determination in twisted WSe2 via Optical Moiré Phonons
Nicolai-Leonid Bathen, Thorsten Deilmann, Ana Senkić et al. (+7 more)
Twisted
bilayers of transition metal dichalcogenides (TMDC) form moiré superlattices resulting in moiré minibands in momentum space and hosting localized
excitons in real space. While moiré superlattices provide access to Mott-Hubbard physics, their energy potential landscape and electronic correlations are highly sensitive to fluctuations of the twist angle, disorder and
lattice reconstructions. However, fast and non-invasive experimental access to local twist angle and its spatial variations is challenging. Here, we systematically correlate twist angle variations of twisted WSe2
bilayers across micrometer length scales using a combined lateral force microscopy (LFM) and a micro- Raman spectroscopy approach. These measurements uncover lateral variations in the twist angle by more than 1{\deg} across length scales relevant to optical and transport measurements. We demonstrate that twist angles in the range of 3{\deg} < $\alpha$ < 12{\deg} show distinct Raman response from scattering on optical moiré
phonons allowing twist angle determination with high precision and sub-micrometer spatial resolution under ambient conditions. These modes are particularly sensitive in the low-angle twist regime, predicted to host emergent
quantum phases. Our results establish micro-Raman spectroscopy of optical moiré
phonons as a rapid, non-invasive probe to determine twist angle and to screen local twist angle variations with a precision better than $\pm$ 0.3{\deg} and a lateral resolution below one micrometer. This methodology is also applicable to fully hBN-encapsulated
heterostructures.
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All authors Nicolai-Leonid Bathen, Thorsten Deilmann, Ana Senkić, Hendrik Lambers, Rami Dana, Kenji Watanabe, Takashi Taniguchi, Frances M. Ross, Julian Klein, Ursula Wurstbauer