Mesoscale and Nanoscale Physics
Tailoring Germanium Heterostructures for Quantum Devices with Machine Learning
Patrick Del Vecchio, Kevin Rossi, Giordano Scappucci et al. (+1 more)
Germanium (Ge)
quantum wells are emerging as versatile platforms for
quantum devices, supporting high-quality
spin qubits and integration with superconducting leads. These applications benefit from strong intrinsic
spin-orbit interaction (SOI), enabling efficient electrical control and engineering of
spin degrees of freedom. The most advanced Ge/SiGe
heterostructures to date, based on compressively strained Ge channels within strain-relaxed silicon-germanium (SiGe) barriers, exhibit weak SOI due to the heavy-hole character of the wave function, posing challenges for
spin-based
quantum devices and requiring complex device designs for fast
qubit manipulation. In this work, we demonstrate that concrete
heterostructure modifications can overcome these limitations, enhancing SOI by up to three orders of magnitude. Specifically, we propose to enrich unstrained Ge channels by localized, strained silicon spikes. Leveraging a multi-objective
Bayesian optimization, we optimize the spike profile to maximize SOI, while ensuring compatibility with current epitaxial growth processes and robustness against realistic variations of growth parameters. Our
heterostructure substantially enhances device performance, yielding up to two orders of magnitude higher
quantum-dot
spin qubit quality factors than state-of-the-art materials. We also predict GHz-scale
spin splittings for hybrid superconducting Andreev
spin qubits. These novel Ge
heterostructures with engineered Si concentration profiles can open pathways to scalable
quantum and spintronic applications.
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All authors Patrick Del Vecchio, Kevin Rossi, Giordano Scappucci, Stefano Bosco
Other Condensed Matter · Cross-listed from quant-ph
Entanglement of two optical emitters mediated by a terahertz channel
Yanis Le Fur, Diego Martín-Cano and Carlos Sánchez Muñoz
Quantum technologies in the terahertz (THz) require a coherent interface between addressable
qubits and THz
quantum channels – a capacity that so far, remains largely underdeveloped. Here, we propose and demonstrate the generation of steady-state
entanglement between polar
quantum emitters, mediated by THz
photons. We exploit strong visible-light driving of the emitters to create Rabi-split dressed eigenstates whose energy separation can be optically tuned into the THz regime. The polar nature of the emitters activates THz transitions within these eigenstates, allowing them to couple to a THz photonic mode that induces collective dissipative dynamics. A coherent driving and control of these effective THz emitters is achieved by using a sideband optical drive with detuning close to the THz transition frequency. The resulting interplay of collective dissipation and driving activates a mechanism to generate steady-state
entanglement with high values of the concurrence ($C>0.9$), attainable under experimentally feasible parameters. Crucially, both coherent manipulation and
quantum state
tomography are implemented entirely through optical means, avoiding direct THz control and detection. This establishes a hybrid visible-THz
quantum interface in which a THz channel mediates
qubit-
qubit entanglement (a key operational requirement for THz
quantum technologies) while remaining optically accessible.
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Mesoscale and Nanoscale Physics
Disorder-induced crossover from phase-averaging to mode-mixing regimes in magnetic domain walls of a second-order topological insulator
Dong Zhou and Zhe Hou
We investigate electronic transport across a
magnetic domain wall (DW) in a three-dimensional (3D) second-order topological
insulator subject to Anderson disorder. In the clean limit, the DW hosts two co-propagating one-dimensional (1D) topological edge states that act as the two arms of an effective Aharonov-Bohm (AB) interferometer, inducing a sinusoidal conductance oscillation. Upon the introduction of disorder, the AB oscillations are suppressed, while a half-quantized plateau of $0.5 e^2/h$ for the ensemble-averaged conductance emerges. Notably, within this plateau, the conductance fluctuation exhibits a distinctive two-step plateau structure, with values of $\sim 0.35 e^2/h$ at moderate disorder, followed by a second plateau at $\sim0.29 e^2/h$ under strong disorder. By developing theoretical frameworks that account for the random-phase interference and inter-mode mixing of the two arms, we identify the first fluctuation plateau as a signature of the phase-averaging regime (PAR) and the second as a signature of the mode-mixing regime (MMR). Furthermore, we show that, in the PAR the conductance follows a U-shaped beta distribution, while it evolves into a uniform distribution in the MMR. The Fano factor associated with shot noise is also computed, which exhibits a similar two-step plateau structure at $1/4$ and $1/3$, corresponding to the PAR and MMR, respectively. Our work provides a clear demonstration of the disorder-induced crossover from PAR to MMR, and highlights the crucial role of second-order conductance cumulants in identifying these transport regimes. The results suggest disorder-engineering as a powerful route for controlling electronic transport across DW-based devices.
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Soft Condensed Matter
Self-phoretic colloids in chiral active fluids
Michalis Chatzittofi, Yuto Hosaka, Andrej Vilfan et al. (+1 more)
Autonomous and driven transport in
chiral active fluids have been shown to exhibit features that cannot be accommodated within the classical formulation of fluid mechanics, due to the role of odd viscosity. We generalize the theory of phoretic active matter to fluid environments with odd viscosity and derive expressions for translational and rotational self-propulsion velocities in the case of a spherical swimmer with arbitrary activity and mobility surface profiles. We discuss specific examples of chemically active colloids with axisymmetric and non-axisymmetric coatings and the resulting interplay between
symmetry and chirality. Our results can be applied to study the emergent collective dynamics of phoretic particles in fluid media with broken time-reversal and parity
symmetries.
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All authors Michalis Chatzittofi, Yuto Hosaka, Andrej Vilfan, Ramin Golestanian
Superconductivity
Effect of Mn Substitution on Superconductivity in PrFeAs(O,F): Role of Magnetic Impurities
Priya Singh, Konrad Kwatek, Tatiana Zajarniuk et al. (+5 more)
We investigate Mn substitution at the Fe site in PrFe1-xMnxAsO0.7F0.3 (0 to 0.1) using structural, Raman, density functional theory (DFT), transport, and
magnetic measurements. X-ray diffraction and Raman analyses confirm preferential Mn incorporation into the FeAs planes, accompanied by
lattice expansion and suppression of Fe-related vibrational modes. Electrical transport reveals a systematic decrease of the superconducting transition temperature from 48 K (x = 0) to complete suppression at x = 0.1, together with low-temperature resistivity upturns evolving toward insulating-like behavior. Magnetization and magnetotransport measurements show degradation of superconducting coherence, critical current density, upper critical field, and
vortex activation energy with increasing Mn content. The results demonstrate that Mn acts as an efficient
magnetic impurity, strongly perturbing the electronic and
magnetic environment of the FeAs layers. Comparative analysis indicates relatively enhanced robustness of superconductivity in the Pr-based system, highlighting the role of rare-earth-dependent electronic correlations in
impurity effects.
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All authors Priya Singh, Konrad Kwatek, Tatiana Zajarniuk, Taras Palasyuk, Cezariusz Jastrzębski, A. Szewczyk, Michał Wierzbicki, Shiv J. Singh
Materials Science
Self-consistent evaluation of the Berry connection for Wannier functions
Martin Thümmler, Thomas Lettau, Alexander Croy et al. (+2 more)
The Berry connection is a gauge-dependent quantity frequently used to describe the optical response of solids. Its evaluation requires a k-derivative with respect to the
cell periodic-part of the Bloch-functions and is commonly calculated in the Wannier basis by using overlap
matrices of
cell-periodic parts of Bloch-functions at neighboring k-points. So far, all proposed interpolation schemes for the Berry connection do not account for the
matrix structure of the overlap
matrices explicitly but treat the
matrix elements as independent, or only distinguish between diagonal and off-diagonal entries. In this work, we propose a self-consistent interpolation scheme based on the
matrix logarithm resulting in a strongly improved accuracy. Furthermore, we discuss how the basis set incompleteness of the bands used in the ab-initio calculation imposes constraints on the accuracy. We quantify the basis incompleteness based on the singular values of the overlap
matrices and relate it to the invariant part of the spread functional $\Omega_\mathrm{I}$ of the Wannier functions. Numerical calculations for monolayer MoS$_2$ and bulk Si demonstrate that the proposed interpolation scheme is much less sensitive to the Wannierization details and leads to an improved quality of the velocity
matrix and the optical conductivity.
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All authors Martin Thümmler, Thomas Lettau, Alexander Croy, Ulf Peschel, Stefanie Gräfe
Soft Condensed Matter · Cross-listed from physics.bio-ph
Shaping nematic order in bacterial films with single-cell resolution patterning
Matthias Le Bec, Guillem Pérez Martín, Cameron Boggon et al. (+7 more)
Bacterial colonies composed of elongated
cells form active nematic fluids that spontaneously self-organise into ordered domains of aligned
cells and exhibit self-generated chaotic flows powered by
cell growth. While their dynamics have attracted significant
attention, the role of initial conditions remains largely unexplored due to a lack of precise patterning methods. Here, we harness the precision of capillary assembly to pattern Bacillus subtilis endospores into arrays with controlled positions and orientations at single-
cell resolution. Upon germination and growth of
cell chains, we quantify the dynamics and morphologies of the resulting bacterial films. While orthogonally seeded spores lead to chaotic dynamics, seeding them with parallel orientations yields films with high nematic order across millimetres, which subsequently synchronously buckle upon further growth. Our observations are captured by numerical simulations and a model that describes the buckling dynamics starting from the mechanical properties of individual filaments. By programming local
cell orientation with single-
cell precision, we finally harness nematic
alignment to create macroscopic bacterial films with local optical anisotropy, via structural colouration and light polarisation. Our findings demonstrate that initial conditions play a key role and offer exciting opportunities to control the spatio-temporal organization of bacterial assemblies towards addressing open biological questions and realizing living materials with tailored properties.
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All authors Matthias Le Bec, Guillem Pérez Martín, Cameron Boggon, Yiyao Hu, Leonardo Puggioni, Rosa Heydenreich, Alexander Mathys, Luca Giomi, Eleonora Secchi, Lucio Isa
Mesoscale and Nanoscale Physics
Stable Wave-Function Zeros Indicate Exciton Topology
Yoonseok Hwang, Henry Davenport and Frank Schindler
Excitons are bound states of electrons and holes whose band
topology arises from an interplay between the
topology of the underlying electronic bands and the structure of the electron-hole interaction. In crystalline solids,
symmetry representations and topological invariants of the conduction and valence bands constrain the structure of the
exciton envelope wave function. In particular, we show that crystalline
symmetry can enforce stable zeros in the
exciton wave function. These occur at high-
symmetry momenta, including the optically accessible total momentum p=0. We work out how the stable zeros constrain both the relative
exciton-band
topology (the difference of
exciton and non-interacting topological invariants) and the relative band
topology (the difference of valence and conduction band invariants), all without requiring detailed knowledge of the band structure or interactions. We establish these results for two-band
excitons in inversion- and rotation-symmetric systems in one and two dimensions, where the relevant topological invariants are the Berry phase in one dimension and the Chern number (modulo the rotation order) in two dimensions. In two dimensions, the
exciton Chern number itself can also be constrained by zero patterns.
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Superconductivity
Two-gap to Single-gap Transition and Two-dome-like Superconductivity in Alkali-Metal Intercalated Bilayer PdTe2
Yu-Lin Han, Shu-Xiang Qiao, Kai-Yue Jiang et al. (+5 more)
PdTe2 has been synthesized with controllable thickness down to the monolayer limit. Based on first-principles calculations within the fully anisotropic Migdal-Eliashberg framework, this work reveals that alkali-metal intercalation markedly enhances the weak superconductivity of
bilayer PdTe2, boosting the transition temperature from 1.4 K to 5.0 -13.5 K and yielding a two-dome-like
evolution of Tc. Rubidium intercalation induces the highest Tc of 13.5 K, which can be further increased to 14.5 K under biaxial tensile strain. The strain-dependent
evolution of Tc also exhibits a two-dome-like behavior, reflecting the interplay between strain-induced band structure modifications and electron-
phonon coupling (EPC). Moreover, a systematic correlation is identified between interlayer interaction and superconducting gap. Lithium intercalation induces a distinct two-gap state, whereas intercalants with larger atomic radii (Na, K, Rb, and Cs) drive the system into a single-gap character. The two-gap to single-gap transition originates from the modulation of interlayer coupling through intercalation-induced interlayer expansion. In addition, pristine and Li/Na-intercalated
bilayers exhibit nontrivial band
topology, suggesting that layered PdTe2 provides a promising platform for realizing the coexistence of superconductivity and nontrivial
topology. These results provide detailed anisotropic insights into EPC and offer viable pathways for enhancing Tc and achieving diverse properties in layered PdTe2 systems.
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All authors Yu-Lin Han, Shu-Xiang Qiao, Kai-Yue Jiang, Jie Zhang, Bao-Tian Wang, Ping Zhang, C. S. Ting, Hong-Yan Lu
Mesoscale and Nanoscale Physics
DC Cryogenic Modeling of Open-Source SkyWater 130 nm MOSFETs at 77 K Using BSIM4
F.Beall, A.Rimal, O.Seidel et al. (+7 more)
Cryogenic applications in high-energy physics (HEP) demand reliable, low-power CMOS electronics capable of operating at
liquid nitrogen temperatures (77 K). The open-source SkyWater 130nm (SKY130) CMOS process has previously been shown to operate at temperatures as low as 4 K making it a promising candidate for HEP applications. In this work, we characterize and model SKY130 low-threshold voltage transistors at 77 K, which is a temperature commonly used in modeling applications for
liquid argon detectors. DC characteristic measurements were performed at both room temperature and
liquid nitrogen temperature. We created a cryogenic modeling approach to produce a SPICE-compatible, isothermal BSIM4-based model for select transistor sizes at 77 K. The resulting model agrees with data at 77 K with an average error on the order of 20% (relative RMS). However, our models had a systematic overprediction specifically for the measured pMOS devices at the lowest measured drain bias. Due to the open-source nature of SKY130, we have made our models publicly available on Github. We hope this work will continue the trend for democratizing
circuit design at cryogenic temperatures in high-energy physics by enabling open access to accurate CMOS device models at 77 K.
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All authors F.Beall, A.Rimal, O.Seidel, Y.Mei, A.D.McDonald, I. Parmaksiz, V.A.Chirayath, J.Asaadi, D.Braga, J.B.R.Battat
Materials Science
Emergence of a non-bulk hexagonal Fe$_2$S$_2$ single layer via phase transformation
Affan Safeer, Wejdan Beida, Felix Oberbauer et al. (+8 more)
Two-dimensional materials can stabilize
crystal structures that are absent from their bulk counterparts, offering opportunities for materials design. Here, we report the synthesis of a previously unknown hexagonal Fe$_2$S$_2$ single layer with $\beta$-CuI structure, a buckled layer of two vertically stacked FeS honeycomb
lattices, realized by thermally induced transformation of single layer mackinawite grown on
graphene/Ir(111). In situ scanning tunneling microscopy and low-energy electron diffraction reveal a transition from a tetragonal to a hexagonal
lattice accompanied by distinct morphological and electronic signatures. The hexagonal Fe$_2$S$_2$ forms reproducibly upon annealing and represents a new structural motif within the Fe-S material family. First-principles calculations identify the $\beta$-CuI structure as most consistent with experiment. The calculations suggest that on-site Coulomb interactions and
magnetic order are relevant to understanding the stability of the new 2D Fe-S compound. The preferred nucleation of single-layer mackinawite, despite being energetically disfavored, is speculated to result from its low edge energy, analogous to the 3D case. Our results establish Fe$_2$S$_2$ as a platform for exploring structural polymorphism in two dimensions and demonstrate that reduced dimensionality can stabilize
crystal structures not accessible in bulk materials.
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All authors Affan Safeer, Wejdan Beida, Felix Oberbauer, Nicolae Atodiresei, Gustav Bihlmayer, Max Wolfertz, Chiara Schlichte, Wouter Jolie, Stefan Blügel, Jeison Fischer, Thomas Michely
Statistical Mechanics · Cross-listed from physics.chem-ph
Reaction-Diffusion Processes with Surface Autocatalysis
Denis S. Grebenkov
Autocatalytic processes underlie diverse systems in which replication is triggered at interfaces, including heterogeneous catalysis on solid substrates, enzyme activity at membranes, viral infections, biofilm growth, and spatially structured ecosystems. In a typical scenario, particles move in a bulk medium and interact with surface regions, where they may either disappear or reproduce through branching, splitting or fission. Here, we develop a general theoretical framework to understand such surface-mediated autocatalytic processes. We show that the interplay between loss and replication at surfaces gives rise to rich population dynamics. For this purpose, we derive a renewal-type nonlinear integral equation for the generating function of the population size, providing access to its full probability distribution and statistical moments. We further establish an equivalent description in terms of a Fokker-Planck equation with nonlinear Robin-type boundary conditions that encode surface reactions. Our results identify distinct dynamical regimes and universal scaling laws, and provide a unified framework to predict when surface activity promotes extinction or explosive growth. These findings offer quantitative insight into catalytic efficiency, metabolic regulation, and population persistence in spatially heterogeneous environments.
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Statistical Mechanics · Cross-listed from quant-ph
Zejian Li, Anna Delmonte and Rosario Fazio
We propose a semiclassical framework for solving open
quantum dynamics in driven-dissipative
spin systems. Our method consists of generalized
spin-wave approximations tailored to describing
quantum trajectories unravelled from the master equation, and generically applies to regimes beyond the reach of conventional
spin-wave theories, including short-range interactions and local
quantum jumps, enabling the efficient simulation of large-scale interacting
spins. We illustrate the versatility of our framework by studying a variable-range driven-dissipative Ising model on a 2D
lattice. When the dissipation acts along the drive axis, we find a continuous phase transition breaking the $\mathbb{Z}_2$
symmetry, and demonstrate that the interaction range, when tuned from fully-connected to nearest-neighbour, profoundly alters the universality class of the criticality. With the dissipation along the interaction axis, we show the emergence of a first-order transition. Demonstrated with both state-
diffusion and
quantum-jump types of trajectory dynamics, our framework provides a powerful toolbox for the efficient semiclassical description of non-
equilibrium dynamics and many-body phases in
spin systems.
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Strongly Correlated Electrons
Dynamical mean-field theory for dense spin systems at finite temperature
Przemysław Bieniek, Timo Gräßer and Götz S. Uhrig
In recent years, a method for computing
spin dynamics at infinite temperature (spinDMFT) was developed. It utilizes the ideas of dynamical mean-field theory for
fermions: single-site approximation and a self-consistency condition to approximate time-dependent
spin correlations. In this work, we develop a crucial extension of the method to systems at finite temperature, able to compute imaginary-time correlations and thermodynamical quantities. We
benchmark the method by comparison to results in finite-size systems, obtaining very good agreement with correlations in a random-coupling system, good agreement for a
ferromagnetic system and large discrepancies in the case of an antiferromagnet. We note the appearance of
ferromagnetic order in the method. We discuss possible extensions and potential applications of the approach.
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Mesoscale and Nanoscale Physics
Magnetic-flux tunable electronic transport through domain walls in a three-dimensional second-order topological insulator
Zhe Hou and Ai-Min Guo
The three-dimensional (3D) topological
insulators (TIs), hosting topologically protected helical surface states, can be promoted into second-order TIs when a diagonal Zeeman term, typical of
magnetic doping, is introduced. The latter hosts exotic
chiral one-dimensional (1D) topological hinge states (THSs). In this paper, we investigate the electronic transport of THSs through a
magnetic domain wall (DW) in a 3D TI nanowire. Due to the sign reversal of the out-of-plane magnetization across the DW, four 1D topological boundary states, residing on the edge of the DW, arise and form an enclosed loop mediating the counterpropagating THSs. By applying a uniform
magnetic field parallel to the nanowire, we obtain a perfect sinusoidal Aharonov-Bohm oscillation in the two-terminal conductance $G$, formulated by $G=\frac{e^2}{2h} \left[ 1- \cos(\pi \Phi/\Phi_0) \right]$, with $\Phi$ the
magnetic flux through the DW and $\Phi_0 = h/2e$ the flux
quantum. Applying a phenomenological scattering
matrix approach, we explain this novel Aharonov-Bohm oscillation perfectly, and attribute the constructive (destructive) interference of transmission at $\Phi = \Phi_0$ (0) to the $\pi$-
spin rotation of the THSs traveling through the DW. Extending our study to a double-DW junction, where the central region has antiparallel magnetization to the leads, we observe Fabry-Pérot oscillations, in which the conductance minima are tuned by the
magnetic flux. Our findings open a new avenue for finely controlling the
quantum transport of THSs in
magnetic systems using
magnetic flux, and provide a faithful way for detecting THSs in experiments.
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Superconductivity
Superconductivity induced by altermagnetic spin fluctuations in high-pressure MnB$_4$
Danylo Radevych, Mercè Roig, Daniel F. Agterberg et al. (+1 more)
Recent experiments found superconductivity in nonmagnetic MnB$_4$ with a high critical temperature ($T_{c}$) reaching 14 K at 158 GPa. However, ab initio calculations of the electron-
phonon coupling predict a $T_{c}$ below 1 K, suggesting that a conventional mechanism cannot explain this phenomenon. In this Letter, we find that MnB$_4$ is close to an altermagnetic instability in density-functional theory calculations. We propose that the superconductivity is driven by altermagnetic
spin fluctuations. To verify the pairing
symmetry, we have constructed a two-orbital tight-binding model, where boron states at the
Fermi level are integrated out. Using this model, we identify an extended-$s$
symmetry as the leading pairing instability. If confirmed, this will be the first reported case of superconductivity driven by altermagnetic
spin fluctuations.
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All authors Danylo Radevych, Mercè Roig, Daniel F. Agterberg, Igor I. Mazin
Statistical Mechanics
Dean-Kawasaki fluctuating hydrodynamics for backscattering hard rods
Mrinal Jyoti Powdel
We study a system of backscattering hard rods in one dimension. Contrary to the usual ballistic hard rods, these hard rods flip the sign of their velocities with a rate $\gamma$. This leads to the decay of the odd moments of velocity while preserving the even moments: the number of conserved quantities in the system becomes half. The introduction of the flipping rate $\gamma$ is an integrability-breaking perturbation, and this leads to a change in the transport properties in the system. We show using a Dean-Kawasaki fluctuating hydrodynamic formulation that the unequal space-time correlation of the normal mode phase space densities attains a diffusive form at late times. Also, we show that for $t \gg 1/\gamma$, the two-time density-density correlation of mass densities spreads in a diffusive manner, and for $t \ll 1/\gamma$, the correlation spreads ballistically, for a background state given by the Boltzmann distribution. Our results present an elegant framework to study systems where integrability is broken by a
stochastic noise.
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Mesoscale and Nanoscale Physics · Cross-listed from physics.optics
Modulation of Spin Angular Momentum of Emission in Symmetric 1D Plasmonic Crystals by Cathodoluminescence
Yuxin Yang, Izzah Machfuudzoh, Qiwen Tan et al. (+1 more)
The
spin angular momentum (SAM) of light has become a cornerstone of numerous photonic applications, including optical communication and
chiral photonics. Because SAM is inherently associated with circularly polarized light (CPL), the ability to modulate CPL in a controlled and efficient manner is essential not only for advancing fundamental studies of light-matter interactions but also for enabling next-generation photonic technologies. However, such modulation is commonly realized by structurally
chiral systems, which inherently limits the feasibility of dynamic tuning. Here, we demonstrate that one-dimensional plasmonic
crystals (1D PlCs), despite their structural
symmetry, can serve as a platform for controllable CPL generation. By employing an electron beam in scanning transmission electron microscopy (STEM), we coherently excite transition radiation and emission from 1D PlC modes. Their interference produces energy- and momentum- (emission angle-) resolved CPL, which clearly reveals its dispersion and spatial dependence at the nanoscale, providing direct guidance for its manipulation and offering insights into the design of plasmonic devices including the phase information. Furthermore, interference with surface plasmon polariton scattering at the structural boundary enables the efficiency modulation of CPL generation via the excitation position along the terrace.
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All authors Yuxin Yang, Izzah Machfuudzoh, Qiwen Tan, Takumi Sannomiya
Soft Condensed Matter · Cross-listed from physics.flu-dyn
Unified Hydrodynamic Analogue of Aharonov-Bohm and Lense-Thirring Effects
Aditya Singh, Joseph Samuel, Chien-chia Liu et al. (+3 more)
We show that surface waves in a draining-bathtub
vortex provide a hydrodynamic realization of both Aharonov-Bohm phase shifts and Lense-Thirring frame dragging within a single system. A static time transformation maps the flat (2+1)-dimensional wave equation onto the convected shallow-water equation, yielding an effective vector potential set by the background flow. In this geometry, the circulation defines a global phase holonomy that controls wave structure. Traveling waves exhibit wavefront dislocations characteristic of Aharonov-Bohm scattering, while standing-wave superpositions produce nodal patterns that rotate at an angular velocity fixed by the circulation, providing a direct analogue of frame dragging. For noninteger circulation, the problem is naturally defined on the universal cover, ensuring single-valued partial-wave solutions. Experiments on a controlled
vortex confirm these predictions and establish a laboratory platform in which topological phase and inertial effects, central to gauge and gravitational physics, emerge from a measurable velocity field.
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All authors Aditya Singh, Joseph Samuel, Chien-chia Liu, Luiza Angheluta, Andrés Concha, Mahesh Bandi
Mesoscale and Nanoscale Physics
Nihad Abuawwad and Samir Lounis
Chiral spin textures such as skyrmions have attracted considerable
attention due to their nontrivial
topology, chirality, stability at the nanoscale, and potential for low-power spintronic devices. The recent discovery of intrinsic magnetism in van der Waals (vdW) materials and the ability to engineer their
heterostructures has opened a new platform to study and manipulate such textures. In these layered systems, atomically sharp interfaces, strong
spin-orbit coupling, and tunable
symmetry breaking provide unique opportunities to stabilize and control
chiral magnetic states. This review summarizes the fundamental mechanisms underlying the formation of
chiral spin textures in vdW
heterostructures, including the roles of exchange interactions,
magnetic anisotropy, Dzyaloshinskii-Moriya interaction, and dipolar effects. We highlight key experimental advances in the observation and manipulation of
chiral textures, discuss their dynamical properties and transport signatures, while overviewing selected theoretical investigations. Finally, we outline current challenges and future directions toward realizing robust, room-temperature
chiral spin textures for practical spintronic technologies.
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Statistical Mechanics · Cross-listed from cs.AI
The CriticalSet problem: Identifying Critical Contributors in Bipartite Dependency Networks
Sebastiano A. Piccolo and Andrea Tagarelli
Identifying critical nodes in complex networks is a fundamental task in graph mining. Yet, methods addressing an all-or-nothing coverage mechanics in a bipartite dependency network, a graph with two types of nodes where edges represent dependency relationships across the two groups only, remain largely unexplored. We formalize the CriticalSet problem: given an arbitrary bipartite graph modeling dependencies of items on contributors, identify the set of k contributors whose removal isolates the largest number of items. We prove that this problem is NP-hard and requires maximizing a supermodular set function, for which standard forward greedy
algorithms provide no approximation guarantees. Consequently, we model CriticalSet as a coalitional game, deriving a closed-form centrality, ShapleyCov, based on the Shapley value. This measure can be interpreted as the expected number of items isolated by a contributor's departure. Leveraging these insights, we propose MinCov, a linear-time iterative peeling
algorithm that explicitly accounts for connection redundancy, prioritizing contributors who uniquely support many items. Extensive experiments on synthetic and large-scale real
datasets, including a Wikipedia graph with over 250 million edges, reveal that MinCov and ShapleyCov significantly outperform traditional baselines. Notably, MinCov achieves near-optimal performance, within 0.02 AUC of a
Stochastic Hill Climbing metaheuristic, while remaining several orders of magnitude faster.
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Superconductivity
Pairing mechanism and superconductivity in 1313 phase La$_3$Ni$_2$O$_7$
Cui-Qun Chen, Ming Zhang, Fan Yang et al. (+1 more)
Recently, the observation of superconductivity (SC) with $T_c$ $\approx$ 3.6 K in the pressurized 1313 La$_3$Ni$_2$O$_7$ has attracted considerable interest. Here, we systematically investigate the electronic properties and superconducting mechanism of 1313 La$_3$Ni$_2$O$_7$ using density functional theory plus dynamical mean-field theory (DFT+DMFT) and random phase approximation (RPA). Our DFT+DMFT calculations reveal that the single-layer (SL) subsystem exhibits nearly insulating behavior, with the $d_{z^2}$ orbital showing Mott physics, while the trilayer (TL) subsystem remains metallic. This indicates that SC primarily resides in the TL subsystem, whose Ni-$e_g$ orbitals are found to be hole-doped relative to bulk La$_4$Ni$_3$O$_{10}$. Based on DFT+DMFT-derived low-energy
Hamiltonian, RPA-based analysis yields an $s^{\pm}$-wave pairing
symmetry within the TL subsystem. Importantly, we identify two key factors that contribute to the significant suppression of $T_c$ in 1313 La$_3$Ni$_2$O$_7$ compared to bulk La$_4$Ni$_3$O$_{10}$. First, the hole doping in the TL subsystem, as established by DMFT, leads to a decreased pairing strength, as confirmed by RPA calculations – a trend resembling that in bulk La$_4$Ni$_3$O$_{10}$. Second, the SL subsystem acts as a bridge connecting adjacent superconducting TL subsystems, thereby forming an S-N-S Josephson junction. The resulting interlayer Josephson coupling governs the phase coherence between TL subsystems and further suppresses the global $T_c$. Combinedly, our findings suggest that the high-$T_c$ phase in the RP La$_3$Ni$_2$O$_7$ family should be attributed to the 2222 La$_3$Ni$_2$O$_7$ rather than the 1313 La$_3$Ni$_2$O$_7$.
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All authors Cui-Qun Chen, Ming Zhang, Fan Yang, Dao-Xin Yao
Strongly Correlated Electrons
Igor F. Herbut and Samson C.H. Ling
The internal low-energy
symmetry of the massless Lorentz-invariant Dirac
Hamiltonian in $2+1$ dimensions is known to be $O(2N)$, where $N$ is the number of two-component Dirac
fermions. Here we point out that there exists an analogous internal
symmetry of the single-particle quadratic-band-touching
Hamiltonian in two spatial dimensions, and it is the
unitary symplectic group, $USp(2N)$. All fermionic bilinears belong to one of the three small irreducible representations of this group. The interacting theory that respects the $USp(2N)$
symmetry and the spatial rotations is constructed and found to allow two independent interaction terms. When these interactions are infrared-relevant the
symplectic symmetry either remains preserved or becomes spontaneously broken to $USp(N) \times USp(N)$. The
symmetry in the
lattices such as honeycomb to infinite order in the dispersion's expansion in powers of local momentum is given by the overlap of the
symplectic and the orthogonal groups. We show that this overlap is $O(2N) \bigcap USp(2N) = U(N)$.
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Statistical Mechanics · Cross-listed from quant-ph
Quantum jump correlations in long-range dissipative spin systems via cluster and cumulant expansions
Giulia Salatino, Anna Delmonte, Zejian Li et al. (+2 more)
We characterize nonequilibrium phases in long-range dissipative
spin systems through the statistical properties of
quantum jump trajectories. While the average dynamics governed by the Lindblad master equation provides access to steady-state expectation values of order parameters, the
quantum trajectory framework reveals features encoded in the spatial and temporal correlations of detection events. Focusing on a model exhibiting a paramagnetic-to-
ferromagnetic phase transition, we investigate the full counting statistics of
quantum jumps using a tilted Lindbladian approach. We combine this with cluster mean-field and cumulant expansion techniques, which allow us to capture, respectively, the short- and long-range structure of jump correlations. In addition, we study the waiting-time distributions of detection events. We show that
quantum jump correlations display clear signatures of the underlying phases and reveal distinct dynamical features across the transition. Our results highlight the potential of trajectory-resolved observables as probes of collective behavior in open
quantum many-body systems and provide new insights into the role of long-range interactions in shaping nonequilibrium dynamics.
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All authors Giulia Salatino, Anna Delmonte, Zejian Li, Rosario Fazio, Alberto Biella
Statistical Mechanics
How to quantify long-time rotational motion in molecular systems
Romain Simon, Hadrien Bobas, François Villemot et al. (+2 more)
We show that all existing methods quantifying rotational motion in molecular fluids eventually have severe limitations in systems undergoing complex rotational motion characterized by slow, heterogeneous, or intermittent dynamics. This impacts in particular the study of rotational dynamics in molecular supercooled
liquids near their glass transition, as well as discussions of the decoupling between rotational and translational motion and violations of the Debye-Stokes-Einstein relation. We present a brief overview of existing methods and explain why none of them can accurately capture the
evolution of rotational dynamics from a diffusive fluid to an arrested solid, thus resolving inconsistent literature results. We then introduce an empirical method that efficiently solves all issues. We
benchmark our method devising a family of continuous time random walk models for rotational dynamics. Our method correctly quantifies the statistics of free and caged rotational motion, as well as non-Gaussian and non-Fickian rotational dynamics, and should allow a better characterization of dynamic heterogeneity in the rotational motion of supercooled molecular fluids.
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All authors Romain Simon, Hadrien Bobas, François Villemot, Jean-Louis Barrat, Ludovic Berthier
Mesoscale and Nanoscale Physics
Design optimization of flux concentrators for magnetic tunnel junctions-based sensors
Thomas Brun, Javier Rial, Lucia Risoli et al. (+6 more)
Miniaturized, ultra-sensitive and easily integrable magnetometers are needed for many applications, like space exploration or health monitoring. Achieving this goal requires a
magnetic sensor with high sensitivity and low noise. High sensitivity (>1000 %/mT) can be obtained by integrating high gain permalloy flux concentrators (FC). And reducing the
magnetic 1/f noise can be realized by increasing the number of
magnetic tunnel junctions (MTJs) in the air-gap of the FC. However, this is obtained at the expense of a wider air-gap and consequently a decrease of the
magnetic gain and thus of the sensitivity. In this paper, we explore a design optimization scheme in order to find the best trade-off between high FC gain and low
magnetic noise. To model the gain of the flux concentrator, we propose two complementary approaches; one is based on finite elements simulations of the FC gain where the influence of geometrical parameters of the air-gap is investigated. Then, in a second step, we propose an analytical formula consistent with all our simulations results and based on
magnetic reluctance. Finally, we derive an analytical model of the sensor detectivity from which we can extract the optimal sensor design which allows an improvement by three orders of magnitude of the performances compared to a single junction.
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All authors Thomas Brun, Javier Rial, Lucia Risoli, Johanna Fischer, Philippe Sabon, Guillaume Jannet, Matthieu Kretzschmar, Helene Bea, Claire Baraduc
Superconductivity
Controlled Manipulation of Intermediate State in a Type-I Superconductor
Xin-Sheng Gao, Qun Wang, Ya-Xun He et al. (+5 more)
The intermediate state of type-I
superconductors presents a classic paradigm of modulated pattern formation, arising from the competition between short-range attractive and long-range repulsive
vortex-
vortex interactions. However, direct visualization and, more importantly, active control over the
topology and dynamics of these flux structures have remained significant challenges, limiting our ability to manipulate them for fundamental studies and potential applications. Here, using low-temperature
magnetic force microscopy, we achieve direct imaging and controllable manipulation of the flux structures in a high-purity tantalum single
crystal. We systematically track the
evolution of flux morphology - from tubes to stripes - during flux penetration and expulsion, revealing a pronounced topological hysteresis originating from the
geometric barrier. Furthermore, we demonstrate precise local control by using the
magnetic tip to drag and merge individual flux tubes and to reconfigure entire stripe domains. Under global alternating current (AC) excitation, we discover a reversible stripe-grid-stripe transition, a dynamic reorganization driven by current-induced flux penetration and pinning effects. The corresponding phase diagram shows that the threshold current decreases with
magnetic field but increases with AC frequency. Our work establishes a pathway for active flux manipulation in type-I
superconductors, revealing rich dynamics and paving the way for flux-based superconducting devices.
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All authors Xin-Sheng Gao, Qun Wang, Ya-Xun He, Xing-Jian Liu, Jun-Han Zhang, Kang-Hong Yin, Jia-Ying Zhang, Jun-Yi Ge
Materials Science
Data-Driven Thermal and Mechanical Modeling of Defective Covalent Organic Frameworks
Aleksander Szewczyk, Leonardo Medrano Sandonas, David Bodesheim et al. (+2 more)
Covalent Organic Frameworks (COFs) are versatile two-dimensional (2D) materials for flexible electronics, catalysis, and sensing, owing to their tunable architectures and large surface areas. However, like most materials, COFs inevitably contain synthesis-induced defects, which-similar to
graphene-can strongly influence intrinsic properties, such as thermal transport and mechanical strength. To address this challenge, we have assessed the performance of a set of machine learning interatomic potentials (MLIP) capable of efficient large-scale simulations of COFs with
quantum accuracy. In doing so, QCOF models (
Quantum COF) were developed by tuning the state-of-the-art MACE architecture on an extensive
dataset of non-
equilibrium COF conformations generated from high-fidelity density functional theory calculations. The accuracy, computational efficiency,
memory footprint, and transferability to unseen chemical environments of these models were benchmarked against general-purpose MACE models and their fine-tuned variants. Our results show that an invariant QCOF model with a small descriptor dimensionality and cutoff outperforms all other models in most validation tasks, including scalability to large systems, force prediction in defective COFs, and
phonon dispersion calculations. The best-performing QCOF model was then used to run large-scale simulations of thermal conductivity for defective CTF-1 and COF-LZU1 systems via non-
equilibrium MD, revealing a more pronounced sensitivity of CTF-1 to structural defects. Stress-strain curves were also investigated, showing that the mechanical response remains nearly invariant at low defect densities, while asymmetric behaviour emerges at large strains. This work thus provides a foundation for the design of robust
quantum-informed MLIP for large-scale property simulations of defective of extended network materials.
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All authors Aleksander Szewczyk, Leonardo Medrano Sandonas, David Bodesheim, Bohayra Mortazavi, Gianaurelio Cuniberti
Materials Science
Intertwined charge density wave, tunable anti-dome superconductivity, and topological states in kagome metal VSn
Shu-Xiang Qiao, Ya-Ping Li, Jie Zhang et al. (+5 more)
These years, kagome materials with 1:1 stoichiometry have garnered increasing
attention, among which FeSn, CoSn, and FeGe have been the focus of current studies. However, all of them are
antiferromagnetic, thereby hindering the observation of superconductivity and other novel physical properties. Here, we predict a novel 1:1 kagome metal VSn, which is an intrinsic charge density wave (CDW) material. Interestingly, with increasing pressure or doping concentration, the CDW order is progressively suppressed, followed by the emergence of superconductivity characterized by a non-monotonic transition temperature that exhibits a rare anti-dome-shaped dependence. Above a critical threshold, a reentrance of the CDW phase occurs. The anti-dome superconductivity originates from the first hardening and then softening of
phonon modes, together with band reconstruction. Crucially, VSn retains nontrivial topological properties across the entire superconducting regime, a feature of paramount importance for realizing robust topological superconductivity. These intertwined CDW, superconductivity, and topological phenomena elucidate the correlations among multiple
quantum states in VSn. Therefore, this research paves the way for for designing 1:1 kagome superconducting topological metals and establishes a platform for exploring the interplay of multiple phases in kagome systems.
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All authors Shu-Xiang Qiao, Ya-Ping Li, Jie Zhang, Yi Wan, Na Jiao, Meng-Meng Zheng, Hong-Yan Lu, Ping Zhang
Materials Science · Cross-listed from eess.SY
Monolithically Integrated VO$_2$ Mott Oscillators for Energy-Efficient Spiking Neurons
Fabio Bersano, Cyrille Masserey, Vanessa Conti et al. (+6 more)
Brain-inspired non-Boolean computing and sensing enable energy-efficient, error-tolerant, and highly parallel information processing, yet their deployment remains limited by the lack of compact, scalable spiking hardware. Mott phase-transition materials offer a promising route because their abrupt
insulator-to-metal transitions enable
neuron-like thresholding and oscillations. Among them, vanadium dioxide (VO$_2$) is particularly attractive owing to its near-room-temperature transition, fast switching, and scalability. However, existing VO$_2$ neuristors rely on discrete components, limiting integration density. Here, we report monolithic back-end-of-the-line (BEOL) integration of one-transistor-one-VO$_2$-memristor (1T-1MR) spiking
neurons on a CMOS-compatible platform. VO$_2$ nanosheets are fabricated by pulsed-
laser deposition atop dielectrically isolated silicon-on-
insulator (SOI) p-type junctionless field-effect transistors (JLFETs) below 430 $^\circ$C. The architecture exhibits gate-tunable oscillations from 40 to 410 kHz in 60 nm-thin VO$_2$ devices with a 6 $\mu$m$^2$ active area, achieving 18 pJ per spike and 8 $\mu$W at room temperature, with potential for sub-3 $\mu$W operation. We uncover a non-monotonic dependence of oscillation frequency on bias current and temperature and analyze bias-dependent
stochastic firing, revealing the nonlinear physics of integrated VO$_2$ thin-film memristors. Finally, we demonstrate voltage-controlled oscillator functionality and on-chip resistive coupling between two nano-oscillators mediated by a JLFET. These results establish a pathway toward dense, energy-efficient, monolithically integrated Mott neuromorphic hardware compatible with future computing and spiking sensing systems.
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All authors Fabio Bersano, Cyrille Masserey, Vanessa Conti, Andrea Iaconeta, Niccolo' Martinolli, Ehsan Ansari, Anna Varini, Igor Stolichnov, Adrian Mihai Ionescu