Statistical Mechanics
Quantum Monte Carlo in Classical Phase Space with the Wigner-Kirkwood Commutation Function. II. Diagonal Approximation in Position Space
Phil Attard
A third order expansion for Wigner-Kirkwood commutation function, a complex function in classical phase space that accounts for the Heisenberg uncertainty relation, is approximated and integrated over momentum to give a real function in position configuration space. Metropolis Monte Carlo computer simulation results are given for
liquid Lennard-Jones $^4$He below 10\,K.
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Materials Science
Non-collinear Altermagnetic Phases in the Mott Insulator NiS$_2$
Mengli Hu, Mikel I. Iraola, Paul McClarty et al. (+2 more)
Altermagnets (A$\ell$Ms) constitute a novel family of
magnetic materials characterized by the absence of net magnetization and the presence of
spin-polarized band structures. Whereas A$\ell$M phases were initially proposed in collinear structures, the recently discovered noncollinear
chiral A$\ell$Ms stand out for their distinct hedgehog
spin texture and multifunctionality in spintronics. In this work, we deepen the characterization of these systems by constructing a Landau theory for noncollinear achiral A$\ell$Ms. Furthermore, we demonstrate that the achiral
symmetry of the
crystal is reflected in the
spin texture in reciprocal space, which presents only spatial-even multipoles. These multipoles, distinguished from those in collinear A$\ell$Ms via the high-order secondary order parameters, can couple to many phenomena such as the
spin Hall effect and piezomagnetic effect. To exemplify our theory, we study the noncollinear achiral magnet NiS$_2$ within the framework of altermagnetism, showcasing both
spin Hall and piezomagnetic effects in a prototypical correlated Mott
insulator that provides an ideal platform to explore the interplay between strong electronic correlations,
crystal symmetry, and altermagnetic
spin textures. Interestingly, altermagnetism emerges in two
magnetic ordered phases of NiS$_2$ upon lowering the temperature. The non-collinearity strengthens the robustness of A$\ell$M order, as the anti-ferromagnetism induced by the strong correlations will not impose effective time-reversal
symmetry as in the collinear case. Our results suggest non-collinear achiral A$\ell$Ms as a promising platform for spintronics applications due to the potential to achieve various
spin textures with different
magnetic orders.
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All authors Mengli Hu, Mikel I. Iraola, Paul McClarty, Jeroen van den Brink, Maia G. Vergniory
Statistical Mechanics
Linearization Principle: The Geometric Origin of Nonlinear Fokker-Planck Equations
Hiroki Suyari
Anomalous
diffusion and power-law distributions are observed in various complex systems. To provide a consistent dynamical foundation for these phenomena, we present a
geometric derivation of the nonlinear Fokker-Planck equation by introducing the Linearization Principle directly at the dynamical stage. By identifying the generalized chemical potential as the natural dynamical ansatz, we construct a general thermodynamic framework where the drift term remains linear in the probability density, preserving the standard form of the Einstein relation. Within this framework, we show that the $q$-deformed geometry, corresponding to Tsallis statistics, exhibits a fundamental duality between the dynamic index $q$ and the thermodynamic index $2-q$: the stationary state is a $q$-Gaussian distribution that minimizes a free energy functional defined by a generalized
entropy of index $2-q$. We prove the $H$-
theorem for the derived equation and demonstrate its application to the harmonic oscillator and the free particle. This framework describes anomalous
diffusion without relying on ad-hoc constraints or phenomenological nonlinear drift forces.
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Quantum Gases
Exact Density Profiles of 1D Quantum Fluids in the Thomas-Fermi Limit: Geometric Hierarchy to the Tonks-Girardeau Gas
Hiroki Suyari
We present a
geometric framework for 1D
quantum fluids across interaction regimes in the Thomas-
Fermi limit. Based on the Linearization Principle via the $q$-logarithm, macroscopic density profiles form a discrete hierarchy: the ideal Bose gas ($q=1$), the mean-field Gross-Pitaevskii condensate ($q=-1$), and the strongly correlated Tonks-Girardeau gas ($q=-3$). We further derive a universal sound velocity scaling, $c \propto \rho^{(1-q)/4}$, valid in the interacting regimes ($q \le -1$). This establishes a non-perturbative link between static geometry and dynamical excitations in many-body systems.
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Materials Science
The completed High-Low method for interface state density analysis in MOS capacitors
Brian D. Rummel, Sarit Dhar and Robert J. Kaplar
Interface state densities, $D_{IT}$, in metal-
oxide-
semiconductor (MOS) capacitors are rarely reported in the accumulation energy range. It is recognized that the determination of $D_{IT}$ in accumulation is fundamentally obscured by small inaccuracies in the user-defined
oxide capacitance, $C_{OX}$. This source of error prevents the High-Low frequency technique from reporting accumulation $D_{IT}$, even for sufficiently fast high-frequency measurements. To resolve this, an electrostatic constraint that is uniquely satisfied by a physically consistent $C_{OX}$ is derived from the established theory, thereby completing the High-Low framework. The "completed" framework's theoretical validity is confirmed using simulated capacitance data for an n-SiC MOS structure, and the method's frequency limitations are demonstrated. This analytical advancement ensures a physically consistent extraction of $D_{IT}$ near the band edge, overcoming a fundamental limitation in MOS capacitor characterization.
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Mesoscale and Nanoscale Physics
Sub-Sharvin conductance and Josephson effect in graphene
Adam Rycerz
Titov and Beenakker [Phys. Rev. B 74, 041401(R) (2006)] found, by solving the Dirac-Bogoliubov-De-Gennes equation, that the product of critical current and normal-state resistance for
superconductor-
graphene-
superconductor (S-g-S) Josephson junction takes values (for a short junction and zero temperature) between $I_cR_N\approx{}2.1$ and $I_cR_N\approx{}2.4$ in units of $e/\Delta_0$, where $\Delta_0$ is the superconducting gap. These values are notably higher than the tunnelling bound ($\pi/2$), but lower than the ballistic bound ($\pi$). Here we analyze numerically the tunneling of Cooper pairs through S-g-S junctions in which the longitudinal electrostatic potential profile is tuned, within gates electrodes, from a rectangular to a
parabolic one. In the unipolar regime (i.e., when the chemical potential is above the top of a barrier, $\mu>0$), it is found that $I_cR_N$ gradually evolves from the
graphene-specific to the ballistic value. At the same time, the normal-state conductance increases from the sub-Sharvin value of $1/R_N\approx(\pi/4)\,G_{\rm Sharvin}$ towards to the Sharvin value $G_{\rm Sharvin}=g_0|\mu|W/(\pi\hbar{}v_F)$, with the conductance
quantum $g_0=4e^2/h$, the junction width $W$, and the
Fermi velocity in
graphene $v_F$. In contrast, in the tripolar regime ($\mu<0$), both normal-state conductance and the critical current are suppressed when smoothing the potential; however, $I_c{}R_N$ remains close to the
graphene-specific range, even for a
parabolic potential. The skewness of the current-phase relation is also discussed.
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Materials Science · Cross-listed from physics.comp-ph
NEP-CG and NEP-AACG: Efficient coarse-grained and multiscale all-atom-coarse-grained neuroevolution potentials
Zheyong Fan, Wenjun Zhang, Zhenhao Zhang et al. (+3 more)
Machine-learned coarse-grained (CG) models often suffer from noisy training data, limiting their accuracy and transferability. We propose a method to generate low-noise training data based on the potential of mean force by constraining CG beads during atomistic simulations and accumulating time-averaged forces. Implemented within the neuroevolution potential (NEP) framework, our approach achieves training accuracy comparable to atomistic models trained on density functional theory data. For
liquid water, the NEP-CG model accurately reproduces densities from 1 bar to 1 GPa, successfully extrapolating beyond the 0.5 GPa training limit, with a virial correction essential for the correct equation of state. For an anisotropic C$_{60}$ monolayer, distinguishing crystallographically distinct bead types reduces stress errors by an order of magnitude and captures directional thermal conductivity. We further introduce a multiscale NEP-AACG model integrating all-atom (AA) and CG degrees of freedom, demonstrated for gold nanowire fracture at an experimentally relevant strain rate. Computational speeds for NEP-CG models reach hundreds to thousands of ns/day using a single consumer-grade GPU. This work provides a robust framework for constructing accurate, transferable, and efficient CG models across diverse systems.
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All authors Zheyong Fan, Wenjun Zhang, Zhenhao Zhang, Ke Xu, Xuecheng Shao, Haikuan Dong
Superconductivity
Scanning Tunneling Microscopy in high vectorial magnetic fields
Jaime Rumeu Ozores, Miguel Águeda Velasco, Edwin Herrera et al. (+10 more)
The Scanning Tunneling Microscope (STM) is a powerful instrument to study electronic density of states at surfaces down to atomic scale. Many interesting samples require studying variations as a function of the
magnetic field, which is most often applied perpendicular to the surface. Conventional STM designs make it challenging to perform measurements when the
magnetic field must be applied in other directions. Here we present a new STM setup installed on a rotatable platform. We have designed and built a new STM, which is small enough to allow for full rotation on a space with a diameter of 37 mm, well below the available space within many magnets. We show that the new rotatable STM setup preserves the performance of state-of-the-art STMs in terms of noise and accuracy. Our new approach significantly enhances control over the direction of the applied
magnetic field and opens exciting new possibilities to study
quantum materials.
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All authors Jaime Rumeu Ozores, Miguel Águeda Velasco, Edwin Herrera, Pablo García Talavera, Jose D. Bermúdez-Pérez, José A. Moreno, Paula Obladen, Rafael Álvarez Montoya, José Navarrete, Juan Ramón Marijuan, José A. Galvis, Isabel Guillamón, Hermann Suderow
Disordered Systems and Neural Networks
Deep-layered machines have a built-in Occam's razor
Thomas M. A. Fink
Input-output maps are prevalent throughout science and technology. They are empirically observed to be biased towards simple outputs, but we don't understand why. To address this puzzle, we study the archetypal input-output map: a deep-layered machine in which every node is a Boolean function of all the nodes below it. We give an exact theory for the distribution of outputs, and we confirm our predictions through extensive computer experiments. As the network depth increases, the distribution becomes exponentially biased towards simple outputs. This suggests that deep-layered machines and other learning methodologies may be inherently biased towards simplicity in the models that they generate.
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Strongly Correlated Electrons · Cross-listed from hep-lat
Continuum limit of a qubit-regularized SU(3) lattice gauge theory on a plaquette chain
Rui Xian Siew, Shailesh Chandrasekharan and Tanmoy Bhattacharya
We show that a simple
qubit-regularized $\mathrm{SU}(3)$
lattice gauge theory on a plaquette chain admits a continuum limit with massive gauge-invariant excitations, providing a minimal toy model of strong interactions without
quarks. By mapping the plaquette-chain
Hamiltonian to the three-state
quantum clock model in a
magnetic field, we demonstrate that the theory can be tuned to a continuum limit governed at short distances by the $\mathbb{Z}_3$ parafermion conformal field theory, which serves as the ultraviolet fixed point. A small relevant
magnetic perturbation then drives the system to a massive continuum
quantum field theory in the infrared, featuring relativistic particles. In this continuum theory we compute two universal ratios: the mass ratio of the lightest massive particles with opposite charge conjugation, $m^{-}/m^{+} = 1.459(2)$, and $\sqrt{\sigma}/m^{+} = 0.2648(2)$, where $\sigma$ denotes the string tension between a static
quark and antiquark.
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Superconductivity
Superconducting diode effect in multichannel Majorana wires
Sagar Santra, Dibyendu Samanta and Sudeep Kumar Ghosh
The superconducting diode effect (SDE) enables nonreciprocal dissipationless transport when inversion and time-reversal
symmetries are simultaneously broken. Rashba nanowires proximitized by conventional s-wave
superconductors provide a minimal setting where
spin-orbit coupling and Zeeman fields generate asymmetric finite-momentum pairing. While most studies focus on the single-channel limit, which typically yields small diode efficiencies and requires multiple Zeeman-field components, realistic devices generically host multiple transverse subbands (channels). Here, we investigate the SDE in multichannel Rashba nanowires with harmonic and rectangular
quantum-well confinement using a self-consistent Bogoliubov-de Gennes formalism. Both geometries support asymmetric Fulde-Ferrell (FF) states driving pronounced nonreciprocal supercurrents. Crucially, this current-driven FF state stabilizes a topological phase with Majorana zero modes, where Cooper pair momentum is controlled by an externally injected supercurrent, enabling direct topological manipulation. Pairing susceptibility analysis reveals that field-induced asymmetries favor directional Cooper pairing, explaining the diode response's nonmonotonic Zeeman-field dependence. Harmonic confinement yields diode efficiencies of ~60% (interacting channels) and ~55% (independent channels). Notably, interchannel coupling enables a finite response from a transverse Zeeman field alone. Rectangular confinement achieves ~60% efficiency across both regimes, alongside a tunable sign reversal of efficiency when channels interact. These results establish the robustness of the SDE and FF states against transverse confinement variations, highlighting multichannel nanowires as powerful platforms for high-efficiency nonreciprocal transport and current-controlled topological superconductivity.
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Statistical Mechanics
Ultra slow sub-logarithmic diffusion of a sluggish random walker subject to resetting with memory
Denis Boyer and Satya N. Majumdar
We solve a model of sluggish
stochastic motion in which a Brownian particle diffuses with a
diffusion coefficient that decays algebraically with the distance to the origin, as $|x|^{-\alpha}$. Additionally, the particle resets with a constant rate $r$ to positions previously visited in the past, so that frequently visited regions are more likely to be revisited. An exact expression is obtained at all times for the position distribution in arbitrary spatial dimensions. At late times, the typical displacement of the walker from the origin grows extremely slowly, as $[\ln(rt)]^{1/(\alpha +2)}$, and the position distribution tends to a scaling law. For any $\alpha>0$, the scaling function has a bimodal shape with a minimum at $x=0$ and non-Gaussian tails. Although the mean square displacement is hard to compute, some generalized moments of this process can be calculated exactly at all times in one dimension, and are shown to be closely related to the moments of the well-studied model with a constant
diffusion coefficient.
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Mesoscale and Nanoscale Physics
Intrinsic topological spin probes for electrical imaging of nanoscale energy landscapes
Liam K. Mitchell, Benjamin J. Brown and Gang Xiao
Disorder in
magnetic materials prevents reliable control of
spin textures and constrains their integration into spintronic devices. Existing methods access disorder only indirectly through external imaging probes or bulk transport measurements, leaving the internal energy landscape inaccessible. We introduce an intrinsic
magnetic microscopy method in which a topological
spin texture serves as a mobile probe of disorder, directly mapping energy landscapes inside multilayer devices without probe-sample separation. Using a ~10-nm
magnetic vortex core confined within a
magnetic tunnel junction, we track its displacement with nanometer-scale sensitivity to resolve intrinsic and engineered defect-induced potentials and directly quantify local pinning forces. This framework establishes
spin textures as internal spectroscopic probes of disorder and enables quantitative engineering of pinning structures in functional
magnetic systems.
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Other Condensed Matter · Cross-listed from quant-ph
Ergotropy from Geometric Phases in a Dephasing Qubit
Fernando C. Lombardo and Paula I. Villar
We analyze the
geometric phase and dynamic phase acquired by a
qubit coupled to an environment through pure dephasing, establishing a direct connection between phase accumulation and ergotropy. We show that the dynamic phase depends solely on the incoherent ergotropy, reflecting its purely energetic origin. In contrast, the
geometric phase exhibits a nontrivial dependence on both the coherent and incoherent contributions to the total ergotropy, encoding the interplay between coherence, dissipation, and energy extraction. By performing a perturbative expansion in the
qubit-environment coupling strength, we demonstrate that, in the weak-coupling and long-time regime, the
geometric phase becomes determined exclusively by the incoherent ergotropy, which coincides with the asymptotic value of the total ergotropy reached under decoherence. These results provide a clear physical distinction between dynamic and
geometric phases in open
quantum systems and establish
geometric phases as sensitive probes of energetic resources. Furthermore,~in superconducting
circuit implementations, our findings suggest that the ergotropy of a two-level system could be inferred indirectly from
geometric-phase measurements using standard techniques such as
quantum state
tomography.
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Mesoscale and Nanoscale Physics
Interband response in spin-orbit coupled nodal line semimetals
Vivek Pandey, Monu and Pankaj Bhalla
This study investigates the interband conductivity for nodal line semimetals (NLSMs) in the presence of
spin-orbit coupling (SOC), where the disorder reshapes the transport properties. The SOC breaks
spin degeneracy, thus fundamentally altering the band dispersion and enabling multiple interband transport channels. Using a
quantum kinetic framework, we analyze the interband conductivity originating from disorder-driven (extrinsic) and field-driven (intrinsic) mechanisms. We find that the interband response shows an anisotropic nature due to disorder driven counterparts. Additionally, our predictions show a tunable prominent transition peak arising from non-Pauli-blocked states that can be controlled via band parameters as well as external stimuli. To have an experimental relevance, we provide a numerical estimation for the interband response of TaAs using density functional theory estimated parameters. These results suggest the investigation of disorder-enabled signatures in
spin systems.
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Superconductivity
Doping evolution of spin excitations in La$_{3-x}$Sr$_{x}$Ni$_2$O$_7$/SrLaAlO$_4$ superconducting thin films
Hengyang Zhong, Bo Hao, Anni Chen et al. (+11 more)
Ambient-pressure superconductivity in compressively strained
bilayer nickelate films provides a unique platform to test pairing scenarios, yet the
evolution of magnetism with carrier doping remains largely unexplored. Here, we utilize Ni $L_3$-edge resonant inelastic x-ray scattering to systematically track the
evolution of
spin and electronic excitations in coherently strained La$_{3-x}$Sr$_x$Ni$_2$O$_7$/SrLaAlO$_4$ thin films, spanning the superconducting ($x \le 0.21$) and overdoped non-superconducting ($x = 0.38$) regimes. We reveal that dispersive
spin excitations, characterized by double-stripe correlations and nearly doping-independent exchange scales, persist robustly throughout the entire superconducting dome. In stark contrast, upon entering the overdoped non-superconducting state, this coherent
magnetic framework undergoes an abrupt collapse, melting into a heavily damped, low-spectral-weight continuum. We show that this
magnetic breakdown is fundamentally driven by a selective doping-induced orbital reconstruction. While the invariant $\sim\!1.0$~eV intra-atomic $dd$ peak confirms an intact local octahedral
crystal field, the concurrent quenching of the $\sim\!0.4$~eV and $\sim\!1.6$~eV features signifies a severe degradation of the apical-oxygen-mediated $d_{z^2}$–$p_z$–$d_{z^2}$ singlet sector and
bilayer charge-transfer coherence. The synchronized demise of coherent
spin excitations and macroscopic pairing establishes a direct, doping-controlled link, underscoring that maintaining the localized $d_{z^2}$
magnetic framework and robust apical-oxygen coupling is the fundamental prerequisite for high-$T_c$ superconductivity in
bilayer nickelates.
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All authors Hengyang Zhong, Bo Hao, Anni Chen, Xinru Huang, Chunyi Li, Wenting Zhang, Chang Liu, Yuxun Zhu, Dao-Xin Yao, Kurt Kummer, Nicholas Brookes, Yuefeng Nie, Thorsten Schmitt, Xingye Lu
Materials Science
Networking Molecular Quantum Emitters on a Single Chain : From Single to Cooperative Emitters
Jean-Baptiste Marceau, Juliette Le Balle, Christel Poujol et al. (+4 more)
Engineering light-matter interactions between multiple free-space
quantum emitters is a central challenge for scalable
quantum photonic technologies. In particular, accessing regimes of coherent emitter-emitter interactions, where several emitters are coupled through a shared electromagnetic environment, is essential for coherent emission and
quantum functionalities. Such interactions require precise control over emitter separation and stabilization at sub-wavelength distances, a level of spatial organization that remains extremely difficult to achieve at the molecular scale in solid-state systems. Here we introduce Encoded
Quantum Chains (EQC), a one-dimensional architecture in which cooperative radiative behaviour is programmed through spatial encoding of identical molecular emitters. Organic emitters and inert spacer molecules are co-encapsulated inside dielectric boron nitride nanotubes (BNNTs), enabling statistical control of intermolecular spacing from nanometres to micrometres while enforcing dipole
alignment and one-dimensional confinement. Time-resolved fluorescence under ambient conditions reveals accelerated radiative decay, enhanced emission rates per emitter, and the emergence of non-mono-exponential dynamics as spacing falls below the optical wavelength, consistent with cooperative radiative states in one dimension. Bundling of EQCs enables coupling between emitters in neighbouring BNNTs, driving a dimensional crossover toward higher-dimensional delocalisation of the excitation. This modular building-block approach provides a scalable route to engineer light-matter interactions and many-body optical phenomena in confined molecular systems, opening new opportunities for distributed single-
photon sources, programmable
quantum emitters, and photonic architectures for
quantum technologies.
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All authors Jean-Baptiste Marceau, Juliette Le Balle, Christel Poujol, Frédéric Fossard, Annick Loiseau, Gaëlle Recher, Etienne Gaufrès
Materials Science
Design of 2D V<sub>6</sub>S<sub>n</sub>Se<sub>6-n</sub>Cl<sub>6</sub> (n=0, 2, 3, 5) with multilayer kagome lattice and ultrahigh electron mobility
Xing-Yu Wang, En-Qi Bao, Su-Yang Shen et al. (+2 more)
Two-dimensional (2D) kagome materials have attracted considerable
attention due to their unique electronic properties. Based on first-principles calculations and employing the "1+3" design strategy, we designed a class of composition-tunable 2D multilayer kagome materials, V<sub>6</sub>S<sub>n</sub>Se<sub>6-n</sub>Cl<sub>6</sub>, and identified four stable structures: V<sub>6</sub>Se<sub>6</sub>Cl<sub>6</sub>, V<sub>6</sub>S<sub>2</sub>Se<sub>4</sub>Cl<sub>6</sub>, V<sub>6</sub>S<sub>3</sub>Se<sub>3</sub>Cl<sub>6</sub>, and V<sub>6</sub>S<sub>5</sub>Se<sub>1</sub>Cl<sub>6</sub>. 2D V<sub>6</sub>S<sub>n</sub>Se<sub>6-n</sub>Cl<sub>6</sub> possesses three kagome layers, two of which are vanadium-based kagome layers, and the other is a sulfur or selenium atomic layer. Electronic structure analysis reveals that 2D V<sub>6</sub>S<sub>n</sub>Se<sub>6-n</sub>Cl<sub>6</sub> is a narrow direct-bandgap
semiconductor with a bandgap ranging from 0.568 to 0.742 eV, and exhibits ultrahigh electron mobility up to 4*10<sup>4</sup> cm<sup>2</sup>V<sup>-1</sup>s<sup>-1</sup> . Orbital analysis further demonstrates that the bands contributed by the V-based kagome layers form flat bands and Dirac cones below the
Fermi level, and show a relatively high
Fermi velocity. In summary, 2D V<sub>6</sub>S<sub>n</sub>Se<sub>6-n</sub>Cl<sub>6</sub> provides an excellent platform for kagome physics research and the fabrication of nanoelectronic devices, adaptable to various device scenarios.
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All authors Xing-Yu Wang, En-Qi Bao, Su-Yang Shen, Jun-Hui Yuan, Jiafu Wang
Materials Science
Nonsymmorphic Time-Reversal-Doubled Axion Insulators
Yue Xie, Haohao Sheng, Quansheng Wu et al. (+4 more)
The
axion insulator exhibits a topological magnetoelectric effect characterized by an
axion angle $\theta=\pi$, while the time-reversal-doubled
axion insulator (T-DAXI) can be viewed as two copies of an
axion insulator related by time-reversal
symmetry. In this work, we show that a nonsymmorphic topological crystalline
insulator with glide (or screw)
symmetry can host the nonsymmorphic T-DAXI phase, diagnosed by the nontrivial hourglass (screw) invariant $\delta_h=1$ ($\delta_s=1$). In this phase, the partial
axion angles ($\theta^\pm=\pi $) are quantized by the glide and/or screw
symmetry, and the gapped surfaces realize half-quantized
quantum spin Hall states. Furthermore, we show that nonsymmorphic T-DAXIs also exhibit the
spin-magnetoelectric effect. Namely, an external
magnetic field can induce a topological nonlocal
spin polarization in real space. When the
magnetic field is time-periodic, this leads to an alternating
spin current detectable in experiment. Using ab initio calculations, we demonstrate that mixed bismuth monohalides Bi4Br3I and Bi4BrI3 realize the nonsymmorphic T-DAXIs. Our findings not only reveal the
symmetry-enforced T-DAXIs in nonsymmorphic topological crystalline
insulators, but also demonstrate the
spin-magnetoelectric effect as a detectable topological
spin response in nonsymmorphic T-DAXIs.
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All authors Yue Xie, Haohao Sheng, Quansheng Wu, Xi Dai, Zhong Fang, Hongming Weng, Zhijun Wang
Superconductivity
On estimating superconducting shielding volume fraction from susceptibility in pressurized Ruddlesden-Popper nickelates: Response to arXiv:2602.19282
Yinghao Zhu, Di Peng, Enkang Zhang et al. (+10 more)
In a recent preprint (arXiv:2602.19282) [1], the authors questioned the procedure we used to evaluate the demagnetization-corrected superconducting shielding volume fraction in pressurized Ruddlesden-Popper nickelates [2-5]. They further claimed that this methodology has neither been derived nor used previously, and they proposed an alternative normalization scheme. Here we clarify that our evaluation follows directly from the standard magnetostatic self-consistency relation for finite samples and has been widely adopted in the superconductivity literature for decades. We also demonstrate that the discrepancies claimed in Ref. [1] stem from a fundamental flaw in their approach, namely, the assumption that the measured diamagnetic moment is linearly proportional to the superconducting shielding volume fraction in the presence of a finite demagnetization factor N. This assumption is not valid for strongly demagnetized, thin disk-like specimens, where the internal field and the measured moment are coupled self-consistently through the demagnetizing field.
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All authors Yinghao Zhu, Di Peng, Enkang Zhang, Bingying Pan, Xu Chen, Zhenfang Xing, Cuiying Pei, Feiyu Li, Yanpeng Qi, Junjie Zhang, Qiaoshi Zeng, Jian-gang Guo, Jun Zhao
Strongly Correlated Electrons
Resonant inelastic x-ray scattering in layered trimer iridate Ba4NbIr3O12: the density functional approach
D.A. Kukusta, L.V. Bekenov and V.N. Antonov
We have investigated the electronic structure of Ba4NbIr3O12 within the density-functional theory (DFT) using the generalized gradient approximation while considering strong Coulomb correlations (GGA+U) in the framework of the fully relativistic
spin-polarized Dirac linear muffin-tin orbital band-structure method. Ba4NbIr3O12 has a quasi-2D structure composed of corner-connected Ba3NbIr3O12 rimers containing three distorted face-sharing IrO6 octahedra. The Ir atoms are distributed over two symmetrically inequivalent sites: the center of the trimer (Ir1) and its two tips (Ir2). The Ir1- Ir2 distance within the trimer is quite small and equals to 2.547 A, at low temperature. As a result, there is clear formation of bonding and antibonding states. The large bonding-antibonding splitting stabilizes the dzz-orbital-dominant antibonding state of 5d holes and produces a wide energy gap at the
Fermi level. The ground state of Ba4NbIr3O12 is a nonmagnetic singlet with relatively moderate
spin-orbit coupling (SOC). We have theoretically calculated the x-ray absorption spectroscopy (XAS) spectra at the Ir L2, and Nb L3 edges as well as the photoemission spectrum of Ba4NbIr3O12. We have also presented a comprehensive investigation of the resonant inelastic x-ray scattering (RIXS) spectra at the Ir L3$ O K, Nb K, L3, M3, M5, and N3 edges. The RIXS spectrum of Ba4NbIr3O12 at the Ir L3 edge possesses several sharp features below 2 eV corresponding to transitions within the Ir t2g levels. The peak located at 3.2 eV is found to be due to t2g to eg transitions. The high energy fine structure above 5.3 eV is mostly determined by 5dO to tg and O2p to eg transitions. The spectral features between 8 and 12 eV are due to 5dO to eg transitions.
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Soft Condensed Matter
Nematic equilibria in isosceles triangles: The effects of edge length and apex angle on solution landscapes in a reduced Landau-de Gennes framework
Prabakaran Rajamanickam, Yucen Han, Thuriya Alhinai et al. (+1 more)
We study
equilibrium configurations of nematic
liquid crystals confined to two-dimensional isosceles triangles, subject to tangent boundary conditions. This toy problem is motivated by the effects of geometrical asymmetry on
equilibria in variational problems arising in
liquid crystal theory. There are two key geometrical parameters for an isosceles triangle - the triangle edge length and the apex angle. The nematic
equilibria are modelled by minimizers of a reduced Landau-de Gennes free energy in this setting. For small edge lengths, we provide a universal, angle-based local classification of nematic
equilibria near the vertices as to whether the nematic director exhibits a splay, bend or singular profile depending on the vertex opening angle. In the large domain limit, we demonstrate the existence of multiple competing nematic
equilibria – the three rotated solutions, for which the nematic director bends between a pair of adjacent vertices, and a trefoil solution featuring an interior point defect. For acute apex angles, we show that the trefoil solution is stable for small edge lengths. The interior point defect of the trefoil solution migrates to one of the base vertices, as the edge length increases, and is finally expelled giving way to the rotated solutions, if the apex angle is small enough. Our numerical results suggest that there is a unique trefoil solution on the equilateral triangle for all edge lengths, and a unique rotated solution on isosceles triangles with wide apex angles. These results yield interesting insight into how geometrical asymmetry can tailor
equilibria and self-assembly processes in confined nematic systems.
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All authors Prabakaran Rajamanickam, Yucen Han, Thuriya Alhinai, Apala Majumdar
Superconductivity
Non-reciprocal properties of 2D superconductors
Xingrong Ren, Huiqing Ye and Tian Le
Two-dimensional (2D)
superconductors, characterized by their inherent
quantum confinement, strong
spin-orbit coupling, and diverse forms of
symmetry breaking, provide an ideal platform for exploring novel
quantum transport phenomena. This review summarizes recent experimental progress in the non-reciprocal properties of 2D
superconductors, focusing on second harmonic resistance in the resistive superconducting state and the supercurrent diode effect (SDE) in the dissipationless superconducting regime. We discuss the various origins of these phenomena, distinguishing between intrinsic mechanisms, such as finite-momentum Cooper pairing, and extrinsic mechanisms driven by asymmetric
vortex dynamics and device geometry. We present a systematic classification of zero-field SDE into polarity-reversed and polarity-locked behaviors, a distinction governed by the interplay between intrinsic time-reversal
symmetry breaking and external
magnetic response. Furthermore, we examine how the efficiency and polarity of SDE are modulated by tuning parameters including
magnetic/electric fields, strain, device geometry, thermodynamic conditions, and microwave irradiation. We conclude by highlighting the application potential of these tunable diodes in high-efficiency rectification, superconducting logic, and neuromorphic computing.
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Statistical Mechanics
Fixed points of Boolean networks with sparse connections
Stav Marcus, Ari M. Turner, Guy Bunin et al. (+1 more)
We study fixed points of cellular automata with $N$ sites on random sparse graphs. In the large $N$ limit such models are known to exhibit phase transitions, from a “frozen” phase, where at most a finite number of sites fluctuate at long times, to a “fluctuating” phase where a finite fraction of sites fluctuate. We consider several models, calculating the first and second moments of the number of fixed points, and find that these moments remain finite in the large $N$ limit, except at the transitions where they become singular. The singularities can take several forms, including divergence of the mean or variance of the number of fixed points, on one or both sides of the transition. The type of singularity is related to properties of the mean field dynamics or dynamics of the distance between copies of the system. In configuration space, we find that fixed points are organized into clusters, each consisting of sets of fixed points that agree with one another except for on a finite number of sites. In the frozen phase there is only one cluster, while in the fluctuating phase there may be multiple clusters. If there are multiple clusters, the distance between fixed points in different clusters is extensive. We show that the differences within the clusters correspond to local changes near short cycles in the directed graph of connections whose influence is eventually limited. In the frozen phase, we calculate the full distribution of the number of fixed points.
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All authors Stav Marcus, Ari M. Turner, Guy Bunin, Bernard Derrida
Strongly Correlated Electrons
Magnetic fluctuations near the Van Hove singularity in the kagome-lattice Hubbard model at finite doping
Jingyao Wang, Zixuan Jia, Zenghui Fan et al. (+2 more)
The kagome-
lattice Hubbard model attracts widespread interest due to its flat-band and Van Hove singularity features, which can give rise to unconventional magnetism. We employ determinant
quantum Monte Carlo simulations to systematically investigate the uniform
magnetic susceptibility across a range of on-site interactions and electron fillings on a two-dimensional kagome
lattice. Beyond the Van Hove singularity, dominant
ferromagnetic fluctuations emerge.
Magnetic susceptibility grows markedly with increasing interaction strength and decreasing temperature, indicating that the Van Hove singularity acts as a critical point for the crossover of dominant
magnetic fluctuations. Finite-size analysis further suggests the potential stabilization of a finite-temperature
ferromagnetic phase. We also examine the sign problem to identify numerically reliable parameter regimes. These results provide valuable insights into controlling
magnetic fluctuations in kagome systems and establish a computational framework for exploring flat-band physics in regimes characterized by novel
quantum phases and competing orders.
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All authors Jingyao Wang, Zixuan Jia, Zenghui Fan, Qingzhuo Duan, Tianxing Ma
Materials Science
Nanoscale imaging reveals critical plating and stripping mechanisms in anode-free lithium and sodium solid-state batteries
J. Diaz-Sanchez, P. Hernandez-Martin, N. Kwiatek-Maroszek et al. (+12 more)
Achieving reversible anode-free solid-state batteries hinges on controlling alkali-metal plating and stripping at buried interfaces, yet the underlying nanoscale mechanisms remain unresolved. Here we introduce virtual-electrode low-energy electron microscopy (VE-LEEM), an imaging platform that enables nanoscale visualization of anode formation and dissolution by combining electron beam-induced plating with ultraviolet-driven stripping. By integrating VE LEEM with synchrotron-based photoemission electron microscopy and atomic force microscopy, we track the chemical and morphological
evolution of Li and Na anodes during cycling. We uncover a shared dynamic scaling regime governing anode growth, analogous to high mobility thin film deposition, but emerging through distinct morphological pathways dictated by metal-specific surface energetics. This universal scaling behaviour establishes a transferable quantitative framework for comparing anode-free plating across chemistries. In contrast, stripping proceeds through sequential grain-boundary unzipping and cluster decay mechanisms, demonstrating that dissolution is intrinsically asymmetric with respect to plating and leaves behind a persistent interfacial residual layer. These results overturn the common assumption of mirrored plating-stripping dynamics and identify interfacial and grain boundary energetics as fundamental constraints on reversibility. VE LEEM thus provides a general route to resolve buried electrochemical interfaces at the nanoscale and establishes an energetic framework to guide the design of durable, high energy anode free solid state batteries.
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All authors J. Diaz-Sanchez, P. Hernandez-Martin, N. Kwiatek-Maroszek, H.R. Bratlie, R. Anton, A. Lowack, A. Galindo, K. Kataoka, E. Vasco, K. Nikolowski, D. Rettenwander, E.G. Michel, M.A. Nino, M. Foerster, C. Polop
Quantum Gases
Spin and density excitations of one-dimensional self-bound Bose-Bose droplets
Ritu, Rajat, Manpreet Singh et al. (+2 more)
We study
spin and density excitations of one-dimensional self-bound Bose-Bose droplets within Bogoliubov theory, and show that
spin excitations come alive, especially as the interspecies coupling is made less attractive. We argue that
spin excitations are particularly relevant in the one-dimensional droplet regime, where droplets are realized within the mean-field stability regime, as has been confirmed by the
quantum Monte Carlo simulations. As the interspecies coupling strength increases within the mean-field stability regime,
spin modes ultimately fall below the particle-emission threshold, thus becoming observable in the droplet spectrum. We analyze the Bogoliubov model for both pseudospinor and population-imbalanced scalar mixtures, encompassing both the density and
spin sectors. We corroborate our findings through variational analysis of density- and
spin-breathing modes, which offers physical insight into the mode structure and independently validates the spectrum, as well as through real-time dynamics. Additionally, we compare our results with both Petrov's original theory, which considers the Lee-Huang-Yang (LHY) correction at the attractive edge of the mean-field stability regime, and a beyond-LHY description of Bose-Bose mixtures.
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All authors Ritu, Rajat, Manpreet Singh, Rajesh Kumar Gupta, Sandeep Gautam
Materials Science
Unfolding Bloch States in Disordered Systems
T. Thuy Hoang, Kunihiro Yananose, Sungjong Woo et al. (+4 more)
In crystalline solids, disorder breaks translational
symmetry and obscures k-resolved Bloch states, limiting an accurate description of wavefunction-based observables. In this work, we present a method that unfolds not only the band structures but also the corresponding Bloch states in disordered systems, going beyond conventional band-unfolding techniques. As a prototype application, we study defective
graphene and demonstrate the capabilities by capturing key wavefunction-level responses, including disorder-driven redistribution of Berry
curvature.
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All authors T. Thuy Hoang, Kunihiro Yananose, Sungjong Woo, Seongjin Ahn, Dong Han, Xian-Bin Li, Junhyeok Bang
Materials Science
Experimental Powder X-ray Diffraction Crystal Structure Determination with RealPXRD-Solver
Qi Li, Mingyu Guo, Rui Jiao et al. (+14 more)
Determining
crystal structures from experimental powder X-ray diffraction data remains challenging because peak overlap, preferred orientation, and
impurity phases obscure atomic arrangements. We present RealPXRD-Solver, a generative model trained on 6,250,238 theoretical structures with experiment-mimicking augmentations and a universal encoder of d-spacing–intensity fingerprints, enabling both
lattice-conditioned and
lattice-free inference. RealPXRD-Solver reaches a 98.3% Top-20 match rate on a 10,000-structure theoretical
benchmark and achieves Top-1/Top-20 accuracies of 77.9%/91.9% on CNRS and 78.8%/92.9% on RRUFF experimental
datasets, and it solved 39 previously unreported Powder Diffraction File entries.
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All authors Qi Li, Mingyu Guo, Rui Jiao, Jing Gao, Fanjie Xu, Haonan Xue, Weixiong Zhang, Wenbing Huang, Junchi Yan, Linfeng Zhang, Cheng Wang, Zhuang Yan, Guolin Ke, Weinan E, Zhiyong Tang, Shifeng Jin, Lin Yao
Superconductivity
Tuning of superconducting properties with disorder in NbxSn nanocrystalline thin films
Mahesh Poojary, Vishwanadh Bathula, Yash Kumar et al. (+3 more)
Nanocrystalline superconducting films offer an excellent platform to explore the interplay between disorder, granularity, and dimensionality. In this work, we investigate two series of NbxSn thin films with near-stoichiometric (x =3) and slightly Sn-rich (x =2.5) compositions, deposited on Si (100) substrates via DC magnetron sputtering. Both series exhibit nanocrystalline morphology, with the Sn-rich films displaying smaller grain sizes and a more granular microstructure. A suppression of the superconducting transition temperature (Tc) with decreasing film thickness is observed in both series. Notably, a disorder-driven crossover to an insulating state emerges, occurring at a thickness of approximately 11 nm for the Sn-rich films-about twice that of the stoichiometric films. The estimated disorder parameter (kFl=0.4) in the thinnest films indicates proximity to the Anderson localization regime for these films. Magneto-transport measurements reveal a thickness-driven 3D to 2D crossover, with its onset strongly dependent on film stoichiometry. Furthermore, a pronounced suppression of superfluid stiffness is observed in the Sn-rich films, corroborating the structure-property correlations identified in this study. This work highlights the role of stoichiometry controlled disorder in tuning superconductivity in granular NbxSn thin films.
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All authors Mahesh Poojary, Vishwanadh Bathula, Yash Kumar, Amar Verma, Ekta Kadam, Sangita Bose