Mesoscale and Nanoscale Physics
Collective charge measurement in quantum dot chains: controlling barrier occupation and tunneling current
Alok Nath Singh, Rafael Sánchez and Andrew N. Jordan
We investigate nonequilibrium transport in a triple-
quantum-dot (TQD) system, where the central dot acts as a discrete tunnel barrier, subject to continuous monitoring by a
quantum point contact (QPC) that is capacitively coupled to all three dots with independently tunable strengths. We show that this global measurement scheme affects transport in a qualitatively distinct manner from single-site measurement. By engineering structured dephasing, measurement provides a significant improvement in the barrier occupation and tunneling current. In the strong-measurement limit, the steady state becomes independent of the underlying
Hamiltonian parameters, and the barrier occupation can approach 1/2 for suitable measurement configurations. We identify an optimal measurement configuration that maximizes the steady-state current and show that near-optimal performance can be achieved with a simple central-dot readout scheme.
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Statistical Mechanics
Non-Gaussianity of random quantum states
Filiberto Ares, Sara Murciano and Pasquale Calabrese
We study the fermionic non-Gaussianity in typical
quantum states, focusing on Haar random states of
qubits with or without a global $U(1)$
symmetry. Using the Weingarten calculus, we derive analytical predictions for the non-Gaussianity, defined as the relative
entropy between the reduced density
matrix and its Gaussianized counterpart. We identify two regimes controlled by the ratio between the subsystem and the system size, $\ell/L$. For $\ell/L < 1/2$, the non-Gaussianity vanishes in the absence of
symmetries, because typical reduced density
matrices are exponentially close to the maximally mixed state. In the presence of a global $U(1)$
symmetry, instead, it remains small but finite. By contrast, in the regime $\ell/L > 1/2$, the non-Gaussianity becomes extensive. These results establish the typical scaling of fermionic non-Gaussianity in random states and analyze how this is modified by the presence of global
symmetries.
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Strongly Correlated Electrons
I. V. Lukin, M. O. Luhanko, Yu. V. Slyusarenko et al. (+1 more)
We study ground-state properties and phase diagram of the $J_{1}$-$J_{2}$
antiferromagnetic XY model on the honeycomb
lattice by means of the developed corner transfer
matrix renormalization group
algorithm with the two-site unit
cell and the infinite spiral projected entangled pair states ansatz. We identify the main phases: Néel, Ising, collinear, and incommensurate spiral phases, as well as the transitions between them, as functions of the ratio $J_{2}/J_{1}$. In the regime of competing types of ordering, we show that the energies of the dimerized states are systematically higher than the energies in the collinear phase. This collinear phase transforms to the incommensurate spiral phase through the second-order phase transition upon a further increase of $J_2/J_1$.
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All authors I. V. Lukin, M. O. Luhanko, Yu. V. Slyusarenko, A. G. Sotnikov
Quantum Gases · Cross-listed from gr-qc
Collective excitations in quantum gravity condensates
Andrea Calcinari, Adrià Delhom and Daniele Oriti
A central open problem in
quantum gravity is to understand how continuum spacetime emerges from
quantum-
geometric degrees of freedom in a background-independent setting. A many-body perspective suggests that spacetime emerges as a hydrodynamic phase of many atoms of
quantum geometry. This idea underlies several approaches to
quantum gravity, and it has been explicitly realised in the group field theory formalism. However,
quantum fluctuations beyond the mean-field regime remain largely unexplored. We fill this gap by importing Bogolyubov theory to
quantum gravity condensates, showing that leading beyond-mean-field effects manifest as collective excitations, in direct analogy with
phonons in laboratory BECs. We implement the construction in a tractable group field theory model, where condensates of
quantum-
geometric atoms reproduce nonsingular expanding cosmologies, and derive the leading beyond-mean-field corrections to the emergent Friedmann dynamics. These results identify a new class of
quantum-
gravity excitations and establish a controlled bridge between microscopic
quantum-gravitational dynamics, many-body collective phenomena, and signatures of spacetime emergence.
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Superconductivity
Signatures of Gaussian superconducting fluctuations in nonlocal noise magnetometry
Dror Orgad
We calculate the two-point
magnetic noise spectrum arising from Gaussian superconducting fluctuations, a quantity directly measurable by
spin qubit pairs such as nitrogen vacancy centers in diamond. The analysis utilizes the time-dependent Ginzburg-Landau theory, reflecting the direct contribution of fluctuating Cooper pairs to the current correlations and consequent
magnetic noise. We treat both two-dimensional systems and wires, considering them in
equilibrium and under a uniform electric field. The signal is expected to be strongest in high-temperature
superconductors, and we contrast our findings with the predicted signatures of a
vortex liquid to offer an additional route to elucidate the nature of fluctuations in these systems.
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Quantum Gases
Generalized Hydrodynamics of Bloch Oscillations in the Absence of a Lattice
Stefano Scopa, Philip Zechmann, Michael Knap et al. (+2 more)
Objects subjected to a constant force generally increase their velocity over time. This expectation fails whenever their energy is a smooth and periodic function of momentum, resulting in periodic Bloch oscillations instead. Periodic dispersions, typical of
lattice systems, can also emerge in continuum media through strong interactions. Here, we study the phenomenon of such Bloch oscillations in the absence of a
lattice in a paradigmatic model of integrable
quantum gases: the two-component Yang-Gaudin model. We derive a generalized-hydrodynamic theory of Bloch oscillations for a finite density of
impurities embedded in a homogeneous interacting background, which we show to persist superimposed to a drift due to the acceleration of the center of mass. Moreover, we show the single-
impurity oscillation period is renormalized at finite
impurity density when two-
magnon bound states are populated. Our results are relevant for ultracold atom experiments, where
impurities can be created at controllable densities.
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All authors Stefano Scopa, Philip Zechmann, Michael Knap, Jacopo De Nardis, Alvise Bastianello
Strongly Correlated Electrons
Imaging stripe dynamics in trilayer nickelate La$_4$Ni$_3$O$_{10}$
Uladzislau Mikhailau, Luke Rhodes, Siri A. Berge et al. (+5 more)
Since the discovery of high-temperature superconductivity in nickelate
superconductors, it is an open question how closely the superconducting state resembles that of cuprate
superconductors. One salient feature of the phase diagram of the high-temperature cuprate
superconductors is stripe order. Despite their prevalence, real-space imaging has been limited to the charge sector. Here we use
spin-polarised scanning tunnelling microscopy to visualize the local
magnetic and charge distribution emerging due to a stripe order in the trilayer nickelate La$_4$Ni$_3$O$_{10}$. The stripe order exhibits a four unit
cell periodicity, closely resembling that seen in cuprates, and opens a near-complete $\sim66\mathrm{meV}$ gap at the
Fermi level. Crucially, discrete phase slips can be triggered by tunneling electrons above a $\sim 20\mathrm{meV}$ threshold, allowing imaging of stripe dynamics at the atomic scale. These results highlight the importance of correlation physics driving stripe-like orders in lanthanum nickelates with striking similarities to the cuprates.
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All authors Uladzislau Mikhailau, Luke Rhodes, Siri A. Berge, Matthias Hepting, Masahiko Isobe, Carolina A. Marques, Pascal Puphal, Peter Wahl
Statistical Mechanics · Cross-listed from quant-ph
Noise-induced Simulability Transition from Operator Scrambling
Neil Dowling, Xhek Turkeshi, Jacopo De Nardis et al. (+1 more)
The complexity of simulating
quantum many-body dynamics, or
quantum computations, in the Heisenberg picture is governed by the scrambling of initially simple operators into superpositions of exponentially many Pauli strings. The corresponding expansion coefficients define the Pauli spectrum, whose structure controls the performance of classical
algorithms based on truncating Pauli expansions. Here we determine the finite-depth Pauli spectrum of random
quantum circuits, both in the noiseless case and in the presence of local noise, through its moments, given by the operator stabilizer Rényi
entropies. In noiseless
circuits, we uncover a hierarchy in the approach to the fully scrambled regime: low moments equilibrate at relatively short depths, while higher moments, which are sensitive to rare, large-amplitude Pauli coefficients, require parametrically larger depths. In noisy
circuits, scrambling competes with an effective suppression of operator spreading. Above a critical error per cycle $\gamma_c N=\mathcal{O}(1)$, the operator fails to reach the fully scrambled distribution and remains supported on an atypically sparse subset of Pauli strings. Conversely, below this scale, we rigorously show that classical simulation remains exponentially hard, demonstrating that finite noise does not automatically imply classical simulability. The resulting noise-induced transition in operator complexity therefore delineates the boundary between intrinsically hard
quantum dynamics and those that remain classically accessible.
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All authors Neil Dowling, Xhek Turkeshi, Jacopo De Nardis, Guglielmo Lami
Superconductivity
Detecting vortex motion through spatially correlated nonequilibrium noise
Yifan F. Zhang, Rhine Samajdar and Sarang Gopalakrishnan
Resistive transport near a superconducting phase can arise from the motion of normal-state quasiparticles or that of
vortices. The conductivity alone does not distinguish between these mechanisms. We propose an unambiguous method for telling them apart, using the recently developed experimental tool of covariance magnetometry, which uses nitrogen-vacancy centers in diamond to probe real-time spatiotemporal correlations in
magnetic noise. Our key insight is that, under an applied current, the underlying charge carriers leave a directional fingerprint in the spatially correlated
magnetic noise above the sample: ordinary electric carriers drift parallel to the current, whereas
vortices, owing to the Magnus force, drift perpendicular to it. The noise covariance detects this anisotropy and identifies the
vortex-driven nature of transport. We compute the noise correlations expected for a representative thin-film
superconductor and demonstrate that the anisotropic signal is well within the reach of current experimental capabilities.
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Materials Science · Cross-listed from nlin.PS
Bifurcation of the quasi-stationary velocity of strongly discrete transition waves driven by gravity
Zehuan Tang, Qing Xia, Hui Chen et al. (+2 more)
Transition waves are common in multistable mechanical metamaterials, and the dynamics of weakly discrete transition waves under driving forces have been extensively discussed. However, as
lattice effects become more pronounced, strongly discrete transition waves may exhibit dynamics that cannot be predicted by the continuum limit. Here, by tilting a bistable chain, we introduce a gravitational perturbation term into the dynamical equations, under which the transition waves are continuously accelerated. In the strongly discrete regime, we find that transition waves under gravitational driving possess quasi-stationary velocity plateaus (QSVPs), and the number of these plateaus first increases and then decreases as the tilt angle increases. We theoretically elucidate that the emergence of the velocity plateaus originates from the balance between gravitational driving and
phonon radiation. In further analysis, the theoretical model reveals that the balance point undergoes a bifurcation at the radiation resonance, which leads to a change in the number of velocity plateaus. Our study extends the investigation of transition waves into the strongly discrete regime, and the emergence of multiple velocity plateaus opens up new possibilities for programmable solitary waves.
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All authors Zehuan Tang, Qing Xia, Hui Chen, Songyang Fu, Yuanwen Gao
Quantum Gases
Can machine learning for quantum-gas experiments be explainable?
I. B. Spielman amd J. P. Zwolak
Virtually all aspects of many-body atomic physics are challenging: experiments are technically demanding,
datasets have become enormous, and the
memory and CPU requirements for classical simulation of generic
quantum systems often scale exponentially with system size. Machine learning (ML) methods are already assisting in each of these areas and are poised to become transformative. Here, we focus on two specific applications of ML to cold-atom-based
quantum simulators. These devices generally generate data in the form of images; we first showcase denoising of raw images and then identify solitonic waves in Bose-Einstein condensates. In both of these examples, we comment on the interplay between performance, model complexity, and interpretability.
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Mesoscale and Nanoscale Physics
Effect of electric current on optical response of viscous electron-hole plasma
Yu. A. Pusep, M. A. T. Patricio, G. M. Jacobsen et al. (+3 more)
The influence of the
Hall voltage on the photoluminescence of a dense hydrodynamic electron-hole
plasma laser generated in a mesoscopic n-doped GaAs channel under intense
laser excitation is studied.
Laser excitation induces an interband current determined by the recombination of photogenerated electron-hole pairs. As a result, background electrons drifting under the influence of the
Hall voltage form an effective
Hall current. The Coulomb drag caused by the
Hall current causes the accumulation of light holes, leading to the appearance of a double photoluminescence line formed by the recombination of
excitons and trions. In contrast, in the absence of a
Hall current, the shift in the photoluminescence energy associated with heavy holes occurs due to the electric field created by the
Hall potential difference.
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All authors Yu. A. Pusep, M. A. T. Patricio, G. M. Jacobsen, M. D. Teodoro, G. M. Gusev, A. K. Bakarov
Materials Science
Electronic mechanism of sub-100-fs demagnetization induced by a femtosecond light pulse
Konrad J. Kapcia, Victor Tkachenko, Flavio Capotondi et al. (+4 more)
A quantitative understanding of the processes that trigger light-induced demagnetization on ultrashort timescales is crucial for achieving an ultrafast, radiation-controlled
magnetic response in materials. This milestone is essential for developing next-generation
magnetic storage devices and ultrafast
magnetic switches. In this theoretical study, we investigated demagnetization triggered in a single
magnetic domain by light pulses ranging from a few to a few tens of femtoseconds in duration, with
photon energies spanning the optical and X-ray regimes, under strongly non-
equilibrium conditions. We predicted a loss of magnetization in the sub-100-fs range in all cases, primarily due to the excitation of the electronic system and the subsequent redistribution of electrons within the magneto-sensitive band. The considered timescales were too short for
phonon-mediated processes or inter-site Heisenberg exchange processes to contribute significantly. These findings pave the way for highly accurate, radiation-driven magnetization control in
magnetic materials at sub-100-femtosecond timescales with potential practical applications.
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All authors Konrad J. Kapcia, Victor Tkachenko, Flavio Capotondi, Alexander Lichtenstein, Serguei Molodtsov, Przemysław Piekarz, Beata Ziaja
Superconductivity · Cross-listed from hep-th
Salvatore Santoro, Roberto Auzzi and Stefano Bolognesi
We investigate field theory models of
holographic superconductors in which the condensation of the order parameter is induced by a Robin boundary condition. Assuming large-$c$ factorization, we study the phase diagram of a two-dimensional CFT deformed by a relevant double-trace perturbation. Using modular invariance, we relate the high- and low-temperature phases, reproducing analytically the results for the zero-winding sector of the
holographic model. Moreover, we match the near-critical behaviour of the condensate with an effective Ginzburg–Landau field theory description. Another important feature of the
holographic superconductor is the presence of
vortices that carry fractional
magnetic flux. We investigate a field theory toy model with similar properties and interpret it as a fractional Little–Parks effect.
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Statistical Mechanics · Cross-listed from cs.LG
Pointwise Generalization in Deep Neural Networks
Shaojie Li and Yunbei Xu
We address the fundamental question of why deep neural networks generalize by establishing a pointwise generalization theory for fully connected networks. This framework resolves long-standing barriers to characterizing the rich nonlinear feature-learning regime and builds a new statistical foundation for representation learning. For each trained model, we characterize the hypothesis via a pointwise Riemannian Dimension, derived from the
eigenvalues of the learned feature representations across layers. This establishes a principled framework for deriving hypothesis-dependent, representation-aware generalization bounds. These bounds offer a systematic upgrade over approaches based on model size, products of norms, and infinite-width linearizations, yielding guarantees that are orders of magnitude tighter in both theory and experiment. Analytically, we identify the structural properties and mathematical principles that explain the tractability of deep networks. Empirically, the pointwise Riemannian Dimension exhibits substantial feature compression, decreases with increased over-parameterization, and captures the implicit bias of optimizers. Taken together, our results indicate that deep networks are mathematically tractable in practical regimes and that their generalization is sharply explained by pointwise, feature-spectrum-aware complexity.
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Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Krylov complexity and fidelity susceptibility in two-band Hamiltonians
Rishav Chaudhuri, Ayush Raj, Soham Ray et al. (+1 more)
We investigate Krylov spread complexity for the ground state of two-band
Hamiltonians, where the reference state is a generic state on the Bloch sphere. The spread complexity is obtained by using a purely
geometric formulation in terms of Bloch sphere data without constructing the
circuit Hamiltonian. For generic reference states, the derivative of the spread complexity is logarithmically divergent at the topological phase transition in the Su-Schrieffer-Heeger (SSH) model. We demonstrate that the derivative of the spread complexity is bounded by fidelity susceptibility for general two-band models, indicating the sensitivity of the spread complexity to any gap closing (topological or trivial). This is illustrated in the massive Dirac
Hamiltonian with a trivial gap closing. Finally, we introduce a non-
unitary duality in the SSH model between the topological and trivial phases, which manifests itself in the spread complexity and fidelity susceptibility.
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All authors Rishav Chaudhuri, Ayush Raj, Soham Ray, Sai Satyam Samal
Superconductivity
Phase dynamics and dissipation in tunnel ferromagnetic Josephson junctions
F. Calloni, R. Satariano, R. Ferraiuolo et al. (+16 more)
We investigate tunnel
ferromagnetic Josephson junctions based on
Superconductor-
Insulator-thin
superconductor-Ferromagnet-
Superconductor multilayers. A comparative study of their electrodynamic properties is performed for junctions with niobium and aluminum (Al) electrodes, featuring different
ferromagnetic interlayer materials and lateral dimensions ranging from the micrometric to the submicrometric scale. The parameters extracted from the fitting of the current-voltage characteristics using the tunnel junction microscopic model are found to be consistent with those independently estimated from switching current distribution measurements. Submicrometric Al-based devices exhibit electrodynamic properties comparable to those implemented in state-of-the-art transmon
qubits and display clear signatures of
quantum phase
diffusion. The strong agreement between transport modelling and escape dynamics establishes a robust framework for describing hybrid
ferromagnetic Josephson junctions consistent with their energy scales and supports their potential integration into superconducting
quantum and classical digital
circuits.
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All authors F. Calloni, R. Satariano, R. Ferraiuolo, H.G. Ahmad, D. Gatta, E. Raja, G. Santo, G. Serpico, R. Vidyasagar, D. Montemurro, N. Poccia, A. Vettoliere, G. Ausanio, C. Granata, L. Parlato, G.P. Pepe, A. Bruno, F. Tafuri, D. Massarotti
Materials Science
Defect Control via Cu Enrichment Enhances Multifunctional Properties in the Polar Semiconductor Cu1+xMn1-ySiTe3
Subrata Ghosh, Yu Liu, Saugata Sarker et al. (+15 more)
Polar materials have recently attracted significant interest due to their rich multifunctional properties. The chalcogenide polar
semiconductor Cu1-xMn1+ySiTe3 (Cu-deficient) is an emerging multiferroic system in which electric polarization is coupled to magnetization. However, its macroscopic ferroelectric polarization is strongly suppressed due to the presence of a high density of stacking faults. In this work, we demonstrate that these
crystal defects, likely originating from non-stoichiometry, can be substantially reduced by increasing the Cu content. Cu-enriched samples, Cu1+xMn1-ySiTe3, crystallize in a noncentrosymmetric monoclinic structure (space group Pm) as the Cu-deficient counterpart but show a nearly stacking-fault-free phase, which is attributed to the emergence of an interstitial site. Consequently, the Cu-enriched samples show a pronounced enhancement of the second-harmonic generation (SHG) response compared to Cu-deficient compositions. Magnetically, the Cu-enriched
crystals retain long-range
antiferromagnetic order with a Neel temperature of TN ~ 33 K without a glassy state but manifest a distinct
spin-flop transition along the polar b-axis that is absent in the Cu-deficient compositions. Furthermore, the electronic ground state evolves from insulating to doped semiconducting behavior upon Cu enrichment. Together, these results establish this material system as a unique and versatile platform for elucidating the interplay among composition,
crystal defects, and multifunctional properties, offering a route to design
magnetic polar systems with tunable
quantum functionalities.
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All authors Subrata Ghosh, Yu Liu, Saugata Sarker, Boyang Zheng, Sreekant Anil, Soumi Mondal, Yuxi Zhang, Sai Venkata Gayathri Ayyagari, Mingyu Xu, Yingdong Guan, Tsung-Han Yang, Xiaoping Wang, Vincent H. Crespi, Nasim Alem, Weiwei Xie, Venkatraman Gopalan, Qiang Zhang, Zhiqiang Mao
Soft Condensed Matter
A geometry-first tutorial for time-resolved morphological analysis with PyPETANA
Benjamin Evert Himberg and Sanghita Sengupta
We present a step-by-step, reproducible tutorial for PyPETANA, an open-source Python framework for geometry-first, time-resolved quantification of evolving morphology from image data. Starting from time-lapse
video input, the tutorial demonstrates how to extract binary masks, compute time-resolved
geometric observables including area, perimeter, circularity, and effective fractal dimensions, and analyze their temporal
evolution. The workflow emphasizes direct reconstruction of morphology from images without assuming microscopic growth mechanisms. In addition to compactness-sensitive
geometric descriptors, the framework supports multiscale boundary analysis through supersampled box-counting methods applied to filled morphologies and finite-width boundary bands. The
benchmark suite further demonstrates applicability to invasive tumor morphologies and multiscale boundary
evolution in time-resolved cancer-growth interfaces. This tutorial accompanies the computational workflow underlying arXiv:2602.05958 and provides a reproducible foundation for geometry-based analysis of evolving non-
equilibrium morphologies.
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Strongly Correlated Electrons
Charge order on a triangular lattice with Mott physics and arbitrary charge density
Aleksey Alekseev, Agnieszka Cichy and Konrad Jerzy Kapcia
Triangular-
lattice systems attract a lot of
attention due to various frustration-induced and strongly correlated effects. Here, we focus on the charge-ordering phenomenon by means of investigation of the extended Hubbard model with dynamical mean-field theory (DMFT). By considering the intersite nearest-neighbor interaction we have found a very rich phase diagram that contains large number of features, phases, and phase transitions. Among them are pinball-
liquid (PL) phases where we distinguish charge-transfer-driven and Mott-localization-driven PLs; phase transitions that change their order as model parameters evolve (from discontinuous to continuous); very strong particle-hole asymmetry. Various features of the phase diagram are found to be better understood by means of the simple mean-field approximation (MFA). Moreover, besides helping with interpretation of the phase diagram, the MFA results together with results for the atomic-limit model are found to be able to set rather good expectations on how the DMFT phase diagram should look like. Nevertheless, a few features were not expected and are found within the DMFT, such as a small-region intermediate metallic phase on an electron-doped side of the phase diagram.
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Statistical Mechanics
Localization of a quantum particle in a classical one-component plasma.III. Mutual coherence and coherence degradation in Coulomb-disordered media
Yury A. Budkov
We derive the mutual coherence function of an electron beam propagating through a static or dynamic Coulomb-disordered medium and show that its decay introduces an intrinsic coherence-reduction mechanism relevant for electron microscopy in Coulomb-disordered media. Using the Efimov path-integral formalism, the coherence length $\rho_c$ is expressed through the same disorder correlator that governs the single-particle localization length $\ell$. For both a static electrolyte and a dynamic
plasma we obtain a universal relation $\rho_c \sim \lambda_D \sqrt{\ell/L}$, where $\lambda_D$ is the Debye length and $L$ the sample thickness. In the static case $\ell\propto k^{2}$ (electron momentum), whereas in the dynamic slow-particle regime $\ell\propto k$, leading to qualitatively different energy dependences of the coherence scale. The ion thermal velocity cancels out in the final expression, demonstrating a formal connection between transverse coherence decay and longitudinal localization phenomena. Exact analytical results are given for the phase structure function of a model electrolyte, and numerical estimates indicate that disorder-induced phase decorrelation may contribute appreciably to the attenuation of high-spatial-frequency contrast under experimentally relevant
liquid-
cell electron microscopy conditions. Possible implications for cryo-EM, disordered
liquids, soft condensed matter, and biological media are discussed. In an appendix we extend the theory to the relativistic regime relevant for transmission electron microscopy.
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Quantum Gases
Vinicius Zampronio, Matteo Ciardi and Fabio Cinti
We investigate the finite-temperature phase diagram of polar molecules confined in a quasi-two-dimensional geometry by a harmonic potential along the polarization axis. We employ
Quantum Monte Carlo simulations to explore the strongly correlated regime accessible with current experimental setups. By tuning temperature and confinement strength, we identify a rich set of phases, including normal fluid, superfluid, supersolid, cluster
crystal, and
bilayer crystal states. Our results reveal the emergence of crystallization upon increasing temperature, highlighting the nontrivial role of thermal fluctuations in dipolar systems. In particular, we show that a
bilayer crystal with one molecule per
lattice site can be stabilized by varying the confinement strength at fixed interaction. Moreover, we show evidence of layering of superfluid states with phase coherence between the two layers. These findings provide insight into the interplay between interactions, confinement, and temperature in low-dimensional dipolar systems, and suggest new directions for engineering
quantum phases with ultracold polar molecules.
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Strongly Correlated Electrons
Interlayer electronic coherence links magnetism and superconductivity in Ruddlesden-Popper nickelates
Feiyang Liu, Lixing Chen, Enkang Zhang et al. (+2 more)
The extent to which electronic dimensionality influences magnetism and superconductivity in Ruddlesden-Popper (RP) nickelates remains unsettled. Here we report high-precision crystallographic-axis-resolved dc transport measurements on high-quality single
crystals of
bilayer and trilayer RP nickelates. Using a six-terminal geometry, we self-consistently determine the intrinsic in-plane ($\rho_\parallel$) and out-of-plane ($\rho_\bot$) resistivities on the same
crystal, while minimizing uncertainties associated with current redistribution in highly anisotropic conductors. We uncover strong intrinsic electronic anisotropy in both
bilayer and trilayer nickelates, in contrast to the weak anisotropy inferred from conventional four-probe measurements. Moreover, $\rho_\bot$ exhibits a nonmonotonic temperature dependence, revealing a universal coherent-to-incoherent crossover in interlayer transport. Across the RP nickelate series, the maximum superconducting transition temperature ($T_c$) observed under pressure is inversely correlated with the ambient-pressure resistivity anisotropy, suggesting that stronger interlayer electronic coherence is favorable for superconductivity. In addition, $\rho_\bot$ serves as an exceptionally sensitive and selective probe of
magnetic and density-wave orders, exhibiting pronounced anomalies, whereas only weak signatures are observed in $\rho_\parallel$. Our results highlight interlayer coherence as a key organizing parameter that both tracks the relevant
magnetic correlations and is closely tied to superconductivity, providing stringent constraints on microscopic theories of high-$T_c$ superconductivity in nickelates.
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All authors Feiyang Liu, Lixing Chen, Enkang Zhang, Ying-Jie Zhang, Jun Zhao
Materials Science · Cross-listed from cs.AI
A Practical Noise2Noise Denoising Pipeline for High-Throughput Raman Spectroscopy
David Martin-Calle, Cesar Alvarez Llamas, Vincent Motto- Ros et al. (+3 more)
A lightweight and reproducible denoising pipeline for high-throughput Raman spectroscopy is presented. The approach relies on a one-dimensional convolutional autoencoder trained using a Noise2Noise strategy, requiring neither external spectral libraries nor high signal-to-noise reference spectra for training. From a reduced training subset composed of repeated short-exposure acquisitions, the model learns to reconstruct Raman spectra while efficiently suppressing
stochastic noise. The method is evaluated on a heterogeneous mineral sample, using both quantitative spectral fidelity metrics (RMSE, SNR, SSIM) and task-oriented criteria based on unsupervised K-means classification. Results demonstrate that integration times as short as 5 ms per spectrum, which are typically insufficient for reliable interpretation, yield denoised spectra with high fidelity to the reference data while preserving chemically coherent maps. This work provides a practical trade-off between spectral quality and acquisition speed, enabling fast, adaptable Raman workflows compatible with routine laboratory use. It also offers a transferable framework for other one-dimensional spectroscopic modalities.
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All authors David Martin-Calle, Cesar Alvarez Llamas, Vincent Motto- Ros, Christophe Dujardin, Jérémie Margueritat, David Rodney
Mesoscale and Nanoscale Physics
Probing Dielectric Screening in van der Waals Heterostructures via Pressure-Tuned Exciton Rydberg Series
Shalini Badola, Adlen Smiri, Thomas Pelini et al. (+7 more)
Excitons in two-dimensional
semiconductors are directly exposed to the environment and are sensitive to the dielectric properties of their surrounding. Here, we show that the Rydberg series of excited states of
excitons in a monolayer WSe$_2$ encapsulated in hexagonal boron nitride (hBN) can be used to probe the pressure-induced modifications of the surrounding dielectric properties. We propose a model based on the pressure induced
evolution of the interlayer distances in this van der Waals
heterostructure and on the bulk dielectric properties of hBN. This approach allows a direct measurement of the dielectric constant of pressurized hBN and establishes a new methodology for dielectric sensing.
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All authors Shalini Badola, Adlen Smiri, Thomas Pelini, Aditi Moghe, Tristan Riccardi, Amit Pawbake, Kenji Watanabe, Takashi Taniguchi, Iann C. gerber, Clement Faugeras
Materials Science · Cross-listed from quant-ph
Quantum Emitters at Telecommunication Wavelengths based on Carbon Defects in Transition Metal Dichalcogenides
Chanaprom Cholsuk, Sujin Suwanna and Tobias Vogl
Low-dimensional materials have emerged as promising hosts for
quantum emitters, whose emission typically arises from either strain-induced band bending or defect-induced two-level systems. Among these materials, transition metal dichalcogenide (TMD) monolayers have attracted particular
attention; however, their performance is limited by strong photoluminescence (PL) quenching at room temperature. As TMDs transition from a direct to an indirect bandgap when moving from monolayers to multilayers, we herein propose a strategy to overcome this quenching limitation by exploiting the indirect bandgap of TMD
bilayers in combination with a point defect doping. The indirect gap suppresses excitonic PL, while specific defects enable robust defect-mediated
quantum emission. Using hybrid-functional density functional theory, we investigate substitutional carbon defects at chalcogen sites (S and Se) in WS2, WSe2, MoS2, and MoSe2
bilayers and comprehensively characterize their optical properties. Both neutral and singly negative charge states are found to be thermodynamically stable. Neutral defects exhibit singlet configurations with emission in the O- and C-band telecommunication windows, whereas negatively charged defects adopt doublet configurations featuring
spin-selective transitions and near-infrared emission. The electron-
phonon coupling strength, radiative lifetime, and dipole orientation are found to depend sensitively on both the host material and defect site, providing distinct fingerprints for experimental identification. Our findings, therefore, establish carbon-doped TMD
bilayers as promising platforms for room-temperature defect-based
quantum emitters operating at telecommunication wavelengths.
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Strongly Correlated Electrons · Cross-listed from quant-ph
Quantum magic of strongly correlated fermions $-$ the Hubbard dimer
Edoardo Zavatti, Gabriele Bellomia and Massimo Capone
We study the non-stabilizerness (
quantum magic) content of the Hubbard dimer, an analytically solvable, yet completely non-trivial, model of strongly correlated
fermions. We consider zero- and finite-temperature properties as well as the time
evolution after a
quantum quench drives the system out of
equilibrium. We evaluate local and nonlocal non-stabilizerness using both the robustness of magic and the stabilizer Renyi
entropy, demonstrating how the latter often fails in detecting the mixed stabilizer states that are typically found in this kind of systems. Finally, we compare the non-stabilizerness with other genuine resources of
quantum-state complexity, i.e., the fermionic non-Gaussianity and the superselected two-site
entanglement. Our findings corroborate the role of non-stabilizerness as a fundamental
quantum resource, capturing aspects of
quantum complexity that elude traditional information-theoretic measures and providing a novel perspective on fermionic systems with tunable interactions.
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Materials Science
Termination-Preserved Ultra-high Tunneling Magnetoresistance in Altermagnetic KV2Se2O
Junnan Guo, Himanshu Mavani, Wenhui Fang et al. (+6 more)
Altermagnets exhibit nonrelativistic
spin splitting without net magnetization, establishing a new platform for next-generation spintronic devices. Although altermagnetic tunnel junctions (AMTJs) represent the most promising realizations, their practical applications are hindered by low tunnel magnetoresistance (TMR) ratios and strong sensitivity to interfacial configurations. Here, we systematically explore the transport properties and microscopic mechanisms of AMTJs based on the recently discovered d-wave altermagnet KV2Se2O. Using first-principles calculations and orbital-resolved analysis, we demonstrate that the synergy between compressed nodal-point like
spin-degenerate channels and coplanar interfacial
magnetic order yields an ultra-high intrinsic TMR above 105% for all interfacial terminations. More importantly, K-termination effectively preserves bulk
spin polarization through its unique passivation characteristics, leading to an ultra-high TMR up to 1012%. These results identify the coupling between momentum-space
topology and interfacial passivation provides a reliable strategy for realizing
giant magnetoresistive responses in altermagnetic spintronic devices.
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All authors Junnan Guo, Himanshu Mavani, Wenhui Fang, Jifeng Tang, Wenhao Li, Weikang Wu, Hui Li, Evgeny Y. Tsymbal, Lishu Zhang
Materials Science
Spatially-Localized Second Harmonic Generation via Spin Wave Concentration in Patterned YIG Structures
Stephanie R. Lake, Marc Eger, Philipp Geyer et al. (+3 more)
The anisotropic dispersion and inherent nonlinearity of magnetostatic
spin waves in thin films and confined structures provide unique opportunities for implementation in next-generation magnonic devices for data and signal processing. A particular challenge is to establish an effective means to locally generate higher harmonics and subsequently exploit them while avoiding extraneous nonlinear losses. Here we demonstrate that deterministically and locally tuning the dispersion relation by
geometric confinement through standard patterning processes, allows the creation spatially localized, high-intensity
magnons hundreds of $\mu m$ or even further from the excitation source. The local intensity obtained in passive, lithographically patterned YIG funnel structures is sufficient to achieve second harmonic generation in localized regions via conventional
magnon scattering processes. We verify these effects are truly nonlinear processes by direct measurement and comparison of the 1-$\omega$ and 2-$\omega$
magnon signals as determined by highly sensitive frequency- and spatially-resolved SNS-MOKE technique. This lays the foundation for using similar devices in future
magnon-based infrastructures to localize and enhance sensitivity of readout, downstream
magnon-based logic operations, and for other higher harmonic generation-related phenomena and low-power magnonics applications.
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All authors Stephanie R. Lake, Marc Eger, Philipp Geyer, Rouven Dreyer, Seth W. Kurfman, Georg Schmidt
Mesoscale and Nanoscale Physics
Spin-caloritronic signatures of soft magnons in bilayer CrSBr
Rob den Teuling, Ping Tang, Gerrit E. W. Bauer et al. (+1 more)
Spin transport in
magnetic insulators is often treated by assuming that
magnons carry a fixed
spin angular momentum of $\hbar$, which does not hold in general, however. Here we calculate the
magnon spin angular momentum of a layered antiferromagnet as a function of applied
magnetic field and wave vector. We show that the triaxial anisotropy and intralayer dipolar interactions in
bilayer CrSBr renormalize the
magnon spin angular momentum, which diverges upon field-induced
magnon softening. This divergence gives rise to a pronounced peak in the thermal
spin Seebeck response and provides a clear
spin-caloritronic signature of soft
magnons.
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All authors Rob den Teuling, Ping Tang, Gerrit E. W. Bauer, Yaroslav M. Blanter