Other Condensed Matter · Cross-listed from hep-th
A ribbon ZX calculus for gauge theory
Gabriel Wong, Razin A. Shaikh and William Donnelly
ZX calculus provides a graphical formalism for
reasoning about
quantum processes, built from two interacting Frobenius
algebras associated with the Z and X bases of a
qubit. While it has found widespread application in
quantum information and computing, its relationship to
quantum field theory has only recently begun to be explored. In this work, we further develop this connection by providing a generalization of ZX calculus to two-dimensional Yang Mills theory with a compact gauge group. The key observation is that both frameworks can be organized around the
Hopf Frobenius algebraic structure associated with a group
algebra, which can in turn be described by the diagrammatics of two dimensional topological
quantum field theory. Given the well known relationship between gauge theory and
gravity in two and three dimensions, our work paves the way for applications of ZX to low dimensional
gravity.
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Materials Science
Symmetry-electronic fingerprints reveal competing magnetic phases in two-dimensional materials
Addis Fuhr, Zachary R. Fox, David Parker et al. (+1 more)
Two-dimensional magnets offer compelling platforms for spintronics and
quantum technologies, yet predicting their
magnetic ground states, moments, and anisotropy remains challenging. This limitation primarily arises because existing machine-learning representations encode chemical environments without capturing the
symmetry or exchange physics that govern magnetism. In this work, we introduce the
symmetry-electronic fingerprint (SEF), a physically interpretable representation that encodes crystallographic
symmetry operations, Wyckoff-site geometry, together with site-resolved electronic structure. Combined with ensemble learning with random forests, the SEF accurately classifies
magnetic ordering while regressing moments alongside anisotropy energies while simultaneously resolving the distinct regimes of itinerant Stoner ferromagnetism from localized superexchange. What sets the SEF-trained models apart is that regions of elevated model uncertainty are not a failure but a diagnostic, identifying materials where these mechanisms compete. First-principles calculations on Co- and Ni-based halides and
oxides confirm that these regions correspond to genuine near-degenerate FM and AFM phases with
magnetic frustration, suppressed anisotropy, and emergent non-collinear ordering. By encoding
symmetry together with exchange physics directly into the representation unlike conventional descriptors, the SEF transforms model uncertainty into a compass pointing toward two-dimensional materials where small perturbations drive transitions between collinear, frustrated, or non-collinear
magnetic phases.
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All authors Addis Fuhr, Zachary R. Fox, David Parker, Ayana Ghosh
Strongly Correlated Electrons
Overview of the Theory of Extremely Correlated Fermi Liquids
B Sriram Shastry
The Extremely Correlated
Fermi Liquids (ECFL) theory is reviewed as a framework for understanding the $t$-$J$ model in metallic systems close to the Mott insulating limit. This overview presents the underlying ideas and the resulting equations in a form accessible to nonexperts. We compare theoretical results with all available resistivity data for single-layer High-T$_{c}$ systems, and with some spectral data. The highlighted results include a density dependent quasilinear T-dependence in resistivity, an unusually small quasiparticle weight, and distinct low-temperature emergent scales that dominate transport, thermodynamics and spectral properties of single-layer High T$_c$ systems. Suggestions are made for further experiments to probe the physics of these challenging
quantum many-body systems.
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Mesoscale and Nanoscale Physics
Micron-sized magnonic 3-port rectilinear circulator
Kevin S. Weber, Loic Temdie, Vincent Castel et al. (+6 more)
The development of miniaturized non-reciprocal microwave technologies compatible with integrated
circuit architectures remains a critical challenge for modern information technology. Here, we present the first experimental characterization of a micron-sized prototypical
magnon circulator. Taking advantage of the
chiral excitation of
spin-waves via nanowire gratings, we propose an original design of a circulator involving three channels of rectilinear and unidirectional
spin-wave beams. We demonstrate via a full 3-port
spin-wave spectroscopy a genuine
spin-wave circulation between the three ports. The narrow frequency band of operation can be tuned over a broad range of frequencies ($2$-$8$ GHz) with both an external field of up to $100$ mT, and the dimensions of the grating specifying the wavevectors. This proposed scheme opens up possibilities for new architectures of integrated and miniaturized non-reciprocal microwave devices.
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All authors Kevin S. Weber, Loic Temdie, Vincent Castel, Timmy Reimann, Morris Lindner, Carsten Dubs, Yves Henry, Matthieu Bailleul, Vincent Vlaminck
Superconductivity
Band-Selective Tunneling and Anisotropic Multiband Superconductivity in V$_2$Ga$_5$
Jozef Haniš, Jozef Kačmarčík, Filip Košuth et al. (+7 more)
Multiband
superconductors with structural anisotropy offer a fertile ground for exploring unconventional
quantum states, yet disentangling their directional pairing characteristics remains a formidable challenge. Here, we present a comprehensive thermodynamic and spectroscopic study of the tetragonal intermetallic
superconductor $\text{V}_2\text{Ga}_5$ ($T_{\rm c} \approx 3.5$~K), combining first-principles electronic structure calculations with highly sensitive AC calorimetry and directional low-temperature scanning tunneling spectroscopy. By constructing a self-consistent, anisotropic multiband singlet $s$-wave pairing model within the fully symmetric $A_{1g}$ representation, we successfully reconcile the experimental specific heat and upper critical field anomalies. Crucially, we reveal that the apparent reversal of bulk gap hierarchies in directional tunneling experiments is a direct consequence of band-selective tunneling. This effect is governed by an elegant interplay between localized
Fermi velocity 'hot spots' and specific
Fermi surface
topologies, rather than raw thermodynamic gap magnitudes alone. Our findings provide a clear microscopic picture of direction-dependent, band-selective tunneling in a highly uniaxial anisotropic
superconductor, demonstrating how orientation-dependent transport constraints shape the observable signatures of multiband
quantum condensates.
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All authors Jozef Haniš, Jozef Kačmarčík, Filip Košuth, Levente Faber, Pavol Szabo, Szymon Królak, Michał J. Winiarski, Tomasz Klimczuk, Peter Samuely, Martin Gmitra
Superconductivity
Viktor Frilen, Annica M. Black-Schaffer and Ankita Bhattacharya
We investigate the anomalous
Hall response (AHR) in a multiband
superconductor at optical frequencies, a phenomenon intimately related to the polar Kerr effect, a key probe of time-reversal
symmetry breaking in
superconductors. In translationally invariant multiband systems with purely intraband pairing, Galilean invariance decouples center-of-mass and relative motion of Cooper pairs, leading to the widespread expectation that a finite AHR requires either disorder or finite interband pairing amplitudes. However, this restriction can be lifted by the
quantum geometric effects inherent to multiband Bloch states. Using a honeycomb
lattice tight-binding model with Kane-Mele
spin-orbit coupling, we analyze the AHR for the time-reversal
symmetry broken
chiral $d$-wave
spin-singlet and
chiral $p$-wave equal-
spin-triplet pairing states with intraband pairing only. We demonstrate, through both analytical and numerical calculations, that the
spin-singlet state yields a vanishing AHR, even with its broken time-reversal
symmetry, whereas the equal-
spin triplet state exhibits a finite AHR, even when it is
spin-
unitary. We attribute the latter to orbital nonunitarity, which, in the presence of
spin-orbit coupling, generates the
spin-polarized Bogoliubov quasiparticle states required for a finite AHR. The response is mediated by interband velocity
matrix elements governed by the
quantum geometry. This finding establishes that
spin-
unitary, but orbitally nonunitary pairing, can generate a finite AHR even without interband pairing and thereby revises the criteria for Kerr signals in
superconductors.
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Superconductivity
Current patterns and loss contributions in CORT cables carrying AC current
Benoît Vanderheyden, Julien Dular, Louis Denis et al. (+4 more)
Conductor-on-round-tube (CORT) cables are a potential solution for carrying AC power in a small cross-section. Due to the geometry of the cable and the helical arrangement of the coated conductors (CC), the current follows a non-trivial pattern inside each CC. For instance, for the case of a single-layer cable, the current flow is mostly axial along the outer face of the CCs and mostly azimuthal along their inner face. Such a current distribution, known as the Garber current pattern, affects the transport AC losses. In numerical models, commonly adopted simplifications are either based on straight conductors or infinitely thin CCs. Such approaches neglect the Garber current pattern and thus misrepresent both the detailed current flow within the CC and the resulting 3D distribution of the fields. In this work, the detailed 3D current distribution in the CCs is investigated in a one-layer CORT cable, as a function of the cable geometrical parameters such as the conductor thickness, the pitch angle, and the gap between adjacent CCs. In particular, the impact of the Garber current pattern is studied on the two largest contributions to the AC losses, namely the surface losses (associated with the penetration of the component of the
magnetic field parallel to the wide faces of the superconducting layer) and the edge losses (associated with the penetration of the perpendicular component of the
magnetic field occurring in the vicinity of the gaps between the CCs). The detailed distribution of the currents in the CCs is examined and its relationship with the different AC loss mechanisms is established. This study is carried out by means of an effective 2D model that uses a system of coordinates conforming with the helical structure of the cable.
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All authors Benoît Vanderheyden, Julien Dular, Louis Denis, Steffen Elschner, Christophe Geuzaine, Mariusz Wozniak, Francesco Grilli
Statistical Mechanics · Cross-listed from quant-ph
A thermodynamic analysis of nonsecular master equations, beyond strict energy conservation and Gibbs equilibrium state
Mohamed Boubakour, Talia Szikman and Cyril Elouard
We present a systematic thermodynamic analysis of nonsecular GKLS master equations. When some energy transitions in the system are comparable with the dissipative rate, the secular approximation is not valid, and the positivity of the dynamics must be ensured via other approximations. The dynamics then presents features reminiscent from strong coupling to the environment: e.g. the
equilibrium state with an environment at thermal
equilibrium is not a Gibbs state of the local system
Hamiltonian and the dynamics couples energy coherences and populations. Nonetheless, we build a unified, consistent thermodynamic framework for those dynamics. We focus on two approximations beyond the full secular approximation (the local and the more accurate
geometric-arithmetic approximations), and then employ systematic perturbation theory on microscopic expressions for the first and second law of thermodynamics which relate irreversibility to the increase of system-environment correlations. We show that, in spite of the weak system-bath coupling, the system-bath interaction energy participates to the energy balance, and is directly linked to the Lamb-shift
Hamiltonian. We compare this microscopic
entropy production with the definition based on the contractivity of the reduced system dynamics (Spohn inequality). We show that, unlike for secular master equations, the two
entropy production rates differ because of the presence of non-vanishing stationary coherences in the energy eigenbasis. However, in the case of a single thermal bath, the difference is purely transient, and no work can be cyclically extracted from the steady-state despite its non-Gibbs form. Finally, we illustrate our results with simple examples, clarifying and completing the thermodynamic picture of Markovian dynamics in the
quantum regime.
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Quantum Gases
Quasi-two-dimensional trapped tilted dipoles at zero and finite temperatures in the strongly dipolar regime
Juan Sánchez-Baena
Motivated by the recent experimental observation of dipolar supersolid stripes in a quasi two-dimensional geometry [arXiv:2512.13280 (2025)], we study a trapped system of fully polarized dipoles in a strongly axially confined geometry, both at zero and finite temperatures, by means of Bogoliubov theory. The dipoles are strongly harmonically trapped along the z axis and subjected to a box trap in the x-y plane. We characterize the physics of the trapped system at zero and finite temperatures as a function of the tilting angle of the dipoles, the number of particles and the scattering length, restricting ourselves to the experimentally relevant regime of large condensate fractions. We also illustrate the influence of the aspect ratio of the box trap in the
liquid character of the system and its structure. We observe a remarkable promotion of spatial modulations when temperature is increased while keeping the total particle number constant for specific configurations, in qualitative agreement with previous Monte Carlo results in a 3D geometry. Our results are useful to understand the zero temperature physics of the trapped dipolar system in the quasi-2D limit and in the strongly dipolar regime. In addition, they allow to assess the effect of temperature in its
equilibrium properties in experimentally relevant conditions, which may be useful for thermometry applications.
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Mesoscale and Nanoscale Physics
Thermoelectric information engine driven by an autonomous Maxwell demon across quantum-to-classical transitions
Maximiliano Bernal Santibañez, Felipe Barra and Jose Mondaca
We study a three-terminal thermoelectric engine, focusing on the role of
quantum coherence and information flow. A double-dot connects two reservoirs at different chemical potentials, while a third dot monitors their occupation via Coulomb interaction and can be interpreted as an autonomous Maxwell demon. Within the parameter range where the device operates as an engine, we identify conditions under which this interpretation holds. The system dynamics is described within a Redfield master equation that allows us to identify two distinct dynamical regimes with steady states well captured by suitable Lindblad approximations. These two regimes define a first
quantum-to-classical transition controlled by the interdot tunneling strength. We further consider the effect of a
phonon bath coupled to the double-dot, which induces a second
quantum-to-classical transition by generating incoherent transport and decoherence in the small interdot tunneling regime. We identify a parameter region where
phonon-induced decoherence suppresses both the coherent transport contribution and the information flow toward the monitoring dot, suggesting that coherence can enhance the demon mechanism in this regime. By tracking information and transport properties across these crossovers, our model shows how coherent tunneling, decoherence, and incoherent
phonon-assisted transport compete in an autonomous information engine, while clarifying which thermodynamic Lindblad description is appropriate in each regime.
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Statistical Mechanics
Population dynamics of surface-mediated autocatalytic processes
Denis S. Grebenkov and Yilin Ye
We investigate the population dynamics of surface-mediated autocatalytic processes, in which particles diffuse in a complex environment towards surface regions where they can be either killed or replicated. These opposite mechanisms compete with each other and lead to a sophisticated
stochastic evolution of the population size. We provide a systematic analysis of the generating function of the population size. We also deduce its distribution, mean, variance and higher-order moments. For this purpose, we employ several equivalent descriptions of these quantities in terms of nonlinear integral equations and partial differential equations with nonlinear boundary conditions. We inspect the long-time behavior of the population dynamics in three regimes when the mean population size vanishes, reaches a steady-state level, or grows exponentially. A numerical solution of the underlying integral equations and independent Monte Carlo simulations support our theoretical predictions.
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Soft Condensed Matter
Tracking microscopic irreversibility during yielding of a colloidal fractal gel with Rheo-Echo-XPCS
William Chèvremont, Julien Bauland, Emmeline Brassac et al. (+4 more)
Understanding how microscopic structural dynamics relate to macroscopic mechanical response during yielding remains a central challenge in soft matter physics. Here, we introduce rheo-echo X-ray
photon correlation spectroscopy (rheo-echo-XPCS) with nonlinear acquisition synchronized to oscillatory shear, enabling direct measurement of irreversible nanoscale dynamics under strain amplitude control. Applying this to a carbon black colloidal fractal gel, we resolve time-periodic echoes in the vorticity-direction intensity autocorrelation function whose decay encodes non-affine structural rearrangements. We find: (i)~ballistic-like decorrelation with $\tau \propto q^{-1}$ at all strains, where the decorrelation velocity $v_\tau = 1/\langle q\tau \rangle$ scales linearly with the loss tangent $\tan\delta = G''/G'$, establishing $\tan\delta$ as a direct macroscopic signature of the rate of irreversible structural decorrelation; (ii)~functional form continuous
evolution from compressed exponential ($\alpha \simeq 1.5$) at low strain, consistent with three-dimensional dipolar strain fields in the intact network-to stretched exponential ($\alpha \simeq 0.5$) at high strain, reflecting a dimensional reduction from $d_f = 3$ to $d_f = 1$ as stress transmission shifts from bulk to quasi-one-dimensional filamentary backbones during network fragmentation.
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All authors William Chèvremont, Julien Bauland, Emmeline Brassac, Gonzalo Sanchez Vera, Stefano Aime, Frédéric Pignon, Thomas Gibaud
Mesoscale and Nanoscale Physics
Phonon polariton confinement in isotopically pure MOVPE-grown BN triangles
Maximilian Scharpey, Oskar Schröer, Daniel Wigger et al. (+5 more)
Phonon polaritons, quasiparticles formed by the resonant hybridization of light and
lattice vibrations, exhibit unique properties like the possibility of
hyperbolic dispersions. In this context, exfoliated hexagonal boron nitride (hBN) has emerged as a promising material for
phonon polariton-based research. However, to advance toward practical applications, it is essential to demonstrate efficient
phonon-polariton propagation and confinement in large-area epitaxial BN. To address this topic, we use metalorganic vapor phase epitaxy (MOVPE)-grown BN and investigate the
phonon polariton properties using scattering-type scanning near-field optical microscopy (s-SNOM) and nanoscale
Fourier transform infrared spectroscopy (nano-FTIR). We report remarkably long
phonon polariton propagation lengths, indicating the high crystalline quality of the BN layer. By using epitaxially grown isotopically pure triangular islands, we further demonstrate efficient
phonon-polariton confinement with mode patterns tunable by the incident light wavelength. Our results pave the way for implementing all-epitaxial, microscale, high-quality polariton resonators for nanophotonics and
quantum optics.
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All authors Maximilian Scharpey, Oskar Schröer, Daniel Wigger, Lena Miler, Jakub Iwański, Andrzej Wysmołek, Johannes Binder, Iris Niehues
Disordered Systems and Neural Networks · Cross-listed from physics.optics
Optical Implementation of Equilibrium Propagation Using Spatial Photonic Ising Machines
Dimitri Vanden Abeele, Daniele Veraldi, Davide Pierangeli et al. (+2 more)
Equilibrium Propagation offers a compelling alternative to traditional machine learning for training energy-based networks. Here we demonstrate a hybrid optical-digital implementation of EP using a Spatial Photonic Ising Machine (SPIM). The SPIM exploits the gauge transformation method to optically encode both continuous
neuron states and rank-1 binary trainable patterns as phase modulations via a spatial light modulator, with inference realized using a finite difference scheme. The experimental system is evaluated on the Wine classification
dataset. The potential of this approach, including the use of continuous couplings and structured coupling
matrices, is evaluated numerically on the more complex MNIST
dataset. Our work provides a concrete pathway toward energy-efficient physical implementations of
Equilibrium Propagation.
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All authors Dimitri Vanden Abeele, Daniele Veraldi, Davide Pierangeli, Claudio Conti, Serge Massar
Materials Science · Cross-listed from math.NA
Momentum Space Algorithm for Electronic Structure of Double-Incommensurate Trilayer Graphene
Ken Beard and Daniel Massatt
Numerical
algorithms for computing electronic structure of incommensurate 2D materials using ab initio models is critical for predicting material properties and guiding experiment. For
bilayers, momentum space and continuum models have been introduced to approximate observables of ab initio tight-binding models using a momenta description despite the lack of periodicity in the tight-binding model required for Bloch theory. A similar structure has been introduced for double-incommensurate trilayers using a continuum model, where the three
lattices are all mutually incommensurate. However, this description leads to a four-dimensional
lattice space, and numerical convergence of the density of states was observed to have poor convergence. In this work, we introduce a momentum space framework for double incommensurate trilayer
graphene, and introduce an efficient truncation scheme of the four-dimensional
lattice to drastically improve convergence of the density of states and momentum local density of states (a parallel object to classical band structure). We implement this
algorithm on an ab initio model of twisted trilayer
graphene and validate convergence estimates. We further verify numerically that the momentum space
algorithm, inherently higher order than the continuum model as it is an exact transformation of the tight-binding model, captures altered band behavior near the flat bands at magic angles.
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Strongly Correlated Electrons · Cross-listed from hep-lat
Numerical Hints for Dyon Condensation at $\theta=2\pi$ via Wilson-'t Hooft Loops in $SU(2)$ Yang-Mills Theory
Hiromasa Watanabe, Issaku Kanamori, Okuto Morikawa et al. (+3 more)
Yang-Mills theories at $\theta$ and $\theta+2\pi$ are unitarily equivalent, but their $2\pi$ periodicity has a nontrivial realization. Recent developments in generalized
symmetries rigorously prove that confinement
vacua at $\theta=0$ and $2\pi$ should belong to different
symmetry-protected topological (SPT) states with the $1$-form center
symmetry. For its examination, we measure the Wilson-'t Hooft loop operators at $\theta=2\pi$ for the $SU(2)$ Wilson
lattice gauge action and discuss their long-distance behaviors. This requires us to identify the gauge topological charge in the presence of defects, and we employ the $1$-form covariant DBW2 gradient flow to smear
lattice gauge fields. We find a clear perimeter-law signal for the dyonic Wilson-'t Hooft loop at $\theta=2\pi$, providing numerical evidence in the pure $SU(2)$ Yang-Mills theory for the theoretically expected dyon condensation at $\theta=2\pi$.
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All authors Hiromasa Watanabe, Issaku Kanamori, Okuto Morikawa, Yuki Nagai, Yuya Tanizaki, Akio Tomiya
Materials Science
Dopant-induced modifications of the optical properties of GaSe
Jakub Sójka, Katarzyna Olkowska-Pucko, Kacper Walczyk et al. (+5 more)
Doping plays a crucial role in tailoring the electronic, optical, and
magnetic properties of
semiconductors, enabling control of carrier dynamics and the formation of functional states for optoelectronic applications. We investigate the influence of Fe dopants on the optical properties of GaSe
crystals using photoluminescence (PL) spectroscopy under varying excitation power, temperature, and
magnetic field. Fe incorporation introduces multiple sharp emission lines in addition to intrinsic excitonic transitions, including free and localised
excitons. Power- and temperature-dependent measurements indicate that these emission features are associated with Fe-related dopant centres (Fe-bound
excitons). Magneto-PL measurements reveal two distinct families of $g$-factors, enabling the identification of intrinsic excitonic transitions and Fe-induced defect states. These results demonstrate that Fe doping creates optically and magnetically active centres in GaSe, providing insight into defect-related excitonic processes and their potential relevance for magneto-optoelectronic and
quantum photonic applications.
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All authors Jakub Sójka, Katarzyna Olkowska-Pucko, Kacper Walczyk, Zakhar R. Kudrynskyi, Volodymyr Boledzjuk, Adam Babiński, Maciej R. Molas, Grzegorz Krasucki
Materials Science
The phase composition and physical properties of melt-quenched multicomponent alloy FeCoNiB0.7Si0.3Be
Oleksandr I. Kushnerov, Sergey I. Ryabtsev, Pavlo O. Galagan et al. (+1 more)
The structure and physical properties of the high-
entropy multicomponent
alloy FeCoNiB0.7Si0.3Be in the as-cast and melt-quenched states were studied. The cooling rate of the melt-quenched films was estimated to be approximately 10^6 K/s based on the film thickness. X-ray analysis revealed a multiphase structure, including a BCC-type ordered phase (structural type B2) and intermetallic compounds (Fe, Ni, Co)2B. In melt-quenched samples, the fraction of the B2 phase increased, leading to a decrease in microhardness from 10400 MPa in the as-cast state to 8900 MPa in the melt-quenched state.
Magnetic studies confirmed the
ferromagnetic nature of the FeCoNiB0.7Si0.3Be
alloy. The coercive field of melt-quenched samples (17500 A/m) was significantly higher than that of the as-cast ones (5200 A/m), which is attributed to structure refinement and an increased level of microstresses.
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All authors Oleksandr I. Kushnerov, Sergey I. Ryabtsev, Pavlo O. Galagan, Valerij F. Bashev
Materials Science
Physics-informed time-series forecasting of perovskite photoluminescence stability
Alexander Wieczorek, Manuel Kober-Czerny, Fábio Lopes et al. (+5 more)
Accelerated ageing using elevated temperatures and illumination is one of the most common methods to rapidly study the stability of novel
semiconductor materials. However, as the pace of materials discovery continues to accelerate, even faster stability evaluations are needed. A physics-informed time-series
forecasting algorithm designed to predict the long-term photoluminescence stability of metal halide perovskites is presented. A diverse experimental
dataset of 167 metal halide perovskites is collected, including different crystallinities and compositions. These are stressed using heat and light, while the photoluminescence (PL) is monitored. The >86k collected PL spectra are featurized using a physics-informed model, and a hybrid CNN-LSTM model is trained to forecast the PL intensity during degradation of samples unseen during model training. Notably, the approach generalizes across the material groups and outperforms baseline
benchmarks. Furthermore, the physics-based featurization ensures explainability, enabling analysis to identify critical stability descriptors for given predictions. It is expected that this approach will be adapted to other types of time-series data and enables a pathway to significantly reduce experimental testing times.
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All authors Alexander Wieczorek, Manuel Kober-Czerny, Fábio Lopes, Austin George Kuba, Leon Müller, Christian M. Wolff, Jason Hattrick-Simpers, Sebastian Siol
Materials Science
Enhanced Photocurrent Response in Epitaxial 0.5PZT-0.5PFN Multiferroic Thin Films
Lucia Imhoff, Miguel A. Rengifo, Jose M. Caicedo Roque et al. (+4 more)
The exploration of novel multiferroic materials with strong coupling between ferroelectric polarization and photovoltaic effects is crucial for next-generation optoelectronic devices. In this study, we characterized highly oriented 0.5Pb(Zr0.52Ti0.48)O3-0.5Pb(Fe0.5Nb0.5)O3 multiferroic thin films grown by pulsed
laser deposition on SrTiO3 (001) substrates with a SrRuO3 bottom electrode. The films exhibited excellent crystalline quality, with a single perovskite phase and (001) orientation. They displayed good ferroelectric properties (remanent polarization $\sim$17 $\mu$C/cm$^2$, PUND; coercive field $\sim$150 kV/cm), alongside weak
ferromagnetic behavior at room temperature (remanence 1.30 emu/cm$^3$; coercive field 90 Oe). Photovoltaic measurements demonstrated a robust, polarization-dependent photoresponse under 403 nm monochromatic
laser illumination, achieving Jsc values between $\pm$20 $\mu$A/cm$^2$. This compelling observation confirms the intrinsic coupling between ferroelectric polarization and photovoltaic effects, highlighting the considerable promise of these single-phase multiferroic thin films for advanced photovoltaic and optoelectronic
memory applications.
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All authors Lucia Imhoff, Miguel A. Rengifo, Jose M. Caicedo Roque, Jessica Padilla-Pantoja, Jose Santiso, Marcelo G. Stachiotti, Myriam H. Aguirre
Materials Science
Polarizing ultrathin ferroelectric BaTiO3 films through interfacial layer polarization
Ipek Efe, Edith Simmen, Tobias Goldenberger et al. (+3 more)
An important requirement for the integration of ferroelectric thin films into devices is deterministic control of the polarization state in films of only a few unit
cells in thickness. Here, we utilize the charged atomic planes of (001)-oriented SmNiO$_3$ (SNO) buffer layers as a polarizing template to stabilize the polarization in ferroelectric BaTiO$_3$ (BTO) model system thin films. We show that an upwards (downwards) oriented polarization is achieved by selection of the [SmO]$^+$ ([NiO$_2$]$^-$) buffer termination. Most importantly, the charged atomic planes of SNO suppress the depolarizing-field-induced critical thickness in BTO, and we record the emergence of a net polarization in our BTO films from the first unit
cell deposited. Our experiments, guided by density-functional-theory (DFT) calculations, further highlight the impact of charged defects on the polarizing effectiveness of the SNO buffer. Specifically, oxygen vacancies counteract the polarizing field of the negatively charged, [NiO$_2$]$^-$-terminated surface of the SNO buffer. Our findings provide important insights into the interplay of defect chemistry and polarizing interfaces to stabilize ferroelectric polarization down to the single-unit-
cell limit.
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All authors Ipek Efe, Edith Simmen, Tobias Goldenberger, Manfred Fiebig, Nicola A. Spaldin, Morgan Trassin
Superconductivity
Andreev Reflection to Probe Momentum-Dependent Spin Polarization in Altermagnet CrSb
Yan Zhang, Yixuan Luo, Yue Yang et al. (+7 more)
Altermagnetic materials have recently emerged as promising candidates for next-generation spintronic applications, characterized by the k-dependent
spin-splitted band structure and a simultaneous zero-net-magnetization. Among them, altermagnetic candidate CrSb has attracted considerable
attention, owing to its g-wave
spin splitting and high Néel temperature. In this article, we employed mechanical point-contact spectroscopy (MPCS) with superconducting Nb tips to probe the Andreev reflection on CrSb single
crystals along three principal crystallographic orientations. The extracted momentum-dependent
spin polarizations are approximately 73.4% for the (0001) plane, 67.9% for the (-1-120) plane, and 61.9% for the (10-10) plane, respectively, distinct from conventional antiferromagnets. Furthermore, conductance spectra from spatial line-scans on the sample surface support the existence of altermagnetic domains with a characteristic size of 250-500 nm separated by domain-walls with width about 250 nm. These results strongly support the momentum-dependent
spin polarization in altermagnetic CrSb and establish Andreev reflection as a new paradigm to probe k-dependent
spin textures.
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All authors Yan Zhang, Yixuan Luo, Yue Yang, Zilong Li, Weilong Qiu, Lunhui Hu, Yuanfeng Xu, Yanfeng Guo, Chao Cao, Xin Lu
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Steady-State Noise Signatures of Lindbladian Exceptional Points
Shihang Pan, Gianmichele Blasi and Géraldine Haack
Exceptional points (EPs) are non-Hermitian degeneracies at which two or more
eigenvalues and their corresponding eigenvectors coalesce. In open
quantum systems, exceptional points can arise in the Lindbladian governing the dissipative dynamics. Their signatures have so far been mainly identified in finite-time observables, such as transient currents, while steady-state average currents generally provide no direct evidence of the underlying exceptional-point structure. In this work, we demonstrate that signatures of Lindbladian EPs can nevertheless be accessed in the steady-state regime through current noise. We derive general expressions for current correlation functions within a Lindblad master-equation framework and show, in particular, how exceptional points affect their behaviour as a function of the time delay. We illustrate these results with the paradigmatic example of two interacting
qubits coupled to two reservoirs, where the steady-state noise clearly distinguishes overdamped, underdamped, and critical regimes. Our results establish current correlation functions as a steady-state probe of Lindbladian EPs in open
quantum systems.
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Strongly Correlated Electrons
Variational Monte Carlo study of a two-orbital Hubbard model for the iron pnictides
Vito Marino, Gabriele Gatti, Massimo Capone et al. (+1 more)
We study a two-orbital Hubbard-Kanamori model, which has been originally proposed for iron-based
superconductors, using variational Monte Carlo. We span the nonmagnetic sector at both hole-doping and electron-doping, with respect to the half-filled case $n=2$. We report the presence of a superconductive region with a $s^{\pm}$
symmetry only when the half-filled system is in a Mott state, while orbital selectivity is absent. These results are qualitatively different from what was reported in the three-orbital Hubbard-Kanamori model, where a more extended superconductive region was observed with a concomitant development of orbital selectivity, and they are to some extent more reminiscent of the single-band Hubbard model.
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All authors Vito Marino, Gabriele Gatti, Massimo Capone, Luca F. Tocchio
Strongly Correlated Electrons
Modeling strained Cd$_3$As$_2$ thin films and their behavior in magnetic fields
M. Smith, A.A. Burkov, P. P. Orth et al. (+2 more)
We present a systematic analysis of the behavior of thin films of Cd$_3$As$_2$ under different strain profiles and in
magnetic fields. In each case, we construct effective $k \cdot p$ models by considering the reduction of
symmetry and all constraints imposed by the remaining
symmetries. Our analysis naturally describes both in-plane biaxial and uniaxial strain. Biaxial strain is expected to preserve in-plane $C_4$ rotational
symmetry while breaking inversion, allowing for a description in terms of the $4mm$ point group. Uniaxial strain, on the other hand, breaks $C_4$
symmetry. For this case, we consider two scenarios: one preserving inversion, described by the $mmm$ group, and one breaking it, leading to $2mm$
symmetry. After deriving the models, we examine the effects of out-of-plane
magnetic fields, identifying two possible microscopic mechanisms that can account for the experimental results reported in Ahadi et al. (2025). Importantly, our analysis proposes a new method for differentiating between them. By incorporating the effects of multiple subbands along the confinement direction, we show that the opening of a gap in the lowest Landau level requires either reducing the
symmetry down to $2mm$, breaking both inversion and $C_4$ rotations, or a topological transition of the band structure due to strain-induced band renormalization. Furthermore, we demonstrate that a two-dimensional Dirac semimetal phase can be induced by sufficiently large in-plane
magnetic fields. This phase is highly sensitive to different strain profiles, with band touchings occurring when the field is applied perpendicular to preserved mirror planes, serving as a powerful probe of the material's strain profile.
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All authors M. Smith, A.A. Burkov, P. P. Orth, I. Martin, Victor L. Quito
Mesoscale and Nanoscale Physics
Understanding quantum behaviors of an electron in a uniform magnetic field alternatively
Jin-Ming Wang, Yuan-Zao Gao, Dai-Lin Cun et al. (+1 more)
Quantum mechanically, an electron moving in a uniform
magnetic field forms Landau levels. A curious feature is that for states with a negative angular
quantum number, the total probability current vanishes, which appears to contradict the classical picture of cyclotron motion. While a
geometric interpretation based on classical orbits exists, alternative interpretations remain of interest. In this paper, we examine the probability current density and identify a critical radius that naturally partitions the plane into an inner clockwise-flow region and an outer counterclockwise-flow region. We show that the vanishing total current results from an exact cancellation between these two regions. Furthermore, by defining a partitioned kinetic angular momentum with respect to the critical radius, we reveal an intrinsic competitive structure: the electron simultaneously carries two opposing rotational components. The negative
quantum number manifests in the strength of the inner counter-rotation, while the net kinetic angular momentum remains positive. This bidirectional flow picture also provides a dynamical interpretation of the infinite degeneracy of Landau levels.
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All authors Jin-Ming Wang, Yuan-Zao Gao, Dai-Lin Cun, Jian Jing
Strongly Correlated Electrons
Frustration effects on the magnetization plateau physics in a trimerized quantum spin-1/2 chain
L. M. Ramos, M. Schmidt and F. M. Zimmer
We investigate frustration-induced instabilities in a trimerized
quantum spin chain motivated by recent experimental findings for the compound Na$_2$Cu$_3$Ge$_4$O$_{12}$. Employing a cluster mean-field approach combined with Lanczos exact diagonalization, we analyze the ground-state and
quantum-information properties of a Heisenberg model with competing interactions in a
magnetic field. In the weakly frustrated regime, the system exhibits a robust $1/3$ magnetization plateau associated with a collective ferrimagnetic-like trimer state. Increasing the next-nearest-neighbor intratrimer coupling drives a pronounced reorganization of
spin correlations, leading to a crossover toward a doublon-like correlation regime and providing a static ground-state picture consistent with the composite excitations observed dynamically in trimerized chains. The resulting low-energy behavior can be interpreted in terms of weakly interacting emergent
spins, offering a microscopic explanation for the extended stability of the magnetization plateau. Furthermore, through finite-size scaling analyses of the energy gap, von Neumann
entanglement entropy, and fidelity susceptibility, we characterize the zero-field criticality of the model. Ultimately, our results suggest that frustration gives rise to qualitatively distinct
quantum states and provide a microscopic framework for understanding the emergence of fractionalized excitations in trimerized
quantum spin systems.
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Strongly Correlated Electrons
Phase diagram of the Kitaev-Heisenberg-$\Gamma$ model: Classical and quantum magnetism, frustration, and subdominant interactions
Kiyu Fukui and Yukitoshi Motome
The Kitaev
spin liquid provides a rare example of exactly solvable
quantum spin liquid states. Intensive research over the past two decades has identified a variety of its candidate materials. In real materials, however, the Kitaev interaction is inevitably accompanied by additional
magnetic interactions such as the Heisenberg and $\Gamma$ interactions. These interactions often induce
magnetic ordering at low temperatures, making it essential to clarify their effects in the search for and design of Kitaev
spin liquid candidate materials. In this study, we revisit the ground-state phase diagram of the Kitaev-Heisenberg-$\Gamma$ model from both classical and
quantum perspectives, using state-of-the-art numerical techniques. In the classical case, we reveal a $zoo$ $of$ $noncollinear$ $orders$, where a variety of noncollinear multiple-$Q$
magnetic orders with and without incommensurate modulations emerge. In the
quantum case, we unravel that
quantum fluctuations suppress many of the competing orders found in the classical case, resulting in a reduced number of dominant incommensurate orders. We further identify $highly$ $frustrated$ regions, where spiral
spin liquid states as well as new magnetically ordered states are potentially stabilized by other additional
magnetic interactions. Our results provide a comprehensive perspective on the Kitaev-Heisenberg-$\Gamma$ model for both classical and
quantum spins and offer a valuable guide not only for interpreting experimental results on candidate materials, but also for searching and designing new materials to realize the Kitaev
spin liquid.
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Strongly Correlated Electrons
Selective stabilization of antiferromagnetic orders in FeTe films via local strain engineering
Hao Xu, Jing Jiang, Xuesong Gai et al. (+5 more)
The parent compound FeTe hosts a complex
magnetic landscape that is highly susceptible to
lattice distortions. Although theoretical models have predicted a bicollinear to dimer
antiferromagnetic (AFM) phase transition under tensile strain, its experimental realization and deterministic control has remained elusive owing to severe
magnetic frustration. Here, combining high-resolution scanning tunneling microscopy (STM) and density functional theory (DFT) calculations, we demonstrate the selective stabilization of bicollinear and dimer AFM orders in few-layer FeTe films via local uniaxial strain engineering. By mapping the strain fields near dislocation areas in FeTe films and FeTe/FeSe
heterostructures, we establish a direct correspondence between specific strain components and the resulting
magnetic ground states. We find that uniaxial compression along the Fe-Fe next-nearest-neighbor direction stabilizes the bicollinear AFM order, with the stripe orientation aligning parallel to the compression axis. Crucially, we report the experimental realization of the long-range dimer AFM order, which emerges under anisotropic strain along the Fe-Fe nearest-neighbor direction. This phase manifests as a distinct $\sqrt{2} \times \sqrt{2}$ electronic reconstruction and shares a common Neel temperature with the bicollinear phase. Our findings reveal that anisotropic strain effectively lifts the
magnetic degeneracy among competing states. This work provides a robust strategy for the manipulation of elusive
magnetic orders and offers insights into the interplay between
lattice,
spin, and electronic degrees of freedom in iron-based
superconductors.
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All authors Hao Xu, Jing Jiang, Xuesong Gai, Haicheng Lin, Kai Liu, Zhong-Yi Lu, Kai Chang, Chong Liu
Materials Science
Thickness-Independent Quantum Geometric Responses Driven by Interlayer Antiferroic Coupling
Zhiming Xu and Huaqing Huang
Two-dimensional ferroic materials exhibit rich and intriguing physical phenomena, but their response properties generally depend sensitively on thickness, requiring precise layer-number control and thereby limiting practical applications. Here, we propose a general strategy for realizing thickness-independent
quantum geometric responses through
symmetry engineering induced by interlayer antiferroic coupling. Using spatial-dependent
symmetry analysis, we show that thickness-independent behavior emerges when the
symmetry breaking required for a given response is generated by interlayer
antiferromagnetic (AFM) or antiferroelectric (AFE) coupling, without invoking topological mechanisms. Our first-principles calculations predict that multilayer MnS in the G-type AFM configuration exhibits a surface-dominated anomalous
Hall effect, whose thickness-independent behavior can be significantly influenced by the stacking order. We further propose design principles for achieving thickness-independent anomalous and nonlinear
Hall effects driven by interlayer AFE coupling, and suggest potential applications in distinguishing
magnetic structures. Our findings open a new route towards robust functional devices based on antiferroic materials.
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