Strongly Correlated Electrons
Raman signatures of a non-reciprocal magnetic phase transition in Ca$_2$RuO$_4$
Giacomo Jarc, Giovanni Tartaglia, Francesco Gabriele et al. (+17 more)
The
magnetic behavior of Ca$_2$RuO$_4$ represents a unique puzzle due to the interplay of strong electronic correlations, magneto-elastic interactions, and large
spin-orbit coupling. At low temperatures, an anomalous Mott insulating state emerges, characterized by a complex antiferromagnetic order with a collective amplitude excitation of the
magnetic moment which has been discussed in analogy with the
Higgs mode. We report here evidence of a
magnetic first-order phase transition driven by an out-of-plane
magnetic field along the crystallographic $c$-axis of Ca$_2$RuO$_4$. Raman measurements in
magnetic field reveal the emergence of mode of
magnetic origin and a concomitant modification of the coupling between a
phonon and the
Higgs amplitude mode. Both the Raman features are characterized by a non-reciprocal hysteresis in
magnetic field. Surprisingly, the observed phase transition does not affect the Raman scattering from the in-plane
magnons, indicating that the dipolar antiferromagnetic order is preserved. This is consistent with the onset of a new quadrupolar field-controlled state, whose fluctuations structure can trigger an hybridization between the
lattice and the
magnetic Higgs mode resulting in the observed Raman features.
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All authors Giacomo Jarc, Giovanni Tartaglia, Francesco Gabriele, Filomena Forte, Anita Guarino, Angela Montanaro, Enrico Maria Rigoni, Nitesh Khatiwada, Costanza Lincetto, Gabriele Bartolini, Antonio Mastropasqua, Shahla Yasmin Mathengattil, Marco Malvestuto, Muhammad Waqee Ur Rehman, Rosalba Fittipaldi, Joachim Deisenhofer, Alexander A. Tsirlin, Antonio Vecchione, Mario Cuoco, Daniele Fausti
Materials Science
Switchable Altermagnetism in a Layered van der Waals Metal-Organic Framework Driven by Spin-Crossover
Diego López-Alcalá, Alberto M. Ruiz, Andrei Shumilin et al. (+1 more)
Dynamical control of altermagnetism is a key requirement for translating its unique
spin-dependent functionalities into practical spintronic devices, yet effective switching mechanisms remain largely unexplored. Here, we open an unprecedented, versatile and programmable route based on
spin-crossover to switch altermagnetism on demand in molecular materials. Using density functional calculations, we demonstrate an altermagnetic ground state in the layered van der Waals MOFs MnX$_2$(tdz)$_2$ (X = Cl, Br; tdz = thiadiazole), stabilized by anisotropic interlayer exchange interactions, which gives rise to a characteristic d-wave momentum-space
spin splitting and an associated
spin-splitter transport response. Our findings reveal that under hydrostatic pressure, a high-
spin to low-
spin transition reconfigures the Mn d-orbital occupation, thus modifying the
magnetic exchange network, and stabilizing a different antiferromagnetic ground state whose
symmetry suppresses the nonrelativistic
spin splitting. Crucially,
spin-crossover switches altermagnetism not by directly altering the electronic structure, but by changing the
symmetry of the
magnetic ground state. These results establish molecular
spin-crossover altermagnets as a platform for externally reconfigurable spintronic devices.
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All authors Diego López-Alcalá, Alberto M. Ruiz, Andrei Shumilin, José J. Baldoví
Superconductivity
Interference-controlled magnetic bound states and subgap transport in a Square–octagon superconductor
Ravi Kiran
The square–octagon
lattice provides a useful setting for studying
magnetic adatoms because its multisublattice structure allows different adsorption geometries to probe distinct combinations of the host electronic states. We study
magnetic adatoms in an $s$-wave superconducting square–octagon
lattice, focusing on the interplay between adsorption geometry, narrow and flat-band states, and subgap transport. We find that the large spectral weight associated with a flat band does not necessarily imply strong impurity–host coupling. For symmetric square-hollow adsorption, destructive interference strongly suppresses the overlap with the flat-band
manifold, whereas top and octagon-hollow adsorption retain substantial overlap. This selectivity is reflected in the
magnetic bound states, with the square-hollow channel supporting a predominantly atomic state, while the top and octagon-hollow states are strongly hybridized with the superconducting host. The effect develops continuously as the relevant band becomes flatter and remains pronounced in a material-motivated parameter regime. In a normal–
superconductor–normal geometry, these differences are also reflected in the nonlocal subgap conductance. At a representative exchange splitting, square-hollow adsorption suppresses the low-bias conductance relative to the clean device, whereas octagon-hollow adsorption enhances it, with the square-hollow response showing a much sharper dependence on exchange splitting. Our results show that the
magnetic-adatom response in narrow and flat-band
superconductors is governed by the available spectral weight and by the
symmetry and wave-function structure of the impurity–host hybridization.
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Superconductivity
Doping-controlled topological superconducting transition in misfit layer compounds
Hugo Le Du, Robin Salvatore, Justine Cordiez et al. (+12 more)
Achieving topological superconductivity is a key goal in
quantum physics, offering a path to fault-tolerant
quantum computers. A central challenge in this field is to continuously drive a material through a topological
quantum phase transition to directly observe the
evolution from trivial to topological superconductivity. However, finding a robust platform that allows such extreme and precise tuning remains a challenge. Here, we demonstrate a doping-controlled phase transition from a conventional to a topological superconducting state in the bulk misfit layer compound (LaxPb1-xSe)1.14(NbSe2)2. We reveal a non-monotonic phase diagram characterized by two distinct superconducting regimes separated by a non-superconducting phase at a precise doping. In the highly doped regime, the superconducting phase becomes remarkably sensitive to non-
magnetic disorder, and orientation-selective in-gap modes emerge at atomic step edges. Supported by Bogoliubov-de Gennes calculations, these emergent spatial signatures are consistent with a time-reversal-symmetric crystalline-topological order parameter. Our results establish misfit compounds as a platform to engineering topological superconductivity.
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All authors Hugo Le Du, Robin Salvatore, Justine Cordiez, Ludovica Zullo, Arindam Mukherjee, Daniel Schmieg, Dominik Volavka, Francois Debontridder, Marie Herve, Tomas Samuely, Shunsuke Sasaki, Florent Pawula, Etienne Janod, Laurent Cario, Tristan Cren
Superconductivity
Nearly Isotropic Vortex Solid in $\mathbf{(La,Pr)_{3}Ni_{2}O_{7}}$ Thin Films
Yaolong Bian, Yaqi Chen, Heng Wang et al. (+14 more)
The discovery of superconductivity in bulk bilayer nickelates has established a new platform for exploring high-$T_c$ superconductivity beyond the cuprates. The role of the Ni $3d_{z^2}$-derived $\gamma$ band in the superconductivity of bilayer nickelates remains unresolved. By performing simultaneous resistance and diamagnetism measurements on (La,Pr)$_3$Ni$_2$O$_7$ thin films, we map the
vortex melting phase diagram for both in-plane and out-of-plane
magnetic fields. For $H\parallel c$, the
geometric confinement effect gives rise to pancake
vortices. Remarkably, the anisotropy parameter of the
vortex melting field $\gamma_{H_m} \equiv H_m^{ab}/H_m^c$ decreases monotonically with decreasing temperature and approaches unity at low temperatures. Within the anisotropic Ginzburg–Landau scaling, $H_m^{ab}/H_m^c = \sqrt{\rho_s^{ab}/\rho_s^c}$ tracks the superfluid-density anisotropy. Such a
vortex solid implies a nearly isotropic superfluid density, which is irreconcilable with the strictly two-dimensional $3d_{x^2-y^2}$-derived bands, but naturally explained by a substantial interlayer superfluid contribution from the $3d_{z^2}$-derived $\gamma$ band. Our results provide thermodynamic evidence for a substantial contribution of the $\gamma$ band to superconductivity in bilayer nickelate thin films.
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All authors Yaolong Bian, Yaqi Chen, Heng Wang, Guangdi Zhou, Fei Peng, Zichen Lv, Jiaqiang Cai, Yifan Chen, Wenjie Meng, Ze Wang, Haoliang Huang, Daohua Zhang, Mingliang Tian, Jinfeng Jia, Qi-kun Xue, Zhuoyu Chen, Jinglei Zhang
Statistical Mechanics · Cross-listed from q-bio.GN
Human mutation field reveals an equilibrium-like structure with irreversible circulation
Isabella Caranzano, Daniel Maria Busiello, Stefano Priorelli et al. (+2 more)
The
evolution of DNA sequences can be viewed as
stochastic dynamics on a high-dimensional discrete space, but it is unclear when empirical transition biases reduce to an effective energy landscape versus retain irreducible non-
equilibrium circulation. Human context-dependent mutation probabilities offer a direct test: every single-nucleotide substitution in a local context has a reverse substitution, so the logarithm of the forward-to-reverse probability ratio defines an antisymmetric field-the human mutation field. We show this field has a dominant gradient component and a smaller but reproducible curl component. Using seven-base human germline substitution probabilities, we infer an effective mutational landscape with a Siamese neural network constrained to predict only energy differences. This model predicts forward-to-reverse log-ratios for held-out mutations with a correlation of about 0.93, close to both an unconstrained predictive reference (0.948) and the empirical reversible ceiling from Hodge projection (about 0.96). Although trained only on mutation probabilities, the inferred landscape largely recovers short-word genomic composition and Chargaff reverse-complement
symmetry for sequences up to length four. Deviations from
equilibrium structure reveal a small but detectable nonequilibrium component: a residual irreversible circulation violating the Kolmogorov cycle condition for detailed balance, reproducible across African, Asian, and European populations, and strongest in CpG-linked cycles and CpG-transition edges, consistent with methylcytosine deamination. These results give a thermodynamic decomposition of the human mutation field: most mutation bias is organized by a local
equilibrium-like energy landscape aligned with genome composition, while the residual circulation points to specific directional mutational mechanisms.
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All authors Isabella Caranzano, Daniel Maria Busiello, Stefano Priorelli, Amos Maritan, Piero Fariselli
Statistical Mechanics
Exact Hamiltonian Dynamics of Rare Events in Active Matter
Andrea Crisanti and Matteo Paoluzzi
Active systems navigate complex environments through non-
equilibrium fluctuations, rendering standard
equilibrium transition-rate theories inadequate. Moreover, transition rates provide only partial information on how
stochastic dynamics explore metastable states, whereas knowledge of the optimal paths offers deeper physical insight. Using an active Ornstein-Uhlenbeck particle, i.e., a particle driven by exponentially correlated noise, as a paradigmatic model, we establish an exact mapping of the non-Markovian optimal path onto a higher-dimensional
Hamiltonian dynamical system so that, for arbitrary force fields, optimal paths can be computed systematically by solving the corresponding Hamilton equations. Tuning the conserved energy allows us to explore diverse dynamical regimes, ranging from classical instanton trajectories strictly confined to the zero-energy surface to finite-time optimal paths at non-zero energies, which can spiral around shoulders of the energy landscape, a distinct signature of the non-Markovian active dynamics.
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Materials Science
Benchmarking Universal Machine Learning Force Fields for Crystal Structure Prediction of High-Energy Molecular Systems
Musiha Mahfuza Mukta, Osman Goni Ridwan, Romain Perriot et al. (+1 more)
Recent developments of universal machine learning interatomic potentials (UMLIPs) offer a fast route for screening molecular
crystals based on geometry relaxation and energy ranking, but their reliability across chemically diverse energetic materials remains elusive. In particular, it is unclear whether or not these UMLIPs are over-sensitive to break the desired molecular connectivity for relaxing the periodic
crystals. Herein we tested the hypothesis that classical force-field pre-relaxation can provide a more suitable starting geometry for subsequent UMLIP relaxation on a large database of high energy molecular
crystals. Three models (MACE, MACE-OFF and UMA) in conjunction with the General Amber Force Field (GAFF) were applied to test this hypothesis. Among them, direct MACE-OFF and UMA showed very high relaxation success and preserved the reference geometries most closely, but they still exhibit failures for some rare cases. Using GAFF pre-relaxation can systematically reduce the number of failed relaxations with lower computational costs. Our comparative failure and robustness analyses revealed distinct trade-offs among the evaluated models. Among them, MACE-OFF achieves a better compromise between potential energy surface smoothness, structural fidelity, and stress convergence, serving as a good choice to provide a reliable foundation for automated structural optimization.
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All authors Musiha Mahfuza Mukta, Osman Goni Ridwan, Romain Perriot, Qiang Zhu
Materials Science · Cross-listed from eess.SY
Noninvasive Anisotropic Identification of Magnetic Properties in Toroidal Shaped Magnetic Steel
Xusen Qin, Reza Zeinali and Mitrofan Curti
This research proposes a model-free inverse approach for identifying the nonlinear anisotropic single-valued
magnetic constitutive characteristics of soft
magnetic materials from boundary measurements. Using the harmonic approximation, the internal
magnetic flux density B and
magnetic field strength H are independently reconstructed from the measured boundary data, thus avoiding the limitation of using a predefined parametric B–H mapping function. Subsequently, the reconstructed fields are spatially averaged along selected collection lines to recover the B–H characteristics of the principal directions. Numerical results demonstrate high reconstruction accuracy for unperturbed data and good robustness against Gaussian perturbations of the boundary measurements, with the overall mean error remaining below 5% for a 10% noise level. These results indicate that under the harmonic-field assumptions, the field-based reconstruction provides a simple and computationally efficient framework for non-invasive identification of nonlinear anisotropic
magnetic constitutive characteristics.
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Disordered Systems and Neural Networks
Graph neural networks and the energetic cavity method for combinatorial optimization
Joe Bacchus George and George T. Cantwell
We study the use of graph neural networks (GNNs) for finding approximate ground states of Ising models. Efficiently finding these ground states is of broad significance because many combinatorial optimization problems can be formulated as an Ising model with the appropriate choice of couplings and fields. Exactly solving these problems is hard but there are many good heuristic methods. A lineage of these heuristics build from mean-field approximations: one approach uses the leading eigenvector of an appropriately defined
matrix, another is the min-sum
algorithm, also known as the energetic cavity method. Without modification, GNNs perform worse than both of these methods. We consider small modifications to the GNN to incorporate these heuristics and find that this considerably improves performance. While the modified approach is competitive against other deep-learning approaches, we still find that simulated annealing is reliably at least as good as deep learning methods for the same computational cost.
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Mesoscale and Nanoscale Physics
Direct Realization of Near-Ideal Carbyne in Ultrathin Boron Nitride Nanotubes
Iryna Ivanenko, Pietro Marabotti, Yifan Zhang et al. (+8 more)
Carbyne, the sp-hybridized one-dimensional allotrope of carbon, is predicted to be the stiffest known material, with electronic and optical properties set by a single structural parameter, the bond length alternation. However, its intrinsic properties have never been measured: chains synthesized through molecular chemistry carry endgroup and finite-length perturbations that persist even in the longest molecules available, while chains grown inside carbon nanotubes strongly couple to the host, which renormalizes their vibrational frequency by up to 110 cm$^{-1}$ in a diameter-dependent manner. Here, we show that encapsulating and thermally converting hydrogen-capped polyynes inside ultrathin boron nitride nanotubes, structural analogues of carbon nanotubes but electrically insulating, yields carbyne chains in a near-ideal regime, where endgroup, finite length, and host-guest perturbations are reduced to secondary effects. Statistical Raman spectroscopy across 245 locations returns a vibrational frequency distribution an order of magnitude narrower than in carbon nanotubes, an anharmonicity consistent with the universal law for carbyne-like materials, and a bond length alternation matching correlated calculations for the free chain. No photoluminescence is detected, despite the transparent host, as expected for the dipole-forbidden emission of an unperturbed carbyne chain. Boron nitride nanotubes give experimental access to carbyne in its near-ideal form.
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All authors Iryna Ivanenko, Pietro Marabotti, Yifan Zhang, Getulio Silva e Souza Júnior, Johannes M. A. Lechner, Pablo Hernández López, Martin Magg, Shivani Shivaprakash, Carlo Spartaco Casari, Sebastian Heeg, Benjamin S. Flavel
Mesoscale and Nanoscale Physics
Charge-spin conversion in altermagnets: electronic anisotropy versus magnon-mediated spin drag
Koki Mizuno
Altermagnets acquire a momentum-dependent
spin splitting without net magnetization or
spin-orbit coupling. This raises the question of whether the transport anisotropy originates in the electrons or the
magnons, and whether the
magnon-mediated channel distinguishes an altermagnet from a conventional antiferromagnet. We compute the
spin-resolved conductivity of a metallic ferromagnet, antiferromagnet, and altermagnet within a common model, treating the
spin-diagonal channel with the
magnon self-energy and the
spin-flip channel to leading order in the electron-
magnon coupling. The anisotropy of the charge-
spin conversion is dominated by the electronic
spin splitting, the
magnon branches contributing only marginally. The
magnon-mediated
spin-flip channel is even under $C_{4}$, so it carries no signature at first order in the anisotropy and cannot on its own distinguish an altermagnet from a conventional antiferromagnet. It does, however, respond linearly to a sublattice-selective perturbation that lowers the bulk $B_{1g}$
symmetry. The resulting susceptibility vanishes identically in the antiferromagnet, is small in the ferromagnet, and is finite in the altermagnet, where the electronic anisotropy ties
spin and sublattice together, so that among magnets with no net magnetization it is unique to altermagnetic order. Being even in the
magnetic domain index, this response can be measured without preparing a single
magnetic-domain sample.
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Mesoscale and Nanoscale Physics
Layer-Dependent Phonons, Excitons, and Magneto-Optical Phenomena in CrSBr: A Mini Review
Muhammad Aftab, Chinmay Kumar Mohanty, Zain Ashfaq et al. (+5 more)
Two-dimensional layered
magnetic materials offer a versatile platform for exploring low-dimensional magnetism and coupled many-body interactions in these materials. Chromium sulfur bromide (CrSBr) is a promising candidate for advanced spintronic and optoelectronic applications because of its intrinsic air stability, semiconducting nature, strong in-plane anisotropy, and A-type antiferromagnetic ordering. This review summarizes recent advances in the understanding of the layer-dependent vibrational and excitonic properties of CrSBr, as well as its magneto-optical response, from bulk
crystals to the monolayer limit. We examined its
crystal structure,
magnetic anisotropy, and interlayer
spin reorientation, followed by insights into vibrational dynamics and
spin-
phonon coupling. Particular emphasis is placed on the excitonic landscape, including
magnetic-field-sensitive photoluminescence, localized excitonic states, and the coexistence of Frenkel- and Wannier-Mott
excitons in the bandgap. Finally, we discuss the challenges and prospects of harnessing the unique layer-dependent properties of CrSBr in spintronic, magneto-optical, and
quantum photonic technologies.
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All authors Muhammad Aftab, Chinmay Kumar Mohanty, Zain Ashfaq, Warisha Mehmood, Xiaoli Wang, Clément Faugeras, Wajid Ali, Maciej R. Molas
Materials Science
Quantifying thermal and driven magnon populations with femtosecond noise correlation spectroscopy
F. S. Herbst, M. A. Weiss, A. Leitenstorfer et al. (+5 more)
Precise knowledge of the total number of
magnons, including both coherent and incoherent (e.g. thermal) excitations, is imperative for the advancement of fundamental
spin-wave physics and the development of next-generation magnonic devices. In particular, quantifying
magnons is key to understanding
magnon transport phenomena, the nonlinear regime, or ultrafast magnetization dynamics. Typically, incoherent
magnons are accessed by frequency-domain techniques, which lack the temporal resolution required for ultrafast processes, while ultrafast time-domain methods are generally sensitive only to the coherent dynamics. In this work, we demonstrate that femtosecond noise correlation spectroscopy enables a fully quantitative, time-domain measurement of both thermal and coherently excited
magnon modes in bismuth-substituted yttrium iron garnet driven by a free-running microwave. We model the experimental data and extract the
magnon number by simulating the
magnon band structure of the sample, the magneto-optical response function, and the optical spot size used in the experiment. Our analysis establishes a connection between
magnon mode calculations and experimentally accessible
magnetic properties and fiducially reproduces the waveform and amplitude of the magneto-optical correlation signal for different experimental conditions. These results open a new pathway towards the optical
tomography of
magnon modes in non-linear or non-
equilibrium conditions and can be readily extended to study ultrafast incoherent dynamics in other condensed matter systems.
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All authors F. S. Herbst, M. A. Weiss, A. Leitenstorfer, M. Lammel, N. Beaulieu, J. Ben Youssef, R. Schlitz, S. T. B. Goennenwein
Quantum Gases
Spontaneous counterflow in rotating supersolids
Silvia Trabucco, Elena Poli, Massimo Mannarelli et al. (+1 more)
Rotating supersolids challenge the conventional notion of superfluid flow: quantized
vortices coexist with crystalline order arising from the system's intrinsic density modulation. Drawing on concepts developed in the context of superfluid helium, this seemingly paradoxical state is often described phenomenologically in terms of a dual response, combining superfluid flow with rigid-body-like motion. Here we show that these apparently distinct behaviors emerge from a single microscopic velocity field, globally constrained by irrotationality. By applying a Helmholtz decomposition, we disentangle a divergence-free incompressible component, which carries
vortex circulation, from a curl-free compressible component generated by the intrinsic density modulation. In absence of
vortices, the response is entirely encoded in the compressible field: the droplets co-rotate with the external drive, while the interstitial fluid develops an oppositely directed counterflow that preserves vanishing circulation. Above the
vortex nucleation threshold, the incompressible component carries the usual quantized circulation, whereas the compressible field counteracts the
vortex-induced angular momentum, reducing the total jump with respect to an unmodulated condensate. Our results recast supersolid rotation in terms of a flow-counterflow response, providing a microscopic interpretation of the phenomenological rigid/superfluid partitioning.
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All authors Silvia Trabucco, Elena Poli, Massimo Mannarelli, Francesca Ferlaino
Materials Science
How to enhance the applicability of Murnaghan equation of state
V.V. Bannikov
The paper presents the brief overview of known isothermal equations of state for solids and of theoretical background to construct them, focusing on widely used Murnaghan equation. Since the latter has a limited range of application, failing to reproduce reliably both near-
equilibrium and high-pressure regions simultaneously, the paper proposes simple, but rather efficient way to improve it. The suggested modification favors its applicability at high pressures, allowing to expand considerably the region of reliable reproducing of experimental or computational data. The proposed improved equation has been tested in fitting of U(V) data, obtained within ab initio computations, as well as of experimental V-P data for a representative selection of solids. In comparison with ordinary Murnaghan equation, it has found significant advantages, extending the range, where the computational data may be reproduced trustworthy (from the
equilibrium state to the pressures, appreciably higher, the ordinary equation could). As for the fitting of experimental data, the proposed improved Murnaghan equation reproduces them, in the presented examples, at least not worse than other well-known equations (Vinet, Birch-Murnaghan, Mao) do. Some aspects of fitting process, as well as some alternative approaches to obtain the proposed equation of state in various forms are also discussed.
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Statistical Mechanics
Fragility from Enthalpy Fluctuations and Fictive-Temperature Dynamics
Biman Bagchi
Fragility and fictive temperature are two central measures of glass formation, but their connection is usually expressed indirectly through structural relaxation times or cooling-rate dependence. Here we formulate this connection in terms of configurational enthalpy fluctuations. The time
evolution of the fictive temperature during cooling or aging is controlled by the enthalpy–enthalpy correlation function that also determines the frequency-dependent configurational heat capacity. Fragility enters through the strong temperature dependence of the structural relaxation time and therefore controls how rapidly the corresponding enthalpy-relaxation spectrum shifts to long times near the glass transition. This leads to a direct time-domain description of the onset and growth of the fictive-temperature lag, including the Debye limit, and connects calorimetric relaxation, fragility, and nonequilibrium structural arrest within a common framework.
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Mesoscale and Nanoscale Physics
Static-Dynamic Correlations and Complex Spin-Wave Eigenmodes in Single- and Multilayer Diamond-Shaped Nanomagnets Without Bias Field
Krishna Begari
Diamond-shaped nanomagnets provide a suitable platform for developing microwave devices with reconfigurable characteristics. In this study, the static and dynamic
magnetic behaviour of single layer and multilayer diamond-shaped nanomagnets was systematically investigated using micromagnetic simulations. Two distinct remanent
magnetic configurations were obtained through a simple
magnetic field initialization process. These configurations exhibited different magnetization patterns and dynamic responses. Their resonance characteristics could be modified by applying a nanosecond-scale
magnetic field pulse, enabling reconfigurable microwave operation. A clear resonance frequency shift in the sub-GHz (0.9 GHz) range was observed for the single-layer structure, while the multilayer structure exhibited a significantly larger frequency shift in the GHz range (3 GHz). The larger frequency tunability observed in the multilayer configuration arises primarily from the enhanced dipolar coupling between the vertically coupled
magnetic layers, which modifies the local effective
magnetic field and consequently influences the magnetization dynamics. These findings demonstrate that diamond-shaped nanomagnets can provide a simple and effective route toward reconfigurable microwave functionality, with potential applications in ultralow-power, ultrafast, and frequency tunable microwave devices.
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Mesoscale and Nanoscale Physics
Trion-mediated quantum operations on a double-dot charge qubit
Alexander Tsukanov
A scheme for controlling a charge
qubit on a
semiconductor asymmetric double
quantum dot with suppressed tunnel coupling between individual
quantum dots is proposed.
Laser pulses convert the logical single-electron states of the
qubit into auxiliary trion states, for which the resonant tunneling condition is restored due to the compensation of structural asymmetry by the Coulomb interaction of the particles. The conditions for performing orthogonal single-
qubit rotations are formulated. For a two-dimensional structure, the parameters of the
qubit are calculated, and the dependence of the fidelity of the inversion operation on the parameters of the
laser field and the rates of dissipative processes is obtained. It is shown that the considered
algorithm is characterized by high speed and reliability.
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Disordered Systems and Neural Networks
Storing Infinite Dynamical Attractors in Nonreciprocal Associative Neural Networks
Miguel Aguilera and Daniele De Martino
We develop a dynamical mean-field theory for nonreciprocal associative networks that store an extensive number of dynamical attractors, from limit cycles to strange attractors. Using a path integral calculation under quenched disorder, we derive self-consistent dynamical mean-field equations for pattern overlaps, autocorrelations and response functions.
Memory retrieval capacity is governed by the spectral structure of the coupling
matrices encoding stored patterns. When their
eigenvalues are coherently aligned, retarded self-interactions and quenched noise feed back destructively: at zero eigenphase (fixed point attractors) the classical
equilibrium capacity bound is recovered, while for limit cycles
retrieval collapses far below it. In contrast, for uniformly distributed eigenphases, retarded self-interactions and much of the quenched noise cancels, reducing the dynamics to an effective single-
spin process and amplifying capacity substantially. We validate the theory against microscopic simulations for limit-cycle and chaotic attractors, identifying
eigenvalue decoherence as the mechanism enabling enhanced storage of dynamical
memories.
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Statistical Mechanics
Emergent Equilibrium Structure Along a Critical Cluster Recursion
Shuo Wei, Abbas Ali Saberi and Youjin Deng
Critical universality does not determine the microscopic conditional structure of a probability measure. We study a bicolored cluster recursion constrained to remain critical at every generation, with no
equilibrium spin measure or fixed coupling imposed. In both two and three dimensions, the resulting history-dependent sequence develops a common Ising/Fortuin–Kasteleyn (FK) compatibility structure: the second-shell dependence of a one-site conditional law is strongly suppressed, nearest-neighbor effective couplings move progressively toward one another near the critical Ising value, and cluster and interface observables organize around the corresponding FK geometry. An exact cluster-coloring factorization singles out $q=2$ as the point where the residual connectivity weight disappears from the two-color
spin marginal. Thus
equilibrium-compatible conditional structure can emerge along a trajectory that remains critical throughout.
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Mesoscale and Nanoscale Physics
Unveiling the Scaling Potential of Drain Merge through Active (DMtA) in CFETs: Breaking the Super-Via Bottlenecks and Unlocking New PPA Boosters
Jingru Jiang, Haoran Lu, Kairong Guo et al. (+11 more)
Drain merge (DM), a super via vertically connecting the common S/D terminals of stacked n/pFETs in Complementary FETs (CFETs), blocks further parasitic optimization and
cell scaling. For the first time, this work systematically investigates the state-of-the-art Drain Merge through Active (DMtA), a revolutionary technology reported recently with the DM embedded in the active region, through a comprehensive DTCO framework spanning process integration, contact-configuration-dependent (CTCD) compact modeling, standardcell design, RO evaluation and block-level PPA
benchmark on a 32-bit RISC-V Ibex core. By reducing DM parasitics and enabling DM-width optimization, DMtA improves RO frequency by 11.7% over its conventional Drain Merge through field (DMtF) counterpart. Active widening and Area Borrowing, the latter first reported in [8] and exploiting spatial slack in adjacent
cells to further enlarge the nanosheet width (WNS), increase the maximum Ibex-core frequency by up to 34.8%. More importantly, DMtA also enables the once GAA-exclusive Hyper-
cells on CFETs by merging the active regions across adjacent
cell rows, providing a further 8.7% frequency gain. A post-routing floating-output-pin-aware optimization further removes redundant S/D contacts (CTs) and reduces power by 5.3%. Finally, DMtA facilitates more area-efficient 2.5T
cell scaling by preserving single-row
cell compatibility, reducing post-PR core area by 25.7%.
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All authors Jingru Jiang, Haoran Lu, Kairong Guo, Yibo Zhang, Yifei Chen, Wanyue Peng, Yu Liu, Jiacheng Sun, Xiaoyan Xu, Ming Li, Yibo Lin, Runsheng Wang, Ru Huang, Heng Wu
Materials Science
Modular and Cost-effective Scanning Photocurrent Microscopy System for Sub-micron characterization of 2D optoelectronic devices
Nuria Jiménez-Arévalo, Dan Zheng, Yong Xie et al. (+8 more)
Scanning photocurrent microscopy (SPCM) is a powerful technique for probing local optoelectronic phenomena in 2D semiconducting devices. However, commercial setups remain costly, complex and often lack flexibility and adaptability. In this work, we present a home-built SPCM platform built around the retrofitting of a conventional metallographic microscope by coupling it with different light sources (single-mode fiber-coupled
lasers and multimode fiber-coupled high-power LEDs), a motorized XY stage, a digital camera and an electronic readout module. This system enables simultaneous acquisition of photocurrent and reflection intensity maps, requiring minimal modifications of the microscope. We reached sub-micron spatial resolution and high imaging fidelity by correlating photocurrent maps with reflection maps, optical micrographs and AFM topography data on different devices fabricated with different materials (InSe, MoS2, WSe2, Gr), on different substrates (Si/SiO2, compact disk). This work provides a reliable, accessible and reproducible high-performance SPCM platform that can be easily implemented in most laboratories for microscale optoelectronic characterization of 2D devices.
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All authors Nuria Jiménez-Arévalo, Dan Zheng, Yong Xie, Peng Cheng, Yi Liu, Rafael Luque Merino, Haiwen Yu, Tao Wang, Riccardo Frisenda, Andres Castellanos-Gomez, Qinghua Zhao
Materials Science
Metallic-Phase-Fe$_3$GaTe$_2$ Enabled Interface Engineering for Self-Powered and High-Gain WS$_2$ Photodetectors
Wajid Ali, Ming Huang, Juan Li et al. (+7 more)
Two-dimensional transition-metal dichalcogenides offer strong light-matter interaction but suffer from inefficient carrier separation and contact-related losses in photodetectors. Here, we demonstrate a high-gain WS$_2$/Fe$_3$GaTe$_2$ van der Waals
heterostructure photodetector, where metallic Fe$_3$GaTe$_2$ serves as an active interfacial contact. The work-function mismatch, together with interfacial charge redistribution and asymmetric contact geometry, contributes to a built-in field that supports self-powered photodetection at zero bias. Under 450 nm illumination, the device delivers a zero-bias responsivity of 23.5 A/W and an apparent external
quantum efficiency of 6.4 x 10$^3$%. At -1 V biasing, the
heterostructure exhibits photoresponse at 450, 520 and 633 nm, achieving a responsivity of 9.7 x 10$^3$ A/W and a noise derived specific detectivity of 2.3 x 10$^13$ Jones at 100 Hz under 450 nm illumination. The high photoresponse is attributed to interfacial carrier separation, efficient extraction, and a likely contribution from trap-assisted photogating in multilayer WS$_2$. These results establish Fe$_3$GaTe$_2$-enabled interface engineering as an effective route for self-powered, highly sensitive 2D photodetectors.
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All authors Wajid Ali, Ming Huang, Juan Li, Jianhua Huang, Liuli Yang, Sajid Ur Rehman, Chinmay K. Mohanty, Zahir Muhammad, Ziwei Li, Maciej R. Molas
Mesoscale and Nanoscale Physics · Cross-listed from physics.chem-ph
Mixed quantum-classical evolution in open molecular systems
Michael Galperin and Abraham Nitzan
We consider a mixed
quantum-classical formulation for open nonequilibrium molecular systems. We employ the pseudoparticle nonequilibrium Green's function (PP-NEGF) method as a fully
quantum description and a starting point for introducing classical nuclear dynamics for an open system. We use this formulation to derive a density-
matrix equation of motion describing the
quantum-classical
evolution. We compare our results with previous formulations and highlight important differences related to the nonequilibrium and open character of the molecular system. We also analyze the approximations needed to reduce full
quantum-classical dynamics to the fewest-switches surface hopping (FSSH) method and show that these approximations are unreasonable when adiabatic surfaces come close to each other.
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Mesoscale and Nanoscale Physics
Lindbladian Phase Geometry and Hall Transport in Open Bloch Systems
Zhihao Jiang, Longjun Xiang and Jian Wang
Quantum geometry underlies a wide range of transport phenomena in Bloch systems. How
quantum-
geometric transport is modified when Bloch electrons are coupled to an environment, however, remains largely unexplored, even though the environment can alter both the electronic state and the physical current operator. Here we formulate dc linear response within a trace-preserving Lindblad kinetic theory by defining the physical velocity as the Liouvillian time derivative of the position operator. This construction reveals an environment-induced contribution to the current vertex whose momentum-space curl generates new Hall responses governed by the gauge-invariant phase geometry encoded by Lindblad jump amplitudes, which characterize electron-environment coupling. To leading order in the dissipative coupling, this geometry gives rise to interband shift-vector and diagonal-vorticity Hall responses arising from off-diagonal and diagonal jump amplitudes, respectively. Remarkably, both mechanisms can produce a finite Hall conductivity even when the conventional Berry-
curvature anomalous Hall effect vanishes identically. Our work establishes Lindbladian phase geometry as an independent
geometric origin of transverse transport in open
quantum matter.
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Disordered Systems and Neural Networks
Finite-rank multiplicative perturbations of rotationally invariant non-Hermitian random matrices
Pierre Bousseyroux and Marc Potters
We study finite-rank multiplicative deformations of rotationally invariant non-Hermitian random
matrices. More precisely, we consider models of the form $\mathbf{A}(\mathbf{I}+\mathbf{T})$, where $\mathbf{A}$ is a large rotationally invariant non-Hermitian random
matrix, $\mathbf{T}$ is a finite-rank normal perturbation, and $\mathbf{I}$ denotes the identity
matrix. We characterize the emergence of outlier
eigenvalues, their fluctuations, and the associated eigenvector overlaps. Our results provide a multiplicative non-Hermitian counterpart to the classical Baik–Ben Arous–Péché framework.
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Materials Science
Angular compliance, not amplitude, governs the dielectric response of BaTiO3
Ryotaro Sahashi, Po-Yen Chen and Teruyasu Mizoguchi
Soft-mode theory specifies a frequency, not what a local polar unit does. What real-space motion underlies the dielectric response of BaTiO3 therefore remains unclear. Using electric-field-induced molecular dynamics with a machine-learning force field, we show that the permittivity tracks the field-induced angular redistribution of local Ti-O off-centering, not its magnitude. Temperature and biaxial strain modify the local structure through different microscopic routes, yet both dielectric responses collapse onto a common relation with the same orientational descriptor, providing a real-space counterpart to soft-mode behavior.
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Materials Science
Groove-shaped defects in as-grown (001)-oriented $\beta$-Ga$_2$O$_3$ epilayers prepared by halide vapor phase epitaxy
Yongzhao Yao, Daiki Katsube, Hirotaka Yamaguchi et al. (+1 more)
Groove-shaped defects (GSDs) degrade the surface flatness of as-grown (001)-oriented $\beta$-Ga$_2$O$_3$ epilayers and necessitate chemical mechanical polishing before device fabrication, increasing processing costs and the risk of damage. We investigated the morphology, subsurface structure, and formation mechanism of GSDs in a homoepitaxial layer grown by halide vapor phase epitaxy using synchrotron X-ray topography and electron microscopy. The GSDs extended several millimeters along [010] and consisted predominantly of (-102) basal facets bounded by steep (100) sidewalls. Their wafer-scale distribution showed a spatial correspondence with variations in wafer
curvature, suggesting that local surface orientation influences GSD formation. Careful
alignment of surface images with transmission X-ray topographs revealed no one-to-one correspondence between GSDs and substrate defects, providing no evidence that substrate dislocations serve as their nucleation sites. Instead, transmission electron microscopy revealed planar defects localized near the terminal boundaries where the faceted GSD sectors met the surrounding (001) growth region; no such defects were observed in specimens extracted from the middle of GSDs. These defects exhibited {\alpha}-fringe contrast characteristic of inclined translational planar defects, with the dominant segments assigned to the (1-21) plane. The observations suggest that variations in local surface orientation and step supply may promote three-dimensional faceted growth, producing persistent (-102)/(100) sectors. The localized planar defects are therefore interpreted as consequences of growth-sector coalescence rather than the origins of GSD nucleation. These findings provide insight into the roles of wafer
curvature and surface step supply in GSD formation.
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All authors Yongzhao Yao, Daiki Katsube, Hirotaka Yamaguchi, Yukari Ishikawa
Quantum Gases
Precision tests of nonlinear and stochastic modifications of quantum mechanics with a 1D quantum gas
Yi Zeng, Angelo Bassi, Grigori E. Astrakharchik et al. (+3 more)
We propose a cold-atom platform for precision tests of nonlinear and
stochastic modifications to the Schrödinger equation, utilizing strongly correlated ultracold $^{133}$Cs in a uniform array of one-dimensional tubes formed by a two-dimensional optical
lattice. Objective collapse models can be tested using the metastable super-Tonks-Girardeau gas. Based on a calibration test performed on our existing experimental setup, we project a sensitivity to the Continuous Spontaneous Localization collapse rate of $\lambda_c \simeq 1.8\times10^{-11}\,\mathrm{s^{-1}}$ at a correlation length of $r_c = 10^{-7}\,$m. This would establish a new bound an order of magnitude below the strongest existing constraint that remains robust against a cutoff in the collapse noise spectrum. Additionally, we can test deterministic nonlinear modifications by probing the
symmetry-protected breathing mode frequency of the Tonks-Girardeau gas in harmonic traps. Crucial to both measurement schemes is the capability to independently tune the atom number and the linear density. By exploiting the different scaling laws associated with these parameters, we can cleanly distinguish genuine new physics signals from technical systematics.
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All authors Yi Zeng, Angelo Bassi, Grigori E. Astrakharchik, Yanliang Guo, Manuele Landini, Hanns-Christoph Nägerl