Disordered Systems and Neural Networks
Low energy excitations in a long prism geometry: testing the lower critical dimension of the Ising spin glass
Massimo Bernaschi, Luis Antonio Fernández, Isidoro González-Adalid Pemartín et al. (+3 more)
We propose a general method for studying systems that display low-energy excitations in their low-temperature phase. We argue that in a rectangular right-prism geometry (the 3-dimensional generalization of a strip), with one longitudinal size much larger than the transverse size, correlations decay exponentially (at all temperatures) along the longitudinal direction. Still, the scaling of the correlation length with the transverse size carries crucial information from which the lower critical dimension can be inferred. The method is applied in the particularly demanding context of Ising
spin glasses at zero
magnetic field. The lower critical dimension and the multifractal spectrum for the correlation functions are computed from large-scale numerical simulations. Several technical novelties (such as the unexpectedly crucial performance of Houdayer's cluster method or the convenience of using open—rather than periodic—boundary conditions) allow us to study three-dimensional prisms with transverse dimensions up to $L=24$ and effectively infinite longitudinal dimensions, down to low temperatures. The value that we find for the exponent controlling the behavior of the correlation length agrees with predictions from the Replica
Symmetry Breaking (RSB) theory. We argue that our novel setting holds promise in clarifying which of the two competing theories, RSB or the Droplet Model, more accurately describes three-dimensional
spin glasses.
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All authors Massimo Bernaschi, Luis Antonio Fernández, Isidoro González-Adalid Pemartín, Víctor Martín-Mayor, Giorgio Parisi, Federico Ricci-Tersenghi
Strongly Correlated Electrons
Extraordinary boundary correlations at deconfined quantum critical points
Hao-Ran Cui and Hart Goldman
Recent years have seen a growing appreciation for the effects of
quantum critical fluctuations on gapless boundary degrees of freedom. Here we consider the boundary dynamics of the non-compact $\mathbb{CP}^{N-1}$ (NCCP$^{N-1}$) model in two spatial dimensions, with $N$ complex
boson species coupled to a fluctuating $\mathrm{U}(1)$ gauge field. These models describe
quantum phase transitions beyond the Landau paradigm, such as the deconfined
quantum critical point between superconducting (SC) and
quantum spin Hall (QSH) phases. We show that, in a large-$N$ limit and with the bulk tuned to criticality, boundaries of the NCCP$^{N-1}$ model display logarithmically decaying, or “extraordinary-log,” correlations. In particular, when monopole operators exhibit quasi-long-ranged order at the boundary, we find that the extraordinary-log exponent of the NCCP$^{N-1}$ model in the large-$N$ limit is $q=N/4$, signifying a new family of boundary universality classes parameterized by $N$. In the context of the QSH – SC transition, the
quantum critical point inherits helical edge modes from the QSH phase, and this extraordinary-log behavior manifests in their Cooper pair correlations.
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Strongly Correlated Electrons
Geometric Spin Rotation in Triangular Antiferromagnets
Grigor Adamyan, Bastian Pradenas, Boris Ivanov et al. (+1 more)
We describe a
geometric phenomenon in which a traveling wave made of degenerate Goldstone modes leaves behind a transformed ground state. In a triangular Heisenberg antiferromagnet, a pulse of circularly polarized
spin waves rotates the
spins within their plane. An exact solution of the nonlinear equations of motion demonstrates that the accumulated rotation is a
geometric phase related to parallel transport of the order parameter. We point out a curious analogy between the motion of the
magnetic order parameter and that of a wobbling coin. This phenomenon opens a new route for controlling
antiferromagnetic order by
spin waves and may extend to other frustrated magnets as well as other physical systems with noncommuting broken-
symmetry generators.
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All authors Grigor Adamyan, Bastian Pradenas, Boris Ivanov, Oleg Tchernyshyov
Materials Science · Cross-listed from physics.ins-det
Achieving Ultrahigh Resolution with High Efficiency: Optical Design of the 2D-RIXS Spectrometer at NanoTerasu BL02U
Jun Miyawaki
A state-of-the-art Resonant Inelastic X-ray Scattering (RIXS) facility, composed of a dedicated beamline and a 2D-RIXS spectrometer, has been constructed and commissioned at BL02U in NanoTerasu, Japan. This paper reports the optical design and optimization of this spectrometer, aiming for an ultrahigh energy resolution of <10 meV in the soft X-ray range. Conventional RIXS spectrometers using monochromatic incident X-rays suffer from a severe trade-off between energy resolution and measurement efficiency, which makes achieving resolutions of <10 meV practically unfeasible. To overcome this limitation, we adopted the $h\nu^2$ concept using dispersive incident X-rays, based on a comparative study. This approach decouples the energy resolution from the incident bandwidth. We estimate that our 2D-RIXS spectrometer improves efficiency by more than a factor of 10 compared to conventional spectrometers. The 2D-RIXS spectrometer has been successfully commissioned, demonstrating that sub-10 meV resolution measurement is achievable with practical throughput. While development continues towards the ultimate design resolution, the successful implementation validates the design strategy and offers a pathway for future high-performance RIXS instrumentation.
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Materials Science
Low-temperature Spark Plasma Sintering of fine refractory composite powders core-shell: A case of the powders W@Ni
A. V. Nokhrin, E. A. Lantcev, L. S. Alekseeva et al. (+9 more)
The mechanisms of fast low-temperature Spark
Plasma Sintering (SPS) of W + 10% wt. Ni powders were investigated. The powder compositions were obtained in two methods: (i) by mixing W and Ni powders in a specified ratio (hereinafter referred to as W + Ni); (ii) by Ni deposition on the surface of submicron W particles allowing the formation of particles with a core W - shell Ni structure (hereinafter referred to as W@Ni). To reduce the concentrations of oxygen and
oxides, the powders were annealed in hydrogen. The solid-phase sintering was performed at various temperatures (1000-1150{\deg}C), pressures (40-80 MPa), heating rates (50-500{\deg}C/min), and isothermal holding times (0-20 min). The sintering temperatures corresponded to the onset of intense dissolution of W in Ni. The samples had high relative density and small grain sizes. The activation energy of SPS of the mixed powders was close to the one of the grain boundary
diffusion. The key mechanism for the compaction of W@Ni particles in the SPS process is Coble creep. The increasing of the sintering temperature was shown to lead to an increase in the solubility of W in Ni and, consequently, to an increase in the number of secondary Ni4W particles formed during cooling down. The grain growth has a minor effect on the mechanical properties of the W
alloy compared to the changes in its phase composition.
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All authors A. V. Nokhrin, E. A. Lantcev, L. S. Alekseeva, N. V. Malekhonova, M. S. Boldin, Yu. V. Blagoveshchenskiy, N. V. Isaeva, A. V. Terentyev, K. E. Smetanina, N. V. Sakharov, N. V. Melekhin, V. D. Chupriyanova
Strongly Correlated Electrons
Interface roughening in the 3-D Ising model with tensor networks
Atsushi Ueda, Lander Burgelman, Luca Tagliacozzo et al. (+1 more)
Interfaces in three-dimensional many-body systems can exhibit rich phenomena beyond the corresponding bulk properties. In particular, they can fluctuate and give rise to massless low energy degrees of freedom even in the presence of a gapped bulk. In this work, we present the first tensor-network study of the paradigmatic interface roughening transition of the 3-D Ising model using highly asymmetric
lattices that are infinite in the $(xy)$ direction and finite in $z$. By reducing the problem to an effective 2-D tensor network, we study how truncating the $z$ direction reshapes the physics of the interface. For a truncation based on open boundary conditions, we demonstrate that varying the interface width gives rise to either a $\mathbb{Z}_2$
symmetry breaking transition (for odd $L_z$) or a smooth crossover(for even $L_z$). For antiperiodic boundary conditions, we obtain an effective $\mathbb{Z}_q$ clock model description with $q=2L_z$ that exhibits an intermediate Luttinger
liquid phase with an emergent $\U(1)$
symmetry.
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All authors Atsushi Ueda, Lander Burgelman, Luca Tagliacozzo, Laurens Vanderstraeten
Disordered Systems and Neural Networks · Cross-listed from quant-ph
Computing quantum magic of state vectors
Piotr Sierant, Jofre Vallès-Muns and Artur Garcia-Saez
Non-stabilizerness, also known as “magic,” quantifies how far a
quantum state departs from the stabilizer set. It is a central resource behind
quantum advantage and a useful probe of the complexity of
quantum many-body states. Yet standard magic quantifiers, such as the stabilizer Rényi
entropy (SRE) for
qubits and the mana for qutrits, are costly to evaluate numerically, with the computational complexity growing rapidly with the number $N$ of qudits. Here we introduce efficient, numerically exact
algorithms that exploit the fast Hadamard transform to compute the SRE for
qubits ($d=2$) and the mana for qutrits ($d=3$) for pure states given as state vectors. Our methods compute SRE and mana at cost $O(N d^{2N})$, providing an exponential improvement over the naive $O(d^{3N})$ scaling, with substantial parallelism and straightforward GPU acceleration. We further show how to combine the fast Hadamard transform with Monte Carlo sampling to estimate the SRE of state vectors, and we extend the approach to compute the mana of mixed states. All
algorithms are implemented in the open-source Julia package HadaMAG ( https://github.com/bsc-quantic/HadaMAG.jl/ ), which provides a high-performance toolbox for computing SRE and mana with built-in support for multithreading, MPI-based distributed parallelism, and GPU acceleration. The package, together with the methods developed in this work, offers a practical route to large-scale numerical studies of magic in
quantum many-body systems.
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Quantum Gases · Cross-listed from physics.optics
Measurement-based acceleration of optical computations
I. V. Vovchenko, A. A. Zyablovsky, A. A. Pukhov et al. (+1 more)
Analog coprocessors are intensively developing nowadays with the aim to optimize energy computations of neural networks. In this work we focus on the possibility of using detection of collective oscillations in optical systems for computational purposes. We show that in a system of coupled resonators, collective oscillations can be used to implement
matrix-vector multiplication. The
matrix is formed by the coupling constants between the resonators, and the input vector is formed by the initial occupancies of the involved modes. The frequency of the collective oscillations is growing with the number of the involved modes, similarly to Rabi oscillations. The time needed for their detection, i.e., averaging, decreases with an increase in the input vector dimension. We discuss the limitations imposed on parallel computation in the system by restriction of the allowed optical frequency band.
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All authors I. V. Vovchenko, A. A. Zyablovsky, A. A. Pukhov, E. S. Andrianov
Strongly Correlated Electrons
Ising Supercriticality and Universal Magnetocalorics in Spiral Antiferromagnet Nd$_3$BWO$_9$
Xinyang Liu, Enze Lv, Xueling Cui et al. (+8 more)
The celebrated analogy between the pressure-temperature phase diagram of a
liquid-gas system and the field-temperature phase diagram of a ferromagnet has long been a cornerstone for understanding universality of phase transitions and critical phenomena. Here we extend this analogy to a highly frustrated antiferromagnet, the spiral Ising compound Nd$_3$BWO$_9$ with kagome layers. In its phase diagram, we identify a metamagnetic transition line with a critical endpoint (CEP) located at $\mu_0H_{\mathrm{c}} \simeq 1.04$ T and $T_{\mathrm{c}} \simeq 0.3$ K. Above the CEP, an Ising supercritical regime emerges with crossover lines that follow a universal scaling law, as evidenced by the specific heat,
magnetic susceptibility, and magnetocaloric measurements. Remarkably, we observe highly sensitive
magnetic cooling near the emergent CEP, characterized by a divergent
magnetic Grüneisen ratio $\Gamma_H \propto 1/t^{\beta+\gamma-1}$, with $\beta + \gamma \simeq 1.563$ the sum of critical exponents of the 3D Ising universality class and $t \equiv (T-T_{\rm c})/T_{\rm c}$ the reduced temperature. Adiabatic demagnetization from 2 K and 4 T reaches a minimum temperature of 195 mK, via a self-cascading process that combines supercritical and topological cooling. Our findings open a new avenue for studying supercritical phenomena and
magnetic refrigeration with the frustrated rare-earth compounds RE$_3$BWO$_9$ and, more broadly, in Ising-anisotropic antiferromagnets such as
spin ices.
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All authors Xinyang Liu, Enze Lv, Xueling Cui, Han Ge, Fangyuan Song, Zhaoming Tian, Gang Su, Kan Zhao, Junsen Xiang, Peijie Sun, Wei Li
Strongly Correlated Electrons
Rigorous Anderson-type lower bounds on the ground-state energy of the pyrochlore Heisenberg antiferromagnet
Péter Kránitz and Karlo Penc
We construct rigorous Anderson-type lower bounds on the ground-state energy of the
spin-$S$ Heisenberg antiferromagnet on the pyrochlore
lattice. By formulating and optimizing a hierarchy of local cluster motifs ordered by size, we generate a sequence of increasingly tight bounds. A seven-site "hourglass" cluster composed of two corner-sharing tetrahedra furnishes an optimal lower bound that admits a closed-form expression for arbitrary
spin $S$. We also derive exact lower bounds for generalized models with further-neighbor exchange, ring exchange, and scalar
spin-chirality interactions. For $S=1/2$ and $S=1$, numerical optimization of an 18-site "crown" cluster containing a hexagonal loop yields rigorous lower bounds on the ground-state energy per site of the nearest-neighbor Heisenberg model with unit exchange, $e_\mathrm{GS} \geq -0.549832$ and $e_\mathrm{GS} \geq -1.632985$, respectively. We compare the resulting bounds with numerical ground-state energy estimates from the literature.
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Mesoscale and Nanoscale Physics
Nonlinear interaction theory for parametrically-excited spin-wave modes in confined micromagnetic systems
Massimiliano d'Aquino, Salvatore Perna, Hugo Merbouche et al. (+1 more)
We present a general theoretical approach for the quantitative description of parametric excitation of
spin-wave modes in confined micromagnetic systems. This type of problem belongs to a broader class of nonlinear modal dynamics that arise across many areas of physics and engineering. The
ferromagnetic sample is driven by parallel pumping with an external applied
magnetic field having two tones at different frequencies, which are able to trigger parametric instability of two resonant modes. The two excited
spin-wave modes interact in a strongly nonlinear fashion giving rise to quasiperiodicity, hysteresis and non-commutativity of steady-state oscillation regimes. To disentangle such a complex variety of dynamics, we develop a reduced-order model based on magnetization normal modes that is amenable of appropriate analytical treatment, leading to quantitative description of parametric instability thresholds, post-instability steady-state amplitude saturation and complete determination of phase diagrams for steady-state oscillation regimes. We have performed validation of the theory using numerical simulations. The phase diagrams allow to predict and explain all the features of the nonlinear interaction between the parametrically-excited
spin-wave modes and can be directly compared with experimental results.
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All authors Massimiliano d'Aquino, Salvatore Perna, Hugo Merbouche, Grégoire de Loubens
Mesoscale and Nanoscale Physics
Resonant magnetic proximity hot spots in Co/hBN/graphene
Klaus Zollner, Lukas Cvitkovich, Riccardo Silvioli et al. (+2 more)
Magnetic proximity effects in Co/hBN/
graphene heterostructures are systematically analyzed via first-principles calculations, demonstrating a pronounced localized spatial variation of the induced
spin polarization of
graphene's Dirac states. The proximity-induced exchange coupling,
magnetic moments, and tunneling
spin polarization (TSP) are shown to depend sensitively on the atomic registry at the interfaces. We analyze more than twenty distinct stackings, including high- and low-
symmetry configurations, and reveal that the
spin splittings of
graphene's Dirac bands span a wide range from 1 to 100 meV, depending on the local hybridization of Co $d_{z^2}$, hBN $p_z$, and
graphene $p_z$ orbitals. The strongest proximity effects emerge at
geometric resonances, or "proximity hot spots", where the three orbital states overlap maximally. The local
spin polarization also depends sensitively on energy: Dirac states aligned with resonant Co orbitals experience the most pronounced exchange interaction. At these energies, the pseudospin
Hamiltonian description of
magnetic proximity effects breaks down. Outside these resonances, the pseudospin picture is restored. Our findings highlight the intrinsically local nature of proximity effects, governed by the spectral resonance and interlayer wavefunction overlap. We further quantify how additional hBN layers, interlayer twist, and multilayer
graphene modify the proximity exchange and TSP, offering microscopic insight for designing spintronic van der Waals
heterostructures with engineered interfaces and optimized
spin transport.
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All authors Klaus Zollner, Lukas Cvitkovich, Riccardo Silvioli, Andreas V. Stier, Jaroslav Fabian
Disordered Systems and Neural Networks
Serial vs parallel recall in the Blume-Every-Griffiths neural networks
Linda Albanese, Andrea Alessandrelli, Adriano Barra et al. (+1 more)
Fully connected Blume-Emery-Griffiths neural networks performing pattern recognition and associative
memory have been heuristically studied in the past (mainly via the replica trick and under the replica symmetric assumption) as generalization of the standard Hopfield reference. In these notes, at first, by relying upon Guerra interpolation, we re-obtain the existing picture rigorously. Next we show that, due to dilution in the patterns, these networks are able to switch from serial recall (where one pattern is retrieved per time) to parallel recall (where several patterns are retrieved at once) and the larger the dilution, the stronger this emerging multi-tasking capability. In particular, we inspect the regimes of mild dilution (where solely a low storage of pattern can be enabled) and extreme dilution (where a medium storage of patterns can be sustained) separately as they give rise to different outcomes: the former displays hierarchical recall (distributing the amplitudes of the retrieved signals with different amplitudes), the latter – instead – performs a equal-strength recall (where a O(1) fraction of all the patterns is simultaneously retrieved with the same amplitude per pattern). Finally, in order to implement graded responses in the
neurons, variations on theme obtained by enlarging the possible values of neural activity these
neurons may sustain are also discussed generalizing the Ghatak-Sherrington model for inverse freezing in Hebbian terms.
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All authors Linda Albanese, Andrea Alessandrelli, Adriano Barra, Emilio N. M. Cirillo
Quantum Gases
Phase transition, phase separation and mode softening of a two-component Bose-Einstein condensate in an optical cavity
Jia-Ying Lin, Wei Qin and Renyuan Liao
We investigate the superradiant phase transition in a two-component Bose-Einstein condensate with distinct atomic detunings, confined in an optical cavity and driven by a transverse pump
laser. By combining perturbation theory and numerical simulations, we demonstrate that the phase transition is dominated by the red-detuned component, resulting in a phase diagram completely different from that of a single-component case under blue-detuned condition. The system exhibits spontaneous phase separation between the two components, manifested as alternating stripe patterns in the normal phase and distinct Bragg gratings in the superradiant phase. Furthermore, the Bogoliubov excitation spectrum reveals roton-type mode softening, indicating that the phase transition also corresponds to the superfluid-to-
lattice supersolid transition. Our findings provide insights into the interplay between atomic detunings and collective
quantum many-body phenomena, offering potential applications in
quantum simulation and optical switching technologies.
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Materials Science
A DFT study of B-doped graphene as a metal-anchor: effects of oxidation and strain
Nikola Veličković, Natalia V. Skorodumova and Ana S. Dobrota
In this work, we present a systematic DFT investigation of the interaction between B-doped
graphene and four selected metals: Mg and Zn, relevant for next-generation metal-ion batteries, and Cu and Pt, important for single-atom catalysis. Three different boron doping concentrations were considered to elucidate how dopant density influences the binding strength, charge transfer, and electronic structure of the resulting systems. In addition, the effects of biaxial strain and surface oxidation were examined to assess their impact on the reactivity and stability of B-doped
graphene. The results show that boron doping substantially enhances
graphene's affinity toward metal adsorption, though the extent and nature of this effect depend strongly on the metal type and doping level. For some of the metals investigated, the interaction is found to be almost entirely charge-transfer driven, with minimal orbital hybridization. Mechanical strain is found to enable fine-tuning of the metal/substrate interaction, while surface oxidation introduces a more pronounced effect by enabling direct interaction between metal atoms and oxygen functional groups in most cases, thereby significantly altering adsorption geometry and strength. These findings provide valuable insights into the design of boron-doped
graphene materials for energy conversion and storage applications.
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Materials Science
Resolving the energy alignment between methylammonium lead iodide and C60: an in-situ photoelectron spectroscopy study
Alberto García-Fernández, Karen Radetzky, Stefania Riva et al. (+6 more)
Understanding and controlling the energy level
alignment at interfaces between lead halide perovskites and electron transport layers is crucial for optimizing perovskite-based devices such as
solar cells. In this work, we investigated the energy level
alignment of C60 on in-situ cleaved MAPbI3 single
crystals in multiple repeat experiments using photoelectron spectroscopy aiming to resolve inconsistencies reported in earlier studies. Our results show that both materials remain chemically stable upon interface formation, in contrast to the strong reactions typically seen when metals are evaporated on perovskite surfaces. By analyzing the Pb 4f and C 1s binding energies in detail, we determined that C60 consistently exhibits a downward energy shift toward MAPbI3, which works against efficient charge extraction. The magnitude of this shift, however, varies between different sample positions, highlighting that small variations in sample surfaces can lead to significant differences in energetic
alignment. These findings underscore the decisive role of surface chemistry on interfacial energetics, explain performance variability in perovskite devices, and demonstrate the need to control and accurately measure surface properties. Furthermore, the observed energetic
alignment can explain why further interface modification by charge blocking layers or surface passivation is needed for optimized device efficiencies.
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All authors Alberto García-Fernández, Karen Radetzky, Stefania Riva, Birgit Kammlander, Brian Rydgren, Evelyn Johannesson, Rahul Mahavir Varma, Håkan Rensmo, Ute B. Cappel
Materials Science
Ultrafast control of spin order by linearly polarized light in noncollinear antiferromagnetic metals
J. Kimak, M. Nerodilova, K. Carva et al. (+15 more)
The non-thermal optical control of
magnetic order offers a promising route to ultrafast, energy-efficient information technologies. Although optical manipulation of magnetism in metals has been extensively studied, experimentally demonstrated effects have so far been limited to heat-driven dynamics or helicity-dependent mechanisms. Here, we report ultrafast non-thermal control of
spin order in noncollinear
antiferromagnetic Mn-based antiperovskite nitrides Mn3NiN and Mn3GaN, driven solely by the polarization orientation of linearly polarized femtosecond
laser pulses. Using time-resolved magneto-optical pump-probe experiments based on the Voigt effect, we observe sub-picosecond changes in
magnetic order followed by picosecond relaxation. The magneto-optical response depends on the relative orientation of the pump and probe polarization planes, with linear-polarization dependence reaching up to 95%, a value unprecedented in metallic magnets. This phenomenon is observed in two different materials and persists over a wide range of excitation wavelengths, fluences, and temperatures, demonstrating its robustness.
Symmetry analysis and microscopic modeling indicate that optically induced torques alone cannot fully explain the observed dynamics. We therefore propose
laser-induced formation of transient
spin-spiral states as a possible excitation mechanism.
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All authors J. Kimak, M. Nerodilova, K. Carva, S. Ghosh, J. Zelezny, T. Ostatnicky, J. Zemen, F. Johnson, D. Boldrin, F. Rendell-Bhatti, B. Zou, A.P. Mihai, X. Sun, F. Yu, E. Schmoranzerova, L. Nadvornik, L.F. Cohen, P. Nemec
Materials Science
PFT: Phonon Fine-tuning for Machine Learned Interatomic Potentials
Teddy Koker, Abhijeet Gangan, Mit Kotak et al. (+2 more)
Many materials properties depend on higher-order derivatives of the potential energy surface, yet machine learned interatomic potentials (MLIPs) trained with a standard loss on energy, force, and stress errors can exhibit error in
curvature, degrading the prediction of vibrational properties. We introduce
phonon fine-tuning (PFT), which directly supervises second-order force constants of materials by matching MLIP energy Hessians to DFT-computed force constants from finite displacement
phonon calculations. To scale to large supercells, PFT stochastically samples Hessian columns and computes the loss with a single Hessian-vector product. We also use a simple co-training scheme to incorporate upstream data to mitigate catastrophic forgetting. On the MDR
Phonon benchmark, PFT improves Nequix MP by 55% on average across
phonon thermodynamic properties and achieves state-of-the-art accuracy among models trained on Materials Project trajectories. PFT also generalizes to improve properties beyond second-derivatives, improving thermal conductivity predictions that rely on third-order derivatives of the potential energy.
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All authors Teddy Koker, Abhijeet Gangan, Mit Kotak, Jaime Marian, Tess Smidt
Soft Condensed Matter
Controlling microalgae populations by phototactic memory
Gianni Jacucci, Davide Breoni, Pierre Illien et al. (+4 more)
Motile microorganisms navigate environments that vary in space and time by coupling sensory inputs to internal physiological states and active motion. In photosynthetic microorganisms, such coupling can be mediated by phototaxis, yet how temporal sensing combines with spatial variations of the environment to shape population organisation remains poorly understood. To probe this coupling, we expose populations of the phototactic microalga Chlamydomonas reinhardtii to structured light landscapes. Under ring-shaped illumination,
cells robustly accumulate at the center of the illuminated region, rather than at the light-intensity maximum. Single-
cell tracking shows that
cells steer relative to local intensity gradients and undergo a non-trivial phototactic response, where, on average,
cells outside the ring perform positive phototaxis while
cells inside perform negative phototaxis. Population experiments, numerical simulations and analytical modelling show that this trapping cannot be reproduced by an instantaneous switching rule, but requires a finite phototactic
memory acting on the transition between positive and negative phototaxis. This internal timescale couples to the geometry of the light field and to the persistence of active motion, enabling controllable spatial localisation without physical confinement. Our results generically show how
memory in a single-
cell sensory response can control population-level organisation in a living active system.
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All authors Gianni Jacucci, Davide Breoni, Pierre Illien, Luca Tubiana, Jean-François Allemand, Sylvain Gigan, Raphaël Jeanneret
Disordered Systems and Neural Networks
Universal time-temperature scaling of conductivities in random site energy and associated random barrier model
Sven Lohmann, Quinn Emilia Fischer, Justus Leiber et al. (+1 more)
Universal time-temperature scaling of conductivity spectra in disordered solids has been explained by thermally activated hopping of noninteracting particles over random energy barriers. An open problem is whether the random barrier model accounts for site energy disorder in real materials. Through mapping many-particle hopping in a disordered site energy landscape to that of independent particles in a barrier landscape, we show that time-temperature scaling is correctly described by the associated barrier model in the low temperature limit. However, the site energy model displays good scaling behavior at substantially higher temperatures than the barrier model, in agreement with experimental observations. Extending the mapping to different types of mobile charge carriers allows us to understand why time-temperature superposition can be absent in mixed alkali glasses.
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All authors Sven Lohmann, Quinn Emilia Fischer, Justus Leiber, Philipp Maass
Superconductivity
Prediction of superconductivity in mass-asymmetric electron-hole bilayers
Luca Nashabeh and Liang Fu
We study density-balanced, mass-asymmetric electron-hole
bilayers as a tunable platform for correlated
quantum phases. With independent control of carrier density and interlayer separation, the system exhibits a rich phase diagram, including
exciton condensates, Wigner
crystals, and for large hole-to-electron mass ratios, an electron-
liquid hole-
crystal phase. This mixed phase is an analog of two-dimensional metallic hydrogen, featuring an electron
liquid immersed in and coupled to a
lattice of heavy holes. We show that acoustic plasmons mediate an attractive interaction between electrons, leading to BCS-type superconductivity at experimentally accessible parameters. The superconducting transition temperature is calculated from first principles, and experimental realization in van der Waals
heterostructures is discussed.
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Materials Science
Geometric Time-Dependent Density Functional Theory
Éric Cancès, Théo Duez, Jari van Gog et al. (+3 more)
We provide a new formulation of Time-Dependent Density Functional Theory (TDDFT) based on the
geometric structure of the set of states constrained to have a fixed density. Orbital-free TDDFT is formulated using a hydrodynamics equation involving a new density-to-current functional map. In the corresponding Kohn–Sham equation, the density is reproduced using a non-local operator. Finally, we present numerical simulations for one-dimensional soft-Coulomb systems.
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All authors Éric Cancès, Théo Duez, Jari van Gog, Asbjørn Bækgaard Lauritsen, Mathieu Lewin, Julien Toulouse
Materials Science
Geometric theory of constrained Schrödinger dynamics with application to time-dependent density-functional theory on a finite lattice
Eric Cancès, Théo Duez, Jari van Gog et al. (+3 more)
Time-dependent density-functional theory (TDDFT) is a central tool for studying the dynamical electronic structure of molecules and solids, yet aspects of its mathematical foundations remain insufficiently understood. In this work, we revisit the foundations of TDDFT within a finite-dimensional setting by developing a general
geometric framework for Schrödinger dynamics subject to prescribed expectation values of selected observables. We show that multiple natural definitions of such constrained dynamics arise from the underlying geometry of the state
manifold. The conventional TDDFT formulation emerges from demanding stationarity of the action functional, while an alternative, purely
geometric construction leads to a distinct form of constrained Schrödinger
evolution that has not been previously explored. This alternative dynamics may provide a more mathematically robust route to TDDFT and may suggest new strategies for constructing nonadiabatic approximations. Applying the theory to interacting
fermions on finite
lattices, we derive novel Kohn–Sham schemes in which the density constraint is enforced via an imaginary potential or, equivalently, a nonlocal Hermitian operator. Numerical illustrations for the Hubbard dimer demonstrate the behavior of these new approaches.
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All authors Eric Cancès, Théo Duez, Jari van Gog, Asbjørn Bækgaard Lauritsen, Mathieu Lewin, Julien Toulouse
Mesoscale and Nanoscale Physics
Effects of random vacancies on the spin-dependent thermoelectric properties of silicene nanoribbon
D. Zambrano, C. D. Núñez, P. A. Orellana et al. (+2 more)
The
spin-dependent thermoelectric properties of silicene nanoribbon
heterostructures are investigated, in which the central conductor contains a random distribution of vacancies and is connected to two pristine leads of the same material, placed in proximity to
ferromagnetic insulators. The
magnetic moments of the leads are analyzed in both parallel and antiparallel configurations. A tight-binding
Hamiltonian and the Green's function formalism are employed to calculate the
spin-resolved thermoelectric properties of the system as functions of geometrical confinement and vacancy concentration. The results demonstrate an enhancement in charge and
spin-dependent thermopower, resulting in an improved thermoelectric efficiency at room temperature, which overcomes the limitations imposed by the classical Wiedemann-Franz law. These findings indicate that defective silicene nanoribbons are promising platforms for the development of efficient thermoelectric and
spin-caloritronic devices.
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All authors D. Zambrano, C. D. Núñez, P. A. Orellana, J. P. Ramos-Andrade, L. Rosales
Superconductivity
From perovskite to infinite-layer nickelates: hole concentration from x-ray absorption
R. Pons, M. Flavenot, K. Fürsich et al. (+12 more)
The difficulty of determining cation concentrations and oxygen stoichiometry in infinite-layer nickelate thin films has so far prevented clear experimental identification of the nickel electron configuration in the superconducting phase. We used soft x-ray absorption spectroscopy to study the successive changes in PrNiO$_x$ thin films at various intermediate stages of topotactic reduction with $x=2-3$. By comparing the Ni-$L$ edge spectra to single and double cluster ligand-field calculations, we find that none of our samples exhibit a pure $d^9$ configuration. Our quantitative analysis using the charge sum rule shows that even when films are maximally reduced, the averaged number of nickel $3d$ holes is 1.35. Superconducting samples have even higher values, calling into question the previously assumed limit of hole doping. Concomitant changes in the oxygen $K$-edge absorption spectra upon reduction indicate the presence of oxygen $2p$ holes, even in the most reduced films. Overall, our results suggest a complex interplay of hole doping mechanisms resulting from self-doping effects and oxygen non-stoichiometry.
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All authors R. Pons, M. Flavenot, K. Fürsich, E. Schierle, E. Weschke, M. R. Cantarino, E. Goering, P. Nagel, S. Schuppler, G. Kim, G. Logvenov, B. Keimer, R. J. Green, D. Preziosi, E. Benckiser
Materials Science
Spin-lattice model simulations of tetragonal FePt system
Jakub Šebesta and Dominik Legut
Magnetic materials play a key role in the contemporary industry, providing unique features with a wide application potential. To study physical phenomena and design new materials, it is important to possess an appropriate tool, a model allowing simulation of desired behavior.
Spin-
lattice model simulations can be used to investigate spacious systems containing thousands of atoms, while complex phenomena arising from the interplay of
lattice and
spin dynamics can be modeled. One of the important phenomena that can be modeled in the
spin lattice simulation is magnetoelastic behavior, offering direct conversion between the mechanical and
magnetic energy. However, so far, only models for systems with cubic
symmetry have been introduced. Therefore, here, a
spin-
lattice model for a system with tetragonal
symmetry is proposed, where its strength is manifested by simulation of magnetoelastic properties of a characteristic representative L1$_{0}$ FePt system.
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Materials Science
Noise2Void for Denoising Atomic Resolution Scanning Transmission Electron Microscopy Images
William Thornley, Sam Sullivan-Allsop, Rongsheng Cai et al. (+3 more)
The Noise2Void technique is demonstrated for successful denoising of atomic-resolution scanning transmission electron microscopy (STEM) images. The technique is applied to denoising atomic resolution images and
videos of gold adatoms on a
graphene surface within a
graphene liquid cell, with the denoised experimental data qualitatively demonstrating improved visibility of both the Au adatoms and the
graphene lattice. The denoising performance is quantified by comparison to similar simulated data and the approach is found to significantly outperform both total variation and simple Gaussian blurring. Compared to other denoising methods, the Noise2Void technique has the combined advantages that it requires no manual intervention during training or denoising, no prior knowledge of the sample and is compatible with real time data acquisition rates of at least 45 frames per second.
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All authors William Thornley, Sam Sullivan-Allsop, Rongsheng Cai, Nick Clark, Roman Gorbachev, Sarah J. Haigh
Soft Condensed Matter · Cross-listed from quant-ph
Finite-Memory Extension of Tegmark's Decoherence Bound in Biological Media
Ramandeep Dewan
Tegmark's decoherence bound is derived under the assumption of a strictly memoryless environment. We show that this result corresponds to the singular limit of a finite-
memory theory. For exponentially correlated environments decoherence is generically quadratic at short times and the decoherence time scales as the square root of the bath correlation time. For the Ornstein-Uhlenbeck bath we derive the exact non-Markovian coherence equation and verify the predicted scaling using an exact pseudomode mapping. Tegmark's bound is recovered only in the vanishing-
memory limit.
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Materials Science
A density functional theory study of amino acids on Mg and Mg-based alloys
John Bolin, Amanda Goold, Olof Hildeberg et al. (+2 more)
Magnesium (Mg) has mechanical properties similar to bone tissue, and Mg ions take part in the metabolism. This makes Mg of interest for biocompatible degradable body implants, provided that its high corrosion rate can be inhibited. Slightly alloying Mg and adding surface coatings can slow down the corrosion processes without significantly changing the mechanical properties. Use of coating molecules that are native to the body increase the likelihood of making the surface biocompatible, for example by use of amino acids. We here present a density functional theory (DFT) study of the adsorption on Mg(0001) of the amino acids glycine, L-proline, and L-hydroxyproline (Hyp), the main amino acid content of collagen. We investigate how binding of the functional groups of Hyp are affected when Mg(0001) is slightly alloyed with zinc, lithium or aluminium, and we also model the immersion of the systems in a water environment to see how this affects the binding.
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All authors John Bolin, Amanda Goold, Olof Hildeberg, Alva Limbäck, Elsebeth Schröder
Quantum Gases
From coherent to fermionized microwave photons in a superconducting transmission line
Alberto Tabarelli de Fatis, Stephanie Matern, Gianluca Rastelli et al. (+1 more)
We investigate superconducting transmission lines as a novel platform for realizing a
quantum fluid of microwave
photons in a propagating geometry. We predict that the strong
photon-
photon interactions provided by the intrinsic nonlinearity of Josephson junctions are sufficient to enter a regime of strongly interacting
photons for realistic parameters. A suitable tapering of the transmission line parameters allows for the adiabatic conversion of an incident coherent field into a Tonks-Girardeau gas of fermionized
photons close to its ground state. Signatures of the strong correlations are anticipated in the correlation properties of the transmitted light.
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All authors Alberto Tabarelli de Fatis, Stephanie Matern, Gianluca Rastelli, Iacopo Carusotto