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Physics Condensed Matter

cond-mat Watch Condensed Matter

Thursday 4 December

Mesoscale and Nanoscale Physics · Cross-listed from physics.optics

Quantum open system description of a hybrid plasmonic cavity

Marco Vallone

We present a unified quantum open system framework for lossy plasmonic cavities in which coherent dynamics, relaxation, dephasing, and irreversible absorption are treated on equal footing. The Dyson equation for the cavity photon propagator in the random-phase approximation yields a complex self-energy S that accounts for both the renormalization and the damping of hybrid plasmon-photon modes (polaritons, in a quasi-particle description). Tracing out the electronic and photonic environments leads to a Liouvillian for the upper (UP) and lower (LP) polaritonic branches, incorporating leakage through the imaginary part of the self-energy, internal UP-LP scattering rates, and dephasing. Time evolution equations for polariton populations, interbranch coherence, and driven amplitudes in closed form also provide analytic expressions for their steady-state values, the quench rate of UP-LP oscillations and polaritonic lineshapes, valid in the limit of low polaritonic density, but covering light-matter ultrastrong coupling. The theory establishes a self-consistent description of dissipative polariton dynamics in plasmonic and nanophotonic cavities, directly applicable to response spectra, time-domain measurements, and dissipation engineering.
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Statistical Mechanics

Comparison of some geometric frameworks for dissipative evolution in multiscale non-equilibrium thermodynamics

Miroslav Grmela and Michal Pavelka

In this paper, we review and compare some geometric frameworks for dissipation in non-equilibrium thermodynamics. We start with a brief overview of classical irreversible thermodynamics and gradient dynamics. Then we discuss several specific frameworks including Rayleigh dissipation potential and the dissipative d'Alembert framework, showing their relations with gradient dynamics. Finally, we discuss frameworks for dissipative evolution generated from Poisson brackets.
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Materials Science

Modeling Compressive Instability in Two-Dimensional Ti2COx MXenes

Hossein Darban

In practical applications, MXenes are often subjected to a variety of loads, including compression. While their mechanical response under different loading conditions, such as tensile loading, has been extensively studied, their compressive instability remains largely unexplored. The compressive and post-buckling behavior of Ti2C and Ti2CO2 MXene nanosheets is studied using molecular dynamics (MD) simulations and a nonlocal formulation. The employed interatomic potential is first validated against experimental and density functional theory (DFT) data for structural and mechanical properties. The results indicate that classical continuum mechanics underestimates the buckling strains, whereas the nonlocal formulation adequately captures the observed response. A systematic examination of various defect types up to a defect fraction of 3% reveals that while isolated point defects primarily reduce the critical buckling stress, vacancy clusters significantly alter the buckling mode shapes. Lateral confinement pressure and oxygen surface termination substantially increase the buckling stress. Atomistic analysis reveals opposite stress states in the top and bottom Ti layers due to curvature-induced strain gradients. Under biaxial compression, the nanosheet buckles in a dome-like shape, whereas shear loads produce elliptical deflection modes. The presented findings may stimulate future studies on MXene morphological transformations, such as the development of nanotube, nanoscroll, and folded architectures.
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Soft Condensed Matter

Correlation between the boson peak frequency and transverse Ioffe-Regel limit in four-dimensional structural glasses

Licun Fu, Xinyu Chang and Lijin Wang

The emergence of excess vibrational modes over the Debye prediction, typically manifested as the well-known boson peak in the plot of vibrational density of states scaled by the Debye prediction, has become a hallmark of various amorphous solids. The origin of the boson peak has been attracting considerable attention but is still under debate. A popular view is that the position of the boson peak coincides well with that of the Ioffe-Regel limit for transverse modes in both two- and three-dimensional glasses, which is primarily derived from simulation studies of model structural glasses. However, it remains unknown whether the proposed coincidence could be generalized to higher spatial dimensions, and addressing this could contribute to the advancement of relevant phenomenological theories. Here, we find that the transverse Ioffe-Regel limit frequency is higher than and not proportional to the boson peak frequency in our studied four-dimensional glasses. Our findings therefore suggest that the proposed coincidence between the boson peak frequency and the transverse Ioffe-Regel limit depends on spatial dimensions, which was not anticipated previously.
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Mesoscale and Nanoscale Physics

Global phase diagram of two-dimensional dirty hyperbolic Dirac liquids

Christopher A. Leong, Daniel J. Salib and Bitan Roy

Within the framework of the canonical nearest-neighbor tight-binding model for spinless fermions, a family of two-dimensional bipartite hyperbolic lattices hosts massless Diraclike excitations near half-filling with the iconic vanishing density of states (DOS) near zero energy. We show that a collection of such ballistic quasiparticles remains stable against sufficiently weak pointlike charge impurities, a feature captured by the vanishing average [$\rho_{a}(0)$] and typical [$\rho_{t}(0)$] DOS at zero energy, computed by employing the kernel polynomial method in sufficiently large $\{ 10, 3\}$ hyperbolic lattices (Schläfli symbol) with open boundary condition containing more than $10^8$ and $10^6$ sites, respectively. However, at moderate disorder the system enters a metallic state via a continuous quantum phase transition where both $\rho_{a}(0)$ and $\rho_{t}(0)$ become finite. With increasing strength of disorder, ultimately an Anderson insulator sets in, where only $\rho_{t}(0) \to 0$. The resulting phase diagram for dirty Dirac fermions living on a hyperbolic space solely stems from the background negative spatial curvature, as confirmed from the vanishing $\rho_{t}(0)$ for arbitrarily weak disorder on honeycomb lattices, fostering relativistic fermions on a flatland, as the thermodynamic limit is approached.
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Mesoscale and Nanoscale Physics

Multimode RF Reflectometry for Spin Qubit Readout and Device Characterization

Joffrey Rivard, Alexis Morel, Olivier Romain et al. (+10 more)

We introduce a multimode superconducting inductor architecture that enables radio-frequency reflectometry at multiple discrete frequencies up to 2 GHz, addressing limitations of conventional single-mode designs. The spiral inductor's distributed inter-turn capacitance yields distinct resonant modes with varied impedance-matching conditions. By probing a quantum dot across several modes, we extract tunneling rates over a broad frequency range and identify signatures of nearby charge defects. Using one of the higher-order modes, we demonstrate single-shot spin readout via a radio-frequency single-electron transistor (RF-SET), achieving singlet-triplet readout with an integration time of 8 us and a readout fidelity of 98%. These results establish multimode inductance as a scalable and flexible component for fast spin-qubit readout and device-quality characterization.
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All authors Joffrey Rivard, Alexis Morel, Olivier Romain, El Bachir Ndiaye, Idris Aboubakari, Christian Lupien, Clément Godfrin, Julien Jussot, Stefan Kubicek, Kristiaan De Greve, Danny Wan, Claude Rohrbacher, Eva Dupont-Ferrier

Materials Science · Cross-listed from physics.optics

Anisotropic Response in Metamaterials with Elliptically Perforated Plates: Applications to Near-Field Radiative Heat Transfer

J. E. P'erez-Rodr'iguez, R. Esquivel-Sirvent and A. Camacho de la Rosa

Metamaterials with tunable optical properties provide a versatile platform for controlling electromagnetic interactions at the nanoscale. This study explores the anisotropic thermal behavior of metamaterials composed of planar plates perforated with periodic arrays of cylinders possessing elliptical cross sections. In contrast to conventional circular perforations, elliptical geometries inherently break rotational symmetry, introducing anisotropy in the effective electromagnetic and thermal response of the structure. Using a fluctuation electrodynamics framework combined with full-wave numerical simulations, we quantify the near-field radiative heat transfer between such elliptically perforated plates as a function of ellipse orientation, aspect ratio, and separation distance. The results reveal that elliptical perforations enable enhanced spectral and directional control of evanescent mode coupling and surface polariton excitation, leading to significant modulation of the near-field heat flux. These findings highlight the potential of geometrically engineered anisotropy for advanced thermal management and energy conversion applications, and offer new design strategies for the development of thermally functional metamaterials operating in the near-field regime.
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Statistical Mechanics · Cross-listed from quant-ph

Thermodynamic universality across dissipative quantum phase transitions

Laetitia P. Bettmann, Artur M. Lacerda, Mark T. Mitchison et al. (+1 more)

We study finite-time driving across second-order dissipative quantum phase transitions described by Lindblad dynamics. We show that the nonadiabatic entropy production, which quantifies deviations from the instantaneous nonequilibrium steady state, exhibits universal power-law scaling with the ramp duration in analogy to the Kibble-Zurek mechanism for closed systems. This establishes the universality of irreversible dissipation induced by driving an open quantum system near criticality. Furthermore, in systems described by bosonic Gaussian states, our scaling laws predict that the nonadiabatic entropy production is independent of driving speed to leading order, revealing a distinctive feature of Gaussian dissipative quantum phase transitions. We validate these analytical predictions in the thermodynamic limit of the driven-dissipative Dicke model and via finite-size scaling in the open Kerr model. Our results establish a general framework for understanding universal nonequilibrium response and thermodynamic irreversibility in critical open quantum systems.
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All authors Laetitia P. Bettmann, Artur M. Lacerda, Mark T. Mitchison, John Goold

Statistical Mechanics · Cross-listed from hep-th

On the six-loop scaling dimensions of the $(\phi^2)^n$ operators in $d=3$

A.V. Bednyakov, M.V. Kompaniets and A.V. Trenogin

We consider a class of singlet operators $(\phi^2)^n$ in the three-dimensional $O(N)$ model with $\lambda^2 \phi^6$ interaction. Recently, the corresponding anomalous dimensions $\gamma_{2n}$ were computed by semiclassical methods and the all-loop result for the leading-$n$ corrections in the small $\lambda$ limit was found. In this paper, we obtain the six-loop expressions not only for the leading-$n$ contribution but also for the subleading one. While the leading correction confirms the predictions of recent semiclassical calculation, the subleading one is a new result and will serve as a future welcome check for all-loop expressions. As an important by-product of our calculation, we provide a full dependence on $n$ of the four-loop $\gamma_{2n}$ in the $O(N)$ case.
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Mesoscale and Nanoscale Physics

Axionic tunneling from a topological Kondo insulator

Saikat Banerjee, Anuva Aishwarya, Fei Liu et al. (+4 more)

Discoveries over the past two decades have revealed the remarkable ability of quantum materials to emulate relativistic properties of the vacuum, from Dirac cones in graphene to Dirac surface states of topological insulators. Yet one of the most elusive consequences of topology in quantum matter – the axionic ${\bf E}\cdot{\bf B}$ contribution to the electromagnetic response, predicted to produce strong magnetoelectric effects – remains experimentally challenging to detect. Here we report evidence for an axion-like magnetoelectric response obtained through scanning tunneling microscopy (STM) using a SmB$_6$ nanowire tip on an antiferromagnetic Fe$_{1+x}$Te sample. Our measurements reveal a striking voltage-induced magnetization: millivolt biases generate measurable tip magnetizations that reverse with the voltage. The magnitude, tunability, and reversibility of this signal are consistent with an axion-like ${\bf E} \cdot {\bf B}$ coupling, which naturally accounts for the voltage-odd magnetic component of the tip spectral function while strongly constraining a conventional static-magnetism interpretation. Moreover, millivolt-scale control of spin polarization in a tunnel junction provides a new route for probing axionic electrodynamics and opens avenues for future STM and spintronic applications.
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All authors Saikat Banerjee, Anuva Aishwarya, Fei Liu, Lin Jiao, Vidya Madhavan, Eugene J. Mele, Piers Coleman

Mesoscale and Nanoscale Physics

High Fidelity Qubit Control in a Natural Si-MOS Quantum Dot using a 300 mm Silicon on Insulator Wafer

Xander Peetroons, Xunyao Luo, Tsung-Yeh Yang et al. (+26 more)

We demonstrate high-fidelity single qubit control in a natural Si-MOS quantum dot fabricated in an industrial 300 mm wafer process on a silicon on insulator (SOI) wafer using electron spin resonance. A relatively high optimal Rabi frequency of 5 MHz is achieved, dynamically decoupling the electron spin from its 29-Si environment. Tracking the qubit frequency reduces the impact of low frequency noise in the qubit frequency and improves the $T^{Rabi}$ from 7 to 11 $\mu$s at a Rabi frequency of 5 MHz, resulting in Q-factors exceeding 50. Randomized benchmarking returns an average single gate control fidelity of 99.5 $\pm$ 0.3%. As a result of pulse-area calibration, this fidelity is limited by the Rabi Q-factor. These results show that a fast Rabi frequency, low charge noise, and a feedback protocol enable high fidelity in these Si-MOS devices, despite the low-frequency magnetic noise.
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All authors Xander Peetroons, Xunyao Luo, Tsung-Yeh Yang, Normann Mertig, Sofie Beyne, Julien Jussot, Yosuke Shimura, Clement Godfrin, Bart Raes, Ruoyu Li, Roger Loo, Sylvain Baudot, Stefan Kubicek, Shuchi Kaushik, Danny Wan, Takeru Utsugi, Takuma Kuno, Noriyuki Lee, Itaru Yanagi, Toshiyuki Mine, Satoshi Muraoka, Shinichi Saito, Digh Hisamoto, Ryuta Tsuchiya, Hiroyuki Mizuno, Kristiaan De Greve, Charles Smith, Helena Knowles, Andrew Ramsay

Materials Science

Prediction of Novel Li-AgII-F Compounds using Evolutionary Algorithms

Katarzyna Kuder and Wojciech Grochala

This work provides a theoretical exploration of the thermodynamic stability and magnetic behaviour of previously unknown ternary Li AgII F compounds. Convex-hull analysis shows that all predicted structures lie slightly above the LiF plus AgF2 decomposition line, indicating a natural tendency toward phase separation; nevertheless, their negative formation energies relative to AgF, LiF, and F2 or F suggest that alternative synthetic pathways may be feasible for these compounds. All studied structures show preference for antiferromagnetic ground state. Notably, the triclinic LiAgF3 type2 is predicted to exhibit an exceptionally large superexchange constant, J equal to minus 358 meV, within Ag2F7 dimers, placing it above the strongest known magnetic exchange interactions reported to date.
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Materials Science · Cross-listed from math.MG

Geometric Data Science

Olga D Anosova and Vitaliy A Kurlin

This book introduces the new research area of Geometric Data Science, where data can represent any real objects through geometric measurements. The first part of the book focuses on finite point sets. The most important result is a complete and continuous classification of all finite clouds of unordered points under rigid motion in any Euclidean space. The key challenge was to avoid the exponential complexity arising from permutations of the given unordered points. For a fixed dimension of the ambient Euclidean space, the times of all algorithms for the resulting invariants and distance metrics depend polynomially on the number of points. The second part of the book advances a similar classification in the much more difficult case of periodic point sets, which model all periodic crystals at the atomic scale. The most significant result is the hierarchy of invariants from the ultra-fast to complete ones. The key challenge was to resolve the discontinuity of crystal representations that break down under almost any noise. Experimental validation on all major materials databases confirmed the Crystal Isometry Principle: any real periodic crystal has a unique location in a common moduli space of all periodic structures under rigid motion. The resulting moduli space contains all known and not yet discovered periodic crystals and hence continuously extends Mendeleev's table to the full crystal universe.
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Statistical Mechanics · Cross-listed from math-ph

Cumulant expansions of operator groups of quantum many-particle systems

V.I. Gerasimenko and I.V. Gapyak

The article presents a method of cluster expansions for groups of operators associated with the von Neumann equations for states and the Heisenberg equations for observables, aiming to construct generating operators for nonperturbative solutions to the Cauchy problem for hierarchies of evolution equations of many-particle quantum systems.
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Mesoscale and Nanoscale Physics

Transverse response from anisotropic Fermi surfaces

Abhiram Soori

We demonstrate that an anisotropic and rotated Fermi surface can generate a finite transverse response in electron transport, even in the absence of a magnetic field or Berry curvature. Using a two-dimensional continuum model, we show that broken $k_y \to -k_y$ symmetry inherent to anistropic bandstructures leads to a nonzero transverse conductivity. We construct a lattice model with direction-dependent nearest- and next-nearest-neighbor hoppings that faithfully reproduces the continuum dispersion and allows controlled rotation of the Fermi contour. Employing a multiterminal geometry and the Büttiker-probe method, we compute the resulting transverse voltage and establish its direct correspondence with the continuum transverse response. The effect increases with the degree of anisotropy and vanishes at rotation angles where mirror symmetry is restored. Unlike the quantum Hall effect, the transverse response predicted here is not quantized but varies continuously with the band-structure parameters. Our results provide a symmetry-based route to engineer transverse signals in low-symmetry materials without magnetic fields or topological effects.
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Mesoscale and Nanoscale Physics

Suppressing metal molecule charge transfer with a phosphorus interlayer

Mattia Bassotti, Luca Floreano, Luca Schio et al. (+5 more)

Porphyrins are organic molecules that exhibit excellent opto-electronics properties, making them suitable for a variety of applications. Nevertheless, their functionality strongly depends on the surface onto which they are deposited, and on the interaction between the molecules and the substrate itself, which often leads to an undesired alteration in their electronic properties. In this study, we use a phosphorus interlayer on a Cu(110) surface as a buffer layer for the electronic decoupling of Zinc-TetraPhenylPorphyrin (ZnTPP) molecules. Using a combination of complementary techniques, such as Near Edge X-ray Absorption Fine Structure (NEXAFS), X-ray and Ultraviolet Photoemission Spectroscopy (XPS, UPS) as well as Scanning Tunneling Spectroscopy (STS) techniques, it is shown how the charge transfer from the metal, responsible for quenching the ZnTPP lowest unoccupied molecular level (LUMO) levels, is effectively prevented by the presence of a phosphorus reconstruction in between.
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All authors Mattia Bassotti, Luca Floreano, Luca Schio, Sergio Salaverria, Dimas G. de Oteyza, Giacomo Giorgi, Frederik Schiller, Alberto Verdini

Materials Science

A meta-GGA perspective on the altermagnetism of RuO2

Markus Meinert

The metallic oxide RuO$_2$ hosts a fascinating edge case of magnetism: while nonmagnetic in ideal bulk material, density functional theory (DFT) predicts an altermagnetic ground state within the DFT$+U$ method. The magnetic state of strained or doped thin films remains controversial, but evidence for a nontrivial magnetic state is ample. Here, I study the altermagnetic ground state of RuO$_2$ on a higher rung of Jacob's ladder of density functional approximations, the meta-GGA level including the kinetic energy density and the density Laplacian. While the workhorse functional of solid-state physics is a generalized gradient approximation (GGA), the modern r$^2$SCAN-L functional has been established as a general-purpose functional which can replace GGA, while systematically improving solid-state properties without introducing spurious errors like erroneous magnetic ground states. Comparison of LSDA+U, GGA+U, and meta-GGA+U results on RuO$_2$ shows systematic enhancement of the exchange interaction, leading to a reduction of the onset value of the Hubbard $U$ parameter at different levels of density functional approximation. However, the magnetic ground state, studied at the experimental lattice constants, remains nonmagnetic with r$^2$SCAN-L. I demonstrate that altermagnetism is easily formed upon lattice expansion, hole doping, and uniaxial strain on the c-axis. The r$^2$SCAN-L calculations set conservative thresholds for distortions and doping levels for the onset of altermagnetism in a parameter-free framework.
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Strongly Correlated Electrons

Tracing the horizon of tetragonal-to-monoclinic distortion in pressurized trilayer nickelate La4Ni3O10

Sitaram Ramakrishnan, Yingzheng Gao, Valerio Olevano et al. (+18 more)

The crux of understanding the superconducting mechanism in pressurized Ruddlesden-Popper nickelates hinges on elucidating their structural phases. Under ambient conditions, the trilayer nickelate La4Ni3O10 stabilizes in a twinned monoclinic structure with space group P21/c. Upon heating, it undergoes a structural transition to the tetragonal I4/mmm phase at Ts ~ 1030 K, while a second transition associated with the onset of density-weave (DW) ordering emerges upon cooling below TDW ~ 135 K. Here from pressure-temperature x-ray diffraction on high quality flux-grown single crystals we demonstrate a direct tetragonal-to-monoclinic transition without an intermediate orthorhombic Bmab phase. Ab initio density-functional theory calculations as a function of pressure corroborate the experimental observations. The tetragonal-to-monoclinic transition unfolds as the formation of a two-fold superstructure, as evidenced by the emergence of commensurate superlattice reflections and can be progressively suppressed from 1030 K down to 20 K under 14 GPa. Notably, from XRD we establish the observation of weak incommensurate satellite reflections associated with the DW ordering in flux-grown samples, as previous findings were confined only to crystals grown by the floating-zone technique. This is further reinforced by Raman spectroscopy that reveal the emergence of additional phonon modes below 130 K, concomitant with the onset of the incommensurate DW state.
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All authors Sitaram Ramakrishnan, Yingzheng Gao, Valerio Olevano, Elise Pachoud, Abdellali Hadj-Azzem, Gaston Garbarino, Matteo d'Astuto, Olivier Perez, Alain Pautrat, Diego Valenti, Matthieu Quenot, Sebastien Pairis, Dmitry Chernyshov, Leila Noohinejad, Carsten Paulmann, Johnathan Bulled, Alexei Bosak, Sander van Smaalen, Pierre Toulemonde, Marie-Aude Measson, Pierre Rodiere

Other Condensed Matter · Cross-listed from quant-ph

Convergence of sample-based quantum diagonalization on a variable-length cuprate chain

L. Andrew Wray, Cheng-Ju Lin, Vincent Su et al. (+1 more)

Sample-based quantum diagonalization (SQD) is an algorithm for hybrid quantum-classical molecular simulation that has been of broad interest for application with noisy intermediate scale quantum (NISQ) devices. However, SQD does not always converge on a practical timescale. Here, we explore scaling of the algorithm for a variable-length molecule made up of 2 to 6 copper oxide plaquettes with a minimal molecular orbital basis. The results demonstrate that enabling all-to-all connectivity, instituting a higher expansion order for the SQD algorithm, and adopting a non-Hartree-Fock molecular orbital basis can all play significant roles in overcoming sampling bottlenecks, though with tradeoffs that need to be weighed against the capabilities of quantum and classical hardware. Additionally, we find that noise on a real quantum computer, the Quantinuum H2 trapped ion device, can improve energy convergence beyond expectations based on noise-free statevector simulations.
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All authors L. Andrew Wray, Cheng-Ju Lin, Vincent Su, Hrant Gharibyan

Materials Science

Tuning the Electronic States of Bi2Se3 Films with Large Spin-Orbit Interaction Using Molecular Heterojunctions

Matthew Rogers, Craig Knox, Bryan Hickey et al. (+13 more)

An electric bias can shift the Fermi level along the Dirac cone of a topological insulator and modify its charge transport, but tuning the electronic states and spin-orbit interaction (SOI) without destroying the surface topology is challenging. Here, we show that thin film Bi2Se3/n-p (p-n) molecular diodes form ordered interfaces where charge transfer and orbital re-hybridisation result in a decrease (increase) of the carrier density and improved mobility. In Bi2Se3 the spin-orbit lifetime, t_so, is 0.13 ps, which is comparable to the strongest spin-orbit materials. This lifetime drops further to 0.06 ps (0.09 ps) with the addition of p-n (n-p) molecular diodes, at the limit of measurable values. This strengthened spin-orbit interaction occurs even though molecules are made of light elements and increase the mean free path of the charge carriers by almost 50%, indicating changes to the Berry curvature and/or Rashba splitting around the hybridisation points. Raman spectroscopy gives evidence that the coupling effect may be controlled by optical irradiation, opening a pathway towards the design of heavy-light element hybrids with optically tunable quantum transport.
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All authors Matthew Rogers, Craig Knox, Bryan Hickey, Lida Ansari, Farzan Gity, Timothy Moorsom, Mairi McCauley, Gilberto Teobaldi, Manuel dos Santos Dias, Hari B. Vasili, Manuel Valvidares, Mannan Ali, Gavin Burnell, Ahmet Yagmur, Satoshi Sasaki, Oscar Cespedes

Materials Science

In search of the electron-phonon contribution to total energy

Samuel Poncé and Xavier Gonze

The total energy is a fundamental characteristic of solids, molecules, and nanostructures. In most first-principles calculations of the total energy, the nuclear kinetic operator is decoupled from the many-body electronic Hamiltonian and nuclear potential, and the dynamics of the nuclei is reintroduced afterward. This two-step procedure introduced by Born and Oppenheimer (BO) is approximate. Energies beyond the electronic and vibrational (or phononic) main contributions might be relevant when small energy differences are important, such as when predicting stable polymorphs or describing magnetic energy landscape. We clarify the different flavors of BO decoupling and give an exact formulation for the total energy in the basis of BO electronic wavefunctions. Then, we list contributions, beyond the main ones, that appear in a perturbative expansion in powers of $M_0^{-1/4}$, where $M_0$ is a typical nuclear mass, up to sixth order. Some of these might be grouped and denoted the electron-phonon contribution to total energy, $E^{\textrm{elph}}$, that first appears at fourth order. The electronic inertial mass contributes at sixth order. We clarify that the sum of the Allen-Heine-Cardona zero-point renormalization of eigenvalues over occupied states is not the electron-phonon contribution to the total energy but a part of the phononic contribution. The computation of the lowest-order $E^{\textrm{elph}}$ is implemented and shown to be small but non-negligible (3.8~meV per atom) in the case of diamond and its hexagonal polymorph. We also estimate the electronic inertial mass contribution and the quasi-harmonic one. We confirm the size consistency of all computed terms.
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Mesoscale and Nanoscale Physics

Optical Readout of Reconfigurable Layered Magnetic Domain Structure in CrSBr

Aleksandra Łopion, Pierre-Maurice Piel, Thomas Kliewer et al. (+9 more)

The van der Waals magnetic semiconductor CrSBr combines multistable magnetic order with strong light–matter coupling, enabling optical access to a rich and reconfigurable layered magnetic domain structure. A purely optical, non-destructive, and non-contact readout of layered magnetic configurations is realized here by magneto-reflectance measurements and interpreted using an optical multilayer model. The magnetic state is tunable by applied magnetic fields and by interfacing CrSBr with the antiferromagnet MnPS$_3$. Applying an external magnetic field along the easy axis drives the hysteretic antiferromagnetic–to–ferromagnetic transition, which is not universally binary but instead develops through a cascade of intermediate magnetic configurations whose multiplicity and stability scale systematically with layer thickness and can be tailored by magnetic interfaces. The intertwined optical and magnetic properties of CrSBr provide a readout mechanism for information encoded in and processed through its magnetic configuration that is compatible with modern on- and off-chip photonic and electronic technologies. These properties identify CrSBr as a promising platform for intelligent matter and for spin-optoelectronics, in particular for neuromorphic architectures that can learn and evolve in response to changing environments.
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All authors Aleksandra Łopion, Pierre-Maurice Piel, Thomas Kliewer, Manuel Terbeck, Jan-Hendrik Larusch, Jakob Henz, Marie-Christin Heißenbüttel, Kseniia Mosina, Thorsten Deilmann, Michael Rohlfing, Zdenek Sofer, Ursula Wurstbauer

Materials Science

Controlling Carbon Nanostructure Synthesis in Thermal Plasma Jet: Correlation of Process Parameters, Plasma Characteristics, and Product Morphology

Taki Aissou, Jerome Menneveux, Fanny Casteignau et al. (+2 more)

Thermal plasma has emerged as an effective approach for producing carbon nanostructures without the need for specific catalysts nor substrates. While efforts have focused on the effect of process parameters such as reaction pressure, input power or carbon source, the intricate role and relationship with plasma characteristics like density and temperature are often overlooked due to the complexity of the environment. This study addresses this gap by establishing a correlation between process parameters, plasma characteristics, and product morphology, essential for controlling the growth of carbon nanostructures. We explored the impact of carbon precursor type (CH4 and C2H2), hydrogen, pressure, and flow rate on nanostructure formation. Using in situ optical emission spectroscopy (OES), we mapped the distribution of both temperature and dicarbon molecule (C2) density within the plasma jet. We demonstrate that the growth of low-density nanostructures, such as carbon nanohorns (CNHs), is favoured at dilute C2 local densities and high temperatures, while denser nanostructures, such as onion-like polyhedral graphitic nanocapsules (GNCs), are favoured at higher C2 densities and lower temperatures. The carbon density can be controlled by the flow rate and the pressure, which in turn significantly influence the nanostructure morphology, evolving from graphene nanoflakes (GNFs) to GNCs as either parameter increases. Increasing the H/C ratio from 1 to 8 resulted in a morphological transition from CNHs to GNFs. During the synthesis, the plasma jet temperature surpassed 3,000 K, with crystalline growth occurring 50 to 100 mm below the nozzle.
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All authors Taki Aissou, Jerome Menneveux, Fanny Casteignau, Nadi Braidy, Jocelyn Veilleux

Materials Science

Valley Splittings in Si/SiGe Heterostructures from First Principles

Lukas Cvitkovich, Tancredi Salamone, Christoph Wilhelmer et al. (+3 more)

We compute valley splittings in Si/SiGe superlattices using ab initio density functional theory (DFT). This first-principle approach is expected to provide an excellent description of interfaces, strains, and atomistic disorder without empirically fitted parameters. We benchmark atomistic tight-binding (TB) and the “$2k_0$” theory within the effective mass (EM) approximation against DFT. We show that DFT supports the main conclusions of the 2$k_0$ theory, but reveals some limitations of semi-empirical methods such as the EM and TB, in particular about the description of atomistic disorder. The DFT calculations also highlight the effects of strong valley-orbit mixing at large valley splittings. Nevertheless, TB and the 2$k_0$ theory shall provide reasonable valley splitting statistics in many heterostructures of interest for spin qubit devices.
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All authors Lukas Cvitkovich, Tancredi Salamone, Christoph Wilhelmer, Biel Martinez, Tibor Grasser, Yann-Michel Niquet

Materials Science

Isostructural phase transition and equation of state of type-I and type-VIII metallic sodium borosilicide clathrates

M. Demoucron, S. Pandolfi, Y. Guarnelli et al. (+10 more)

Electronic properties of silicon-based clathrates can be tuned by boron incorporation into the silicon cage network. Sodium borosilicides clathrate outstands with uncommon stoichiometry and expected metallic properties, in contrast to other alkali metal semiconductive Zintl borosilicides. In this study, we report an experimental investigation of the high-pressure behavior of type-I and type-VIII sodium borosilicide clathrates. An isostructural phase transition, marked by an abrupt volume collapse at 13 GPa, is observed exclusively in type-I sodium borosilicide clathrates. This transition is attributed to the pressure-induced diffusion of silicon atoms from the Si(6c) site. This mechanism provides the first experimental validation of a transition predicted theoretically for this class of materials. Isostructural phase transitions were only observed in type-I borosilicide. In contrast, the type-VIII borosilicide phase exhibits conventional elastic compression. The metallic character was established using reflectance spectroscopy over a wide energy range, in good agreement with crystallographic data on the boron content.
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All authors M. Demoucron, S. Pandolfi, Y. Guarnelli, B. Baptiste, P. Chauvigne, N. Guignot, D. Portehault, T.A. Strobel, M. Bykov, T.B. Shiell, W.A. Crichton, Y. Le Godec, A. Courac

Statistical Mechanics

Balancing information and dissipation with partially observed fluctuating signals

Giorgio Nicoletti, Ivan Di Terlizzi and Daniel Maria Busiello

Biological systems sense and extract information from fluctuating signals while operating under energetic constraints and limited resolution. We introduce a general chemical model in which a sensor, coupled to a signaling pathway activated by hidden signals, can allosterically tune the production of a readout molecule. We propose viable strategies for the sensor to estimate, and eventually balance, information gathering on the hidden process and the associated dissipative cost relying solely on counting statistics of observed trajectories. We show that these strategies can be successfully implemented to adapt the readout production even with finite-time measurements and limited dynamic resolution, and remain effective in the presence of inhibitory regulatory mechanisms. Our study provides a plausible mechanism to actively balance information and dissipation, paving the way for an implementable design principle underpinning biological and biochemical adaptation.
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Statistical Mechanics

Degrees of universality in wave turbulence

Jiasheng Liu, Vladimir Rosenhaus and Gregory Falkovich

Turbulence of weakly interacting waves displays a great deal of universality: independence of the details of the interaction and of the pumping and dissipation scales. Here we study how inverse turbulent cascades (from small to large scales) transition from weak to strong. We find that while one-loop corrections can be dependent on excitation and dissipation scales, new types of universality appear in strong turbulence. We contrast turbulence of spin waves in ferromagnets with turbulent cascades in the Nonlinear Schrödinger Equation (NSE) and in an MMT-like model in higher dimensions having a multiplicative interaction vertex: vertex renormalization gives rise to dependence on the pumping (UV scale) in the former but not in the latter. As a result of this spectral nonlocality, spin-wave turbulence stops being weak if one is sufficiently far from the pumping scale, even when the interaction of waves with comparable wavenumbers is weak. We paraphrase this as: nonlocality enhances nonlinearity. We then describe strong turbulence in a multi-component version of these models with a large number of components. We argue that strong spin-wave turbulence is similar to turbulence of the focusing NSE, as it realizes a critical-balance state. However, UV nonlocality causes the level of spin-wave turbulence at large scales to decrease with increasing pumping level, culminating in a state that is independent of the level of pumping.
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Materials Science

Interband and kinetic corrections to the electronic Boltzmann transport equation

Elena Trukhan and Nakib H. Protik

Interband effects such as coherence/tunneling have recently been shown to give an important contribution to the charge and heat transport properties under certain conditions. These can be captured by adding corrective terms to the semiclassical Boltzmann transport equation. In recent derivations of this type of transport equations that are based on the density matrix formalism, there remain, however, certain omissions. These derivations also rely on a particular type of relaxation time approximation and a band-diagonal form of the interaction self-energies. In this work we derive the interband terms of the electronic Boltzmann transport equation starting from the Keldysh formulation of the quantum kinetic equation and considering the band non-diagonality of the electron-impurity and electron-phonon self-energies. We introduce a minimally modified Kadanoff-Baym Ansatz, and find a quantum-corrected, matrix Boltzmann transport equation that is well beyond the current state of the art theory. We show that the occupations and coherences are interdependent, and that the kinetic corrections due to the included interactions cannot, in general, be ignored. This work clarifies the various approximations that must be introduced in an ab initio derivation of Boltzmann-like equations and finds a new matrix Boltzmann transport equation that is suitable for parameters-free numerical implementations.
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Materials Science

Interfacial Synergy in Ag-Doped CuO-AgCl-g-C3N4 Composites for Efficient Charge Separation and Low-power Methylene Blue Degradation

Suresh Chandra Baral, Uttama Kumar Saint, Dilip Sasmal et al. (+5 more)

An Ag-doped CuO-AgCl-g-C3N4 heterostructure has been designed to achieve rapid Methylene Blue (MB) degradation through a synergistic photo-Fenton mechanism driven by low-power UV illumination. The composite integrates narrow-bandgap CuO, plasmonic Ag/AgCl, and visible-responsive g-C3N4 into a dual Z-scheme configuration that promotes efficient interfacial charge transfer while preserving strong redox potentials. Diffuse reflectance UV-Vis spectra ascertained the bandgap positions of the composite corresponding to those of its constituents: 2.9 eV (g-C3N4) and 1.42 eV (Ag-doped CuO-AgCl), indicating enhanced absorption and efficient charge carrier generation. BET analysis confirmed the presence of mesoporosity and revealed an effective surface area, ensuring the availability of abundant adsorption and reaction sites. A commercial 11 W UV irradiation was used for the photocatalytic test. Almost complete degradation of MB occurred within 10 min, following pseudo-first-order kinetics with a high apparent rate constant of 0.45/min. The remarkable activity arises from the synergistic interplay of Fenton-like redox cycling and efficient photoinduced charge carrier generation and separation. In addition, it has been demonstrated that intentionally incorporated AgCl plays an active role as a plasmonic-semiconducting interface, strengthening charge separation and catalyst stability under neutral conditions, rather than acting as a passive chloride byproduct. Overall, by linking defect engineering, heterojunction design, and photo-Fenton synergy, this study establishes a low-power, catalytic platform offering a viable pathway towards sustainable dye wastewater remediation.
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All authors Suresh Chandra Baral, Uttama Kumar Saint, Dilip Sasmal, Sradhanjali Lenka, Ashish Kalkal, A. Mekki, Sudhagar Pitchaimuthu, Somaditya Sen

Superconductivity

Interplay between Superconductivity and Altermagnetism in Disordered Materials and Heterostructures

Rodrigo de las Heras, Tim Kokkeler, Stefan Ilić et al. (+2 more)

We study the interplay between superconductivity and altermagnetism in disordered systems using recently derived quantum kinetic transport equations. Starting from this framework, we derive the Ginzburg-Landau free energy and identify, in addition to the conventional pair-breaking term, a coupling between the spin and the spatial variation of the superconducting order parameter. Two distinct effects emerge from this coupling. The first is a nonlinear magnetoelectric effect, in which a supercurrent (i.e., a phase gradient) induces a spin texture; this contribution is quadratic in the phase gradient. The second effect arises when the magnitude, rather than the phase, of the superconducting order parameter varies in space, likewise leading to a finite magnetization. We show that these two contributions compete in the case of an Abrikosov vortex, where both the amplitude and phase of the order parameter vary spatially. The effect associated with amplitude variations also gives rise to a proximity-induced magnetization (PIM) in hybrid structures composed of a superconductor (S) and an altermagnet (AM). Using quasiclassical theory, we analyze the PIM in diffusive S/AM bilayers and S/AM/S Josephson junctions, and determine the induced magnetization profiles. In Josephson junctions, where both the PIM and the nonlinear magnetoelectric effect coexist, we further predict the occurrence of $0$-$\pi$ transitions.
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All authors Rodrigo de las Heras, Tim Kokkeler, Stefan Ilić, Ilya V. Tokatly, F. Sebastian Bergeret