Showing 1–50 of 922 results for author: De, C

Topological insulator realization induced by fermionic interaction through BF mediators

Authors: G. B. de Gracia, R. da Rocha, A. A. Nogueira, M. A. C. de Barcelos

Abstract: This paper demonstrates that ordinary fermions, interacting via a BF mediator, form a renormalized structure with non-trivial topological properties. We explore the analogy between the renormalized fermion and a subset of real three-dimensional topological insulators (TIs) in the vicinity of their single Dirac cones. Using the typical magnitude of TI lattice and gaps, we constrain model parameters… ▽ More This paper demonstrates that ordinary fermions, interacting via a BF mediator, form a renormalized structure with non-trivial topological properties. We explore the analogy between the renormalized fermion and a subset of real three-dimensional topological insulators (TIs) in the vicinity of their single Dirac cones. Using the typical magnitude of TI lattice and gaps, we constrain model parameters. The topological structure induced by radiative corrections enters a class of modified Dirac equations, ensuring the existence of helical gapless near-boundary modes. We derive an effective potential for inter-quasi-particle interactions that incorporates finite-size effects in the axial direction, revealing signatures of spin-orbit coupling and time-reversal invariance. Remarkably, particles with different spins do not interact via the characteristic spin-orbit coupling, and a non-central spin-dependent force arises. We also address the behavior of the system in the phase transition associated with the thin-film limit. △ Less

Submitted 17 August, 2026; originally announced August 2026.

Comments: 13 pages, 2 figures, to be published in Phys. Lett. A

What makes a useful molecular model of biochar? A community roadmap

Authors: Valentina Sierra-Jimenez, Jonathan P. Mathews, Luca Bellucci, Edo Boek, Carla de Tomas, Manuel Garcia-Perez, Stef Ghysels, Paola Giudicianni, Corinna Maria Grottola, Kelly Anne Hawboldt, Robert L. Johnson, Fenna B. E. Kolff, Jean-Marc Leyssale, Diego Liberati, Francisco J. Martin-Martinez, Jacob W. Martin, Ondřej Mašek, Mohammad Mezbah Ul Hoque, Audrey Ngambia, Amaël Obliger, Frederik Ossler, Muhammad Riaz, John M. Tobin, Xiaolei Zhang, Valentina Erastova

Abstract: Biochars are disordered carbonaceous materials produced by biomass pyrolysis, with applications spanning soil amendment, water remediation, carbon storage, and functional materials. Although they share structural features with other disordered carbons such as coal, kerogen, and activated carbons, the questions posed to biochar models are distinct, and no single model can answer all of them equally… ▽ More Biochars are disordered carbonaceous materials produced by biomass pyrolysis, with applications spanning soil amendment, water remediation, carbon storage, and functional materials. Although they share structural features with other disordered carbons such as coal, kerogen, and activated carbons, the questions posed to biochar models are distinct, and no single model can answer all of them equally well. Model usefulness must be defined relative to a specific question and validated against independent experimental observables. This community roadmap, arising from a CECAM workshop, critically maps current molecular approaches: experimentally guided top-down reconstruction, mimetic bottom-up simulation, and hybrid methods. We argue that first-generation models have been more successful than is often acknowledged, provided they are built at sufficient length scale and with explicit control over microporosity and bulk chemistry. Structural and equilibrium interfacial properties are increasingly tractable with classical force fields, whereas dynamic and reactive behaviours require selective use of reactive methods within multiscale workflows. A parallel, largely unaddressed gap concerns the mineral and ash components of biochar, and the changes the material undergoes during ageing in soil. We identify seven open questions current models cannot yet answer reliably, and five community priorities: force field benchmarking, open model and data repositories, shared classification and metadata standards, ensemble validation, and training in reproducible practice. Across these, sustained interaction with experimentalists is essential to ground models in real observables and document where they fail. Progress will be accelerated by adapting transferable methods from coal, kerogen, and clay-organic matter frameworks rather than repeating trial-and-error development. △ Less

Submitted 15 August, 2026; originally announced August 2026.

A formal framework for higher-order spin models via hypergraphs, polymatroids, and the Tutte polynomial

Authors: Khallil Berrekkal, Joanna A. Ellis-Monaghan, Merijn Moody, Clélia de Mulatier

Abstract: We develop a rigorous mathematical framework for statistical mechanics models on hypergraphs, and give conditions for lifting the classical connection between Potts model partition functions and the Tutte polynomial from graphs to hypergraphs. We define hypergraphical models and their associated partition functions, and extend these to special classes of models induced by families of interaction f… ▽ More We develop a rigorous mathematical framework for statistical mechanics models on hypergraphs, and give conditions for lifting the classical connection between Potts model partition functions and the Tutte polynomial from graphs to hypergraphs. We define hypergraphical models and their associated partition functions, and extend these to special classes of models induced by families of interaction functions. For boolean interaction families, whose interaction functions map to $\{0,1\}$, we show that the partition function is determined by a combinatorial rank function, and we establish sufficient conditions for a hypergraph deletion-contraction recurrence and for when the rank function defines a polymatroid. We illustrate the theory by applying it to three hypergraph interaction families: Parity Ising, Delta Potts, and And Ising. The induced hypergraphical models are not isomorphic to each other, but the first two reduce to the same graphical Ising models. We identify three polymatroids naturally associated with hypergraphs for these models: respectively, the binary matroid of the incidence matrix over $\mathbb{F}_2$, the hypergraphical polymatroid, and the boolean polymatroid. For graphs, the first two reduce to the classical graphical matroid, and their partition functions recover the multivariate Tutte polynomial. The Tutte polynomial thus admits at least two distinct generalizations for hypergraphs, both satisfying a deletion-contraction recurrence: the Tutte polynomial of the binary matroid of the hypergraph incidence matrix, and a multivariate version of the Poincaré polynomial of the hypergraphical polymatroid. The partition functions of And Ising models are likewise multivariate versions of the Poincaré polynomial, here of the boolean polymatroid. These examples illustrate the much greater range of hypergraphical models and underscore the need for the unifying theory. △ Less

Submitted 23 July, 2026; originally announced August 2026.

MSC Class: 82B20; 05C31; 05C65; 05B35

Microscopic dynamics of consensus formation in multi-agent LLM Naming Games

Authors: Cristiano De Nobili, Vijayasri Iyer, Alessandro Codello, Raffaella Burioni

Abstract: Decentralized populations of Large Language Model (LLM) agents can spontaneously reach consensus on shared conventions, yet the microscopic mechanisms by which their internal stochasticity shapes macroscopic ordering remain unexplored. We study a minimal LLM Naming Game in which the listener's decision is a single-token LLM call at decoding temperature $T$, replacing the inventory check of the det… ▽ More Decentralized populations of Large Language Model (LLM) agents can spontaneously reach consensus on shared conventions, yet the microscopic mechanisms by which their internal stochasticity shapes macroscopic ordering remain unexplored. We study a minimal LLM Naming Game in which the listener's decision is a single-token LLM call at decoding temperature $T$, replacing the inventory check of the deterministic Naming Game. Each interaction decomposes into an in-inventory and an out-inventory channel with conditional rates $π(T)\!\equiv\!P(\text{YES}\mid w\in P_j)$ and $φ(T)\!\equiv\!P(\text{YES}\mid w\notin P_j)$, whose balance controls an ordering-disordering drift. A mean-field theory of the two-rate dynamics yields an analytical ordering condition that generalizes the consensus threshold of the stochastic Naming Game to a critical line in the $(π,φ)$ plane. Across three open-weight architectures, consensus is always reached, but through three distinct listener regimes: permissive (repaint-noise dominated), near-deterministic, and conservative (missed-collapse dominated). The effective finite-size exponent $β(T)$ in $t_{\rm conv}\!\sim\!N^β$ shifts with temperature, and the temperature-sensitivity $α$ in $t_c\!\sim\!e^{αT}$ ranges from ${\approx}\,0.67$ to ${\approx}\,0$ across architectures. Decoding temperature thus emerges as an architecture-dependent control parameter for decentralized LLM populations, quantitatively characterized by the statistical-physics toolkit. △ Less

Submitted 3 August, 2026; originally announced August 2026.

Comments: 8 pages, 8 figures, 1 table, 1 appendix

Localization and Topological Properties of SU(3) Fermions in non-Abelian Gauge Fields: Color-Orbit Coupling and Color-Flip Fields

Authors: Bar Alluf, C. A. R. Sá de Melo

Abstract: The interplay between disorder, gauge fields, and internal degrees of freedom fundamentally affects localization and topological properties of quantum many-body systems. Motivated by recent experimental realizations of synthetic non-Abelian gauge fields for SU(3) colored fermions, we investigate their localization and topological properties in 1D bichromatic optical lattices consisting of strong a… ▽ More The interplay between disorder, gauge fields, and internal degrees of freedom fundamentally affects localization and topological properties of quantum many-body systems. Motivated by recent experimental realizations of synthetic non-Abelian gauge fields for SU(3) colored fermions, we investigate their localization and topological properties in 1D bichromatic optical lattices consisting of strong and weak laser beams. Describing the non-Abelian gauge field via color-orbit coupling and color-flip (Rabi) fields, we obtain a tight-binding description of trapped SU(3) colored fermions corresponding to a generalized three-color Aubry-André model. We show that these fields explicitly break the conventional self-duality of a simple three-color Aubry-André system. This duality breaking generates mobility regions across the energy spectrum, demonstrating that non-Abelian fields can either enhance or hinder color localization. Using exact diagonalization, density-of-states evaluations, and finite-size scaling of the inverse participation ratio, we obtain phase diagrams that identify regions of extended or localized bulk states. Furthermore, the color-orbit and Rabi fields induce edge states with topological properties. We develop an exact mapping from our 1D disorder model into a 2D color Harper model with a fictitious magnetic flux ratio and dimension controlled by the weak laser beam's phase. Using this mapping, we evaluate topological invariants, such as the charge-charge Chern number, for edge states emerging in energy gaps, revealing the topological insulating nature of several gapped phases. Lastly, we identify that these topological color-insulator phases can energetically neighbor three configurations: two extended, two localized, or one of each. This sharply contrasts with conventional topological insulators, which always neighbor two extended phases. △ Less

Submitted 2 July, 2026; originally announced July 2026.

GaAs/AlAs Acoustic Nanocavities for Coherent GHz-THz Phonon Engineering

Authors: S. Sandeep, E. R. Cardozo de Oliveira, E. Mehdi, N. D. Lanzillotti-Kimura

Abstract: The controlled confinement of high-frequency acoustic phonons in semiconductor nanostructures has emerged as a key ingredient for functional nanophononic and hybrid quantum technologies. In this Review, we summarize recent advances that have established GaAs/AlAs acoustic nanocavities as a versatile and scalable platform for GHz-THz phonon engineering. Compared with alternative nanophononic platfo… ▽ More The controlled confinement of high-frequency acoustic phonons in semiconductor nanostructures has emerged as a key ingredient for functional nanophononic and hybrid quantum technologies. In this Review, we summarize recent advances that have established GaAs/AlAs acoustic nanocavities as a versatile and scalable platform for GHz-THz phonon engineering. Compared with alternative nanophononic platforms, GaAs/AlAs offers a particularly favorable combination of mature epitaxial growth, strong photoelastic coupling, and simultaneous optical-acoustic mode colocalization across the GHz-THz regime. We focus on distributed Bragg reflector (DBR)-based architectures, with particular emphasis on micropillar resonators enabling three-dimensional phonon confinement and strong colocalization of acoustic and optical fields. Recent developments in ultrafast optical techniques, including picosecond ultrasonics and Brillouin scattering, have provided unprecedented access to phonon dynamics, coherence, and dissipation at the nanoscale. These advances, combined with strong optophononic coupling, have enabled efficient coherent generation, detection, and manipulation of confined acoustic modes. We discuss key performance metrics, integration strategies, and remaining challenges, notably in acousto-optic transduction efficiency and scalable electrical control. Finally, we outline near-term perspectives for nonlinear phononics, hybrid quantum systems, and integrated phononic circuits, positioning GaAs/AlAs heterostructures as a robust and scalable platform for next-generation nanophononic functionalities. △ Less

Submitted 29 June, 2026; originally announced June 2026.

High-Performance Nanophononic Resonators in Self-Suspended WSe$_2$ Domes and Drums

Authors: Jens-Christian Drawer, Bo Han, Edson Rafael Cardozo de Oliveira, Chushuang Xiang, Vita Solovyeva, Kenji Watanabe, Takashi Taniguchi, Norberto Daniel Lanzillotti-Kimura, Christian Schneider, Martin Esmann

Abstract: Van der Waals materials are ideally suited for the implementation of high-frequency nanophononic resonators with atomically flat interfaces. Here, we present two versatile van der Waals-based nanophononic architectures: First, we introduce self-supporting nano-domes of WSe$_2$ as a scalable platform for the simultaneous generation of hundreds of high-quality nanoacoustic resonators with resonance… ▽ More Van der Waals materials are ideally suited for the implementation of high-frequency nanophononic resonators with atomically flat interfaces. Here, we present two versatile van der Waals-based nanophononic architectures: First, we introduce self-supporting nano-domes of WSe$_2$ as a scalable platform for the simultaneous generation of hundreds of high-quality nanoacoustic resonators with resonance frequencies in the 100 GHz range. Second, we engineer self-supporting nano-drums that reach record-high working frequencies for 2D-semiconductor transducers beyond 1 THz. Through optical pump-probe spectroscopy experiments and photoelastic linear chain model calculations, we gain a detailed understanding of the intricate interplay between phononic mode hybridization across heterostructures, the differences between modes close to the center and edge of the acoustic Brillouin zone, and the temporal structure of the photoelastic response. Both architectures have potential applications in low-cost nanoacoustic probing and the ultrafast modulation of quantum emitters in two-dimensional semiconductors. While nano-drums surpass the THz frequency barrier, nano-domes appear as an accessible, low-cost alternative for developing scalable nanophononic technologies. △ Less

Submitted 24 June, 2026; originally announced June 2026.

Controllable Quantum Spin Hall Phases in Bi$_2$Te$_3$-Family van der Waals Heterobilayers

Authors: Emmanuel V. C. Lopes, Pedro H. Sophia, Felipe Crasto de Lima, Adalberto Fazzio

Abstract: The tunability and control of topological edge/surface states are crucial for the development of new device applications. In this work, by combining first-principles calculations and Wannier-based tight-binding methods, we show the emergence of quantum spin Hall phases in van der Waals heterostructures formed by stacking two trivial quintuple layers from the Bi$_2$Te$_3$ family. We demonstrate the… ▽ More The tunability and control of topological edge/surface states are crucial for the development of new device applications. In this work, by combining first-principles calculations and Wannier-based tight-binding methods, we show the emergence of quantum spin Hall phases in van der Waals heterostructures formed by stacking two trivial quintuple layers from the Bi$_2$Te$_3$ family. We demonstrate the tunability of the edge states under interlayer strain and external electric field effects, suggesting the possibility of switching topological edge states on/off by external control. Additionally, the quantum spin Hall edge channels remain robust against interlayer twist, highlighting their stability against external perturbations. Our results provide a new way to create and manipulate two-dimensional topological phases in systems based on Bi$_2$Te$_3$ family, which can be valuable for practical applications, such as topological field effect transistors and spintronic devices. △ Less

Submitted 18 June, 2026; originally announced June 2026.

A physical adaptive material motor unit neural network: a hygromorph composite material machine

Authors: Charles de Kergariou, David Correa, Adam W. Perriman, Helmut Hauser, Fabrizio Scarpa

Abstract: Advances in novel materials science enable structures to function as intelligent machines by embedding memory and learning capabilities directly into materials. Our work introduces a physical adaptive material motor unit neural network,leveraging a new generation of controllable actuators composed of wood- and carbon black-based composites, sensitive to temperature and relative humidity. These mat… ▽ More Advances in novel materials science enable structures to function as intelligent machines by embedding memory and learning capabilities directly into materials. Our work introduces a physical adaptive material motor unit neural network,leveraging a new generation of controllable actuators composed of wood- and carbon black-based composites, sensitive to temperature and relative humidity. These material actuators are assembled into a motor unit-like structure inspired by muscle contraction trigger, forming an intelligent machine capable of dynamic shading control that can be used, for example, in buildings. The machine is governed by a neural network trained on over 350 experimental data points collected under diverse environmental conditions. By establishing a new data-aware backpropagation training, we show that the machine predicts shading responses and learns to predict appropriate behaviour incrementally as the database expands. We also demonstrate the ability of the machine to optimise configurations to achieve similar shading outputs under two distinct conditions. △ Less

Submitted 5 June, 2026; originally announced June 2026.

Comments: 35 pages, 16 figures

Tunable Electronic and Transport Properties of Biphenylene via Fluorination and Disorder

Authors: Lucas Soares Sousa, Felipe Crasto de Lima, Roberto Hiroki Miwa

Abstract: Biphenylene (BPN) network is a newly synthesized 2D carbon allotrope hosting anisotropic Dirac electronic states. Here, we investigate how fluorination and correlated chemical disorder modify the electronic structure and charge transport of fluorinated biphenylene (F/BPN) using density functional theory, Wannier-based tight-biding Hamiltonian, and quantum transport simulations. We show that fluori… ▽ More Biphenylene (BPN) network is a newly synthesized 2D carbon allotrope hosting anisotropic Dirac electronic states. Here, we investigate how fluorination and correlated chemical disorder modify the electronic structure and charge transport of fluorinated biphenylene (F/BPN) using density functional theory, Wannier-based tight-biding Hamiltonian, and quantum transport simulations. We show that fluorination reshapes the transport response of BPN, producing concentration-dependent anisotropic conduction regimes. For pristine and ordered fluorinated systems, we identified the emergence of negative differential resistance (NDR) and a bias-induced inversion of the preferred transport direction, from armchair to zigzag and vice versa. In contrast, disorder suppresses the NDR, driving the system toward an approximately Ohmic transport regime. At high fluorine coverage, we further observed a nonmonotonic dependence of the armchair current on adatom concentration, which we attribute to the formation of correlated quasi-linear fluor conformation that promote armchair-oriented C-$π$ transport channels while simultaneously suppressing transport along the zigzag direction. Our results demonstrate that correlated fluorination can be used as an active mechanism to engineer electronic transport. △ Less

Submitted 16 June, 2026; originally announced June 2026.

A Collective-Spin Derivation of the Uniform Magnon Hamiltonian in Cavity Magnonics

Authors: Tomas Aguiar, Marcos Cesar de Oliveira

Abstract: We present a direct collective-spin derivation of the effective uniform-mode Hamiltonian used in cavity magnonics. Starting from a nearest-neighbor Heisenberg ferromagnet coupled to long-wavelength magnetic fields, we show that the relevant dynamics can be restricted to the fully symmetric spin sector, where the exchange interaction contributes only a constant energy shift and the ferromagnet beha… ▽ More We present a direct collective-spin derivation of the effective uniform-mode Hamiltonian used in cavity magnonics. Starting from a nearest-neighbor Heisenberg ferromagnet coupled to long-wavelength magnetic fields, we show that the relevant dynamics can be restricted to the fully symmetric spin sector, where the exchange interaction contributes only a constant energy shift and the ferromagnet behaves as a macrospin of length $Ns$. Applying the Holstein--Primakoff transformation directly to this total spin yields the usual uniform magnon mode and its leading nonlinear corrections without first introducing site-resolved bosonic operators. This collective formulation makes explicit the interpretation of the ferromagnet as a synthetic large-spin atom and provides a compact route to the effective Hamiltonians used in driven and Floquet cavity magnonics. As a physical consequence, the leading nonlinear correction produces an occupation-dependent reduction of the effective magnon--photon coupling, providing a simple signature of finite-spin saturation under strong uniform-mode driving. △ Less

Submitted 11 June, 2026; originally announced June 2026.

Inverse supersymmetry in finite temperature Bose-Fermi mixtures

Authors: Zachary Gazzillo, Carlos A. R. Sá de Melo

Abstract: We investigate nearly degenerate Bose-Fermi mixtures and show that the breaking of generalized supersymmetry (gSUSY) between bosons and fermions, with up to two internal states, manifests itself through the emergence of fermionic Goldstino modes with up to four flavors. In particular, we draw a distinction between typical supersymmetry (SUSY), where bosons have pseudospin 0 and fermions have pseud… ▽ More We investigate nearly degenerate Bose-Fermi mixtures and show that the breaking of generalized supersymmetry (gSUSY) between bosons and fermions, with up to two internal states, manifests itself through the emergence of fermionic Goldstino modes with up to four flavors. In particular, we draw a distinction between typical supersymmetry (SUSY), where bosons have pseudospin 0 and fermions have pseudospin 1/2, and inverse supersymmetry (iSUSY), where bosons have pseudospin 1/2 and fermions have pseudospin 0. In such systems, we highlight that the Goldstino pseudospin is carried by either its constituent fermion (SUSY) or boson (iSUSY). We then distinguish between these two cases by depicting their differing effects on the spectral functions of the bosonic and fermionic atomic species. Lastly, we propose radio-frequency- or microwave-spectroscopy experiments, analogous to momentum (angular) resolved photoemission in condensed matter physics, to measure the pseudospin-dependent spectral functions and detect the emergence of Goldstino modes in mixtures of $^{39}$K and $^{40}$K. △ Less

Submitted 5 June, 2026; originally announced June 2026.

Towards Engineering Material Neural Networks

Authors: Charles de Kergariou, Hortense le Ferrand, Ali Momeni, Romain Fleury, Kunal Masania, Adam W Perriman, Fabrizio Scarpa

Abstract: Structures that capture functionality in the form of animate or intelligent machines have the potential to transform modern engineering applications. Animation and embedded intelligence are typically realised by integrating advanced capabilities such as reversibility, adaptive responses and learning directly into the materials themselves. Currently, the majority of adaptive material systems rely o… ▽ More Structures that capture functionality in the form of animate or intelligent machines have the potential to transform modern engineering applications. Animation and embedded intelligence are typically realised by integrating advanced capabilities such as reversibility, adaptive responses and learning directly into the materials themselves. Currently, the majority of adaptive material systems rely on predefined adaptive designs combined with in-service, electronics-based computing to dynamically modify the structural behaviour. However, structural configurations with interconnected adaptable nodes are able to approximate continuous functions, providing new possibilities and opportunities than classical metamaterials and computational materials. We discuss here the potential to design load-bearing engineering materials with trainable physical parameters and neural network-inspired morphologies, embedding intelligence directly into their structure, a concept we define as Engineering Material Neural Networks (EMNNs) as a subcategory of Physical Neural Networks. In this perspective, we first establish the foundational concept of EMNNs; we then detail the mechanical and multifunctional properties required for such structural configurations. Finally, we evaluate existing and emerging engineering materials that hold promise for enabling this innovative approach. Key material candidates for realising EMNNs include composites, architected, biological and engineering living materials. We also outline future directions in materials science and structural engineering for developing EMNNs. △ Less

Submitted 5 June, 2026; originally announced June 2026.

Comments: 37 pages, 8 pages

Aqueous-alcohol mixtures in dimension two: miscibility and micro-segregation

Authors: Camille de la Vaissiere, Ayse Butuner, Aurélien Perera

Abstract: Two dimensional site interaction models of water and alcohols are mixed in various proportions and studied by Monte Carlo simulations, with the purpose to clarify problems related to simulation of real micro-heterogeneous systems. Three alcohols are considered, methanol, pentanol and octanol. The main finding is that, while real alcohols demix with water from butanol onward, their 2D analogs are a… ▽ More Two dimensional site interaction models of water and alcohols are mixed in various proportions and studied by Monte Carlo simulations, with the purpose to clarify problems related to simulation of real micro-heterogeneous systems. Three alcohols are considered, methanol, pentanol and octanol. The main finding is that, while real alcohols demix with water from butanol onward, their 2D analogs are always fully miscible, while developing increasingly pronounced micro-segregation as the alcohol tail length increases. This is not a consequence of the intrinsically higher fluctuations in 2D, but rather a reorganization of these fluctuations under the charge ordering mechanism. The second finding is that water drives the micro-segregation through strong self-aggregation, but this is not enough to achieve full phase separation because of the water-alcohol contact at the outer rim of the water domains. In this work we examine how this local heterogeneity develops with increasing alcohol alkyl tails, monitored with the study of pair correlation functions, structure factors and Kirkwood-Buff integrals. The absence of clear local self-averaging of the latter provides an illustration of the tension between energy driven maintaining of local structures and entropy driven global homogeneity. In that, the 2D modelisation of real hydrogen bonding mixtures allows to better capture and reveal the physics behind the chemistry of these liquids. △ Less

Submitted 4 June, 2026; originally announced June 2026.

Comments: 24 pages, 17 fgures

Modeling Discrete Data with High-Order Vector Potts Models

Authors: Aaron De Clercq, Merijn Moody, Clélia de Mulatier

Abstract: Modeling high-dimensional data is challenging, yet essential to understanding many complex systems. Maximum entropy models such as Ising and Potts models have been used extensively to capture pairwise interactions from correlation patterns in data, allowing to infer graphical representations of complex systems from observations (e.g., from protein sequences or neural population activity). Recently… ▽ More Modeling high-dimensional data is challenging, yet essential to understanding many complex systems. Maximum entropy models such as Ising and Potts models have been used extensively to capture pairwise interactions from correlation patterns in data, allowing to infer graphical representations of complex systems from observations (e.g., from protein sequences or neural population activity). Recently, there has been growing interest in modeling higher-order correlation patterns involving simultaneously three or more variables. While progress has been made in binary data with high-order Ising models, we extend this framework to the more general case of discrete data. We introduce q-state spin models, a complete family of maximum entropy models that generalize the vector Potts model to include long-range and arbitrary high-order interactions. In the pairwise case, our models allow for more diverse interaction types compared to the standard vector Potts model. We discuss their statistical interpretation with examples and relate them to discrete Fourier analysis. Using a loop expansion of the partition function, we show that the statistical properties of spin models are fully captured by the algebraic structure of their interactions. We define gauge transformations under which this structure, and thus the partition function, remains invariant. Models equivalent under gauge transformations can be seen as different representations of the same abstract statistical model, despite generally having interactions of different orders, extending results from the binary case. For practical application to data analysis, we focus on a subset of models known in the binary case as Minimally Complex Models, generalizing them to discrete data. We obtain a closed-form expression for the marginal likelihood of these models, enabling fast model selection. We illustrate their use with simple real-world examples. △ Less

Submitted 2 June, 2026; originally announced June 2026.

Comments: 89 pages, 16 figures

Impact of Cu-Mn ratio on Structure and Defects in Layered Multiferroic Cu1-xMn1+ySiTe3

Authors: Sai Venkata Gayathri Ayyagari, Boyang Zheng, Sreekant Anil, Subrata Ghosh, Yuxi Zhang, Yu Liu, Chandan De, Ke Wang, Jeffrey Shallenberger, Weiwei Xie, Vincent H. Crespi, Zhiqiang Mao, Nasim Alem

Abstract: Multiferroic materials exhibit the coexistence of magnetic and ferroelectric order, enabling control of magnetism through electric fields and vice versa. These properties make them attractive for spintronic and memory device applications. Recent studies on Cu1-xMn1+ySiTe3 (0.04 \leq x \leq 0.26; 0.03 \leq y \leq 0.15) have revealed strong magnetoelectric coupling, with variations in Mn-to-Cu conce… ▽ More Multiferroic materials exhibit the coexistence of magnetic and ferroelectric order, enabling control of magnetism through electric fields and vice versa. These properties make them attractive for spintronic and memory device applications. Recent studies on Cu1-xMn1+ySiTe3 (0.04 \leq x \leq 0.26; 0.03 \leq y \leq 0.15) have revealed strong magnetoelectric coupling, with variations in Mn-to-Cu concentration leading to variations in optical, electronic, and magnetic responses. Despite these findings, the influence of nanoscale structure and defects on the observed properties remains poorly understood. In this study, we investigate the structure and nanoscale defects in Cu-deficient Cu1-xMn1+ySiTe3 (Cu:Mn ratio <1, i.e., with 0.04 \leq x \leq 0.26 and 0.03 \leq y \leq 0.15) and Cu-rich Cu1+xMn1-ySiTe3 (Cu:Mn ratio >1, i.e., with 0.04 \leq x \leq 0.3 and 0.13 \leq y \leq 0.31) crystals using scanning/transmission electron microscopy and single-crystal X-ray diffraction. Cu-deficient crystals exhibit extensive stacking faults correlated with chemical inhomogeneity between Mn and Cu, along with variations in Te stacking. In contrast, Cu-rich crystals show fewer stacking faults but contain other local structural variations, such as needle-shaped precipitates and loop-like features. These distinct local structural features between Cu-rich and Cu-deficient crystals can be correlated to variations in their observed properties. Complementary density functional theory calculations confirm that the Cu-rich structure is more polar than the Cu-deficient structure. Overall, this study provides a comprehensive understanding of how subtle changes in chemistry influence the nanoscale structure, defect distribution, and functional properties in Cu1-xMn1+ySiTe3, offering guidance for designing multiferroic materials with tailored performance. △ Less

Submitted 30 May, 2026; originally announced June 2026.

Entanglement entropy of an acoustic black hole

Authors: P. C. van de Graaf, H. T. C. Stoof

Abstract: We introduce a method to numerically compute the entanglement entropy of an acoustic black hole. It is shown that the entanglement entropy of sufficiently large subregions scales linearly with size and thus shows a volume law instead of an area law. The origin of this scaling can be traced back to the non-separable long-distance correlations due to the production of phonon pairs at the horizon. Th… ▽ More We introduce a method to numerically compute the entanglement entropy of an acoustic black hole. It is shown that the entanglement entropy of sufficiently large subregions scales linearly with size and thus shows a volume law instead of an area law. The origin of this scaling can be traced back to the non-separable long-distance correlations due to the production of phonon pairs at the horizon. The system is shown to be locally thermal, such that the part of the entanglement entropy scaling with volume is well approximated by the thermal entropy of the outgoing Hawking radiation. △ Less

Submitted 28 May, 2026; originally announced May 2026.

Native defects and erbium impurities in CaWO4

Authors: Minseok Choi, Mark E. Turiansky, BaiQing Zhao, Jeff D. Thompson, Chris G. Van de Walle

Abstract: We perform hybrid density functional calculation to study the energetics, electronic properties, optical transitions, and migration barriers of native defects in CaWO$_4$. Oxygen and calcium vacancies are most likely to form in the absence of doping, but interstitials could also incorporate. Tungsten-related defects are unlikely to be present. The positively charged $V_{\rm O}$ and the negatively… ▽ More We perform hybrid density functional calculation to study the energetics, electronic properties, optical transitions, and migration barriers of native defects in CaWO$_4$. Oxygen and calcium vacancies are most likely to form in the absence of doping, but interstitials could also incorporate. Tungsten-related defects are unlikely to be present. The positively charged $V_{\rm O}$ and the negatively charged $V_{\rm Ca}$ are likely to form complexes. Calculated optical transition levels indicate that experimentally observed absorption and emission peaks can be attributed mainly to oxygen-related defects. Calculations of migration barriers allow us to conclude that Ca$_i^{2+}$, $V_{\rm O}^{2+}$ and O$_i^{2-}$ are highly mobile, even below room temperature. We have also examined Er dopants, finding that erbium easily substitutes on the Ca site in a positive charge state. Erbium can form complexes with $V_{\rm Ca}$ and O$_i$, which would deactivate the Er. If Er is introduced by implantation, Er interstitials are likely present, which will produce emission that is prone to spectral diffusion and blinking. Our calculated properties of Er$_i$ explain why annealing at modest temperatures allows the interstitials to move into substitutional sites and point defects to move away, resulting in stable emission. △ Less

Submitted 23 May, 2026; originally announced May 2026.

Charge dynamics at nitrogen impurities and nitrogen-vacancy centers in diamond

Authors: Chandan Kumar Vishwakarma, J. K. Nangoi, Mark E. Turiansky, Chris G. Van de Walle

Abstract: The nitrogen-vacancy (NV) center in diamond is the prototype quantum defect that enables a variety of diamond-based quantum technologies. However, charge-state instability and spectral diffusion, often induced by substitutional nitrogen impurities (N$_{\rm C}$), remain key challenges for device performance. Here, we employ first-principles density functional theory calculations to quantitatively i… ▽ More The nitrogen-vacancy (NV) center in diamond is the prototype quantum defect that enables a variety of diamond-based quantum technologies. However, charge-state instability and spectral diffusion, often induced by substitutional nitrogen impurities (N$_{\rm C}$), remain key challenges for device performance. Here, we employ first-principles density functional theory calculations to quantitatively investigate nonradiative carrier capture processes mediated by multiphonon emission at both the NV center and the N$_{\rm C}$ impurity. For relevant cases, we also compute the rates of radiative and thermal emission processes. For N$_{\rm C}^0$ $\to$ N$_{\rm C}^-$, we obtain an electron capture coefficient of $2.2 \times 10^{-8}$ cm$^3$s$^{-1}$ at 300 K. Both the magnitude and temperature dependence are in excellent agreement with experimentally measured capture cross sections. Electron capture at N$_{\rm C}^+$ is even faster, with a capture coefficient of $1.0 \times 10^{-4}$ cm$^3$s$^{-1}$ at 300 K. For the NV center, we find that carrier capture rates involving only the ground states of NV$^0$ and NV$^-$ are negligibly slow. However, capture into the excited states (NV$^{0*}$ and NV$^{-*}$) is significantly faster. In particular, the capture coefficient for the hole capture process NV$^-$ $\to$ NV$^{0*}$ is as large as $1.8 \times 10^{-7}$ cm$^3$s$^{-1}$ and largely temperature-independent. Hole capture at NV$^-$ will thus occur via nonradiative capture into an excited state of NV$^{0}$ followed by fast radiative decay to the NV$^0$ ground state. Similarly, electron capture at NV$^0$ will occur via the NV$^0$ $\to$ NV$^{-*}$ $\to$ NV$^-$ pathway, but with a lower nonradiative capture coefficient ($2.1 \times 10^{-9}$ cm$^3$s$^{-1}$ at 300 K). Our calculated capture coefficients and rates provide essential information for analyzing charge-state dynamics. △ Less

Submitted 23 May, 2026; originally announced May 2026.

Comments: Submitted to Physical Review B

Direct Simulation of LiNi0.8Mn0.1Co0.1O2 Transport Properties Using an Efficient and Accurate Machine Learning Potential

Authors: Jian He, Constantijn H. J. A. van de Wetering, Rolande W. Nolsen, Nongnuch Artrith

Abstract: The rate capability of layered lithium nickel manganese cobalt oxide (NMC) cathode materials plays a decisive role in high-power applications such as fast charging, necessitating a detailed understanding of lithium-ion diffusion. However, the mechanisms governing lithium-ion transport in NMC remain insufficiently understood, both experimentally and computationally. In this study, we employ an adva… ▽ More The rate capability of layered lithium nickel manganese cobalt oxide (NMC) cathode materials plays a decisive role in high-power applications such as fast charging, necessitating a detailed understanding of lithium-ion diffusion. However, the mechanisms governing lithium-ion transport in NMC remain insufficiently understood, both experimentally and computationally. In this study, we employ an advanced and efficient machine learning potential (MLP) to simulate lithium self-diffusion in LiNi0.8Mn0.1Co0.1O2 (NMC811), enabling direct large-scale molecular dynamics (MD) simulations. The workflow integrates a fine-tuned MACE (Message Passing Atomic Cluster Expansion) foundation model as a structural generator and leverages an active learning strategy applied to a near-ground-state dataset. This approach enables the construction of a reliable MLP for NMC811 in a data-efficient manner using a limited number of density functional theory (DFT) reference calculations. Based on this potential, we performed MD simulations to predict lithium diffusion coefficients. The MLP-based simulations preserve the accuracy of DFT while overcoming its time and length scale limitations, thereby allowing direct simulation of lithium self-diffusion in NMC811. △ Less

Submitted 19 May, 2026; originally announced May 2026.

Lattice Relaxation in Moiré Heterobilayers

Authors: Christophe De Beule, Yiyang Lai, Liangtao Peng, Daniel Bennett, Shaffique Adam

Abstract: We develop an analytical theory for lattice relaxation in twisted moiré heterobilayers, accounting for lattice mismatch, twist, external biaxial heterostrain, and different elastic constants. Starting from continuum elasticity, we derive the self-consistent equations for the in-plane displacement fields and obtain simple perturbative expressions for the layer-resolved in-plane displacement fields… ▽ More We develop an analytical theory for lattice relaxation in twisted moiré heterobilayers, accounting for lattice mismatch, twist, external biaxial heterostrain, and different elastic constants. Starting from continuum elasticity, we derive the self-consistent equations for the in-plane displacement fields and obtain simple perturbative expressions for the layer-resolved in-plane displacement fields induced by lattice relaxation. We apply our theory to graphene on hBN and representative 2H transition metal dichalcogenide heterobilayers, including MoTe$_2$/WSe$_2$ and WSe$_2$/WS$_2$. Our analytical results agree very well with full numerical solutions over experimentally relevant parameters. We further show that heterobilayers can exhibit a buckling instability near alignment, driven by compressive in-plane strain due to moiré relaxation. Our results provide a simple theoretical framework for incorporating lattice relaxation in realistic moiré heterostructures. △ Less

Submitted 17 May, 2026; originally announced May 2026.

Comments: 7 + 7 pages, 3 + 3 figures

Coupled Topological Interface States and Phonon Molecules in GaAs/AlAs Superlattices

Authors: S. Sandeep, O. Colmegna, C. Xiang, E. R. Cardozo de Oliveira, K. Papatryfonos, M. Morassi, A. Lemaitre, N. D. Lanzillotti-Kimura

Abstract: Topological interface states in one-dimensional superlattices provide spatially localized phonon modes protected by the topology of the underlying band structure. In GaAs/AlAs distributed Bragg reflectors (DBRs), such states can be engineered through band inversion between superlattices with opposite Zak phases within the Su-Schrieffer-Heeger (SSH) framework. Here, we demonstrate topological phono… ▽ More Topological interface states in one-dimensional superlattices provide spatially localized phonon modes protected by the topology of the underlying band structure. In GaAs/AlAs distributed Bragg reflectors (DBRs), such states can be engineered through band inversion between superlattices with opposite Zak phases within the Su-Schrieffer-Heeger (SSH) framework. Here, we demonstrate topological phonon molecules and extended chains formed by coupled nanophononic interface states. By concatenating three superlattices with alternating topology, we realize two coupled interface states that hybridize into symmetric and antisymmetric modes, whose splitting can be tuned over tens of gigahertz by varying the reflectivity of the central DBR. Extending this concept, we engineer chains of up to N=6 coupled interface states that form narrow topological minibands while remaining strongly localized at the interfaces. We experimentally observe these coupled states in molecular-beam-epitaxy-grown GaAs/AlAs heterostructures using time-domain pump-probe transient reflectivity measurements, and reproduce their behavior using transfer-matrix calculations and a simple analytical model for the mode splitting. These results establish topological interface states as a robust platform for engineering coupled phononic systems and tunable nanophononic architectures in the GHz regime. △ Less

Submitted 12 May, 2026; originally announced May 2026.

Collective Alignment in LLM Multi-Agent Systems: Disentangling Bias from Cooperation via Statistical Physics

Authors: Cristiano De Nobili

Abstract: We investigate the emergent collective dynamics of LLM-based multi-agent systems on a 2D square lattice and present a model-agnostic statistical-physics method to disentangle social conformity from intrinsic bias, compute critical exponents, and probe the collective behavior and possible phase transitions of multi-agent systems. In our framework, each node of an $L\!\times\!L$ lattice hosts an ide… ▽ More We investigate the emergent collective dynamics of LLM-based multi-agent systems on a 2D square lattice and present a model-agnostic statistical-physics method to disentangle social conformity from intrinsic bias, compute critical exponents, and probe the collective behavior and possible phase transitions of multi-agent systems. In our framework, each node of an $L\!\times\!L$ lattice hosts an identical LLM agent holding a binary state ($+1$/$-1$, mapped to yes/no) and updating it by querying the model conditioned on the four nearest-neighbor states. The sampler temperature $T$ serves as the sole control parameter. Across three open-weight models (llama3.1:8b, phi4-mini:3.8b, mistral:7b), we measure magnetization and susceptibility under a global-flip protocol designed to probe $\mathbb{Z}_2$ symmetry. All models display temperature-driven order-disorder crossovers and susceptibility peaks; finite-size scaling on even-$L$ lattices yields effective exponents $γ/ν$ whose values are model-dependent, close to but incompatible with the 2D Ising universality class ($γ/ν=7/4$). Our method enables the extraction of effective $β$-weighted couplings $\tilde{J}(T)$ and fields $\tilde{h}(T)$, which serve as a measure of social conformity and intrinsic bias. In the models we analyzed, we found that collective alignment is dominated by an intrinsic bias ($\tilde{h}\gg\tilde{J}$) rather than by cooperative neighbor coupling, producing field-driven crossovers instead of genuine phase transitions. These effective parameters vary qualitatively across models, providing compact collective-behavior fingerprints for LLM agents and a quantitative diagnostic for the reliability of multi-agent consensus and collective alignment. △ Less

Submitted 11 May, 2026; originally announced May 2026.

Comments: 10 pages, 7 figures

Chemical transformation of MgH2/V2O5 composite to Mg-V-O rock salt and its influence on the electrochemical Li conversion and hydrogen storage characteristics of MgH2

Authors: D. Pukazhselvan, Ihsan Caha, Francisco J. A. Loureiro, Francis Leonard Deepak, Catarina de Lemos, Aliaksandr L. Shaula, Sergey M. Mikhalev, Duncan Paul Fagg

Abstract: This study investigates the lithium conversion behavior of a hydrogen storage material based on vanadium oxide added magnesium hydride. To understand the chemical interaction between vanadium oxide and magnesium hydride, detailed X ray diffraction and X ray photoelectron spectroscopy analyses were performed on ball milled composites with varying compositions. The results confirm the formation of a… ▽ More This study investigates the lithium conversion behavior of a hydrogen storage material based on vanadium oxide added magnesium hydride. To understand the chemical interaction between vanadium oxide and magnesium hydride, detailed X ray diffraction and X ray photoelectron spectroscopy analyses were performed on ball milled composites with varying compositions. The results confirm the formation of a combined magnesium vanadium oxide with a rock salt structure, indicating strong chemical interaction between the components. It is further shown that the presence of a small amount of this oxide additive significantly influences the lithium reaction with magnesium hydride, leading to a high initial discharge capacity and limited recharge capacity in lithium ion coin cells. Post use analyses confirm the presence of magnesium hydride, suggesting that volume expansion is not responsible for the observed irreversibility. Electrochemical impedance spectroscopy using differential function of relaxation times indicates that electrolyte degradation is not a major issue. Instead, slow charge transfer processes are identified as the limiting factor, and these are sensitive to the composition of the additive. These findings highlight that improving electrode and electrolyte compatibility is essential for enhancing performance in this system. △ Less

Submitted 28 April, 2026; originally announced April 2026.

Comments: 22 pages, 8 Figures

Dynamics of one-dimensional Bose-Josephson Junction in a Box Trap: From Coherent Oscillations to Many-Body Dephasing and Dynamical Freezing

Authors: Abhik Kumar Saha, L. F. Calazans de Brito, Cesare Vianello, Rhombik Roy, Romain Dubessy, Barnali Chakrabarti, Arnaldo Gammal

Abstract: Understanding how coherent quantum dynamics give way to correlation-dominated behavior in low-dimensional systems remains a central challenge in quantum many-body physics. Here, we investigate a one-dimensional Bose-Josephson junction confined in a box trap using the multiconfigurational time-dependent Hartree method for bosons (MCTDHB). By varying the interaction strength and initial population i… ▽ More Understanding how coherent quantum dynamics give way to correlation-dominated behavior in low-dimensional systems remains a central challenge in quantum many-body physics. Here, we investigate a one-dimensional Bose-Josephson junction confined in a box trap using the multiconfigurational time-dependent Hartree method for bosons (MCTDHB). By varying the interaction strength and initial population imbalance, we identify distinct dynamical regimes governed by the competition between coherence and correlation-induced fragmentation. Weak interactions support coherent Josephson oscillations, whereas increasing imbalance leads to damping. At intermediate interaction strength, varying only the initial imbalance induces a crossover from nearly pure coherent oscillations to many-body dephasing with collapse-and-revival dynamics, and ultimately to equilibration accompanied by strong fragmentation and the saturation of many-body observables. In the strongly interacting regime, the system enters a dynamical freezing regime characterized by pronounced fragmentation, well-separated particle-resolved density peaks, and strongly suppressed tunneling. A systematic comparison with the Bose-Hubbard model reveals excellent agreement in the weakly interacting regime, while progressively larger deviations emerge as higher-orbital occupations beyond the two-mode approximation become significant. These results provide a unified picture of the emergence and competition of coherence, many-body dephasing, equilibration, and dynamical freezing, while delineating the regime of validity of the Bose-Hubbard description. △ Less

Submitted 6 August, 2026; v1 submitted 20 April, 2026; originally announced April 2026.

Comments: 23 pages, 21 figures, added a coauthor

Seed Layer Engineering for Effective Charge Transfer Doping of MoS$_2$ Transistors

Authors: Sahej Sharma, Shao-Heng Yang, Himani Jawa, Rana Yuvraj, Bach Nguyen, Chang Niu, Shiva Radhakrishnan, Shalini Tripathi, Dennis Lin, Cesar Javier Lockhart de la Rosa, Pierre Morin, Dmitry Zemlyanov, Francesca Iacopi, Zhihong Chen, Joerg Appenzeller, Thomas E. Beechem

Abstract: Integrating two-dimensional semiconductors such as MoS$_2$ with dielectric materials remains a central challenge for their use in future logic technologies. While seed layers are typically introduced to promote dielectric nucleation and adhesion, we show that they also critically govern charge-transfer doping and, in turn, transistor performance. Back-gated monolayer MoS$_2$ transistors passivated… ▽ More Integrating two-dimensional semiconductors such as MoS$_2$ with dielectric materials remains a central challenge for their use in future logic technologies. While seed layers are typically introduced to promote dielectric nucleation and adhesion, we show that they also critically govern charge-transfer doping and, in turn, transistor performance. Back-gated monolayer MoS$_2$ transistors passivated on their top-surface with a Ta-seed/HfO$_x$ dielectric stack were fabricated and characterized electrically and physically using Raman, photoluminescence, and X-ray photoelectron spectroscopies. Threshold voltage and on-current varied strongly with Ta-seed thickness and deposition conditions, and these changes correlated with signatures observed across all spectroscopic probes. The results reveal that the seed layer both introduces disorder into the MoS$_2$ channel and modifies the interfacial charge environment controlling charge transfer between HfO$_x$ and MoS$_2$. Optical spectroscopy shows that on-current tracks seed-induced disorder, whereas X-ray photoelectron spectroscopy indicates that threshold voltage correlates with shifts in the local electrostatic environment associated with interfacial charge transfer. Better performance was obtained with ultrathin 0.2 nm Ta seed layers deposited under oxygen-poor conditions, which limit deposition-induced damage while facilitating charge transfer. These findings identify seed-layer engineering as a key strategy for controlling disorder and interfacial doping in MoS$_2$ devices and establish multimodal spectroscopy as a practical during-fabrication approach for process development and monitoring. △ Less

Submitted 4 June, 2026; v1 submitted 19 April, 2026; originally announced April 2026.

Comments: 27 pages, 7 figures

Atomically-Thin Tsumoite (BiTe) based All-Photonic-Isolator, Information Converter, and Logic-Gate

Authors: Saswata Goswami, Caique Campos de Oliveira, Abhijith M. B., Varinder Pal, Vidya Kochat, Pulickel M. Ajayan, Samit K. Ray, Pedro A. S. Autreto, Chandra Sekhar Tiwary

Abstract: Two-dimensional tsumoite (BiTe), a polymorph of Bi2Te3, has emerged as a promising candidate for nonlinear photonic devices owing to its strong spin-orbit coupling, tunable bandgap, and high carrier mobility characteristics. This work presents a thorough examination of the third-order nonlinear optical response of BiTe dispersions using spatial self-phase modulation (SSPM) spectroscopy. The nonlin… ▽ More Two-dimensional tsumoite (BiTe), a polymorph of Bi2Te3, has emerged as a promising candidate for nonlinear photonic devices owing to its strong spin-orbit coupling, tunable bandgap, and high carrier mobility characteristics. This work presents a thorough examination of the third-order nonlinear optical response of BiTe dispersions using spatial self-phase modulation (SSPM) spectroscopy. The nonlinear refractive index (n2) and third-order nonlinear susceptibility are quantitatively derived from the diffraction ring patterns, demonstrating third-order nonlinear susceptibility values, similar to or surpassing those of advanced 2D materials. The temporal development and distortion of the SSPM rings are examined using the wind-chime model, and thermal factors influencing the SSPM pattern are analyzed. First-principles electronic band structure studies reveal that the elevated nonlinear susceptibility arises from band dispersion. Direct correlation between carrier transport and third-order nonlinear susceptibility is established. Utilizing these qualities, all photonic devices, including a photonic isolator based on a 2D BiTe-2D hBN heterostructure, are depicted to show asymmetric propagation. A photonic information converter and a logic gate are designed using the cross-phase modulation technique. These findings establish 2D BiTe nanostructure as a formidable nonlinear optical platform for advanced photonic signal processing and integrated photonic applications. △ Less

Submitted 13 April, 2026; originally announced April 2026.

Heterogeneous Molecular Signatures of Human Odor Perception

Authors: P. Zanineli, E. V. C. Lopes, G. R. Schleder, L. N. Lemos, F. Crasto de Lima, A. Fazzio

Abstract: Understanding how molecular structure gives rise to odor perception remains a long-standing challenge, with ongoing debate over whether olfaction is primarily governed by molecular shape, vibrational properties, or their interplay at the level of olfactory receptors. Here, we ask whether different odors rely on common molecular determinants or instead emerge from distinct physicochemical regimes.… ▽ More Understanding how molecular structure gives rise to odor perception remains a long-standing challenge, with ongoing debate over whether olfaction is primarily governed by molecular shape, vibrational properties, or their interplay at the level of olfactory receptors. Here, we ask whether different odors rely on common molecular determinants or instead emerge from distinct physicochemical regimes. Using interpretable machine-learning models trained on molecular descriptors derived from first-principles calculations that span electronic, vibrational, and structural properties, we analyze feature contributions for odor categories and their associated receptors. We find that no single descriptor class universally dominates odor prediction; instead, different odors exhibit strongly odor-specific patterns of feature importance, with substantial variability across physicochemical domains. This heterogeneity is consistent across different models, suggesting that a universal encoding scheme does not capture odor perception but reflects receptor- and odor-dependent structure-odor relationships. Our results provide statistical constraints on competing olfactory theories and offer a data-driven framework for organizing odor space. △ Less

Submitted 10 April, 2026; originally announced April 2026.

High-threshold decoding of non-Pauli codes for 2D universality

Authors: Julio C. Magdalena de la Fuente, Noa Feldman, Jens Eisert, Andreas Bauer

Abstract: Topological codes have many desirable properties that allow fault-tolerant quantum computation with relatively low overhead. A core challenge for these codes, however, is to achieve a low-overhead universal gate set with limited connectivity. In this work, we explore a non-Pauli stabilizer code that can be used to complete a universal gate set on topological toric and surface codes in strictly two… ▽ More Topological codes have many desirable properties that allow fault-tolerant quantum computation with relatively low overhead. A core challenge for these codes, however, is to achieve a low-overhead universal gate set with limited connectivity. In this work, we explore a non-Pauli stabilizer code that can be used to complete a universal gate set on topological toric and surface codes in strictly two dimensions. Fault-tolerant syndrome extraction for the non-Pauli code requires mid-circuit $X$ corrections, a key difference to conventional Pauli codes. We construct and benchmark a just-in-time (JIT) matching decoder to reliably decide these corrections. Under a phenomenological error model with equally likely physical and measurement errors, we find a high threshold of $\approx 2.5\,\%$, close to the $\approx 2.9\,\%$ of a decoder with access to the full syndrome history. We also perform a finite-size scaling analysis to estimate how the logical error rate scales below threshold and verify an exponential suppression in both physical error rate and in the system size. A second global decoding step for $Z$ errors is required and the non-Clifford gates in the circuit reduce the threshold from $\approx 2.9\,\%$ to $\approx 1.8\,\%$ with a naive decoder. We show how $Z$ decoding can be improved using knowledge of the $X$ corrections, pushing the threshold to $\approx 2.2\,\%$. Our results suggest non-Clifford logic in 2D codes could perform comparably to 2D quantum memory. Our formalism for efficient benchmarking and decoding directly generalizes to a broader family of CSS codes whose $X$ stabilizers are twisted by diagonal Clifford operators, and spacetime versions thereof, defined by CSS-like circuits enriched by $CCZ$, $CS$, and $T$ gates. △ Less

Submitted 2 April, 2026; originally announced April 2026.

Comments: 21 pages, 10 figures

Coexistence of ferromagnetism and ferroelectricity in the van der Waals multiferroic CuIn0.2V0.8P2S6

Authors: Subrata Ghosh, Rosalin Mohanty, Yuwei Sun, Soumi Mondal, Chandan De, Jose G. Jimenez, Weiwei Xie, Cheng Gong, Zhiqiang Mao

Abstract: Two-dimensional (2D) van der Waals (vdW) multiferroics have emerged as a promising platform for next-generation multifunctional devices. Although recent studies have demonstrated that artificial heterostructures can combine dual ferroic orders and exhibit strong magnetoelectric coupling, their performance is sometimes limited by poor interface quality and inadequate long-term stability. By contras… ▽ More Two-dimensional (2D) van der Waals (vdW) multiferroics have emerged as a promising platform for next-generation multifunctional devices. Although recent studies have demonstrated that artificial heterostructures can combine dual ferroic orders and exhibit strong magnetoelectric coupling, their performance is sometimes limited by poor interface quality and inadequate long-term stability. By contrast, the realization of intrinsic single-phase materials with coexisting ferromagnetism and ferroelectricity remains a longstanding challenge in the field. Here we report the realization of a single-phase 2D vdW multiferroic system, CuIn0.2V0.8P2S6, which exhibits both ferromagnetism and room-temperature ferroelectricity. The intrinsic ferroelectric nature of CuIn0.2V0.8P2S6 was probed using ferroelectric tunnel junctions, which exhibit a large tunneling electroresistance with an ON/OFF ratio of 107 at 295 K. CuIn0.2V0.8P2S6 develops ferromagnetic ordering with the Curie temperature (TC) of 14.6 K, as evidenced by pronounced magnetic hysteresis and a relatively large remanent magnetization. Notably, the appearance of a magnetodielectric response below TC is consistent with the anticipated interplay between the ferromagnetic and ferroelectric orders. These results highlight a promising route toward single-phase van der Waals multiferroics with coexisting ferroic orders. △ Less

Submitted 29 March, 2026; originally announced March 2026.

Comments: 14 pages

From Classical Stochastic to Monitored Quantum Dynamics: Dynamical Phase Coexistence in East Circuit Models

Authors: Marcel Cech, Johan du Buisson, Cecilia De Fazio, Federico Carollo, Igor Lesanovsky

Abstract: Kinetically constrained models have been widely studied in the context of glass formers and non-equilibrium statistical mechanics. Although their simple local rules often result in structureless static properties, their dynamics exhibit intricate emergent phenomena. In this work, we investigate monitored quantum circuit models that interpolate between classical stochastic and unitary quantum dynam… ▽ More Kinetically constrained models have been widely studied in the context of glass formers and non-equilibrium statistical mechanics. Although their simple local rules often result in structureless static properties, their dynamics exhibit intricate emergent phenomena. In this work, we investigate monitored quantum circuit models that interpolate between classical stochastic and unitary quantum dynamics. For any finite measurement strength, the measurement records provide an experimentally accessible probe of the emergence of dynamical phases. By interpreting space-time resolved records as microstates of a fictitious 1+1D spin system, we employ thermodynamic concepts that allow us to investigate the dynamical coexistence between an active and inactive phase. We combine insights from classical stochastic dynamics and numerical simulations of monitored quantum dynamics to investigate different signatures of this dynamical phase coexistence as the measurement strength is varied. Our results shed light on the persistence of dynamical phase coexistence in the quantum regime, offering insights into future experimental studies of complex many-body dynamics in quantum simulators. △ Less

Submitted 18 March, 2026; originally announced March 2026.

Comments: 7+13 pages, 4+5 figures, comments welcome

Engineering Quantum Phases in Two Dimensions via Vacancy-Induced Electronic Reconstruction

Authors: Emmanuel V. C. Lopes, Felipe Crasto de Lima, Caio Lewenkopf, Adalberto Fazzio

Abstract: Topological phases of matter are commonly understood as emerging either from crystalline symmetry and intrinsic spin-orbit coupling or from disorder-driven electronic renormalization. In realistic materials, however, structural defects naturally combine both ingredients. Here, we demonstrate a general and material-independent mechanism by which atomic vacancies can induce topological phase transit… ▽ More Topological phases of matter are commonly understood as emerging either from crystalline symmetry and intrinsic spin-orbit coupling or from disorder-driven electronic renormalization. In realistic materials, however, structural defects naturally combine both ingredients. Here, we demonstrate a general and material-independent mechanism by which atomic vacancies can induce topological phase transitions in two-dimensional semiconductors that are otherwise topologically trivial. Vacancies generate locally ordered dangling-bond states governed by well-defined hopping and spin-orbit interactions, while their spatial distribution and mutual coupling introduce long-range disorder. As vacancy concentration increases, the hybridization of these defect states forms an emergent electronic subspace that undergoes a topological transition. Using a tight-binding framework supported by large-scale density functional theory calculations, we show that this vacancy-induced electronic reconstruction can robustly stabilize quantum spin Hall, quantum anomalous Hall, and Weyl semimetal phases, depending on symmetry breaking and spin polarization. Our results establish vacancies not merely as perturbations, but as active design elements capable of transforming trivial insulators into topological quantum matter, opening realistic routes for defect-engineered topological devices. △ Less

Submitted 17 March, 2026; originally announced March 2026.

A defect in diamond with millisecond-scale spin relaxation time at room temperature

Authors: Sounak Mukherjee, Anran Li, Johannes Eberle, Sean Karg, Zi-Huai Zhang, Mayer M. Feldman, Yilin Chen, Mark E. Turiansky, Mengen Wang, Yogendra Limbu, Tharnier O. Puel, Yueguang Shi, Matthew L. Markham, Rajesh L. Patel, Patryk Gumann, Michael E. Flatte, Chris G. Van de Walle, Stephen A. Lyon, Nathalie P. de Leon

Abstract: Spin defects in diamond are promising platforms for quantum sensing. The longest electron spin relaxation times ($T_1$) at room temperature for solid-state defects are observed in nitrogen vacancy centers in diamond, which can reach 6.67 ms, and substitutional nitrogen ("P1 centers") in diamond, which exhibit a $T_1$ of 2 ms. No other solid-state defect has exhibited millisecond-scale spin relaxat… ▽ More Spin defects in diamond are promising platforms for quantum sensing. The longest electron spin relaxation times ($T_1$) at room temperature for solid-state defects are observed in nitrogen vacancy centers in diamond, which can reach 6.67 ms, and substitutional nitrogen ("P1 centers") in diamond, which exhibit a $T_1$ of 2 ms. No other solid-state defect has exhibited millisecond-scale spin relaxation times at room temperature thus far. Here, we characterize the spin properties of the WAR5 defect in diamond with pulsed electron spin resonance. The observed $T_1$ is one of the longest for solid-state spin defects: 0.97(27) ms at room temperature and 14.38(19) min at 4 K. The observed coherence time ($T_2$) is 246(7) $μ$s, which can be extended to 6.49(34) ms at 4 K with dynamical decoupling. Furthermore, we demonstrate optical spin polarization with a range of wavelengths from 405 nm to 500 nm and propose potential zero-phonon line candidates. △ Less

Submitted 7 March, 2026; originally announced March 2026.

Strain effects on $n$-type doping in AlN

Authors: Haochen Wang, Chris G. Van de Walle

Abstract: Controllable doping in AlN and its alloys is essential for deep-ultraviolet light sources. Ionization energies for donors in AlN ($\mathrm{Si_{Al}}$, $\mathrm{S_N}$, $\mathrm{Se_N}$) are high. We report first-principles calculations demonstrating that strain engineering can result in a reduction in ionization energies. The donor levels for $\mathrm{S_N}$ and $\mathrm{Se_N}$ shift closer to the con… ▽ More Controllable doping in AlN and its alloys is essential for deep-ultraviolet light sources. Ionization energies for donors in AlN ($\mathrm{Si_{Al}}$, $\mathrm{S_N}$, $\mathrm{Se_N}$) are high. We report first-principles calculations demonstrating that strain engineering can result in a reduction in ionization energies. The donor levels for $\mathrm{S_N}$ and $\mathrm{Se_N}$ shift closer to the conduction-band minimum (CBM) under in-plane tensile strains, driven by a downward shift of the CBM. The most widely used donor, $\mathrm{Si_{Al}}$, forms a $DX$ center in AlN. We find that a 2.5% in-plane tensile strain (which would be induced by pseudomorphic growth on GaN in experiment) shifts the ($+/-$) transition level from 271 meV to 98 meV below the CBM, which would enhance the electron concentration by three orders of magnitude. These results demonstrate that strain engineering offers an effective route to enhance doping levels in AlN. △ Less

Submitted 3 March, 2026; originally announced March 2026.

Comments: 4 pages, 3 figures

Scalable tight-binding model for strained graphene

Authors: Ming-Hao Liu, Christophe De Beule, Alina Mreńca-Kolasińska, Hsin-You Wu, Aitor Garcia-Ruiz, Denis Kochan, Klaus Richter

Abstract: We generalize the scalable tight-binding model for graphene, which allows for efficient quantum transport simulations in the Dirac regime, to account for elastic strain. We show that the original scalable model with scaling factor $s$ is readily applicable to strained graphene, provided that the displacement fields corresponding to the deformed graphene lattice are properly scaled. In particular,… ▽ More We generalize the scalable tight-binding model for graphene, which allows for efficient quantum transport simulations in the Dirac regime, to account for elastic strain. We show that the original scalable model with scaling factor $s$ is readily applicable to strained graphene, provided that the displacement fields corresponding to the deformed graphene lattice are properly scaled. In particular, we show that the long-wavelength theory remains invariant when the strain tensor is scaled by $s$. This is achieved in practice by scaling the in-plane displacement fields by $s$ while the out-of-plane displacements have to be scaled by $\sqrt{s}$. We confirm these scaling laws by extensive numerical simulations, starting with the pseudomagnetic field and the local density of states for different scaled lattices. The latter allows us to study pseudo-Landau levels as well as hybrid Landau levels in the presence of an external magnetic field. Finally, we consider quantum transport simulations motivated by a recent experiment, where a uniaxial strain barrier is engineered in monolayer graphene by vertically misaligned gates. Our work generalizes the scalable tight-binding model to allow for efficient modeling of quantum transport in large-scale strained graphene devices. △ Less

Submitted 26 May, 2026; v1 submitted 2 March, 2026; originally announced March 2026.

Comments: 13 pages, 7 figures; published version

Journal ref: Phys. Rev. B 113, 195429 (2026)

Equal-spin and opposite-spin density-density correlations in the BCS-BEC crossover: Gauge Symmetry, Pauli Exclusion Principle, Wick's Theorem and Experiments

Authors: Nikolai Kaschewski, Axel Pelster, Carlos A. R. Sá de Melo

Abstract: We develop a general theory of spin-dependent density-density correlations, that is valid for any temperature, interactions, dimensions and mass or population status of Fermi gases with two internal states. We use gauge invariance and the Pauli principle to establish constraints on the spin-dependent density-density correlations that are consistent with the fluctuation-dissipation and Wick's theor… ▽ More We develop a general theory of spin-dependent density-density correlations, that is valid for any temperature, interactions, dimensions and mass or population status of Fermi gases with two internal states. We use gauge invariance and the Pauli principle to establish constraints on the spin-dependent density-density correlations that are consistent with the fluctuation-dissipation and Wick's theorem. As an example, we study the spin-dependent density-density correlations from the BCS to the Bose regime in two dimensions at zero temperature, inspired by experiments in 6Li. We show that two-particle irreducible contributions involving collective excitations, many-particle scattering and vertex corrections, are essential to describe experiments. In particular they turn out to be responsible for the emergence of an experimentally observed minimum in the opposite-spin density-density correlations. △ Less

Submitted 1 June, 2026; v1 submitted 26 February, 2026; originally announced February 2026.

Comments: 5 Pages, 5 figures, 2 Pages END MATTER

Impact of magnetic field direction on anti-dot-based superconducting diodes

Authors: E. B. de Melo Junior, E. Strambini, F. Giazotto, C. I. L. de Araujo

Abstract: The superconducting diode effect (SDE) is a fundamental building block for dissipationless nonreciprocal electronics, yet its microscopic origins in thin films often involve competing mechanisms that remain debated. Here, we demonstrate that the SDE can be engineered in niobium films by patterning macroscopic asymmetric antidots, revealing distinct control mechanisms under in-plane and out-of-plan… ▽ More The superconducting diode effect (SDE) is a fundamental building block for dissipationless nonreciprocal electronics, yet its microscopic origins in thin films often involve competing mechanisms that remain debated. Here, we demonstrate that the SDE can be engineered in niobium films by patterning macroscopic asymmetric antidots, revealing distinct control mechanisms under in-plane and out-of-plane magnetic fields. We identify two dominant contributions to nonreciprocal transport: edge flux pinning, which governs the low-field and in-plane field regimes via surface-barrier asymmetry, and bulk flux pinning, which drives the high-field response and correlates directly with the geometric asymmetry of the antidots. Supported by time-dependent Ginzburg-Landau simulations and an analytical model, we provide a unified description of these regimes, linking the diode efficiency to the specific pinning landscape. These findings establish a flexible design principle for engineering superconducting diodes with tunable functionality, paving the way for their integration into next-generation quantum and cryogenic circuits. △ Less

Submitted 23 February, 2026; originally announced February 2026.

Emulation of large-scale qubit registers with a phase-space approach

Authors: Christian de Correc, Denis Lacroix, Corentin Bertrand

Abstract: A phase-space approach is used and benchmarked for the simulation of the continuous-time evolution of large registers of qubits. It is based on a statistical ensemble of independent mean-field trajectories, where mean field is introduced at the level of the qubits, substituting quantum fluctuations/correlations with classical ones. The approach only involves at worse a quadratic cost in the system… ▽ More A phase-space approach is used and benchmarked for the simulation of the continuous-time evolution of large registers of qubits. It is based on a statistical ensemble of independent mean-field trajectories, where mean field is introduced at the level of the qubits, substituting quantum fluctuations/correlations with classical ones. The approach only involves at worse a quadratic cost in the system size, allowing to simulate up to several thousands of qubits on a classical computer. It provides qualitatively accurate description of one-qubit observables evolutions, making it a useful reference in comparison to techniques limited to small qubit numbers. The predictive power is, however, less robust for multi-qubits observables. We benchmark the method on the $k$-local transverse-field Ising model, considering a large variety of systems ranging from local to all-to-all interactions, and from weak to strong coupling regimes, with up to 2000 qubits. To showcase the versatility of the approach, simulations on 2D and 3D Ising models are also made. △ Less

Submitted 10 May, 2026; v1 submitted 11 February, 2026; originally announced February 2026.

Comments: 18 pages, 14 figures. Comments are welcome!

Journal ref: APS Open Sci. 1, 000017 (2026)

Disorder-induced symmetry breaking in moiré bands of marginally twisted bilayer MoS$_2$

Authors: Pablo Reséndiz-Vázquez, Christophe de Beule, Thi-Hai-Yen Vu, Kaijian Xing, Daniel McEwen, Daniel Bennett, Liangtao Peng, Héctor González-Herrero, Shaffique Adam, Mark T. Edmonds, Michael S. Fuhrer

Abstract: Twisted transition-metal dichalcogenides host highly tunable moiré potentials, flat bands, and correlated electronic phases, yet the role of disorder in shaping these emergent properties remains largely unresolved. Using scanning tunneling spectroscopy, we investigate the impact of electrostatic disorder on the electronic structure of marginally twisted ($θ\approx 0.95^\circ$) bilayer MoS$_2$. Dif… ▽ More Twisted transition-metal dichalcogenides host highly tunable moiré potentials, flat bands, and correlated electronic phases, yet the role of disorder in shaping these emergent properties remains largely unresolved. Using scanning tunneling spectroscopy, we investigate the impact of electrostatic disorder on the electronic structure of marginally twisted ($θ\approx 0.95^\circ$) bilayer MoS$_2$. Differences of 15 meV in the onset energies of the valence and conduction bands between MX- and XM-stacked regions are observed and are unexpected based on symmetry considerations. We further observe spatially correlated disorder in the band onset energy that is consistent with a background random charge density of a few $10^{11}\,\mathrm{cm}^{-2}$. Continuum model calculations for twisted MoS$_2$ reveal dramatic changes in the low-energy moiré bands in response to an electric displacement field, in quantitative agreement with experiment. Moreover, the calculated local density of states including disorder broadening reproduces the experimental observations only when structural relaxation is taken into account. These results highlight the critical role of electrostatic disorder in determining the electronic structure of moiré materials at the nanoscale. △ Less

Submitted 5 February, 2026; originally announced February 2026.

Energy-Transfer-Enhanced Emission and Quantum Sensing of VB- Defects in hBN-PbI2 Heterostructures

Authors: Eveline Mayner, Yaroslav Zhumagulov, Cristian de Giorgio, Feihong Chu, Prabhu Swain, Georg Fantner, Andras Kis, Oleg Yazyev, Aleksandra Radenovic

Abstract: Spin defects in two-dimensional materials hold significant potential for quantum information technologies and sensing applications. The negatively charged boron vacancy (VB-) in hexagonal boron nitride (hBN) has attracted considerable attention as a quantum sensor due to its demonstrated sensitivity to temperature, magnetic fields, and pressure.1 However, its applications have thus far been limite… ▽ More Spin defects in two-dimensional materials hold significant potential for quantum information technologies and sensing applications. The negatively charged boron vacancy (VB-) in hexagonal boron nitride (hBN) has attracted considerable attention as a quantum sensor due to its demonstrated sensitivity to temperature, magnetic fields, and pressure.1 However, its applications have thus far been limited by inherently dim photoluminescence (PL). By fabricating a van der Waals heterostructure with a sensitizing donor layer, lead iodide (PbI2), we effectively enhance the PL intensity from the VB- by 5-45x, while maintaining compatibility with other heterostructures and vdW optoelectronic platforms. The type-I band alignment at the heterojunction enables efficient exciton migration while suppressing back-electron transfer, and the strong spectral overlap between the PbI2 emission and defect absorption supports efficient fluorescence resonance energy transfer. Ab initio density functional theory (DFT) predicts a photon-ratcheting mechanism that boosts absorption and emission while maintaining magnetic resonance (ODMR) contrast through minimal hybridization. Experimentally, the heterostructure exhibits enhanced continuous-wave ODMR sensitivity and functions as a precise probe of external magnetic fields. This work establishes a proof-of-concept for amplifying weak defect signals in nanomaterials, highlighting a new strategy for engineering their optical and magnetic responses. △ Less

Submitted 2 February, 2026; originally announced February 2026.

Comments: 15 pages, 5 figures

Facilitating electrical and laser-induced skyrmion nucleation with a dipolar-field enhanced effective DMI

Authors: Mark C. H. de Jong, Dinar Khusyainov, Julian Hintermayr, Bart Sanders, Dmitry Kozodaev, Aleksei V. Kimel, Bert Koopmans, Theo H. M. Rasing, Reinoud Lavrijsen

Abstract: We demonstrate experimentally how the nucleation of skyrmions in an Ir, Co, and Pt based magnetic multilayer is affected by introducing a layer dependent sign for the Dzyaloshinskii-Moriya interaction (DMI). In one stack, the bottom half of the stack is given a positive DMI and the top half a negative DMI, and as a result, the in-plane component of the dipolar field is aligned parallel to the effe… ▽ More We demonstrate experimentally how the nucleation of skyrmions in an Ir, Co, and Pt based magnetic multilayer is affected by introducing a layer dependent sign for the Dzyaloshinskii-Moriya interaction (DMI). In one stack, the bottom half of the stack is given a positive DMI and the top half a negative DMI, and as a result, the in-plane component of the dipolar field is aligned parallel to the effective field of the DMI in every layer, enhancing the effective DMI. We show that this enhanced DMI facilitates the nucleation and stability of skyrmions using both current-driven and laser-induced skyrmion nucleation. In the devices with an enhanced effective DMI, the density of nucleated skyrmions is greater by up to a factor 20 and skyrmions can be observed in stronger magnetic fields - suggesting that their stability is also improved. These results show that skyrmion nucleation depends strongly on the magnitude of the effective DMI in a magnetic multilayer and that the dipolar field within such a multilayer presents an effective route towards controlling the effective DMI, and thereby, the nucleation of chiral magnetic textures. △ Less

Submitted 2 February, 2026; originally announced February 2026.

Stochastic dynamics from maximum entropy in action space

Authors: Fabricio de Souza Luiz, José Carlos Bellizotti Souza, Luísa Toledo Tude, Marcos César de Oliveira

Abstract: We develop an information-theoretic formulation of stochastic dynamics in which the fundamental stochastic variable is the total action connecting spacetime points, rather than individual paths. By maximizing Shannon entropy over a joint distribution of actions and endpoints, subject to normalization and a constraint on the mean action, we obtain a Boltzmann-like distribution in action space. This… ▽ More We develop an information-theoretic formulation of stochastic dynamics in which the fundamental stochastic variable is the total action connecting spacetime points, rather than individual paths. By maximizing Shannon entropy over a joint distribution of actions and endpoints, subject to normalization and a constraint on the mean action, we obtain a Boltzmann-like distribution in action space. This framework reproduces the standard Brownian propagator in the nonrelativistic limit and naturally extends to relativistic regimes, where the Wiener construction fails to preserve Lorentz covariance. The approach bypasses functional integration over paths, makes the role of entropic degeneracy explicit through an action-space density of states, and provides a transparent connection between the principle of least action and statistical inference. We derive the density of states explicitly using large deviation theory, showing that it takes a Gaussian form centered at the minimal action, and rigorously justify the saddle-point approximation in the diffusive regime. The Markovian property of the resulting propagator is verified to hold via the Chapman--Kolmogorov equation, following from the additivity of the minimal action for free-particle dynamics. In the diffusive regime, the resulting dynamics are governed by a competition between extremization of the action and entropic effects, which can be interpreted in terms of an effective action free energy. Our results establish an unified, covariant, and information-based foundation for classical and relativistic stochastic processes. △ Less

Submitted 17 January, 2026; originally announced January 2026.

Comments: 21 pages, 1 figures

Unexpected Anisotropic Mn-Sb Anti-site Distribution and Van der Waals Epitaxy of MnSb2Te4

Authors: Gustavo Chavez Ponce de Leon, Ahmad Dibajeh, Gert ten Brink, Majid Ahmadi, Bart Jan Kooi, George Palasantzas

Abstract: Mn-Sb site mixing directly impacts both the magnetic and topological properties of MnSb2Te4. This study reveals, unlike previously believed, that these anti-sites can be unevenly distributed within the crystal. To that end, a polycrystalline sample was created with a two-step synthesis using MnTe and Sb2Te3 as precursors. DC-SQUID magnetometry was used to confirm its magnetic properties. In additi… ▽ More Mn-Sb site mixing directly impacts both the magnetic and topological properties of MnSb2Te4. This study reveals, unlike previously believed, that these anti-sites can be unevenly distributed within the crystal. To that end, a polycrystalline sample was created with a two-step synthesis using MnTe and Sb2Te3 as precursors. DC-SQUID magnetometry was used to confirm its magnetic properties. In addition, the use of High-Resolution Scanning Transmission Electron Microscopy combined with Energy-Dispersive X-ray Spectroscopy allowed us to identify the presence of an inversion-breaking asymmetry in the anti-site distribution. This reduced-symmetry structure bears resemblance to the recently proposed class of Janus materials and thus warrants further exploration due to its potential for combining topology and magnetism with other effects, such as non-linear optics and piezoelectricity. Finally, to further elucidate the interplay between site mixing, doping, topology, and magnetism, a method for growing MnSb2Te4 thin films over amorphous SiOx using Sb2Te3 seeds is introduced. The successful Van der Waals epitaxy of MnSb2Te4 over Sb2Te3 seeds using Pulsed Laser Deposition is confirmed using Scanning Transmission Electron Microscopy. This represents a crucial step in incorporating these materials into a Si-based architecture, which offers the possibility of controlling the Fermi lever via gating. △ Less

Submitted 16 January, 2026; originally announced January 2026.

Comments: 9 pages, 4 figures, 1 ToC figure, 16 pages of supplementary material

Gate-Tunable Resonances and 1D Channel in a Graphene Nanoslide

Authors: Christophe De Beule, Ming-Hao Liu, Bart Partoens, Lucian Covaci

Abstract: We present a theory of the graphene nanoslide, a fundamental device for graphene straintronics that realizes a single pseudogauge barrier. We solve the scattering problem in closed form and demonstrate that the nanoslide gives rise to a hybrid pseudogauge and electrostatic cavity in the bipolar regime, and hosts one-dimensional transverse channels. The latter can be tuned using a bottom gate betwe… ▽ More We present a theory of the graphene nanoslide, a fundamental device for graphene straintronics that realizes a single pseudogauge barrier. We solve the scattering problem in closed form and demonstrate that the nanoslide gives rise to a hybrid pseudogauge and electrostatic cavity in the bipolar regime, and hosts one-dimensional transverse channels. The latter can be tuned using a bottom gate between valley-chiral or counterpropagating modes, as well as one-dimensional flatbands. Hence, the local density of states near the barrier depends strongly on the gate voltage with a tunable sublattice and electron-hole asymmetry. In the presence of electron-electron interactions, the nanoslide allows for \textit{in-situ} tuning between a chiral and ordinary Tomonaga-Luttinger liquid. △ Less

Submitted 15 May, 2026; v1 submitted 28 December, 2025; originally announced December 2025.

Comments: 6 + 12 pages, 4 + 1 figures

Journal ref: Phys. Rev. B 113, L201403 (2026)

Perturbative Input-Output Theory of Floquet Cavity Magnonics and Magnon Energy Shifts

Authors: T. Aguiar, M. C. de Oliveira

Abstract: We develop a perturbative input-output formalism to compute the reflectance and transmittance spectra of cavity magnonics systems subject to a Floquet modulation. The method exploits the strong hierarchy between the magnetic-dipole couplings transverse (drive field) and parallel (modulation field) to the static bias field, which naturally introduces the small parameter $ε= (2Ns)^{-1/2}$ associated… ▽ More We develop a perturbative input-output formalism to compute the reflectance and transmittance spectra of cavity magnonics systems subject to a Floquet modulation. The method exploits the strong hierarchy between the magnetic-dipole couplings transverse (drive field) and parallel (modulation field) to the static bias field, which naturally introduces the small parameter $ε= (2Ns)^{-1/2}$ associated with the total spin $Ns$ of the ferromagnet. By organizing the cavity and magnon fields in a systematic expansion in $ε$, we obtain compact analytic expressions for the spectra up to second order. Using these results, we reproduce the characteristic sideband structure observed in recent Floquet cavity electromagnonics experiments. Furthermore, accounting for the Zeeman interaction between the modulation field and the fully polarized ground state - a contribution typically neglected in previous treatments - we predict an additional magnon detuning of approximately $0.8\,\mathrm{GHz}$, independent of both modulation frequency and sample size and determined solely by the spatial volume occupied by the modulation field. This identifies a measurable and previously overlooked shift relevant for the interpretation and design of cavity magnonics experiments. △ Less

Submitted 11 June, 2026; v1 submitted 12 December, 2025; originally announced December 2025.

Journal ref: New J. Phys. 28 043501 (2026)

Electrical Stability of Cr2O3/\b{eta}-Ga2O3 and NiOx/\b{eta}-Ga2O3 Heterojunction Diodes

Authors: Yizheng Liu, Haochen Wang, Carl Peterson, Chinmoy Nath Saha, Chris G. Van de Walle, Sriram Krishnamoorthy

Abstract: This work reports the electrical characteristics comparison study between Cr2O3 and NiOx based heterojunction diodes (HJD) on halide vapor phase epitaxy (HVPE) grown \b{eta}-Ga2O3 epitaxial layers. Both as-fabricated Cr2O3 and NiOx HJDs exhibited forward current density in a range of 130-150 A/cm^2 at 5 V with rectifying ratios >10^10 and a reverse leakage current density at 10^-8 A/cm^2 at -5 V.… ▽ More This work reports the electrical characteristics comparison study between Cr2O3 and NiOx based heterojunction diodes (HJD) on halide vapor phase epitaxy (HVPE) grown \b{eta}-Ga2O3 epitaxial layers. Both as-fabricated Cr2O3 and NiOx HJDs exhibited forward current density in a range of 130-150 A/cm^2 at 5 V with rectifying ratios >10^10 and a reverse leakage current density at 10^-8 A/cm^2 at -5 V. The differential specific on-resistance of Cr2O3 and NiOx HJDs was 12.01 mΩ*cm^2 and 12.05 mΩ*cm^2, respectively. Breakdown voltages of Cr2O3 HJDs ranged from 1.4-1.9 kV and 1.5-2.3 kV for NiOx HJDs. Theoretical band alignment between Cr2O3 and \b{eta}-Ga2O3 was calculated from first principles. The ambient exposed NiOx/HVPE \b{eta}-Ga2O3 HJDs forward current density degraded after 10 days while that of Cr2O3/HVPE \b{eta}-Ga2O3 HJDs remained nearly unchanged after the same amount of time. It was later confirmed that the ambient exposed sputtered NiOx sheet resistance (Rsh) degradation gave rise to the reduction of the forward current density of the NiOx based HJDs, and water (H2O) was qualitatively determined to be the agent attributed to the forward conduction degradation by measuring the Rsh of NiOx-on-sapphire reference wafer after exposing it to different environments. The Cr2O3/HVPE \b{eta}-Ga2O3 HJD also exhibited enhanced thermal stability compared to the NiOx/\b{eta}-Ga2O3 heterostructures at elevated temperatures. Interfacial nickel gallate (Ga2NiO4) phase formation expected from phase diagrams can explain the reduced thermal stability of NiOx/\b{eta}-Ga2O3 HJDs. This study indicates that Cr2O3 is a stable p-type oxide for the realization of robust multi-kV \b{eta}-Ga2O3 HJDs. △ Less

Submitted 11 December, 2025; originally announced December 2025.

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

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

Abstract: 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… ▽ More 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. △ Less

Submitted 4 December, 2025; originally announced December 2025.

Comments: Supplementary Information Available

Charge state equilibration of nitrogen-vacancy center ensembles in diamond: The role of electron tunneling

Authors: Audrius Alkauskas, Chris G. Van de Walle, Lukas Razinkovas, Ronald Ulbricht

Abstract: The charge state stability of nitrogen-vacancy (NV) centers critically affects their application as quantum sensors and qubits. Understanding charge state conversion and equilibration is critical not only for NV centers in diamond but also for defects and impurities in wide-bandgap materials in general. The mechanisms by which these centers change charge state upon optical or electronic excitation… ▽ More The charge state stability of nitrogen-vacancy (NV) centers critically affects their application as quantum sensors and qubits. Understanding charge state conversion and equilibration is critical not only for NV centers in diamond but also for defects and impurities in wide-bandgap materials in general. The mechanisms by which these centers change charge state upon optical or electronic excitation without the presence of mobile carriers remain unclear, potentially affecting the performance of applications ranging from phosphors to power electronics. Here, we elucidate this issue for the case of photoionization of NV center ensembles. Using pump-probe spectroscopy, we ionize negatively charged NV centers and monitor the recovery of $\NVm$ on timescales of up to several seconds. We find that the recovery rate depends strongly on the concentration of surrounding nitrogen donors. Remarkably, the equilibration dynamics exhibit no discernible dependence on temperature, ruling out thermally activated processes. The multiphonon-assisted electron tunneling model, supported by density-functional calculations, explains the measurements and identifies tunneling as the equilibration mechanism. △ Less

Submitted 30 November, 2025; originally announced December 2025.

Resonant states and nuclear dynamics in solid-state systems: the case of silicon-hydrogen bond dissociation

Authors: Woncheol Lee, Mark E. Turiansky, Dominic Waldhör, Byounghak Lee, Tibor Grasser, Chris G. Van de Walle

Abstract: Bond breaking in the presence of highly energetic carriers is central to many important phenomena in physics and chemistry, including radiation damage, hot-carrier degradation, activation of dopant-hydrogen complexes in semiconductors, and photocatalysis. Describing these processes from first principles has remained an elusive goal. Here we introduce a comprehensive theoretical framework for the d… ▽ More Bond breaking in the presence of highly energetic carriers is central to many important phenomena in physics and chemistry, including radiation damage, hot-carrier degradation, activation of dopant-hydrogen complexes in semiconductors, and photocatalysis. Describing these processes from first principles has remained an elusive goal. Here we introduce a comprehensive theoretical framework for the dissociation process, emphasizing the need for a non-adiabatic approach. We benchmark the results for the case of silicon-hydrogen bond dissocation, a primary process for hot-carrier degradation. Passivation of Si dangling bonds by hydrogen is vital in all Si devices because it eliminates electrically active mid-gap states; understanding the mechanism for dissociation of these bonds is therefore crucial for device technology. While the need for a non-adiabatic approach has been previously recognized, explicitly obtaining diabatic states for solid-state systems has been an outstanding challenge. We demonstrate how to obtain these states by applying a partitioning scheme to the Hamiltonian obtained from first-principles density functional theory. Our results demonstrate that bond dissociation can occur when electrons temporarily occupy the antibonding states, generating a highly repulsive excited-state potential that causes the hydrogen nuclear wavepacket to shift and propagate rapidly. Based on the Menzel-Gomer-Redhead (MGR) model, we show that after moving on this excited-state potential on femtosecond timescales, a portion of the nuclear wavepacket can continue to propagate even after the system relaxes back to the ground state, allowing us to determine the dissociation probability. Our results provide essential insights into the fundamental processes that drive carrier-induced bond breaking in general, and specifically elucidate hydrogen-related degradation in Si devices. △ Less

Submitted 29 November, 2025; originally announced December 2025.

Comments: 26 pages, 15 figures

Journal ref: Phys. Rev. B 113, 075304 (2026)

Cr2O3/\b{eta}-Ga2O3 Heterojunction Diodes with Orientation-Dependent Breakdown Electric Field up to 12.9 MV/cm

Authors: Yizheng Liu, Haochen Wang, Carl Peterson, James S. Speck, Chris Van De Walle, Sriram Krishnamoorthy

Abstract: We report the fabrication of Cr2O3/\b{eta}-Ga2O3 heterojunction diodes using reactive magnetron sputtering of Cr2O3 on highly doped \b{eta}-Ga2O3 bulk substrates along (100), (010), (001), (110), and (011) orientation dependence of high electric field handling capability in \b{eta}-Ga2O3. Additional relative permittivity values in (110) and (011) orientations of \b{eta}-Ga2O3 were computed by usin… ▽ More We report the fabrication of Cr2O3/\b{eta}-Ga2O3 heterojunction diodes using reactive magnetron sputtering of Cr2O3 on highly doped \b{eta}-Ga2O3 bulk substrates along (100), (010), (001), (110), and (011) orientation dependence of high electric field handling capability in \b{eta}-Ga2O3. Additional relative permittivity values in (110) and (011) orientations of \b{eta}-Ga2O3 were computed by using first-principles calculation methods for accurate apparent charge density (ND-NA) extraction and breakdown electric field analysis from capacitance-voltage measurements. The HJDs fabricated on n+ (110) exhibited breakdown electric fields >10 MV/cm up to 12.9 MV/cm, showing the highest experimentally observed parallel-plane junction electric field among \b{eta}-Ga2O3-based junctions. Breakdown electric fields among (100), (010), (001), and (011) orientations showed distinct distribution in the range of 5.13-5.26 MV/cm, 5.10-7.05 MV/cm, 2.70-3.33 MV/cm, and 3.88-4.38 MV/cm, respectively, validating the orientational dependence of parallel-plane junction electric field at breakdown in low-symmetry monoclinic \b{eta}-Ga2O3. The parallel-plane breakdown electric fields (EBr,||) reported in this work were extracted when the device experienced catastrophic breakdown at 100 mA/cm^2 current density compliance, and should not be confused with critical electric field (Ec) as a function of drift layer doping concentration, which accounts for electric-field dependent impact ionization coefficients in Si, SiC and GaN. This study can guide the choice of crystal orientation for high performance gallium oxide-based devices that require high electric field handling capability. △ Less

Submitted 25 November, 2025; originally announced November 2025.