Mesoscale and Nanoscale Physics
Brightening of dark trions in monolayer WS$_2$ via localization of surface plasmons
Sreyan Raha, Tara Shankar Bhattacharya, Indrani Bose et al. (+1 more)
Among all excitonic complexes in transition-metal dichalcogenides (TMDs), dark and semi-dark trions are poised to play a
stellar role in future
quantum technologies due to their long lifetimes, about two orders of magnitude greater than those of their bright counterparts. In monolayer (ML) tungsten disulphide (WS$_2$), accessing these states via a suitable brightening mechanism remains challenging, specially, at elevated temperatures. Here, we demonstrate the brightening of dark trions from ML WS$_2$ over the temperature range, 83 K-115 K, enabled by localized surface plasmon modes in a disordered gold substrate. The resulting photoluminescence (PL) spectrum reveals a distinct spectral doublet with the twin peaks of semi-dark and bright trion states, separated by $\sim$ 45 meV. The origin of the semi-dark trion state lies in intervalley electron-electron scatterings, while its visibility in the PL spectrum is made possible by the enhanced out-of-plane electromagnetic field associated with plasmon localization. We also report on the negative degree of circular polarization in ML WS$_2$ at the energy of the semi-dark trion state. Our results establish a scalable plasmonic route to access valley-polarized semi-dark trions, opening new opportunities for
quantum and valleytronic applications.
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All authors Sreyan Raha, Tara Shankar Bhattacharya, Indrani Bose, Achintya Singha
Materials Science
Suman Itani, Yibo Zhang, Ranjit Itani et al. (+1 more)
Large
language models (LLMs) offer new opportunities for automated data extraction and property prediction across materials science, yet their use in superconductivity research remains limited. Here we construct a large experimental database of 78,203 records, covering 19,058 unique compositions, extracted from scientific literature using an LLM-driven workflow. Each entry includes chemical composition, critical temperature, measurement pressure, structural descriptors, and critical fields. We fine-tune several open-source LLMs for three tasks: (i) classifying
superconductors vs. non-
superconductors, (ii) predicting the superconducting transition temperature directly from composition or structure-informed inputs, and (iii) inverse design of candidate compositions conditioned on target Tc. The fine-tuned LLMs achieve performance comparable to traditional feature-based models and in some cases exceed them, while substantially outperforming their base versions and capturing meaningful chemical and structural trends. The inverse-design model generates chemically plausible compositions, including 28% novel candidates not seen in training. Finally, applying the trained predictors to the GNoME database identifies unreported materials with predicted Tc > 10 K. Although unverified, these candidates illustrate how integrating an LLM-driven workflow can enable scalable hypothesis generation for superconductivity discovery.
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All authors Suman Itani, Yibo Zhang, Ranjit Itani, Jiadong Zang
Statistical Mechanics · Cross-listed from hep-th
Analyticity and positivity of Green's functions without Lorentz
Paolo Creminelli, Alessandro Longo, Borna Salehian et al. (+1 more)
We study the properties imposed by microcausality and positivity on the retarded two-point Green's function in a theory with spontaneous breaking of Lorentz invariance. We assume invariance under time and spatial translations, so that the Green's function $G$ depends on $\omega$ and $\vec k$. We discuss that in
Fourier space microcausality is equivalent to the analyticity of $G$ when $\Im (\omega,\vec k)$ lies in the forward light-cone, supplemented by bounds on the growth of $G$ as one approaches the boundaries of this domain. Microcausality also implies that the imaginary part of $G$ (its spectral density) cannot have compact support for real $(\omega,\vec k)$. Using analyticity, we write multi-variable dispersion relations and show that the spectral density must satisfy a family of integral constraints. Analogous constraints can be applied to the fluctuations of the system, via the fluctuation-dissipation
theorem. A stable physical system, which can only absorb energy from external sources, satisfies $\omega \cdot \Im G(\omega,\vec k) \ge 0$ for real $(\omega,\vec k)$. We show that this positivity property can be extended to the complex domain: $\Im [\omega\, G(\omega,\vec k)] >0$ in the domain of analyticity guaranteed by microcausality. Functions with this property belong to the Herglotz-Nevanlinna class. This allows to prove the analyticity of the permittivities $\epsilon(\omega,k)$ and $\mu^{-1}(\omega,k)$ that appear in Maxwell equations in a medium. We verify the above properties in several examples where Lorentz invariance is broken by a background field, e.g. non-zero chemical potential, or non-zero temperature. We study subtracted dispersion relations when the assumption $G \to 0$ at infinity must be relaxed.
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All authors Paolo Creminelli, Alessandro Longo, Borna Salehian, Ahmadullah Zahed
Materials Science
Computational Approach to Investigate Structure-Property Relationship of a series of Carbazole Containing Thermally Activated Delayed Fluorescent Molecules
Md. Asif and Nazia Chawdhury
Donor-acceptor type compounds are an important category of organic materials that show properties suitable for light emission applications. To achieve a full understanding of the mechanism of thermally activated delayed fluorescence (TADF) process, we studied the structure-property relationship for a series of carbazole based TADF emitters, 2CzPN, 4CzPN, 4CzIPN, 4CzBN and 5CzBN. We applied density functional theory to investigate kinetic and electronic properties. We find that the energetic position of triplet excited state of these emitters depends on their molecular structure. Our findings emphasize that to enable reverse intersystem crossing and eventually TADF, strong
spin orbit coupling and minimal energy difference between singlet and triplet states $\Delta E_{ST}$ must be obtained simultaneously. We also find that the reverse intersystem crossing rates $k_{RISC}$ values are higher where $\Delta E_{ST}$ values are closer to reorganization energy. Furthermore, a small change in the absorption peak of optical absorption spectra with and without
spin orbit coupling (SOC) is observed for each emitter. This result is extremely beneficial for the design of new TADF molecules, and we believe that our work contributes to the progress of future development of high-performance organic molecular light-emitting devices.
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Statistical Mechanics · Cross-listed from physics.flu-dyn
The dynamics of thermalisation in the Galerkin-truncated, three-dimensional Euler equation
Rajarshi, Mohammad Saif Khan, Prateek Anand et al. (+1 more)
The inviscid, partial differential equations of hydrodynamics when projected via a Galerkin-truncation on a finite-dimensional subspace spanning wavenumbers $-{\bf K}_{\rm G} \le {\bf k} \le {\bf K}_{\rm G}$, and hence retaining a finite number of modes $N_{\rm G}$, lead to absolute
equilibrium states. We review how the Galerkin-truncated, three-dimensional, incompressible Euler equation thermalises and its connection to questions in
turbulence. We also discuss an emergent pseudo-dissipation range in the energy spectrum and the time-scales associated with thermalisation.
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All authors Rajarshi, Mohammad Saif Khan, Prateek Anand, Samriddhi Sankar Ray
Materials Science
Towards ultra-scaled nanoelectronics using the zipper material system $Bi_2O_2Se/Bi_2SeO_5$
Mohammad Rasool Davoudi, Mina Bahrami, Axel Verdianu et al. (+19 more)
Two-dimensional (2D) materials could overcome the scaling bottleneck of nanoelectronics by enabling atomically thin channels, superior electrostatic control, and reduced short-channel effects. However, progress is limited by the lack of
semiconductor–
insulator interfaces being simultaneously scalable, stable, and reliable. Conventional 2D interfaces are often low quality or require transferring dissimilar materials, limiting reproducibility and scalability. We show that the zipper
heterostructure formed by the high-mobility 2D
semiconductor Bi<sub>2</sub>O<sub>2</sub>Se and its native high-<i>κ</i>
oxide Bi<sub>2</sub>SeO<sub>5</sub> addresses these challenges, providing an atomically sharp, chemically matched interface with excellent electrostatics and promising scaling potential. We further present the first comprehensive multiscale assessment of Bi<sub>2</sub>O<sub>2</sub>Se/Bi<sub>2</sub>SeO<sub>5</sub> transistors targeting thermal stability, reliability, and scalability by linking atomic-scale structure and defects to device-level behavior across <i>four</i> transistor generations (top-gated, fin, and two gate-all-around architectures). Benchmarking against IRDS-2035 targets indicates that Bi<sub>2</sub>O<sub>2</sub>Se/Bi<sub>2</sub>SeO<sub>5</sub> devices could deliver high drive current with low gate leakage under aggressive scaling, potentially surpassing the targets in the upper-bound region of the sensitivity analysis. Finally, we identify oxygen-related
oxide defects as the dominant origin of hysteresis consistent with a beneficial role of encapsulation and oxygen-rich annealing. Together, our findings support the potential of this zipper material system as a technologically-credible and manufacturing-relevant platform for future nanoelectronics.
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All authors Mohammad Rasool Davoudi, Mina Bahrami, Axel Verdianu, Pedram Khakbaz, Dominic Waldhoer, Mahdi Pourfath, Alexander Karl, Christoph Wilhelmer, Yury Illarionov, Seyed Mehdi Sattari-Esfahlan, Yichi Zhang, Junchuan Tang, Aftab Nazir, Ye Li, Xiaoying Gao, Congwei Tan, Yu Zheng, Changze Liu, Michael Waltl, Hailin Peng, Theresia Knobloch, Tibor Grasser
Materials Science
Composition/structure directed search for new chalcogenide compounds
Alon Hever, Ohad Levy, Stefano Curtarolo et al. (+1 more)
This work presents a simple scheme for finding new crystalline compounds by adapting structure types from neighbor atoms compounds. The approach is demonstrated for the selenide and sulfide families of binary compounds. It predicts ten new compounds that are not currently included in the inorganic
crystal structure database (ICSD). The compounds primarily originated from a small search domain that includes near neighbors. Comparison with extended searches that include structures from binary systems of more remote atoms in the periodic table demonstrate the relative efficiency of near neighbor screening. This points at the possibility of using similar directed searches as a heuristic rule for efficiently finding new stable compounds in additional compound families.
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All authors Alon Hever, Ohad Levy, Stefano Curtarolo, Amir Natan
Strongly Correlated Electrons
Phase structure of the one-dimensional $\mathbb{Z}_2$ lattice gauge theory with second nearest-neighbor interactions
Yeimer Zambrano, Aleksey Alekseev, Konrad J. Kapcia et al. (+2 more)
We investigate the ground-state phase diagram of a one-dimensional $\mathbb{Z}_2$
lattice gauge theory (LGT) model with hard-core
bosons at half-filling, extending previous studies by including second nearest-neighbor (2NN) interactions. Using
matrix product state techniques within the density
matrix renormalization group, we compute charge gap, static structure factor, pair-pair correlation functions, and
entanglement entropy for various interaction strengths and field parameters. We analyze two representative neatest-neighbor interaction strengths ($V_1$) that correspond to the Luttinger
liquid (LL) and Mott
insulator (MI) phases in the absence of the 2NN interactions. We introduce the 2NN coupling $V_2$ and investigate its impact on the system. Our results reveal very rich behavior. As the 2NN repulsion increases, in the case of small $V_1$, we observe a direct transition from the LL phase to a charge-ordered
insulator (COI) phase with four-site ordering pattern, whereas for large $V_1$, we observe a transition from the MI phase with two-site ordering pattern (previously found with only $V_1$ included), going through an intermediate LL region, and finally reaching the COI regime. Additionally, the inclusion of 2NN interactions enhances charge order and suppresses pair coherence, evidenced by sharp peaks in the structure factor and rapid decay in pair-pair correlators. Our work extends the well-studied phase structure of 1D $\mathbb{Z}_2$ LGT models and demonstrates the interplay between gauge fields, confinement, and extended interactions.
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All authors Yeimer Zambrano, Aleksey Alekseev, Konrad J. Kapcia, Krzysztof Cichy, Agnieszka Cichy
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Understanding Surface-Induced Decoherence of NV Centers in Diamond
Jonah Nagura, Mykyta Onizhuk and Giulia Galli
Nitrogen vacancy centers (NV) in proximity to diamond surfaces are promising nanoscale
quantum sensors. However, their coherence properties are negatively affected by
magnetic and electric surface noise, whose origin and detailed impact have remained elusive. Using atomistic models of diamond surfaces derived with density functional theory, together with decoherence time calculations with cluster correlation expansion methods, we quantify the effects of surface crystallographic orientation and functionalization, and of the density of unpaired electrons on the NV Hahn-echo time $T_2$. We determine a crossover depth at which $T_2$ ceases to be limited by surface
nuclear spins and recovers the bulk-limited value. We find that for static surface-electron baths, the ratio between the NV depth and the separation between surface electron
spins determines a transition from fast-fluctuating to quasi-static noise, leading to a dependence of $T_2$ on orientation for specific surfaces. We also find that the modulation of $T_2$ by
spin-
phonon relaxations leads to motional-narrowing at sub-microsecond relaxation times. Importantly, our calculations show that it is only when accounting for surface-
spin in-sequence hopping that measured $T_2$ values as a function of depth can be reproduced, thus highlighting the importance of hopping-mediated models to describe the surface
spin noise affecting NV sensors. Overall, our work provides clear guidelines for engineering diamond surfaces to achieve enhanced NV coherence for
quantum sensing and information processing applications.
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Strongly Correlated Electrons
Magnetic anisotropy and dipolar interactions in the frustrated triangular-lattice magnet NaGdS_2
J. Grumbach, E. Häußler, S. Luther et al. (+12 more)
In this comprehensive study, we present results of bulk measurements (magnetization, specific heat, ac susceptibility, thermal expansion, and magnetostriction) combined with local methods such as
nuclear magnetic resonance (^23Na NMR) and electron
spin resonance (ESR) and simulations (McPhase) on polycrystalline and single-crystalline NaGdS_2 samples. The rare-earth delafossite NaGdS_2 is a triangular-
lattice magnet with S = 7/2
spin-only Gd^3+ moments with suppressed single-ion anisotropy. In our study, we estimate that NaGdS_2 has a weak
antiferromagnetic exchange (J_H/k_B is about 52mK) and signs of long-range
magnetic order are absent down to lowest temperature. However, indications of short range
magnetic order are found below 180 mK in the ac susceptibility and thermal expansion. Our results indicate an interplay of Heisenberg-type and dipolar exchange. Due to the large moment of the Gd^3+ ions, one expects a strong impact of the dipolar coupling in NaGdS_2, in contrast to the related NaYbS_2. ESR and ^23Na NMR measurements, indeed, indicate the formation of short-range
ferromagnetic correlations. NaGdS_2 appears to be a rare system, in which
magnetic order is suppressed by a competition between Heisenberg and dipolar interactions.
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All authors J. Grumbach, E. Häußler, S. Luther, J. Sichelschmidt, K. M. Ranjith, T. Herrmannsdörfer, M. Rotter, S. Granovsky, H. Kühne, M. Uhlarz, J. Wosnitza, H.-H. Klauß, M. Baenitz, T. Doert, M. Doerr
Quantum Gases · Cross-listed from math.AP
$\Phi^4_2$ theory limit of a many-body bosonic free energy
Lucas Jougla and Nicolas Rougerie
We consider the
quantum Gibbs state of an interacting Bose gas on the 2D
torus. We set temperature, chemical potential and coupling constant in a regime where classical field theory gives leading order asymptotics. In the same limit, the repulsive interaction potential is set to be short-range: it converges to a Dirac delta function with a rate depending polynomially on the other scaling parameters. We prove that the free-energy of the interacting Bose gas (counted relatively to the non-interacting one) converges to the free energy of the $\Phi^4_2$ non-linear Schrödinger-Gibbs measure, thereby revisiting recent results and streamlining proofs thereof. We combine the variational method of Lewin-Nam-Rougerie to connect, with controled error, the
quantum free energy to a classical Hartree-Gibbs one with smeared non-linearity. The convergence of the latter to the $\Phi^4_2$ free energy then follows from arguments of Fröhlich-Knowles-Schlein-Sohinger. This derivation parallels recent results of Nam-Zhu-Zhu.
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Materials Science · Cross-listed from physics.soc-ph
The Physics of Sustainability: Material and Power Constraints for the Long Term
José Halloy, Petros Chatzimpiros, François Graner et al. (+1 more)
Much of today's sustainability discourse emphasizes efficiency, clean technologies, and smart systems, but largely underestimates fundamental physical constraints relating to energy-matter interactions. These constraints stem from the fact that Earth is a materially closed yet energetically open system, driven by the sustained but low power-density flux of
solar radiation. This Perspective reframes sustainability within these axiomatic limits, integrating relevant timescales and orders of magnitude. We argue that fossil-fueled industrial metabolism is inherently incompatible with long-term viability, while post-fossil systems are surface-, materials-, and power-intensive. Long-term sustainability must therefore be defined not only by how much energy or material is used, but also by how it is used: favoring organic, carbon-based chemistry with limited reliance on purified metals, operating at low power density, and maintaining low throughput rates. Achieving this requires radical technological shifts toward life-compatible systems and biogeochemical circular processes, and, likely as a consequence, a paradigm change toward degrowth to a steady-state. These two shifts are mutually reinforcing and together provide the necessary foundation for any viable future.
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All authors José Halloy, Petros Chatzimpiros, François Graner, Thomas Gregor
Materials Science
Ferroelectric metal-organic frameworks as wide band gap materials
Monirul Shaikh, Sathiyamoorthy Buvaneswaran, Asif Latief Bhat et al. (+2 more)
Wide band gap materials are particularly relevant at high temperatures. The band gap shrinkage at higher temperatures prevents device applications with narrow band gap
semiconductors. Considering $\alpha$-phase strontium cyanurate as a prototype structure, we identify a group of metal-organic frameworks (MOFs) that exhibit ultra-wide band gaps ranging from 5.5 to 5.7 eV. Recently, a strontium cyanurate compound was found to undergo a phase transition from a high-
symmetry $\beta$-phase to a low-
symmetry ferroelectric $\alpha$-phase when the temperature was reduced. In the present study, utilizing group theory techniques, we unravel that a zone-center $\Gamma_2^-$
phonon mode modifies our structures from high-
symmetry $\beta$-phase to a low-
symmetry $\alpha$-phase for A$_3$(O$_3$C$_3$N$_3$)$_2$ MOFs with A = Mg, Ca, Sr, and Ba. We implement first-principles calculations to investigate structural, ferroelectric, and optical properties of these compounds in $\alpha$-phase. The switching barriers between bistable polar states are also estimated. Further, to realize their feasibility, we examine the dynamical and thermal stabilities for all of these MOFs.
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All authors Monirul Shaikh, Sathiyamoorthy Buvaneswaran, Asif Latief Bhat, Trilochan Sahoo, Saurabh Ghosh
Strongly Correlated Electrons · Cross-listed from quant-ph
Efficient simulation of low-entanglement bosonic Gaussian states in polynomial time
Tong Liu, Hui-Ke Jin, Tao Xiang et al. (+1 more)
Bosonic Gaussian states are ubiquitous in
quantum optics and condensed matter physics. While they are efficiently handled within the Gaussian formalism, sampling requires calculating amplitudes in the
boson occupation basis. This step, however, is hindered by a significant bottleneck due to the hafnian. We present an efficient
algorithm that converts pure bosonic Gaussian states into
matrix product states (MPSs), thereby establishing a versatile tool for probing bosonic Gaussian systems in settings where direct Gaussian-formalism-based calculations become inefficient. Our method combines a Gaussian singular value decomposition with a projected-creation-operator mapping that constructs local MPS tensors without computing hafnians. Benchmarking on covariance
matrices from the Jiuzhang 2.0 and Jiuzhang 4.0 Gaussian
boson sampling experiments demonstrates substantial speedups over previous tensor-network approaches in the low-
entanglement regime relevant to lossy devices. The method provides a scalable classical simulation framework for bosonic Gaussian states with limited
entanglement. In this regime, a target accuracy can be achieved with a bond dimension that remains computationally tractable, thereby extending the applicability of MPS-based methods to a broad range of bosonic systems.
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All authors Tong Liu, Hui-Ke Jin, Tao Xiang, Hong-Hao Tu
Disordered Systems and Neural Networks
Stability of the symmetry-protected topological phase and Ising transitions in a disordered U(1) quantum link model on a ladder
Mykhailo V. Rakov, Luca Tagliacozzo, Maciej Lewenstein et al. (+2 more)
We revisit the U(1)
quantum link model in a ladder geometry, finding, by finite-size scaling, that the critical exponent $\nu=1$ and the central charge $c=1/2$ are consistent with the Ising universality class for all phase transitions observed. A blind application of the Harris criterion would suggest that this criticality is lost in the presence of the disorder. It turns out not to be the case. For the disorder affecting ladder's rung hoppings only, we have found that the transitions survive disappearing only for quite strong disorder. The disorder in the ladder's legs destroys the nonzero mass phase criticality, while the
symmetry-protected topological phase for zero mass survives a small disorder. The observed robustness against disorder is explained qualitatively using field-theoretic arguments.
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All authors Mykhailo V. Rakov, Luca Tagliacozzo, Maciej Lewenstein, Jakub Zakrzewski, Titas Chanda
Materials Science
Thermal and Size Effects in Ferroelastic Domains by Machine Learning
Luka Geddis Zellmann, Sumner B. Harris, John R. R. Scott et al. (+4 more)
Ferroelastic domain walls (DWs) underpin key functionalities in complex
oxides. In free-standing ferroic thin films, where elastic interactions are highly thickness dependent, understanding DW behaviour across length scales and external stimuli is crucial. A thickness-dependent monopolar-to-dipolar crossover in elastic DW behaviour has been reported; however, how temperature influences this regime remains unexplored. Here, LaAlO3 thin films spanning the dipolar ($<200$ nm) and crossover (200-300 nm) regimes are investigated using in situ heating scanning transmission electron microscopy (STEM) and a machine-learning-driven image analysis approach. By tracking DW
curvature and density from above $T_C$ (approximately $550,^\circ$C) to room temperature (RT), a distinct interplay between temperature and thickness is identified. In the dipolar regime, DWs are mobile and curved near $T_C$ and gradually freeze upon cooling, consistent with the well-known temperature freezing regime. In contrast, within the crossover regime, DWs are nearly static, with minimal reconfiguration through cooling and
curvature an order of magnitude lower at RT. These results map the
evolution of DWs across the thermally driven super-elastic to freezing regimes, revealing how thickness and temperature govern DW morphology and dynamics, and providing insight relevant for domain engineering in free-standing
oxide thin films.
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All authors Luka Geddis Zellmann, Sumner B. Harris, John R. R. Scott, Yi-Chieh Yang, Joerg Jinschek, Rama Vasudevan, Miryam Arredondo
Mesoscale and Nanoscale Physics
Edge states of a Bi$_2$Se$_3$ nanosheet in a perpendicular magnetic field
Stan P. J. Koenis, Lucas Maisel Licerán and Henk T. C. Stoof
Conventional wisdom dictates that the conducting edge states of two-dimensional topological
insulators of the Bi$_2$Se$_3$ family are protected by time-reversal
symmetry. However, theoretical bulk calculations and a recent experiment show that the edge states persist in the presence of large external
magnetic fields. To address this apparent contradiction, we have developed an analytical description for the edge-state wave function of a semi-infinite sample in a perpendicular
magnetic field. Our description relies on the usual bulk Landau levels, together with additional states arising due to the presence of the hard wall, which are unnormalizable in the infinite system. The analytical wave functions agree extremely well with numerical calculations and can be used to directly analyze the behavior of the edge states in a
magnetic field.
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Materials Science
Epitaxial Sr(Sn, Ge)$_{x}$Ti$_{1-x}$O$_{3}$ buffer layers for continuous strain engineering on SrTiO$_{3}$ substrates
Ruben Hamming-Green, Ewout van der Veer and Beatriz Noheda
Epitaxial strain plays a key role in determining the structure and functionality of thin films, with the choice of substrate being traditionally used to control the magnitude of the applied strain. However, even in the large family of perovskite materials, this allows for only a limited, discrete set of strain states to be achieved. Here we report on an approach to controlling epitaxial strain for the growth of perovskite materials by involving a single SrTiO$_{3}$ substrate (the most available perovskite in single
crystal form) and a buffer layer that consists of the solid solution Sr(Sn, Ge)$_{x}$Ti$_{1-x}$O$_{3}$, of which the
lattice parameter can be tuned in a continuous fashion, from 3.880 Å up to 4.007 Å, while maintaining coherent epitaxial growth on SrTiO$_{3}$ with high quality interfaces. Using a BaTiO$_{3}$ overlayer as a model system, we show that changes to the buffer layer composition, i.e. increase of in-plane
lattice parameter, change the strain state of BaTiO$_{3}$ from fully relaxed, through highly compressively strained, to an exotic state showing 'inverted' epitaxy in which the buffer layer is relaxed from the substrate but
lattice matched to the overlayer.
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Materials Science
An intermediately-homogenized peridynamics approach to failure of microstructually disordered materials
Shucheta Shegufta and Michael Zaiser
Peridynamics provides a versatile tool for fracture modelling in materials where fracture pathways cannot be predicted beforehand, but must be envisaged as an emergent features of the deformation process. One class of materials where this is surely the case are materials with strong microstructural disorder such as random composites, random porous materials or disordered metamaterials. For this class of materials we propose an intermediately-homogenized peridynamic modelling approach where the disordered microstructure is not resolved in full spatial detail but described in terms of random order parameter fields which retain essential information about the local heterogeneity and spatial correlations of material properties.
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Statistical Mechanics
Multiloop calculations with parametric integration in critical dynamics: the four-loop analytic study of model A of $\phi^4$ theory
Loran Ts. Adzhemyan, Diana A. Davletbaeva, Daniil A. Evdokimov et al. (+1 more)
We perform an analytical four loop calculation of exponent $z$ in model A of critical dynamics in $d=4-2\varepsilon$ dimensions. This is the first time such a large order of perturbation theory has been calculated analytically for models of critical dynamics. To do this, we apply the modern method of parametrical integration with hyperlogaritms. We discuss in detail peculiarities of application of this method to critical dynamics, e.g. the problem of linear-irreducible diagrams already present in four loop (contrary to statics where the first linear-irreducible diagram appears in six loop).
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All authors Loran Ts. Adzhemyan, Diana A. Davletbaeva, Daniil A. Evdokimov, Mikhail V. Kompaniets
Strongly Correlated Electrons
Binding of holes and competing spin-charge order in simple and extended Hubbard model on cylindrical lattice: An exact diagonalization study
Md Fahad Equbal and M. A. H. Ahsan
We investigate the binding of holes and the emergence of competing
spin-charge order in the simple and extended Hubbard model using exact diagonalization on the 3x4 cylindrical
lattice. For the simple Hubbard model (V=0), we find weakly bound hole pairing mediated by
magnetic correlations at intermediate repulsive U, without any evidence of phase separation. Introducing nearest-neighbor interaction V reveals a rich phase diagram: attractive V drives multi-hole clustering and phase separation with localized
magnetic quenching, while repulsive V stabilizes charge-density-wave (CDW) order that coexists with bound hole pairs within a modulated
magnetic background. At strong coupling (U=10), the competition sharpens, with attractive V overcoming on-site repulsion to form magnetically quenched clusters and repulsive V producing robust CDW order that constrains pairing. Real-space analysis of
spin and charge correlations provides microscopic evidence of distinct binding mechanisms – phase separation versus correlation-mediated pairing – depending on the sign and strength of intersite interaction V . Our results establish a comprehensive picture of how nonlocal Coulomb interactions reshape the landscape of hole-binding and collective order in correlated electron systems.
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Statistical Mechanics
Janus Percolation in Anisotropic Limited-Degree Networks
Jacopo A. Garofalo, Nuno A.M. Araújo, Lucilla de Arcangelis et al. (+2 more)
Many real-world infrastructures, from sensor and road networks to power grids, are spatially embedded and anisotropic, with constraints on the maximum number of links each node can establish. Such systems can be represented as anisotropic limited-degree networks, in which each node forms at most q outgoing links preferentially oriented along a fixed direction. By increasing the node density sigma at fixed q, we uncover a reentrant percolation transition: a
giant strongly connected component emerges, but unexpectedly disintegrates again at high densities. This counterintuitive behavior implies that adding nodes, normally expected to enhance robustness, can instead reduce mutual accessibility and weaken global connectivity. The critical behavior displays two coexisting "faces": random-percolation scaling along the preferred direction and directed-percolation scaling transversely, therefore we name this phenomenon Janus percolation, in analogy with the dual-faced Roman god. These findings demonstrate that anisotropy and degree limitation can jointly induce a novel reentrant connectivity with mixed universality that bridges the universality classes of random and directed percolation, providing fresh insight into how structural constraints shape connectivity and resilience in spatial networks.
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All authors Jacopo A. Garofalo, Nuno A.M. Araújo, Lucilla de Arcangelis, Alessandro Sarracino, Eugenio Lippiello
Materials Science · Cross-listed from physics.med-ph
Event-sparse stack denoising for 4D-STEM applications
Gregory Nordahl, Rebekka Klemmt and Espen Drath Bøjesen
We introduce a denoising method for four-dimensional scanning transmission electron microscopy (4D-STEM) that relies on processing local, scan position-independent electron event-sparse data stacks, called event-sparse stack denoising. This method adds an extra time dimension during data collection by recording multiple electron event-sparse diffraction patterns. The resulting
datasets are effectively five-dimensional, referred to as locally time-resolved STEM (LTR-STEM). Diffraction data stacks at each scan position are processed using one of two sparsity denoising pipelines: 1) the density-based spatial clustering of applications with noise (DBSCAN)
algorithm followed by multi-step persistence thresholding, or 2) sparse principal component analysis (sparse PCA), followed by single-step thresholding. Both methods perform well for diffraction data denoising, as shown by simulated peak signal-to-noise ratio (PSNR) curves, denoised experimental data for virtual imaging, and application-specific denoising for defect detection. PSNR analysis indicates that sparsity-denoised 4D-STEM data reaches the same PSNR as raw data at approximately 16% of the exposure time, demonstrating comparable image quality with a lower dose. In defect detection, a 4.1x increase in sensitivity to relative radial disk shift is observed in the denoised data. Moreover, the LTR-STEM technique may be used to inspect material degradation by tracking changes in diffraction disk intensity, allowing for critical dose estimation and exposure-selective imaging.
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Soft Condensed Matter
Friction modifies the quasistatic mechanical response of a confined, poroelastic medium
Térence Desclaux, Callum Cuttle, Chris W. MacMinn et al. (+1 more)
The mechanical response of elastic porous media confined within rigid geometries is central to a wide range of industrial, geological, and biomedical systems. However, current models for these problems typically overlook the role of wall friction, and particularly its interaction with confinement. Here, we develop a theoretical framework to describe the interplay between the mechanics of the medium and Coulomb friction at the confining walls for slow, quasistatic deformations in response to two canonical uniaxial forcings: piston-driven loading (i.e., an imposed effective stress at the top boundary) and fluid-driven loading (i.e., an imposed fluid pressure at the top boundary) followed by unloading. We find that, during compression, the stress field evolves according to a quasistatic advection-
diffusion equation, extending classical poroelasticity results. The magnitude of friction is controlled by a single dimensionless number proportional to the friction coefficient and the aspect ratio of the confining geometry. During decompression, a portion of the solid
matrix remains stuck due to friction, leading to hysteresis and to the propagation of a slip front. In piston-driven loading, the frictional stress is directly coupled to the solid effective stress, leading to exponential damping of the loading and striking changes to the displacement field. However, this coupling limits the energy dissipated by friction. In fluid-driven loading, the pressure gradient locally adds energy, decoupling elastic energy storage and frictional energy dissipation. The displacement remains qualitatively unchanged but is quantitatively reduced due to large energy dissipation. In both cases, friction can have a substantial impact on the apparent mechanical properties of the medium.
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All authors Térence Desclaux, Callum Cuttle, Chris W. MacMinn, Olivier Liot
Soft Condensed Matter
A molecular dynamics study of surface-directed spinodal decomposition on a chemically patterned amorphous substrate
Syed Shuja Hasan Zaidi, Hema Teherpuria, Santosh Mogurampelly et al. (+1 more)
We employ a molecular dynamics (MD) study to explore pattern selection in binary fluid mixtures ($AB$) undergoing surface-directed spinodal decomposition on a chemically patterned amorphous substrate. We chose a checkerboard pattern with chemically distinct square patches of a side $M$, with neighboring patches preferring different particle types. We report the efficient transposition of the substrate's pattern as a registry to the fluid cross sections in its vicinity when the pattern's periodicity $\lambda/\sigma \simeq 2M$ ($\sigma$ being the fluid particle size) is larger than the mixture's spinodal length scale $\lambda_c/\sigma \simeq 2\pi/\xi_B$ ($\xi_B$ being the bulk correlation length). Our correlation analysis between the surface field and the surface-registries in the substrate's normal direction shows that the associated decay length, $L_{\perp}(t)$, increases with decreasing pattern periodicity ($\lambda$). $L_{\perp}(t)$ also exhibits diffusive growth with time $\sim t^{1/3}$, similar to wetting-layer growth for chemically homogeneous walls. Our MD results also show the emergence of composition waves parallel to the substrate, whose wavelength exhibits dynamical scaling with a power-law growth in time $L_{||}(z,t)\sim t^{\alpha}$. $L_{||}(z,t)$ shows dynamical crossovers from a transient surface-registry regime to universal phase-separation regimes for cross-sections with registries. We also give an account of the scaling of registry's formation and melting times with patch sizes.
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All authors Syed Shuja Hasan Zaidi, Hema Teherpuria, Santosh Mogurampelly, Prabhat K. Jaiswal
Strongly Correlated Electrons
Effect of doping on the electronic structure, orbital-dependent renormalizations, and magnetic correlations in bilayer La$_3$Ni$_2$O$_7$
I. V. Leonov
Using the DFT+dynamical mean-field theory approach we study the effects of electronic correlations and doping on the normal state electronic structure of the double-layer nickelate
superconductor La$_3$Ni$_2$O$_7$ under pressure. In agreement with experiments, we obtain significant orbital-dependent quasiparticle renormalizations of the Ni $x^2-y^2$ and $3z^2-r^2$ bands, accompanied by incoherence (bad metal behavior) of the $3z^2-r^2$ states, caused by the proximity of the Ni $3d$ states to orbital-dependent localization. Our results demonstrate a sensitive, non-monotonic dependence of $m^*/m$ on doping, with a remarkable, by about 20%, increase for the Ni $x^2-y^2$ orbitals upon electron doping $x \sim 0.2$ (per Ni ion), implying a significant enhancement of orbital-dependent correlations with oxygen deficiency in LNO. We observe a reconstruction of the low-energy electronic structure of LNO upon doping above $x\sim -0.3$ and 0.2. It is associated with the Lifshitz transition, with a crossover to a self-doping regime characterized by partial occupation of the La $5d$ bands (upon an electron doping $x>0.2$). Our analysis of the static
magnetic susceptibility $\chi({\bf q})$ suggests the possible formation of the
spin and charge density wave stripes, implying strong
spin and charge correlations in LNO. We show that this behavor is associated with suppression of the Néel AFM ordering of the Ni$^{2+}$ ions upon hole doping. Interestingly, upon a moderate electron doping of the Ni$^{2.5+}$ ions, we find a significant enhancement of the strength of in-plane
spin fluctuations. We note a close resembles of our results to those for the
bilayer Hubbard model, which shows the boosting of superconductivity as one of the two electron bands approaches the Lifshitz transition. Our results suggest that
spin and charge stripe fluctuations play a key role in pressure-driven superconductivity in LNO.
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Materials Science
Bio-Organic Materials Based Resistive Switching Memories
Rahul Deb, Debajyoti Bhattacharjee and Syed Arshad Hussain
Resistive switching (RS) devices, based on soft materials such as organic, biomolecules as well as natural plant extracts etc., has emerged as a promising alternative to the conventional
memory technologies. They offer simple device structures, low power requirements, rapid switching and compatibility with high-density device integration. Over the last two decades, these classes of materials have been explored for both non-volatile
memory and artificial synapse functions. This chapter provides a brief overview of RS fundamentals, their major classifications, key applications, and recent trends in the use of organic and bio-derived materials.
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Mesoscale and Nanoscale Physics
Thermally-controlled interlayer exchange and field-induced anisotropy in synthetic antiferromagnets
O. Kozlov, V. Kalita, S. Reshetniak et al. (+3 more)
Interlayer exchange in synthetic antiferromagnets incorporating thin paramagnetic spacers can be controlled thermally. The spacer provides an additional
ferromagnetic contribution that renormalizes the otherwise temperature-independent interlayer coupling. As a result, the system shows
antiferromagnetic alignment at high temperatures and
ferromagnetic alignment at low temperatures. This behavior is observed in Fe(2 nm)/Cr(0.4 nm)/Fe$_{17.5}$Cr$_{82.5}$(0.9 nm)/Cr(0.4 nm)/Fe(2 nm) multilayers with the inner spacer Fe$_{17.5}$Cr$_{82.5}$ paramagnetic at and above room temperature, and is shown to be due to the spacer being significantly magnetically polarized on lowering the temperature toward its Curie point. Although the Fe layers lack intrinsic magnetocrystalline anisotropy, the magnetization reversal demonstrates a field-induced uniaxial anisotropy of
antiferromagnetic character. The resulting reversal process resembles that of a metamagnet with a
spin-flip transition.
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All authors O. Kozlov, V. Kalita, S. Reshetniak, A. Kravets, D. Polishchuk, V. Korenivski
Statistical Mechanics
Discreteness-induced spatial chaos versus fluctuation-induced spatial order in stochastic Turing pattern formation
Yusuke Yanagisawa and Shin-ichi Sasa
We investigate Turing pattern formation in a
stochastic reaction-
diffusion model defined on $N$
lattice sites, where each
lattice site is associated with a reaction vessel of volume $\Omega$. We focus on a regime where spatial discreteness plays a crucial role, namely when the characteristic length of patterns is comparable to the
lattice spacing. In this setting, we compare two different limiting procedures and show that they lead to qualitatively different outcomes. If we first take the deterministic limit $\Omega \to \infty$ and then the long-time limit $t \to \infty$, the stationary solutions of the corresponding spatially discrete deterministic equations become spatially chaotic in the limit $N\to\infty$. In contrast, if we first take the limit $t \to \infty$ and then take an appropriate limit of $\Omega \to \infty$ and $N\to\infty$, the resulting patterns are spatially periodic.
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Soft Condensed Matter
Relaxation in Polymer Networks under Uniaxial Extension and Biaxial Compression
Volker Kraus, Wolfgang Hamm and Miklos Zrinyi
Predicting the time and temperature dependent behavior of
polymer networks under complex loading is essential for the design of advanced elastomeric materials. Many practical applications involve combinations of deformation modes, such as uniaxial extension and biaxial compression, yet a unified description of their mechanical response remains challenging. In this study, we apply a consistent theoretical framework to describe both uniaxial and biaxial deformation modes, using the same constitutive formalism based on van der Waals network theory. The time dependence of the material response in both cases is governed by a substance specific relaxation spectrum, introduced through irreversible thermodynamics as a linear coupling to the quasi static reference state of the permanent network. The temperature dependence of the relaxation times is well described by the Williams Landel Ferry (WLF) equation in the high temperature or low strain rate regime, demonstrating that the same physical mechanisms underlie time dependent behavior across different loading geometries. Experimental results are presented for cross linked poly(methyl methacrylate) (PMMA) and polyvinyl acetate (PVAc), validating the theoretical model across both materials and deformation modes.
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