Statistical Mechanics
Non-Normal Eigenvector Amplification in Multi-Dimensional Kesten Processes
Virgile Troude and Didier Sornette
Heavy-tailed fluctuations and power law statistics pervade physics, finance, and economics, yet their origin is often ascribed to systems poised near criticality. Here we show that such behavior can emerge far from instability through a universal mechanism of non-normal eigenvector amplification in multidimensional Kesten processes $x_{t+1}=A_t x_t+\eta_t$, where $A_t$ are random interaction
matrices and $\eta_t$ represents external inputs, capturing the evolving interdependence among $N$ coupled components. Even when each random multiplicative
matrix is spectrally stable, non-orthogonal eigenvectors generate transient growth that renormalizes the Lyapunov exponent and lowers the tail exponent, producing stationary power laws without
eigenvalues crossing the stability boundary. We derive explicit relations linking the Lyapunov exponent and the tail index to the statistics of the condition number, $\gamma\!\sim\!\gamma_0+\ln\kappa$ and $\alpha\!\sim\!-2\gamma/\sigma_\kappa^2$, confirmed by numerical simulations. This framework offers a unifying
geometric perspective that help interpret diverse phenomena, including
polymer stretching in
turbulence,
magnetic field amplification in dynamos,
volatility clustering and wealth inequality in financial systems. Non-normal interactions provide a collective route to scale-free behavior in globally stable systems, defining a new universality class where multiplicative feedback and transient amplification generate critical-like statistics without spectral criticality.
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Materials Science
Epitaxial Electrodeposition of Fe with Controlled In-Plane Variants for Reversible Metal Anode in Aqueous Electrolyte
Chenxi Sui, Ching-Tai Fu, Guangxia Feng et al. (+6 more)
The development of reversible metal anodes is a key challenge for advancing aqueous battery technologies, particularly for scalable and safe stationary energy storage applications. Here we demonstrate a strategy to realize epitaxial electrodeposition of iron (Fe) on single-
crystal copper (Cu) substrates in aqueous electrolytes. We compare the electrodeposition behavior of Fe on polycrystalline and single-crystalline Cu substrates, revealing that the latter enables highly uniform, dense, and crystallographically aligned Fe growth. Comprehensive electron backscatter diffraction (EBSD) and X-ray diffraction (XRD) analysis confirms the formation of Fe with specific out-of-plane and in-plane orientations, including well-defined rotational variants. Our findings highlight that epitaxial electrodeposition of Fe can suppress dendritic growth and significantly enhance Coulombic efficiency during plating/stripping cycles. This approach bridges fundamental crystallography with practical electrochemical performance, providing a pathway toward high-efficiency aqueous batteries utilizing Earth-abundant materials.
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All authors Chenxi Sui, Ching-Tai Fu, Guangxia Feng, Yuqi Li, Junyan Li, Gangbin Yan, Po-Chun Hsu, Steven Chu, Yi Cui
Strongly Correlated Electrons
Comparing Symmetrized Determinant Neural Quantum States for the Hubbard Model
Louis Sharma, Ahmedeo Shokry, Rajah Nutakki et al. (+3 more)
Accurate simulations of the Hubbard model are crucial to understanding strongly correlated phenomena, where small energy differences between competing orders demand high numerical precision. In this work, Neural
Quantum States are used to probe the strongly coupled and underdoped regime of the square-
lattice Hubbard model. We systematically compare the Hidden
Fermion Determinant State and the Jastrow-Backflow ansatz, parametrized by a
Vision Transformer, finding that in practice, their accuracy is similar. We also test different symmetrization strategies, finding that output averaging yields the lowest energies, though it becomes costly for larger system sizes. On cylindrical systems, we consistently observe filled stripes. On the
torus, our calculations display features consistent with a doped Mott
insulator, including
antiferromagnetic correlations and suppressed density fluctuations. Our results demonstrate both the promise and current challenges of neural
quantum states for correlated
fermions.
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All authors Louis Sharma, Ahmedeo Shokry, Rajah Nutakki, Olivier Simard, Michel Ferrero, Filippo Vicentini
Mesoscale and Nanoscale Physics
Chirality reversal at finite magnetic impurity strength and local signatures of a topological phase transition
Ruiqi Xu, Arnab Seth and Itamar Kimchi
We study the honeycomb
lattice with a single
magnetic impurity modeled by adding imaginary next-nearest-neighbor hopping ih on a single hexagon. This Haldane defect gives a topological mass term to the gapless Dirac cones and generates chirality. For a small density of defects Neehus et al [arXiv:2405.19289] found that the system's chirality reverses at a critical hc ~ 0.95 associated with an unexpected tri-critical point of Dirac
fermions at zero defect density. We investigate this zero-density limit by analyzing a single defect and computing two experimentally relevant measures of chirality: (1) orbital magnetization via local Chern marker, a bulk probe of all occupied states; and (2) electronic currents of low-energy states. Both probes show a chirality reversal at a critical hc ~ 0.9–1. Motivated by this consistency we propose a defect-scale toy model whose low energy states reverse their chirality at hc' ~ 0.87. Remarkably, the same pair of zero energy bound states also generate the critical point hc in the full
impurity projected T-
matrix. Our results show how the chirality reversal produced by an
impurity can be observed either in local probes or in the global
topology and suggest a possible role of the microscopic defect structure at the critical point.
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Statistical Mechanics · Cross-listed from quant-ph
The Magic Barrier before Thermalization
Lukas Ebner, Berndt Müller, Andreas Schäfer et al. (+3 more)
We investigate the time dependence of anti-flatness in the
entanglement spectrum, a measure for non-stabilizerness and lower bound for non-local
quantum magic resource, on a subsystem of a linear SU(2) plaquette chain during thermalization. Tracing the time
evolution of a large number of initial states, we find that the anti-flatness exhibits a barrier-like maximum during the time period when the
entanglement entropy of the subsystem grows rapidly from the initial value to the microcanonical
entropy. The location of the peak is strongly correlated with the time when the
entanglement exhibits the strongest growth. This behavior is found for generic highly excited initial computational basis states and persists for coupling constants across the ergodic regime, revealing a universal structure of the
entanglement spectrum during thermalization. We conclude that quantitative simulations of thermalization for nonabelian gauge theories require
quantum computing. We speculate that this property generalizes to other
quantum chaotic systems, a
conjecture supported by analogous behavior observed in real-time simulations of the mixed-field Ising model.
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All authors Lukas Ebner, Berndt Müller, Andreas Schäfer, Leonhard Schmotzer, Clemens Seidl, Xiaojun Yao
Quantum Gases · Cross-listed from quant-ph
Observation of ballistic plasma and memory in high-energy gauge theory dynamics
Daniel K. Mark, Federica M. Surace, Thomas Schuster et al. (+4 more)
Gauge theories describe the fundamental forces of nature. However, high-energy dynamics, such as the formation of
quark-
gluon plasmas, is notoriously difficult to model with classical methods.
Quantum simulation offers a promising alternative in this regime, yet experiments have mainly probed low energies. Here, we observe the formation of a ballistic
plasma and long-time
memory effects in high-energy gauge theory dynamics on a high-precision
quantum simulator. Both observations are unexpected, as the initial state - fully filled with particle-antiparticle pairs - was thought to rapidly thermalize. Instead, we find correlations spreading ballistically to long distances and a
memory of charge clusters. Our observations cannot be explained by many-body scars, but are captured by a new theory of
plasma oscillations between electric field and current operators, persisting all the way to the continuum limit of the (1+1)D Schwinger model, of which we simulate a
lattice version. Adapting techniques from
quantum optics, we visualize
plasma oscillations as rotations of Wigner distributions, leading to a novel set of predictions which we test in experiment and numerics. The new framework encompasses both our scenario and scars, which show up as coherent states of the
plasma. The experimental surprises we observe in the high-energy dynamics of a simple gauge theory point to the potential of high-precision
quantum simulations of gauge theories for general scientific discovery.
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All authors Daniel K. Mark, Federica M. Surace, Thomas Schuster, Adam L. Shaw, Wenjie Gong, Soonwon Choi, Manuel Endres
Strongly Correlated Electrons
Spinon mediation of witness spin dynamics in herbertsmithite
Hiroto Takahashi, Jack Murphy, Mitikorn Wood-Thanan et al. (+12 more)
The kagome
lattice of
spin-1/2 copper atoms in herbertsmithite is conjectured to sustain a
quantum spin liquid state with spinon quasiparticles. Ideally, the kagome
crystal planes are each separated by a plane of spinless zinc atoms. However, in real
crystals some
spin-1/2 copper atoms substitute randomly onto these inter-kagome zinc sites. Here we reconceptualize such '
impurity' atoms as
quantum witness
spins whose dynamics is designed to probe the
spin liquid state. We then introduce
spin noise spectroscopy to measure the frequency and temperature dependence of witness
spin dynamics, demonstrating that their phenomenology is consistent with extensive interactions between witness
spins mediated by propagation of spinons through a
quantum spin liquid. Ultimately, a sharp transition occurs at around 260 mK, below which the properties of both
spin noise and
magnetic susceptibility suggest that the witness
spins form a
spin glass phase. Among theoretical models considered, we demonstrate that our observations are only consistent with spinon-mediated interactions between witness
spins by either a Z2 or U(1)
quantum spin liquid, with the former model more closely matching the data. Our work demonstrates that
quantum mechanical witness
spins may now conceivably be used as a widely applicable probe of
quantum spin liquid physics.
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All authors Hiroto Takahashi, Jack Murphy, Mitikorn Wood-Thanan, Pascal Puphal, Miguel-Ángel Sánchez-Martínez, Fabian Jerzembeck, Chun-Chih Hsu, Jonathan Ward, Masahiko Isobe, Yosuke Matsumoto, Hidenori Takagi, Stephen J. Blundell, Michael R. Norman, Felix Flicker, J. C. Séamus Davis
Quantum Gases
Finite-temperature phase diagram and collective modes of coherently coupled Bose mixtures
Sunilkumar V Rajat, Sandeep Gautam and Arko Roy
We investigate the
ferromagnetic-paramagnetic phase transition in coherently (Rabi) coupled Bose-Einstein condensates at zero and finite temperatures, exploring different routes to the transition by tuning the Rabi coupling or increasing the temperature at a fixed coupling. Using the Hartree-Fock-Bogoliubov theory within the Popov approximation, we map out the finite-temperature phase diagram of a three-dimensional homogeneous condensate and identify the critical line through the softening of the
spin gap. Magnetization and the
spin dispersion branch reveal the progressive suppression of the
ferromagnetic order with increasing temperature. In quasi-one-dimensional harmonic traps, the transition, driven by Rabi coupling, is inferred through the softening of the
spin breathing mode with its minimum shifting to lower coupling values with increasing temperature. Notably, the thermally driven transition causes monotonic hardening of all the
spin modes. For both coupling and temperature-driven transition, the hybridized density modes in the
ferromagnetic phase acquire more density character while approaching the critical point.
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Materials Science
Strain-induced multiferroicity in Cr1/3NbS2
Y. Sun, Y. Ahn, D. Sapkota et al. (+7 more)
Multiferroic materials, in which electric polarization and
magnetic order coexist and couple, offer rich opportunities for both fundamental discovery and technology. However, multiferroicity remains rare due to conflicting electronic requirements for ferroelectricity and magnetism. One route to circumvent this challenge is to exploit the noncollinear ordering of
spin cycloids, whose
symmetry permits the emergence of polar order. In this work, we introduce another pathway to multiferroic order in which strain generates polarization in materials that host nonpolar
spin spirals. To demonstrate this phenomenon, we chose the
spin spiral in the well-studied helimagnet Cr1/3NbS2. To detect the induced polarization, we introduce the technique of magnetoelectric birefringence (MEB), an optical probe that enables spatially-resolved and unambiguous detection of polar order. By combining MEB imaging with strain engineering, we confirm the onset of a polar vector at the
magnetic transition, establishing strained Cr1/3NbS2 as a type-II multiferroic.
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All authors Y. Sun, Y. Ahn, D. Sapkota, H. S. Arachchige, R. Xue, S. Mozaffari, D. G. Mandrus, L. Zhao, J. Orenstein, V. Sunko
Materials Science
Deterministic hBN bubbles as a versatile platform for studies on single-photon emitters
Piotr Tatarczak, Tomasz Fąs, Jan Pawłowski et al. (+5 more)
Single-
photon emitters (SPEs) in two-dimensional materials are highly promising candidates for
quantum technologies. SPEs in hexagonal boron nitride (hBN) have been widely investigated, but mostly in exfoliated or powder samples that require an activation process, making it difficult to compare studies and reproduce results. Here, we address this problem and propose a platform based on large-area metaloraganic vapour phase epitaxy (MOVPE)-grown hBN, which combines reproducibility and scalability with the ability to readily host SPEs without activation. Through the creation of bubbles via electron-beam irradiation, we achieve additional functionalities, including an interference-mediated enhancement of emission by approximately 100-200%, dedicated structures that allow the relocation of individual emitters across different systems, and the opportunity to investigate strain-induced effects. Moreover, in contrast to other gas-filled bubbles that deflate at low temperatures, our bubbles remain stable under cryogenic conditions, allowing studies as a function of temperature. To improve the control over the shape and position of bubbles, we demonstrate a~mask-based method that enables deterministic control over bubble formation. The presented hBN bubbles constitute a versatile platform for reproducible studies of hBN-based emitters, providing a reliable insight into their nature and properties.
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All authors Piotr Tatarczak, Tomasz Fąs, Jan Pawłowski, Aleksandra Krystyna Dąbrowska, Jan Suffczyński, Piotr Wróbel, Andrzej Wysmołek, Johannes Binder
Statistical Mechanics
Flux confinement-deconfinement transition of dimer-loop models on three-dimensional bipartite lattices
Souvik Kundu and Kedar Damle
Motivated by recent work that mapped the low-temperature properties of a class of frustrated
spin $S=1$ kagome antiferromagnets with competing exchange and single-ion anisotropies to the fully-packed limit (with each vertex touched by exactly one dimer or nontrivial loop) of a system of dimers and nontrivial (length $s > 2$) loops on the honeycomb
lattice, we study this fully-packed dimer-loop model on the three-dimensional bipartite cubic and diamond
lattices as a function of $w$, the relative fugacity of dimers. We find that the $w \rightarrow 0$ O($1$) loop-model limit is separated from the $w \rightarrow \infty$ dimer limit by a
geometric phase transition at a nonzero finite critical fugacity $w_c$: The $w>w_c$ phase has short loops with an exponentially decaying loop-size distribution, while the $w<w_c$ phase is dominated by large loops whose loop-size distribution is governed by universal properties of the critical O($1$) loop soup. This transition separates two distinct Coulomb
liquid phases of the system: Both phases admit a description in terms of a fluctuating divergence-free polarization field $P_{\mu}(\mathbf{r})$ on links of the
lattice and are characterized by dipolar correlations at long distances. The transition at $w_c$ is a flux confinement-deconfinement transition. Equivalently, and independent of boundary conditions, half-integer test charges $q=\pm 1/2$ are confined for $w>w_c$, but become deconfined in the small-$w$ phase. Although both phases are unstable to a nonzero fugacity for the charge $\pm 1/2$ excitations, the destruction of the $w >w_c$ Coulomb
liquid is characterized by an interesting slow crossover, since test charges with $q=\pm 1/2$ are confined in this phase.
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Materials Science
Ab-initio calculation of magnetic exchange interactions using the spin-spiral method in VASP: Self-consistent versus magnetic force theorem approaches
Umit Dogan Daglum, Maria Stamenova, Ersoy Sasioglu et al. (+1 more)
We present an ab initio investigation of
magnetic exchange interactions using the
spin-spiral method implemented in the VASP code, with a comparative analysis of the self-consistent (SC) and
magnetic force
theorem (MFT) approaches. Using representative 3d ferromagnets (Fe, Co, Ni) and Mn-based full Heusler compounds, we compute
magnon dispersion relations directly from
spin-spiral total energies and extract real-space Heisenberg exchange parameters via
Fourier transformation. Curie temperatures are subsequently estimated within both the mean-field and random-phase approximations. The SC
spin-spiral calculations yield exchange parameters and
magnon spectra in excellent agreement with previous theoretical data, confirming their quantitative reliability across different classes of
magnetic systems. In contrast, the MFT approach exhibits systematic quantitative deviations: it overestimates
spin-spiral energies and exchange couplings in high-moment systems such as bcc Fe and the Mn-based Heuslers, while underestimating them in low-moment fcc Ni. The magnitude of these discrepancies increases strongly with
magnetic moment size, exceeding several hundred percent in the high-moment compounds. These findings underscore the decisive role of self-consistency in accurately determining
magnetic exchange parameters and provide practical guidance for future first-principles studies of
spin interactions and excitations using the
spin-spiral technique.
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All authors Umit Dogan Daglum, Maria Stamenova, Ersoy Sasioglu, Stefano Sanvito
Statistical Mechanics · Cross-listed from quant-ph
Quantum Synchronization of Perturbed Oscillating Coherences
Yi J. Zhao, Joel E. Moore, Juzar Thingna et al. (+1 more)
Quantum mutual synchronization has recently been explored through the persistent oscillation of local observables that arises from undamped eigenmodes of dissipative dynamics. However, these oscillating modes require strictly fine-tuning the system to satisfy algebraic constraints. Here, we investigate the robustness of synchronization against generic perturbations that break these constraints. We identify conditions under which the steady state of the perturbed system exhibits correlations that indicate mutual synchronization, even as the oscillations decay. That synchronization persists as imprints in the time-independent, asymptotic steady state directly bridges the dynamical notion of synchronization with the steady-state notion, which have so far been treated as distinct phenomena. Moreover, we discover in a
spin-1 model that the resulting steady-state synchronization is manifested in unexpected geometries of locked phases that are multiples of $\pi/3$. Our work establishes a link between the two primary paradigms of
quantum synchronization while demonstrating its inherent robustness against generic perturbations.
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All authors Yi J. Zhao, Joel E. Moore, Juzar Thingna, Christopher W. Wächtler
Soft Condensed Matter
Disorder to Order Transition in 1D non-reciprocal Cahn-Hilliard Model
Navdeep Rana and Ramin Golestanian
We present the phenomenology of the one dimensional non-reciprocal Cahn Hilliard model for varying non-reciprocity $(\alpha)$ and different boundary conditions. At small $\alpha$, a perturbed uniform state evolves to a defect laden configuration that lacks global polar order. Defects are the sources and sinks of travelling waves. For a given $\alpha$, defects with a unique wave number that increases monotonically with $\alpha$ are selected. A critical threshold $\alpha_c$ marks the onset of a transition to states with finite global polar order. For periodic boundary conditions, above $\alpha_c$, the system shows travelling waves that are completely ordered. In contrast, travelling waves are incompatible with the Neumann and Dirichlet boundary conditions. Instead, for $\alpha \gtrsim \alpha_c$, we find fluctuating domains that show intermittent polar order and at large $\alpha$, the system partitions into two domains with opposite polar order.
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Materials Science · Cross-listed from physics.comp-ph
Optimal parallelisation strategies for flat histogram Monte Carlo sampling
Hubert J. Naguszewski, Christopher D. Woodgate and David Quigley
Flat histogram methods, such as Wang–Landau sampling, provide a means for high-throughput calculation of phase diagrams of atomistic/
lattice model systems. Many parallelisation schemes with varying degrees of complexity have been proposed to accelerate such sampling simulations. In this study, several widely used schemes are benchmarked – both in isolation and in combination – to establish best practice. The schemes studied include energy domain decomposition with both static sizing of energy sub-domains, as well as a dynamic sub-domain sizing scheme which we propose. We also assess the benefits both of replica exchange and of including multiple random walkers per sub-domain, to determine which factors have the largest impact on parallel efficiency. Additionally, the influence of energy sub-domain overlap regions is discussed. As illustrative test cases, we implement and apply the aforementioned strategies to a
lattice-based model describing the internal energy of a substitutional
alloy, studying the AlTiCrMo refractory high-
entropy superalloy as well as the binary CuZn system, both of which crystallographically order into a B2 (CsCl) structure with decreasing temperature. We find that – while all of the proposed strategies confer a non-negligible speedup – parallelisation across energy domains which are non-uniform in size offers the most appreciable performance improvements. This work offers concrete recommendations for which parallelisation strategies should be prioritised to optimally accelerate flat-histogram Monte Carlo simulations.
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Strongly Correlated Electrons
Spinons, solitons and random singlets in the spin-chain compound copper benzoate
Ying Chen, Guijing Duan, Yuejiu Zhao et al. (+15 more)
The $S=1/2$
antiferromagnetic Heisenberg chain is a paradigmatic
quantum system hosting exotic excitations such as spinons and
solitons, and forming random singlet state in the presence of quenched disorder. Realizing and distinguishing these excitations in a single material remains a significant challenge. Using
nuclear magnetic resonance (NMR) on a high-quality single
crystal of copper benzoate, we identify and characterize all three excitation types by tuning the
magnetic field at ultra-low temperatures. At a low field of 0.2 T, a temperature-independent
spin-
lattice relaxation rate ($1/T_1$) over more than a decade confirms the presence of spinons. Below 0.4 K, an additional relaxation channel emerges, characterized by $1/T_1 \propto T$ and a spectral weight growing as $-\ln(T/T_0)$, signaling a random-singlet ground state induced by weak quenched disorder. At fields above 0.5 T, a field-induced
spin gap $\Delta \propto H^{2/3}$ observed in both $1/T_1$ and the Knight shift signifies
soliton excitations. Our results establish copper benzoate as a unique experimental platform for studying one-dimensional
quantum integrability and the interplay of disorder and correlations.
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All authors Ying Chen, Guijing Duan, Yuejiu Zhao, Ning Xi, Bingying Pan, Xiaoyu Xu, Zhanlong Wu, Kefan Du, Shuo Li, Ze Hu, Rui Bian, Xiaoqun Wang, Wei Li, Long Zhang, Yi Cui, Shiyan Li, Rong Yu, Weiqiang Yu
Materials Science · Cross-listed from physics.app-ph
Unlocking High-Throughput Heterojunction Discovery
Thomas W. Gries, Davide Regaldo, Yanyan Duan et al. (+8 more)
Photoluminescence (PL) is a ubiquitous proxy for material quality in optoelectronic devices, widely used for high-throughput materials discovery. However, we demonstrate that in the presence of charge-selective contacts, PL loses its predictive reliability and can exhibit strong quenching even in highly efficient photovoltaic devices under open-
circuit conditions. By combining steady-state and transient PL with contactless transient surface photovoltage measurements we disentangle the intertwined processes of extraction and recombination, clarifying the physical origin of this phenomenon. This joint approach reveals extraction dynamics not captured by PL alone. A digital replica of the interface shows that Coulomb attraction and interfacial recombination are the fundamental mechanisms driving quenching after charge extraction. Based on these insights, we present a decision tree for heterojunction classification and PL interpretation applicable across diverse optoelectronic systems, including photovoltaics, photodetectors, and LEDs. Our approach supports systematic screening and optimization of half-devices, bridging the gap between accelerated materials discovery and accelerated device discovery.
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All authors Thomas W. Gries, Davide Regaldo, Yanyan Duan, Florian Scheler, Maxim Simmonds, Valerio Stacchini, Annamaria Petrozza, Eva Unger, Antonio Abate, Jean-Paul Kleider, Artem Musiienko
Materials Science
Effects of strain on the stability of the metallic rutile and insulating M1 phases of vanadium dioxide
Peter Mlkvik, Lena Geistlich, Nicola A. Spaldin et al. (+1 more)
We present a systematic density-functional theory study of the effects of strain on the structural and electronic properties in vanadium dioxide (VO$_2$), with particular emphasis on its effect on the relative stability of the metallic rutile and the insulating monoclinic M1 phases. We consider various strain conditions that can be related to epitaxial strain present in VO$_2$ films grown on different
lattice planes. Our calculations confirm the dominant role of $c$ axis strain, i.e., along the direction of the V-V dimerization in the M1 phase. Our analysis suggests that this effect stems primarily from the weakening of the
lattice stiffness, with the hopping along the $c$ axis playing a minor role. We also confirm that, in strain scenarios that deform the basal plane, the $c$ axis strain still has a dominant effect on the phase stability.
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All authors Peter Mlkvik, Lena Geistlich, Nicola A. Spaldin, Claude Ederer
Materials Science
Enhancing the Plasmonic Hotspot Density via Structural Engineering of Multi-layered MoO3-Ag-Au Systems Under Extreme Electronic Excitation Conditions for Ultra-Sensitive SERS Applications
Om Prakash, Sharmistha Dey, Mayur Khan et al. (+4 more)
We illustrate ion-beam engineering of MoO3 Ag Au multilayer plasmonic substrates to improve SERS performance, We illustrate ion-beam engineering of MoO3-Ag-Au multilayer plasmonic substrates to improve SERS performance. Orthorhombic {\alpha}-MoO3 microflakes were produced via chemical vapour deposition (CVD) on Si-SiO2 substrates. Thin films of Ag (5 nm) and Au (5 nm) were thermally evaporated onto the MoO3 flakes, and the samples were subjected to 100 MeV Ag8+ swift heavy ion irradiation at fluences of 3e11 and 3e12 ions cm-2. Irradiation causes dewetting of metal films, prompting structural and morphological changes that result in the formation of dispersed Ag-Au nanoparticles, enhanced surface roughness, and defect generation within the MoO3
lattice. X-ray diffraction (XRD) verifies the {\alpha}-MoO3 phase; field emission scanning electron microscopy (FESEM) elucidates nanoparticle formation and surface reorganisation; Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) disclose vibrational alterations and binding-energy shifts in Mo 3d, indicative of oxygen vacancies (V_O) and partial reduction of Mo. SERS measurements of molecular probes demonstrate significantly increased Raman intensities following ion irradiation.
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All authors Om Prakash, Sharmistha Dey, Mayur Khan, Abhijith T, Udai Bhan Singh, Ambuj Tripathi, Santanu Ghosh
Strongly Correlated Electrons
Improved time-translationally invariant tensor network influence functional method for Anderson impurity problems
Zhijie Sun, Zhenyu Li and Chu Guo
The Anderson
impurity model (AIM) is of fundamental importance in condensed matter physics for studying strongly correlated phenomena. However, accurately simulating its long-time dynamics still remains a significant numerical challenge. A class of recently developed numerical approaches represents the Feynman-Vernon influence functional (IF), which encodes all the bath effects on the
impurity, as a
matrix product state (MPS) in the temporal domain. The computational cost of this approach is largely determined by the bond dimension $\chi$ of the temporal MPS. In this work, we propose an efficient and accurate method that, when the hybridization function in the IF can be approximated as a sum of $n$ exponential functions, systematically constructs the IF as an MPS by multiplying $O(n)$ small MPSs, each with bond dimension $2$. Our method yields a worst case scaling of $\chi$ as $2^{8n}$ and $2^{2n}$ for real- and imaginary-time
evolution respectively. We demonstrate the performance of our method for two commonly used bath spectral functions, and show that the required bond dimensions are significantly smaller than the worst case.
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Statistical Mechanics
Nonanaliticities and ergodicity breaking in noninteracting many-body dynamics via stochastic resetting and global measurements
David Soldner, Igor Lesanovsky and Gabriele Perfetto
Stochastic resetting generates nonequilibrium steady states by interspersing
unitary quantum dynamics with resets at random times. When the state to which the system is reset is chosen conditionally on the outcome of a global and spatially resolved measurement, the steady state can feature collective behavior similar to what is typically observed at phase transitions. Here we investigate such conditional reset protocol in a system of noninteracting
spins, where the reset state is chosen as a magnetization eigenstate, that is selected (conditioned) on the outcome of a previous magnetization measurement. The stationary states that emerge from this protocol are characterized by the density of
spins in a given magnetization eigenstate, which is the analogue of the order parameter. The resulting stationary phase diagram features multiple nonanalytic points. They are of first-order type for half-integer
spin, while multicritical behavior, signalled by both first and second-order discontinuities, is found for integer
spin. We also show that the associated dynamics is nonergodic, i.e., which stationary state the system ultimately assumes is determined be the initial state. Interestingly, the mechanism underlying these phenomena does not rely on interactions, but the emergent nonlinear behavior is solely a consequence of correlations induced by the measurement.
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Mesoscale and Nanoscale Physics
Intermediate chiral edge states in quantum Hall Josephson junctions
Partha Sarathi Banerjee, Rahul Marathe and Sankalpa Ghosh
A transfer-
matrix-based theoretical framework is developed to study transport in
superconductor-
quantum Hall-
Superconductor (SQHS) Josephson junctions modulated by local potential barriers in the
quantum-
Hall regime. The method allows one to evaluate the change in the conductivity of such SQHS Josephson junctions contributed by the intermediate
chiral edge states (ICES) induced by these local potential barriers at their electrostatic boundaries at specific electron filling-fractions. It is particularly demonstrated how these ICES created at different Landau levels (LL) overlap with each other through intra- and inter-LL ICES mixing with the change in strength and width of the potential barriers. This results in different mechanisms for forming Landau bands when an array of such potential barriers are present. It is also demonstrated that our theoretical framework can be extended to study the
lattice effect in a bounded domain in such SQHS Josephson junctions by simultaneously submitting the normal region to a transverse
magnetic field and periodic potential.
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Strongly Correlated Electrons
A minimal and universal representation of fermionic wavefunctions (fermions = bosons + one)
Liang Fu
Representing fermionic wavefunctions efficiently is a central problem in
quantum physics, chemistry and materials science. In this work, we introduce a universal and exact representation of continuous antisymmetric functions by lifting them to continuous symmetric functions defined on an enlarged space. Building on this lifting, we obtain a parity-graded representation of fermionic wavefunctions, expressed in terms of symmetric feature variables that encode particle configuration and antisymmetric feature variables that encode exchange statistics. This representation is both exact and minimal: the number of required features scales as $D\sim N^d$ ($d$ is spatial dimension) or $D\sim N$ depending on the symmetric feature maps employed. Our results provide a rigorous mathematical foundation for efficient representations of fermionic wavefunctions and enable scalable and systematically improvable neural network solvers for many-electron systems.
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Materials Science
Host-atom-driven transformation of a honeycomb oxide into a dodecagonal quasicrystal
Martin Haller, Julia Hewelt, V. Y. M. Rajesh Chirala et al. (+5 more)
Dodecagonal
oxide quasicrystals (OQCs) have so far been limited to a few elemental systems, with no general formation mechanism established. Here, we demonstrate a versatile approach to OQC formation via a host-atom-induced transformation of a metal-
oxide honeycomb (HC) network. Adsorption of Ba, Sr, or Eu onto the HC layer triggers its reorganization into a dodecagonal tiling, as revealed by low-energy electron diffraction and scanning tunneling microscopy. Full conversion occurs when 73% of the honeycomb rings are occupied. Kelvin probe and UV photoelectron spectroscopy show a linear decrease in work function with increasing host coverage, followed by a sharp increase upon quasicrystal formation due to reduced host dipoles. This transformation mechanism enables the fabrication of structurally precise OQCs, including a new Eu-Ti-O phase that extends the field to lanthanide quasicrystals, forming a 2D grid of localized
magnetic moments. The method offers a general route to explore
lattice-matched substrates for epitaxial growth and may be adapted to other 2D honeycomb materials - such as
graphene, hexagonal ice, and silica - paving the way for engineered aperiodic systems beyond transition metal
oxides.
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All authors Martin Haller, Julia Hewelt, V. Y. M. Rajesh Chirala, Loi Vinh Tran, Ankur Bhide, Muriel Wegner, Stefan Förster, Wolf Widdra
Mesoscale and Nanoscale Physics
Deterministic Switching in Altermagnets via Asymmetric Sublattice Spin Current
Sayan Sarkar, Sunit Das and Amit Agarwal
We demonstrate a deterministic switching mechanism in collinear altermagnets driven by asymmetric sublattice
spin currents. Unlike conventional antiferromagnets, where combined parity-time-reversal
symmetry enforces purely staggered sublattice
spin torques, altermagnets host
symmetry-protected nonrelativistic
spin splitting that produces unequal torques on the two sublattices. Using doped FeSb$_2$ as a representative $d$-wave altermagnet, our Landau–Lifshitz–Gilbert simulations show that these torques enable
magnetic-field-free and deterministic 180$^\circ$ Néel vector reversal over picosecond timescale. The mechanism is generic to even-parity altermagnets and remains effective even in centrosymmetric, weak
spin-orbit coupled systems, where the Néel
spin-orbit torque mechanism fails. Our results establish an experimentally accessible mechanism for switching of altermagnetic order, opening pathways for realizing ultrafast, low-power altermagnet spintronic devices.
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Superconductivity
Nonequilibrium spin-splitter effect in altermagnet superconductor hybrids
Tim Kokkeler, Tero T. Heikkilä and F. Sebastian Bergeret
We study the nonequilibrium
spin-splitter effect in superconducting altermagnets and
superconductor altermagnet hybrids by computing the alternating
spin current and edge the
spin density in the presence of an alternating electric field. We show that while in the normal state the effect is not sensitive to the field frequency, in the superconducting state, there is a strong effect for frequencies on the scale of $\Delta_0$ or lower. We contrast the effect to the
spin accumulation induced by the
spin-
Hall effect, by showing that for the altermagnet
spin-splitter effect the out-of-phase
spin density does not diverge in the adiabatic limit. This difference is attributed to the absence of any
equilibrium spin-splitter effect in altermagnets. In fact, the out-of-phase component vanishes below the gap excitation frequency $2\Delta_0$, because below this frequency the absence of dissipation and the behavior of the system under time-reversal directly determine the relative phase between the charge current,
spin current, and
spin accumulation. The nonequilibrium effect can be tuned by external parameters like temperature. In fact, it has a nonmonotonic temperature dependence, taking its largest value for temperatures around $0.8T_{c}$. The value at this temperature can be significantly larger than the normal state
spin density or the low temperature
spin density. Thus, besides using the nonequilibrium
spin-splitter effect to identify altermagnets, its tunability makes it also suitable for applications.
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Materials Science
Electron-phonon coupling in magnetic materials using the local spin density approximation
Á. A. Carrasco Álvarez, M. Giantomassi, J. Lihm et al. (+4 more)
Magnetic materials are crucial for manipulating electron
spin and
magnetic fields, enabling applications in data storage, spintronics, charge transport, and energy conversion, while also providing insight into fundamental
quantum phenomena. In numerous applications, the interaction between electrons and
lattice vibrations, known as electron-
phonon coupling, can be of significant importance. In that regard, we extend the EPW package to be able to interpolate the electron-
phonon matrix elements combining perturbation theory and maximally localized Wannier functions. This allows to use dense momentum grids at a reasonable computational cost when computing electron-
phonon-related quantities and physical properties. We validate our implementation considering
ferromagnetic iron and nickel, where we explore the
phonon induced mass enhancement and Eliashberg spectral function finding different importance of each
spin channel for both compounds. Furthermore, we evaluate the carrier resistivity at finite temperatures for both systems, considering the role of the
magnetic phase in carrier transport. Our findings indicate that in the case of Fe, the primary contributor to resistivity is electron-
phonon scattering. In contrast, for Ni, electron-
phonon scattering constitutes less than one-third of the resistivity, underscoring a fundamental difference in the transport properties of the two systems.
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All authors Á. A. Carrasco Álvarez, M. Giantomassi, J. Lihm, G. E. Allemand, M. Mignolet, M. Verstraete, S. Poncé
Mesoscale and Nanoscale Physics
One-dimensional topology and topolectrics of nonsymmorphic Kramers degenerate systems
Max Tymczyszyn and Edward McCann
We describe nonsymmorphic four-band tight-binding models in one dimension with Kramers degeneracy, and propose topolectric-
circuit realizations of their topological phases. We begin with a representative model in the nonsymmorphic AII class with symmorphic time-reversal
symmetry and nonsymmorphic charge-conjugation and
chiral symmetries, resulting in a $\mathbb{Z}_2$ invariant. We also provide a Bogoliubov-de Gennes model in the nonsymmorphic D class with symmorphic charge-conjugation
symmetry and nonsymmorphic time-reversal and
chiral symmetries, which supports a $\mathbb{Z}_4$ classification. To compute these invariants, we extend an open-path winding-number formulation previously used for non-Kramers-degenerate nonsymmorphic $\mathbb{Z}_2$ phases to Kramers-degenerate four-band systems. We propose topolectric
circuit implementations of nonsymmorphic systems, beginning with a comparison between the symmorphic Su-Schrieffer-Heeger and nonsymmorphic charge-density-wave models. We then extend this methodology to topolectric realizations of the AII and $\mathbb{Z}_4$ models, finding that the impedance response reproduces the predicted phase boundaries and associated zero energy modes. Finally, we analyze disorder in the $\mathbb{Z}_4$ model and find that, although disorder breaks the nonsymmorphic
symmetries, certain domain-wall zero modes in the minimal nearest-neighbor model remain pinned at zero energy because the disorder has no first-order coupling to the
soliton subspace; longer-range terms satisfying relevant
symmetries lift this emergent property.
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Soft Condensed Matter
Behavior of passive polymeric tracers of different topologies in a dilute bath of active Brownian particles
Ramanand Singh Yadav, Ralf Metzler and Rajarshi Chakrabarti
Using computer simulations in two dimensions we investigate the dynamics and structure of passive polymeric tracer with different
topologies immersed in a low-density active particle bath. One of the key observations is that
polymer exhibit faster dynamics compared to passive colloidal particles at high activity, for the same particle density, in both linear and
star polymer topologies. This enhanced motion is attributed to the accumulation of active particles, which induces prolonged and persistent movement of the
polymer. Further analysis reveals that
star polymers exhibit more complex and intriguing behavior than their linear counterparts. Notably, the accumulation of active particles promotes the pairing of arms in
star polymers. For instance, a three-armed
star polymer adopts a conformation similar to a linear
polymer with two-arms due to this pairing as a result, at high activity, the dynamics of both the
polymers converge. Finally, we explore the dynamics of a linear
polymer with the same total number of beads as the
star polymer. Interestingly, at high activity – where arm pairing in the
star polymer is significant – the
star polymer demonstrates faster dynamics than the linear
polymer, despite having the identical number of beads. These findings contribute to a broader understanding of the interactions between active and passive components of varying
topologies in dilute systems and highlight their potential for innovative applications ranging from materials science to biomedicine.
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Superconductivity
Superconducting spin valve effect in Fe/Si$_3$N$_4$/Pb/Si$_3$N$_4$/Fe heterostructures
A. A. Kamashev, N. N. Garif'yanov, A. A. Validov et al. (+3 more)
The structures of the superconducting
spin valve (SSV) Fe/Si$_3$N$_4$/Pb/Si$_3$N$_4$/Fe (where Si$_3$N$_4$ is a dielectric insulating layer of controlled thickness) were investigated. The dependence of the magnitude of the SSV effect on the thicknesses of the superconducting (S) and insulating (I) layers was studied. Optimization of the S and I layer thicknesses enabled a complete switching between the normal and superconducting states when the mutual orientation of the magnetizations of the
ferromagnetic (F) layers changed from antiparallel to parallel. A maximal SSV effect value of 0.36\,K was achieved in an external
magnetic field of 1\,kOe. These results demonstrate that SSV structures with tunable S/F interface transparency controlled by insulating interlayers are promising for achieving a significant magnitude of the effect. This opens new avenues for the development of such systems and their potential applications in spintronic devices.
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All authors A. A. Kamashev, N. N. Garif'yanov, A. A. Validov, A. S. Osin, Ya. V. Fominov, I. A. Garifullin