Statistical Mechanics
Approach to zigzag and checkerboard patterns in spatially extended systems
Manoj C. Warambhe and Prashant M. Gade
Zigzag patterns in one dimension or checkerboard patterns in two dimensions occur in a variety of pattern-forming systems. We introduce an order parameter `phase defect' to identify this transition and help to recognize the associated universality class on a discrete
lattice. In one dimension, if $x_{i}(t)$ is a variable value at site $i$ at time $t$. We assign
spin $s_i(t)=1$ for $x_{i}(t)>x_{i-1}(t)$, $s_i(t)=-1$ if $x_{i}(t)<x_{i-1}(t)$, and $s_i(t)=0$ if $x_{i}(t)=x_{i-1}(t)$. The phase defect $D(t)$ is defined as $D(t)={\frac{\sum_{i=1}^N \vert s_i(t)+s_{i-1}(t)\vert} {2N}}$ for a
lattice of $N$ sites with periodic boundary conditions. It is zero for a zigzag pattern. In two dimensions, $D(t)$ is the sum of row-wise as well as column-wise phase defects and is zero for the checkerboard pattern. The persistence $P(t)$ is the fraction of sites whose
spin value did not change even once till time $t$. We find that $D(t)\sim t^{-\delta}$ and $P(t)\sim t^{-\theta}$ for the parameter range over which the zigzag or checkerboard pattern is realized. We observe that $\delta=0.5$ and $\theta=3/8$ for 1-d coupled logistic maps or Gauss maps, and $\theta=0.22$ and $\delta=0.45$ in 2-d logistic or Gauss maps. The exponent $\theta$ matches with the persistence exponent at zero temperature for the Ising model, and $\delta$ matches with the exponent for the Ising model at the critical temperature. This power-law decay is observed over a range of parameter values and not just critical point.
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Superconductivity
Revisiting YH$_9$ Superconductivity and Predicting High-T$_c$ in GdYH$_5$
M. A. Rastkhadiv
The discovery of superconductivity in $\mathrm{YH_{9}}$ with a critical temperature of approximately $T_c\sim 243 \ K$ has opened a new window toward room temperature superconductivity. In this work, we employ the lowest order constrained variational method to investigate the thermodynamic and
magnetic properties of the $\mathrm{YH_{9}}$ structure, obtaining results in good agreement with experimental data. % Based on the robustness of the LOCV approach for describing high-$T_c$
superconductors, we further extend our analysis to the gadolinium-yttrium-hydrogen system across various stoichiometries. The key finding of this study is the prediction of a superconducting phase transition at $T_c = 223.2~\mathrm{K}$ for $\mathrm{GdYH_{5}}$ under a critical pressure of approximately $157~\mathrm{GPa}$. This compound crystallizes in a tetragonal structure with space group $P4/mmm$. Moreover, the calculated gap ratio confirms that $\mathrm{GdYH_{5}}$ is a type-II
superconductor with a critical current density suitable for potential industrial applications.
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Materials Science
Ultra-transient grating spectroscopy for visualization of surface acoustics
Tomáš Grabec, Pavla Stoklasová, Kristýna Repček et al. (+5 more)
Ultrasonic wave propagation across material surfaces reveals essential information about the materials' elastic behavior. All direction- and frequency-dependent features of the propagation are encoded in the Green's function. Here we present a direct experimental visualization of the frequency-domain angle-resolved Green's function, including all its complexity resulting from elastic anisotropy. We achieve this visualization using transient grating spectroscopy (TGS), otherwise well established for measuring Rayleigh-type surface acoustic waves (SAWs). But here we focus on early-time thermoacoustic phenomena in the TGS experiment, revealing that, along with the transient standing-wave patterns of SAWs, there also emerge oscillations with at least an order of magnitude shorter lifetimes. These oscillations superpose into dynamic displacement patterns that are transient with respect to the classical transient timescales in TGS; the optical diffraction signal from these ultra-transient gratings enables capturing the surface acoustic response in full detail. By utilizing this feature, ultra-transient grating spectroscopy (UTGS) opens pathways for studying anisotropic materials.
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All authors Tomáš Grabec, Pavla Stoklasová, Kristýna Repček, Jakub Kušnír, David Mareš, Martin Ševčík, Petr Sedlák, Hanuš Seiner
Disordered Systems and Neural Networks · Cross-listed from stat.ML
High-Dimensional Learning Dynamics of Quantized Models with Straight-Through Estimator
Yuma Ichikawa, Shuhei Kashiwamura and Ayaka Sakata
Quantized neural network training optimizes a discrete, non-differentiable objective. The straight-through
estimator (STE) enables backpropagation through surrogate gradients and is widely used. While previous studies have primarily focused on the properties of surrogate gradients and their convergence, the influence of quantization hyperparameters, such as bit width and quantization range, on learning dynamics remains largely unexplored. We theoretically show that in the high-dimensional limit, STE dynamics converge to a deterministic ordinary differential equation. This reveals that STE training exhibits a plateau followed by a sharp drop in generalization error, with plateau length depending on the quantization range. A fixed-point analysis quantifies the asymptotic deviation from the unquantized linear model. We also extend analytical techniques for
stochastic gradient descent to nonlinear transformations of weights and inputs.
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Strongly Correlated Electrons
Santhosh M, Jorge Dukelsky and Gerardo Ortiz
We present and analyze an exactly solvable interacting fermionic pairing model, which features interactions that entangle states at momenta $\mathbf{k}$ and $-\mathbf{k}$. These interactions give rise to novel correlated ground states, leading to a rich phase diagram that includes superconducting, multiple metallic, and Mott-insulating phases. At finite interaction strengths, we observe the emergence of multiple many-body
Fermi surfaces, which violate Luttinger's
theorem and challenge the conventional Landau-
Fermi liquid paradigm. A distinguishing feature of our model is that it remains
quantum integrable, even with the addition of pairing interactions of various
symmetries, setting it apart from the Hatsugai-Kohmoto model. Our results provide an analytically tractable framework for studying strong correlation effects that give rise to fractionalized excitations and unconventional superconductivity, offering valuable insights into a broad class of integrable many-body systems.
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Soft Condensed Matter · Cross-listed from math-ph
A topological counting rule for shells
Hussein Nassar
Holding a shell in their hands, one can apply six loads: three by pulling and shearing, and three by bending and twisting. Here, it is shown that the shell resists exactly three load cases and comply with the other three, provided the shell is simply connected, meaning it has no holes and no handles. Formally, it is shown that the space of homogeneous membrane and bending strains, defined in the sense of plate theory, that can be relaxed into an infinitesimal isometry by a periodic, or a statistically homogeneous, deflection is three-dimensional for any simply-connected periodic, or statistically homogeneous, shell, be it corrugated, creased or wrinkled.
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Materials Science
Near-room-temperature antiferromagnetism in Janus Fe$X$F ($X$ = O, S) monolayers
Xixiang Zhang, Busheng Wang, Yanfeng Ge et al. (+2 more)
Inspired by the recently synthesized hexagonal layered phase of FeF$_2$, we studied the
magnetic properties of the 1T-FeF$_2$ monolayer and its Janus Fe$X$F ($X$ = O, S) derivatives by first-principles calculations. Our results confirm that these materials are
antiferromagnetic semiconductors, and that anion substitution effectively tunes their material properties: the band gap shifts from 3.37 eV (direct, FeF$_2$) to 2.35 eV (direct, FeOF) and 1.13 eV (indirect, FeSF); the
magnetic moment of Fe ions increases; and the Néel temperature ($T_N$) rises dramatically to 248 K (FeSF) and 207 K (FeOF). Janus structures exhibit enhanced
magnetic moment and direct AFM coupling. Under compression, $T_N$ is further optimized to 274 K ($-2$% strain, FeSF) and 244 K ($-5$% strain, FeOF). Both Janus materials retain their semiconducting nature and direction of easy magnetization axis under $\pm5$% strain. This study validates the Janus structure as a viable approach to enhance 2D antiferromagnetism and highlights Fe-based oxyhalides as promising spintronic materials.
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All authors Xixiang Zhang, Busheng Wang, Yanfeng Ge, Yong Liu, Wenhui Wan
Mesoscale and Nanoscale Physics
Non-unitary Time Evolution via the Chebyshev Expansion Method
Áron Holló, Dániel Varjas, Cosma Fulga et al. (+2 more)
The Chebyshev expansion method is a well-established technique for computing the time
evolution of
quantum states, particularly in Hermitian systems with a bounded spectrum. Here, we show that the applicability of the Chebyshev expansion method extends well beyond this constraint: It remains valid across the entire complex plane and is thus suitable for arbitrary non-Hermitian
matrices. We identify that numerical rounding errors are the primary source of errors encountered when applying the method outside the conventional spectral bounds, and they are not caused by fundamental limitations. By carefully selecting the spectral radius and the time step, we show how these errors can be effectively suppressed, enabling accurate time
evolution calculations in non-Hermitian systems. We derive an analytic upper bound for the rounding error, which serves as a practical guideline for selecting time steps in numerical simulations. As an application, we illustrate the performance of the method by computing the time
evolution of wave packets in the Hatano-Nelson model.
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All authors Áron Holló, Dániel Varjas, Cosma Fulga, László Oroszlány, Viktor Könye
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Quantum-Squeezing-Induced Algebraic Non-Hermitian Skin Effects and Ultra Spectral Sensitivity
Zhao-Fan Cai and Tao Liu
The well-established non-Bloch band theory predicts exponential localization of skin-mode eigenstates in one-dimensional (1D) non-Hermitian systems. Recent studies, however, have uncovered anomalous algebraic localization in higher dimensions. Here, we extend these ideas to Hermitian bosonic quadratic
Hamiltonians incorporating
quantum squeezing, offering a genuine
quantum framework to explore non-Hermitian phenomena without external reservoirs. We construct a two-dimensional (2D) bosonic
lattice model with two-mode squeezing and study its spectral properties of bosonic excitation within the Bogoliubov-de Gennes (BdG) formalism. We demonstrate an algebraic non-Hermitian skin effect (NHSE), characterized by quasi-long-range power-law localization of complex eigenstates. The system shows ultra spectral sensitivity to double infinitesimal on-site and long-range hopping
impurities, while remaining insensitive to single
impurities. Analytical treatment via the Green's function reveals that this sensitivity originates from the divergence of the nonlocal Green's function associated with the formation of nonlocal bound states between
impurities. Our study establishes a framework for realizing novel higher-dimensional non-Hermitian physics in Hermitian bosonic platforms such as superconducting
circuits, photonic
lattices, and optomechanical arrays, with the demonstrated ultraspectral sensitivity enabling
quantum sensing and amplification via bosonic squeezing.
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Materials Science
Topology and Martensitic Phase Transformations
M. Yin and D. D. Vvedensky
Triply periodic minimal surfaces (TPMS) are discovered to conform to surfaces of given charge density distributions embedded in
crystals [Z. Kristallogr. 170, 138 (1985)]. Based on our previous work [Phys. Rev. Mater. 9, 073802 (2025)], we discovered that
crystals can have surfaces of a given charge density converging to TPMS. We also discovered that end states connected by a martensitic phase transformation should have their corresponding TPMS being topologically equivalent. In this work, we gave an explanation for the topological continuity of a martensitic phase transformation and studied how TPMS indicate whether a non-
magnetic crystal can undergo a martensitic phase transformation or not.
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Materials Science
Weak-anti-localization-to-spin-dependent scattering at a proximity-magnetized heavy metal interface
Hisakazu Matsuki, Guang Yang, Jiahui Xu et al. (+9 more)
A change in a materials electrical resistance with
magnetic field (magnetoresistance) results from
quantum interference effects and, or
spin-dependent transport, depending on materials properties and dimensionality. In disordered conductors, electron interference leads to weak localization or anti-localization; in contrast,
ferromagnetic conductors support
spin-dependent scattering, leading to
giant magnetoresistance (GMR). By varying the thickness of Au between 4 and 28 nm in a EuS/Au/EuS
spin-switches, we observe a crossover from weak anti-localization to interfacial GMR. The crossover is related to a
magnetic proximity effect in Au due to electron scattering at the insulating EuS interface. The proximity-induced exchange field in Au suppresses weak anti-localization, consistent with Maekawa-Fukuyama theory. With increasing Au thickness, GMR emerges along with
spin Hall magnetoresistance. These findings demonstrate
spin transport governed by interfacial exchange fields, building a framework for spintronic functionality without metallic magnetism.
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All authors Hisakazu Matsuki, Guang Yang, Jiahui Xu, Vitaly N. Golovach, Yu He, Jiaxu Li, Alberto Hijano, Niladri Banerjee, Iuliia Alekhina, Nadia Stelmashenko, F. Sebastian Bergeret, Jason W. A. Robinson
Mesoscale and Nanoscale Physics
RKKY interaction in Weyl semimetal nanowires
Rohit Mukherjee and Asutosh Dubey
We investigate the effective couplings induced between localized
impurities on the surface of a Weyl semimetal (WSM) nanowire within the framework of Ruderman–Kittel–Kasuya–Yosida (RKKY) theory. The itinerant electrons from the
chiral Fermi arc surface states mediate
impurity-
impurity interaction at low energies. As a result, the
spin-momentum locking naturally plays a central role in shaping the
spin-
spin correlations. We show that the dominant interaction channels have distinct origins: while the azimuthal coupling, $J_{\phi\phi}$ term arises exclusively from
Fermi arc states with identical
spin polarization, the couplings $J_{\mu\nu}$ ($\mu,\nu = z,r$) are governed by
Fermi arc states with opposite
spin polarizations. Furthermore, we demonstrate that purely surface-mediated contributions exhibit different scaling behavior compared to those involving
Fermi arcs and low-energy bulk states. We systematically untangle the contributions from bulk and surface states to the RKKY couplings, using analytical and numerical methods. Our results establish WSM nanowires as a versatile platform for engineering and simulating a broad class of
spin models.
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Statistical Mechanics · Cross-listed from quant-ph
Uniformity Bias in Ground-State Sampling Induced by Replica Alignment in Quantum Monte Carlo for Quantum Annealing
Naoki Maruyama, Masayuki Ohzeki and Kazuyuki Tanaka
Quantum annealing (QA) with a transverse field often fails to sample degenerate ground states fairly, limiting applicability to problems requiring diverse optimal solutions. Although
Quantum Monte Carlo (QMC) is widely used to simulate QA, its ability to reproduce such unfair ground-state sampling remains unclear because
stochastic and coherent
quantum dynamics differ fundamentally. We quantitatively evaluate how accurately QMC reproduces the sampling bias in QA by comparing the final ground-state distributions from the QMC master equation and the Schrödinger equation. We find QMC tends to produce uniform ground-state probabilities, unlike QA's biased distribution, and that this uniformity bias strengthens as annealing proceeds. Our analysis reveals that this bias originates from replica
alignment – the dominance of configurations in which all Trotter replicas coincide – caused by the energetic suppression and entropic reduction of kink configurations (replica mismatches). These findings clarify a fundamental limitation of discrete-time QMC in faithfully simulating QA dynamics, highlighting the importance of replica correlations and transition rules in achieving realistic ground-state sampling.
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Materials Science
Breaking the Sabatier Principle by Dynamic Adsorption-Desorption Decoupling in Electrocatalytic Hydrogen Evolution
Zi-Xuan Yang, Lei Li, Tao Huang et al. (+5 more)
The Sabatier principle establishes a fundamental trade-off in heterogeneous electrocatalysis.In the hydrogen
evolution reaction (HER), this trade-off is manifested by the coupling of Volmer step, which requires strong hydrogen adsorption, with the Heyrovsky/Tafel step, which favors facile desorption, thus giving rise to the classical volcano relationship and limiting activity even at $\Delta G=0$. Here, we demonstrate a ferroelectric platform with dynamic tunability – monolayer GeS$_2$ decorated with transition metal atoms as a proof-of-concept – where polarization-driven surface electronic reconstruction enables real-time modulation of intermediate binding strength, thereby breaking the Sabatier constraint. Reversible control of hydrogen adsorption allows strong H binding to accelerate the Volmer step, followed by weakened adsorption to promote the Heyrovsky/Tafel step.This dynamic adsorption-desorption decoupling not only surpasses the volcano limit to achieve unprecedented HER activity, but also establishes a general paradigm for designing adaptive electrocatalysts capable of reconfiguring under operating conditions.
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All authors Zi-Xuan Yang, Lei Li, Tao Huang, Hui Wan, X.S. Wang, Gui-Fang Huang, Wangyu Hu, Wei-Qing Huang
Materials Science
Near room temperature magnetoelectric response and tunable magnetic anisotropy in the two-dimensional magnet 1T-CrTe2
Fengping Li, Bheema Lingam Chittari, Chao Lei et al. (+1 more)
Magnets with controllable magnetization and high critical temperature are essential for practical spintronics devices, among which the two-dimensional 1T-CrTe2 stands out because of its high experimental critical temperature up to about 300K down to the single layer limit. By using ab initio density functional theory, we investigate the
magnetic properties of monolayer and
bilayer 1T-CrTe2 and demonstrate that the
magnetic properties, such as the magnetocrystalline anisotropy, critical Curie temperature and magnetizations, can be influenced by strain or electric fields.
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All authors Fengping Li, Bheema Lingam Chittari, Chao Lei, Jeil Jung
Superconductivity
Supercurrent interference and its transfer in a kagome superconductor
Heng Wu, Houssam el Mrabet Haje, Michiel Dubbelman et al. (+4 more)
Superconductivity represents a macroscopic
quantum state notable for its rich manifestations of electronic coherence and collective behavior. Kagome materials AV3Sb5 (A= K, Cs, Rb) possess cascade intertwined
quantum phases including superconductivity,
symmetry-breaking charge orders, nematic orders and topological states, making them attractive materials for exploring exotic superconducting states. However, the superconducting properties and the Cooper pairing behaviors have not been fully explored and understood. In this work, by studying both the magnetoresistance and critical current behaviors in KV3Sb5 ring and pristine flakes, we reveal the charge 2e paring in KV3Sb5 although anomalous oscillations with smaller periodicity were observed, and report the intrinsic superconducting phase coherence in KV3Sb5 flakes. The former is demonstrated by the careful verification of the Little-Parks oscillations in differential resistance colormaps, and the latter indicates the existence of superconducting domains in KV3Sb5. Moreover, we observed a special phenomenon: the transfer of supercurrent interference patterns between the superconducting ring and the superconducting flake, which demonstrates the global critical current effect of the superconducting phase coherence. These findings provide new insights into the Cooper pairing behaviors in KV3Sb5 and highlight the importance of global effect of superconducting phase coherence in the understanding of the superconducting behaviors.
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All authors Heng Wu, Houssam el Mrabet Haje, Michiel Dubbelman, Brenden R. Ortiz, Stephen D. Wilson, Mazhar N. Ali, Yaojia Wang
Mesoscale and Nanoscale Physics
Robust protocols to reveal anyonic time-exchange phase
Ines Safi
We consider hierarchical
quantum Hall edge states with $N$ modes and a spatially local
quantum point contact (QPC). In general, the field of an injected anyon does not directly acquire the universal statistical phase $\theta$. Short-range inter-edge interactions split the universal anyon charge and phase into $N$ fractionalized charges associated with nonuniversal phases $\pi\delta_m$. In contrast, their sum $\delta=\sum_{m=1}^N\delta_m$, which defines the local scaling dimension at the QPC, remains protected and is tied to the statistical angle through $\pi\delta=\theta$. If the injected anyon is of the same species as the one dominating backscattering at the QPC, time-domain braiding with phase $\theta$ is recovered either in the absence of inter-edge interactions with equal mode velocities, or by performing a spatially local anyon injection at the QPC. We then exploit a more robust local anyonic time-exchange (ATE) link between anyons and quasiholes at the QPC, which is also a necessary ingredient for realizing such braiding. This allows us to propose minimal single-QPC protocols that do not rely on diluted anyon sources and that disentangle the role of $\theta$ as a genuine statistical phase from that as a scaling dimension. From the ATE link we derive two novel nonequilibrium fluctuation–dissipation relations (FDRs) that isolate $\theta$. They relate the DC backscattering noise either to an integral over the DC current or to the phase shift of the AC current with respect to an applied AC voltage (i.e., the phase of the admittance), accessible down to low frequencies. For thermalized edges, we show that in the
quantum regime this admittance phase directly yields $\theta$ whenever $\delta>1/2$.
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Materials Science
A ferroelectric junction transistor memory made from switchable van der Waals p-n heterojunctions
Baoyu Wang, Lingrui Zou, Tao Wang et al. (+18 more)
Van der Waals (vdW) p-n heterojunctions are important building blocks for advanced electronics and optoelectronics, in which high-quality heterojunctions essentially determine device performances or functionalities. Creating tunable depletion regions with substantially suppressed leakage currents presents huge challenges, but is crucial for heterojunction applications. Here, by using band-aligned p-type SnSe and n-type ferroelectric {\alpha}-In2Se3 as a model, we report near-ideal multifunctional vdW p-n heterojunctions with small reverse leakage currents (0.1 pA) and a desired diode ideality factor (1.95). We realize ferroelectric-tuned band
alignment with a
giant barrier modulation of 900 meV. Based on such tunable heterojunctions, we propose and demonstrate a fundamental different
memory device termed ferroelectric junction field-effect transistor
memory, which shows large
memory windows (1.8 V), ultrafast speed (100 ns), high operation temperature (393 K), and low cycle-to-cycle variation (2%). Additionally, the reliable synaptic characteristics of these
memory devices promise low-power neuromorphic computing. Our work provides a new device platform with switchable
memory heterojunctions, applicable to high performance
brain-inspired electronics and optoelectronics.
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All authors Baoyu Wang, Lingrui Zou, Tao Wang, Lijun Xu, Zexin Dong, Chuan Qin, Xin He, Shangui Lan, Yinchang Ma, Meng Tang, Maolin Chen, Chen Liu, Zheng-Dong Luo, Lijie Zhang, Zhenhua Wu, Yan Liu, Genquan Han, Bin Yu, Xixiang Zhang, Kai Chang, Fei Xue
Mesoscale and Nanoscale Physics
Constructing a Nanopipette-based DNA Electro-Mechanical Device
Cengiz J. Khan, Oliver J. Irving, Rand A. Al-Waqfi et al. (+2 more)
Solid-state nanopore and nanopipette sensors are powerful devices for the detection, quantification and structural analysis of biopolymers such as DNA and
proteins, especially in carrier-enhanced resistive-pulse sensing. However, hundreds of different molecules typically need to be sampled from solution and analysed to obtain statistically robust information. This limits the applicability of such sensors and complicates associated workflows. Here, we present a new strategy to trap DNA structures in the sensing region of a nanopipette through end functionalisation and nanoparticle capping. We develop a robust set of descriptors to characterise the insertion and presence of nanoparticle-DNA constructs in the nanopipette tip and, furthermore, show that they remain mobile and responsive to external electric fields over extended periods of time. This allows for repeated readout of the same DNA structure and could enable new applications for such sensors, for example in flow and in confined environments.
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All authors Cengiz J. Khan, Oliver J. Irving, Rand A. Al-Waqfi, Giorgio Ferrari, Tim Albrecht
Materials Science
Resolving the Structural Duality of Graphene Grain Boundaries
Haojie Guo, Emiliano Ventura-Macías, Mariano D. Jiménez-Sánchez et al. (+9 more)
Grain boundaries (GBs) are ubiquitous in large-scale
graphene samples, playing a crucial role in their overall performance. Due to their complexity, they are usually investigated as model structures, under the assumption of a fully relaxed interface. Here, we present cantilever-based non-contact atomic force microscopy (ncAFM) as a suitable technique to resolve, atom by atom, the complete structure of these linear defects. Our experimental findings reveal a richer scenario than expected, with the coexistence of energetically stable and metastable
graphene GBs. Although both GBs are structurally composed of pentagonal and heptagonal like rings, they can be differentiated by the irregular
geometric shapes present in the metastable boundaries. Theoretical modeling and simulated ncAFM images, accounting for the experimental data, show that metastable GBs form under compressive uniaxial strain and exhibit vertical corrugation, whereas stable GBs remain in a fully relaxed, flat configuration. By locally introducing energy with the AFM tip, we show the possibility to manipulate the metastable GBs, driving them toward their minimum energy configuration. Notably, our high-resolution ncAFM images reveal a clear dichotomy: while the structural distortions of metastable grain boundaries are confined to just a few atoms, their impact on
graphene's properties extends over significantly larger length scales.
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All authors Haojie Guo, Emiliano Ventura-Macías, Mariano D. Jiménez-Sánchez, Nicoleta Nicoara, Pierre Mallet, Jean-Yves Veuillen, Vincent T. Renard, Antonio J. Martínez-Galera, Pablo Pou, Julio Gómez-Herrero, Rubén Pérez, Iván Brihuega
Materials Science
Anisotropic Strain Engineering in La0.7Sr0.3MnO3/LaFeO3 Superlattice: Structural Relaxation and Domain Formation
Yu Liu, Thea Marie Dale, Emma van der Minne et al. (+7 more)
Anisotropic strain engineering in epitaxial
oxide films provides new opportunities to control the
antiferromagnetic and structural properties crucial for advancements of
antiferromagnetic spintronics. Here we report on a (La0.7Sr0.3MnO3/LaFeO3)4 superlattice grown on (101)o DyScO3 substrate which imposes significant anisotropic in-plane strain. Reciprocal space mapping reveals selective strain relaxation along the tensile in-plane [010]o axis, while compression along the perpendicular in-plane [-101]o axis remains strained. Scanning precession electron diffraction and higher-order Laue zone analysis show that the relaxation is accommodated by structural domain formation in the LaFeO3 layers, initiating from the second
bilayer and propagating out-of-plane. These domains minimise structural defects and correlate with the substrate step edges. X-ray
magnetic dichroism measurements reveal bulk-like in-plane
antiferromagnetic order with polydomain signature as previously reported. Our findings reveal the presence of structural domains coexisting with
antiferromagnetic polydomain states, showing a strain-domain-magnetism relationship that provides insights for applications of strain engineering in spintronics applications.
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All authors Yu Liu, Thea Marie Dale, Emma van der Minne, Susanne Boucher, Romar Avila, Christoph Klewe, Gertjan Koster, Magnus Nord, Mari-Ann Einarsrud, Ingrid Hallsteinsen
Materials Science
Growth control of highly textured Bi2Te3 thin films by pulsed laser deposition
Damian Brzozowski, Yu Liu, Karola Neeleman et al. (+2 more)
Two-dimensional materials have attracted growing interest due to their unique electronic properties and potential applications in spintronics. Interfacing strongly
spin-orbit-coupled chalcogenides with functional
oxides such as perovskites has a particularly high potential. In this work, highly textured Bi2Te3 thin films were deposited on (111) oriented SrTiO3 by pulsed
laser deposition. We show that, by careful selection of the temperature and pressure of growth, the film's stoichiometry can be manipulated between direct stoichiometry transfer from the target and tellurium-deficient phases. Optimized pulsed
laser deposition enables the growth of films with coalesced, faceted grains with grain sizes reaching up to 430 nm, while preserving crystalline quality comparable to that of molecular-beam-epitaxy-grown films. We show striking differences arising from tuning the
laser's pulsing frequency and fluence, which lead to changes in surface roughness, the film's porosity, and grain boundaries, as well as grain shape. Analysis of cross-sectional transmission electron microscopy images reveals a sharp substrate-film interface without atomic intermixing and without the formation of amorphous intermediate layers. The results demonstrate that pulsed
laser deposition is a viable method for producing high-quality Bi2Te3 thin films and opens the door to the integration of chalcogenides with perovskites with this growth technique.
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All authors Damian Brzozowski, Yu Liu, Karola Neeleman, Magnus Nord, Ingrid G. Hallsteinsen
Statistical Mechanics · Cross-listed from physics.flu-dyn
The significance of two-way coupling in two-dimensional, dusty turbulence
Harshit Joshi, Amal Manoharan and Samriddhi Sankar Ray
The significance of small-scale forcing of particles on the carrier two-dimensional turbulent flow has been shown to influence the spectral scaling properties of the carrier fluid. We investigate possible consequences of such two-way coupling in a turbulent suspension of inertial particles through one- and two-point Eulerian and Lagrangian statistics. In particular, we find signatures of enhanced intermittency in the vorticity distributions. We characterize the changes in the small-scale geometry of the flow via the Okubo-Weiss parameter. Finally, we examine the scaling properties of the second-order vorticity structure functions and find a non-trivial form of scale-invariance at finite mass loading. Motivated by these observations, we propose an effective multiscale forcing framework in which particle feedback is modeled as a spatially localized small-scale forcing. This dual-scale forcing captures the emergence of modified spectral scaling and provides a minimal Eulerian description of particle-laden
turbulence that reproduces key statistical signatures of the system.
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Statistical Mechanics
Proof of the exact diffusion constant via first passage time in quasi-periodic potentials
Ming Gong
Brownian motion in terms of Lifson and Jackson (LJ) formula has been widely explored in periodic systems and it has been believed for a long time that the LJ formula only applies to periodic potentials. Recently we show that for the following Brownian motion $\gamma \dot{x} = -U'(x) + \xi$, where $U(x)$ is the quasi-periodic potential, the effective
diffusion constant can still be described by the LJ formula $D^* = D/(\langle \exp(\beta U)\rangle \langle \exp(-\beta U)\rangle)$, where the average is redefined as $\langle \exp(\beta U)\rangle = \lim_{L\rightarrow \infty} L^{-1} \int_0^L \exp(\beta U(x))dx$. In this manuscript we prove this result exactly using the mean first passage time $\tau(x)$, with boundary conditions $\tau(\pm L) = 0$, and show that the effective
diffusion constant can be determined using $D^* =\lim_{L \rightarrow \infty} L^2/(2\tau(0))$, where $\pm L$ is the two positions of the absorbing boundary. We exactly solve the equation of motion of $\tau(x)$ and obtain the above result with the aid of Jacobi-Anger expansion method. Our result can be generalized to the other potentials and even higher dimensions, which can greatly broaden our understanding of Brownian motion in more general circumstances. The requirement for a well-defined effective
diffusion constant $D^*$ in more general potentials is also discussed.
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Materials Science
Electric Polarization-Driven Modulation of Fe Adatoms on Ferroelectric $\alpha$-In$_2$Se$_3$
Monirul Shaikh and Aleksander L. Wysocki
The interplay among structural, electronic, and
magnetic properties of Fe adatoms on the surface of two-dimensional ferroelectric {\alpha}-In$_2$Se$_3$ is investigated using first-principles electronic structure calculations, with a focus on how these properties are modulated by the direction of the electric polarization of the substrate. We identify two competing adsorption sites for Fe adatoms, whose relative stability depends on the adatom concentration and can be reversed by switching the electric polarization of {\alpha}-In$_2$Se$_3$. The calculated energy barrier for thermally activated hopping between these sites is approximately 0.4 eV, corresponding to a blocking temperature of around 100 K. The hybridization between Fe and In$_2$Se$_3$ orbitals strongly depends on the adsorption site and polarization direction, driven by variations in the local adatom geometry. As a result, the electronic configuration of adatom,
magnetic moment, and
magnetic anisotropy exhibit a pronounced site dependence and can be effectively modulated by switching the electric polarization of the In$_2$Se$_3$ layer. In particular, at higher adatom concentrations, an exceptionally large perpendicular
magnetic anisotropy, exceeding 200 meV per Fe atom, emerges for one polarization direction, but is largely diminished when the polarization is reversed. These findings indicate that ferroelectric substrates offer a promising route for voltage-controlled tuning of
magnetic adatom properties via reversible polarization switching.
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Mesoscale and Nanoscale Physics
Breakdown of the Wiedemann-Franz law in an interacting quantum Hall metamaterial
Patrice Roche, Carles Altimiras, François D. Parmentier et al. (+1 more)
Coulomb interactions deeply affect
quantum transport in simple ballistic systems, but their impact on scaled up ballistic structures remains underexplored. Here we theoretically consider a chain of small metallic dots with frozen charge dynamics, connected by ballistic channels. We identify a neutral mode of transport, that is specific to a chain with at least two islands, and entwines local
diffusion by neutral excitations with long-range correlations between islands' charge states. We show, as an experimentally measurable signature of this many-body behavior, that the Wiedemann-Franz law is violated with a Lorenz ratio scaling as the square root of the chain's length.
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All authors Patrice Roche, Carles Altimiras, François D. Parmentier, Olivier Maillet