Disordered Systems and Neural Networks
Glass Patterns in Twisted Disordered Crystals
Aaron Dunbrack
Twisting and stacking two copies of a 2D
crystal can produce a long-wavelength periodic interference pattern known as a moiré pattern. Performing the same procedure with an aperiodic structure instead generates a single moiré spot at the rotation center, known as a Glass pattern. We explore the implications of these patterns across a variety of models: they allow measurement of microscopic parameters from mesoscopic resistivity measurements; they generate an
impurity that modifies the properties of a moiré
lattice at the rotation center; and they allow for domain formation in amorphous magnets. These results establish Glass patterns as a generic feature of twisted disordered systems and provide a framework for future theoretical and experimental exploration.
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Materials Science
Machine learning descriptors for predicting the high temperature oxidation of refractory complex concentrated alloys
Akhil Bejjipurapu, Alejandro Strachan, Kenneth H. Sandhage et al. (+1 more)
Refractory Complex Concentrated
Alloys (RCCAs) can exhibit exceptional high-temperature strength, making such
alloys promising candidates for high-temperature structural applications. However, current RCCAs do not possess the high-temperature oxidation resistance required to survive in oxidizing environments for more than a few hours at or above 1000$^\circ$C, without relying primarily on an environmental barrier coating. Here, we present a machine-learning framework designed to predict the oxidation-induced specific mass changes of RCCAs exposed for 24 h at 1000$^\circ$C in air, in order to support the search for oxidation-resistant
alloys over a wide range of compositions. A database was constructed of experimental specific mass change data, upon oxidation at 900-1000$^\circ$C for 24 h in air, for 77 compositions comprised of simple elements, binary
alloys, and higher-order elemental systems. We then developed a Gaussian Process Regression (GPR) model with physics-informed descriptors based on oxidation products, capturing the fundamental chemistry of
oxide formation and stability. Application of this GPR model to the database yielded a MAE (mean absolute error) test score of 5.78 mg/cm$^2$, which was a significant improvement in accuracy relative to models only utilizing traditional
alloy-based descriptors. Our model was used to screen over 5,100 quaternary RCCAs, revealing compositions with significantly lower predicted specific mass changes compared to existing literature sources. Overall, this work establishes a versatile and efficient strategy to accelerate the discovery of next-generation RCCAs with enhanced resistance to extreme environments.
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All authors Akhil Bejjipurapu, Alejandro Strachan, Kenneth H. Sandhage, Michael S. Titus
Materials Science
Exposing Altermagnetism through Momentum Density Spectroscopy
Wenhan Chen, Alyn D. N. James and Stephen B. Dugdale
Materials which show a strong time-reversal
symmetry-breaking response leading to
spin-polarization phenomena, in conjunction with antiparallel
magnetic alignments producing zero net magnetization, have recently been identified, classified, and been given the name 'altermagnets'. However, measuring and diagnosing possible candidates as altermagnetics still remains a challenge. From the uncertainty of the material being an altermagnet, additional experimental probes are essential to resolve this. Here, we propose using
spin-dependent and
magnetic momentum density probes such as
spin-polarised positron annihilation and revisiting
magnetic Compton scattering. By looking at the previously claimed altermagnetic candidates RuO2, CrSb and MnTe, we present theoretical altermagnetic calculations of the experimental quantities measured by these probes. We show that these quantities should produce a measurable signal and unequivocally confirm the altermagnetic state. We also highlight the additional benefits from these probes such as extracting
spin-resolved
Fermi surfaces which are key for further understanding the nature of the altermagnetic state.
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Materials Science
Domain Morphology, Electrocaloric Response, and Negative Capacitance States of Ferroelectric Nanowires Array
Anna N. Morozovska, Oleksii V. Bereznykov, Maksym V. Strikha et al. (+4 more)
We analyzed the domain morphology, electrocaloric response, and negative capacitance states in a one-dimensional array of uniformly oriented, radial symmetric ferroelectric nanowires, whose spontaneous polarization is normal to their
symmetry axis. The wires are densely packed between flat electrodes. Using finite element modeling based on the Landau-Ginzburg-Devonshire approach, electrostatics, and elasticity theory, we calculated the distributions of spontaneous polarization, domain structures, electric potential, electric field, dielectric permittivity, and electrocaloric response in the nanowires. Due to size and depolarization effects, the paraelectric and ferroelectric (poly-domain or single-domain) states of the wires can be stable, depending on their radius and the dielectric permittivity of the surrounding medium. It is demonstrated that dipole-dipole interaction between the nanowires determines the stability of the polar (or anti-polar) state in the array when the wire radius is significantly smaller than the critical size of the paraelectric transition in an isolated wire. We reveal that a large region of a mixed state, characterized by poly-domain ferroelectric states with nonzero average polarization inside each wire and zero average polarization of the whole array, can be stable. By selecting the dielectric permittivity of the surrounding medium and the nanowire radius, one can maximize the negative capacitance effect in the capacitor with densely packed wires. It is also possible to achieve maximal enhancement of the electrocaloric response due to size effects in the wires. The underlying physics of the predicted enhancement is the combined action of size effects and the long-range electrostatic interactions between the ferroelectric dipoles in the nanowires and the image charges in the electrodes
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All authors Anna N. Morozovska, Oleksii V. Bereznykov, Maksym V. Strikha, Oleksandr S. Pylypchuk, Zdravko Kutnjak, Eugene A. Eliseev, Dean R. Evans
Strongly Correlated Electrons
Strongly Forbidden Thermodynamic Oscillations in Quasi-One-Dimensional Conductors
Andrei G. Lebed
We theoretically show that strongly forbidden oscillations of a specific heat have to exist in metallic phases of some quasi-one-dimensional (Q1D) conductors. They appear due to electron-electron interactions under condition of the
magnetic breakdown phenomenon between the so-called open interference electron orbits. We argue that such forbidden thermodynamic oscillations can exist in Q1D conductors (TMTSF)$_2$ClO$_4$ and (Per)$_2$Au(mnt)$_2$, where TMTSF stands for tetramethyltetraselenafulvalene, Per is polycyclic aromatic hydrocarbon and mnt is mononitrotoluene, and suggest to discover them.
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Strongly Correlated Electrons
Non Fermi-Liquid Magnetoresistance Oscillations in Quasi-One-Dimensional Conductors
Andrei G. Lebed
We theoretically demonstrate that strong non
Fermi-
liquid magnetic oscillations of electron-electron scattering time can exist in quasi-one-dimensional (Q1D) conductors under condition of the
magnetic breakdown between two open electron orbits. They are shown to be due to electron-electron interactions in a metallic phase under condition of the
magnetic breakdown and they are beyond the
Fermi-
liquid theory. In particular, we consider as example the organic conductor (TMTSF)$_2$ClO$_4$ and perform both analytical and numerical calculations for its known electron spectrum. We also argue that similar oscillations of resistivity can exist in a metallic phase of another Q1D organic conductor - (Per)$_2$Au(mnt)$_2$.
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Strongly Correlated Electrons
Improved contraction of finite projected entangled pair states
Markus Scheb
We present an improved version of the
algorithm contracting and optimizing finite projected entangled pair states (fPEPS) in conjunction with projected entangled pair operators (PEPOs). Our work has two components to it. First, we explain in detail the characteristic contraction patterns that occur in fPEPS calculations and how to slice them such that peak
memory occupation remains minimal while ensuring efficient parallel computation. Second, we combine controlled bond expansion [A. Gleis, J.-W. Li, and J. von Delft, Phys. Rev. Lett. 130, 246402 (2023)] with randomized singular value decomposition [V. Rokhlin, A. Szlam, and M. Tygert, SIAM J.
Matrix Anal. Appl. (2009)] and apply it throughout the fPEPS
algorithm. We present
benchmark results for the Hubbard model for system sizes up to 8x8 and SU(2) symmetric bond dimension of up to D = 6 for PEPS bonds and $\chi$ = 500 for the environment bonds. Finally, we comment on the state and future of the fPEPS-PEPO framework.
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Disordered Systems and Neural Networks · Cross-listed from stat.ML
Binary perceptron computational gap – a parametric fl RDT view
Mihailo Stojnic
Recent studies suggest that asymmetric binary perceptron (ABP) likely exhibits the so-called statistical-computational gap characterized with the appearance of two phase transitioning constraint density thresholds: \textbf{(i)} the satisfiability threshold $\alpha_c$, below/above which ABP succeeds/fails to operate as a storage
memory; and \textbf{(ii)} algorithmic threshold $\alpha_a$, below/above which one can/cannot efficiently determine ABP's weight so that it operates as a storage
memory. We consider a particular parametric utilization of fully lifted random duality theory (fl RDT) [85] and study its potential ABP's algorithmic implications. A remarkable structural parametric change is uncovered as one progresses through fl RDT lifting levels. On the first two levels, the so-called $\c$ sequence – a key parametric fl RDT component – is of the (natural) decreasing type. A change of such phenomenology on higher levels is then connected to the $\alpha_c$ – $\alpha_a$ threshold change. Namely, on the second level concrete numerical values give for the critical constraint density $\alpha=\alpha_c\approx 0.8331$. While progressing through higher levels decreases this estimate, already on the fifth level we observe a satisfactory level of convergence and obtain $\alpha\approx 0.7764$. This allows to draw two striking parallels: \textbf{(i)} the obtained constraint density estimate is in a remarkable agrement with range $\alpha\in (0.77,0.78)$ of clustering defragmentation (believed to be responsible for failure of locally improving
algorithms) [17,88]; and \textbf{(ii)} the observed change of $\c$ sequence phenomenology closely matches the one of the negative Hopfield model for which the existence of efficient
algorithms that closely approach similar type of threshold has been demonstrated recently [87].
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Strongly Correlated Electrons
Superlinear Hall angle and carrier mobility from non-Boltzmann magnetotransport in the spatially disordered Yukawa-Sachdev-Ye-Kitaev model on a square lattice
Davide Valentinis, Jörg Schmalian, Subir Sachdev et al. (+1 more)
Exact numerical results for the dc magnetoconductivity tensor of the two-dimensional spatially disordered Yukawa-Sachdev-Ye-Kitaev (2D-YSYK) model on a square
lattice, at first order in applied perpendicular
magnetic field, are obtained from the self-consistent disorder-averaged solution of the 2D-YSYK saddle-point equations. This system describes
fermions endowed with a
Fermi surface and coupled to a bosonic scalar field through spatially random Yukawa interactions. The resulting local and energy-dependent fermionic self-energies are employed in the Kubo formalism to calculate the longitudinal and
Hall conductivities, the
Hall coefficient, the carrier mobility, and the cotangent of the
Hall angle, at fixed
fermion density. From the interplay between YSYK interactions and square-
lattice embedding, and the non-Boltzmann frequency-dependent self energies, we find nontrivial
evolution of the magnetotransport coefficients as a function of temperature and YSYK interaction strength, notably a superlinear
evolution of the
Hall-angle cotangent and the inverse carrier mobility with temperature, concomitant with linear-in-temperature resistivity, in an extended crossover regime above the low-temperature Marginal
Fermi Liquid (MFL) ground state. Our model and results provide a controlled theoretical framework to interpret magnetotransport experiments, at linear order in applied
magnetic field, in strange-metal phases found in strongly correlated solid-state electron systems.
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All authors Davide Valentinis, Jörg Schmalian, Subir Sachdev, Aavishkar A. Patel
Materials Science
Polaronic-Distortion-Driven Enhancement of Excitonic Auger Recombination in ZnO Nanoparticles
Fuyong Hua, Zheng Zhang, Zhong Wang et al. (+5 more)
The surface effect and
quantum confinement render nanomaterials the optoelectronic properties more susceptible to nonradiative processes than their bulk counterparts. These nonradiative processes usually contain a series of interwoven and competing sub-processes, which are challenging to disentangle. Here, we investigate the structural origin of Auger recombination in ZnO nanoparticles using transient absorption spectroscopy and ultrafast electron diffraction. The photogenerated hot holes are captured by oxygen vacancies through an Auger mechanism, inducing significant local structural distortions around the oxygen vacancy and its neighboring zinc tetrahedron on a sub-picosecond timescale. The recombination of trapped holes accelerates the
lattice thermalization and stabilizes the formed small hole polarons. Subsequently, the recombination of localized polarons forms a confined
exciton-polaron complex that may account for the long-lived (>7 ns) visible luminescence observed in ZnO nanoparticles. Our findings are potentially applicable to other transition metal
oxide nanomaterials, bringing insights for the optimization of their functional properties.
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All authors Fuyong Hua, Zheng Zhang, Zhong Wang, Yang Liu, Changchang Gong, Chunlong Hu, Yinhua Zhou, Wenxi Liang
Mesoscale and Nanoscale Physics
Intrinsic Moiré Higher-Order Topology Beyond Effective Moiré Lattice Models
Xianliang Zhou, Yifan Gao, Laiyuan Su et al. (+5 more)
Moiré superlattices provide a compelling platform for exploring exotic correlated physics. Electronic interference within these systems often results in flat bands with localized electrons, which are typically described by effective moiré
lattice models. While conventional models treat moiré sites as indivisible, analogous to atoms in a
crystal, this picture overlooks a crucial distinction: unlike a true atom, a moiré site is composed of tens to thousands of atoms and is therefore spatially divisible. Here, we introduce a universal mechanism rooted in this spatial divisibility to create topological boundary states in moiré materials. Through tight-binding and density functional theory calculations, we demonstrate that cutting a moiré site with a physical boundary induces bulk topological polarization, generating robust boundary states with fractional charges. We further show that when the net edge polarization is canceled, this mechanism drives the system into an intrinsic moiré higher-order topological
insulator (mHOTI) phase. As a concrete realization, we predict that twisted
bilayer tungsten disulfide ($WS_2$) is a robust mHOTI with experimentally detectable corner states when its boundaries cut through moiré hole sites. Our findings generalize the theoretical framework of moiré higher-order
topology, highlight the critical role of edge terminations, and suggest new opportunities for realizing correlated HOTIs and higher-order superconductivity in moiré platforms.
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All authors Xianliang Zhou, Yifan Gao, Laiyuan Su, Z. F. Wang, Li Huang, Angel Rubio, Zhiwen Shi, Lede Xian
Statistical Mechanics
Generalized Finite-time Optimal Control Framework in Stochastic Thermodynamics
Atul Tanaji Mohite and Heiko Rieger
Optimal processes in
stochastic thermodynamics represent a frontier for understanding the control and design of non-
equilibrium systems, with broad practical applications in biology, chemistry, and nanoscale/mesoscale systems. Optimal transport theory and thermodynamic geometry have emerged as leading optimal control methodologies, but both rely on slow–driving and close-to-
equilibrium assumptions. An optimal control framework in
stochastic thermodynamics for finite–time driving remains elusive. Here, we solve an optimal control problem for driving the control parameters of a discrete-state far-from-
equilibrium process from an initial to a final value in finite time. Optimal driving protocols are derived that minimize the total finite–time dissipation cost of the driving process. Our framework reveals that discontinuous endpoint jumps are a generic, model-independent physical mechanism that minimizes the optimal driving
entropy production — `
geometric thermodynamic far-from-
equilibrium shortcuts in swift state-to-state transformations' — whose importance is further amplified in far-from-
equilibrium systems. The thermodynamic and dynamical interpretation of discontinuous endpoint jumps is formulated. An exact mapping between the finite–time and slow–driving optimal control formulations is elucidated, advancing the state of the art in optimal transport theory and thermodynamic geometry, which has been the prevailing paradigm for studying optimal processes in
stochastic thermodynamics under slow–driving assumptions. Our framework opens up a broad range of applications to the thermodynamically efficient control of far-from-
equilibrium systems in finite time, and thereby a route towards their efficient design principles.
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Statistical Mechanics
Thermodynamic Length in Stochastic Thermodynamics of Far-From-Equilibrium Systems: Unification of Fluctuation Relation and Thermodynamic Uncertainty Relation
Atul Tanaji Mohite and Heiko Rieger
The Boltzmann distribution for an
equilibrium system constrains the statistics of the system by the energetics. Despite the non-
equilibrium generalization of the Boltzmann distribution being studied extensively, a unified framework valid for far-from-
equilibrium discrete state systems is lacking. Here, we derive an exact path-integral representation for discrete state processes and represent it using the exponential of the action for
stochastic transition dynamics. Solving the variational problem, the effective action is shown to be equal to the inferred
entropy production rate (a thermodynamic quantity) and a non-quadratic dissipation function of the thermodynamic length (TL) defined for microscopic
stochastic currents (a dynamic quantity). This formulates a far-from-
equilibrium analog of the Boltzmann distribution, namely, the minimum action principle. The non-quadratic dissipation function is physically attributed to incorporating non-Gaussian fluctuations or far-from-
equilibrium non-conservative driving. Further, an exact large deviation dynamical rate functional is derived. The equivalence of the variational formulation with the information
geometric formulation is proved. The non-quadratic TL recovers the non-quadratic thermodynamic-kinetic uncertainty relation (TKUR) and the speed limits, which are tighter than the close-to-
equilibrium quadratic formulations. Moreover, if the transition affinities are known, the non-quadratic TL recovers the fluctuation relation (FR). The minimum action principle manifests the non-quadratic TKUR and FR as two faces corresponding to the thermodynamic inference and partial control descriptions, respectively. In addition, the validity of these results is extended to coarse-grained observable currents, strengthening the experimental/numerical applicability of them.
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Statistical Mechanics
Minimum Action Principle for Entropy Production Rate of Far-From-Equilibrium Systems
Atul Tanaji Mohite and Heiko Rieger
The Boltzmann distribution connects the energetics of an
equilibrium system with its statistical properties, and it is desirable to have a similar principle for non-
equilibrium systems. Here, we derive a variational principle for the
entropy production rate (EPR) of far-from-
equilibrium (fEQ) discrete state systems, relating it to the action for the transition probability measure of discrete state processes. This principle leads to a tighter, nonquadratic formulation of the dissipation function, speed limits, the thermodynamic-kinetic uncertainty relation, the large deviation rate functional, and the fluctuation relation, all within a unified framework of the thermodynamic length. Additionally, the optimal control of non-conservative transition affinities using the underlying geodesic structure is explored, and the corresponding slow–driving and finite–time optimal driving exact protocols are analytically computed. We demonstrate that discontinuous endpoint jumps in optimal protocols (defined as kinks) are a generic, model–independent physical mechanism that reduces
entropy production (EP) during finite–time driving of fEQ systems: `
Geometric thermodynamic far-from-
equilibrium shortcuts in swift state-to-state transformations'.
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Disordered Systems and Neural Networks · Cross-listed from math-ph
Large deviations of spectral determinants of matrix-valued random Schrödinger operators and Dyson Brownian motion in cubic potentials
Yan Fyodorov, Pierre Le Doussal and Alexander Ossipov
We study the moments of $\overline{|\det(H-E)|^q}$ and the associated large deviations of $\log |\det(H-E)|$ where $H$ are random
matrix operators involving Laplace operators and random potentials. This includes as a special case Hessians of random elastic
manifolds at a generic energy configuration. In one dimension $d=1$ these are $N \times N$
matrix valued random Schrödinger operators and $\log | \det(H-E) | $ is the sum of the $N$ associated Lyapunov exponents. Using a mapping to a
stochastic matrix Ricatti equation we make a connection between the spectral properties of these operators and the total $N$ particle current of a Dyson Brownian motion (DBM) in a cubic potential. The latter model was studied by Allez and Dumaz [1] who showed that for $N=+\infty$ it exhibits a sharp transition between a phase with non-zero current and a confined (zero current) phase. We compute the barrier-crossing probability of the DBM at large but finite $N$, which gives an estimate of the exponential tail of the average density of states of a
matrix Schrodinger operator below the edge of its spectrum. The barrier behaves as $\sim N (-E)^{3/2}$ at large negative energy and vanishes as $\sim N(E^*-E)^{5/4}$ near the edge. For $q=1$ the present work provides an independent derivation of the total complexity of stationary points for an elastic string embedded in $N$ dimension in presence of disorder.
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Strongly Correlated Electrons
Exploring the limit of the Lattice-Bisognano-Wichmann form describing the Entanglement Hamiltonian: A quantum Monte Carlo study
Siyi Yang, Yi-Ming Ding and Zheng Yan
As a powerful theoretical construct, the
entanglement Hamiltonian (EH) encapsulates the essential
entanglement properties of a
quantum many-body system. From the EH, one can extract a variety of
entanglement quantities, such as
entanglement entropies, negativity, and the
entanglement spectrum. However, its general analytical form remains largely unknown. While the Bisognano-Wichmann
theorem gives an exact EH form for Lorentz-invariant field theories, its validity on
lattice systems is limited, especially when Lorentz invariance is absent. In this work, we propose a general scheme based on the
lattice-Bisognano-Wichmann (LBW) ansatz and multi-replica-trick
quantum Monte Carlo methods to numerically reconstruct the
entanglement Hamiltonian in two-dimensional systems and systematically explore its applicability to systems without translational invariance, going beyond the original scope of the
primordial Bisognano-Wichmann
theorem. Various
quantum phases–including gapped and gapless phases, critical points, and phases with either discrete or continuous
symmetry breaking–are investigated, demonstrating the versatility of our method in reconstructing
entanglement Hamiltonians. Furthermore, we find that when the
entanglement boundary of a system is ordinary (i.e., free from surface anomalies), the LBW ansatz provides an accurate approximation well beyond Lorentz-invariant cases. Our work thus establishes a general framework for investigating the analytical structure of
entanglement in the complex
quantum many-body systems.
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Quantum Gases · Cross-listed from math-ph
A Self Propelled Vortex Dipole Model on Surfaces of Variable Negative Curvature
Khushi Banthia and Rickmoy Samanta
We investigate
vortex dipoles on surfaces of variable negative
curvature, focusing on a catenoid of arbitrary throat radius as a concrete example. We construct the effective dynamical system including mutual and
geometric self-interaction terms and show that the resulting
Hamiltonian dynamics makes dipoles follow catenoid geodesics, in agreement with recent works, Gustafsson (J. Nonlinear Sci. 32, 62, 2022) and by Drivas, Glukhovskiy and Khesin (Int. Math. Res. Not. 2024, 14, 10880-10894). We utilize the
symplectic structure to find a conserved momentum map J related to the U(1)
symmetry along the azimuthal direction. We verify the conservation of both the
Hamiltonian and this momentum for arbitrary throat radius. We then demonstrate direct and exchange scattering of classical
vortices on the catenoid, and we contrast this with the collective rotational motion (with azimuthal drift) that arises for
chiral pairs. Finally, we build a finite-dipole dynamical system on the catenoid and show that the self-propulsion terms emerge to leading order in the dipole size. This provides a concrete realization, on a curved minimal surface, of the intuitive statement that a finite dipole propels orthogonal to the dipole axis, with a speed modulated by
curvature.
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Materials Science
Validation of Semi-Empirical xTB Methods for High-Throughput Screening of TADF Emitters: A 747-Molecule Benchmark Study
Jean-Pierre Tchapet Njafa, Elvira Vanelle Kameni Tcheuffa, Aissatou Maghame et al. (+1 more)
Thermally activated delayed fluorescence (TADF) emitters are essential for next-generation, high-efficiency organic light-emitting diodes (OLEDs), yet their rational design is hampered by the high computational cost of accurate excited-state predictions. Here, we present a comprehensive
benchmark study validating semi-empirical extended tight-binding (xTB) methods – specifically sTDA-xTB and sTD-DFT-xTB – for the high-throughput screening of TADF materials. Using an unprecedentedly large
dataset of \num{747} experimentally characterized emitters, our framework demonstrates a computational cost reduction of over \qty{99}{\percent} compared to conventional TD-DFT, while maintaining strong internal consistency between methods (Pearson $r \approx \num{0.82}$ for \deltaest), validating their utility for relative molecular ranking. Validation against \num{312} experimental \deltaest values reveals a mean absolute error of approximately \qty{0.17}{\electronvolt}, a discrepancy attributed to the vertical approximation inherent to the HTS protocol, underscoring the methods' role in screening rather than quantitative prediction. Through large-scale data analysis, we statistically validate key design principles, confirming the superior performance of Donor-Acceptor-Donor (D-A-D) architectures and identifying an optimal D-A torsional angle range of \qtyrange{50}{90}{\degree} for efficient TADF. Principal Component Analysis reveals that the complex property space is fundamentally low-dimensional, with three components capturing nearly \qty{90}{\percent} of the variance. This work establishes these semi-empirical methods as powerful, cost-effective tools for accelerating TADF discovery and provides a robust set of data-driven design rules and methodological guidelines for the computational materials science community.
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All authors Jean-Pierre Tchapet Njafa, Elvira Vanelle Kameni Tcheuffa, Aissatou Maghame, Serge Guy Nana Engo
Superconductivity
Point-contact enhanced superconductivity in trigonal PtBi2: quest for the origin of high-Tc
O. E. Kvitnitskaya, L. Harnagea, G. Shipunov et al. (+6 more)
We studied enhanced superconductivity in point contacts (PCs) based on a type-I Weyl semimetal trigonal t-PtBi2 using both normal metal (Ag, Cu, Pt) and
ferromagnetic (Fe, Co, Ni) tips by measuring the differential resistance dV/dI(V) curves. In most cases, the value of the superconducting critical temperature Tc ranges between 3 and 5 K, which is several times higher than the maximum bulk Tc. Notably, among the various PCs we examined, a few achieved Tc values as high as 8 K, including those with both normal and
ferromagnetic tips. Additionally, the critical
magnetic field is also highly enhanced in these PCs and reaches up to several Tesla. The common reason for the Tc increase may be related to pressure/strain caused during the PC's formation. It is worth noting that a greater increase in Tc is observed in PCs formed at the edge of the sample flake, compared to those formed on the plane of the platelet. The results also reveal that the enhancement of Tc in PCs based on t-PtBi2 is compatible with
ferromagnetic tip, which may suggest a potentially complex nature of enhanced superconductivity. Our findings besides suggest that t-PtBi2 is a promising candidate for realizing topological superconductivity at more accessible temperatures.
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All authors O. E. Kvitnitskaya, L. Harnagea, G. Shipunov, S. Aswartham, I. Kovalchuk, V. V. Fisun, D. V. Efremov, B. Büchner, Yu. G. Naidyuk
Superconductivity
Field-Tunable Anisotropic Fulde-Ferrell Phase in NbSe$_2$/CrSiTe$_3$ Heterostructures
Jiadian He, Xin-Zhi Li, Chen Xu et al. (+11 more)
The emergence of superconductivity in two-dimensional transition metal dichalcogenides with strong
spin orbit coupling (SOC) has opened new avenues for exploring exotic superconducting states. Here, we report experimental observation of an anisotropic Fulde-Ferrell (FF) phase in few-layer NbSe$_2$/CrSiTe$_3$
heterostructures under in-plane
magnetic fields. Through combined magnetoresistance and nonreciprocal transport measurements, we find that due to the couplings from the
ferromagnetic CrSiTe$_3$, a half-dome-shaped region emerges in the
magnetic field-temperature ($B$-$T$) diagram. Importantly, the half-dome-shaped region exhibits finite second harmonic resistance with in-plane anisotropy, indicating that the superconducting state is an anisotropic FF phase. Through a
symmetry analysis combined with mean field calculations, we attribute the emergent anisotropic FF phase to the CrSiTe$_3$ layer induced Rashba SOC and three-fold rotational
symmetry breaking. These results demonstrate that
heterostructure stacking is a powerful tool for
symmetry engineering in
superconductors, which can advance the design of
quantum devices in atomically thin superconducting materials.
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All authors Jiadian He, Xin-Zhi Li, Chen Xu, Yifan Ding, Yueshen Wu, Jinghui Wang, Peng Dong, Yan-Fang Li, Wei Li, Xiang Zhou, Yanfeng Guo, Yulin Chen, Wen-Yu He, Jun Li
Materials Science · Cross-listed from physics.bio-ph
New avenues for characterizing individual mineralized collagen fibrils with transmission electron microscopy
Tatiana Kochetkova, Stephanie M. Ribet, Lilian M. Vogl et al. (+5 more)
Bone serves as a remarkable example of nature's architectured material with its unique blend of strength and toughness, all at a lightweight design. Given the hierarchical nature of these materials, it is essential to understand the governing mechanisms and organization of its constituents across length scales for bio-inspired structural design. Despite recent advances in transmission electron miscoscopy (TEM) that have allowed us to witness the fascinating arrangement of bone at micro-down to the nano-scale, we are still missing the details about the structural organization and mechanical properties of the main building blocks of bone – mineralized collagen fibrils (MCFs). Here, we propose a novel approach for extracting individual MCFs from nature's model material via a dropcasting procedure. By isolating the MCFs onto TEM-compatible substrates, we visualized the arrangement of organic and mineral phases within the individual MCFs at the nanoscale. Using a 4D-STEM approach, the orientation of individual mineral
crystals within the MCFs was examined. Furthermore, we conducted first-of-its-kind in situ tensile experiments, revealing exceptional tensile strains of at least 8%, demonstrating the intricate relationship between structural organization and the mechanical behavior of MCFs. The capabilities of TEM allow us to resolve MCF organization and composition down to the nanoscale level. This new knowledge of the ultrastructure of the bone-building blocks and the proposed sample extraction and in situ mechanical testing opens up new avenues for research into nature's inspired material design.
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All authors Tatiana Kochetkova, Stephanie M. Ribet, Lilian M. Vogl, Daniele Casari, Rohan Dhall, Philippe K. Zysset, Andrew M. Minor, Peter Schweizer
Soft Condensed Matter · Cross-listed from hep-th
Black hole interiors of homogeneous holographic solids under shear strain
Yuanceng Xu, Li Li and Wei-Jia Li
We investigate the interior of AdS black holes under finite shear strain in a class of
holographic axion models, which are widely used to describe strongly-coupled systems with broken translations. We demonstrate that the shear anisotropy necessarily eliminates the inner Cauchy horizon, such that the deformed black hole approaches a spacelike singularity. The anisotropic effect induced by the
axion fields triggers a collapse of the Einstein-Rosen bridge at the would-be Cauchy horizon, accompanied by a rapid change in the anisotropy of the spatial geometry. In addition, for a power-law
axion potential, sufficiently large shear deformations give rise to a domain wall solution that includes a Lifshitz like scaling geometry near the boundary as well as a near horizon Kasner epoch with the Kasner exponents determined by the powers of the potential. Finally, we find that the interior dynamics of black holes generally enter an era described by an anisotropic Kasner universe at later interior time. Depending on the form of the potential, they either tend to stable Kasner universes, or exhibit an endless alternation of different Kasner epochs toward the singularity.
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Strongly Correlated Electrons
Representation of the Luttinger Liquid with Single Point-like Impurity as a Field Theory for the Phase of Scattering
V. V. Afonin
A new approach describing Luttinger
Liquid with point-like
impurity as field theory for the phase of scattering is developed. It based on a matching of the electron wave functions at
impurity position point. As a result of the approach, an expression for non-local action has been taken. The non-locality of the theory leads to convergence of the observed values in an ultraviolet region. It allows studying conductance of the channel up to electron-electron interaction strength of the order of unit. Expansion of the non-local action in small frequency powers makes possible to develop a new approach to the renormalization group analysis of the problem. This method differs from the "poor man's"\ approach widely used in solid-state physics. We have shown, in the Luttinger
Liquid "poor man's"\ approach breaks already in two-loop approximation. We analyse the reason of this discrepancy. The qualitative description of the phenomenon is discussed in detail.
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Other Condensed Matter
Optimized mouldboard design for efficient soil inversion using the discrete element method
Vinay Badewale, Sujith Reddy Jaggannagari, Prasad Avilala et al. (+1 more)
The design of a mouldboard (MB) plough is critical for achieving efficient soil inversion, which directly impacts soil aeration, weed control, and overall agricultural productivity. In this work, a design modification of the cylindroid-shaped MB plough is proposed, focusing on optimizing its surface profile to enhance performance. The discrete element method is used to simulate the ploughing process and evaluate the performance of the modified plough profile. The modified plough profile is compared against a previously proposed design to assess its impact on soil inversion efficiency, wear reduction, and stress distribution. A novel methodology is introduced to evaluate the plough's performance in soil inversion. The modified design demonstrates superior soil inversion efficiency, with improvements of up to $32.95\%$ in the inversion index for different velocities. The modified design achieves a notable reduction in wear up to $23.7\%$, compared to the original design. Although a slight increase in stress is observed in the modified design due to higher forces, the induced stresses remain well within the permissible limits for the plough material. Overall, the findings highlight the advantages of the modified plough design, including enhanced soil inversion efficiency and reduced wear, underscoring its potential for improved performance in tillage applications. However, the current study is limited to simulation-based analysis without experimental or field validation. Future work will focus on full-scale physical experiments to validate the simulation outcomes and incorporate additional factors such as depth-dependent moisture, soil cohesion, and multi-factor wear models for improved predictive accuracy.
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All authors Vinay Badewale, Sujith Reddy Jaggannagari, Prasad Avilala, Ratna Kumar Annabattula
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Optimizing magnetic coupling in lumped element superconducting resonators for molecular spin qubits
Marcos Rubín-Osanz, David Rodriguez, Ignacio Gimeno et al. (+18 more)
We engineer lumped-element superconducting resonators that maximize
magnetic coupling to molecular
spin qubits, achieving record single-
spin couplings up to $100$ kHz and collective couplings exceeding $10$ MHz. The resonators interact with PTMr organic free radicals, model
spin systems with $S=1/2$ and a quasi-isotropic $g \simeq 2$, dispersed in
polymer matrices. The highest collective
spin-
photon coupling strengths are attained with resonators having large inductors, which therefore interact with most
spins in the molecular ensemble. By contrast, the coupling of each individual
spin $G_{1}$ is maximized in resonators having a minimum size inductor, made of a single wire. The same platform has been used to study
spin relaxation and
spin coherent dynamics in the dispersive regime, when
spins are energetically detuned from the resonator. We find evidences for the Purcell effect, i.e. the
photon induced relaxation of those
spins that are most strongly coupled to the
circuit. The rate of this process gives access to the distribution of single
spin photon couplings in a given device. For resonators with a $50$ nm wide constriction at the inductor center, single maximum $G_{1}$ values reach $\sim 100$ kHz. Pumping the
spins with strong pulses fed through an independent transmission line induces coherent Rabi oscillations. The
spin excitation then proceeds via either direct resonant processes induced by the main pulse frequency or, in the case of square-shaped pulses, via the excitation of the cavity by sideband frequency components. The latter process measures the cavity mode hybridization with the
spins and can be eliminated by using Gaussian shaped pulses. These results establish a scalable route toward integrated molecular-
spin quantum processors.
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All authors Marcos Rubín-Osanz, David Rodriguez, Ignacio Gimeno, Wenzel Kersten, Nerea González-Prato, María C. Pallarés, Sebastián Roca-Jerat, Marina C. de Ory, Marta Mas-Torrent, J. Alejandro de Sousa, Lorenzo Tesi, Daniel Granados, Jaume Veciana, David Zueco, Anabel Lostao, Jörg Schmiedmayer, Imma Ratera, Joris van Slageren, Núria Crivillers, Alicia Gomez, Fernando Luis
Soft Condensed Matter
Competition between Glassy Five-Fold Structures and Locally Dense Packing Structures Governs Two-Stage Compaction of Granular Hexapods
Rudan Luo, Houfei Yuan, Yi Xing et al. (+9 more)
Using X-ray
tomography, we experimentally investigate the structural
evolution of packings composed of 3D-printed hexapod particles, each formed by three mutually orthogonal spherocylinders, during tap-induced compaction. We identify two distinct structural compaction mechanisms: an initial stage dominated by enhanced particle interlocking, which yields local mechanically stable structures through strong
geometric entanglement, and a later stage characterized by the formation of dense polytetrahedral aggregates and a sharp increase in the number of five-ring motifs. The emergence of these five-fold symmetric structures indicates that, despite their highly concave geometry, hexapod packings can be effectively treated as hard-sphere-like systems and exhibit similar glass-like disordered configurations. The frustration between local mechanically stable structures and global glassy order suggests a universal organizational principle underlying the structure of uniform and isotropic disordered granular materials.
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All authors Rudan Luo, Houfei Yuan, Yi Xing, Yeqiang Huang, Jiahao Liu, Wei Huang, Haiyang Lu, Zhuan Ge, Yonglun Jiang, Chengjie Xia, Zhikun Zeng, Yujie Wang
Superconductivity
Instability toward Superconducting Stripe Phase in Altermagnets with Strong Rashba Spin-Orbit Coupling
Kohei Mukasa and Yusuke Masaki
We numerically investigate finite-momentum superconductivity in noncentrosymmetric metallic altermagnets with $d$-wave
spin-splitting and strong Rashba-type
spin-orbit coupling. Focusing on a stripe phase in which Cooper pairs acquire multiple center-of-mass momenta, we construct phase diagrams that reveal phase boundaries between the stripe phase and a helical phase characterized by a single center-of-mass momentum. Our results show that the stripe phase emerges at low temperatures and exhibits a reentrant behavior as a function of the strength of the altermagnetic splitting. We further analyze the stripe phase within a linearized gap equation, and uncover the mechanism of the pairing formation unique to the stripe phase. This mechanism originates from the anisotropic deformation of the
Fermi surfaces induced by the altermagnetic splitting, highlighting the intriguing interplay between the
spin-orbit coupling and the altermagnets.
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Mesoscale and Nanoscale Physics
Exchange operation of Majorana zero modes in topological insulator-based Josephson trijunctions
Yunxiao Zhang, Zhaozheng Lyu, Xiang Wang et al. (+19 more)
Majorana zero modes are anyons obeying non-Abelian exchange statistics distinct from
fermions or
bosons. While significant progresses have been achieved in the past two decades in searching for these exotic excitations in solid-state systems, their non-Abelian nature remains unverified, as definitive proof requires braiding operations. Here, we report preliminarily experimental advances in creating, manipulating, and exchanging the presumed Majorana zero modes in an envelope-shaped Josephson device composed of multiple trijunctions on a topological
insulator surface. We observed the signatures of in-gap states migration consistent with the expectations of the Fu-Kane model, supporting the realization of an exchange operation. This work would establish a critical pathway toward ultimately braiding Majorana zero modes in the Fu-Kane scheme of topological
quantum computation.
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All authors Yunxiao Zhang, Zhaozheng Lyu, Xiang Wang, Yukun Shi, Duolin Wang, Xiaozhou Yang, Enna Zhuo, Bing Li, Yuyang Huang, Zenan Shi, Anqi Wang, Heng Zhang, Fucong Fei, Xiaohui Song, Peiling Li, Bingbing Tong, Ziwei Dou, Jie Shen, Guangtong Liu, Fanming Qu, Fengqi Song, Li Lu
Soft Condensed Matter · Cross-listed from physics.bio-ph
Optimal Undulatory Swimming with Constrained Deformation and Actuation Intervals
Fumiya Tokoro, Hideki Takayama, Shinji Deguchi et al. (+2 more)
In nature, many unicellular organisms are able to swim with the help of beating filaments, where local energy input leads to cooperative undulatory beating motion. Here, we investigate by employing reinforcement learning how undulatory microswimmers modeled as a discretized bead-bend-spring filament actuated by torques which are constrained locally. We show that the competition between actively applied torques and intrinsic bending stiffness leads to various optimal beating patterns characterized by distinct frequencies, amplitudes, and wavelengths. Interestingly, the optimum solutions depend on the action interval, i.e.\ the time scale how fast the microswimmer can \rev{change the applied torques} based on its internal state. We show that optimized stiffness- and action-interval-dependent beating is realized by bang-bang solutions of the applied torques with distinct optimum time-periodicity and phase shift between consecutive joints, which we analyze in detail by a systematic study of possible bang-bang wave solution patterns of applied torques. Our work not only sheds light on how efficient beating patterns of biological microswimmers can emerge based on internal and local constraints, but also offers actuation policies for potential artificial elastic microswimmers.
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All authors Fumiya Tokoro, Hideki Takayama, Shinji Deguchi, Andreas Zöttl, Daiki Matsunaga
Superconductivity
Magneto-Chiral Anisotropy in Josephson Diode Effect of All-Metallic Lateral Junctions with Interfacial Rashba Spin-Orbit Coupling
Maximilian Mangold, Lorenz Bauriedl, Johanna Berger et al. (+7 more)
We explore the role of interfacial Rashba
spin-orbit coupling (SOC) for the Josephson diode effect in all-metal diffusive Josephson junctions. Devices with Fe/Pt and Cu/Pt weak links between Nb leads reveal a Josephson diode effect in an in-plane
magnetic field with magneto-
chiral anisotropy according to the point
symmetry of Rashba SOC. The Rashba SOC originates from inversion
symmetry breaking at the metal-metal interfaces. A control sample with a plain Cu-layer as weak link, in contrast, exhibits an axis-symmetric diode effect. The Fraunhofer patterns display an apparent inverted hysteresis which can be traced back to stray fields resulting from the conventional hysteretic
vortex pinning in the Nb contacts.
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All authors Maximilian Mangold, Lorenz Bauriedl, Johanna Berger, Chang Yu-Cheng, Thomas N.G. Meier, Matthias Kronseder, Pertti Hakonen, Christian H. Back, Christoph Strunk, Dhavala Suri