Strongly Correlated Electrons
On-Shell Methods for Quantum Matter: Strongly correlated Dirac materials
Jeff Murugan
We propose a framework for applying on-shell scattering amplitude methods to emergent relativistic phases of
quantum matter. Many strongly correlated systems, from Dirac and Weyl semimetals to topological-
insulator surfaces, exhibit low-energy excitations that are effectively massless relativistic spinors. We show that physical observables such as nonlinear optical and
Hall responses can be obtained from compact on-shell amplitudes, bypassing the complexity of Feynman diagrams. As a concrete demonstration, we derive the nonlinear
Hall conductivity of a Dirac semimetal from a single parity-odd three-
photon amplitude, highlighting the analytic and conceptual power of amplitude-based approaches for strongly correlated condensed-matter systems.
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Materials Science
Antisolvent-Assisted Growth of Centimeter-Scale CsPbBr$_3$ Perovskite Single Crystals: A Theory-Guided Approach
I.O. Simonenko, R.G. Nazmitdinov and T.N. Vershinina
The fabrication of large, high-quality single
crystals (SCs) of all-inorganic cesium lead bromide (CsPbBr$_3$) via accessible methods remains a significant challenge. This work presents a systematic approach to optimize the antisolvent vapor-assisted crystallization (AVC) method, where the experimental design is guided by a theoretical methods at each step. A synergistic 9:1 (v/v) DMSO/DMF binary solvent was selected to balance solubility and kinetics, a choice rationalized by an analysis of Gutmann's donor numbers. Subsequently, ethanol was selected as a promising antisolvent by evaluating its properties against key criteria of miscibility and
diffusion rate using Hansen Solubility Parameters (HSP) and Fick's law expressed in terms of saturated vapor pressure. Within this rationally-defined chemical system, the "growth window" was experimentally mapped, identifying an optimal precursor concentration of 0.35 M and a preliminary titration step to induce a controlled metastable state. The optimized protocol consistently yields phase-pure, orthorhombic CsPbBr$_3$ SCs up to 1 cm in size within one week at room temperature. The resulting
crystals exhibit high crystallinity and thermal stability up to \SI{550}{\celsius}
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Quantum Gases
Engineering Anderson Localization in Arbitrary Dimensions with Interacting Quasiperiodic Kicked Bosons
H. Olsen, P. Vignolo and M. Albert
We study the interplay of interactions and quasiperiodic driving in the Lieb-Liniger model of one-dimensional
bosons subjected to a sequence of delta kicks. Building on the known mapping between the kicked rotor and the Anderson model, we show that both interparticle interactions and quasiperiodic modulations of the kicking strength can independently and simultaneously generate synthetic dimensions. In the absence of modulation, interactions between two
bosons already promote an effective two-dimensional Anderson model. Introducing one or two additional incommensurate frequencies further extends the system to three and four effective dimensions, respectively. Through extensive numerical simulations of the two-body dynamics and finite-time scaling analysis, we observe Anderson localization and the associated critical behavior characteristic of the orthogonal universality class. This combined use of interactions and quasiperiodic driving thus provides a versatile framework for emulating Anderson localization and its transition in arbitrary dimensions.
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Materials Science
Influence of Bi Alloying on GaAs Valence Band Structure
Joshua J. P. Cooper, Jared W. Mitchell, Shane Smolenski et al. (+9 more)
Bi alloying is predicted to transform GaAs from a
semiconductor to a topological
insulator or semi-metal. To date, studies of the GaAs$_{1-x}$Bi$_x$
alloy band structure have been limited, and the origins of Bi-induced enhancement of the
spin-orbit splitting energy, $\Delta_\mathrm{SO}$, are unresolved. Here, we present high-resolution angle-resolved photoemission spectroscopy (ARPES) of droplet-free epitaxial GaAs$_{1-x}$Bi$_x$ films with $x_{\mathrm{Bi}}$ = 0.06. In addition to quantifying the Bi-induced shifts of the light-hole and heavy-hole valence bands, we probe the origins of the Bi-enhanced $\Delta_\mathrm{SO}$. Using exact-two-component density functional theory calculations, we identify the key role of Bi p-orbitals in the upward shift of the light-hole and heavy-hole bands that results in the Bi-enhanced $\Delta_\mathrm{SO}$.
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All authors Joshua J. P. Cooper, Jared W. Mitchell, Shane Smolenski, Ming Wen, Eoghan Downey, Chris Jozwiak, Aaron Bostwick, Eli Rotenberg, Kai Sun, Dominika Zgid, Na Hyun Jo, Rachel S. Goldman
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Quantum non-Markovian Hatano-Nelson model
Sumit Kumar Jana, Ryo Hanai, Tan Van Vu et al. (+2 more)
While considering non-Hermitian
Hamiltonians arising in the presence of dissipation, in most cases, the dissipation is taken to be frequency independent. However, this idealization may not always be applicable in experimental settings, where dissipation can be frequency-dependent. Such frequency-dependent dissipation leads to non-Markovian behavior. In this work, we demonstrate how a
quantum non-Markovian Hatano-Nelson model arises microscopically in a quasi-one-dimensional dissipative
lattice. This is achieved using non-
equilibrium Green's functions without requiring any approximation like weak system-bath coupling or a time-scale separation, which would have been necessary for a Markovian treatment. The resulting effective system exhibits nonreciprocal hopping, the defining characteristic of the Hatano-Nelson model, as well as uniform dissipation, both of which are frequency-dependent. This holds for both bosonic and fermionic settings. We find solely non-Markovian nonreciprocal features like unidirectional frequency blocking in bosonic settings, and a particular type of non-
equilibrium dissipative
quantum phase transition in fermionic settings, that cannot be captured in a Markovian theory, nor have any analog in reciprocal systems. Our results lay the groundwork for describing and engineering non-Markovian nonreciprocal
quantum lattices.
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All authors Sumit Kumar Jana, Ryo Hanai, Tan Van Vu, Hisao Hayakawa, Archak Purkayastha
Other Condensed Matter
Directional Photocurrent Generated by Quantum Interference Control
Yiming Gong, Kai Wang and Steven T. Cundiff
Although the absorption of light in a bulk homogeneous
semiconductor produces photocarriers with non-zero momentum, it generally does not produce a current in the absence of an applied electric field because equal amounts of carriers with opposite momentum are injected. The interference of absorption processes, for example, between one-
photon and two-
photon absorption, can produce a current because constructive interference for carriers with one momentum can correspond to destructive interference for carriers with the opposite momentum. We show that for the interference between two-
photon and three-
photon absorption, the current has a narrower angular spread, i.e., a “beam” of electrons in a specified direction is produced in the
semiconductor.
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Materials Science · Cross-listed from physics.chem-ph
Spin covalent chemistry of carbon
E.F. Sheka
This review presents the covalent chemistry of carbon within the
spin-radical concept of electron interaction. Using the
language of valence bond trimodality, the regions of classical spinless covalence and its
spin counterpart are defined. Carbon is the only element exhibiting
spin covalent chemistry. Classical covalent chemistry of carbon concerns molecular substances whose valence bond structure includes segregate or chained single sp3C-C bonds. Substances with double sp2C-C and triple sp1C-C bonds are the subject of
spin covalent chemistry of carbon. The mathematical apparatus of
spin covalence forms the basis of
algorithms governing the chemical modification of carbon substances, polymerization processes, and catalysis involving them, making it possible to supplement the empirical
spin covalent chemistry of carbon with its virtual analog.
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Strongly Correlated Electrons
The action of the nearest neighbor Coulomb repulsion on the homogeneity in the high concentration domain for itinerant systems
Zsolt Gulacsi
Exact results are presented for itinerant systems demonstrating that the nearest neighbor Coulomb repulsion (V) destroys the homogeneity in the high concentration regime, this property being not present in the low concentration domain. Since the effects of V often seems contradictory, and the number of phases in which it could appear is extremely large, this result underlines that the action of the nearest neighbor repulsion is not necessarily routed in the characteristics of phases on which it acts, but could be intimately related to V itself. The $V > 0$ case usually means non-integrability, hence the deduced exact ground states are related to non-integrable systems, the technique being based on positive semidefinite operator properties.
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Disordered Systems and Neural Networks · Cross-listed from physics.chem-ph
Fuzzy Neural Network Performance and Interpretability of Quantum Wavefunction Probability Predictions
Pedro H. M. Zanineli, Matheus Zaia Monteiro, Vinicius Francisco Wasques et al. (+2 more)
Predicting
quantum wavefunction probability distributions is crucial for computational chemistry and materials science, yet machine learning (ML) models often face a trade-off between accuracy and interpretability. This study compares Artificial Neural Networks (ANNs) and Adaptive Neuro-Fuzzy Inference Systems (ANFIS) in modeling
quantum probability distributions for the H$_{2}^+$ ion, leveraging data generated via Physics-Informed Neural Networks (PINNs). While ANN achieved superior accuracy (R$^2$ = 0.99 vs ANFIS's 0.95 with Gaussian membership functions), it required over 50x more parameters (2,305 vs 39-45). ANFIS, however, provided unique interpretability: its Gaussian membership functions encoded spatial electron localization near
proton positions ($\mu = 1.2 A$), mirroring Born probability densities, while fuzzy rules reflected
quantum superposition principles. Rules prioritizing the internuclear direction revealed the system's 1D
symmetry, aligning with Linear Combination of Atomic Orbitals theory–a novel data-driven perspective on orbital hybridization. Membership function variances ($\sigma$) further quantified electron delocalization trends, and peak prediction errors highlighted unresolved
quantum cusps. The choice of functions critically impacted performance: Gaussian/Generalized Bell outperformed Sigmoid, with errors improving as training data increased, showing scalability. This study underscores the context-dependent value of ML: ANN for precision and ANFIS for interpretable, parameter-efficient approximations that link inputs to physical behavior. These findings advocate hybrid approaches in
quantum simulations, balancing accuracy with explainability to accelerate discovery. Future work should extend ANFIS to multi-electron systems and integrate domain-specific constraints (e.g., kinetic energy terms), bridging data-driven models and fundamental physics.
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All authors Pedro H. M. Zanineli, Matheus Zaia Monteiro, Vinicius Francisco Wasques, Francielle Santo Pedro Simões, Gabriel R. Schleder
Statistical Mechanics · Cross-listed from quant-ph
Generating function and Bloch representation for quantum Fisher tensor
Felipe P. Abreu and Wei Chen
The Uhlmann relative amplitude between two density
matrices is shown to be a generating function, through which the
quantum Fisher tensor that contains both the
quantum Fisher information
matrix and the mean Uhlmann
curvature can be obtained via differentiation over system parameters. In the pure state limit, our generating function recovers that of the
quantum geometric tensor proposed by Hetényi and Lévay, and also clarifies the fidelity and phase between two
quantum states as the generating functions of the
quantum metric and Berry
curvature, respectively. A generic expression for the
quantum Fisher tensor in terms of the Bloch representation of density
matrices is derived, which facilitates the calculation of the tensor, mean Uhlmann
curvature, and
geometric properties derived from the
quantum Fisher information
matrix. Canonical ensembles of
spins are adopted to demonstrate our formalism, which reveals a constant
Ricci scalar, a
vacuum Einstein equation, and a cosmological constant on the 3D Euclidean
manifold of the
magnetic field
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Materials Science
Uniaxial stress tuning of the anomalous Hall effect in Mn3Ge
G. A. Lombardi, L. O. Kutelak, M. M. Piva et al. (+6 more)
Tunable electronic properties in
magnetic materials lead to novel physical phenomena that have the potential to be exploited in the design of new spintronic devices. Here, we report the effect of uniaxial stress on the anomalous
Hall effect (AHE) in the hexagonal frustrated
antiferromagnetic Heusler compound Mn3Ge. Our x-ray diffraction results show that the c/a ratio varies linearly with strain when stress is applied along the a axis, as well as a significantly higher Young's modulus along the c direction. The linear behavior of the c/a ratio under uniaxial stress mirrors that seen under hydrostatic pressure up to 1.8 GPa, but results in a characteristically different behavior of the AHE. Stress applied along the a axis induces a distortion in the ab plane, smoothing the abrupt jump in the AHE signal at zero
magnetic field. In contrast, stress applied along the c axis has little effect, presumably due to the higher Young's modulus. We argue that this is due to pronounced changes in
magnetic order.
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All authors G. A. Lombardi, L. O. Kutelak, M. M. Piva, V. E. S. Frehse, G. A. Calligaris, K. Manna, C. Felser, R. D. dos Reis, M. Nicklas
Materials Science · Cross-listed from physics.chem-ph
Fast Evaluation of Unbiased Atomic Forces in ab initio Variational Monte Carlo via the Lagrangian Technique
Kousuke Nakano, Stefano Battaglia and Jürg Hutter
Ab initio
quantum Monte Carlo (QMC) methods are state-of-the-art electronic structure calculations based on highly parallelizable
stochastic frameworks for accurate solutions of the many-body Schrödinger equation, suitable for modern many-core supercomputer architectures. Despite its potential, one of the major drawbacks that still hinders QMC applications, especially when targeting dynamical properties of large systems or extensive
datasets, is the lack of an affordable method to compute atomic forces that are consistent with the corresponding potential energy surfaces (PESs), also known as unbiased atomic forces. Recently, one of the authors in the present paper proposed a way to obtain unbiased forces with the Jastrow-correlated Slater determinant ansatz, where the determinant part is frozen to the values obtained by a mean-field method, such as Density Functional Theory. However, the proposed method has a significant drawback for its applications: for a system with $N$
nuclei, one requires 6$N$ additional DFT calculations to get unbiased forces. This paper presents a way to replace the 6$N$ DFT calculations with a single coupled-perturbed Kohn-Sham calculation, following the so-called Lagrangian technique established in
quantum chemistry. We also demonstrate that the developed unbiased VMC force calculation improves not only the consistency with PESs, but also its accuracy, by investigating three molecules from the rMD17
benchmark set, and comparing the unbiased VMC forces with those obtained by CCSD(T) calculations. We found that the bare VMC forces are biased from the CCSD(T) ones, while the unbiased ones give values closer to those of the CCSD(T) ones. Our
benchmark test also reveals that the unbiased VMC forces yield very consistent values with hybrid and meta GGAs, but do not necessarily yield values that are very close to those of CCSD(T).
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Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Scaling behavior of dissipative systems with imaginary gap closing
Jinghui Pi, Xingli Li and Yangqian Yan
Point-gap
topology, characterized by spectral winding numbers, is crucial to non-Hermitian topological phases and dramatically alters real-time dynamics. In this paper, we study the
evolution of
quantum particles in dissipative systems with imaginary gap closing, using the saddle-point approximation method. For trivial point-gap systems, imaginary gap-closing points can also be saddle points. This leads to a single power-law decay of the local Green's function, with the asymptotic scaling behavior determined by the order of these saddle points. In contrast, for nontrivial point-gap systems, imaginary gap-closing points do not coincide with saddle points in general. This results in a dynamical behavior characterized by two different scaling laws for distinct time regimes. In the short-time regime, the local Green's function is governed by the dominant saddle points and exhibits an asymptotic exponential decay. In the long-time regime, however, the dynamics is controlled by imaginary gap-closing points, leading to a power-law decay envelope. Our findings advance the understanding of
quantum dynamics in dissipative systems and provide predictions testable in future experiments.
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Soft Condensed Matter
Phase separation with non-local interactions
Filipe C. Thewes, Yicheng Qiang, Oliver W. Paulin et al. (+1 more)
Phase separation in complex systems is a ubiquitous phenomenon. While simple theories predict coarsening until only macroscopically large phases remain, concrete models often exhibit patterns with finite length scales. To unify such models, we here propose a general field-theoretic model that combines phase separation with non-local interactions. Our analysis reveals that long-range interactions generally suppress coarsening, whereas systems with non-local short-range interactions additionally exhibit a continuous phase transition to patterned phases. Only the latter system allows for the coexistence of homogeneous and patterned phases, which we explain by mapping to the conserved Swift-Hohenberg model. Taken together, our generic model reveals an underlying framework that describes similar phenomena observed in many complex phase-separating systems.
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All authors Filipe C. Thewes, Yicheng Qiang, Oliver W. Paulin, David Zwicker
Strongly Correlated Electrons
Exact analysis of the interplay of charge order and unconventional pairings in the 2D Hatsugai-Kohmoto model
Carlos Eduardo S. P. Corsino and Hermann Freire
We provide here a study of some competing ordering tendencies exhibited by the exactly solvable 2D Hatsugai-Kohmoto (HK) model on a square
lattice. To this end, we investigate the interplay between superconductivity, charge-density wave (CDW) and pair-density wave (PDW) orders as a function of interaction, doping parameter,
magnetic field, and uniaxial strain. As a result, we confirm the intertwined nature of CDW and PDW fluctuating orders for intermediate-to-strong couplings. We also verify that, while an applied
magnetic field favors the formation of a CDW and allows the subsequent emergence of a PDW as a secondary order, strain effects favor unidirectional PDW as a primary order over the subdominant appearance of a stripe-like CDW. These results underscore the value of the HK model as an interesting platform in order to investigate (via an exactly solvable framework) the emergence of charge order and unconventional superconductivity in fermionic systems with strong interactions. Finally, we briefly discuss an orbital generalization of the HK model, which has been recently argued to be relevant to describe the properties of realistic strongly correlated systems.
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Mesoscale and Nanoscale Physics
Altermagnetic Spin Precession and Spin Transistor
Li-Shuo Liu, Kai Shao, Hai-Dong Li et al. (+3 more)
Altermagnets hold great potential for spintronic applications, yet their intrinsic
spin dynamics and associated transport properties remain largely unexplored. Here, we investigate
spin-resolved
quantum transport in a multi-terminal setup based on a $d$-wave altermagnet. It is found that the altermagnetic
spin splitting in momentum space induces an interesting
spin precession in two-dimensional real space, giving rise to characteristic
spin patterns. This altermagnetic
spin precession manifests as a spatial modulation of the transverse
Hall-like voltage, whose oscillation period provides a direct measure of the
spin-splitting strength. When the altermagnetism is electrically tunable, the proposed setup functions as a prototype for a highly efficient
spin transistor. The key physical effects are shown to be robust against dephasing and crystalline warping. Our work not only identifies a fingerprint signature of altermagnets, offering a direct probe of the altermagnetic
spin splitting, but also represents an important step toward bridging their fundamental physics with practical spintronic applications.
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All authors Li-Shuo Liu, Kai Shao, Hai-Dong Li, Xiangang Wan, Wei Chen, D. Y. Xing
Statistical Mechanics
Application of boundary functionals of the theory of random processes to aerosol coagulation
V. V. Ryazanov
A new approach to describing aerosol behavior is proposed. Boundary functionals of random process theory are applied to describe the behavior of aerosol concentrations during coagulation. It is shown that considering the first-passage time of a given aerosol concentration level corresponds to experimental results for the time dependence of aerosol concentration. Probabilities for aerosol concentrations to attain specific values are obtained, as well as expressions for average aerosol concentrations.
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Superconductivity
Interplay between altermagnetism and superconductivity in two dimensions: intertwined symmetries and singlet-triplet mixing
Kinga Jasiewicz, Paweł Wójcik, Michał Nowak et al. (+1 more)
We study the interplay between altermagnetism and unconventional superconductivity for the case of two-dimensional square- and triangular-
lattice systems. Our approach is based on an effective single particle
Hamiltonian which mimics the alternating
spin splitting characteristic for the $d$-$wave$ and $i$-$wave$ altermagnetic state. By supplementing the model with intersite pairing term we characterize the principal features of the coexistent altermagnetic-superconducting state as well as the possibility of inducing the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase. Our calculations show that the subtle interplay between the
symmetries of the superconducting and altermagnetic order parameters as well as the shape/size of the
Fermi surface lead to various types of anisotropic behaviors of the resultant non-zero momentum pairing, which has not been possible in the originally proposed FFLO state. Moreover, in the considered systems additional pairing
symmetries appear leading to an exotic multi-component order parameter with singlet-triplet mixing. To interpret the obtained data we analyze the Cooper pair density in the momentum space and the corresponding
Fermi wave vector mismatch resulting from the altermagnetic
spin splitting. We discuss our result in the context of possible applications like, e.g., the superconducting diode.
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All authors Kinga Jasiewicz, Paweł Wójcik, Michał Nowak, Michał Zegrodnik
Materials Science
Systematic global structure search of bismuth-based binary systems under pressure using machine learning potentials
Hayato Wakai, Shintaro Ishiwata and Atsuto Seko
Machine learning potentials (MLPs) have significantly advanced global
crystal structure prediction by enabling efficient and accurate property evaluations. In this study, global structure searches are performed for 11 bismuth-based binary systems, including Na-Bi, Ca-Bi, and Eu-Bi, under pressures ranging from 0 to 20 GPa, employing
polynomial MLPs developed specifically for these systems. The searches reveal numerous compounds not previously reported in the literature and identify all experimentally known compounds that are representable within the explored configurational space. These results highlight the robustness and reliability of the current MLP-based structure search. The study provides valuable insights into the discovery and design of novel bismuth-based materials under both ambient and high-pressure conditions.
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Materials Science
LeMat-Bulk: aggregating, and de-duplicating quantum chemistry materials databases
Martin Siron, Inel Djafar, Ali Ramlaoui et al. (+10 more)
The rapid expansion of materials science databases has driven machine learning-based discovery while also posing challenges in data integration, duplication, and interoperability. Robust standardization and de-duplication methods are needed to address these issues and streamline materials research. We present LeMat-Bulk, a unified
dataset combining Materials Project, OQMD, and Alexandria, encompassing over 5.3 million PBE-calculated materials and also representing the largest collection of PBESol and SCAN functional calculations. Our methodology standardizes calculations across databases that utilize different parameters, effectively addressing redundancy and enhancing cross-compatibility. To de-duplicate, we propose a hashing function which we termed the Bonding
Algorithm Weisfeiller-Lehman (BAWL). We comprehensively
benchmark this fingerprint under atomic noise,
lattice strain, and
symmetry transformations, demonstrating that it outperforms existing fingerprinting techniques such as SLICES, and CLOUD in robustness while offering greater computational efficiency than similarity-based approaches such as Pymatgen's StructureMatcher. Additionally, the fingerprint facilitates the analysis of functional-dependent trends (PBE, PBESol, SCAN) offering a scalable framework for data-driven materials science.
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All authors Martin Siron, Inel Djafar, Ali Ramlaoui, Etienne du Fayette, Amandine Rossello, Edvin Fako, Matthew McDermott, Felix Therrien, Luis Barroso-Luque, Flaviu Cipcigan, Philippe Schwaller, Thomas Wolf, Alexandre Duval
Strongly Correlated Electrons
An explicit formula for perturbation theory at any order with infinitely many perturbations
Joseph M. Jones and M. W. Long
We provide a systematic formula, in terms of integer partitions, that generates perturbation theory explicitly at an arbitrary order. Our approach naturally includes an infinite number of perturbations and uses a single
matrix equation that contains the information for both the
eigenvalue and eigenvector corrections. The formula reduces to the standard case of one perturbation in the appropriate limit. This formulation streamlines the derivations that are traditionally tedious in perturbation theory, facilitating high-order calculations.
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Mesoscale and Nanoscale Physics
Unexpected increase of intensity-dependent excitonic second- and third-harmonic generation induced by static electric fields
Ruixin Zuo, Matthias Reichelt, Cong Ngo et al. (+3 more)
We compute and analyze the dependence of excitonic second- and third-harmonic generation (SHG/THG) as a function of the optical excitation intensity in the presence of static electric fields by solving the
semiconductor Bloch equations. Our simulations are performed for excitation of the strongly bound intralayer
exciton of an inversion-symmetric homobilayer of MoS2 with in-plane electric fields. We demonstrate that for resonant excitation at the 1s K-
exciton the SHG and the THG show complex dependencies on both the strength of the static field and the peak amplitude of the optical pulse. For sufficiently intense optical excitation, the THG increases and the SHG increases superlinearly with the amplitude of the static field as long as
exciton ionization is not yet dominating. Microscopic simulations demonstrate that these dependencies arise from an interplay between several effects including static and transient Stark shifts,
exciton ionization, Wannier-Stark localization, off-resonant Rabi oscillations, and a modified interference between optical nonlinearities induced by the intraband acceleration. Our findings offer several new possibilities for controlling the strong-field dynamics of systems with strongly bound
excitons.
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All authors Ruixin Zuo, Matthias Reichelt, Cong Ngo, Xiaohong Song, Weifeng Yang, Torsten Meier
Strongly Correlated Electrons
Tim Bauer and Johannes Reuther
Quasiparticle hybridization remains a major challenge to realizing and controlling exotic states of matter in existing
quantum simulation platforms. We report the absence of hybridization for compact localized states (CLS) emerging in the
chiral spin liquid described by the Yao-Kivelson model. The CLS form due to destructive
quantum interference at fine-tuned coupling constants and populate perfectly flat quasiparticle bands on an effective kagome
lattice. Using a formalism for general Majorana-hopping
Hamiltonians, we derive exact expressions for CLS for various flux configurations and both for the topological and trivial phases of the model. In addition to finite-energy matter
fermions with characteristic
spin-
spin correlations, we construct compact localized Majorana zero modes attached to $\pi$-flux excitations, which enable non-Abelian braiding of Ising anyons with minimal separation. Our results inform the
quantum simulation of topologically ordered states of matter and open avenues for exploring flat-band physics in
quantum spin liquids.
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Mesoscale and Nanoscale Physics
V. N. Mantsevich, D. S. Smirnov and E. L. Ivchenko
The polarization
entanglement of
photons emitted by
semiconductor quantum dots is unavoidably limited by the
spin fluctuations of the host
lattice nuclei. To overcome this limitation, we develop a theory of entangled
photon pair generation by a symmetric colloidal
quantum dot mediated by a triplet
exciton. We derive general analytical expressions for the concurrence as a function of the hyperfine interaction strength and show that it is intrinsically higher than that in conventional doublet-
exciton systems such as self-assembled
quantum dots. The concurrence sensitively depends on the shape anisotropy and the strain applied to a nanocrystal. In particular, we uncover a possibility of completely suppressing the detrimental effect of the hyperfine interaction due to the interplay between nanocrystal anisotropy and electron-hole exchange interaction. We argue that this represents the ultimate limit for the generation of entangled
photon pairs by
semiconductor quantum dots.
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Materials Science
Probing the atomic dynamics of ultrafast melting with femtosecond electron diffraction
M. Z. Mo, M. B. Maigler, T. Held et al. (+12 more)
Melting is an everyday phase transition that is determined by thermodynamic parameters like temperature and pressure. In contrast, ultrafast melting is governed by the microscopic response to a rapid energy input and, thus, can reveal the strength and dynamics of atomic bonds as well as the energy flow rate to the
lattice. Accurately describing these processes remains challenging and requires detailed insights into transient states encountered. Here, we present data from femtosecond electron diffraction measurements that capture the structural
evolution of copper during the ultrafast solid to
liquid phase transformations. At absorbed energy densities 2 to 4 times the melting threshold, melting begins at the surface slightly below the nominal melting point followed by rapid homogeneous melting throughout the volume. Molecular dynamics simulations reproduce these observations and reveal a weak electron
lattice energy transfer rate for the given experimental conditions. Both simulations and experiments show no indications of rapid
lattice collapse when its temperature surpasses proposed limits of superheating, providing evidence that inherent dynamics limits the speed of disordering in ultrafast melting of metals.
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All authors M. Z. Mo, M. B. Maigler, T. Held, B. K. Ofori-Okai, A. Bergermann, Z. Chen, R. K. Li, X. Shen, K. Sokolowski-Tinten, R. Redmer, X. J. Wang, J. Schein, D. O. Gericke, B. Rethfeld, S. H. Glenzer
Statistical Mechanics · Cross-listed from quant-ph
Bounds on quantum Fisher information and uncertainty relations for thermodynamically conjugate variables
Ye-Ming Meng and Zhe-Yu Shi
Uncertainty relations represent a foundational principle in
quantum mechanics, imposing inherent limits on the precision with which mechanically conjugate variables such as position and momentum can be simultaneously determined. This work establishes analogous relations for thermodynamically conjugate variables – specifically, a classical intensive parameter $\theta$ and its corresponding extensive
quantum operator $\hat{O}$ – in
equilibrium states. We develop a framework to derive a rigorous thermodynamic uncertainty relation for such pairs, where the uncertainty of the classical parameter $\theta$ is quantified by its
quantum Fisher information $\mathcal{F}_\theta$. The framework is based on an exact integral representation that relates $\mathcal{F}_{\theta}$ to the autocorrelation function of operator $\hat{O}$. From this representation, we derive a tight upper bound for the
quantum Fisher information, which yields a thermodynamic uncertainty relation: $\Delta\theta\,\overline{\Delta O} \ge k_\text{B}T$ with $\overline{\Delta O}\equiv\partial_\theta\langle\hat{O}\rangle\,\Delta\theta$ and $T$ is the system temperature. The result establishes a fundamental precision limit for
quantum sensing and metrology in thermal systems, directly connecting it to the thermodynamic properties of linear response and fluctuations.
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Strongly Correlated Electrons
Coupled dimerized alternating-bond quantum spin chains in the distorted honeycomb-lattice magnet Cu$_5$SbO$_6$
C. Piyakulworawat, K. Morita, Y. Fukumoto et al. (+9 more)
We analyze powder-averaged inelastic
neutron scattering and magnetization data for the distorted honeycomb compound Cu$_5$SbO$_6$ using a first-order dimer expansion calculation and
quantum Monte Carlo simulations. We show that, in contrast to the previously proposed honeycomb
lattice model, Cu$_5$SbO$_6$ accommodates interacting dimerized
spin chains with alternating
ferromagnetic-
antiferromagnetic couplings along the chain. Moreover, unlike the typical couplings observed in other Cu$^{2+}$-based distorted honeycomb magnets, the
spin chains in Cu$_5$SbO$_6$ primarily couple through an
antiferromagnetic coupling that arises between the honeycomb layers, rather than the expected interchain coupling in the layers. This finding reveals a different
magnetic coupling scheme for Cu$_5$SbO$_6$. In addition, utilizing x-ray spectroscopy and transmission electron microscopy, we also refine the
crystal structure and stacking-fault model of the compound.
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All authors C. Piyakulworawat, K. Morita, Y. Fukumoto, W.-Y. Hsieh, W.-T. Chen, K. Nakajima, S. Ohira-Kawamura, Y. Zhao, S. Wannapaiboon, P. Piyawongwatthana, T. J. Sato, K. Matan
Strongly Correlated Electrons
Anisotropy of linear magnetoresistance in Kagome metal ZrV$_6$Sn$_6$
Yifan Deng, Ming Cheng, Lanxin Liu et al. (+9 more)
The Kagome
lattice has attracted extensive
attention due to the diverse
magnetic properties and non-trivial electronic states generated by its unique atomic arrangement, which provides an excellent system for exploring macroscopic
quantum behavior. Here, we report the anomalous transport properties in 166-type Kagome metal ZrV$_6$Sn$_6$ single
crystals. The quadratic and linear magnetoresistance (LMR) can be observed depending on the directions of the field and the current. Integrating
Hall resistivity and
quantum oscillation measurements, we found that the LMR could match well with the Abrikosov model. However, this model encounters difficulties in explaining the anisotropy of the magnetoresistance. To solve the issue, we extrapolate the Abrikosov model to the case of two-dimensional linear dispersion. It was found that when the field is parallel to the linear dependence momentum, the quantized energy is $\epsilon_n^{\pm}$ = $\pm v\sqrt{p^2+2eHn/c}$, resulting in LMR. By contrast, when it is parallel to the non-linear dependence momentum, the energy is $\epsilon_n^{\pm}$ = $\pm v\sqrt{2eHn/c}$, without yielding LMR. Through the combination of experiment and theory, the modified Abrikosov model could interpret the macroscopic
quantum transport in ZrV$_6$Sn$_6$
crystal. The present research provides a new perspective for understanding the LMR behavior.
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All authors Yifan Deng, Ming Cheng, Lanxin Liu, Nan Zhou, Yu Zhao, Ruihuan Lan, Yongqiang Pan, Wenhai Song, Yuyan Han, Xiaoguang Zhu, Xuan Luo, Yuping Sun
Materials Science
Ultrafast Terahertz Photoconductivity and Near-Field Imaging of Nanoscale Inhomogeneities in Multilayer Epitaxial Graphene Nanoribbons
Arvind Singh, Jan Kunc, Tinkara Troha et al. (+2 more)
We study broadband terahertz (THz) conductivity and ultrafast photoconductivity spectra in lithographically fabricated multilayer epitaxial
graphene nanoribbons grown on C- face of 6H-SiC substrate. THz near-field spectroscopy reveals local conductivity variations across nanoscale structural inhomogeneities such as wrinkles and grain boundaries within the multilayer
graphene. Ultrabroadband THz far-field spectroscopy (0.15-16 THz) distinguishes doped
graphene layers near the substrate from quasi-neutral layers (QNLs) further from the substrate. Temperature-dependent THz conductivity spectra are dominated by intra-band transitions both in the doped and QNLs. Photoexcitation then alters mainly the response of the QNLs: these exhibit a very high carrier mobility and a large positive THz photoconductivity with picosecond lifetime. The response of QNLs strongly depends on the carrier temperature $T_c$: the scattering time drops by an order of magnitude down to ~10 fs upon an increase of $T_c$ from 50 K to $T_c >$ 1000 K, which is attributed to an enhanced electron-electron and electron-
phonon scattering and to an interaction of electrons with mid-gap states.
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All authors Arvind Singh, Jan Kunc, Tinkara Troha, Hynek Němec, Petr Kužel
Materials Science
Disorder-broadened topological Hall phase and anomalous Hall scaling in FeGe
Chaman Gupta, Chris Matsumura, Hongbin Yang et al. (+9 more)
Magnetic skyrmions are topologically protected
spin textures that are promising candidates for low-power spintronic
memory and logic devices. Realizing skyrmion-based devices requires an understanding of how structural disorder affects their stability and transport properties. This study uses Ne$^{+}$ ion irradiation at fluences from $10^{11}$ to $10^{14}$ ions-cm$^{-2}$ to systematically vary defect densities in 80 nm epitaxial FeGe films and quantify the resulting modifications to
magnetic phase boundaries and electronic scattering. Temperature- and field-dependent
Hall measurements reveal that increasing disorder progressively extends the topological
Hall signal from a narrow window near 200K̃ in pristine films down to 4K̃ at the highest fluence, with peak amplitude more than doubling. Simultaneously, the anomalous
Hall effect transitions from quadratic Berry
curvature scaling to linear skew scattering behavior, with the skew coefficient increasing threefold. These results establish quantitative correlations between defect concentration, skyrmion phase space, and transport mechanisms in a
chiral magnet. It demonstrates that ion-beam modification provides systematic control over both topological texture stability and electrical detectability.
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All authors Chaman Gupta, Chris Matsumura, Hongbin Yang, Sarah Edwards, Rebeca M. Gurrola, Jiun-Haw Chu, Hanjong Paik, Yongqiang Wang, David A. Muller, Robert Streubel, Tzu-Ming Lu, Serena Eley