Materials Science
Single-Atom Tuning of Structural and Optoelectronic Properties in Halogenated Anthracene-Based Covalent Organic Frameworks
Klaudija Paliušytė, Laura Fuchs, Zehua Xu et al. (+7 more)
Strategies for tuning structural and (opto-)electronic properties are fundamental to the rational design of functional materials. Here, we present a molecular design approach for precisely modulating the optoelectronic properties of covalent organic frameworks (COFs) through single-atom halogen substitution on $\pi$-extended anthracene linkers. Using a Wurster-type tetratopic amine (W-NH$_2$) and a series of anthracene-based dialdehydes bearing H, Cl, Br, or I at the 2-position, a family of imine-linked COFs, W-A-X (X = H, Cl, Br, I), was synthesized, all displaying well-ordered porous structures. The halogen substituent strongly influences framework formation, with brominated COFs forming substantially larger crystalline domains than their chloro- and iodo-functionalized analogues. UV-vis absorption and photoluminescence measurements reveal a systematic
redshift across the series $(\mathrm{H < Cl < Br < I})$, demonstrating that a single-atom modification effectively tunes the optical response. Time-dependent density functional theory calculations on both isolated fragments and extended COF models attribute these trends to halogen-induced changes in the COF band structure and provide a mechanistic understanding of how single-atom substitution influences the optoelectronic properties of the extended $\pi$-framework. Overall, this study establishes single-atom halogen substitution as a powerful and modular strategy for tailoring the structural and optical properties of anthracene-based COFs.
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All authors Klaudija Paliušytė, Laura Fuchs, Zehua Xu, Kuangjie Liu, Kornel Roztocki, Shuo Sun, Hendrik Zipse, Achim Hartschuh, Frank Ortmann, Jenny Schneider
Statistical Mechanics
Measurement-induced crossover in quantum first-detection times
Giovanni Di Fresco, Aldo Coraggio, Alessandro Silva et al. (+1 more)
The
quantum first-detection problem concerns the statistics of the time at which a system, subject to repeated measurements, is observed in a prescribed target state for the first time. Unlike its classical counterpart, the measurement back action intrinsic to
quantum mechanics may profoundly alter the system dynamics. Here we show that it induces a distinct change in the statistics of the first-detection time. For a
quantum particle in one spatial dimension subject to stroboscopic measurements, we observe an algebraic decay of the probability of the first-detection time if the particle is free, an exponential decay in the presence of a confining potential, and a time-dependent crossover between these behaviors if the particle is partially confined. This crossover reflects the purely
quantum nature of the detection process, which fundamentally distinguishes it from the first-passage problem in classical systems.
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All authors Giovanni Di Fresco, Aldo Coraggio, Alessandro Silva, Andrea Gambassi
Mesoscale and Nanoscale Physics · Cross-listed from physics.comp-ph
Real-Symmetric Hamiltonian Enables Near-Linear Scaling for Fast Million-Atom Electronic Structure Computations
Zichong Zhang and Shuze Zhu
The exploration of
quantum phenomena in mesoscale materials, such as moire superlattices, is limited by the cubic scaling cost of conventional electronic structure methods. Here, we introduce a scalable tight binding framework that achieves near linear scaling, enabling mesoscopic
quantum simulations. By transforming the complex Hermitian Bloch
Hamiltonian into an equivalent real symmetric form, the method avoids dense diagonalization by combining sparse LDL decomposition with Sylvester's law of inertia for spectral slicing and global rank calibration. This formulation enables efficient band structure calculations for large scale systems, solving magic angle twisted
bilayer graphene in minutes on a standard laptop and extending to 1.5 million atoms within days on a single workstation. Applying this framework to ultra low twist angle structures with atomistic strain relaxation, we find robust isolated low-energy band clusters over several finite ultra low angle windows down to 0.09 degree. Our framework provides an efficient computational platform for studying
quantum materials at experimentally relevant length scales and supports data driven discovery in large scale moire systems.
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Mesoscale and Nanoscale Physics
Ratchet effect in lateral plasmonic crystal: Giant enhancement due to interference of "bright" and "dark" modes
I. V. Gorbenko, S. O. Potashin and V.Yu. Kachorovskii
We develop a theory of the ratchet effect in a lateral plasmonic
crystal (LPC) formed by a two dimensional electron gas under a periodic dual-grating gate. The system is driven by terahertz radiation, and the spatial asymmetry required for the generation of dc photocurrent is introduced by a phase shift between the radiation's near-field modulation and the static electron density profile. In contrast to the commonly used perturbative "minimal model" of the ratchet effect, which assumes weak density modulation, we solve the problem exactly with respect to the static gate-induced potential while treating the radiation field perturbatively. This approach reveals a dramatic enhancement of the plasmonic contribution to the ratchet current due to the interference of "bright" and "dark" plasmon modes, which are excited on an equal footing in the asymmetric LPC. Specifically, we predict a parametric growth of the plasmonic peak as compared with the Drude peak with increasing coupling, and the appearance of a dense super-resonant structure when the spacing between plasmonic sub-bands becomes larger than the damping rate. Hence, the dc response exhibits both resonant and super-resonant regimes observed in recent experiments on the radiation transmission through the LPC. The interplay of bright and dark modes, together with their interference, provides a powerful mechanism for controlling the magnitude and sign of the photocurrent by gate voltages and the radiation frequency.
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Quantum Gases · Cross-listed from quant-ph
Temperature effect on a kicked Tonks-Girardeau gas
Ang Yang, Yue Chen and Lei Ying
It is widely recognized that finite temperatures degrade
quantum coherence and can induce thermalization. Here, we study the effect of finite temperature on a kicked Tonks–Girardeau gas, which is known to exhibit many–body dynamical localization and delocalization under periodic and quasiperiodic kicks, respectively. We find that many–body dynamical localization persists at finite–and even high–temperatures, although the coherence of the localized state is further degraded. In particular, we demonstrate a modified effective thermalization of the localized state by considering the initial temperature. Moreover, we show many–body dynamical localization transition at intermediate temperature. Our work extends the study of many–body dynamical localization and delocalization to the finite–temperature regime, providing guidance for cold-atom experiments, particularly in the strongly-interacting regime.
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Soft Condensed Matter
Space-resolved stress correlations and viscoelastic moduli for polydisperse systems: the faces of the stress noise
Jörg Baschnagel and Alexander N. Semenov
Several advances in the theory of space-resolved viscoelasticity of
liquids and other amorphous systems are discussed in the present paper. In particular, considering long-time regimes of stress relaxation in
liquids we obtain the generalized compressibility equation valid for systems with mass polydispersity, and derive a new relation allowing to calculate the wavevector-dependent
equilibrium transverse modulus in terms of the generalized structure factors. Turning to the basic relations between the spatially-resolved relaxation
moduli and the spatio-temporal correlation functions of the stress tensor, we provide their new derivation based on a conceptually simple argument that does not involve consideration of non-stationary processes. We also elucidate the relationship between the stress noise associated with the classical Newtonian dynamics and the reduced deviatoric stress coming from the Zwanzig-Mori projection operator formalism. The general relations between the stress noise and the tensor of relaxation
moduli are discussed as well.
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Materials Science
Electric Charge Transport and Dielectric Properties of the Barium Titanate Ceramics Obtained by Spark-Plasma Sintering with Different Carbon Content
Oleksandr S. Pylypchuk, Victor V. Vainberg, Denis O. Stetsenko et al. (+9 more)
Barium titanate (BaTiO3) ceramics with a different content of carbon were synthesized by spark-
plasma sintering (SPS) at the temperature of 1100 C in
vacuum under pressure. The concentration and distribution of carbon
impurity inside the samples is estimated by scanning electron microscopy (SEM). The resistivity vs temperature and electric field dependences of the SPS ceramics with different carbon concentration have been studied. It is shown that their conduction is determined by the variable range hopping mechanism and obeys the Mott law. The density of localized states and localization radius of the electron wave function are determined. The difference in low-temperature resistivity of the SPS ceramics is caused by carbon concentration and connected with it variation of the dielectric permittivity. The relative dielectric permittivity of the SPS ceramics is colossal and reaches the values of 10^5 - 10^6 order. The larger carbon concentration is, the smaller the permittivity and resistivity are within the Mott hopping conduction temperature range. In the range from 250 K to 408 K one observes that the dielectric permittivity strongly increases forming a maximum in all samples, which may be related to the phase transition. Along with this, resistivity manifests a simultaneous sharp decrease. The decrease of resistivity along with the characteristic dependence of resistivity vs dielectric permittivity in the Mott conduction temperature range, evidences the validity of Heywang model for the description of SPS ceramics conduction mechanisms. The resistivity strongly decreases with increasing frequency in the AC regime, which agrees both with models of hopping conduction and effects based on the Maxwell-Wagner model. The studied SPS BaTiO3 ceramics are attractive for applications in energy storage and sensorics.
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All authors Oleksandr S. Pylypchuk, Victor V. Vainberg, Denis O. Stetsenko, Oleksii V. Bereznikov, Taisiia O. Kuzmenko, Serhii E. Ivanchenko, Bohdan Pokhylko, Vladyslav Kushnir, Lesya Demchenko, Volodimir N. Poroshin, Victor I. Styopkin, Anna N. Morozovska
Materials Science
Spin-dependent Raman and Brillouin light scattering on excitons in CsPbBr$_3$ perovskite crystals
Ina V. Kalitukha, Victor F. Sapega, Dmitri R. Yakovlev et al. (+5 more)
The
spin properties of
excitons and charge carriers in CsPbBr$_3$ lead halide perovskite
crystals are investigated by
spin-dependent light scattering in
magnetic fields up to 10 T.
Spin-flip Raman scattering spectra measured under resonant excitation of
exciton-polaritons show a rich variety of features provided by the Zeeman splittings of
excitons and of electrons and holes interacting with the
excitons. The magnitudes and anisotropies of their Landé $g$-factors are measured. A detailed consideration of the responsible mechanisms is presented and discussed in relation to the experimental data, in particular on the polarization properties of the Raman spectra. We consider several mechanisms for the combined
spin-flip Raman scattering processes involving resident carriers and photoexcited
excitons and suggest new ones, involving trions in the intermediate scattering state. A double electron
spin-flip caused by the
exciton interaction with two localized or donor-bound electrons is revealed. The spectral lines of Brillouin light scattering on
exciton-polaritons shift in energy and become polarization-sensitive in
magnetic field, evidencing the splitting of the
exciton-polariton dispersion.
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All authors Ina V. Kalitukha, Victor F. Sapega, Dmitri R. Yakovlev, Dennis Kudlacik, Damien Canneson, Yury G. Kusrayev, Anna V. Rodina, Manfred Bayer
Superconductivity
Robustness of the Kohn-Luttinger mechanism against symmetry breaking
Amir Dalal, Jonathan Ruhman and Vladyslav Kozii
We investigate how strongly broken spatial
symmetries affect the Kohn–Luttinger (KL) mechanism, in which superconductivity emerges purely from repulsive interactions. While the original KL argument assumes continuous rotational
symmetry, real materials possess only discrete point-group
symmetries, raising a central question: can sufficiently strong
symmetry breaking suppress or eliminate KL superconductivity? Using controlled perturbation theory and explicit two-dimensional models with Ising and Rashba
spin–orbit coupling (SOC), we find that KL superconductivity is broadly robust and exhibits qualitatively universal behavior across models: the transition temperature $T_c$ is nonmonotonic in the
symmetry-breaking field, shows a pronounced maximum at scales of the order of the
Fermi energy, and decays exponentially toward zero at asymptotically large fields. However, the physical mechanisms determining this suppression may differ between models. Overall, these results demonstrate that KL-type superconductivity can persist across a wide class of
spin–orbit-coupled systems.
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Materials Science
The CP-PAW code package for first-principles calculations from a user's perspective
Peter E. Blöchl, Robert Schade, Lukas Allen-Rump et al. (+5 more)
CP-PAW is a combined electronic structure and ab-initio molecular dynamics code to perform mixed
quantum and classical simulations of atomistic condensed phase systems, such as solids,
liquids, and molecular systems. As the name suggests, the CP-PAW code unifies the all-electron projector augmented-wave method with the Car-Parrinello approach to determine not only the electronic and
nuclear ground state of condensed matter, but also to study their properties and dynamics. In addition to briefly outlining the underlying theory, the focus will be on unique aspects of CP-PAW and how to correctly employ them as a user. How to install CP-PAW using the new build system will also be briefly mentioned.
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All authors Peter E. Blöchl, Robert Schade, Lukas Allen-Rump, Sangeeta Rajpurohit, Amrith Rathnakaran, Konstantin Tamoev, Mani Lokamani, Thomas D. Kühne
Disordered Systems and Neural Networks
Finite-temperature topological transitions in the presence of quenched uncorrelated disorder
Claudio Bonati and Ettore Vicari
We address issues related to the presence of defects at finite-temperature topological transitions, in particular when defects are modeled in terms of further variables associated with a quenched disorder, corresponding to the limit in which the defect dynamics is very slow. As a paradigmatic model, we consider the classical three-dimensional
lattice ${\mathbb Z}_2$ gauge model in the presence of quenched uncorrelated disorder associated with the plaquettes of the
lattice, whose topological transitions are characterized by the absence of a local order parameter. We study the critical behaviors in the presence of weak disorder. We show that they belong to a new topological universality class, different from that of the
lattice ${\mathbb Z}_2$ gauge models without disorder, in agreement with the Harris criterium for the relevance of uncorrelated quenched disorder when the pure system undergoes a continuous transition with positive specific-heat critical exponent.
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Mesoscale and Nanoscale Physics
Magnetoexcitons and Massive Dirac Fermions in Monolayers of Transition Metal Dichalcogenides in a High Magnetic Field
Katarzyna Sadecka, Marek Korkusinski, Ludmiła Szulakowska et al. (+1 more)
We present a theory of the emission spectrum of magnetoexcitons interacting with a $\nu = 1$
quantum Hall state of massive Dirac
fermions in monolayer transition metal dichalcogenides in high
magnetic fields. Using an ab initio-parametrized massive Dirac
fermion model including valley and
spin degrees of freedom, combined with exact diagonalization techniques, we show that interband emission from the massive Dirac
Fermion magnetoexciton interacting with $\nu = 1$ state directly probes intra-conduction-band excitations of the $\nu = 1$. Many-body interactions with the filled massive Dirac
fermion $\nu = 1$ level yield a strong renormalization of the emission spectrum, including fully polarized emission, a pronounced
redshift, and broadening relative to neutral and charged
excitons. The calculated spectra are consistent with recent experiments [1-3], establishing magneto-spectroscopy as a probe of finite carrier densities in massive Dirac systems.
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All authors Katarzyna Sadecka, Marek Korkusinski, Ludmiła Szulakowska, Paweł Hawrylak
Statistical Mechanics
Far tails of the biased CTRW model under the short time limit
Wanli Wang, Kaixin Zhang and Yuda Cheng
It has been observed in numerous experiments, simulations, and various theoretical studies that the spreading of particles can be modeled by the continuous-time random walk. We consider two widely used cases, namely Gaussian and discrete displacements, to compute the position distribution and demonstrate the emergence of exponential decay in the far tails when a bias is introduced. We further analyze the temporal rate function and the positional rate function to examine the convergence of the theoretical predictions. For Gaussian displacements, we also discuss the relationship between the position distributions with and without bias in different asymptotic limits.
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Mesoscale and Nanoscale Physics
Laughlin pumping assisted by surface acoustic waves
Renfei Wang, Xiao Liu, Adbhut Gupta et al. (+8 more)
The
quantum Hall effect is a fascinating electrical transport phenomenon signified by precise quantization of
Hall conductivity $\sigma_\mathrm{xy}$ and vanishing longitudinal conductivity $\sigma_\mathrm{xx}$. Laughlin proposed an elegant explanation in which adiabatic insertion of a flux tube pumps charge through the system. This analysis unveils the fundamental role of gauge invariance and provides a compelling argument about the fractional charge of fractional
quantum Hall states. While it has been used extensively as a theoretical tool, a quantitative experimental investigation is lacking despite multiple attempts. Here we report successful realizations of Laughlin pumping in several integer and fractional
quantum Hall states. One essential technical innovation is using surface acoustic waves to periodically clear the charges accumulated during the pumping process.
Magnetic fluxes are inserted at a constant rate so there is no need to perform complicated data fitting. Furthermore, our setting can reliably extract $\sigma_\mathrm{xx}$ that is several orders of magnitude lower than the limit of conventional techniques. Effective energy gaps can be deduced from the temperature dependence of $\sigma_\mathrm{xx}$, which are drastically different from those provided by conventional transport data. This work not only brings a famous gedanken experiment to reality but also serves as a portal for many future investigations.
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All authors Renfei Wang, Xiao Liu, Adbhut Gupta, Kirk W. Baldwin, Loren Pfeiffer, Wenfeng Zhang, Rui-Rui Du, Mansour Shayegan, Xi Lin, Ying-Hai Wu, Yang Liu
Mesoscale and Nanoscale Physics
Exciton-polaron Umklapp scattering in Wigner crystals
Erfu Liu, Matthew Wilson, Jenny Hu et al. (+9 more)
Strong Coulomb interactions in two-dimensional (2D)
semiconductors give rise to tightly bound
excitons,
exciton polarons, and correlated electronic phases such as Wigner
crystals (WCs), yet their mutual interplay remains poorly understood. Here we report the observation of multi-branch excitonic Umklapp scattering in both electron and hole WCs realized in ultraclean monolayer WSe$_2$, exhibiting exceptionally high melting temperatures (T$_c$ $\approx$ 20-30 K). Robust Wigner crystallization activates multiple finite-momentum optical resonances, including quasilinearly dispersing, light-like
excitons and
exciton polarons, extending far beyond the single excitonic Umklapp feature reported previously. Helicity-resolved magneto-optical measurements reveal a pronounced valley dependence of the scattering processes. Combined experiment and theory identify a polaron-induced brightening mechanism in which
exciton polarons transfer oscillator strength from bright zero-momentum states to otherwise dark finite-momentum states, explaining the emergence of multiple Umklapp branches where conventional
exciton-WC scattering is ineffective. These results establish WC polarons as a new quasiparticle paradigm and introduce polaron-induced Umklapp scattering as a general route to accessing finite-momentum many-body excitations in 2D
quantum materials.
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All authors Erfu Liu, Matthew Wilson, Jenny Hu, Alexandra Zimmerman, Amal Mathew, Tianyi Ouyang, Ao Shi, Takashi Taniguchi, Kenji Watanabe, Tony F. Heinz, Yia-Chung Chang, Chun Hung Lui
Materials Science
Thermodynamic assessment of the Ba-La-S and Ga-La-S systems
Jiayang Wang, Guangyu Hu, Pierre Lucas et al. (+1 more)
This paper presents the first thermodynamic assessment of binary and pseudo-binary phase diagrams in the Ba–La–S and Ga–La–S systems by means of the CALPHAD method. Experimental phase diagram
equilibrium data and thermodynamic properties available from the literature were critically reviewed and assessed using thermodynamic models for the Gibbs energies of individual phases. The associated solution model was used to describe the short-range ordering behavior of the
liquid phases. To supplement the limited experimental data reported in the literature, ab initio molecular dynamics calculations were employed to derive mixing enthalpies of the
liquid phases in the binary subsystems. The resulting phase diagrams and calculated thermodynamic properties show good agreement with available literature within the investigated compositional ranges of binary and pseudo-binary systems.
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All authors Jiayang Wang, Guangyu Hu, Pierre Lucas, Marat I. Latypov
Materials Science
Transition Metal Dichalcogenide MoS${}_2$: oxygen and fluorine functionalization for selective plasma processing
Yury Polyachenko, Yuri Barsukov, Shoaib Khalid et al. (+1 more)
Low-temperature
plasma processing is a promising technique for tailoring transition metal dichalcogenides (TMDs). For chalcogen substitution processing, a key challenge is to identify the ion energy window that enables selective chalcogen removal while preserving the metal
lattice. Using ab-initio molecular dynamics (AIMD), we demonstrate that oxygen and fluorine functionalization widen the processing window by significantly lowering the sulfur sputtering energy threshold ($E_{\text{sputt,S}}$) of MoS${}_2$ from $\sim 30$ eV to $\sim 10$ eV via formation of sputtering products such as SO${}_2$ and SF${}_n$. Additionally, we show that experimentally relevant cryogenic temperatures strongly affect $E_{\text{sputt,S}}$. The dependence is confirmed via AIMD and also predicted by a mechanistic parameter-free theory, suggesting that $E_{\text{sputt}}(T)$ generalizes to other TMDs, functionalization, and surface impacts in general. Our results highlight oxygen/fluorine functionalization, ionic impact angle, and material temperature to be key control parameters for selective, damage-controlled chalcogen removal in TMD processing.
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All authors Yury Polyachenko, Yuri Barsukov, Shoaib Khalid, Igor Kaganovich
Materials Science
Local Structure of Epitaxial Single Crystal UO$_{2+x}$ Thin Films
Jarrod C. Lewis, Steven D. Conradson, Jacek Wasik et al. (+5 more)
The influence of oxygen stoichiometry on the uranium local environment is explored in epitaxial single
crystal uranium
oxide thin films grown by DC magnetron sputtering. Through post-growth annealing, the stoichiometry of as-grown UO$_{2}$ films are tuned over an approximate stoichiometry range of $0.07 \leq x \leq 0.20$, estimated with X-ray photoelectron spectroscopy measurements of the U$-4f$ and O$-1s$ peaks. The local structure of the thin films are then probed using extended X-ray absorption fine structure measurements at the U $L_{3}$ absorption edge. We observe both the
evolution of the U local environment of as a function of oxidation in UO$_{2+x}$, and that the near stoichiometric UO$_{2}$ film replicates the local structure of bulk UO$_{2}$ material standards well. The series of stoichiometrically varied samples highlights the non-trivial transitional behaviour of the UO$_{2+x}$ oxygen sublattice with increasing oxygen content in this stoichiometric regime, while also demonstrating the efficacy of this thin film synthesis route for actinide studies beyond their established use as idealised surfaces, which could be readily adapted for further stoichiometrically tailored material studies and UO$_{2+x}$ device fabrication.
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All authors Jarrod C. Lewis, Steven D. Conradson, Jacek Wasik, Lottie M. Harding, Rebecca Nicholls, Jude Laverock, Chris Bell, Ross Springell
Materials Science
Self-organized defect-phases along dislocations in irradiated alloys
N. Saunders, R. S. Averback and P. Bellon
Patterning of precipitates along dislocation lines arising from nonequilibrium segregation during ion irradiation is investigated in model binary
alloys.
Lattice kinetic Monte Carlo simulations reveal that the competition between solute advection by point defects to the dislocation and thermal
diffusion along the dislocation can stabilize self-organized nanostructures with distinct morphologies, including tubes and quasi-periodic necklaces. The stabilization of nano-necklaces is rationalized by heavy-tail power-law distributions for solute redistribution along the dislocation due to advection.
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