arXiv subjects

Zi-Wu Wang

Publications and source records attributed to Zi-Wu Wang.

17 recordsLinked to original sources

arXiv2025

Antiferromagnetic skyrmion as a magnonic lens

A lens, a device transforming propagation directions in an organized fashion, is one of the fundamental tools for wave manipulation. Spin wave, the collective excitation of ordered magnetizations, stands out as a promising candidate for future energy-saving information technologies. Here we propose theoretically and verify by micromagnetic simulations, that an antiferromagnetic skyrmion naturally serves as a lens for spin wave, when the Dzyaloshinskii-Moriya strength exceeds a threshold. The underlying mechanism is the spin wave deflection caused by Dzyaloshinskii-Moriya interaction, a mechanism that is ordinarily overshadowed by the magnetic topology.

cond-mat.mes-hall↗

arXiv2024

Crossover From Cooper-Pair Hopping to Single-Electron Hopping in Pb$_x$(TiO$_2$)$_{1-x}$ Granular Films

The electrical transport properties of Pb$_x$(TiO$_2$)$_{1-x}$ ($x$ being the Pb volume fraction and ranging from $\sim$0.45 to $\sim$0.69) granular films are investigated experimentally. The charging energy of the Pb granules is reduced to less than the superconducting gap of Pb granules for the low temperature insulating films by using high-$k$ dielectric TiO$_2$ as the insulating matrix. For the insulating films in the vicinity of the superconductor-insulator transition, Cooper-pair hopping governs the low-temperature hopping transport. For these films, the low-temperature magnetoresistance is positive at low field and the resistivity vs temperature for Cooper-pair hopping obeys an Efros-Shklovsii-type variable-range-hopping law. A crossover from Cooper-pair-dominated hopping to single-electron-dominated hopping is observed with decreasing $x$. The emergence of single-electron-dominated hopping in the more insulating films is due to the causation that the intergrain Josephson coupling becomes too weak for Cooper pairs to hop between adjacent superconducting Pb granules.

cond-mat.supr-con↗

arXiv2023

The rotating excitons in two-dimensional materials: Valley Zeeman effect and chirality

We propose the rotational dynamics of the intralayer and interlayer excitons with their inherent momenta of inertia in the monolayer and bilayer transition metal dichalcogenides, respectively, where the new chirality of exciton is endowed by the rotational angular momentum, namely, the formations of left- and right-handed excitons at the +K and -K valleys, respectively. We find that angular momenta exchange between excitons and its surrounding phononic bath result in the large fluctuation of the effective g-factor and the asymmetry of valley Zeeman splitting observed in most recently experiments, both of which sensitively depend on the magnetic moments provided by the phononic environment. This rotating exciton model not only proposes a new controllable knob in valleytronics, but opens the door to explore the angular momentum exchange of the chiral quasiparticles with the many-body environment.

cond-mat.mes-hall↗

arXiv2023

Theory of all-coupling angulon for molecules rotating in many-body environment

The formation of angulon, stemming from the rotor (molecule or impurity) rotating in the quantum many-body field, adds a new member in the quasiparticle's family and has aroused intensively interests in multiple research fields. However, the analysis of the coupling strength between the rotor and its hosting environment remains a challenging task both in theory and experiment. Here, we develop the all-coupling theory of the angulon by introducing an unitary transformation, where the renormalization of the rotational constants for different molecules in the helium nanodroplets are reproduced, getting excellent agreement with the collected experimental data during the past decades. Moreover, the strength of molecule-helium coupling and the effective radius of the solvation shell corotating along with the molecular rotor could be estimated qualitatively. This model not only provides the significant enlightenment for analyzing the rotational spectroscopy of molecules in the phononic environment, but also provides a new method to study the transfer of the phonon angular momentum in angulon frame.

cond-mat.mes-hall↗

arXiv2023

Optical absorption of angulon in metal halide perovskites

We theoretically study the optical absorption of an angulon in the metal halide perovskites (MHP) based on the improved Devreese-Huybrechts-Lemmens model, where the formation of quasiparticle angulon states originates from the organic cation rotating in the inorganic octahedral cage of MHP. We find that the resonance optical absorption peaks are appeared when the energy of incident photon matches the quantum levels of angulon. Moreover, the intensity of absorption depends on the quantum states of phonon angular momentum. These theoretical results provide significant insight to study the redistribution of angular momenta for the rotational molecules immersed into the many-body environment.

cond-mat.mes-hall↗

arXiv2022

Mobile defects as mediated states for charge-carrier trapping in metal halide perovskites quantum dots

The migration motion of defects in metal halide perovskites quantum dots (MHPQDs) results in charge-carrier trapping become more complicated. We study two-step trapping mediated by mobile defects between the ground state of MHPQDs and a fixed-depth defect using a full-configuration defect method, where all possible trapping processes mediated by these mobile defects could be reproduced and the fastest channels among them are picked out. We find that these two-step trapping processes could keep more one order of magnitude faster than these direct ones as mobile defect with the appropriate localization strength, which implies that these indirect trapping should play the crucial rule to determine the non-radiative recombination losses. These results provide the significant explanation for studying non-radiation processes of carriers in the presence of the migration defects in recent experiments. Moreover, this model will be available to analyze some key performance related defects in electronic devices.

cond-mat.mes-hall↗

arXiv2022

Microscopic theory of Raman scattering for the rotational organic cation in metal halide perovskites

A gap exists in microscopic understanding the dynamic properties of the rotational organic cation (ROC) in the inorganic framework of the metal halide perovskites (MHP) to date. Herein, we develop a microscopic theory of Raman scattering for the ROC in MHP based on the angular momentum of a ROC exchanging with that of the photon and phonon. We systematically present the selection rules for the angular momentum transfer among three lowest rotational levels. We find that the phonon angular momentum that arising from the inorganic framework and its specific values could be directly manifested by Stokes (or anti-Stokes) shift. Moreover, the initial orientation of the ROC and its preferentially rotational directions could be judged in Raman spectra. This study lays the theoretical foundation for the high-precision resolution and manipulation of molecular rotation immersed in many-body environment by Raman technique.

cond-mat.mes-hall↗

arXiv2022

Charge carriers trapping by the full-configuration defects in metal halide perovskites quantum dots

Metal halide perovskites quantum dots (MHPQDs) have aroused enormous interesting in the photovoltaic and photoelectric because of their marvelous properties and size characteristics. However, one of key problems that how to systematically analyze charge carriers trapping by different defects is still a challenge task. Here, we study nonradiation multiphonon processes of the charge carrier trapping by various defects in MHPQDs based on the well-known Huang-Rhys model, in which a method of fullconfiguration defect, including different defect species with variable depth and lattice relaxation strength, is developed by introducing a localization parameter in the quantum defect model. With the help of this method, these fastest trapping channels for charge carriers transferring from the quantum dot ground state to different defects are found. Furthermore, the dependences of the trapping time on the radius of quantum dot, the defect depth and temperature are given. These results not only enrich the knowledge of charge carrier trapping processes by defects, but enlighten the designs of MHPQDs-based photovoltaic and photoelectric devices.

cond-mat.mtrl-sci↗

arXiv2022

Infrared optical absorption of Frohlich polaron in metal halide perovskites

The formation of Frohlich polaron in metal halide perovskites, arising from the charge carrierlongitudinal optical (LO) phonon coupling, has been proposed to explain their exceptional properties, but the effective identification of polaron in these materials is still a challenge task. Herein, we theoretically present the infrared optical absorption of Frohlich polaron based on Huang-Rhys model. We find that multiphonon overtones are appeared as the energy of incident photon matches the multiple LO phonons, wherein the average phonon numbers of a polaron can be directly evaluated by the order of the strongest overtone. These multiphonon structures sensitively depend on the scale of electronic distribution in the ground state and the dimensionality of the perovskite materials, which gives the enlightenment for the effective modulation of competing processes between the polaron formation and carrier cooling. Moreover, the order of the strongest overtone shifts to the higher ones with temperature, providing a potential proof of the carriers mobility affected by LO phonons scattering. The present model not only suggests a direct way to verify Frohlich polaron, but also enriches the understanding of the polaron properties in metal halide perovskites.

cond-mat.mes-hall↗

arXiv2021

Self-trapped interlayer excitons in van der Waals heterostructures

The self-trapped state (STS) of interlayer exciton (IX) has been aroused enormous interesting owing to their significant impact on the fundamental properties of the van derWaals heterostructures (vdWHs). Nevertheless, the microscopic mechanisms of STS are still controversial. Herein, we study the corrections of the binding energies of the IXs due to the exciton-interface optical phonon coupling in four kinds of vdWHs and find that these IXs are in the STS for the appropriate ratio of the electron and hole effective masses. We show that these STSs could be classified into the type I with the increasing binding energy in the tens of meV range, which are very agreement with the red-shift of the IXs spectra in experiments, and the type II with the decreasing binding energy, which provides a possible explanation for the blue-shift and broad linewidth of the IXs spectra in the low temperature. Moreover, these two types of self-trapped IXs could be transformed into each other by adjusting the structural parameters of vdWHs. These results not only provide an in-depth understanding for the self-trapped mechanism of IX, but also shed light on the modulations of IXs in vdWHs.

cond-mat.mes-hall↗

arXiv2021

Inelastic electron transfer in olfaction: multiphonons processes

Inelastic electron transfer being regarded as one of the potential mechanisms to explain the odorant recognition in the atomic-scale processes is still a matter of intense debate. Here, we propose multiphonon processes of electrons transfer using the Markvart model and calculate their lifetimes with values of key parameters widely adopted in olfactory systems. We find that these multiphonon processes are as quickly as the single phonon process, which suggest that contributions from different phonon modes of odorant molecule for electrons transfer in olfaction should be included. Meanwhile, temperature dependence of electron transfer could be analyzed effectively based on the reorganization energy is expanded into the linewidth of multiphonon processes. Our theoretical results not only enrich the knowledge of the mechanism of the olfaction recognition, but also provide insights for quantum processes in the biological system.

physics.bio-ph↗

arXiv2021

Energy resonance transfer between quantum defects in metal halide perovskites

Quantum defects have shown to play an essential role for the non-radiative recombination in metal halide perovskites (MHPs). Nonetheless, the processes of charge transfer-assisted by defects are still ambiguous. Herein, we theoretically study the non-radiative multiphonon processes among different types of quantum defects in MHPs using Markvart model for the induced mechanisms of electron-electron and electron-phonon interactions, respectively. We find that charge carrier can transfer between the neighboring levels of the same type shallow defects by multiphonon processes, but it will be distinctly suppressed with the increasing of the defect depth. For the non-radiation multiphonon transitions between donor- and acceptor-like defects, the processes are very fast and independence of the defect depth, which provide a possible explanation for the blinking phenomena of photoluminescence spectra in recent experiment. We also discuss the temperature dependence of these multiphonon processes and find that their variational trends depend on the comparison of Huang-Rhys factor with the emitted phonon number. These theoretical results fill some gaps of defect-assisted non-radiative processes in the perovskites materials.

cond-mat.mes-hall↗

arXiv2020

An explanation for high defect tolerance in metal halide perovskite quantum dots

We propose Auger-like process assisted by quantum defects in metal halide perovskite quantum dots, where a charge carrier in the ground state of the quantum dot is trapped by quantum defects, resulting in another charge carrier in defect is excited and returns back to the ground state of the quantum dot. We find that the whole process is on the femtosecond scale. More importantly, the process is independent of the depth and species of the defects, which is in good agreement with the recent theoretical prediction using ab initio nonadiabatic molecular dynamics simulation. This Auger-like process may provide a potential explanation of high defect tolerance in metal halide perovskite materials.

cond-mat.mes-hall↗

arXiv2019

Anharmonic corrections to the multiphonon deep-level charge capture ab initio calculations for semiconductors

Nonradiative carrier recombination at semiconductor deep centers is of great importance to both fundamental physics and device engineering. In this letter, we provide a revised analysis of K. Huang's original nonradiative multi-phonon (NMP) theory with ab initio calculations. First, we identify at first-principle level that Huang's concise formula gives the same results as the matrix based formula, and Huang's high temperature formula provides an analytical expression for the coupling constant in Marcus theory. Secondly, the anharmonic effects are corrected by taking into account local phonon mode variation at different charge states of the defect. The corrected capture rates for defects in GaN and SiC agree well with experiments.

cond-mat.mtrl-sci↗

arXiv2018

Effect of exciton-phonon coupling on the interlayer excitons in transition metal dichalcogenides double layers

We investigate the correction of interlayer exciton binding energy in transition metal dichalcogenides double layers arising from the exciton-optical phonon coupling using the method of Lee-Low-Pines unitary transformation. We find that the binding energy varies in several tens of meV, depending on the polarizability of materials and interlayer distance between double layers. Moreover, the correction of binding energy results in the remarkable increasing of the critical temperature for the condensation of dilute excitonic gas basing on the Berezinskii-Kosterlitz-Thouless model. These results not only enrich the knowledge for the modulation of interlayer exciton, but also provide potential insights for the Bose-Einstein condensation and superfluid transport of interlayer exciton in two-dimensional heterostructures.

cond-mat.mes-hall↗

arXiv2017

Multiphonons resonance Raman scattering in Landau-quantized graphene

We theoretically investigate multiphonons resonance Raman scattering between the Landau levels in graphene on the polar substrate using the Huang-Rhys's model. We not only present the single and multiple surface optical (SO) phonons scattering, but also propose the combined multiphonons scattering (CMS), which is composed of the SO phonon and longitudinal acoustic phonon. We find that the CMS has a blue-shift behavior with increasing the magnetic field, differing from these SO phonon resonance scattering at a special magnetic field. This behavior may be used to explain the changing shoulder of the Raman spectrum of optical phonon resonance scattering in experiments. The theoretical model could be expanded to analyze the fine structure of Raman spectrum in two-dimensional materials.

cond-mat.mes-hall↗

arXiv2017

Correction of exciton binding energy in monolayer transition metal dichalcogenides

We theoretically investigate the corrections of exciton binding energy in monolayer transition metal dichalcogenides (TMDs) due to the exciton-optical phonon coupling in the Fr$\ddot{o}$hlich interaction model by using the linear operator combined Lee-Low-Pines variational method. We not only consider the excitons couple with the intrinsic longitudinal optical (LO) phonon modes, but also the surface optical phonon modes that induced by the polar substrates underneath the TMDs. We find that exciton binding energies are corrected in a large scale due to these exciton-optical phonon couplings. We discuss the dependences of exciton binding energy on the cut-off wave vector of optical phonon modes, the polarization parameters of materials and the interlayer distance between the polar substrates and TMDs. These results provide potential explanations for the divergence of the exciton binding energy between experiment and theory in TMDs.

cond-mat.mes-hall↗