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 to the quasi-particles' family and has aroused intense interest 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 a unitary transformation, where the renormalization of the rotational constants for different molecules in the helium nanodroplets is reproduced, getting excellent agreement with the experimental data collected during the past decades.

Polaron states of the full-configuration defects in metal halide perovskites.

The systematical analysis for varieties of defects with different depths and lattice relaxation strengths in metal halide perovskites (MHPs) is a challenging task. Here, we study the energy shifts of the full-configuration defects due to the polaron effect based on the all-coupling variational method in MHPs, where these polaron states are formed stemming from different defect species coupling with the longitudinal optical phonon modes via Fro¨hlich mechanism. We find that the polaron effect results in defect levels varying from tens to several hundreds of meV, which are very close to the correction of defect levels due to the defect-polaron effect, especially for these defects migration proved in the recent experiments in MHPs.

Self-Trapped Interlayer Excitons in van der Waals Heterostructures.

The self-trapped state (STS) of the interlayer exciton (IX) has aroused enormous interest owing to its significant impact on the fundamental properties of the van der Waals heterostructures (vdWHs). Nevertheless, the microscopic mechanisms of STS are still controversial. Herein, we study the corrections of the binding energies of the IXs stemming from 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.

Multiphonon processes of the inelastic electron transfer in olfaction.

Inelastic electron transfer, regarded as one of the potential mechanisms to explain odorant recognition in atomic-scale processes, is still a matter of intense debate. Here, we study multiphonon processes of electron transfer using the Markvart model and calculate their lifetimes with the values of key parameters widely adopted in olfactory systems. We find that these multiphonon processes are as quick as the single phonon process, which suggests that contributions from different phonon modes of an odorant molecule should be included for electron transfer in olfaction.

Energy Resonance Transfer between Quantum Defects in Metal Halide Perovskites.

Quantum defects have been shown to play an essential role in nonradiative recombination in metal halide perovskites (MHPs). Nonetheless, the processes of charge transfer assisted by defects are still ambiguous. Herein, we theoretically study the nonradiative multiphonon processes among different types of quantum defects in MHPs using Markvart's model for the induced mechanisms of electron-electron and electron-phonon interactions.

Effective velocities of polaron spin states in monolayer transition metal dichalcogenides.

We propose a theoretical model for studying the effective velocities of polaron spin states in monolayer transition metal dichalcogenides (TMDS) on the substrate. It is found that the effective velocity of polaron shows the splitting with different magnitudes due to the Rashba spin-orbit coupling, which results in the reversed distribution of the effective velocities of polaron spin states. Moreover, the reversed points depend on the truncated wave-vector of optical phonon and can be modulated by the polarity of substrate and the internal distance between monolayer TMDS and substrate.

Quantum defect-assisted multiphonon Raman scattering in metal halide perovskites.

Quantum defects are essential to understand the non-radiative recombination processes in metal halide perovskites-based photovoltaic devices, in which Huang-Rhys factor, reflecting the coupling strength between the charge carrier and optical phonons, plays a key role in determining the non-radiative recombination via multiphonon processes. Herein, we theoretically present multiphonon Raman scattering intermediated by defects arising from the charge carrier of defect coupled with the longitudinal optical (LO) phonon in the deformation potential and Fröhlich mechanisms, respectively. We find that the Raman scattering shows multiple LO phonon overtones at equal interval LO phonons, where Huang-Rhys factor could be evaluated by the order of the strongest overtone.

Infrared optical absorption of magnetopolaron resonance states in graphene on the polar substrates.

We study the infrared optical absorption of magnetopolaron resonance states in graphene in the strong magnetic field based on the Huybrechts's model, in which polaron states are formed due to the strong coupling between electrons and surface optical (SO) phonons induced by the polar substrate. We propose the special magnetopolaron states1/2(|1〉e±|1〉ph), namely, the superposition states between one SO phonon and the first-excited Landau level, which split into two branches of coupling modes and give rise to two optical absorption peaks with different intensities. Moreover, their intensities can be sensitively modulated by the magnetic field, the truncated wave-vector of SO phonon, polarity of substrate and internal distance between graphene and substrate.

Polaron effect on the bandgap modulation in monolayer transition metal dichalcogenides.

We theoretically study the bandgap modulation in monolayer transition metal dichalcogenides (TMDs) originating from the carrier-optical phonon coupling in the Fröhlich polaron model, in which both of the surface optical phonons modes induced by the polar substrate and the intrinsic longitudinal optical phonons modes have been taken into account. We find that the modulated magnitude of the bandgap is in the range of 100-500 meV by altering different polar substrates and tuning the internal distance between TMDs and polar substrate. The large tunability of the bandgap not only provides a possible explanation for the experimental measurements regarding the dielectric environmental sensitivity of the bandgap, but also holds promise for potential applications in optoelectronics and photovoltaics.

The optical phonon resonance scattering with spin-conserving and spin-flip processes between Landau levels in graphene.

In the frame of Huang-Rhys's lattice relaxation model, we theoretically investigate the electron relaxation assisted by optical phonon resonance scattering among Landau levels with spin-conserving and spin-flip processes in graphene. We not only consider the longitudinal optical (LO) phonon scattering, but also the surface optical (SO) phonon scattering induced by the polar substrate under the graphene. The relaxation rate displays a Gaussian distribution by considering the effect of lattice relaxation that arises from the electron-deformation potential acoustic phonon interaction.

Lattice relaxation of graphene under high magnetic field.

We investigate the n = 0 Landau level (LL) in monolayer graphene with high magnetic field. We find that the energy gap is opened in the n = 0 LL by the magnetic-field-dependent lattice relaxation originating from the interactions between the electrons (holes) and longitudinal-deformation-acoustic phonon. Both the linear and square-foot dependence of the energy gap on the magnetic field are obtained depending on the choice of the Debye cut-off wave number for the acoustic phonon.

The effects of the magnetopolaron on the energy gap opening in graphene.

The magnetopolaron is formed via electron-acoustic deformation phonon coupling in the presence of a magnetic field in monolayer graphene. We find that an energy gap (EG) is opened due to the electron-phonon coupling. Both linear and square-root forms for the dependence of the EG on the magnetic field are obtained, which are in agreement with experimental measurements.

Two-phonon processes of intraband relaxation in the terahertz regime in quantum dots.

We theoretically investigate the intraband relaxation of quantum dots in the terahertz regime due to two acoustic phonon scattering by applying a lattice relaxation approach based on the deformation potential coupling between electrons and acoustic phonons. In particular, we find that the relaxation time depends strongly on the ratio of two acoustic phonons. The influences of the energy separation between the ground and first excited state, the quantum dot height, and the lattice temperature on the relaxation time are also discussed.