Optical signature of bipolaron in monolayer transition metal dichalcogenides: all coupling approach

J V Nguepnang,C Kenfack-Sadem,M F C Fobasso,A Kenfack-Jiotsa,Y Sun

doi:10.1007/s11082-021-03365-1

Abstract

We studied the optical signature of bipolaron and its effects on the bandgap modulation in the single-layer Transition Metal Dichalcogenides (TMDs) under magnetic field. Using the Huybrecht method, we derived the ground state energies in the modified zero Landau levels for all Fröhlich coupling constants. We take into account both intrinsic longitudinal optical phonon modes and surface optical phonon modes induced by the polar substrate. We observed that the higher the coupling strength, the stronger is the magnetic field effect. The highest amplitude of the bandgap modulation is obtained for the MoS2 monolayer and the lowest with the WSe2 monolayer. We also found that the bipolaron is stable in TMDs. It is seen that the optical absorption presents the threshold values and respectively increases for WSe2, MoSe2, WS2 and MoS2.

Highlights

Transition metal dichalcogenides belong to the family of lamellar materials of formula MX2
For longitudinal optical phononic modes (LO) phonons, the evaluation of the amounts of band-gap modulation and the relative ratio for the different Transition Metal Dichalcogenides (TMDs) are shown in Table 3 and fixed values of Lm 0.5nm, 0.6nm are taken in all TMDs monolayer [42]
We theoretically studied optical absorption of bipolaron and it effects on the bandgap modulation in quantum dot of single layer transition metal dichalcogenides under magnetic field for all coupling regime, where both LO and surface optical phononic modes (SO) phonon are taken into account

Summary

Introduction

Transition metal dichalcogenides belong to the family of lamellar materials of formula MX2. Polaron is an entity discovered in 1933 by Landau [7], it is use to describe interaction between free charges carriers and induced polarization coming from electron (hole)-atome coupling in solid material This quasiparticle is characterized by some properties as effective mass, energy mobility and absorption coefficient, etc. In a recent paper [23], the study of the modulated bandgap in 2D single-layer TMDs derived from carrier-optic phonon coupling in the Fröhlich model showed that the bandgap magnitude can be modulated in the range of 100-500meV by changing different polar substrates and by varying the internal distance between the TMDs and the polar substrates. The energies of SO and LO bipolaron in the strong coupling 0 are respectively : SO

Magnitude of the bangap modulaton

G 2G

Absorption coefficient

Results and Discussions

G 2 G 2 G

Conclusion