Programme

O.24 -- Oral, VCTP-45

Date: Wednesday, 14 October 2020

Time: 16:40 - 17:00

Online presentation

Band Dispersion and Exciton Creation and Annihilation under Isotropic Strain in Monolayer WS2

Tran Quang Huy (1), Tran Thi Nhan (2), Luong Thi Theu (1), Van An Dinh (3)

(1) Faculty of Physics, Hanoi Pedagogical University 2, Hanoi, Vietnam; (2) Hanoi University of Industry, 298 Cau Dien, Hanoi, Vietnam; (3) Nanotechnology Program, VNU Vietnam Japan University, Luu Huu Phuoc, My Dinh I, Hanoi, Vietnam

We present a density functionals study of the mechanism of creation and annihilation of excitons under strain in the monolayer WS2. With taking into account the influence of spin-orbit coupling (SOC) and van der Waals interaction by using optB86b-vdW functional, we investigate the vertical shift and displacement of the d and s partial orbitals of the W and S atoms, respectively, and the appearance of flattening valley, leading to the creation and decay of excitons under the isotropic strain in monolayer WS2. The crucial findings of this work are: (a) Based on the partial projected band structure, we explain the transition mechanism from the K-K direct to the K-Q and $\Gamma$-K indirect band gap under the isotropic compressive and tensile strained WS2 monolayer, respectively. Therewith, the notably decreased band gap is due to the occurrence of two phenomena, the vertical shifted valley and the flattened valley, in the partial projected band structure. Also due to these two phenomena, the carrier mobility at symmetrical points in the first Brillouin zone (BZ) is enhanced or reduced, and thus its applications as channel materials or high performance electronic devices can be exploited; (b) Thanks to the spin splitting with SOC effect, light and dark excitons are visually shown in the band structure, especially the exciton creation and annihilation with the isotropic strained WS2 monolayer, opening a possible path to manipulate excitons using strain scheme.

Presenter: Lương Thị Thêu