Programme

O.11 -- Oral, VCTP-45

Date: Tuesday, 13 October 2020

Time: 11:20 - 11:40

The correlation between transition of the energy bands and the optical absorption spectrum in bilayer armchair graphene nanoribbons

Phan Dang Thao Nguyen (1), Nguyen Lam Thuy Duong (1), Tran Van Truong (2), Vu Thanh Tra (3)

(1) School of Graduate, Can Tho University, Can Tho, Vietnam (2) SRMP, CEA Saclay, Université Paris-Saclay, F-91191, Gif-sur-Yvette, France (3) Department of Physics, School of Education, Can Tho University, Can Tho, Vietnam

In this work, we investigated the effect of external electric fields including a transverse electric field generated by side gates and a vertical electric field generated by top/back gates on the optical absorption spectra of AB-stacked bilayer armchair graphene nanoribbons (BAGNRs). By using a tight-binding model in combination with the gradient approximation, we first studied the energy band and the density of states (DOS), then absorption spectra A($\omega$). Our results demonstrated that (i) the low-frequency optical absorption spectra displays rich peaks and they vanish at $\omega = 0$; (ii) the number of the absorption peaks, the frequency and the intensity of peaks are strongly associated with the ribbon width and the magnitude of the electric fields. With the wider ribbon width M, more the absorption peaks are created and the lower threshold absorption frequency is observed. More importantly, unlike in the case without electric fields, the AB-stacked systems in the presence of a modulated electric field have lower threshold absorption frequency, more absorption peaks, and weaker spectral intensity; (iii) In semi-metallic structures, vertical fields impact more effectively than transverse fields in terms of opening larger band gap by analyzing the change of frequency of the first peak in the absorption spectrum. (iv) When the increase of electric field, the prominent peaks of the edge-dependent selection rules are lowered, and the sub-peaks satisfying the extra selection rules come to exist. With the obtained results, we expect to contribute to a more comprehensive understanding of the optical properties as well as the electronic structure of BAGNRs. Furthermore, the modulation of the band gap can lead to many interesting and attractive properties to bilayer graphene, that could be applied for various electronic and optical-electronic device applications. Corresponding author: vttra@ctu.edu.vn

Presenter: Phan Dang Thao Nguyen