Program

O.14 -- Oral, NCTP-42

Date: Tuesday, 1 August 2017

Time: 15h10 - 15h30

Determining the local density of states of circular graphene quantum dots: A transfer matrix approach

H. Chau Nguyen (*,1) Nhung T. T. Nguyen (2, 3) and V. Lien Nguyen (2, 4)

(1) Max-Planck-Institut fur Physik komplexer Systeme, Nothnitzer Strae 38, D-01187 Dresden, Germany (2) Institute of Physics, Vietnam Academy of Science and Technology, 10 Dao Tan, Ba Dinh Distr., 118011 Hanoi, Vietnam (3) Graduate University of Science and Technology, Vietnam academy of Science and Technology, 18 Hoang Quoc Viet, Cau Giay Distr., 122121 Hanoi, Vietnam (4) Institute for Bio-Medical Physics, 109A Pasteur, 1st Distr., 710115 Hochiminh City, Vietnam

Graphene quantum dots (GQDs) are unlike conventional semiconductor quantum dots in that they can only trap charge carriers for short times in the so-called quasi-bound states, primarily due to the effect of Klein tunneling. This particular property of GQDs is associated with broad resonance peaks in their local density of states (LDOS). In this work, we propose a method based on the transfer matrix formalism to calculate the local density of states of any circular graphene quantum dot induced by an axially symmetric electrostatic potential on a continuous graphene sheet. Our calculations using a square potential for the graphene quantum dot studied in a recent scanning tunneling microscopy measurement [Gutierrez et al. Nat. Phys. 12, 1069 (2016)] show an excellent agreement between theory and experiment. We also find that resonance widths extracted from our calculated LDOS are consistent with experimental values and match those obtained from the complex energy spectrum of the corresponding Dirac equations. Our method can be used to study the effect of potential shape. As an application, we have calculated the LDOS for a graphene quantum dot with a Lorentzian shape potential and suggest that this potential shape corresponds to that induced by the charged STM-tip in another reported experiment [Schneider & Brouwer, PRB 89, 205437 (2014)].

Presenter: Nguyen Thi Thuy Nhung