Manifestations of intrinsic and induced magneticproperties of graphene nanostructures

by Marko M Grujić

Institution: Univerzitet u Beogradu
Year: 2016
Keywords: grafen; magnetsko polje; magnetni momenat; kvantnatačka; spin-orbitna interakcija; dolina; transport
Posted: 02/05/2017
Record ID: 2078356
Full text PDF: https://fedorabg.bg.ac.rs/fedora/get/o:11427/bdef:Content/get


Electrical and Computer Engineering - Nanoelectronics and Photonics / Elektrotehničko i računarsko inženjerstvo - Nanoelektronika i fotonika The dissertation can be roughly divided into two parts. In the first part it deals with magnetic properties of quasi-zero dimensional graphene structures, such as nanodots and nanorings. In particular, a circular graphene quantum dot is analyzed in Chapter 3 using the Dirac-Weyl equation. The energy and the optical absorption spectra are computed for the case of the present external magnetic field. The results are obtained for two distinct boundary conditions, namely infinite-mass and zigzag boundary conditions, which model different physics in the structure with different edges. It is found that the energy spectrum of a dot with zigzag boundary condition exhibits a zero energy band regardless of the value of the magnetic field, while for the infinite mass boundary condition the zero energy states appear only for high magnetic fields in the form of the zeroth Landau level. The analytical results are compared to those obtained from the tight-binding model in order to show the validity range of the continuum model. It is found that the continuum model with infinite mass boundary condition describes rather well its tight binding counterpart, which can partially be attributed to blurring of the mixed edges by the staggered potential. The mean-field Hubbard model is subsequently used to investigate the formation of the antiferromagnetic phase in hexagonal graphene quantum rings with inner zigzag edges. The outer edge of the ring is taken to be either zigzag or armchair, and it is found that both types of structures exhibit a larger antiferromagnetic interaction than hexagonal quantum dots. This difference could be partially ascribed to the larger number of zigzag edges per unit area in rings than in dots. Furthermore, edge states localized on the inner ring edge are found to hybridize differently than the edge states of dots, which results in important differences in the magnetism of graphene rings and dots. The largest staggered magnetization is found when the outer edge has a zigzag shape. However, narrow rings with armchair outer edge are found to have larger staggered magnetization than zigzag hexagons. The edge defects are shown to have the least effect on magnetization when the outer ring edge is armchair shaped. Advisors/Committee Members: Tadić, Milan. 1964-.