PhD Larisa Chizhova

Electronic and Optical Properties of Graphene and Large-Scale Graphene Nanodevices

Abstract

Graphene, a one-atom thin honeycomb lattice of carbon, has exceptional electronic properties making it a prime candidate for future electronic applications. However, graphene has no band gap which is essential for building logical circuits, and electronic transport is highly sensitive to the edge or (substrate-induced) bulk disorder reducing carrier mobility. In an attempt to overcome these issues, new substrates such as hexagonal boron nitride have proven to reduce the bulk disorder in graphene and even to open a small band gap of 40 meV. Although new substrates help to reduce bulk disorder, electronic transport is still affected by edge roughness and the surrounding chemical environment.

The thesis aims to simulate realistic graphene devices and to provide a theoretical study of several recent experiments performed with graphene. It addresses: (i) electron transport properties of graphene nanoconstrictions; (ii) electronic and optical properties of graphene on hexagonal boron nitride; and (iii) the nonlinear optical response of graphene. In particular, we predict that the conductance of small graphene nanodevices can probe the physics at the edges of the device by extracting the density of localized or trapped edge states from the conductance trace measurements. We also show that new substrates may modify the bandstructure of graphene by opening a small band gap and by creating mini-gaps above and below the Dirac cone. The density of states of graphene with an additional substrate potential in the magnetic field can be probed by optical magnetospectroscopy. Furthermore, due to its linear energy dispersion, graphene demonstrates strong nonlinear response in the THz range highlighting its importance for building THz lasers and detectors. We also prove that graphene can form high-harmonic generation (HHG) spectra under the application of THz laser pulses similar to the HHG in gases.