Date of Award

12-14-2017

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Physics and Astronomy

First Advisor

Dr. Mark I. Stockman

Abstract

In this dissertation, we study theoretically ultrafast processes accessible via the interaction of the ultrafast and intense laser pulses with 2D materials. The ultrafast and strong laser pulse has a duration of a few femtoseconds, and the amplitude of the electric field is about several V/˚A. We investigate the ultrafast electron dynamics in graphene, on a surface of a 3D topological insulator, and on a surface of a 3D crystalline topological insulator. Due to the gapless structure of graphene, surface states of the 3D topological insulator, and a 3D crystalline topological insulator, the electron dynamics is highly irreversible. The irreversibility of the electron dynamics is characterized by nonzero conduction band population in the reciprocal space after the pulse ends. Unlike graphene, electron dynamics on the surface of the 3D topological insulator is chiral in the presence of a single cycle of a circularly polarized pulse. We define the chirality of electron dynamics using the distribution of the residual conduction band population in the reciprocal space. The chirality of the electron dynamics of a 3D topological insulator is due to a cubic term known as a hexagonal warping term in the low energy Hamiltonian. This warping term breaks down the full rotational symmetry of the crystal to the threefold symmetry. Unlike graphene which has a linear energy dispersion at valleys in its Brillouin zone, the crystalline topological insulator has a quadratic energy dispersion at the M point in its (001) crystal face. The ultrafast electron dynamics on the surface of the crystalline topological insulator is anisotropic, i.e., the distribution of the residual conduction band population changes with the angle of the polarization of the applied linearly polarized pulse. For all different 2D materials studied in this work, applied ultrafast laser pulses generate ultrafast charge currents. The generated ultrafast currents follow the vector potentials of the pulse’s electric fields. The asymmetric profile of the ultrafast electric current produces a nonzero transferred charge which also determines the final polarization of the materials.

Available for download on Thursday, November 28, 2019

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