#### 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.

#### Recommended Citation

Oliaei Motlagh, Seyyedeh Azar, "ULTRAFAST PROCESSES IN 2D MATERIALS." Dissertation, Georgia State University, 2017.

https://scholarworks.gsu.edu/phy_astr_diss/99