Date of Award

5-1-2023

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Physics and Astronomy

First Advisor

Vadym Apalkov

Second Advisor

Brian Thoms

Third Advisor

Mukesh Dhamala

Fourth Advisor

Sidong Lei

Abstract

Topological systems are not a recent development in physics, but the study of them has rapidly expanded in recent years due to advances in technology allowing for more accurate experimentation. This in return, has also led to more work for theoretical physicists to explore new possible applications of topological properties. Gaped graphene and transition metal dichalcogenides(TMDCs) are two examples of materials with topological properties due to symmetry points called valleys, where the dipole-transitions are most probable. This document contains two novel examples of those topological properties and their effects of surface plasmons. Firstly, we examine Chiral Berry Plasmons (CBP). CBP Modes have been shown to exist in 2D Dirac materials. These modes exist because of the role Berry Flux (net Berry curvature) plays in the materials themselves and are confined to the boundary in the absence of topological edge states. We show that in an optically pumped gaped graphene model, these CBP modes have an inherent tunability given by the temperature of the electrons in the system, the band gap of the material, and the relative populations created by the optical pumping of the system. Our calculations consider a quasi-equilibrium regime after thermalization but before relaxation, which occurs picoseconds later. In the other, we theoretically examine a TMDC Based Spaser Type II that has been optically pumped using an ultra-fast circularly-polarized pulse. The spasing system consists of a silver nanospheroid and a circular TMDC monolayer flake. The silver nanospheroid screens the incoming pulse and creates a nonuniform distribution of excitations in the TMDC valleys. As expected, these excitations still decay into localized surface plasmons (LSP) along the nanospheroid. However, valley polarization is only preserved in our system for small $K$-valley populations, as the required excited populations to contribute to the spasing "avalanche" are sometimes more significant than those that maintain valley polarization. The spaser also emits far-field radiation, shifting the polarization and magnifying the incoming pulse, showing promise in that area of research.

DOI

https://doi.org/10.57709/35358926

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