Observation of Topological Berry phase in a plasmonic system

Abstract

Topological photonics has attracted great interest in the past few years because it reveals exciting fundamental advances in the way we can control light with engineered materials and the vast opportunities for applications. This area of research draws inspiration from recent advances in condensed matter physics, highlighting the important connection between the topological features of the energy band diagram of infinite periodic media and the electronic response of finite samples. In particular, topological insulators are a class of insulating materials with non-trivial topological characteristics of their bandgap, based on which robust conduction properties are expected at the boundary of any finite sample of such materials. Their inherent robustness is rooted in these topological features and is unaffected by continuous perturbations and local disorder. These electronic properties are protected by the underlying symmetry protection that drives the nontrivial topology. The extraordinary robustness of the features has led to compelling new nano-optical devices such as reconfigurable waveguides, disorder-resistant irreversible transport, quantum optics, and intense lasers. In this thesis, we discovered the existence of a topological phenomenon in a plasmonic system. We observed the Berry phase for surface plasmon polaritons on a flat metallic surface. The observed Berry phase is determined by the thickness of the metal layer which changes the interplay between the directly reflected light and light that outcoupled from the excited plasma. The interference of these out of phase components provides a topological character that can be observed in the complex optical reflectivity coefficient. We found that topological character can lead to stable boundary states which generate complete absorption of light at the boundary between topologically different domains. Our observations of the topological property of surface plasmon polaritons would lead to a new type of plasma-based nanophotonic device. In addition, these results also inspire the discovery of Berry phases and topological properties in other optical systems such as optical resonators

Date of Award	31 Dec 2021
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Coskun Kocabas (Supervisor) & Ahu Gumrah Parry (Supervisor)