Interaction of matter states with the environment: mechanical waves

Author(s)

Helder Faria Andriolo

• Document type: Doctoral Thesis
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Física Gleb Wataghin
• Defense date: 2021-02-02

Examining board members

José Antonio Brum; Kleber Roberto Pirota; Eduardo Miranda; Udson Cabral Mendes

• Advisor: José Antonio Brum; Odilon Divino Damasceno Couto Junior

Abstract

In 2005 Kane and Male studying the quantum spin Hall effect, predicted the existence of a new class of materials with hybrid properties between conductor and insulator, which they called topological insulators. However, due to its model, which was based on calculating the graphene band structure, the gap obtained was too small to be measured experimentally. It was not until the use of CdTe/HgTe/CdTe heterostructures that a non-trivial topological state was observed in these materials above a certain quantum well thickness. This work proposes a way to control the non-trivial topological state through an external environment, using a surface acoustic wave. The research takes place by calculating the energy band structure and wave functions of HgTe-HgCdTe heterostructures. The procedure used for this calculation is based on the k.p method, which is solved numerically by finite difference method. Previous works are revisited as a way to validate the proposed methodology. The numerical procedure allows increasing the complexity of the problem, adding surface acoustic waves to the system. These interact with the heterostructure and introduce periodic modulation of the electronic properties of the crystals. The interaction of the surface acoustic wave with the heterostructure allows the control of the state of matter that occurs in a trivial or non-trivial way depending on the wave’s acoustic power. It is shown that for a HgTe quantum well there is an acoustic power in which the transition from a trivial to non-trivial state is achieved. This important result confirms the possibility of using the surface acoustic wave as an external controller of the heterostructure state (AU)

• FAPESP's process: 16/06233-5 - Interaction of matter states with the environment: optical cavities and mechanical waves
• Grantee: Helder Faria Andriolo
• Support Opportunities: Scholarships in Brazil - Doctorate