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Master thesis: Quantum coherent transport in topological insulator ring structures

Jan 23rd, 2020

About topological insulators

In 2016, the Nobel prize of physics was awarded to the “theoretical discoveries of topological phase transitions and topological phases of matter”. Today this phase of matter is investigated from an experimental point of view. Practical applications for the materials predicted are promising: Not only are they prospective candidates for the building blocks of novel spintronic devices, they are also supposed to host Majorana zero modes which are the fundament of a new concept for robust quantum computation. In the PGI-9 we fabricate these materials and in our state of the art cleanroom in the Helmholtz Nano Facility we build nano-scale devices out of these by applying industrial relevant methods. Their quantum transport properties are characterized at temperatures close to absolute zero. We probe the materials using ultra small currents, inducing superconductivity into these materials and creating quantum
superposition states.

Topological insulator ringTopological insulator ring
Copyright: Jonas Kölzer

Project Description:

In this project you will investigate the quantum coherent transport properties in different topological insulator materials. In order to do so you will focus on developing a process in which you deposit a gate on existing ring structures and measure electron transport phenomena at low temperatures and high magnetic fields. The occurring AharonovBohm oscillations will be analyzed and compared to simulations done in previous work. Studying collective transport phenomena is the
fundament for Majorana based quantum computation proposals.

Aharonov-Bohm oscillations in TI ringsAharonov-Bohm oscillations in TI rings
Copyright: Jonas Kölzer

What you will learn:

You will learn how to operate a cryostat and use the QCoDeS software package, which is a state of the art data acquisition framework by Microsoft, Copenhagen, Delft and Sydney.After implementing your first routine you will start to
perform measurements close to absolute zero temperature. In an additional step you will learn how to fabricate gates and study how changing the Fermi level of the system changes its transport properties.

The central questions that shall be answered within this thesis are:

1. What material offers the best properties for the realization of Majorana quasi particle excitations?
2. What is the influence of changing the Fermi level in the oscillation ring structure on quantum coherence?
3. How do the topological surface states contribute into the transport phenomena measured in these ring structures?

Prof. Dr. Thomas Schäpers
Peter Grünberg Institut PGI-9, Gebäude 02.11, Raum 105
Tel.Nr.: +49 (0)2461 61 2668