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Master thesis: Low-temperature transport in topological insulator - superconductor nanostructures

Jan 3rd, 2019

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.

TI superconductor ringTI superconductor ring
Copyright: Jonas Kölzer

Project Description:

In this project you will investigate the influence of Cooper pairs on the transport in topological insulators. In order to do so you will focus on developing a process in which you deposit a superconductor on top of a topological insulator by using a so called in-situ shadow mask technique. That means that the deposition takes place without exposing the sample in the fabrication process as it would be done in ordinary lithography. Furthermore, you will perform a measurement at temperatures close to zero and high magnetic fields which will enable you to observe so-called Andreev reflections and interference effects.

What you will learn:

You will learn how to design and fabricate topological insulator nano-structures in the high tech clean room in the HNF. In this process you will learn about techniques like selective area growth and in-situ fabrication which we use in a unique way in the field of topological insulators. The central questions that shall be answered are:

1. How can a superconductive in-situ electrode be combined with normal conductive current leads and a top-gate in a fabrication process?
2. Can we observe signatures of Andreev reflections in our transport experiments?
3. How do Andreev reflection contribute to transport phenomena in our material system?

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