Title: A point contact spectroscopy study of the topological superconductivity
Author: Xunchi Chen
Date and Time: Wednesday, March 11th, 2015 at 2pm
Location: Howey N110
Committee:
Professor Zhigang Jiang,
Committee Chair (Advisor)
School of Physics
Georgia Institute of Technology
Professor Martin Mourigal
School of Physics
Georgia Institute of Technology
Professor Phillip First
School of Physics
Georgia Institute of Technology
Professor Jean Bellissard
School of Mathematics
Georgia Institute of Technology
Professor Andrew Zangwill
School of Physics
Georgia Institute of Technology
Abstract:
The study of topological superconductivity has been at the forefront of condensed matter physics for the past few years. Topological superconductors are predicted to have odd parity pairing and host the so called Majorana fermions, which is not only of fundamental importance, but also building block for fault-tolerant quantum computing. In this dissertation, we use point contact spectroscopy to study the pairing symmetry of candidate topological superconducting materials. We study the proximity induced superconductivity in topological insulator Bi2Se3 by a superconducting niobium tip, and propose a model to explain the features in the point contact spectra. We further study the nature of the superconductivity in highly doped superconducting topological insulators, including CuxBi2Se3 and Sn(1-x)InxTe, using both normal metal gold tip and superconducting niobium tip. For CuxBi2Se3, we observe robust zero-bias conductance peak (ZBCP) in the differential conductance spectra with gold point contact, while with niobium point contact we find the height of the peak exhibiting an unusual non-monotonic temperature dependence. We argue that both observations cannot be explained by Andreev reflection within the standard Blonder, Tinkham, Klapwijk (BTK) model, but signifying unconventional superconductivity in the material. For Sn(1-x)InxTe samples, we observe ZBCP in the differential conductance spectra with gold point contact, while with niobium point contact, the temperature dependence of ZBCP is monotonic as expected from conventional theory, leaving the nature of the superconductivity of Sn(1-x)InxTe still an open question.
