Quantum transport properties of high-temperature superconductors

Abstract

In this thesis, We will focus on discussing the Andreev tunneling and Josephson tunneling of underdoped cuprate superconductors. In particular, we emphasize how the pseudogap of the underdoped cuprate influences these tunneling behaviors. Our calculation is based on the theory of YRZ Green’s function in which the pseudogap acts as a precursor to the undoped Mott insulator.

In the study of Andreev tunneling, the tunneling spectroscopy we obtained exhibits a two-gap feature, i. e., a small energy gap associated with Andreev reflection in the transparent limit and a large gap associated with single particle tunneling. Our results are in good agreement with the two-gap scenario observed in tunneling experiments for underdoped cuprate. In the study of Josephson tunneling, we aimed to test the proposal of “cooperon physics” by examining the Josephson coupling between two optimally doped (or overdoped) cuprate superconductors separated by a barrier of an underdoped-cuprate in its pseudogap state with finiteenergy cooperon excitation. Our calculation shows a significant contribution from the cooperon excitation to the Josephson coupling, which is comparable to that from nodal quasiparticles. Moreover, our results give a good description of the temperature-dependent enhanced Josephson tunneling revealed in experiments.