Superconducting fluctuations in boron-doped nanocrystalline diamond films: a study of disordered granular metals using diagrammatic quantum field theory

Abstract

In this thesis, we demonstrate how to generalise the diagrammatic methods of quantum field theory commonly used for calculating transport phenomena in disordered homogeneous metals, such that they may be used for disordered granular metals. The predictions of our granular model are then compared to experimental resistance versus temperature data measured in boron-doped nanocrystalline diamond films. We find semi-quantitative agreement under the assumption of a constant phase breaking rate, $\tau_{\phi}^{-1}$, and explore the possible temperature dependence of $\tau_{\phi}^{-1}$. We find that our current model of a disordered granular metal does not generate a phase breaking mechanism which is able to quantitatively match theory to experiment. We suggest different avenues to explore theoretically and experimentally to determine the origin of the contributions to the fluctuation conductivity in BNCD, so that we better understand the onset of superconductivity in disordered granular metals