Download or read book Experimental Investigations of Magnesium Diboride Josephson Junctions written by Steven A. Carabello and published by . This book was released on 2016 with total page 370 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this thesis, I present the results of experiments on Josephson tunnel junctions that incorporate magnesium diboride (MgB2) as one of the superconducting electrodes. Through explorations of their current vs. voltage and conductance vs. voltage characteristics, I produced high-resolution distributions of the energy gap structure of MgB2. I also explored their resonant modes by performing the first superconducting-to-normal state switching experiments on such "hybrid" junctions. Magnesium diboride exhibits two superconducting energy gaps, sigma and pi. The Josephson junctions measured for this thesis used clean MgB2 thin films grown by hybrid physical-chemical vapor deposition on single-crystal silicon carbide substrates. For some films, only the c-axis is exposed, allowing direct tunneling to the pi gap. In others, the a-b plane is exposed, allowing us to explore the sigma gap as well. Lead or tin were evaporated to form the superconducting counterelectrodes. I performed high-resolution tunneling spectroscopy measurements of these junctions. Their results demonstrate that, for films with little scattering, it is not possible to model the density of states with only two superconducting energy gaps. Instead, at least four gaps are needed and a distribution is more appropriate, as anticipated by several theoretical results. The switching of Josephson junctions from the superconducting to normal states reveals additional interesting physics. There has been some recent theoretical interest in the switching behavior of "hybrid" junctions -- those consisting of one single-gap electrode and one multi-gap electrode, separated by a tunneling barrier. I observed several features of the superconducting-to-normal switching behavior that are not yet explained by theory. However, most of my results are consistent with theories developed for conventional single-gap/single-gap Josephson junctions, suggesting that switching in these junctions is dominated by a single tunneling mode. By measuring the switching behavior across temperatures, with and without microwave excitation, I was able to characterize the resistance, capacitance, critical current, and quality factor of these junctions. Each junction proved to be highly underdamped (quality factor Q ” 1). Because my results also exhibit several signatures of quantum-mechanical behavior, similar junctions may be suitable for quantum device applications.