| Despite nearly a century of research since Kamerlingh Onnes' discovery of superconductivity and half a century since the development of a complete microscopic theory of superconductivity (BCS theory), there is still no general theory able to reliably predict the superconducting critical temperature ( Tc) of a given material or if a material will become superconducting. This holds true even in the case of the elemental solids. The number of elemental superconductors across the periodic table has almost doubled through the application of extreme pressure. Remarkably, these high-pressure superconductors include elements that are magnetic (Fe) or insulating (O, Si, and I) at ambient pressure. Modern high-pressure experimental techniques, capable of reducing average interatomic spacings by 30% or more, can either create or destroy superconductivity and thus provide a powerful tool to investigate the conditions which give rise to superconductivity. In this dissertation I describe the results of ultra-high pressure experiments (up to 1.7 Mbar) on pure elements, alloys and compounds. A variety of probes including resistivity, ac magnetic susceptibility and optical spectroscopy are used to investigate the optimal conditions for high superconducting transition temperatures. |
