The Emergence of Superconductivity in Inhomogeneous Systems

Superconductors are exciting materials for basic physics and applications because they conventionally exhibit zero-resistance and zero-dissipation (i.e., no energy loss). In contrast, unconventional superconductors—including high-temperature superconductors and hybrid superconductor-normal (S-N) systems relevant to quantum computation—combine superconductivity with dissipative normal metal-like states. Yet dissipation has been difficult to control and parametrize. In this talk, I will discuss electrical transport experiments on inhomogeneous superconductor-normal metal systems, and discuss the onset and ground states of superconductivity in these systems. In particular, I will show how superconductivity is established in granular normal-superconducting systems via a "rare-region" or extremal-grain process. These results are relevant to how superconductivity is established in low-dimensional or disordered systems, and in general help determine the role of dissipation in superconducting materials.