Macroscopic character of composite high temperature superconducting wires and enhancement of superconductivity by magnetic field

Condensed Matter Seminars

Speaker: Boris Spivak
Date & Time: November 10, 2016 2:00 - 3:00
Location: Hennings 318
Local Contact: Philip Stamp
Intended Audience: Graduate

D-wave symmetry of the superconducting order in the cuprate high temperature superconductors is a well established fact, and one which identifies them as unconventional. However, in macroscopic contexts including many potential applications (i.e. superconducting wires) the material is a composite of randomly oriented superconducting grains in a metallic matrix, in which Josephson coupling between grains mediates the onset of long-range phase coherence. Here, we analyze the physics at length scales large compared to the size of such grains, and in particular the macroscopic character of the long-range order that emerges. While XY-glass order and macroscopic d-wave superconductivity may be possible, we show that under many circumstances especially when the d-wave superconducting grains are embedded in a metallic matrix the most likely order has global s-wave symmetry. We also show that magnetic field may enhance superfluid density in the wires. Finally, we argue that any of mentioned above features exist in other unconventional disordered superconductors as well.