Colloquium on TUESDAY, May 2nd, 2006

Warren Pickett
University of California Davis

Strong Coupling Superconductivity:
Paradigm Shifts, Alternative Universes

The Migdal-Eliashberg strong-coupling theory of phonon-mediated superconductivity was one of the most successful theories of real materials behavior by the end of the 1970s; for example, the small deviations of the temperature dependence of the critical field (magnetic field that destroys superconductivity) were explained very precisely. A prominent viewpoint at that time on higher temperature phonon-coupled superconductivity was that the situation was clear: T_c=30 K was the most optimistic that could be expected. Then in 2001 MgB2 was discovered to be superconducting at 40 K. The remarkable ultra-strong coupling embodied in the MgB2 paradigm will be described and compared to the earlier conventional wisdom. Surprising developments in a parallel universe will be revealed to the audience.