Date/Time
Date(s) - 01/06/2006
2:30 pm - 3:30 pm

Title: Optics of superconductors out of equilibrium: Eavesdropping the two bands in MgB2

Speaker: Dr. Ricardo Lobo

Institute: ESPCI-CNRS, Paris, France

Location: ABB 163

Description:

From its discovery, MgB2 has been a series of surprises. Not only is it the highest critical temperature conventional superconductor known but also it has two bands at the Fermi energy, both undergoing the superconducting transition at the same temperature. The theoretical mechanisms behind this “two-superconductors-in-one” behavior are now well understood. However they imply interband “scattering” which must be small enough to preserve two distinct superconductors while being large enough to produce a single Tc. Although expected, this communication channel has not yet been clearly identified. In this talk we will show how the optical properties of MgB2 out of the equilibrium can help to unveil this mystery.

Utilizing a pulse of light from a Ti:Sapphire laser, we create a non equilibrium state in MgB2 by breaking Cooper pairs. The laser pulses are synchronized to the far-infrared pulses from beamline U12IR at the NSLS in Brookhaven National Laboratory and an arbitrary delay between both pulses can be set. By varying this delay one can take snapshots of the system throughout its relaxation process. The analysis of quantities such as the number of excess unpaired electrons, the effective relaxation time or the shift induced in the superconducting gap by the broken pairs sets boundaries on the interband scattering process. We will discuss some possible mechanisms and propose future experiments that should narrow the problem.