National Synchrotron Light Source Seminar

"Infrared Spectroscopy of Charge Recombination in Superconductors in a Magnet Field"

Presented by Xiaoxiang Xi, University of Florida

Monday, October 10, 2011, 10:00 am — Seminar Room, Bldg. 725

In a conventional superconductor, electrons of opposite spin and momentum form pairs and
condense to the ground state. When a picosecond laser pulse is used to break the pairs, the
relaxation process involves the recombination of two excess quasiparticles and the creation of a
phonon. A magnetic field can suppress the pairing by coupling to the electron orbital motion or
aligning the spin. Both effects influence the recombination of excess quasiparticles. In this
presentation, I will discuss the magnetic-field-induced weakening of superconductivity observed
in type-II superconductors by infrared spectroscopy. The consequence on the excess
quasiparticle recombination is studied by laser-pump synchrotron-probe time-resolved
spectroscopy. We find that a magnetic field significantly reduces the recombination rate. A
recombination model is proposed to interpret our experimental findings.

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