Evidence for crossover from a Bose-Einstein condensate to a BCS-like superconductor with doping in from quasiparticle relaxation dynamics experiments
Solid State Physics Department, Jozef Stefan
Institute - 1001 Ljubljana, Slovenia
2 Materials Science Department, University of Cambridge - Cambridge, UK
Accepted: 22 November 1995
Time-resolved measurements of quasiparticle (QP) relaxation dynamics on the femtosecond timescale are reported as a function of temperature and doping in for (). In the underdoped state (, there is no evidence for any changes in the low-energy gap structure at Tc from either photoinduced QP absorption or QP relaxation time data. In combination with the sum rule, this implies the existence of pre-formed pairs up to a much higher temperature Near a rapid cross-over is observed, to a state where the QP recombination time diverges and the photoinduced QP density falls to zero at Tc, indicating the existence of a temperature-dependent superconducting gap which closes at Tc.
PACS: 74.25.Dw – Superconductivity phase diagrams / 74.25.Jb – Superconductivity: Electronic structure / 78.47.+p – Time-resolved optical spectroscopies and other ultrafast optical measurements in condensed matter
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