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Lecture Jure Demsar

Rooster

WanneerWaar
25 september 2003 FWN-Building, Nijenborgh 4, 9747 AG, Groningen
Speaker: Jure Demsar
Affiliation: Department for Compex Matter, J. Stefan Institute, Ljubljana, Slovenia and Los Alamos National Lab., Los Alamos, NM, USA.
Title: Dynamics of Cooper pair breaking and superconducting state recovery dynamics in superconductors
Date: Thu Sep 25, 2003
Start: 14.00
Location: FWN-Building
Host: Paul van Loosdrecht
Telephone: +31 363 8149 / 4974 (secr.)

Abstract

In superconductors, the superconducting state results from the long-range phase coherence of Cooper pairs that, individually, are comprised of pairs of quasiparticles. The absorption of a photon by a superconductor and the following electron-electron and electron-phonon scattering processes break Cooper pairs resulting in an excess of quasiparticles that must, to restore thermodynamic equilibrium, recombine. It has proven possible, using ultrafast optical spectroscopy, to follow the temporal evolution of quasiparticle recombination. However, the initial process of Cooper pair breaking (typically described as a rapid avalanche-like process where each photon of energy ħw ph creates ħw ph/ /D quasiparticles) has generally been assumed to be of little importance in understanding the superconducting ground state. The results of pair breaking studies in MgB 2 strongly contrast with this conventional view. In MgB 2 , the pair breaking dynamics (PBD) has been temporally resolved for the first time using ultrafast optical spectroscopic techniques (optical pump – terahertz probe and all-optical pump-probe spectroscopy). Moreover, the PBD are strongly temperature and photoexcitation intensity dependent. Analysis of the PBD using the Rothwarf-Taylor equations implies that the anomalous PBD arises from the fact that in MgB 2 photoexcitation is initially followed by energy relaxation to high frequency phonons instead of, as commonly assumed, e-e thermalization. From the analysis of the PBD in terms of Rothwarf-Taylor equations the bare quasiparticle recombination rate and the probability for pair-breaking by phonons have been determined.

Laatst gewijzigd:22 oktober 2012 14:30