Alireza Akbari, Andreas P. Schnyder, Dirk Manske, Ilya Eremin
We study the nonequilibrium dynamics of multiband BCS superconductors subjected to ultrashort pump pulses. Using density-matrix theory, the time evolution of the Bogoliubov quasiparticle densities and the superconducting order parameters is computed as a function of pump pulse frequency, duration, and intensity. Focusing on two-band superconductors, we consider two different model systems. The first one, relevant for MgB$_2$, describes two-band superconductors with dominant intraband interactions and an attractive but weak interband pair scattering V_{12}. The second model, relevant for iron-based superconductors, deals with the opposite limit where the interband interaction V_{12} is repulsive and much larger than the intraband pairing terms. For ultrashort pump pulses, both of these models exhibit a nonadiabatic behavior which is characterized by oscillations of the superconducting order parameters. We find that for nonvanishing $V_{12}$, the superconducting gap on each band exhibits two oscillatory frequencies which are determined by the long-time asymptotic values of the gaps. The relative strength of these two frequency components depends sensitively on the magnitude of the interband interaction $V_{12}$. Hence, pump-probe experiments on two-band superconductors can give valuable information on the strength of the interband pair scattering $V_{12}$, and thereby shed light on the microscopic pairing mechanism.
View original:
http://arxiv.org/abs/1205.4861
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