Wednesday, June 19, 2013

1306.4238 (P. J. de Visser et al.)

Fluctuations in the electron system of a superconductor exposed to a
photon flux

P. J. de Visser, J. J. A. Baselmans, J. Bueno, N. Llombart, T. M. Klapwijk
We report on fluctuations in the electron system, Cooper pairs and quasiparticles, of a superconducting aluminium film. The superconductor is exposed to pair-breaking photons (1.54 THz), which are coupled through an antenna. The change in the complex conductivity of the superconductor upon a change in the quasiparticle number is read out by a microwave resonator. A large range in radiation power can be chosen by carefully filtering the radiation from a blackbody source. We identify two regimes. At high radiation power, fluctuations in the electron system caused by the random arrival rate of the photons are resolved, giving a straightforward measure of the optical efficiency (48%). At low radiation power fluctuations are dominated by excess quasiparticles, the number of which is measured through their recombination lifetime.
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