The non-equilibrium response of a superconductor to pair-breaking radiation measured over a broad frequency band

We have measured the absorption of terahertz radiation in a BCS superconductor over a broad range of frequencies from 200 GHz to 1.1 THz, using a broadband antenna-lens system and a tantalum microwave resonator. From low frequencies, the response of the resonator rises rapidly to a maximum at the ga...

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Bibliographic Details
Published in:Applied physics letters 2015-06, Vol.106 (25)
Main Authors: de Visser, P. J., Yates, S. J. C., Guruswamy, T., Goldie, D. J., Withington, S., Neto, A., Llombart, N., Baryshev, A. M., Klapwijk, T. M., Baselmans, J. J. A.
Format: Article
Language:English
Subjects:
ABSORPTION
Applied physics
Broadband
CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS
Computing time
Dependence
DISTRIBUTION FUNCTIONS
EFFICIENCY
EQUILIBRIUM
FREQUENCY DEPENDENCE
GHZ RANGE 100-1000
LENSES
MICROWAVE RADIATION
PHONONS
RESONATORS
SUPERCONDUCTORS
TANTALUM
TRAPPING
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Summary:We have measured the absorption of terahertz radiation in a BCS superconductor over a broad range of frequencies from 200 GHz to 1.1 THz, using a broadband antenna-lens system and a tantalum microwave resonator. From low frequencies, the response of the resonator rises rapidly to a maximum at the gap edge of the superconductor. From there on, the response drops to half the maximum response at twice the pair-breaking energy. At higher frequencies, the response rises again due to trapping of pair-breaking phonons in the superconductor. In practice, this is a measurement of the frequency dependence of the quasiparticle creation efficiency due to pair-breaking in a superconductor. The efficiency, calculated from the different non-equilibrium quasiparticle distribution functions at each frequency, is in agreement with the measurements.
ISSN:0003-6951
1077-3118
DOI:10.1063/1.4923097