Observation of a new non-equilibrium state in superconductors caused by sequential tunnellingA. G. Kozorezov1, J. K. Wigmore1, A. Peacock2, R. den Hartog2, D. Martin2, G. Brammertz2, P. Verhoeve2 and N. Rando2
1 Department of Physics, Lancaster University - Lancaster, UK
2 Science Payloads and Advanced Concepts Office, SCI-A European Space Agency, ESTEC - Noordwijk, The Netherlands
(Received 8 October 2003; accepted 5 February 2004)
A previously unrecognised non-equilibrium phenomenon in superconducting tunnel junctions is identified. The situation may arise in low-loss, low-gap, multi-tunnelling devices in which quasiparticles retain accumulated energy through several cycles of sequential forward and back tunnelling. As a consequence, a stable non-equilibrium distribution is established, in which many quasiparticles have energies exceeding the threshold for breaking Cooper pairs, resulting in a large excess current. By solving the system of coupled kinetic equations for quasiparticles and phonons, we have modelled the quasiparticle distribution and excess current, and have confirmed the predictions through experiments on an appropriate superconducting tunnel junction.
74.25.Fy - Transport properties (electric and thermal conductivity, thermoelectric effects, etc.).
74.25.Kc - Phonons.
85.25.-j - Superconducting devices.
© EDP Sciences 2004