Heat transfer coefficient saturation in superconducting Nb tunnel junctions contacted to a NbTiN circuit and an Au energy relaxation layer

Stefan Selig (1) , Marc Westig (2) , Karl Jacobs (1) , Michael Schultz (1) , Netty Honingh (1)

1 I. Physikalisches Institut [Köln]
2 GNE - Groupe Nano-Electronique

In this paper we present the experimental realization of a Nb tunnel junction connected to a high-gap superconducting NbTiN embedding circuit. We investigate relaxation of nonequilibrium quasiparticles in a small volume Au layer between the Nb tunnel junction and the NbTiN circuit. We find a saturation in the effective heat-transfer coefficient consistent with a simple theoretical model. This saturation is determined by the thickness of the Au layer. Our findings are important for the design of the ideal Au energy relaxation layer for practical SIS heterodyne mixers and we suggest two geometries, one, using a circular Au layer and, two, using a half-circular Au layer. Our work is concluded with an outlook of our future experiments.

Keywords: Heat transfer; Niobium SIS junctions; Nonequilibrium; SIS mixers; Superconductivity

Domains: Physics [physics]

Stefan Selig, Marc Westig, Karl Jacobs, Michael Schultz, Netty Honingh. Heat transfer coefficient saturation in superconducting Nb tunnel junctions contacted to a NbTiN circuit and an Au energy relaxation layer. IEEE Transactions on Applied Superconductivity, 2015, 25 (3), pp.2400705. ⟨10.1109/TASC.2014.2378054⟩. ⟨cea-01568587⟩