Superconducting aluminum heat switch and plated press-contacts for use at ultralow temperatures

Abstract

We have measured the thermal conductivity of a 0.1-mm-thick Al foil in the normal and superconducting state down to 58 mK. At this temperature, our data give a ratio for the conductivities of k(n)/k(s)=1600 T(-2). They show that Al is a better material for a heat switch than the usually used superconductors because of its large k(n) and large Debye temperature (reducing the lattice conductivity k(s)). In addition, we describe the design of a heat switch and an excellent performing demountable press-contact between Al and Cu, both gold plated, as joint to the switch.