Superconducting aluminum heat switch with 3 n$\Omega$ equivalent resistance

Abstract

Superconducting heat switches with extremely low normal state resistances are needed for constructing continuous nuclear demagnetization refrigerators with high cooling power. Aluminum is a suitable superconductor for the heat switch because of its high Debye temperature and its commercial availability in high purity. We have constructed a high quality Al heat switch whose design is significantly different than that of previous heat switches. In order to join the Al to Cu with low contact resistance, we plasma etched the Al to remove its oxide layer then immediately deposited Au without breaking the vacuum of the e-beam evaporator. In the normal state of the heat switch, we measured a thermal conductance of $8T$ W/K${}^2$ which is equivalent to an electrical resistance of 3 n$\Omega$ according to the Wiedemann-Franz law. In the superconducting state we measured a thermal conductance that is $2\times 10^6$ times lower than that of the normal state at 50 mK.

References in corpus (5)

• Colloquium: Quantum heat transport in condensed matter systems
• Superconductivity in an extreme strange metal
• Dry demagnetization cryostat for sub-millikelvin helium experiments: refrigeration and thermometry
• Path-Dependent Supercooling of the ${}^3$He Superfluid A-B transition
• Very low resistance Al/Cu joints for use at cryogenic temperatures

Cited by in corpus (1)

• Construction of Continuous Magnetic Cooling Apparatus with Zinc Soldered PrNi${}_5$ Nuclear Stages