Towards cooling nanoelectronic devices to microkelvin temperatures : design, construction and test of a novel type of refrigerator

This work presents an important step towards the realisation of sub-millikelvin
temperatures in nanoelectronic devices. The ability to reach low millikelvin or even
microkelvin temperatures in nanoelectronic devices would open up the chance to
discover new physics in various systems.
We layout a new approach aimed at cooling nanostructures to microkelvin temperature
based on the well established technique of adiabatic nuclear demagnetisation:
each device measurement lead incorporates its own, individual nuclear refrigerator, allowing efficient thermal contact to a microkelvin bath. This scheme
short-circuits two main bottlenecks of cooling electrons: thermal boundary resistance
and electron-phonon coupling.
We have addressed the technical challenges and constructed a parallel network of nuclear refrigerators, yielding a prototype which proved to achieve temperatures
of � 1mK simultaneously on ten measurement leads upon demagnetisation. Thus, we have accomplished the first step towards ultracold nanoscale samples.
It was also found that a field and ramp rate dependent heat leak limited the performance and hindered us to reach for lower temperatures.