Response time of a thermometer based on normal metal–insulator–superconductor (NIS) tunnel junctions

We have measured the thermal response of a superconductor–normal metal–superconductor (SINIS) tunnel junction structure at substrate temperature View the MathML source by directly heating the electron system in the normal metal island. In our structure, we find the response time is determined by the electron–phonon coupling in the electron temperature range 300–View the MathML source. By using AC heating, the cut-off frequency caused by this response time has been measured, showing that SINIS structures operate as a thermometer up to a few MHz in this temperature range.