Temperature scale and heat capacity of superfluid 3He-B in the 100μK range

We have recently performed accurate energy calibrations of a superfluid He-3-B bolometer at very low temperatures. The calibration process provides a measure of the heat capacity of the B-phase superfluid in the low-temperature regime. We conclude that quasiparticle excitations constitute the main; thermal reservoir even for temperatures approaching 100 mu K. Furthermore, we propose that the heat-capacity measurements may be used to define a temperature scale for this temperature regime based on vibrating wire resonators.