Comparison of Coulomb Blockade Thermometers with the International Temperature Scale PLTS-2000

The operation of the primary Coulomb blockade thermometer (CBT) is based on a measurement of the bias-voltage-dependent conductance of arrays of tunnel junctions between normal metal electrodes. Here, a comparison of a CBT with a high-accuracy realization of the PLTS-2000 in the range from 0.008 K to 0.65 K is reported. An overall agreement of about 1 % was found for temperatures above 0.25 K. For lower temperatures, differences increase because the CBT does not reach full thermal equilibrium with its surroundings. This can be accounted for by numerical calculations based on electron-phonon decoupling.