Technique for high-pressure electrical conductivity measurement in diamond anvil cells at cryogenic temperatures

A technique is described for making four-probe electrical conductivity measurements on bulk samples in a diamond anvil cell. The technique has been successfully applied up to 48 GPa and at temperatures below 4.2 K to measure the superconducting transition temperatures (Tc, of Pb, GaP, and Si. A method for analyzing the resistance versus temperature curve in the vicinity of the superconducting transition is also described. This method is applied to determine the pressure dependence of Tc in Si in the region where Tc varies rapidly with pressure.