A diamond anvil cell for the investigation of superconductivity under pressures of up to 50 GPa: Pb as a low temperature manometer

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Abstract
A single-crystal diamond anvil cell is described which has been successfully cycled down to liquid helium temperatures in numerous experiments. Superconducting transitions are detected by a low frequency AC technique employing a radially compensated gradient coil and a commercial RF SQUID system. The pressure is determined at room temperature by the ruby fluorescence technique with a focused laser beam. Pressure changes between room temperature and low temperature are minimised. A recalibration of the superconducting critical temperature, Tc, of Pb as a function of pressure has been carried out. The so-called Pb manometer turns out to be a very suitable pressure gauge up to about 30 GPa. At higher pressures the Tc of Pb is suppressed below 1.2 K and hence, for normal purposes, is inconveniently low. At the present limit of resolution the Pb I-II phase transition at 13 GPa is not reflected in the smooth Tc-P dependence.