Pressure-Dependent Point-Contact Spectroscopy of Superconducting PbTaSe_2 Single Crystals

We develop an experimental tool to investigate the order parameter of superconductors by combining point-contact spectroscopy measurement with high-pressure technique. It is demonstrated for the first time that planar point-contact spectroscopy measurement on noncentrosymmetric superconducting PbTaSe_2 single crystals is systematically subjected to hydrostatic pressures up to 12.1 kbar. Under such a high pressure, the normal-state contact resistance is sensitive to the applied pressure, reflecting the underlying variation of contact transparency upon pressures. In a superconducting state, the pressure dependence of the energy gap \varDelta_0 and the critical temperature T_\rm c for gap opening/closing are extracted based on a generalized Blond–Tinkham–Klapwijk model. The gap ratio 2\varDelta_0/k__\rm BT_\rm c indicates a crossover from weak coupling to strong coupling in electron pairing strength upon pressure for PbTaSe_2. Our experimental results show the accessibility and validity of high-pressure point-contact spectroscopy, offering rich information about high-pressure superconductivity.