Pressure-Dependent Point-Contact Spectroscopy of Superconducting PbTaSe$_2$ Single Crystals
Hai Zi1,2, Ling-Xiao Zhao2, Xing-Yuan Hou2, Lei Shan2, Zhian Ren2, Gen-Fu Chen2, and Cong Ren1,2*
1School of Physics and Astronomy, Yunnan University, Kunming 650500, China 2Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Science, Beijing 100190, China
Abstract：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 $2\varDelta_0/k_{_{\rm B}}T_{\rm c}$ 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.
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2020, Vol. 37 
