Single full gap with mixed type-I and type-II superconductivity on surface of the type-II Dirac semimetal PdTe2 by point-contact spectroscopy

We report our point-contact spectroscopy (PCS) study on the superconducting state of the type-II Dirac semimetal PdTe2 with a superconducting transition temperature T-c similar to 1.65 K. Both mechanical- and soft-PCS differential conductance curves at 0.3 K show a consistent double-peak structure and they can be perfectly fitted by a single s-wave gap based on the Blonder-Tinkham-Klapwijk model. The gap follows a typical BardeenCooper-Schrieffer temperature behavior, yielding Delta(0) similar to 0.29 meV and 2 Delta(0)/k(B)T(c), = 4.15 in the strong-coupling regime. A sudden suppression of the superconducting gap in a magnetic field around H-c1 similar to 130 Oe is observed for most point contacts on PdTe2, characteristic of a first-order transition for type-I superconductors in field. However, for other contacts, a smooth evolution of the PCS conductance persists up to H-c2 similar to 600 Oe, signaling a local type-II superconductivity. The observed admixture of type-I and type-II superconductivity can possibly arise from an inhomogeneous electron mean free path on the surface of PdTe2 due to its topological surface states.