Point-contact enhanced superconductivity in trigonal PtBi2: quest for the origin of ‘high-Tc’

Abstract

We studied enhanced superconductivity in point contacts (PCs) based on a type-I Weyl semimetal trigonal t-PtBi2 using both normal metal (Ag, Cu, Pt) and ferromagnetic (Fe, Co, Ni) tips by measuring the differential resistance dV/dI(V) curves. In most cases, the value of the superconducting critical temperature (Tc) ranges between 3 and 5 K, which is several times higher than the maximum bulk Tc. Notably, among the various PCs we examined, a few achieved Tc values as high as 8 K, including those with both normal and ferromagnetic tips. Additionally, the critical magnetic field is also highly enhanced in these PCs and reaches up to several Tesla. The common reason for the Tc increase may be related to pressure/strain caused during the PC’s formation. It is worth noting that a greater increase in Tc is observed in PCs formed at the edge of the sample flake, compared to those formed on the plane of the platelet. The results also reveal that the enhancement of Tc in PCs based on t-PtBi2 is compatible with ferromagnetic tips, which may suggest a potentially complex nature of enhanced superconductivity. Our findings suggest that t-PtBi2 is a promising candidate for realizing topological superconductivity at more accessible temperatures.