Point-contact enhanced superconductivity in trigonal PtBi 2 : quest for the origin of ‘high- T c ’

Abstract We studied enhanced superconductivity in point contacts (PCs) based on a type-I Weyl semimetal trigonal t -PtBi 2 using both normal metal (Ag, Cu, Pt) and ferromagnetic (Fe, Co, Ni) tips by measuring the differential resistance d V/ d I ( V ) curves. In most cases, the value of the superconducting critical temperature ( T c ) ranges between 3 and 5 K, which is several times higher than the maximum bulk T c . Notably, among the various PCs we examined, a few achieved T c 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 T c increase may be related to pressure/strain caused during the PC’s formation. It is worth noting that a greater increase in T c 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 T c in PCs based on t -PtBi 2 is compatible with ferromagnetic tips, which may suggest a potentially complex nature of enhanced superconductivity. Our findings suggest that t -PtBi 2 is a promising candidate for realizing topological superconductivity at more accessible temperatures.