Interface superconductivity in the point contact between topological semimetals polymorphic PtBi2 and ferromagnetic tips

Abstract

Topological semimetals, possessing topologically non-trivial band structures, serve as excellent platforms for realizing topological superconductivity through hard point-contact experiments. In this study, we successfully induce superconductivity in the three-dimensional Dirac semimetal, cubic PtBi₂, using ferromagnetic and paramagnetic tips in hard point contact experiments. The induced superconductivity is proven to be insensitive to ferromagnetism and exhibits unconventional features in the point-contact spectra. The highest superconducting transition temperature (\(T_{\mathrm{c}}\)) reaches approximately 5.1 K, and the \(T_{\mathrm{c}}\) values are proven to have a positive correlation with the coupling between the tip and the sample. Furthermore, we extend our point-contact experiments to trigonal PtBi₂, a material possessing a type-I Weyl semimetal band structure and triply degenerate points proximate to the Fermi level. Utilizing both ferromagnetic Ni tips and paramagnetic Ag tips, we successfully enhance superconductivity with a \(T_{\mathrm{c}}\) of up to 3.0 K in this material. The findings from point-contact measurements reveal that the enhanced superconductivity is compatible with ferromagnetism and the magnetism of the tip can affect the symmetry of the enhanced superconducting state. Given that the lattice structure remains stable under pressure up to 51.2 GPa for cubic PtBi₂ and 12.9 GPa for trigonal PtBi₂, the emergent superconducting states observed in these two PtBi₂ materials could inherit their topological nontrivial nature and be promising candidates for topological superconductor.