Berezinskii-Kosterlitz-Thouless transition in the type-I Weyl semimetal PtBi$_2$

Abstract

semimetal band structure, with unusually robust two-dimensional superconductivity in thin fims. Transport measurements show that high-quality PtBi 2 crystals are three-dimensional superconductors (T c 600 mK) with an isotropic critical field (B c 50 mT). Remarkably, we evidence in a rather thick flake (60 nm), exfoliated from a macroscopic crystal, the twodimensional nature of the superconducting state, with a critical temperature T c 370 mK and highly-anisotropic critical fields. Our results reveal a Berezinskii-Kosterlitz-Thouless transition with T BKT 310 mK and with a broadening of Tc due to inhomogenities in the sample. Due to the very long superconducting coherence length ξ in PtBi 2 , the vortexantivortex pairing mechanism can be studied in unusually-thick samples (at least five times thicker than for any other two-dimensional superconductor), making PtBi 2 an ideal platform to study low dimensional superconductivity in a topological semimetal.