Surface superconductivity in the topological Weyl semimetal t-PtBi$_2$

Abstract: The advancement of quantum computation is eager on generating fault tolerant qubits, and topological superconductivity is a very promising concept for reaching this goal. Early experimental achievements study hybrid systems as well as doped intrinsic topological or superconducting materials presenting the phenomena at very low temperatures. However, higher critical temperatures are indispensable for technological exploitation. Promising very recent angle-resolved photoemission spectroscopy results reveal that superconductivity of the type-I Weyl semimetal trigonal PtBi$_2$ (t-PtBi$_2$) is located at the Fermi arcs surface states which renders t-PtBi$_2$ a candidate for intrinsic topological superconductivity. Here we show, using scanning tunnelling microscopy and spectroscopy (STM/STS) that t-PtBi$_2$ presents surface superconductivity at elevated temperatures (5 K). The gap magnitude is elusive: it is spatially inhomogeneous and spans from 0 to 20 meV. In particular, the large gap value and the shape of the quasiparticle excitation spectrum resemble the phenomenology of high-Tc superconductors. To our knowledge, this is the largest superconducting gap so far measured in a topological material. Moreover, we show that the superconducting state at 5 K persists up to 12 T magnetic field. Thus, we show that t-PtBi2 is a prime candidate for intrinsic topological superconductivity at technologically relevant temperatures, fields and gap magnitudes.