Atomic Visualization of Bulk and Surface Superconductivity in Weyl Semimetal {\gamma}-PtBi2

TL;DR

This study visualizes coexisting bulk and surface superconductivity in trigonal { extgamma}-PtBi2 using ultra-low-temperature STM/STS, revealing distinct gaps and properties that make it a promising platform for topological superconductivity research.

Contribution

It provides the first direct visualization of simultaneous bulk and surface superconducting gaps in { extgamma}-PtBi2, highlighting their distinct characteristics and coexistence.

Findings

Bulk gap ~0.053 meV with Tc ~0.5 K and vortex lattice.

Surface gap ~0.42 meV persisting up to 3 K and 2 T.

Coexistence of robust surface and bulk superconductivity.

Abstract

A bulk superconductor hosting intrinsic surface superconductivity provides a unique platform to study Majorana bound states. The superconductor, trigonal {\gamma}-PtBi2, is a promising candidate, as surface superconducting gaps and topological surface states have been observed. However, the simultaneous presence of bulk and surface superconductivity has not been resolved. Here, we directly visualize coexisting bulk and surface superconducting gaps in trigonal PtBi2 by using ultra-low-temperature scanning tunneling microscopy/spectroscopy. The bulk gap is {\Delta} ~ 0.053 meV with a critical temperature (Tc) ~ 0.5 K and a critical field below 0.01 T, accompanied by a vortex lattice and bound states, yielding a coherence length of ~200 nm. Remarkably, certain surface regions show a much larger gap of {\Delta} ~ 0.42 meV, persisting up to Tc ~ 3 K and surviving magnetic fields up to 2 T, yet lacking a static vortex lattice. This coexistence of robust surface and bulk superconductivity establishes {\gamma}-PtBi2 as a unique platform for investigating the interplay between bulk and surface Cooper pairings in superconducting topological materials.