Atomic Visualization of Bulk and Surface Superconductivity in Weyl Semimetal γ-PtBi₂

A bulk superconductor hosting intrinsic surface superconductivity provides a unique platform for exploring Majorana bound states. Trigonal γ-PtBi₂, a superconductor, is a promising candidate, as both surface superconducting gaps and topological surface states have been observed. However, the simultaneous presence of bulk and surface superconductivity has remained unresolved. In this study, we directly visualize coexisting bulk and surface superconducting gaps in trigonal PtBi₂ using ultra-low-temperature scanning tunneling microscopy/spectroscopy. The bulk gap, 𝛥, is ∼0.053 meV, with a critical temperature (T_C) of ∼0.5 K and a critical field below 0.01 T, accompanied by a vortex lattice and vortex bound states and yielding a coherence length of ∼200 nm. Remarkably, certain surface regions exhibit a much larger gap (𝛥) of ∼0.42 meV, persisting up to a T_C value of ∼3 K and surviving magnetic fields of up to 2 T, yet lacking a static vortex lattice. This coexistence of robust surface and bulk superconductivity establishes γ-PtBi₂ as a unique platform for exploring the interplay between bulk and surface Cooper pairings in topological superconductors.