Superconducting Density of States of PtPb4

PtPb4 is a type II superconductor with a bulk critical temperature Tc ≈ 3 K and an upper critical field of Hc2 = 0.36
T. PtPb4 is related to non-superconducting PtSn4, which presents nodal arc states at the surface. Here, we measure the
superconducting density of states of PtPb4 using millikelvin Scanning Tunneling Microscopy (STM). We observe a fully
opened superconducting gap of = 0.48 meV similar to expectations from Bardeen, Cooper and Schrieffer (BCS) theory
(0 = 1.76kBTc = 0.49 meV). Measurements under magnetic fields applied perpendicular to the surface show a spatially
inhomogeneous gap structure, presenting superconducting signatures at fields as high as 1.5 T, significantly above Hc2 = 0.36
T. On some locations, we find that the superconducting density of states does not vanish above Tc. We can find signatures of
a superconducting gap up to 5 K.We discuss possible reasons for the observation of superconducting properties above Tc and
Hc2, emphasizing the role played by structural defects.