PtPb$_4$ is a type II superconductor with a bulk critical temperature $T_{ c}\approx 3 $K and an upper critical field of $H_{ c2}=0.36 $T. PtPb$_4$ is related to non-superconducting PtSn$_4$, which presents nodal arc states at the surface. Here we measure the superconducting density of states of PtPb$_4$ using millikelvin Scanning Tunneling Microscopy (STM). We observe a fully opened superconducting gap of $\Delta=0.48$\ meV similar to expectations from Bardeen Cooper and Schrieffer (BCS) theory ($\Delta_0=1.76k_BT_{ c}=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 $H_{ c2}=0.36 $T. On some locations we find that the superconducting density of states does not vanish above $T_{ c}$. We can find signatures of a superconducting gap up to 5K. We discuss possible reasons for the observation of superconducting properties above $T_{ c}$ and $H_{ c2}$, emphasizing the role played by structural defects.
Categories: cond-mat.supr-con cond-mat.mes-hall cond-mat.str-el