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All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Superconducting Density of States of PtPb 4

PtPb 4 is a type II superconductor with a bulk critical temperature T c ≈ 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 Δ = 0.48 meV similar to expectations from Bardeen, Cooper and Schrieffer (BCS) theory (Δ 0 = 1.76k B T 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 5 K. We discuss possible reasons for the observation of superconducting properties above T c and H c2 , emphasizing the role played by structural defects.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Nonsymmorphic symmetry-protected band crossings in a square-net metal PtPb 4

Topological semimetals with symmetry-protected band crossings have emerged as a rich landscape to explore intriguing electronic phenomena. Nonsymmorphic symmetries in particular have been shown to play an important role in protecting the crossings along a line (rather than a point) in momentum space. Here we report experimental and theoretical evidence for Dirac nodal line crossings along the Brillouin zone boundaries in PtPb 4 , arising from the nonsymmorphic symmetry of its crystal structure. Interestingly, while the nodal lines would remain gapless in the absence of spin–orbit coupling (SOC), the SOC, in this case, plays a detrimental role to topology by lifting the band degeneracy everywhere except at a set of isolated points. Nevertheless, the nodal line is observed to have a bandwidth much smaller than that found in density functional theory (DFT). Our findings reveal PtPb 4 to be a material system with narrow crossings approximately protected by nonsymmorphic crystalline symmetries.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on PtPb by Materials Project

PtPb is Molybdenum Carbide MAX Phase-like structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Pt2- is bonded to six equivalent Pb2+ atoms to form a mixture of distorted edge and corner-sharing PtPb6 pentagonal pyramids. All Pt–Pb bond lengths are 2.88 Å. Pb2+ is bonded to six equivalent Pt2- atoms to form a mixture of edge, corner, and face-sharing PbPt6 octahedra. The corner-sharing octahedral tilt angles are 46°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on PtPb by Materials Project

PtPb crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Pt2- is bonded in a distorted body-centered cubic geometry to two equivalent Pt2- and six equivalent Pb2+ atoms. Both Pt–Pt bond lengths are 2.79 Å. All Pt–Pb bond lengths are 2.89 Å. Pb2+ is bonded in a 6-coordinate geometry to six equivalent Pt2- atoms.

36 MATERIALS SCIENCE↗