Band structure, superconductivity, and polytypism in AuSn4

The orthorhombic compound AuSn4 is compositionally similar to the Dirac node arc semimetal PtSn4. AuSn4 is, contrary to PtSn4, superconducting with a critical temperature of T-c = 2.35 K. Recent measurements present indications for quasi-two-dimensional superconducting behavior in AuSn4. Here we present measurements of the superconducting density of states and the band structure of AuSn4 through scanning tunneling microscopy and angular resolved photoemission spectroscopy (ARPES). The superconducting gap values in different portions of the Fermi surface are spread around A0 = 0.4 meV, which is close to but somewhat larger than Delta = 1.76k(B)T(c) expected from BCS theory. We observe superconducting features in the tunneling conductance at the surface up to temperatures about 20% larger than bulk Tc. The band structure calculated with density functional theory follows well the results of ARPES. The crystal structure presents two possible stackings of Sn layers, giving two nearly degenerate polytypes. This makes AuSn4 a rather unique case with a three-dimensional electronic band structure but properties ressembling those of low-dimensional layered compounds.

Automated summary

The orthorhombic compound AuSn4 is similar to the Dirac node arc semimetal PtSn4 in composition. Unlike PtSn4, AuSn4 is a superconductor with a critical temperature of T-c = 2.35 K. Recent measurements indicate quasi-two-dimensional superconducting behavior in AuSn4.