Band structure, superconductivity, and polytypism in AuSn4

Abstract

The orthorhombic compound AuSn 4 is compositionally similar to the Dirac node arc semimetal PtSn 4 . AuSn 4 is, contrary to PtSn 4 , superconducting with a critical temperature of T c = 2.35 K. Recent measurements present indications for quasi-two-dimensional superconducting behavior in AuSn 4 . Here we present measurements of the superconducting density of states and the band structure of AuSn 4 through scanning tunneling microscopy and angular resolved photoemission spectroscopy (ARPES). The superconducting gap values in different portions of the Fermi surface are spread around 0 = 0.4 meV, which is close to but somewhat larger than = 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 T c . 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 AuSn 4 a rather unique case with a three-dimensional electronic band structure but properties ressembling those of low-dimensional layered compounds.

Insights into the Stability and Surface Termination of Topological Semimetal NbAs2

“…Topological materials, a novel class of quantum matter, are distinguished by the robustness of their surface states against non-magnetic perturbations, a consequence of their non-trivial topology. [1] These materials, particularly topological insulators, [2][3][4] semimetals, [5][6][7][8][9] and superconductors, [10][11][12][13] have generated a significant research interest due to their potential implications for quantum computing [14] and spintronics. [15] The exotic phenomena exhibited by these materials, such as the quantum anomalous Hall effect [16][17][18] and Majorana fermions, [19][20][21][22] defy traditional paradigms, requiring innovative theoretical and experimental approaches for their comprehensive understanding.…”