Band structure, superconductivity, and polytypism in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>AuSn</mml:mi><mml:mn>4</mml:mn></mml:msub></mml:math>
Edwin Herrera, Beilun Wu, Evan O’Leary, Alberto M. Ruiz, Miguel Águeda, Pablo García Talavera, Víctor Barrena, Jon Azpeitia, Carmen Munuera, M. Garcı́a-Hernández, Lin‐Lin Wang, Adam Kaminski, P. C. Canfield, José J. Baldoví, Isabel Guillamón, Hermann Suderow
Abstract
The orthorhombic compound ${\mathrm{AuSn}}_{4}$ is compositionally similar to the Dirac node arc semimetal ${\mathrm{PtSn}}_{4}$. ${\mathrm{AuSn}}_{4}$ is, contrary to ${\mathrm{PtSn}}_{4}$, superconducting with a critical temperature of ${T}_{c}=2.35$ K. Recent measurements present indications for quasi-two-dimensional superconducting behavior in ${\mathrm{AuSn}}_{4}$. Here we present measurements of the superconducting density of states and the band structure of ${\mathrm{AuSn}}_{4}$ through scanning tunneling microscopy and angular resolved photoemission spectroscopy (ARPES). The superconducting gap values in different portions of the Fermi surface are spread around ${\mathrm{\ensuremath{\Delta}}}_{0}=0.4$ meV, which is close to but somewhat larger than $\mathrm{\ensuremath{\Delta}}=1.76{k}_{B}{T}_{c}$ 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 ${\mathrm{AuSn}}_{4}$ a rather unique case with a three-dimensional electronic band structure but properties ressembling those of low-dimensional layered compounds.