We report a combined experimental and theoretical study of the surface and bulk electronic structure of aluminium diboride, a nonsuperconducting sister compound of the superconductor ${\mathrm{MgB}}_2$. We perform angle-resolved photoemission measurements with variable photon energy, and compare them to density functional theory calculations to disentangle the surface and bulk contributions to the measured spectra. Aluminium diboride is known to be aluminium deficient, ${\mathrm{Al}}_{1-\delta }{\mathrm{B}}_2$, which would be expected to lead to a hole doping as compared to the nominally stoichimoetric compound. Nonetheless, we find that the bulk $\sigma$ states, which mediate superconductivity in ${\mathrm{MgB}}_2$, remain more than $600\mathrm{meV}$ below the Fermi level. However, we also observe $\sigma$ states originating from the boron terminated surface, with an order of magnitude smaller binding energy of $70\mathrm{meV}$, and demonstrate how surface hole-doping can bring these across the Fermi level.

• Received 6 May 2020
• Accepted 30 June 2020

DOI:https://doi.org/10.1103/PhysRevB.102.035143

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Open access publication funded by the Max Planck Society.

Published by the American Physical Society