Surface electronic structures of superconducting thin film MgB2(0001) -: art. no. 020508

The surface electronic structures of superconducting MgB2 were investigated using the all-electron full-potential linearized augmented plane-wave method. Hexagonal (0001) surfaces with both B terminated (B-Term) and Mg terminated (Mg-Term) were considered. Due to the nearly-free-electron nature of the Mg surface layer, the vacuum screening range of Mg-Term is shorter than that of B-Term, which shows the covalent bonding nature of the B surface layer. Considerably enhanced densities of states near the Fermi level are found at the surface layers especially for B-Term, which is expected to yield an enhanced superconductivity in the surface of thin film MgB2 over that in bulk-assuming no large changes in the electron-ion matrix elements and phonon frequency contributions. While this expectation is contrary to the weakened superconductivity observed in surface-oriented experiments, we attribute this discrepancy to extrinsic surface effects.