BaCuS_2: A Superconductor with Moderate Electron-Electron Correlation

We show that the layered-structure BaCuS_2 is a moderately correlated electron system in which the electronic structure of the CuS layer bears a resemblance to those in both cuprates and iron-based superconductors. Theoretical calculations reveal that the in-plane d–p \sigma^*-bonding bands are isolated near the Fermi level. As the energy separation between the d and p orbitals are much smaller than those in cuprates and iron-based superconductors, BaCuS_2 is expected to be moderately correlated. We suggest that this material is an ideal system to study the competitive/collaborative nature between two distinct superconducting pairing mechanisms, namely the conventional BCS electron-phonon interaction and the electron-electron correlation, which may be helpful to establish the elusive mechanism of unconventional high-temperature superconductivity.