Superconductivity proximate to antiferromagnetism in a copper-oxide monolayer grown on Bi${}_2$Sr${}_2$CaCu${}_2$O${}_{8+\hat{I}´}$

Abstract

A nodeless superconducting (SC) gap was reported in a recent scanning tunneling spectroscopy experiment of a copper-oxide monolayer grown on the Bi${}_2$Sr${}_2$CaCu${}_2$O${}_{8+\hat{I}´}$ (Bi2212) substrate [Y. Zhong {\it et al.}, Sci. Bull. {\bf 61}, 1239 (2016)], which is in stark contrast to the nodal d-wave pairing gap in the bulk cuprates. Motivated by this experiment, we first show with first-principles calculations that the tetragonal CuO (T-CuO) monolayer on the Bi2212 substrate is more stable than the commonly postulated CuO${}_2$ structure. The T-CuO monolayer is composed of two CuO${}_2$ layers sharing the same O atoms. The band structure is obtained by first-principles calculations, and its strong electron correlation is treated with the renormalized mean-field theory. We argue that one CuO${}_2$ sublattice is hole doped while the other sublattice remains half filled and may have antiferromagnetic (AF) order. The doped Cu sublattice can show d-wave SC; however, its proximity to the AF Cu sublattice induces a spin-dependent hopping, which splits the Fermi surface and may lead to a full SC gap. Therefore, the nodeless SC gap observed in the experiment could be accounted for by the d-wave SC proximity to an AF order, thus it is extrinsic rather than intrinsic to the CuO${}_2$ layers.

6+ pages, 4 figures; published version