Nodeless High-Tc Superconductivity in the Highly Overdoped CuO2 Monolayer

We study the electronic structure and superconductivity in a CuO2 monolayer grown recently on the d-wave cuprate superconductor Bi2Sr2Cu2O8+delta Density functional theory calculations indicate a significant charge transfer across the interface such that the CuO2 monolayer is heavily overdoped into the hole-rich regime yet inaccessible in bulk cuprates. We show that both the Cu d(x2-y2) and d(3z)2-(r)2 orbitals become important and the Fermi surface contains one electron and one hole pocket associated with the two orbitals, respectively. Constructing a minimal correlated two-orbital model for the e(g) complex, we show that the spin-orbital exchange interactions produce a nodeless superconductor with extended s-wave pairing symmetry and a pairing energy gap comparable to the bulk d-wave gap, in agreement with recent experiments. The findings point to a direction of realizing new high-T-c superconductors in ozone grown transition-metal-oxide monolayer heterostructures.