Numerical study of magnetic and pairing correlation in a bilayer triangular lattice

By using the determinant Quantum Monte Carlo method, the magnetic and pairing correlation of the NaxCoO2⋅yH2O system are studied within the Hubbard model on a bilayer triangular lattice. The temperature dependence of the spin correlation function and pairing susceptibility with several kinds of symmetries at different electron fillings and interlayer coupling terms are investigated. It is found that the system shows antiferromagnetic correlation around half filling, and the fn-wave pairing correlation dominates over other kinds of pairing symmetry in the low doping region. As the electron filling decreases from half filling, both ferromagnetic correlation and the f-wave pairing susceptibility are enhanced and tend to dominate. It is also shown that both the magnetic susceptibility and pairing susceptibility decrease as the interlayer coupling increases. (paper)