Variational Monte Carlo study of magnetic correlations in bilayer t-J model

We study the magnetic correlations in a t-J bilayer using Variational Monte Carlo (VMC) method, the variational wavefunction being the solution of the Hartree-Fock (HF) t-J Hamiltonian with antiferromagnetic (AF) order. We calculate the spin-spin correlation functions and spin structure factors at half filling and slightly away from half filling. The results show that, at half filling perfect antiferromagnetic long range order (AFLRO) exists, which starts to diminish as soon as holes are introduced. It is observed that the holes drastically reduce the interplanar spin correlations, whereas the effect on the planar correlations is rather small. This is to be contrasted with the experimental results on the cuprates, which show that the AFLRO in the copper oxide planes gets completely destroyed even at a small hole concentration. This is possibly due to the competition of AFLRO with the superconducting order, which has not been incorporated in our calculations. We also examine the effect of the interplanar parameters, e.g. the hopping integral, t(perpendicular to) and exchange constant, J(perpendicular to) on the magnetic correlations. We find that t(perpendicular to) reduces planar correlations while the effect of J(perpendicular to) is small.