Motion of holes in two-dimensional ferromagnetic manganites, comparison with high T-c cuprates

We study the motion of holes in the two-dimensional ferromagnetic manganite s by using the numerically exact diagonalization method on small size clust ers. In the ferromagnetic metallic states of perovskite manganites such as La2-2xSr1+2xMn2O7, the magnetic moment is almost saturated and the spin deg ree of freedom freezes, whereas the orbital degree of freedom due to the tw o-fold degeneracy of the e(g) state of Mn ions affects the dynamics of hole s. The orbital degree of freedom is represented by pseudo-spin with 1/2 in magnitude and the effective Hamiltonian is written as an anisotropic t-J mo del. It is shown that there exists coherent motion of holes and its dispers ion strongly depends on the pseudo-spin structure. The mechanism of the mot ion is, however, completely different from that in the t-J model for high T -c cuprates. This is because of the anisotropy of the system in the pseudo- spin space induced by the symmetry of the e(g) orbitals. (C) 1999 Elsevier Science B.V. All rights reserved.