Jahn-Teller mechanism of stripe formation in doped layered La sub(2-x)Sr sub(x)NiO sub(4) nickelates

We introduce an effective model for e sub(g) electrons to describe quasi-two-dimensional layered La sub(2-x)Sr sub(x)NiO sub(4) nickelates and study it using correlated wavefunctions on 8 x 8 and 6 x 6 clusters. The effective Hamiltonian includes the kinetic energy, on-site Coulomb interactions for e sub(g) electrons (intraorbital U and Hund's exchange J sub(H)) and the coupling between eg electrons and Jahn-Teller distortions (static modes). The experimental ground state phases with inhomogeneous charge, spin and orbital order at the dopings x = 1/3 and 1/2 are reproduced very well by the model. Although the Jahn-Teller distortions are weak, we show that they play a crucial role and stabilize the observed cooperative charge, magnetic and orbital order in the form of a diagonal stripe phase at x = 1/3 doping and a chequerboard phase at x = 1/2 doping.