Carrier dispersion in the two-dimensional t-J model on a triangular lattice

For the case of low concentration the carrier dispersion in the two-dimensional t-J model on a triangular lattice is investigated using Mori's projection operator technique. The dispersion depends strongly on the sign of the hopping constant t and on its ratio to the exchange constant J. For t > 0 minima of the band are located at the wave vectors Q= (2 pi/3, 2 pi/root 3) and (4 pi/3, 0), while for t < 0 they are at alpha Q where the coefficient alpha < 1 decreases with increasing J/vertical bar t vertical bar. In the case t > 0 the width of the band decreases with increasing J/t without substantial change in its shape, while for t < 0 the band shape changes drastically with J/vertical bar t vertical bar. The obtained results are compared with experimental data in Na(x)CoO(2). (c) 2008 Elsevier B.V. All rights reserved.