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

For the case of low concentration the carrier dispersion in the two-dimensional t–Jt–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>0t>0 minima of the band are located at the wave vectors Q=(2π/3,2π/3) and (4π/3,0)(4π/3,0), while for t<0t<0 they are at αQ where the coefficient α<1α<1 decreases with increasing J/|t|J/|t|. In the case t>0t>0 the width of the band decreases with increasing J/tJ/t without substantial change in its shape, while for t<0t<0 the band shape changes drastically with J/|t|J/|t|. The obtained results are compared with experimental data in NaxCoO2.