Effect of ferromagnetic spin fluctuations on the electronic states in image based on two-dimensional triangular lattice 11-band d–p model Original Research Article

Electronic states of the CoO2 plane in NaxCoO2NaxCoO2 are investigated on the basis of the triangular lattice 11-band d–p model by using the second order perturbation (SOP) and the random phase approximation (RPA). Due to the effect of the in-plane ferromagnetic fluctuations enhanced for 0.6≲x≲0.750.6≲x≲0.75, the quasiparticle dispersion near the ΓΓ-point is strongly reduced to yield an almost flat dispersion just above the fermi level. With increasing x , the electronic specific heat coefficient γγ increases towards the critical doping xc∼0.75xc∼0.75 above which the in-plane ferromagnetism takes place. We also find that the six small hole pockets near the K-point are stabilized due to the electron correlation effect within both the SOP and the RPA.