DOPING DEPENDENCE OF THE THERMOPOWER OF HIGH-T(C) CUPRATES - TIGHT-BINDING BAND MODEL

Tight-binding calculatoins are performed which include both Cu-O and O-O interactions in the CuO2 plane. These calculations reconcile inconsistencies in observed behaviors of the thermopower S and the Hall coefficient R(H): the sip of S of high-T(c) cuprates at room temperature becomes negative in the over-doped regime, while R(H) remains positive. A striking feature of the CuO2 antibonding band is that a holelike Fermi surface is formed even when the band is less than half-filled. This brings about an unusual electron state in which the Hall (cyclotron) mass parallel to the Fermi surface is holelike (< 0) but the transport mass perpendicular to it is electronlike (> 0). This electronlike transport mass contributes to negative S, while the holelike Hall mass results in positive R(H). In such a state, the electron on the Fermi surface has complete duality: it is holelike in one direction, but electronlike in another. In the over-doped regime, where R(H) > 0 and S < 0, the hole doping increases the carrier concentration defined as is-proportional-to R(H)-1, but it decreases the carrier concentration defined as (n/m*)D in Drude's formula. This qualitatively explains the recent muon-spin-rotation (muSR) results that the superconducting carrier concentration n(s)/m* approximately (n/m*)D decreases with hole doping in the overdoped regime.