Doping dependence of the thermopower of high-Tccuprates: Tight-binding band model

Tight-binding calculatoins are performed which include both Cu-O and O-O interactions in the ${\mathrm{CuO}}_2$ plane. These calculations reconcile inconsistencies in observed behaviors of the thermopower S and the Hall coefficient ${\mathit{R}}_{\mathit{H}}$: the sign of S of high-${\mathit{T}}_{\mathit{c}}$ cuprates at room temperature becomes negative in the overdoped regime, while ${\mathit{R}}_{\mathit{H}}$ remains positive. A striking feature of the ${\mathrm{CuO}}_2$ 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 (electronlike (>0). This electronlike transport mass contributes to negative S, while the holelike Hall mass results in positive ${\mathit{R}}_{\mathit{H}}$. 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 overdoped regime, where ${\mathit{R}}_{\mathit{H}}$>0 and S${\mathit{R}}_{\mathit{H}}^{\mathrm{-}1}$, but it decreases the carrier concentration defined as (n/${\mathit{m}}^{\mathrm{*}}$ ${)}_{\mathit{D}}$ in Drude’s formula. This qualitatively explains the recent muon-spin-rotation (μSR) results that the superconducting carrier concentration ${\mathit{n}}_{\mathit{s}}$/${\mathit{m}}^{\mathrm{*}}$∼(n/${\mathit{m}}^{\mathrm{*}}$ ${)}_{\mathit{D}}$ decreases with hole doping in the overdoped regime.