Subtle Features in Transport Properties: Evidence for a Possible Coexistence of Holes and Electrons in Cuprate Superconductors
Transport properties of high transition temperature (high Tc) cuprate superconductors are investigated within a two-band model. The doping dependent Hall coefficients of La_{2-x}Sr_xCuO_4 (LSCO) and Nd_{2-x}Ce_xCuO_4 (NCCO) are explained by assuming the coexistence of two carriers with opposite charges, loosely speaking electrons (e) and holes (h). Such a possible electron-hole coexistence (EHC) in other p-type cuprates is also inferred from subtle features in the Hall coefficient R_H and thermopower S. The EHC possibly relates to the pseudogap and sign reversals of transport coefficients near Tc. It also corroborates the electronlike Fermi surface revealed in recent photoemission results. An experimental verification is proposed.