Study on thermopower and resistivity of Nd1.85Ce0.15CuO4+δ single crystals: Evidence for two-band model

Thermopower (S), in-plane resistivity (ρ) and magnetic susceptibility (χ) on electron-doped Nd1.85Ce0.15CuO4+δ single crystals have been investigated. Susceptibility (χ  ) shows a kink at TmTm about 230 K. TmTm is close to the characteristic temperature T∗T∗ of thermopower. A positive thermopower over the whole temperature region suggests the existence of holelike carrier and the behavior of temperature dependent diffusion thermopower can be attributed to two-band model, which means the coexistence of two types of charge carriers and we abbreviate them as holelike band and electronic band in this text. When the temperature increases above T∗T∗, the diffusion thermopower of holelike band contribution satisfies the Heikes formula as a narrow band does and the bandwidth t   is estimated about 0.02 eV. The fitting results of resistivity in deoxygenated and oxygenated samples support the coexistence of two types of charge carriers. A kink is also observed in a derivative plot of in-plane resistivity at the temperature close to T∗T∗.