Thermoelectric power of overdoped Tl2201 crystals: Charge density waves and $T^1$ and $T^2$ resistivities

Abstract

We report measurements of the in-plane thermoelectric power (TEP) for an overdoped (OD) crystal of the single layer cuprate superconductor Tl$_2$Ba$_2$CuO$_{6+x}$ (Tl2201) at several hole concentrations ($p$), from 300 or 400 K to below the superconducting transition temperature ($T_c$). For $p$ = 0.192 and 0.220, small upturns in the TEP below 150 K are attributed to the presence of charge density waves (CDW) detected by resonant inelastic X-ray scattering studies. This suggests that measurement of the TEP could provide a simple and effective guide to the presence of a CDW. Over a certain temperature range, often strongly restricted by the CDW, the TEP is consistent with the Nordheim-Gorter rule and the $T^1$ and $T^2$ terms in the in-plane resistivity of similar crystals observed below 160 K. Two scenarios in which the $T^1$ scattering term is uniform or non-uniform around the Fermi surface are discussed. As found previously by others, for uniform scattering the $T^1$ terms give scattering rates ($\tau^{-1}$) at lower $p$ that are somewhat larger than the Planckian value $k_B T/\hbar$ and fall to zero for heavily OD crystals. Near 160 K, $\tau^{-1}$ from the $T^2$ terms corresponds to the Planckian value.