Absence of resistivity saturation and its implications for the high T/sub c/ superconductors

Temperature-dependent resistivity rho(T) was measured from T/sub c/ to 1100K in ceramic samples of La/sub 1.825/Sr/sub 0.175/CuO4 (LSCO) and YBa2Cu3O7 (YBCO). Measurements above 300 K were performed in a flow of O2. In LSCO rho(T) is linear to 1100K; in YBCO rho(T) is linear to 600 K, increases faster than linear at T > 600 K, owing to the loss of oxygen, and shows a break in slope at the structural phase transition near 950 K. It is argued that the observed absence of saturation in the linear parts of the data implies weak electron-phonon coupling in both superconductors, and, coupled with absolute values of the resistivity, places constraints on band structure parameters. Their results take anisotropy into account explicitly and are combined with recent μSR measurements of the penetration depth to obtain experimental estimates of the plasma energy