Resistivity of La1.825Sr0.175CuO4 and YBa2Cu3O7 to 1100 K: Absence of saturation and its implications

Abstract

Resistivity was measured from $T_c$ to 1100 K for ${\mathrm{La}}_{1.825}$ ${\mathrm{Sr}}_{0.175}$ ${\mathrm{CuO}}_4$, where it is linear to 1100 K, and for ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$, where it is linear to 600 K, increases faster than linear at T>600 K because of loss of oxygen, and changes slope at the 950-K structural transition. The observed absence of saturation in the linear parts of the data implies weak electron-phonon coupling in both superconductors, thus excluding the possibility of phonon-mediated superconductivity. Values of the plasma energy are derived in combination with other experimental data.