The ab-plane resistivity of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_4$${\mathrm{O}}_{8\pm \mathrm{\delta }}$ (1:2:4) films is measured from 68 to 600 K and found to be a nonlinear function of temperature in contrast to that of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ (1:2:3) films. The nonlinearity can be understood in terms of a Bloch-Grüneisen-type behavior with a transport Debye temperature of ${\theta }_D^{\mathrm{*}}$≃500 K, as compared to ${\theta }_D^{\mathrm{*}}$≃200 K for 1:2:3. This difference is attributed to the larger number of charge carriers per unit cell in 1:2:4.

• Received 23 December 1988

DOI:https://doi.org/10.1103/PhysRevB.39.9611