KINETIC FORMULA FOR ESTIMATING RESISTIVE PHONON LIFETIMES

An improved kinetic formula which can be used to estimate the average phonon resistive lifetime tau(R) from thermal conductivity data is pre sented. The relation is kappa = Cc2(2)tau(R), where kappa is the therm al conductivity, C is the specific heat, and c2 is the second sound ve locity. At very low temperatures c2 almost-equal-to c(D)/square-root 3 , where c(D) is the Debye velocity, and the result reduces to the stan dard kinetic formula. However, above about 0.02THETA(D) c2 undergoes a rapid decrease. As a consequence, phonon lifetimes estimated by the m odified formula are considerably longer than those obtained from the s tandard kinetic formula.