Temperature Dependence of the Average Mobility in Graphite

The average mobility (µ) of majority carriers evaluated from the magneto-resistance of highly oriented graphite through B 2 /( Δ ρ/ρ 0 )=( c /µ) 2 +O( B 2 ) is proportional to T -1.6 between 40 K and 80 K, and T -1.2 above 80 K. The T -1.2 dependence was observed by Soule and is in agreement with the theory of Ono and Sugihara. The range in which T -1.6 dependence is observed, coincides with the region where the phonon drag effect is active. This suggests us that the both phenomena are closely correlated: The phonon system receives the momentum from carriers driven by an external field. If the relaxation processes of phonons except for that due to the carrier scattering are totally inactive, the transferred momentum is partly returned to the carrier system from phonons so as to enhance the mobility. Calculations have revealed that µ=(µ) 0 (1+ C T -3 ) between 40 K and 80 K, where (µ) 0 ∝ T -1.2 .