This is a continuation of an
earlier paper “Fractional Powers of Operators” published in this Journal concerning
fractional powers Aα,α ∈ C, of closed linear operators A in Banach spaces X such
that the resolvent (λ + A)−1 exists for all λ > 0 and λ(λ + A)−1 is uniformly
bounded. Various integral representations of fractional powers and relationship
between fractional powers and interpolation spaces, due to Lions and others, of X
and domain D(Aα) are investigated.