Definitions of complex order integrals and derivatives using operator   approach
  For a complex number s, the s-order integral of function f fulfilling some conditions is defined as action of an operator, noted J^s, on f. The definition of the operator J^s is given firstly for the case of complex number s with positive real part. Then, using the fact that the operator of one order derivative, noted D^1, is the left- hand side inverse of the operator J^1, an s-order derivative operator, noted D^s, is also defined for all complex number s with positive real part. Finally, considering the relation J^s=D^(-s), the definition of the s-order integral and s-order derivative is extended for all complex number s.An extension of the definition domain of the operators is given too. 
Raoelina Andriambololona, Tokiniaina Ranaivoson, Rakotoson   Hanitriarivo
math.CV