We state a superconvergence result for the lowest order Raviart-Thomas approximation of eigenvalue problems.
It is known that a similar superconvergence result holds for the mixed approximation
of Laplace problem; here we introduce a new proof, since the one given for the source problem cannot be generalized
in a straightforward way to the eigenvalue problem.
Numerical experiments confirm the
superconvergence property and suggest that it also holds for the lowest order
Brezzi-Douglas-Marini approximation.