Superconvergence of simple conforming mixed finite elements for linear   elasticity on rectangular grids in any space dimension
  This paper is to prove superconvergence of a family of simple conforming mixed finite elements of first orderfor the linear elasticity problem with the Hellinger--Reissner variational formulation. The analysis is based on three main ingredients: a new interpolation operator, a new expansion method, and a new iterative argument for superconvergence analysis. 
Jun Hu and Shangyou Zhang
math.NA