Symmetry operators for Dirac's equation on two-dimensional spin   manifolds
  It is shown that the second order symmetry operators for the Dirac equation on a general two-dimensional spin manifold may be expressed in terms of Killing vectors and valence two Killing tensors. The role of these operators in the theory of separation of variables for the Dirac equation is studied. 
Lorenzo Fatibene, Raymond G. McLenaghan, Giovanni Rastelli, Shane N.   Smith