N=2 Superconformal Description of Superstring in Ramond-Ramond Plane   Wave Backgrounds
  Using the U(4) formalism developed ten years ago, the worldsheet action for the superstring in Ramond-Ramond plane wave backgrounds is expressed in a manifestly N=(2,2) superconformally invariant manner. This simplifies the construction of consistent Ramond-Ramond plane wave backgrounds and eliminates the problems associated with light-cone interaction point operators. 
Nathan Berkovits and Juan Maldacena