Free field realization of current superalgebra $gl(m|n)_k$
  We construct the free field representation of the affine currents, energy-momentum tensor and screening currents of the first kind of the current superalgebra $gl(m|n)_k$ uniformly for $m=n$ and $m\neq n$. The energy-momentum tensor is given by a linear combination of two Sugawara tensors associated with the two independent quadratic Casimir elements of $gl(m|n)$. 
Wen-Li Yang, Yao-Zhong Zhang and Xin Liu