  In the framework of superfield approach to Becchi-Rouet-Stora-Tyutin (BRST)
formalism, the derivation of the (anti-)BRST nilpotent symmetries for the
matter fields, present in any arbitrary interacting gauge theory, has been a
long-standing problem. In our present investigation, the local, covariant,
continuous and off-shell nilpotent (anti-)BRST symmetry transformations for the
Dirac fields $(\psi, \bar\psi)$ are derived in the framework of the augmented
superfield formulation where the four $(3 + 1)$-dimensional (4D) interacting
non-Abelian gauge theory is considered on the six $(4 + 2)$-dimensional
supermanifold parametrized by the four even spacetime coordinates $x^\mu$ and a
couple of odd elements ($\theta$ and $\bar\theta$) of the Grassmann algebra.
The requirement of the invariance of the matter (super)currents and the
horizontality condition on the (super)manifolds leads to the derivation of the
nilpotent symmetries for the matter fields as well as the gauge- and the
(anti-)ghost fields of the theory in the general scheme of the augmented
superfield formalism.
