A Liouville-type theorem for the p-Laplacian with potential term
  In this paper we prove a sufficient condition, in terms of the behavior of a ground state of a singular p-Laplacian problem with a potential term, such that a nonzero subsolution of another such problem is also a ground state. Unlike in the linear case (p=2), this condition involves comparison of both the functions and of their gradients. 
Yehuda Pinchover, Achilles Tertikas, Kyril Tintarev