Eigenvalues of the bilayer graphene operator with a complex valued   potential
  We study the spectrum of a system of second order differential operator perturbed by a non-selfadjoint matrix valued potential. We prove that eigenvalues of the perturbed operator are located near the edges of the spectrum of the unperturbed operator. 
Francesco Ferrulli, Ari Laptev, Oleg Safronov
math.SP