Dirk Hundertmark and Young-Ran Lee Exponential decay of eigenfunctions and generalized eigenfunctions of a non self-adjoint matrix Schr\"odinger operator related to NLS (56K, LaTeX2e) ABSTRACT. We study the decay of eigenfunctions of the non self-adjoint matrix operator $\calH = \left( \begin{smallmatrix} -\Delta +\mu+U & W \\-W & \Delta -\mu -U \end{smallmatrix} \right)$, for $\mu>0$, corresponding to eigenvalues in the strip $-\mu<\re E <\mu$.