Localization transition of random copolymers at interfaces

We consider adsorption of random copolymer chains onto an interface within the model of Garel er al. [Europhys. Lett. 8, 9 (1989)]. By using the replica method the adsorption of the copolymer at the interface is mapped onto the problem of finding the ground state of a quantum mechanical Hamiltonian. To study this ground state we introduce a novel variational principle for the Green's function, which generalizes the well-known Rayleigh-Ritz method of quantum mechanics to nonstationary states. Minimization with an appropriate trial Green's function enables us to find the phase diagram for the localization-delocalization transition for an ideal random copolymer at the interface.