PHASE-BEHAVIOR OF RANDOM COPOLYMERS IN QUENCHED RANDOM-MEDIA

In this paper, we consider the behavior of random heteropolymers in a quenched disordered medium. We develop a field theory and obtain a mea n-field solution that allows for replica symmetry breaking. The presen ce of an external disorder leads to the formation of compact states; a homopolymeric effect. We compute the phase diagram for two classes of problems. First, we consider the situation wherein the bare heteropol ymer prefers like segments to segregate, and second, we examine cases where the bare heteropolymer prefers unlike segments to mix. For the f irst class of systems, we find a phase diagram characterized by a repl ica symmetry broken phase that exists below a particular temperature. This temperature grows with the strength of the external disorder. In the second class of situations, the phase diagram is much richer. Here we find two replica symmetry broken phases with different patterns se parated by a reentrant phase. The reentrant phase and one of the two r eplica symmetry broken phases are induced by interactions with the ext ernal disorder. The dependence of the location of the phase boundaries on the strength of the external disorder are elucidated. We discuss o ur results from a physical standpoint, and note the testable experimen tal consequences of our findings. (C) 1995 American Institute of Physi cs.