FLUCTUATIONS IN THE STRUCTURE OF INTERFACES

We study the stability matrix (the matrix of second derivatives of the free energy functional with respect to the density at each point in t he system) for various phenomenological models of interfaces between c oexisting phases. The eigenvectors and eigenvalues of that matrix are the eigenmodes, and their inverse susceptibilities, of fluctuations of the interface. We find that, due to the presence of the interface, se veral discrete eigenvalues typically appear in addition to the continu ous bands of eigenvalues of the bulk phases. Some features appear to b e generic, while others depend on the details of the model. (C) 1997 E lsevier Science B.V.