Surface and quasisurface states in a strongly anisotropic layered crystal

In Part 1 a relatively simple model of a strongly anisotropic layered crystal is use to study various types of surface waves in the long-wavelength approximation. Particular solutions are obtained for the lattice-dynamics equations in the presence of a surface impurity monolayer. The solutions have frequencies that lying outside (surface states) and inside (quasisurface states) a band in the continuous spectrum of an ideal lattice. In Part 2 shear waves localized near a monatomic layer adsorbed on the free surface of a strongly anisotropic layered crystal are studied at the microscopic level using a vector laltice model with translational and rotational invariance and elastic stability. It is shown that in some cases a noncentral interatomic interaction results in the appearance of surface shear waves of a special type with one or two termination points and a damping parameter that is a nonmonotonic function the two-dimensional wave vector.