Correlation functions in the solid-on-solid model of the fluctuating interface

The correlation functions which are suitable for the delocalized interface are defined and evaluated exactly in the two-dimensional solid-on-solid model. The appropriately defined inverse correlation function, which may be a counterpart of the Ornstein-Zernike correlation function for the delocalized interface, is strictly short ranged in the transverse direction and decays exponentially with the new correlation length, independent of system size, in the longitudinal direction. In a system of length L in the transverse direction the quasiroughening transition takes place at temperature $T_r$ depending on L.