Green's function of a 2D Fermi system undergoing a topological phase transition

An explicit expression is obtained for the single-particle Green's function of a 2D metallic system with attraction between carriers. It is shown that as a result of transverse phase fluctuations, this function is pole-free throughout the entire region of finite temperatures (both above and below the topological phase transition point) corresponding to a nonzero modulus of the complex order field describing the transition from a nonsuperconducting (in this case normal) state to a superconducting state, whose appearance in the 2D case is not accompanied by spontaneous breaking of charge symmetry. (C) 1999 American Institute of Physics. [S0021-3640(99)00902-0].