The theory of topological phase transitions in superconducting thin films and quasi-two-dimensional crystals
Annotatsiya
A theory of topological phase transitions in two-dimensional superconducting films is constructed. It is shown that the Berezinskiĭ, Kosterlitz, and Thouless phase transition is retained in films with finite dimensions, in spite of the fact that the interaction of vortices in such films is not purely logarithmic. It is established that at low temperatures there is one other phase transition, for which a nonzero order parameter ⟨eiϕ(r)⟩ arises near the boundaries of the film. As the distance from the edge of the film increases, this order parameter decreases according to a power law. The reason for the appearance of a boundary order parameter and, together with it, a boundary superconducting layer stems from the coupling between the vortices and their images. It is shown that topological phase transitions in superconducting films are very sensitive to the external magnetic field. The lower critical field Hc1 is calculated.