Microscopic theory of phase transitions and nonlocal corrections for free energy of a superconductor

Abstract

The new approach to the microscopic description of the phase transitions starting from the only first principles was developed on an example of the transition normal metal-superconductor. This means mathematically, that the free energy is calculated in the range of temperatures, which includes a point of pase transition, without introducing any artificial parameters similar to an order parameter, but only starting from microscopic parameters of Hamiltonian. Moreover the theorems about connection of a vacuum amplitude with thermodynamics potentials are realized. The functional of a superconductor's free energy in a magnetic field was obtained with help the developed method. The obtained functional is generalization of Ginzburg-Landau functional for the case of arbitrary value of a gap, arbitrary spatial inhomogeneities and nonlocal magnetic response. The explicit expressions for the extremals of this functional were obtained in the low-temperature limit and the high-temperature limit at the condition of slowness of gap's changes.