The free energy functional for a spin singlet ferromagnetic superconductor

摘要

The aim of this paper is to investigate the coexistence of ferromagnetic and superconducting phase for a system of itinerant fermions using a functional method from the field theory. In this way we present a microscopic derivation of Ginzburg-Landau free energy functional for the singlet Cooper pairing system, where the ferromagnetic order appears as a consequence of spontaneously broken spin-rotation symmetry and a contact interaction both for the Heisenberg and the singlet pairing terms was considered. The result is the expanded form of the free functional energy up to 4-th term. Finally we are focusing on the 4-th term of the free energy functional expansion which exhibits both ferromagnetic and superconducting order.