Magnon exchange mechanism of ferromagnetic superconductivity

Abstract

The magnon exchange mechanism of ferromagnetic superconductivity (FM superconductivity) was developed to explain in a natural way the fact that the superconductivity in UGe2, ZrZn2, and URhGe is confined to the ferromagnetic phase. The order parameter is a spin antiparallel component of a spin-1 triplet with zero spin projection. The transverse spin fluctuations are pair forming and the longitudinal ones are pair breaking. In the present paper, a superconducting solution, based on the magnon exchange mechanism, is obtained which closely matches the experiments with ZrZn2 and URhGe. The onset of superconductivity leads to the appearance of complicated Fermi surfaces in the spin-up and spin-down momentum distribution functions. Each of them consist of two pieces, but they are simple connected and can be made very small by varying the microscopic parameters. As a result, it is obtained that the specific heat depends on the temperature linearly, at low temperature, and the coefficient γ=C/T is smaller in the superconducting phase than in the ferromagnetic one. The absence of a quantum transition from ferromagnetism to ferromagnetic superconductivity in a weak ferromagnets ZrZn2 and URhGe is explained accounting for the contribution of magnon self-interaction to the spin fluctuations’ parameters. It is shown that in the presence of an external magnetic field the system undergoes a first-order quantum phase transition.

Source-reported materials — not catalogue approval

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