Quasi-particle excitations in a ferromagnet, near a quantum critical point

The quasi-particle excitations of a ferromagnet, near a quantum critical point are examined. The weak ferromagnetic state is described by the Hubbard model. The effects of emission of absorption of Goldstone modes on the quasiparticles is examined, as are the effects of the incoherent spin–flip excitations. It is found that, unlike the strong ferromagnet, the Goldstone modes have negligibly small effects on the quasi-particle spectrum and the strongest effects originate from the incoherent spin–flips. The incoherent spin excitations produce large quasi-particle mass enhancements and also produce an incoherent peak in both the off Fermi energy majority and minority spin spectral density. r 2005 Elsevier B.V. All rights reserved. PACS: 71.27.+a; 75.40. s; 75.40.GB