Green's function theory for spin- 1 2 ferromagnets with an easy-plane exchange anisotropy

Daisuke Yamamoto*, Synge Todo, Susumu Kurihara

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

8 Citations (Scopus)


The many-body Green's function theory with the random-phase approximation is applied to the study of easy-plane spin-1/2 ferromagnets in an in-plane magnetic field. We demonstrate that the usual procedure, in which only the three Green's functions Siμ; Sj- (μ=+,-,z) are used, yields unreasonable results in this case. Then the problem is discussed in more detail by considering all combinations of Green's functions. We can derive one more equation, which cannot be obtained by using only the set of the above three Green's functions, and point out that the two equations contradict each other if one demands that the identities of the spin operators are exactly satisfied. We discuss the cause of the contradiction and attempt to improve the method in a self-consistent way. In our procedure, the effect of the anisotropy can be appropriately taken into account and the results are in good agreement with the quantum Monte Carlo calculations.

Original languageEnglish
Article number024440
JournalPhysical Review B - Condensed Matter and Materials Physics
Issue number2
Publication statusPublished - 2008 Jul 30

ASJC Scopus subject areas

  • Condensed Matter Physics


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