TY - JOUR

T1 - Green's function theory for spin- 1 2 ferromagnets with an easy-plane exchange anisotropy

AU - Yamamoto, Daisuke

AU - Todo, Synge

AU - Kurihara, Susumu

PY - 2008/7/30

Y1 - 2008/7/30

N2 - 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.

AB - 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.

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U2 - 10.1103/PhysRevB.78.024440

DO - 10.1103/PhysRevB.78.024440

M3 - Article

AN - SCOPUS:49149094921

SN - 1098-0121

VL - 78

JO - Physical Review B - Condensed Matter and Materials Physics

JF - Physical Review B - Condensed Matter and Materials Physics

IS - 2

M1 - 024440

ER -