Thursday, June 6, 2013

1306.1186 (Junya Otsuki et al.)

Dynamical mean-field theory for quantum spin systems: Test of solutions
for magnetically ordered states

Junya Otsuki, Yoshio Kuramoto
A spin version of dynamical mean field theory is extended for magnetically ordered states in the Heisenberg model. A highly accurate numerical solution is obtained by means of the continuous-time quantum Monte Carlo with fictitious bosons, and the solution is critically tested by known physical properties. In contrast with the mean-field theory, soft paramagnons appear near the transition temperature. Moreover, the Nambu-Goldstone mode (magnon) in the ferromagnetic phase is reproduced reasonably well. However, antiferromagnetic magnons have an energy gap in contradiction to the Nambu-Goldstone theorem. The origin of this failure is identified and discussed.
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