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arXiv · 1306.1186

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

Junya Otsuki·Yoshio Kuramoto
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Abstract

A spin version of dynamical mean-field theory is extended for magnetically ordered states in the Heisenberg model. The self-consistency equations are solved with high numerical accuracy by means of the continuous-time quantum Monte Carlo with bosonic baths coupled to the spin. The resultant 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 discussed in connection with an artificial first-order nature of the transition.

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Junya Otsuki, Yoshio Kuramoto. 2013-06-05. Dynamical mean-field theory for quantum spin systems: Test of solutions for magnetically ordered states. https://doi.org/10.1103/physrevb.88.024427

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