This article is cited in 15 papers

The two-time Green's function and the diagram technique

N. M. Plakida

Joint Institute for Nuclear Research, Dubna, Moscow Oblast, Russia

Abstract: Based on constructing the equations of motion for the two-time Green's functions, we discuss calculating the dynamical spin susceptibility and correlation functions in the Heisenberg model. Using a Mori-type projection, we derive an exact Dyson equation with the self-energy operator in the form of a multiparticle Green's function. Calculating the self-energy operator in the mode-coupling approximation in the ferromagnetic phase, we reproduce the results of the temperature diagram technique, including the correct formula for low-temperature magnetization. We also consider calculating the spin fluctuation spectrum in the paramagnetic phase in the framework of the method of equations of motion for the relaxation function.

Keywords: dynamical spin susceptibility, Heisenberg model, retarded Green's function, advanced Green's function, Tyablikov decoupling, diagram technique for spin Green's functions.

Received: 24.02.2011

DOI: 10.4213/tmf6698

 English version: Theoretical and Mathematical Physics, 2011, 168:3, 1303–1317

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