The~two-time Green's function and the~diagram technique
Teoretičeskaâ i matematičeskaâ fizika, Tome 168 (2011) no. 3, pp. 518-535
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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.
@article{TMF_2011_168_3_a12,
author = {N. M. Plakida},
title = {The~two-time {Green's} function and the~diagram technique},
journal = {Teoreti\v{c}eska\^a i matemati\v{c}eska\^a fizika},
pages = {518--535},
publisher = {mathdoc},
volume = {168},
number = {3},
year = {2011},
language = {ru},
url = {http://geodesic.mathdoc.fr/item/TMF_2011_168_3_a12/}
}
N. M. Plakida. The~two-time Green's function and the~diagram technique. Teoretičeskaâ i matematičeskaâ fizika, Tome 168 (2011) no. 3, pp. 518-535. http://geodesic.mathdoc.fr/item/TMF_2011_168_3_a12/