Narrowing of the exciton lines using WAHUHA method of solid state NMR spectroscopy

A method for allocating of two thermodynamic reservoirs which are not related to each other in high density exciton gas in semiconductors using the Schwinger representation for the projection operators of the effective spin (pseudospin) of the excitons is proposed. It is shown that the method of narrowing the NMR resonance lines in solids under the influence of a sequence of four electromagnetic pulses of the WAHUHA type can be applied for the line narrowing of the recombination emission and absorption of light by excitons in optical spectroscopy. We found out that, in contrast to the averaging to zero of the magnetic dipole-dipole interaction between nuclei, the exciton-exciton interaction is averaged only partially. This analysis for the excitons can be extended to other quasiparticles of boson type, i.e. biexcitons, polaritons and magnons, in solids.