TwoPhonon Response of Anharmonic Lattices in the FirstOrder SelfConsistent Phonon Approximation
Abstract
Further extensions are made to a previously developed analysis for the twotime correlation functions in anharmonic lattices within the firstorder selfconsistent phonon approximation. This stationaryvariation approximation is shown to represent an energy minimum if and only if the onephonon response is stable. An explicit expression is exhibited for the twophonon response and is interpreted as yielding an effective interaction between phonons. It is shown that the firstorder approximation is not fully adequate for describing transport properties (e. g., thermal conductivity) or for investigating resonances or bound states of the two phonons. The distortion of the onephonon peak in the inelasticneutron or Ramanscattering cross section due to the finite size of the momentum transfer is investigated in more detail than the previous analysis.
 Publication:

Physical Review B
 Pub Date:
 January 1972
 DOI:
 10.1103/PhysRevB.5.285
 Bibcode:
 1972PhRvB...5..285W