Dynamics of quantum antiferromagnets from phonon assisted multimagnon infrared absorption

Multimagnon absorption is not allowed in antiferromagnets but can become allowed by the assistance of phonons. This mechanism has been used by several theoretical and experimental groups to investigate the dynamics of low-dimensional anti ferromagnets leading to several breakthroughs. Spinons have been directly observed and its dynamics studied in CuO-based chains. Bound states and quasi bound states of magnons have been reported on ladders and two-dimensional CuO layers. Cyclic exchange of spins has been shown to be important in two-dimensional CuO layers and latter confirmed by neutrons and by studies on ladders. Also spin I systems have been studied in two dimensions and the line shape has been found to be in excellent accord with the theoretical prediction. We will review experimental and theoretical work that establish the technique as a unique tool to study the dynamics of quantum antiferromagnets. (c) 2006 Elsevier B.V. All rights reserved.