Nonlinear absorption of a microwave field by an impurity atom in a spin chain
Аннотация
We have studied the line shape for absorption of a microwave field by an impurity atom in a compound of the type PrCl3, described by a one-dimensional X–Y model. An exact expression is obtained for the absorbed power in the case of an arbitrary field amplitude. In the vicinity of the absorption maximum, in the general case, there are terms logarithmic in the frequency shift or there is a cusp associated with the behavior of the density of states near the edge of the elementary excitation spectrum. At the lowest temperatures, if the field frequency is ω < J/ℏ (where J is the exchange integral), then raising the temperature leads not to smoothing but to a sharpening of the maximum. This characteristic of the low temperature absorption is manifested in sufficiently strong transverse fields.