INFRARED-ABSORPTION AND THE LOSS FUNCTION OF THE HIGH-T(C) SUPERCONDUCTORS

The loss-function tensor associated with the infrared absorption spect ra of the high-T(c) superconductors has been calculated. The model use d is a system of layered two-dimensional electron gases where the char ge carriers interact via an effective potential mediated by intra- and interlayer exchange of acoustic and optical plasmons. The calculation s are applied to La1.85Sr0.15CuO4 where the loss function has recently been obtained from careful measurements of the infrared absorption sp ectra. The shape of the calculated loss function is in good agreement with the experimental curve. The observed peak occurring at a frequenc y about 1.5 times the optical plasmon frequency is shown to correspond to the excitation of a plasmon coupled with electron-hole pairs. This theory also allows for establishment of relations between various phy sical parameters.