Collective modes in layered superconductors

Weakly damped collective oscillations in layered superconductors are examined theoretically. The calculation is based on kinetic equations for Green functions generalized to the case of layered superconductors with weak interlayer coupling. We show that weakly damped plasma oscillations of superconducting electrons can exist in such superconductors and calculate the spectrum of the mode. The oscillations are reminiscent of Josephson plasma oscillations in a superconducting tunnel junction. As the temperature approaches the critical one, these oscillations transform into Carlson-Goldman modes. Possibilities for detecting the plasma mode experimentally are discussed. We found distinctive features in the reflection coefficient for an electromagnetic wave incident at an arbitrary angle on a plane parallel to the layers. The presence of the mode changes also the dispersion relation for the waves propagating along a thin film of a layered superconductor.