Magnetoplasma waves in thin high-temperature-superconducting layers

It is shown that, in thin Bi2Sr2CaCu2O8 layers with thickness d much lower than the London penetration depth λ, two-dimensional magnetoplasma waves can propagate. These collective excitations are analogous to the well-known excitations of the two-dimensional electron gas. The propagation of these plasma waves is possible in both normal and superconducting phases if their frequency ω is lower than the superconducting gap 2Δ(0) at zero temperature. In the case of the magnetic field H perpendicular to the layer, the plasma frequency receives a shift connected with the cyclotron frequency. A magnetoplasma-wave frequency shift like that is possible for a superconducting phase only in the flux-flow regime for very large wave amplitudes. A measurement of the magnetoplasma shift created by the hybridization between plasma and cyclotron waves will give a new direct method for determining both the cyclotron mass of the holes mh in the normal phase and the cyclotron mass of the Cooper pairs m* in the superconducting phase. The checking of the BCS clean-limit relation m*=2mh can be an important tool for understanding the mechanism of high-temperature superconductivity