Magnetic field dependence of the transverse plasmon in SmLa0.8Sr0.2CuO4-delta

The magnetic field and temperature dependence of the transverse and longitudinal plasmons in SmLa0.8Sr0.2CuO4−δ have been investigated. A transition between a vortex-glass and a vortex-liquid regime, which revealed different field dependencies of the resonance frequencies, could be clearly observed. The positions and the spectral weights of the plasmons were successfully described using the multilayer model [Phys. Rev. B 64, 024530 (2001)], which takes the compressibility of the electronic liquid into account. The absolute value of the compressibility is close to that of a two-dimensional noninteracting electron gas