PLASMA RESONANCES AND VORTEX DYNAMICS IN LA2-XSRXCUO4

We studied the c-axis Josephson plasma edge of the La2-xSrxCuO4 system for various doping levels as a function of external magnetic fields u p to 25 T, both in Faraday and Voigt configuration, using broad band F ourier Transform spectrometers and monochromatic mm-wave sources. Only in the underdoped regime we find an appreciable shift of the plasma r esonance with applied magnetic field. We compare the experimental resu lts with recent theoretical predictions. In the long wavelength regime we find a new second plasma resonance which disappears in relatively low magnetic fields. (C) 1997 Elsevier Science B.V.