Josephson plasma excitation of Bi2Sr2CaCu2O8+delta in parallel magneti
c fields is studied by angular alignment with similar to 0.02 degrees
precision. A disappearance of the resonance has been found for angles
within theta similar to 0.2 degrees (theta is an angle between the fie
ld and the CuO2-plane). The origin of the phenomenon is discussed in t
erms of the Josephson plasma oscillation and Josephson vortex oscillat
ion modes. (C) 1997 Elsevier Science B.V.