Abrupt change of Josephson plasma frequency at the phase boundary of the Bragg glass in Bi2Sr2CaCu2O8+delta

We report the first detailed and quantitative study of the Josephson coupli ng energy in the vortex liquid, Bragg glass, and vortex glass phases of Bi2 Sr2CaCu2O8+delta by the Josephson plasma resonance. The measurements reveal ed distinct features in the T and H dependencies of the plasma frequency om ega(p1) for each of these three vortex phases. When going across either the Bragg-to-vortex glass or the Bragg-to-liquid transition line, omega(p1) sh ows a dramatic change. We provide a quantitative discussion on the properti es of these phase transitions, including the first order nature of the Brag g-to-vortex glass transition.