Josephson plasma resonance as a structural probe of vortex liquid

Recent developments of the Josephson plasma resonance and transport c-axis measurements in layered high T-c superconductors allow one to probe Josephson coupling in a wide range of the vortex phase diagram. We derive a relation between the field dependent Josephson coupling energy and the density correlation function of the vortex liquid. This relation provides a unique opportunity to extract the density correlation function of pancake vortices from the dependence of the plasma resonance on the ab component of the magnetic field at a fixed c-axis component.