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 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.