Evidence for linelike vortex liquid phase in Tl{sub 2}Ba{sub 2}CaCu(sub 2}O{sub 8} probed by the Josephson plasma resonance.

We measured the Josephson plasma resonance (JPR) in optimally doped Tl{sub 2}Ba{sub 2}CaCu{sub 2}O{sub 8+{delta}} thin films using terahertz time-domain spectroscopy in transmission. The temperature and magnetic field dependence of the JPR frequency shows that the c-axis correlations of pancake vortices remain intact at the transition from the vortex solid to the liquid phase. In this respect Tl{sub 2}Ba{sub 2}CaCu{sub 2}O{sub 8+{delta}} films, with anisotropy parameter {gamma}{approx}150, are similar to the less anisotropic YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} ({gamma}{approx}8) rather than to the most anisotropic Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} single crystals ({gamma}{approx}500).