Smectic vortex phase in optimally doped YBa2Cu3O7 thin films.
Angular dependent resistivity measurements of optimally doped YBa2Cu3O7 films in fields H pulsed to 50 T are presented. Up to the highest H, the vortex melting field Hm increases and vortex motion is reduced for H aligned with the correlated pinning centers along the main crystalline axes, otherwise 3D anisotropic scaling describes the vortex dynamics. For H parallel ab, the rapid increase in Hm at low temperatures and a critical exponent analysis near Hm confirm the presence of the liquid-crystalline smectic phase predicted for layered superconductors.