Entanglement of Solid Vortex Matter: A Boomerang Shaped Reduction Forced   by Disorder in Interlayer Phase Coherence in Bi2Sr2CaCu2O8+y
  We present evidence for entangled solid vortex matter in a glassy state in a layered superconductor Bi$_2$Sr$_2$CaCu$_2$O$_{8+y}$ containing randomly splayed linear defects. The interlayer phase coherence--probed by the Josephson plasma resonance--is enhanced at high temperatures, reflecting the recoupling of vortex liquid by the defects. At low temperatures in the vortex solid state, the interlayer coherence follows a boomerang-shaped reentrant temperature path with an unusual low field decrease in coherence, indicative of meandering vortices. We uncover a distinct temperature scaling between in-plane and out-of-plane critical currents with opposing dependencies on field and time, consistent with the theoretically proposed "splayed-glass" state. 
T. Kato, T. Shibauchi, Y. Matsuda, J. R. Thompson, and L.   Krusin-Elbaum