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Anisotropy of Vortex-Liquid and Vortex-Solid Phases in Single Crystals of Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$: Violation of the Scaling Law

The vortex-liquid and vortex-solid phases in single crystals of Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ placed in tilted magnetic fields are studied by in-plane resistivity measurements using the Corbino geometry to avoid spurious surface barrier effects. It was found that the anisotropy of the vortex-solid phase increases with temperature and exhibits a maximum at $T\approx 0.97 T_c$. In contrast, the anisotropy of the vortex-liquid rises monotonically across the whole measured temperature range. The observed behavior is discussed in the context of dimensional crossover and thermal fluctuations of vortices in the strongly layered system.