Vortex matter freezing inBi2Sr2CaCu2O8samples with a very dense distribution of columnar defects

We show that the dynamical freezing of vortex structures nucleated at diluted densities in ${\mathrm{Bi}}₂{\mathrm{Sr}}₂{\mathrm{CaCu}}₂{\mathrm{O}}₈$ samples with a dense distribution of columnar defects, $B\ensuremath{\sim}{10}^{\ensuremath{-}2}{B}_{\mathrm{\ensuremath{\Phi}}}$ with ${B}_{\mathrm{\ensuremath{\Phi}}}=5\phantom{\rule{0.16em}{0ex}}\mathrm{kG}$, results in configurations with liquidlike correlations. We propose a freezing model considering a relaxation dynamics dominated by double-kink excitations driven by the local stresses obtained directly from experimental images. With this model we estimate the relaxation barrier and the freezing temperature. We argue that the low-field frozen vortex structures nucleated in a dense distribution of columnar defects thus correspond to an out-of-equilibrium nonentangled liquid with strongly reduced mobility rather than to a snapshot of a metastable state with divergent activation barriers as, for instance, expected for the Bose-glass phase at equilibrium.