Vortex matter freezing in Bi_2Sr_2CaCu_2O_8 samples with a very dense distribution of columnar defects

摘要

We show that the dynamical freezing of vortex structures nucleated at diluted densities in Bi_2Sr_2CaCu_2O_8 samples with a dense distribution of columnar defects, B ～ 10~(-2) B_Φ with B_Φ = 5 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.