BOSE-GLASS BEHAVIOR OF THE VORTEX SYSTEM IN EPITAXIAL BI(2)SR(2)CACU(2)O(8+DELTA) FILMS WITH COLUMNAR DEFECTS

A continuous transition of the vortex ensemble into a Bose-glass state in epitaxial Bi2Sr2CaCu2O8+δ films with columnar defects along the c axis, induced by irradiation with 2.7 GeV U238 ions was observed. The temperature variation of the resistivity, measured with the magnetic field B=μ0H applied parallel to the c axis, fits the expression ρ(T)∼(T-TBG)ν(z-2) at low levels, with a field-independent exponent up to B2 T. At very low fields, the magnetic-field dependence of the Bose-glass transition temperature TBG is in good agreement with the predictions of theory of boson localization in the presence of correlated disorder, 1/TBG-1/Tc0∼B1/4. However, for applied field values significantly larger than the dose-equivalent field Bφ=1 T, the vortex delocalization in our samples seems to proceed via melting, the magnetic-field exponent becoming very close to 1/2. The occurrence of the Bose-glass transition in the case of intrinsically very anisotropic superconductors, as Bi2Sr2CaCu2O8+δ, can be understood through an increase of the tilt modulus in the vortex ensemble in the presence of correlated disorder, which promotes vortex localization. © 1995 The American Physical Society.