Bose-glass Vortex Phase and Pinning by Columnar Defects in HTSC Crystals

Abstract

It is shown that columnar pins introduced into high temperature superconductor (HTSC) single crystals by means of fast-heavy ion-irradiation turn the vortex system into the Bose-glass phase. Experimental evidence for the existence of the Bose glass in Bi2Sr2CaCu2O8 and YBa2Cu3O7-δ crystals is obtained from magnetic relaxation measurements, and from the field angle- and frequency dependence of the AC susceptibility. Vortex creep is initiated by the nucleation of vortex loops, a mechanism specific to the Bose-glass. The appearance of nonlinearity in the I-V curves, seen as the onset of odd harmonic generation in the AC response at very low frequency, is shown to be a fair identification of the phase boundary. The field orientation-dependence of the Bose-glass transition temperature exhibits a sharp peak when the field is aligned with the defects. Also, we analyse the evolution of the phase boundary with the defect density.