Experimental Evidence for the Vortex Glass Phase in Untwinned, Proton Irradiated YBa{sub 2}Cu{sub 3}O{sub 7-{delta}}

We report on magnetoresistance measurements of the effects of 9 MeV proton irradiation on a clean, untwinned single crystal of YBa{sub 2}Cu {sub 3}O{sub 7-{delta}} . For the first time, evidence for a vortex glass transition is detected in an untwinned single crystal of YBa{sub 2}Cu {sub 3}O{sub 7-{delta}} with induced pointlike disorder, in which the first order vortex melting transition is completely suppressed after proton irradiation. Our results suggest that a sufficiently high pinning disorder is required in order for the vortex glass phase to be observed. (c) 2000 The American Physical Society.