Experimental Evidence for the Vortex Glass Phase in Untwinned, Proton Irradiated ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{O}_{7-\delta }$

We report on magnetoresistance measurements of the effects of 9 MeV proton irradiation on a clean, untwinned single crystal of ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$. For the first time, evidence for a vortex glass transition is detected in an untwinned single crystal of ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$ 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.