Effects of the weak point disorder on the vortex matter phase diagram are studied by an irradiation of 2.5 MeV electrons in untwinned ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_y$ single crystals. We find that the point disorder lowers the critical point $H_{\mathrm{cp}}$ of the first-order vortex lattice melting line $H_{\mathrm{m}}\mathrm{}\left(T\right)\mathrm{}$ and has an opposite effect on the vortex glass phase boundary above and below $H_{\mathrm{cp}}.$ Below $H_{\mathrm{cp}},$ the field-driven disordering transition line $H^{*}\mathrm{}\left(T\right)\mathrm{}$ between the Bragg glass and the vortex glass phases shifts to lower fields and the vortex glass phase is expanded after irradiation. Near the vortex liquid-to-glass transition line $H_{\mathrm{g}}\mathrm{}\left(T\right)\mathrm{}$ above $H_{\mathrm{cp}},$ on the other hand, the vortex glass phase is reduced after irradiation, indicating the enhanced vortex wandering by the point disorder in the critical region.

• Received 25 May 1999

DOI:https://doi.org/10.1103/PhysRevB.61.3649