Effects of successive proton irradiation on the peak effect in YBa2Cu3O7−δ single crystals

The effect of increasing the density of uncorrelated defects on the peak effect is studied in a detwinned YBa2Cu3O7−δ single crystal. The defects were introduced with 9 MeV proton irradiation where the total dose ranged from 0.25×1015 to 2×1015 p/cm2. With each successive irradiation, the peak effect shifts down in field and is eventually suppressed in both the electrical resistivity and the dc magnetization by a sufficiently high irradiation dose. The peak effect reappears after a high temperature anneal, suggesting that it is primarily the point defects introduced by the irradiation which interfere with the formation of the peak effect.