Suppression of vortex lattice melting in YBCO via irradiation with fast electrons

Evolution of the excess conductivity in optimally doped YBa 2 Cu 3 O 7 - δ single crystals is investigated after their irradiation with fast electrons at T ≲ 10 K at energies of 0.5–2.5 MeV and a dose of 3 × 10 18 cm - 2 . The measurements were performed in a magnetic field of 15 kOe applied at various angles with respect to the basal plane of the crystals. The temperature dependences of the paraconductivity were analyzed within the framework of the Aslamazov–Larkin theoretical model of fluctuation conductivity and revealed two major effects of the electron irradiation. Namely, (i) the vortex-lattice-melting kinks in the resistivity temperature dependences vanish after electron irradiation and (ii) the resistivity data in the irradiated state allow for a Kouvel-Fisher-type scaling pointing to the presence of a irradiation-induced vortex Bragg-glass phase. These effects are discussed in terms of a competition between intrinsic pinning due to point defects and volume pinning induced by electron irradiation. In all, our findings are relevant for YBCO-based circuitry which is exposed to fast electrons in moderately strong magnetic fields.