Improvement of T c in the Grain Surface Superconductor La 2 CuO 4 by GeV Heavy-Ion Irradiation

The critical temperature of La2CuO4 specimens showing a grain surface superconductivity after annealing under normal O2 pressure can be improved by 2.9 GeV krypton ion bombardment. The midpoint temperature has thus been raised from 32.5 to 35.0 K by a fluence of 4 · 1012 cm-2. Such a result probably enhanced by the high value of the electronic stopping power might be related to the pressure effect of the defects induced by irradiation and/or the existence of a spin density wave phase.