Fig. 2.

Irradiation enhances superconductivity in ${\text{La}}_{1.875}{\text{Ba}}_{0.125}{\mathrm{C}\mathrm{u}\mathrm{O}}_4$. (Upper) Evolution of the superconducting transition temperature $T_{\mathrm{c}}$ (defined as a 50% reduction in magnetization to a complete Meissner effect) of several samples of ${\text{La}}_{1.875}{\text{Ba}}_{0.125}{\mathrm{C}\mathrm{u}\mathrm{O}}_4$, as a function of irradiation dose. (Lower) Normalized magnetization of ${\text{La}}_{1.875}{\text{Ba}}_{0.125}{\mathrm{C}\mathrm{u}\mathrm{O}}_4$ showing the temperature evolution of the Meissner effect as a function of 5-MeV proton-irradiation dose. A clear increase of $T_{\mathrm{c}}$ is observed, in contrast with the expected behavior of a normal d-wave superconductor. The transition temperature, which starts out at 4.28 K, peaks at 6.15 K after irradiation to $6.1\times 10^{16}$ p/${\mathrm{c}\mathrm{m}}^2$, and then falls back to 3.37 K after the last irradiation. The $T_{\mathrm{c}}$ curves stay sharp after the first four irradiations, indicative of uniform superconducting properties and uniform irradiation damage.