Critical current enhancement in proton-irradiated Tl2CaBa2Cu2O8 films

We have measured changes in the superconducting transition temperature Tc and critical current density Jc of epitaxial Tl2CaBa2Cu2O8 films upon exposure to 2 MeV protons. Jc was measured inductively at 4.2 and 77 K and in fields of H=0 and 0.2 T. At 77 K and H=0, Jc decreases monotonically with increasing fluence Φ. The rate of decrease is about 1.8 times greater than for YBa2Cu3O7 films, even though the rate of change of Tc with Φ is comparable. At 4.2 K, Jc is initially enhanced, even at H=0. The maximum observed increase is 34% (to 8 MA/cm2) at Φ∼1016 protons/cm2 and H=0.2 T. This enhancement is attributed to pinning of magnetic flux lines by proton-induced defects