Effect of electron irradiation on YBa₂Cu₃O_7−δ superconductor from London penetration depth measurement

Temperature-dependent London penetration depth λ (T) of optimally doped YBa₂Cu₃O_7−δ single crystals was measured by increasing controlled artificial disorders via 2.5 MeV electron irradiation. The irradiation caused significant suppression of the superconductors critical temperature and the low-temperature behavior of λ (T) evolves from a T-linear in pristine state to a T² behavior after the irradiation, expected for a line-nodal d-wave superconductor. According to the normalized superfluid density analysis, we found that the scattering potential strength is estimated in between Born and Unitary limits with a phase shift to be around 65 degree.