Magnetic penetration-depth measurements of a suppressed superfluid density of superconducting Ca0.5Na0.5Fe2As2 single crystals by proton irradiation

JEEHOON KIM; N. HABERKORN; M. GRAF; I. USOV; F. RONNING; L. CIVALE; E. NAZARETSKI; G. F. CHEN; W. YU; J. D. THOMPSON; R. MOVSHOVICH

PHYSICAL REVIEW B - CONDENSED MATTER AND MATERIALS PHYSICS

American Physical Society

Año: 2012 vol. 86 p. 144509 - 144514

0163-1829

We report on the dramatic eect of random point defects, produced by proton irradiation, on the superfluid density s in superconducting Ca0.5Na0.5Fe2As2 single crystals. The magnitude of the suppression is inferred from measurements of the temperature-dependent magnetic penetration depth (T) using magnetic force microscopy. Our ndings indicate that a radiation dose of 2x10^16 cm^-2 produced by 3 MeV protons results in a reduction of the superconducting critical temperature Tc by approximately 10%. In contrast, l(0) is suppressed by approximately 60%. This break-down of the Abrikosov-Gorkov theory may be explained by the so-called Swiss cheese model, which accounts for the spatial suppression of the order parameter near point defects similar to holes in Swiss cheese. Both the slope of the upper critical eld and the penetration depth (T=Tc)=(0) exhibit similar temperature dependences before and after irradiation. This may be due to a combination of the highly disordered nature of Ca0.5Na0.5Fe2As2 with large intraband and simultaneous interband scattering as well as the s-wave nature of short coherence length superconductivity.