Self-irradiation damage and 5f localization in PuCoGa5

Understanding superconductivity in PuCoGa5 presents several challenges due to the presence of local moments and self-irradiation damage. We present X-ray absorption fine-structure measurements that further establish the presence of local 5f-electrons. Moreover, these data indicate even stronger localization after the PuCoGa5 sample has aged, indicating a possible mixed valent ground state of the Pu atoms. Local structure measurements on this aged sample show an astonishing amount of damage, approximately 40% of the material after about 2 years. This amount of damage indicates that distortions around the Frenkel defects extend beyond the nearest-neighbor, and is qualitatively consistent with a percolation model for the destruction of the superconducting state after sufficient damage has accumulated.