NMR study of hole-doped iron-pnictide superconductor Ba1−xKxFe2As2 (x = 0.27−1)

Abstract

We performed the 75As nuclear magnetic resonance measurements of Ba1−xKxFe2As2 (BKFA) for x = 0.27, 0.39, 0.58, 0.64, 0.69 and 1 to understand gap structure in this system. Temperature dependence of spin lattice relaxation rate (1/T1) below superconducting (SC) transition temperature Tc changes gradually from x = 0.39 to 1.0. This result indicates that the SC gap structure changes smoothly from full gap state with maximum Tc into nodal-line structure state for x = 1 (KFe2As2). BKFA does not have distinct SC symmetry change. The nodal gap structure appears continuously and develops gradually with increasing x.