Exotic d-Wave Superconducting State of Strongly Hole-Doped KxBa1-xFe2As2

We investigate the superconducting phase in the KxBa1-xFe2As2 122 compounds from moderate to strong hole-doping regimes. Using the functional renormalization group, we show that, while the system develops a nodeless anisotropic s(+/-) order parameter in the moderately doped regime, gapping out the electron pockets at strong hole doping drives the system into a nodal (cosk(x) + cosk(y))(cosk(x) - cosk(y)) d-wave superconducting state. This is in accordance with recent experimental evidence from measurements on KFe2As2 which observe a nodal order parameter in the extreme doping regime. The magnetic instability is strongly suppressed.