Possible Multiple Gap Superconductivity with Line Nodes in Heavily Hole-Doped Superconductor KFe2As2 Studied by 75As Nuclear Quadrupole Resonance and Specific Heat

We report the 75 As nuclear quadrupole resonance (NQR) and specific heat measurements of the heavily hole-doped superconductor KFe 2 As 2 (superconducting transition temperature T c ' 3:5 K). The spin-lattice relaxation rate 1=T 1 in the superconducting state exhibits a gradual temperature dependence with no coherence peak below T c . The quasiparticle specific heat C QP =T shows a small jump, which is about 30% of the electronic specific heat coefficient just below T c . The C QP =T suggests the existence of low-energy quasiparticle excitation at the lowest measurement temperature T 0:4 K ' T c =10. The T dependences of 1=T 1 and C QP =T can be explained by a multiple nodal superconducting gap scenario rather than by a multiple fully gapped s AE -wave scenario determined using simple gap analysis.