Possible multiple gap superconductivity with line nodes in heavily hole-doped superconductor KFe 2As 2 studied by 75As nuclear quadrupole resonance and specific heat

Abstract

We report the 75As nuclear quadrupole resonance (NQR) and specific heat measurements of the heavily hole-doped superconductor KFe 2As 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 ±-wave scenario determined using simple gap analysis. © 2009 The Physical Society of Japan.