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

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We report the 75As nuclear quadrupole resonance (NQR) and specific heat measurements of the heavily hole-doped superconductor KFe2As2 (superconducting transition temperature $T_{\text{c}}\simeq 3.5$ K). The spin-lattice relaxation rate $1/T_{1}$ in the superconducting state exhibits a gradual temperature dependence with no coherence peak below $T_{\text{c}}$. The quasiparticle specific heat $C_{\text{QP}}/T$ shows a small jump, which is about 30% of the electronic specific heat coefficient just below $T_{\text{c}}$. The $C_{\text{QP}}/T$ suggests the existence of low-energy quasiparticle excitation at the lowest measurement temperature $T=0.4\,\text{K}\simeq T_{\text{c}}/10$. The $T$ dependences of $1/T_{1}$ and $C_{\text{QP}}/T$ can be explained by a multiple nodal superconducting gap scenario rather than by a multiple fully gapped $s_{\pm}$-wave scenario determined using simple gap analysis.
Physical Society of Japanの論文
2009-08-15