Strong-coupling Spin-singlet Superconductivity with Multiple Full Gaps in Hole-doped Ba${}_{0.6}$K${}_{0.4}$Fe${}_2$As${}_2$ Probed by Fe-NMR

Abstract

We present ${}^{57}$Fe-NMR measurements of the novel normal and superconducting-state characteristics of the iron-arsenide superconductor Ba${}_{0.6}$K${}_{0.4}$Fe${}_2$As${}_2$ ($T_c$ = 38 K). In the normal state, the measured Knight shift and nuclear spin-lattice relaxation rate $(1/T_1)$ demonstrate the development of wave-number ($q$)-dependent spin fluctuations, except at $q$ = 0, which may originate from the nesting across the disconnected Fermi surfaces. In the superconducting state, the spin component in the ${}^{57}$Fe-Knight shift decreases to almost zero at low temperatures, evidencing a spin-singlet superconducting state. The ${}^{57}$Fe-$1/T_1$ results are totally consistent with a $s^{\pm }$-wave model with multiple full gaps, regardless of doping with either electrons or holes.

4 pages, 4 figures, 1 table

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