We report As75 nuclear magnetic resonance studies on a very clean hole-doped single-crystal Ba0.68K0.32Fe2As 2 (Tc=38.5 K). The spin-lattice relaxation rate 1/T 1 shows an exponential decrease below T0.45Tc down to T0.11Tc, which indicates a fully opened energy gap. From the ratio (T1)c/(T1)a, where a and c denote the crystal directions, we find that the antiferromagnetic spin fluctuation is anisotropic in the spin space above Tc. The anisotropy decreases below Tc and disappears at T→0. We argue that the anisotropy stems from spin-orbit coupling whose effect vanishes when spin-singlet electron pairs form with a nodeless gap.
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|Publication status||Published - Apr 18 2011|
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics