Abstract
We report nuclear quadrupole resonance studies on superconducting oxypnictide . The temperature dependence of the spin-lattice relaxation rate decreases below without a coherence (Hebel-Slichter) peak and shows a temperature dependence that is not simple power law nor exponential. We show that the result can be understood in terms of two superconducting gaps of either - or -wave symmetry, with the larger gap and the smaller one . Our result suggests that the multiple-gap feature is universal in the oxypnictide superconductors, which is probably associated with the multiple electronic band structures in this class of materials. We also find that above increases with decreasing temperature, which suggests weak magnetic fluctuations in the normal state.
- Received 9 October 2008
DOI:https://doi.org/10.1103/PhysRevB.78.220506
©2008 American Physical Society