期刊
PHYSICAL REVIEW B
卷 78, 期 22, 页码 -出版社
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevB.78.220506
关键词
d-wave superconductivity; fluctuations in superconductors; high-temperature superconductors; iron compounds; lanthanum compounds; nuclear quadrupole resonance; nuclear spin-lattice relaxation; superconducting energy gap; superconducting transition temperature
资金
- MEXT
- JSPS, Japan
- NSF of China
- ITSNEM program of CAS
We report As-75 nuclear quadrupole resonance studies on superconducting oxypnictide LaFeAsO0.92F0.08 (T-c=23 K). The temperature dependence of the spin-lattice relaxation rate (1/T-1) decreases below T-c 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 d- or +/- s-wave symmetry, with the larger gap Delta(1)similar to 4k(B)T(c) and the smaller one Delta(2)similar to 1.5k(B)T(c). 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 1/T1T above T-c increases with decreasing temperature, which suggests weak magnetic fluctuations in the normal state.
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