Superconductivity and normal state properties of single-crystalline Tl0.47Rb0.34Fe1.63Se2 as seen via 77Se and 87Rb NMR
Abstract
We report both 77Se and 87Rb NMR studies on Tl0.47Rb0.34Fe1.63Se2 single-crystalline superconductors (Tc about 32 K). Singlet superconductivity is decisively determined by a sharp drop of the Knight shift K(T) below Tc, after subtracting the superconducting diamagnetic effect. However, the Hebel-Slichter coherence peak below Tc is not observed in the spin-lattice relaxation rate 1/T1, even with a low in-plane NMR field of 2.6 Tesla. Just above Tc, no evidence of low-energy spin fluctuation is found in the spin-lattice relaxation rate on both the 77Se and the 87Rb sites. Upon warming, however, the Knight shifts and the spin-lattice relaxation rates of both nuclei increase substantially with temperature. In particular, the Knight shift is nearly isotropic and follow a function fit of K=a+bT2 from Tc up to 300 K. These normal state properties may be an indication of thermally activated spin fluctuations. Our observations should put a strong constraint to the theory of magnetism and superconductivity in the newly discovered iron-based superconductors.
Turn this paper into a lesson
ArcXiv compiles a structured reading guide from this paper's metadata: plain-English importance, contributions, prerequisite concepts, which sections to read first, flashcards, and a quiz. Grounded in the abstract, never invented.