Spin dynamics in iron-based layered superconductor (La0.87Ca0.13)FePO revealed by 31P and 139La NMR studies

We report (31)P and (139)La NMR studies of (La(0.87)Ca(0.13))FePO, which is a family member of the recently discovered superconductor LaFeAs(O(1-x)F(x)). In the normal state, Knight shift and nuclear spin-lattice relaxation rate divided by T (1/T(1)T) show that a Fermi-liquid state with moderate ferromagnetic fluctuations emerges below 30 K. From 1/T(1)T of (31)P and (139)La, a quasi-two- dimensional electronic structure is suggested, in which the FeP layer is more conductive than the LaO layer. In the superconducting (SC) state, although a clear Meissner signal was observed, 1/T(1)T increases below T(c), in contrast to a decrease of 1/T(1)T due to the opening of a SC gap, suggesting that novel low-energy spin dynamics develop in the SC state.