1107.2711 (T. Oka et al.)

Antiferromagnetic Spin Fluctuation above the Superconducting Dome and
the Full-Gaps Superconducting State in LaFeAsO1-xFx Revealed by 75As-Nuclear
Quadrupole Resonance    [PDF]

T. Oka, Z. Li, S. Kawasaki, G. F. Chen, N. L. Wang, Guo-qing Zheng

We report a systematic study by 75As nuclear-quadrupole resonance in
LaFeAsO1-xFx. The antiferromagnetic spin fluctuation (AFSF) found above the
magnetic ordering temperature TN = 58 K for x = 0.03 persists in the regime
0.04 < x < 0.08 where superconductivity sets in. A dome-shaped x-dependence of
the superconducting transition temperature Tc is found, with the highest Tc =
27 K at x = 0.06 which is realized under significant AFSF. With increasing x
further, the AFSF decreases, and so does Tc. These features resemble closely
the cuprates La2-xSrxCuO4. In x = 0.06, the spin-lattice relaxation rate (1/T1)
below Tc decreases exponentially down to 0.13 Tc, which unambiguously indicates
that the energy gaps are fully-opened. The temperature variation of 1/T1 below
Tc is rendered nonexponential for other x by impurity scattering.

View original: http://arxiv.org/abs/1107.2711