1302.1429 (Sangwon Oh et al.)

Weak-coupling superconductivity in NaFe$_{0.975}$Co$_{0.025}$As from NMR
Knight shift and penetration depth    [PDF]

Sangwon Oh, A. M. Mounce, J. S. Lee, W. P. Halperin, C. L. Zhang, S. Carr, Pengcheng Dai

Based on ARPES and STM work, Co doped NaFeAs has been reported to be a strongly coupled superconductor, similar to cuprates. However, a recent ARPES result, claims otherwise, with $2\Delta/k_BT_c$ slightly beyond the BCS limit, 3.53. We have performed $^{75}$As and $^{11}$Na nuclear magnetic resonance(NMR) on high-quality, single crystals of NaFe$_{0.975}$Co$_{0.025}$As. The temperature dependence of the $^{75}$As Knight shift, fitted to a Yosida function, suggests moderately weak-coupling superconductivity in a singlet state with $2\Delta/k_BT_c = 4.0\pm0.3$. The temperature dependence of the penetration depth obtained from $^{11}$Na NMR was found to be consistent with the Knight shift results and $\lambda_{ab}(0)$ was found to be $5,327 \pm 78 \AA$.

View original: http://arxiv.org/abs/1302.1429