$^{75}$As NMR of Ba(Fe$_{0.93}$Co$_{0.07}$)$_{2}$As$_{2}$ in High Magnetic Field

Sangwon Oh; A. M. Mounce; S. Mukhopadhyay; W. P. Halperin; A. B. Vorontsov; S. L. Bud'ko; P. C. Canfield; Y. Furukawa; A. P. Reyes; P. L. Kuhns

doi:10.1103/physrevb.83.214501

arXiv · 1101.1021

$^{75}$As NMR of Ba(Fe$_{0.93}$Co$_{0.07}$)$_{2}$As$_{2}$ in High Magnetic Field

Sangwon Oh·A. M. Mounce·S. Mukhopadhyay·W. P. Halperin·A. B. Vorontsov·S. L. Bud'ko·P. C. Canfield·Y. Furukawa·A. P. Reyes·P. L. Kuhns

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Abstract

The superconducting state of an optimally doped single crystal of Ba(Fe$_{0.93}$Co$_{0.07}$)$_2$As$_2$ was investigated by $^{75}$As NMR in high magnetic fields from 6.4 T to 28 T. It was found that the Knight shift is least affected by vortex supercurrents in high magnetic fields, $H>11$ T, revealing slow, possibly higher order than linear, increase with temperature at $T \lesssim 0.5 \, T_c$, with $T_c \approx 23 \, K$. This is consistent with the extended s-wave state with $A_{1g}$ symmetry but the precise details of the gap structure are harder to resolve. Measurements of the NMR spin-spin relaxation time, $T_2$, indicate a strong indirect exchange interaction at all temperatures. Below the superconducting transition temperature vortex dynamics lead to an anomalous dip in $T_2$ at the vortex freezing transition from which we obtain the vortex phase diagram up to $H = 28$ T.

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Sangwon Oh, A. M. Mounce, S. Mukhopadhyay, W. P. Halperin, A. B. Vorontsov, S. L. Bud'ko, P. C. Canfield, Y. Furukawa, A. P. Reyes, P. L. Kuhns. 2011-06-01. $^{75}$As NMR of Ba(Fe$_{0.93}$Co$_{0.07}$)$_{2}$As$_{2}$ in High Magnetic Field. https://doi.org/10.1103/physrevb.83.214501

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