As-75 NMR of Ba(Fe0.93Co0.07)(2)As-2 in high magnetic field

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

来源：Physical Review B, 2011, 83(21): 214501.

DOI：10.1103/PhysRevB.83.214501

The superconducting state of an optimally doped single crystal of Ba(Fe0.93Co0.07)(2)As-2 was investigated by As-75 NMR in high magnetic fields from 6.4 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 less than or similar to 0.5 T-c, with T-c approximate to 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, abrupt changes in vortex dynamics lead to an anomalous dip in T-2, consistent with vortex freezing from which we obtain the vortex phase diagram up to H = 28 T.

• 出版日期2011-6-1
• 单位西北大学