Volume 85, Number 6, March 2009
Article Number 67002
Number of page(s) 5
Section Condensed Matter: Electronic Structure, Electrical, Magnetic and Optical Properties
Published online 30 March 2009
EPL, 85 (2009) 67002
DOI: 10.1209/0295-5075/85/67002

Superconducting gap symmetry of Ba0.6K0.4Fe2As2 studied by angle-resolved photoemission spectroscopy

K. Nakayama1, T. Sato1, 2, P. Richard3, Y.-M. Xu4, Y. Sekiba1, S. Souma3, G. F. Chen5, J. L. Luo5, N. L. Wang5, H. Ding5 and T. Takahashi1, 3

1   Department of Physics, Tohoku University - Sendai 980-8578, Japan
2   TRIP, Japan Science and Technology Agency (JST) - Kawaguchi 332-0012, Japan
3   WPI Research Center, Advanced Institute for Materials Research, Tohoku University - Sendai 980-8577, Japan
4   Department of Physics, Boston College - Chestnut Hill, MA 02467, USA
5   Beijing National Laboratory for Condensed Matter Physics, and Institute of Physics, Chinese Academy of Sciences Beijing 100080, China

received 3 December 2008; accepted in final form 21 February 2009; published March 2009
published online 30 March 2009

We have performed high-resolution angle-resolved photoemission spectroscopy on the optimally doped Ba0.6K0.4Fe2As2 compound and determined the accurate momentum dependence of the superconducting (SC) gap in four Fermi-surface sheets including a newly discovered outer electron pocket at the M-point. The SC gap on this pocket is nearly isotropic and its magnitude is comparable ($\Delta$ ~ 11 meV) to that of the inner electron and hole pockets (~ 12 meV), although it is substantially larger than that of the outer hole pocket (~ 6 meV). The Fermi-surface dependence of the SC gap value is basically consistent with the $\Delta (k)=\Delta _{0}\,{\rm cos}\,k_{x}\,{\rm cos}\,k_{y}$ formula expected for the extended s-wave symmetry. The observed finite deviation from the simple formula suggests the importance of multi-orbital effects.

74.25.Jb - Electronic structure.
74.70.-b - Superconducting materials.
79.60.-i - Photoemission and photoelectron spectra.

© EPLA 2009