1301.3719 (R. S. Gonnelli et al.)

Point-contact spectroscopy in Co-doped CaFe2As2: nodal superconductivity
and topological Fermi surface transition    [PDF]

R. S. Gonnelli, M. Tortello, D. Daghero, R. K. Kremer, Z. Bukowski, N. D. Zhigadlo, J. Karpinski

We performed point-contact Andreev reflection spectroscopy measurements in Ca(Fe_{1-x}Co_x)2As2 single crystals with effective x=0.060 +- 0.005. The spectra of ab-plane contacts show a zero-bias maximum and broad shoulders at about 5-6 meV. Their fit with the three-dimensional Blonder-Tinkham-Klapwijk model (making use of a analytical expression for the Fermi surface that mimics the one calculated from first principles) shows that this compound presents a large isotropic gap on the quasi-2D electronlike Fermi surface sheets and a smaller anisotropic (possibly nodal) gap on the 3D holelike Fermi surface pockets centered at the Z point in the Brillouin zone. These results nicely fit into the theoretical picture for the appearance of nodal superconductivity in 122 compounds.

View original: http://arxiv.org/abs/1301.3719