Point-contact spectroscopy in Co-doped CaFe2As2: nodal superconductivity and topological Fermi surface transition
Superconductor Science and Technology, 2012•iopscience.iop.org
We performed point-contact Andreev-reflection spectroscopy measurements in Ca (Fe 1− x
Co x) 2 As 2 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 (BTK) model (making use of an 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 …
Co x) 2 As 2 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 (BTK) model (making use of an 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 …
Abstract
We performed point-contact Andreev-reflection spectroscopy measurements in Ca (Fe 1− x Co x) 2 As 2 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 (BTK) model (making use of an 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.
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