Among the iron-based pnictide superconductors the material KFe2 As2 is unusual in that its Fermi surface does not consist of quasinested electron and hole pockets. Here we report measurements of the temperature dependent London penetration depth of very clean crystals of this compound with residual resistivity ratio >1200. We show that the superfluid density at low temperatures exhibits a strong linear-in-temperature dependence which implies that there are line nodes in the energy gap on the large zone-centered hole sheets. The results indicate that KFe2 As2 is an unconventional superconductor with strong electron correlations.
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|Publication status||Published - 19 Jul 2010|