Surface impedance of BaFe2-xNixAs2 crystals

Measurements of the real σ1 and imaginary σ2 part of the conductivity were performed in optimally doped BaFe1.9Ni0.1As2 and overdoped BaFe 1.88Ni0.12As2 crystals in the frequency range 20 MHz-1.5 GHz using a single coil technique. The temperature dependence of the London penetration depth follows a T2 law. The conductivity σ1 increases with decreasing temperature below Tc in agreement with the results obtained for the optimally Co doped BaFe 2-xCoxAs2 crystals. The increase of σ1 in the superconducting state is attributed to a rapidly decrease of the quasiparticle scattering rate. © 2014 Elsevier Ltd.