Muon-spin rotation measurements of the magnetic penetration depth in the   Fe-based superconductor Ba_(1-x)Rb_(x)Fe2As2
  Measurements of the magnetic penetration depth (lambda) in the Fe-based superconductor Ba_(1-x)Rb_xFe_2As_2 (x=0.3, 0.35, 0.4) were carried out using the muon-spin rotation muSR technique. The temperature dependence of lambda is well described by a two-gap s+s-wave scenario with a small gap Delta_1 = 1 - 3 mev and a large gap Delta_2 = 7 - 9 mev. By combining the present data with those obtained for RbFe_2As_2 a decrease of the BCS ratio 2Delta_2/(k_B)(T_c) with increasing Rb content x is observed. On the other hand, the BCS ratio 2Delta_1/(k_B)(T_c) is almost independent of x. In addition, the contribution of Delta_1 to the superfluid density is found to increase with x. These results are discussed in the light of the suppression of interband processes upon hole doping. 
Z. Guguchia, Z. Shermadini, A. Amato, A. Maisuradze, A. Shengelaya, Z.   Bukowski, H. Luetkens, R. Khasanov, J. Karpinski, a...
cond-mat.supr-con