Muon-spin rotation measurements of the magnetic penetration depth in the Fe-based superconductor Ba_(1-x)Rb_(x)Fe2As2

TL;DR

This study uses muon-spin rotation to measure the magnetic penetration depth in Ba_(1-x)Rb_xFe_2As_2, revealing a two-gap superconducting scenario and how doping affects the superconducting gaps and superfluid density.

Contribution

It provides detailed measurements of the two-gap structure and doping dependence of superconducting properties in Ba_(1-x)Rb_xFe_2As_2 using muSR.

Findings

Two-gap s+s-wave scenario describes lambda(T)

Decrease of 2Delta_2/(k_B T_c) with Rb doping

Increase of Delta_1 contribution to superfluid density

Abstract

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.