Effect of inelastic scattering on the nuclear magnetic relaxation rate 1/T₁Tin iron-based superconductors

Abstract

We present a microscopic study of the nuclear magnetic relaxation rate 1/T1 based on the fiveorbital model for iron-based superconductors. We mainly discuss the effect of the "inelastic" quasiparticle damping rate γ due to many-body interaction on the size of the coherence peak, for both s++ and s±-wave superconducting states. We focus on Ba(Fe1−xCox)2As2, and systematically evaluate γ in the normal state from the experimental resistivity, from optimally to over-doped compounds. Next, γ in the superconducting state is calculated microscopically based on the second order perturbation theory. In optimally doped compounds (Tc ∼ 30 K), it is revealed that the coherence peak on 1/T1T is completely suppressed due to large γ for both s++ and s±-wave states. On the other hand, in heavily over doped compounds with Tc < 10 K, the coherence peak could appear for both pairing states, since γ at Tc is quickly suppressed in proportion to T 2 c . By making careful comparison between theoretical and experimental results, we conclude that it is difficult to discriminate between s++ and s±-wave states from the present experimental results.

Quasiparticle interference in Fe-based superconductors based on a five-orbital tight-binding model

“…20 Also, the absence of the coherence peak at * yamakawa@s.phys.nagoya-u.ac.jp T c can be explained in terms of both the s ++ -wave and s ± -wave states. 21 The theoretical study of the QPI signal in Fe-based superconductors ware performed by several theoretical groups in Refs. 22-28. By using the STM measurement, the information of the local density of states can be obtained.…”