Superconductivity of LaFe_1-yCo_yAsO_1-xF_x

Abstract

We have prepared the superconducting system LaFe 1-y Co y AsO 1-x F x (x=0.11) and carried out measurements of their electrical resistivities ρ and superconducting diamagnetisms.75 La-NMR studies have also been carried out. The Knight shift observed for 75 As has been found to be suppressed by the superconductivity, while for 135 La, the shift is almost insensitive to the superconductivity. This result presents rather strong experimental evidence for the singlet pairing. The Co-doping effect on the superconducting transition temperature T c is not so significant as expected for superconductors with nodes, suggesting that the potential scattering does not seem to primarily suppress the superconductivity. Even for superconductors without nodes, it may not be so trivial to expect this small effect, if there are two different (disconnected) Fermi surfaces whose order parameters have opposite signs. As a possible explanation of the observed T c suppression, which is found to be small, seems to be related with the loss of the itinerant nature of the electrons..

High-TcSuperconductivity near the Anion Height Instability in Fe-Based Superconductors: Analysis ofLaFeAsO1−xOnari1, Yamakawa2, Kontani3 2014Phys. Rev. Lett.70101000View full textAdd to dashboardCite

“…The s ++ state is realized against the strong Coulomb repulsion due to the retardation effect, since the energy-scale of orbital fluctuations is ∼ T . The s ++ state is consistent with the robustness of T c against the randomness in Fe-pnictides [39][40][41][42][43][44]. Figure 4 (e) shows the gap functions for x = 0.14.…”

Relationship between Superconductivity and Antiferromagnetism in LaFe(As1−xPx)O Revealed by 31P-NMR

“…In all samples of LaFe(As 1−x P x )O, K(T ) slightly decreases upon cooling, as observed in electron-doped systems. 28,29) These temperature dependences can be explained by the energy dependence of the density of states, as proposed by Ikeda. 30) K(T ) is fitted using an activation type equation: Although the Knight shift gradually decreases upon cooling, 1/T 1 T strongly increases toward T N or T c , as shown in Fig.…”

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

“…66 by multiplying the factor 1/3, as discussed in Ref. 11. Using this method, we can fit them by using ρ(T ) = ρ(0) + aT 2 and obtain γ(0)| Tc ∼ 0.0023 eV and V eff ∼ 10.2 eV for LaFeAsO 0.89 F 0.11 (T c = 26 K).…”