Origin of Tc Enhancement Induced by Doping Yttrium and Hydrogen into LaFeAsO-based Superconductors: 57Fe, 75As, 139La, and 1H-NMR Studies

Abstract

We report our extensive 57Fe-, 75As-, 139La-, and 1H-NMR studies of La_{0.8}Y_{0.2}FeAsO_{1-y} (La_{0.8}Y_{0.2}1111) and LaFeAsO_{1-y}H_{x}(La1111H), where doping yttrium (Y) and hydrogen (H) into optimally doped LaFeAsO_{1-y} (La1111(OPT)) increases T_c=28 K to 34 and 32 K, respectively. In the superconducting (SC) state, the measurements of nuclear-spin lattice-relaxation rate 1/T_1 have revealed in terms of a multiple fully gapped s_\pm-wave model that the SC gap and T_c in La_{0.8}Y_{0.2}1111 become larger than those in La1111(OPT) without any change in doping level. In La1111H, the SC gap and T_c also increase slightly even though a decrease in carrier density and some disorders are significantly introduced. As a consequence, we suggest that the optimization of both the structural parameters and the carrier doping level to fill up the bands is crucial for increasing T_c among these La1111-based compounds through the optimization of the Fermi surface topology.

4 pages, 4 figures, 1 table, to be published in J. Phys. Soc. Jpn, Vol. 79, No. 10

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Cited by in corpus (10)

• Enhancement of Superconducting Transition Temperature Due to Antiferromagnetic Spin Fluctuations in Iron-pnictides LaFe(As_{1-x}P_x)(O_{1-y}F_y) : 31P-NMR Studies
• Antiferromagnetic Spin Fluctuations and Unconventional Nodeless Superconductivity in an Iron-based New Superconductor (Ca_4Al_2O_{6-y})(Fe_2As_2):75As-NQR Study
• Coherence Effect of Sign-Reversing s(+-)-wave Cooper Pair State in Heavily Overdoped LaFeAsO-based Superconductor: 75As-Nuclear Quadrupole Resonance
• Orbital-Selective Superconductivity and the Effect of Lattice Distortion in Iron-Based Superconductors
• High-Tc Nodeless s_\pm-wave Superconductivity in (Y,La)FeAsO_{1-y} with Tc=50 K: 75As-NMR Study
• Hydrogen in superconductors
• Synthesis of ErFeAsO-based superconductors by hydrogen doping method
• First-principles Studies for the Hydrogen Doping Effects on Iron-based Superconductors
• High-$T_c$ Iron-phosphide Superconductivity Enhanced by Reemergent Antiferromagnetic Spin Fluctuations in (Sr${}_4$Sc${}_2$O${}_6$)Fe${}_2$(As${}_{1-x}$P${}_x$)${}_2$ probed by NMR
• Enhanced superconductivity and moderate spin fluctuations suppressed at low energies in heavily electron-doped La1111-based superconductor