Abstract
We have investigated Mn, Co and Ni substitution effects on polycrystalline samples of LaFePO0.95F0.05 by resistivity and magnetoresistance measurements. In LaFe1-xMxPO0.95F0.05 (M = Mn, Co and Ni), the superconducting transition temperature (Tc) monotonously decreases with increasing the impurity doping level of x. There is a clear difference of Tc suppression rates among Mn, Co and Ni doping cases, and the decreasing rate of Tc by Mn doping as a magnetic impurity is larger than those by the nonmagnetic doping impurities (Co/Ni). This result indicates that in LaFePO0.95F0.05, Tc is rapidly suppressed by the pair-breaking effect of magnetic impurities, and the pairing symmetry is a full-gapped s-wave. In the nonmagnetic impurity-doped systems, the residual resistivity in the normal state has nearly the same value when Tc becomes zero. The residual resistivity value is almost consistent with the universal value of sheet resistance for two-dimensional superconductors, suggesting that Tc is suppressed by electron localization in Co/Ni-doped LaFePO0.95F0.05.
Highlights
More than a quarter of a century ago, high-Tc superconducting (SC) cuprates were discovered.Since the research field of cuprate superconductors has become one of the most investigated topics in condensed matter physics, and a lot of experimental and theoretical studies have been performed in order to explore new superconductivity in other layered transition metal compounds
Several theoretical research groups have argued that spin or orbital fluctuations play an important role in the pairing mechanism, but this issue is under debate
In spin fluctuation–mediated superconductivity [4,5], the nesting between hole and electron Fermi surfaces induces a sign-changing s±-wave SC state, while the sign-preserving s++-wave SC state is predicted in the orbital fluctuation–mediated superconductivity [6,7]
Summary
More than a quarter of a century ago, high-Tc superconducting (SC) cuprates were discovered. The research field of cuprate superconductors has become one of the most investigated topics in condensed matter physics, and a lot of experimental and theoretical studies have been performed in order to explore new superconductivity in other layered transition metal compounds. The discovery of the iron arsenide superconductor has stimulated many researchers and many families of iron-based SC systems have been found by experimental investigations [3]. Since the discovery of the iron-pnictide superconductor, many researchers have made great efforts to clarify its SC mechanism. Several theoretical research groups have argued that spin or orbital fluctuations play an important role in the pairing mechanism, but this issue is under debate. In spin fluctuation–mediated superconductivity [4,5], the nesting between hole and electron Fermi surfaces induces a sign-changing s±-wave SC state, while the sign-preserving s++-wave SC state is predicted in the orbital fluctuation–mediated superconductivity [6,7]
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