Study of Ni-doping effect of specific heat and transport properties for LaFe1-yNiyAsO0.89F0.11

Takayuki Kawamata, Erika Satomi, Yoshiaki Kobayashi, Masayuki Itoh, Masatoshi Sato

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18 Citations (Scopus)


Specific heats and transport quantities of the LaFe 1-yNiyAsO0.89F0.11 system have been measured, and the results are discussed together with those reported previously by our group mainly for LaFe1-yCoyAsO0.89F0.11 and LaFeAsO0.89-xF0.11+x systems. The y dependence of the electronic specific heat coefficient γ can basically be understood by using the rigid-band picture, where Ni ions provide two electrons to the host conduction bands and behave as nonmagnetic impurities. The superconducting transition temperature Tc of LaFe1-yNiyAsO 0.89F0.11 becomes zero as the carrier density p (= 2y + 0:11) doped to LaFeAsO reaches its critical value, pc ∼ 0:2. This pc value of ∼0:2 is commonly observed for LaFe 1-yCoyAsO0.89F0.11 and LaFeAsO 0.89-xF0.11+x systems, in which the relations p = x + 0:11 and p = y + 0:11 hold, respectively. As we pointed out previously, the critical value corresponds to the disappearance of the hole-Fermi surface. These results indicate that the carrier number solely determines the Tc value. We have not observed appreciable effects of pair breaking, which originates from the nonmagnetic impurity scattering of conduction electrons and strongly suppresses Tc values of systems with sign reversal of the order parameter over the Fermi surface(s). On the basis of the results, the so-called s± symmetry of the order parameter with sign reversal is excluded.

Original languageEnglish
Article number084720
Journaljournal of the physical society of japan
Issue number8
Publication statusPublished - 2011 Aug


  • Fe pnictites
  • Impurity effect
  • Rigid-band picture
  • Superconducting symmetry

ASJC Scopus subject areas

  • Physics and Astronomy(all)


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