Small anisotropy of the lower critical field and the s_±-wave two-gap feature in single-crystal LiFeAs

다국어 초록 (Multilingual Abstract)

<P>The in- and out-of-plane lower critical fields and magnetic penetration depths of LiFeAs were examined. The anisotropy ratio Γ<SUB><I>H</I><SUB><I>c</I>1</SUB></SUB>(0) was smaller than the expected theoretical value, and increased slightly with increasing temperature from 0.6<I>T</I><SUB><I>c</I></SUB> to <I>T</I><SUB><I>c</I></SUB>. The small degree of anisotropy was numerically confirmed by considering the electron correlation effect. The temperature dependence of the penetration depths followed a power law (∼<I>T</I><SUP><I>n</I></SUP>) below 0.3<I>T</I><SUB><I>c</I></SUB>, with <I>n</I>>3.5 for both λ<SUB><I>ab</I></SUB> and λ<SUB><I>c</I></SUB>. Based on theoretical studies of iron-based superconductors, these results suggest that the superconductivity of LiFeAs can be represented by an extended <I>s</I><SUB>±</SUB>-wave due to the weak impurity scattering effect. And the magnitudes of the two gaps were also evaluated by fitting the superfluid density for both the in- and out-of-plane directions to the two-gap model. The estimated values for the two gaps are consistent with the results from angle-resolved photoemission spectroscopy and specific-heat experiments.</P>