Type: Article
Publication Date: 2012-01-18
Citations: 35
DOI: https://doi.org/10.1103/physrevb.85.020504
The characteristic features of the Ca${}_{10}$(Pt${}_{3}$As${}_{8}$)[(Fe${}_{1\ensuremath{-}x}$Pt${}_{x}$)${}_{2}$As${}_{2}$]${}_{5}$ (the ``10-3-8'' phase) superconductor are triclinic symmetry, high anisotropy, and a clear separation of superconducting and antiferromagnetic regions in the $T$ versus doping ($x$) phase diagram, which enables the superconducting gap to be studied without complications due to the coexisting magnetic order. The London penetration depth, measured on the underdoped side of the superconducting ``dome'' ($x=$ 0.028, 0.041, 0.042, and 0.097), shows behavior remarkably similar to other Fe-based superconductors, exhibiting a robust power law, $\ensuremath{\Delta}\ensuremath{\lambda}(T)=A{T}^{n}$. The exponent $n$ decreases from 2.36 ($x=$ 0.097, close to the optimal doping) to 1.7 ($x=$ 0.028, a heavily underdoped composition), suggesting that the superconducting gap becomes more anisotropic at the dome edge. A similar trend is found in the lower anisotropy BaFe${}_{2}$As${}_{2}$ (``122'') -based superconductors, implying that it is an intrinsic property, unrelated to the coexistence of magnetic order and superconductivity or the anisotropy of the normal state.