Structural and magnetic phase transitions in triclinic Ca10(FeAs)10(Pt3As8)

Temperature dependence of the superconducting energy gaps in Ca9.35La0.65(Pt3As8)(Fe2As2)5 single crystal

We measured the optical reflectivity R(ω) for an underdoped (Ca_0.935La_0.065)₁₀(Pt₃As₈)(Fe₂As₂)₅ single crystal and obtained the optical conductivity \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\sigma }_{1}(\omega )$$\end{document}σ1(ω) using the K-K transformation. The normal state \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\sigma }_{1}(\omega )$$\end{document}σ1(ω) at 30 K is well fitted by a Drude-Lorentz model with two Drude components (ω_p1 = 1446 cm⁻¹ and ω_p2 = 6322 cm⁻¹) and seven Lorentz components. Relative reflectometry was used to accurately determine the temperature dependence of the superconducting gap at various temperatures below T_c. The results clearly show the opening of a superconducting gap with a weaker second gap structure; the magnitudes for the gaps are estimated from the generalized Mattis-Bardeen model to be Δ₁ = 30 and Δ₂ = 50 cm⁻¹, respectively, at T = 8 K, which both decrease with increasing temperature. The temperature dependence of the gaps was not consistent with one-band BCS theory but was well described by a two-band (hence, two gap) BCS model with interband interactions. The temperature dependence of the superfluid density is flat at low temperatures, indicating an s-wave full-gap superconducting state.

Doping effect on the physical properties of Ca10Pt3As8(Fe2As2)5 single crystals

Ca₁₀Pt₃As₈(Fe₂As₂)₅ is a unique parent compound for superconductivity, which consists of both semiconducting Pt₃As₈ and metallic FeAs layers. We report the observation of superconductivity induced via chemical doping in either Ca site using rare-earth (RE) elements (RE  =  La, Gd) or Fe site using Pt. The interlayer distance and the normal-state physical properties of the doped system change correspondingly. The coupled changes include (1) superconducting transition temperature T _c increases with increasing both doping concentration and interlayer distance, (2) our T _c value is higher than previously reported maximum value for Pt doping in the Fe site, (3) both the normal-state in-plane resistivity and out-of-plane resistivity change from non-metallic to metallic behavior with increasing doping concentration and T _c, and (4) the transverse in-plane magnetoresistance (MR_ab) changes from linear-field dependence to quadratic behavior upon increasing T _c. For La-doped compound with the highest T _c (~35 K), upper critical fields ([Formula: see text], [Formula: see text]), coherence lengths (ξ _ab, ξ _c), and in-plane penetration depth (λ _ab) are estimated. We discuss the relationship between chemical doping, interlayer distance, and physical properties in this system.

Phonons of Fe-based superconductor Ca10Pt4As8(Fe1-x Pt x As)10

We report the results of inelastic neutron scattering measurements on particular phonons of a superconducting (SC) Ca10Pt4As8(Fe1-x Pt x As)10 with the onset transition temperature T c ~ 33 K to investigate mainly what roles orbital fluctuation plays in Cooper pairing, where we observed a slight softening of the in-plane transverse acoustic mode corresponding to the elastic constant C 66. This softening starts at temperature T well above the SC T c, as T decreases. An anomalously strong change of the scattering intensity of in-plane optical modes was observed at the M point of the pseudo tetragonal reciprocal space in the range of 35  <  ω  <  40 meV with decreasing T from far above T c. Because this ω region mainly corresponds to the motion of Fe and As atoms in the FeAs planes, the finding presents information on the coupling between the orbital fluctuation of Fe 3d electrons and the lattice system, useful for studying the possible roles of orbital fluctuation in the pairing mechanism and/or the appearance of the so-called nematic phase.