Unravelling the mechanism of the semiconducting-like behavior and its relation to superconductivity in (CaFe1−xPtxAs)10Pt3<

Abstract

The temperature-dependence of the in-plane optical properties of (CaFe1−xPtxAs)10Pt3As8 have been investigated for the undoped (x = 0) parent compound, and the optimally-doped (x = 0.1) superconducting material (Tc 12 K) over a wide frequency range. The optical conductivity has been described using two free-carrier (Drude) components, in combination with oscillators to describe interband transitions. At room temperature, the parent compound may be described by a strong, broad Drude term, as well as a narrow, weaker Drude component. Below the structural and magnetic transitions at 96 and 83 K, respectively, strength is transferred from the free-carrier components into a bound excitation at 1000 cm −1 , and the material exhibits semiconducting-like behavior. In the optimally-doped sample, at room temperature the optical properties are again described by narrow and broad Drude responses comparable to the parent compound; however, below T * 100 K, strength from the narrow Drude is transferred into a newly-emergent low-energy peak at 120 cm −1 , which arises from a localization process, resulting in semiconducting-like behavior. Interestingly, below Tc, this peak also contributes to the superfluid weight, indicating that some localized electrons condense into Cooper pairs; this observation may provide insight into the pairing mechanism in iron-based superconductors.

Optical and photoemission investigation of structural and magnetic transitions in the iron-based superconductor Sr0.67Na0.33Fe2AsYang1, Huang2, Zaki3 et al. 2019Phys. Rev. B7130View full textAdd to dashboardCite

“…S2]. This is close to where a peak was observed in (CaFe 1−x Pt x As) 10 Pt 3 As 8 for x = 0.1 at 120 cm −1 [66]; that feature was attributed to a localization process due to impurity scattering described by a classical generalization of the Drude model [67],…”

Physical properties of superconducting Ca10(Pt4As8)((Fe0.92Pt0.08)2As2)5 crystal and comprehensive cognition on the transition temperature for Ca10-3(4)-8

“…shown below. The fact that λ ep could be set to zero illustrates unlike the traditional superconductors which mainly depend on the help of strong interactions between electrons and phonons to form Cooper pairs, for example λ ep =1.6 3 for Hg and λ ep =1.8 35 for Nb 3 Sn [34], the electron-phonon coupling is relatively weak in the Fe based superconductors. From the value of β, the Debye temperature Θ D of the crystal can be evaluated using the expression [33],…”

“…We know that the FeAs layer serves as the superconducting layer in the Fe based superconductors, and, then, any excessive change or deterioration of which will greatly reduce the transition temperature. Compared with Ca10-4-8 containing the same amount of platinum, Ca10-3-8 have one less Pt atom in its PtAs layer and it means that much more Pt atoms will enter FeAs layer, some of them replace the Fe atoms and others may be the interstitial acting as the scattering centers, which add lattice disorder and lead to the free carriers localization within the system [35].…”

Optical Properties in The Hole-Doped Ca8.5Na1.5(Pt3As8)(Fe2As2)5 Single Crystal

“…To study the delicate relationship between electronic structure and superconductivity, various experiments such as transport 1,12 , ARPES 11,13 , upper critical field 10,12,14 , thermally activated vortex pinning 15 , pressure effect 16 , penetration depth 17,18 , infrared spectroscopy experiments [19][20][21] , etc. have already been performed in the Ca10-3-8 family.…”