Optical properties of the iron arsenic superconductorBaFe1.85Co0.15As2

Abstract

The transport and complex optical properties of the electron-doped iron-arsenic superconductor BaFe 1.85 Co 0.15 As 2 with T c = 25 K have been examined in the Fe-As planes above and below T c . A BlochGrüneisen analysis of the resistivity yields a weak electron-phonon coupling constant ph Ӎ 0.2. The lowfrequency optical response in the normal state appears to be dominated by the electron pocket and may be described by a weakly interacting Fermi liquid with a Drude plasma frequency of p,D Ӎ 7840 cm −1 ͑Ӎ0.972eV͒ and scattering rate 1 / D Ӎ 126 cm −1 ͑Ӎ15 meV͒ just above T c . The frequency-dependent scattering rate 1 / ͑͒ has kinks at Ӎ12 and 55 meV that appear to be related to bosonic excitations. Below T c the majority of the superconducting plasma frequency originates from the electron pocket and is estimated to be p,S Ӎ 5200 cm −1 ͑ 0 Ӎ 3000 Å͒ for T Ӷ T c , indicating that less than half the free carriers in the normal state have collapsed into the condensate, suggesting that this material is not in the clean limit. Supporting this finding is the observation that this material falls close to the universal scaling line for a Bardeen, Cooper, and Schrieffer dirty-limit superconductor in the weak-coupling limit. There are two energy scales for the superconductivity in the optical conductivity and photoinduced reflectivity at ⌬ 1 ͑0͒Ӎ3.1Ϯ 0.2 meV and ⌬ 2 ͑0͒ Ӎ 7.4Ϯ 0.3 meV. This corresponds to either the gapping of the electron and hole pockets, respectively, or an anisotropic s-wave gap on the electron pocket; both views are consistent with the s Ϯ model.

Optical spectroscopy study of the collapsed tetragonal phase ofCaFe2(As0.935P0.065)2singl

“…The two Drude components may provide information about different types of carriers in this compound. 40 The temperature dependence of normalized plasma frequency ω 2 p and scattering rate 1/τ are shown in Fig. 3 (e) and (f).…”

Three-dimensionality of band structure and a large residual quasiparticle population in Ba0.67K0.33<

“…The feature has also been observed in the in-plane spectra of a number of other Fe-based materials. [15][16][17][18][19][20] The small difference of the spectra between 45 K and 8 K for E c indicates the presence of a significant amount of quasiparticles which have dominant contribution to the c-axis conductivity.…”

Orbital characters of bands in the iron-based superconductor BaFe1.85Co0.15AsZhang1, Chen2, He3 et al. 2011Phys. Rev. B10127883View full textAdd to dashboardCite

“…Unconventional superconductivity with multi-gap behavior has been reported in such material [17][18][19][20][21] . As this system is optimally doped with electrons, the low energy band structure is well occupied, and free from the complications of the electronic reconstruction in the SDW state [22][23][24][25][26] .…”