Electron-boson spectral density of LiFeAs obtained from optical data

Abstract

Abstract. We analyze existing optical data in the superconducting state of LiFeAs at T = 4 K, to recover its electron-boson spectral density. A maximum entropy technique is employed to extract the spectral density I 2 χ(ω) from the optical scattering rate. Care is taken to properly account for elastic impurity scattering which can importantly affect the optics in an s-wave superconductor, but does not eliminate the boson structure. We find a robust peak in I 2 χ(ω) centered about Ω R ∼ = 8.0 meV or 5.3 k B T c (with T c = 17.6 K). Its position in energy agrees well with a similar structure seen in scanning tunneling spectroscopy (STS). There is also a peak in the inelastic neutron scattering (INS) data at this same energy. This peak is found to persist in the normal state at T = 23 K. There is evidence that the superconducting gap is anisotropic as was also found in low temperature angular resolved photoemission (ARPES) data.

Hidden non-Fermi liquid behavior caused by magnetic phase transition in Ni-doped Ba-122 pnictides

“…Since FeAs-compounds have multibands the compounds can be analyzed approximately with two Drude components as in Dai et al paper8, which corresponds to the two-component analysis for cuprates. The one-component (or extended Drude model) analysis has been applied to Fe-pnictide systems121314 with a single band approximation even though the material systems have multiband characteristics. To resolve the multiband issue one should develop a new method including the multiband nature.…”

Optical conductivity evidence of clean-limit superconductivity in LiFeAs

“…Near normal incidence reflectivity from 20 to 6 000 cm −1 was measured on Bruker IFS113 and IFS66v spectrometers at 5,10,15,20,25,50,100,200, and 300 K. The absolute reflectivity of the sample was obtained with an in situ gold overfilling technique [17]. The reTypeset by REVT E X flectivity has an absolute accuracy better than 0.5% and a relative accuracy better than 0.1%.…”

“…They described their data in the framework of multiple superconducting gaps, and found two fully open, gaps at 2∆ 0 = 3.2 meV and 2∆ 0 = 6.3 meV. These data were further analyzed in terms of Eliashberg theory [15]. STM also finds two homogeneous nodeless gaps, but with values twice as large [5].…”

Electron–boson spectral density function of correlated multiband systems obtained from optical data: Ba0.6K0.4Fe2As2and LiFeAs

“…We used known superconducting gaps of the two materials [32,33]: two superconducting gaps of BKFA are 5.5 meV (∆ 0,1 ) and 12.5 meV (∆ 0,2 ) [32] and two SC gaps of LiFeAs are 1.6 meV and 3.15 meV [33]. We took the sharp mode frequencies from reported values by inelastic neutron scattering study of BKFA [39] and scanning tunneling [40], and optical spectroscopy studies [24]. The obtained I 2 χ(ω) are shown in Fig.…”

“…Many optical studies have been successfully done on cuprate systems for delving and exposing the electron-boson spectral density function [7,16,17,18,19,20,21]. Recently some optical studies [22,23,24] have been done on iron-pnictides to obtain the electron-boson density spectrum by using a singleband approximation method, which has been used for studying cuprates. Charnukha et al [25] have tried to include the multiband coupling information obtained from specific heat measurement study of the same material [26] and showed that observed unusual structure of the optical conductivity in superconducting state can be ascribed to spinfluctuation-assisted process.…”