Optical conductivity of superconducting Rb2Fe4Se5

Abstract

We report the complex dielectric function of high-quality nearly-stoichiometric Rb2Fe4Se5 (RFS) single crystals with Tc=32 K determined by wide-band spectroscopic ellipsometry and time-domain transmission spectroscopy in the spectral range 1 meV<=$\hslash$ω<=6.5 eV at temperatures 4 K<=T<=300 K. This compound simultaneously displays a superconducting and a semiconducting optical response. It reveals a direct band-gap of 0.45 eV determined by a set of spin-controlled interband transitions. Below 100 K we observe in the lowest THz spectral range a clear metallic response characterized by the negative dielectric permittivity ε1 and bare (unscreened) ωpl=100 meV. At the superconducting transition this metallic response exhibits a signature of a superconducting gap below 8 meV. Our findings suggest a coexistence of superconductivity and magnetism in this compound as two separate phases.

4 pages, 4 figures

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• Spin-wave excitations and superconducting resonant mode in Cs(x)Fe(2-y)Se2
• Strong and nonmonotonic temperature dependence of Hall coefficient in superconducting K${}_x$Fe${}_{2-y}$Se${}_2$ single crystals
• Interplay between Superconductivity and Magnetism in Rb0.8Fe1.6Se2 under Pressure
• Superconductivity and magnetism in RbxFe2-ySe2: Impact of thermal treatment on mesoscopic phase separation
• "Cigar" Fermi surface as a possible requisite for superconductivity in iron-based superconductors
• Macroscopic phase segregation in superconducting K0.73Fe1.67Se2 as seen by muon spin rotation and infrared spectroscopy
• Optical conductivity of superconducting K{0.8}Fe{2-y}Se2 single crystals: Evidence for a Josephson-coupled phase
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• Effective medium approximation and the complex optical properties of the inhomogeneous superconductor K_{0.8}Fe_{2-y}Se_2
• Correlated disorder to order crossover in the local structure of K${}_x$Fe${}_{2-y}$Se${}_{2-z}$S${}_z$
• Optical properties of iron-based superconductor LiFeAs single crystal
• Electron-phonon coupling in the superconducting single crystal Rb${}_{0.8}$Fe${}_{1.68}$Se${}_2$
• Tuning orbital-selective correlation effects in superconducting Rb${}_{0.75}$Fe${}_{1.6}$Se${}_{2-z}$S${}_z$
• Spin fluctuations and pairing symmetry in A${}_x$Fe${}_{2-y}$Se${}_2$: dual effect of the itinerant and the localized nature of electrons
• Optical Properties of Superconducting K${}_{0.8}$Fe${}_{1.7}$(Se${}_{0.73}$S${}_{0.27}$)${}_2$ Single Crystals
• On the possibility of neutron spectroscopy of microwave currents in thin superconducting films
• Optical Properties of Iron-Selenide Na${}_{0.27}$K${}_{0.27}$Rb${}_{0.27}$Fe${}_{1.7}$Se${}_2$ Single Crystals
• Phase separation in iron chalcogenide superconductor Rb0.8+xFe1.6+ySe2 as seen by Raman light scattering and band structure calculations