Optical conductivity of superconducting Rb2Fe4Se5 single crystals

Physics Reveiw B 85, 100504(R) (2012)

A. Charnukha¹, J. Deisenhofer², D. Pröpper¹, M. Schmidt², Z. Wang², Y. Goncharov^2,3, A. N. Yaresko¹, V. Tsurkan^2,4, B. Keimer¹, A. Loidl², and A. V. Boris¹ 

¹Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, D-70569 Stuttgart, Germany
²Experimental Physics V, Center for Electronic Correlations and Magnetism, Institute of Physics, University of Augsburg, D-86159 Augsburg, Germany
³Institute of General Physics, Russian Academy of Sciences, 119991 Moscow, Russia
⁴Institute of Applied Physics, Academy of Sciences of Moldova, MD-2028 Chisinau, R. Moldova

Abstract

We report the complex dielectric function of high-quality nearly-stoichiometric Rb₂Fe₄Se₅ single crystals withT_c=32 K determined by wide-band spectroscopic ellipsometry and time domain transmission spectroscopy in the spectral range of 1 meV≤ℏω≤6.5 eV at temperatures of 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, in the lowest terahertz spectral range, we observe a clear metallic response characterized by the negative dielectric permittivity ɛ₁ and bare (unscreened) ω_pl≈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.

for full paper see http://link.aps.org/doi/10.1103/PhysRevB.85.100504

.........Time-domain terahertz (THz) trans- mission measurements were carried out in the 1–10-meV spectral range using a TPS spectra 3000 spectrometer with f/2 focusing optics (TeraView Ltd.). The transmitted intensity .........

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