Intrinsic Charge Dynamics in High-T_{c} AFeAs(O,F) Superconductors

A Charnukha; D Pröpper; N D Zhigadlo; M Naito; M Schmidt; Zhe Wang; J Deisenhofer; A Loidl; B Keimer; A V Boris; D N Basov

doi:10.1103/PhysRevLett.120.087001

Intrinsic Charge Dynamics in High-T_{c} AFeAs(O,F) Superconductors

Phys Rev Lett. 2018 Feb 23;120(8):087001. doi: 10.1103/PhysRevLett.120.087001.

Authors

A Charnukha^{1

2

3}, D Pröpper³, N D Zhigadlo^{4

5}, M Naito⁶, M Schmidt⁷, Zhe Wang⁷, J Deisenhofer⁷, A Loidl⁷, B Keimer³, A V Boris³, D N Basov^{1

8}

Affiliations

¹ Physics Department, University of California-San Diego, La Jolla, California 92093, USA.
² Leibniz Institute for Solid State and Materials Research, IFW, 01069 Dresden, Germany.
³ Max Planck Institute for Solid State Research, 70569 Stuttgart, Germany.
⁴ Laboratory for Solid State Physics, ETH Zurich, CH-8093 Zurich, Switzerland.
⁵ Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, CH-3012 Bern, Switzerland.
⁶ Department of Applied Physics, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588, Japan.
⁷ Experimental Physics V, Center for Electronic Correlations and Magnetism, Institute of Physics, University of Augsburg, D-86159 Augsburg, Germany.
⁸ Department of Physics, Columbia University, New York, New York 10027, USA.

PMID: 29543031
DOI: 10.1103/PhysRevLett.120.087001

Abstract

We report the first determination of the in-plane complex optical conductivity of 1111 high-T_{c} superconducting iron oxypnictide single crystals PrFeAs(O,F) and thin films SmFeAs(O,F) by means of conventional and microfocused infrared spectroscopy, ellipsometry, and time-domain THz transmission spectroscopy. A strong itinerant contribution is found to exhibit a dramatic difference in coherence between the crystal and the film. Using extensive temperature-dependent measurements of THz transmission, we identify a previously undetected 2.5-meV collective mode in the optical conductivity of SmFeAs(O,F), which is strongly suppressed at T_{c} and experiences an anomalous T-linear softening and narrowing below T^{*}≈110 K≫T_{c}. The suppression of the infrared absorption in the superconducting state reveals a large optical superconducting gap with a similar gap ratio 2Δ/k_{B}T_{c}≈7 in both materials, indicating strong pairing.