We report the first determination of the in-plane complex optical conductivity of 1111 high-Tc superconducting iron oxypnictide single crystals PrFeAsO0.6F0.35 and thin films SmFeAsO1-xFx by means of bulk-sensitive conventional and micro-focused 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 Tc and experiences an anomalous T-linear softening and narrowing below T*=110K>>Tc. The suppression of the infrared absorption in the superconducting state reveals a large optical superconducting gap with a similar gap ratio 2D=kBTc=7 in both materials, indicating strong pairing.
@article{arxiv.1804.02021,
title = {Intrinsic charge dynamics in high-Tc AFeAs(O,F) superconductors},
author = {A. Charnukha and D. Pröpper and N. D. Zhigadlo and M. Naito and M. Schmidt and Z. Wang and J. Deisenhofer and A. Loidl and B. Keimer and A. V. Boris and D. N. Basov},
journal= {arXiv preprint arXiv:1804.02021},
year = {2018}
}
Comments
Revised version and supplementary material published in Phys. Rev. Lett. (see https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.120.087001)