Intrinsic Charge Dynamics in High-Tc AFeAs (O,F) Superconductors


Intrinsic Charge Dynamics in High-Tc AFeAs (O,F) Superconductors

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

We report the first determination of the in-plane complex optical conductivity of 1111 high-Tc 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 Tc and experiences an anomalous T-linear softening and narrowing below T∗≈110  K≫Tc. The suppression of the infrared absorption in the superconducting state reveals a large optical superconducting gap with a similar gap ratio 2Δ/kBTc≈7 in both materials, indicating strong pairing.

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Permalink: https://www.hzdr.de/publications/Publ-27316
Publ.-Id: 27316