Study of Electronic States of 1111 Iron Based Superconductors: via Angle-Resolved Photoemission Spectroscopy and Raman Scattering Spectroscopy

概要

Local structure parameter, pnictogen height is predicted to play as a switch between high Tc nodeless pairing and low Tc nodal pairing in Fe-based superconductors. In spin fluctuation model, the γ Fermi surface is important for the nodeless pairing and acts as a switch for different pairing mechanisms, but there is no report of it experimentally thus far. The pnictogen height is controllable by phosphorus doping. The phase diagram of LnFeAs1-xPxO0.9F0.1 reveals a non-monotonic Tc variation, which originates from two different Tc raising pairing mechanisms. With an interest in the pairing mechanisms, the electronic band structure and gap symmetry were studied.

The missing γ band with dxy orbital character was successfully observed in NdFeAs1-xPxO0.9F0.1 using angle-resolved photoemission spectroscopy. However, the γ band are far away from the Fermi level. Besides, a small band dispersion with dxy orbital character was observed just below Fermi level at the zone center. Superconducting condensation was observed on this dxy incipient band, indicating its importance for SC1 region.

Raman scattering spectroscopy revealed the enhancement of electron-phonon interaction with increasing x in B1g spectrum. The full-gapped symmetry was observed on the hole Fermi surfaces for x = 0.

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