The Fermi surfaces (FS) of LaOFeAs (in kz=0 plane) consist of two hole-type circles around Γ point, which do not touch each other, and two electron-type co-centered ellipses around M point, which are degenerate along the M-X line. By first-principles calculations, here we show that additional degeneracy exists for the two electron-type FS, and the crucial role of F-doping and pressure is to enhance this orbital degeneracy. It is suggested that the inter-orbital fluctuation is the key point to understand the unconventional superconductivity in these materials.
@article{arxiv.0803.4487,
title = {Enhanced Orbital Degeneracy in Momentum Space for LaOFeAs},
author = {Hai-Jun Zhang and Gang Xu and Xi Dai and Zhong Fang},
journal= {arXiv preprint arXiv:0803.4487},
year = {2009}
}