We report on the anomalous behavior of the complex conductivity of BaFe2As2, which is related to the Dirac cone, in the terahertz (THz)-frequency region. Above the spin-density-wave (SDW) transition temperature, the conductivity spectra follow the Drude model. In the SDW state, the imaginary part of the complex conductivity, σ2, is suppressed in comparison to that expected according to the Drude model. The real part, σ1, exhibits nearly Drude-like behavior. This behavior (i.e., almost no changes in σ1 and the depression of σ2) can be regarded as the addition of extra conductivity without any dissipations in the Drude-type conductivity. The origin of this ultralow-dissipative conductivity is found to be due to conductivity contribution from quasiparticles within the Dirac cone. In other words, we are able to observe the dynamics of Dirac fermions through the conductivity spectra of BaFe2As2, clearly and directly.
@article{arxiv.1202.0399,
title = {Ultralow-dissipative conductivity by Dirac fermions in BaFe$_2$As$_2$},
author = {Yoshinori Imai and Fuyuki Nabeshima and Daisuke Nakamura and Takayoshi Katase and Hidenori Hiramatsu and Hideo Hosono and Atsutaka Maeda},
journal= {arXiv preprint arXiv:1202.0399},
year = {2013}
}