The charge dynamics of spin-liquid states described by U(1) gauge theory coupling to fermionic spinons is discussed in this paper. We find that the gapless spinons give rise to a power law optical conductivity inside the charge gap. The theory is applied to explain the unusual optical conductivity observed recently in the organic compound κ−(BEDT−TTF)2Cu2(CN)3. We also propose an optical experiment to search for the in-gap excitations in the Kagome spin liquid insulator.
@article{arxiv.0706.0050,
title = {Power-law Conductivity inside the Mott gap: application to $\kappa-(BEDT-TTF)_2Cu_2(CN)_3$},
author = {Tai-Kai Ng and Patrick A. Lee},
journal= {arXiv preprint arXiv:0706.0050},
year = {2009}
}