%0 Journal Article
%T Formation of the density wave energy gap in Na$_2$Ti$_2$Sb$_2$O: an optical spectroscopy study
%A Y. Huang
%A H. P. Wang
%A W. D. Wang
%A Y. G. Shi
%A N. L. Wang
%J Physics
%D 2013
%I arXiv
%R 10.1016/j.jallcom.2013.02.155
%X We performed optical spectroscopy measurement on single crystals of Na$_2$Ti$_2$Sb$_2$O, which is the parent compound for the newly discovered Ti-based superconductors. The study reveals significant spectral change across the phase transition at 114 K and formation of a density-wave type energy gap. The opening of the gap removes most part of the free carrier spectral weight and causes a dramatic reduction of the carrier scattering rate. The ratio of 2$\Delta/k_BT_s\approx$14 is considerably larger than the mean-field value based on the weak-coupling BCS theory. The study also reveals a weak correlation effect in the titanium oxypnictides.
%U http://arxiv.org/abs/1301.1216v1