The infrared conductivity of Na${}_x$CoO${}_2$: evidence of gapped states

J. Hwang, J. Yang, T. Timusk +1

We present infrared ab-plane conductivity data for the layered cobaltate Na${}_x$CoO${}_2$ at three different doping levels ($x=0.25,0.50$, and 0.75). The Drude weight increases monot…