Effects of local oxygen distortions on electronic structures of Na${}_x$CoO${}_2$

Abstract

By using pseudopotential method with local spin density functional approximation, the electronic band structures of Na${}_x$CoO${}_2$ are calculated for $x=0.25$, 0.5, 0.75, and $x=1$ in the presence of the structure relaxations. As increasing Na content, the hybridization between cobalt and oxygen orbitals is decreased, and a phase transition is predicted from a wide-band ferromagnetic to a narrow band paramagnetic metals. The itinerant ferromagnetism is strongly suppressed by the local distortions of the oxygens around the cobalts. Moreover, straining the CoO${}_2$ layers corresponding to the hydrated superconductor Na${}_{0.35}$CoO${}_2\cdot$1.3HO strongly enhances both the hybridization and ferromagnetism.

Revtex 4, 3 pages, 5 figures; the title has been changed to be specific