Cooperative effect of phonons and electronic correlations for superconductivity in cobaltates

Abstract

We propose that unconventional superconductivity in hydrated sodium cobaltate $N{a}_{x}Co{O}_2$ results from an interplay of electronic correlations and electron-phonon interactions. On the basis of the $t-V$ model plus phonons we found evidences for a) unconventional superconductivity, b) realistic values of $T_c$ and c) the dome shape existing near $x\sim 0.35$. This picture is obtained for $V$ close to the critical Coulomb repulsion $V_c$ which separates the uniform Fermi liquid from $\sqrt{3}\times \sqrt{3}$ CDW ordered phase.

4 pages, 3 figures