Electronic structure, disconnected Fermi surfaces and antiferromagnetism in the layered pnictide superconductor Na${}_x$Ba${}_{1-x}$Ti${}_2$Sb${}_2$O

Abstract

We report electronic structure calculations for BaTi${}_2$Sb${}_2$O and discuss the results in relation to the observed superconductivity of this material when hole doped with Na. The Fermi surface shows several sheets. These include a nested nearly 2D cylinder. There are also two sheets, which are three dimensional, in spite of the layered crystal structure. A magnetic instability associated with Fermi surface nesting is found. A sign-changing s-wave state, different from the one in the Fe-based superconductors, is predicted within a scenario of spin-fluctuation mediated superconductivity.

Typos corrected. References updated

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