Superconductivity in bismuth pyrochlore lattice compounds RbBi2 and CsBi2: the role of relativistic effects

Superconducting properties of two bismuthide intermetallic compounds, RbBi2 and CsBi2, were studied by means of experimental measurements and ab initio calculations. We show that in both compounds the superconductivity emerges from the pyrochlore Bi lattice and its formation is heavily influenced by relativistic effects. Based on our analysis of the effect of spin-orbit coupling on the electron-phonon coupling we suggest a possible criterion for finding new superconducting materials by looking for structures featuring relativistically-stabilized hypervalent networks of heavy p-block elements.