Spin-orbit coupling enhanced superconductivity in Bi-rich compounds ABi${}_3$ (A=Sr and Ba)

Abstract

Recently, Bi-based compounds have attracted attentions because of the strong spin-orbit coupling (SOC). In this work, we figured out the role of SOC in ABi${}_3$ (A=Sr and Ba) by theoretical investigation of the band structures, phonon properties, and electron-phonon coupling. Without SOC, strong Fermi surface nesting leads to phonon instabilities in ABi${}_3$. SOC suppresses the nesting and stabilizes the structure. Moreover, without SOC the calculation largely underestimates the superconducting transition temperatures ($T_c$), while with SOC the calculated $T_c$ are very close to those determined by measurements on single crystal samples. The SOC enhanced superconductivity in ABi${}_3$ is due to not only the SOC induced phonon softening, but also the SOC related increase of electron-phonon coupling matrix elements. ABi${}_3$ can be potential platforms to construct heterostructure of superconductor/topological insulator to realize topological superconductivity.