Superconductivity and structural instability in SrTiO3

Mattheiss has recently calculated the effects of the 105°K structural phase transition on the conduction band and Fermi surface of SrTiO₃. The implications of this calculation for the microscopic understanding of superconductivity in SrTiO₃ are explored. In particular, coupling constants for electron-soft phonon interactions are evaluated. Certain pieces of Fermi surface are coupled very strongly to the soft mode which drives the structural instability, but these pieces are depopulated in the distorted phase. It is concluded that, contrary to a suggestion of Appel, soft phonon modes do not affect superconductivity in SrTiO₃.