  Strong spin-orbit coupling can have a profound effect on the electronic
structure in a metal or semiconductor, particularly for low electron
concentrations. We show how, for small values of the Fermi energy compared to
the spin-orbit splitting of Rashba type, a topological change of the Fermi
surface leads to an effective reduction of the dimensionality in the electronic
density of states. We investigate its consequences on the onset of the
superconducting instability. We show, by solving the Eliashberg equations for
the critical temperature as a function of spin-orbit coupling and electron
density, that the superconducting critical temperature is significantly tuned
in this regime by the spin-orbit coupling. We suggest that materials with
strong spin-orbit coupling are good candidates for enhanced superconductivity.
