  Two recent experiments in lightly doped strontium titanate have shown that
the superconducting critical temperature remains constant in a range of carrier
concentrations covering almost three orders of magnitude. The importance of
this phenomenon, hereby dubbed a superconducting plateau, is comparable to the
celebrated superconducting dome. The dramatic empirical evidence impose severe
constraints on any proposal for a superconducting mechanism at low doping. We
analyze the experimental results to see what type of theoretical models can be
suitable in this regime. We show that the low critical current, absence of
diamagnetic screening and the high critical field are all related to the small
momentum of the carriers, which is expected at low densities. We quantify the
dependency of the critical temperature on density by introducing the "density
exponent". We discuss the role of a quantum critical point in the formation of
a plateau and comment on the need for more experimental data.
