Ratio 2Δ0/kTcin superconductivity

In high-temperature superconductors, values of the ratio R=2${\mathrm{\Delta }}_0$/${\mathit{kT}}_{\mathit{c}}$ have been reported in the range 2–10, whereas low-temperature superconductors rarely deviate by as much as 50% from the BCS prediction R=3.54. Could this variability relate to the density of states near the Fermi surface? Our calculations answer this in the negative.