Temperature Dependent Scattering Rates at the Fermi Surface of Optimally Doped ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CaCu}}_2{O}_{8+\mathit{\delta }}$

For optimally doped ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CaCu}}_2{\mathrm{O}}_{8+\delta }$, scattering rates in the normal state are found to have a linear temperature dependence over most of the Fermi surface. In the immediate vicinity of the $(\pi ,0\mathrm{})$ point, the scattering rates are nearly constant in the normal state, consistent with models in which scattering at this point determines the $c$-axis transport. In the superconducting state, the scattering rates away from the nodal direction appear to level off and become temperature independent.