  We present measurements of the microwave surface impedance of the
single-layer cuprate Tl2201, deep in the overdoped regime, with Tc ~ 25 K.
Measurements have been made using cavity perturbation of a dielectric resonator
at 17 discrete frequencies ranging from 2.50 to 19.16 GHz, and at temperatures
from 0.12 to 27.5 K. From the surface impedance we obtain the microwave
conductivity, penetration depth and superfluid density. The superfluid density
displays a strong linear temperature dependence from 2 to 14 K, indicative of
line nodes in the energy gap. The microwave data are compared with theoretical
predictions for a d-wave superconductor with point-like impurities, with the
conclusion that disorder in Tl2201 acts predominantly in the
weak-to-intermediate-strength scattering regime, and that small-angle
scattering is important.
