  There has long been a discrepancy between microwave conductivity measurements
in high temperature superconductors and the conductivity spectrum expected in
the simplest models for impurity scattering in a d-wave superconductor. Here we
present a new type of broadband measurement of microwave surface resistance
that finally shows some of the spectral features expected for a d_{x^2-y^2}
pairing state. Cusp-shaped conductivity spectra, consistent with weak impurity
scattering of nodal quasiparticles, were obtained in the 0.6-21 GHz frequency
range in highly ordered crystals of YBa_2Cu_3O_{6.50} and YBa_2Cu_3O_{6.99}.
