abstract
- The ab-plane optical spectra of one underdoped and one nearly optimally doped single crystal of HgBa_2Ca_2Cu_3O_{8+delta} were investigated in the frequency range from 40 to 40,000 cm^-1. The frequency dependent scattering rate was obtained by Kramers Kronig analysis of the reflectance. Both crystals have a scattering rate gap of about 1000 cm^-1 which is much larger than the 700 cm^-1 gap seen in optical studies of several cuprates with maximum Tc around 93 K. There appears to be a universal scaling between scattering rate gap and maximum Tc for the cuprate superconductors.