Excess wing in the dielectric loss of glass formers:: A Johari-Goldstein β relaxation?

Dielectric loss spectra of glass-forming propylene carbonate and glycerol at temperatures above and below T-g are presented. By performing aging experiments lasting up to five weeks, equilibrium spectra below T-g have been obtained. During aging, the excess wing, showing up as a second power law at high frequencies, develops into a shoulder. The results strongly suggest that the excess wing, observed in a variety of glass formers, is the high-frequency flank of a beta relaxation.