  Employing wide-angle neutron spin echo spectroscopy, we measured the
Q-dependent coherent intermediate scattering function of the prototypical ionic
glass former Ca0.4K0.6(NO3)1.4, in the equilibrium and supercooled liquid
states beyond the hydrodynamic regime. The data reveal a clear two-step
relaxation: an exponential fast process, and a stretched exponential slow alpha
process. de Gennes narrowing is observed in all characteristic variables of the
alpha process: the relaxation time, amplitude, and stretching exponent. At all
length scales probed, the relative amplitude of the alpha-relaxation decreases
with increasing temperature and levels off in the normal liquid state. The
temperature dependence of the stretching exponent and the relaxation time at
different Q's indicate that modifications of the relaxation mechanisms at the
local length scales, manifested as temperature independent dynamic
heterogeneity and smaller deviations from Arrhenius behavior, have occurred
even above the alpha-beta (Johari-Goldstein) bifurcation temperature.
