  We present the results from our search for C IV in the intergalactic medium
at redshifts z=5.3-6.0. We have observed four z~6 QSOs with Keck/NIRSPEC in
echelle mode. The data are the most sensitive yet taken to search for C IV at
these redshifts, being 50% complete at column densities log(N_{CIV})=13.4. We
find no C IV systems in any of the four sightlines. Taking into account our
completeness, this translates into a decline in the number density of C IV
absorbers in the range 13.0 < log(N_{CIV}) < 15.0 of at least a factor 4.4 (95%
confidence) from z~2-4.5, where the number density is relatively constant. We
use our lack of detections to set limits on the slope and normalization of the
column density distribution at z=5.3-6.0. The rapid evolution of C IV at these
redshifts suggests that the decrease in the number density may largely be due
to ionization effects, in which case many of the metals in the z~4.5 IGM could
already be in place at z~5.3, but in a lower ionization state. The lack of weak
systems in our data, combined with the presence of strong C IV absorbers along
at least one other sightline, further suggests that there may be large-scale
variations in the enrichment and/or ionization state of the z~6 IGM, or that C
IV absorbers at these redshifts are associated with rare, UV-bright
star-forming galaxies.
