  This Letter reports an improved search for light sterile neutrino mixing in
the electron antineutrino disappearance channel with the full configuration of
the Daya Bay Reactor Neutrino Experiment. With an additional 404 days of data
collected in eight antineutrino detectors, this search benefits from 3.6 times
the statistics available to the previous publication, as well as from
improvements in energy calibration and background reduction. A relative
comparison of the rate and energy spectrum of reactor antineutrinos in the
three experimental halls yields no evidence of sterile neutrino mixing in the
$2\times10^{-4} \lesssim |\Delta m^{2}_{41}| \lesssim 0.3$ eV$^{2}$ mass range.
The resulting limits on $\sin^{2}2\theta_{14}$ are improved by approximately a
factor of 2 over previous results and constitute the most stringent constraints
to date in the $|\Delta m^{2}_{41}| \lesssim 0.2$ eV$^{2}$ region.
