Systematic Identification of LAEs for Visible Exploration and
  Reionization Research Using Subaru HSC (SILVERRUSH). I. Program Strategy and
  Clustering Properties of ~2,000 Lya Emitters at z=6-7 over the 0.3-0.5
  Gpc$^2$ Survey Area
  We present the SILVERRUSH program strategy and clustering properties
investigated with $\sim 2,000$ Ly$\alpha$ emitters at $z=5.7$ and $6.6$ found
in the early data of the Hyper Suprime-Cam (HSC) Subaru Strategic Program
survey exploiting the carefully designed narrowband filters. We derive angular
correlation functions with the unprecedentedly large samples of LAEs at $z=6-7$
over the large total area of $14-21$ deg$^2$ corresponding to $0.3-0.5$
comoving Gpc$^2$. We obtain the average large-scale bias values of $b_{\rm
avg}=4.1\pm 0.2$ ($4.5\pm 0.6$) at $z=5.7$ ($z=6.6$) for $\gtrsim L^*$ LAEs,
indicating the weak evolution of LAE clustering from $z=5.7$ to $6.6$. We
compare the LAE clustering results with two independent theoretical models that
suggest an increase of an LAE clustering signal by the patchy ionized bubbles
at the epoch of reionization (EoR), and estimate the neutral hydrogen fraction
to be $x_{\rm HI}=0.15^{+0.15}_{-0.15}$ at $z=6.6$. Based on the halo
occupation distribution models, we find that the $\gtrsim L^*$ LAEs are hosted
by the dark-matter halos with the average mass of $\log (\left < M_{\rm h}
\right >/M_\odot) =11.1^{+0.2}_{-0.4}$ ($10.8^{+0.3}_{-0.5}$) at $z=5.7$
($6.6$) with a Ly$\alpha$ duty cycle of 1 % or less, where the results of
$z=6.6$ LAEs may be slightly biased, due to the increase of the clustering
signal at the EoR. Our clustering analysis reveals the low-mass nature of
$\gtrsim L^*$ LAEs at $z=6-7$, and that these LAEs probably evolve into massive
super-$L^*$ galaxies in the present-day universe.
