  The minimum thermal conductance versus supercell size ($d_{s}$) is revealed
in graphene and boron nitride superlattice with $d_{s}$ far below the phonon
mean free path. The minimum value is reached at a constant ratio of
$d_{s}/L\approx 5%$, where $L$ is the total length of the superlattice; thus
the minimum point of $d_{s}$ depends on $L$. The phenomenon is attributed to
the localization property and the number of confined modes in the superlattice.
With the increase of $d_{s}$, the localization of the confined mode is enhanced
while the number of confined modes decreases, which directly results in the
minimum thermal conductance.
