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Minimum thermal conductance in graphene and boron nitride superlattice

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.