  Combining various two-dimensional materials into novel van der Waals (vdW)
heterostructures has been shown to lead to new emergent quantum systems. A
novel heterostructure composed of a vdW topological insulator (TI) such as
Bi$_{2}$Se$_{3}$ with a quantum spin liquid (QSL) such as $\alpha$-RuCl$_{3}$
is of great interest for the potential for the chiral Dirac electrons in the TI
surface states to interact strongly with the fractionalized fermionic spin
excitations in the QSL. We report the heteroepitaxial growth of
Bi$_{2}$Se$_{3}$ thin films on $\alpha$-RuCl$_{3}$ as well as the
characterization of their structural and electrical properties.
Bi$_{2}$Se$_{3}$ thin films with an atomically smooth and uniform surface are
grown by molecular beam epitaxy. The heterostructure exhibits a preferential
epitaxial relationship corresponding to $(5 \times
5)-$Bi$_{2}$Se$_{3}/(2\sqrt{3} \times 2\sqrt{3})R30\deg-\alpha$-RuCl$_{3}$
commensurate supercells with a periodicity of 1.2 nm. The formation of the
superlattice despite a lattice mismatch as large as 60% is attributed to the
van der Waals heteroepitaxy. Magnetotransport measurements as a function of
temperature show Bi$_{2}$Se$_{3}$ films grown on $\alpha$-RuCl$_{3}$ are
heavily $n$-doped, $n_{e}$ ~10$^{14}$ cm$^{-2}$, with mobility $\mu$ ~450
cm$^{2}$ V$^{-1}$ s$^{-1}$ at low temperatures.
