Magnetotransport in heterostructures of transition metal dichalcogenides and graphene

We use a van der Waals pickup technique to fabricate different heterostructures containing WSe₂(WS₂) and graphene. The heterostructures were structured by plasma etching, contacted by one-dimensional edge contacts, and a top gate was deposited. For graphene/WSe₂/SiO₂ samples we observe mobilities of ${~}12{{0.16em}{0ex}}000{{0.28em}{0ex}}{cm}²{{0.16em}{0ex}}{V}^{{-}1}{{0.16em}{0ex}}{s}^{{-}1}$. Magnetic-field-dependent resistance measurements on these samples show a peak in the conductivity at low magnetic fields. This dip is attributed to the weak antilocalization (WAL) effect, stemming from spin-orbit coupling. Samples where graphene is encapsulated between WSe₂(WS₂) and hexagonal boron nitride show a much higher mobility of up to ${~}120{{0.16em}{0ex}}000{{0.28em}{0ex}}{cm}²{{0.16em}{0ex}}{V}^{{-}1}{{0.16em}{0ex}}{s}^{{-}1}$. However, in these samples no WAL peak can be observed. We attribute this to a transition from the diffusive to the quasiballistic regime. At low magnetic fields a resistance peak appears, which we ascribe to a size effect due to boundary scattering. Shubnikov--de Haas oscillations in fully encapsulated samples show all integer filling factors due to complete lifting of the spin and valley degeneracies.