Transport and magneto-transport study of ultrathin $WSe_2$

Atomically thin transition metal dichalcogenides is a promising materials platform for a new generation of electronic and spintronic applications. We fabricate monolayer and bilayer hBN/graphene/$WSe_2$ four-terminal devices using a dry van der Waals transfer technique, where few-layer graphene serves as the electrical contact to $WSe_2$. We discuss the importance of temperature control at each step of the transfer process. A High $\kappa$ $HfO_2$ back gate enables the devices to reach high carrier densities of a few $\times 10^{13}$/cm$^2$. The graphene contacts are ambipolar, ohmic and enable four-terminal measurements at low temperatures. We measure the magnetic field dependence of $\rho_{xx}$ for both electrons and holes in the same device. As the Fermi level is continuously tuned from the valence band to the conduction band, the magneto-resistance exhibits a variety of behavior including weak localization, weak anti-localization and more complex non-monotonic field dependences. We compare our data with theoretical models.