Magnetotransport of High Mobility Holes in Monolayer and Bilayer WSe$_{\mathrm{2}}$

Transition metal dichalcogenides have attracted significant interest because of their two-dimensional crystal structure, large band-gap, and strong spin-orbit interaction which leads to spin-valley locking. Recent advances in sample fabrication [1] have allowed the experimental study of low temperature magneto-transport of high mobility holes in WSe$_{\mathrm{2}}$ [2]. We review here the main results of these studies which reveal clear quantum Hall states in mono- and bilayer WSe$_{\mathrm{2}}$. The data allows the extraction of an effective hole mass of $m^{\ast }=$0.45$m_{e}$ ($m_{e}$ is the bare electron mass) in both mono and bilayer WSe$_{\mathrm{2}}$. A systematic study of the carrier distribution in bilayer WSe$_{\mathrm{2}}$ determined from a Fourier analysis of the Shubnikov-de Haas oscillations indicates that the two layers are weakly coupled. The individual layer density dependence on gate bias shows negative compressibility, a signature of strong electron-electron interaction in these materials associated with the large effective mass. We discuss the interplay between cyclotron and Zeeman splitting using the dependence of the quantum Hall state sequence on carrier density, and the angle between the magnetic field and the WSe$_{\mathrm{2}}$ plane. Work done in collaboration with B. Fallahazad, H. C. P. Movva, K. Kim, S. K. Banerjee, T. Taniguchi, and K. Watanabe. [1] H. C. P. Movva \textit{et al.}, \textit{ACS Nano} \textbf{9}, 10402 (2015). [2] B. Fallahazad \textit{et al.}, \textit{Phys. Rev. Lett.} \textbf{116}, 086601 (2016).