Shubnikov-de Haas Oscillations of High-Mobility Holes in Monolayer and Bilayer WSe2: Landau Level Degeneracy, Effective Mass, and Negative Compressibility

We study the magnetotransport properties of high-mobility holes in monolayer and bilayer WSe2, which display well defined Shubnikov-de Haas (SdH) oscillations, and quantum Hall states in high magnetic fields. In both mono-and bilayer WSe2, the SdH oscillations and the quantum Hall states occur predominantly at even filling factors, evincing a twofold Landau level degeneracy. The Fourier transform analysis of the SdH oscillations in bilayer WSe2 reveals the presence of two subbands localized in the top or the bottom layer, as well as negative compressibility. From the temperature dependence of the SdH oscillations we determine a hole effective mass of 0.45m(0) for both mono-and bilayer WSe2.