Density-Dependent Quantum Hall States and Zeeman Splitting in Monolayer and Bilayer WSe2

We report a study of the quantum Hall states (QHS) of holes in mono- and bilayer WSe2. The QHS sequence transitions between predominantly even and predominantly odd filling factors as the hole density is tuned in the range 1.6-12 x 10(12) cm(-2). Measurements in tilted magnetic fields reveal an insensitivity of the QHS to the in-plane magnetic field, evincing that the hole spin is locked perpendicular to the WSe2 plane. Furthermore, the QHS sequence is insensitive to an applied electric field. These observations imply that the QHS sequence is controlled by the Zeeman-to-cyclotron energy ratio, which remains constant as a function of perpendicular magnetic field at a fixed carrier density, but changes as a function of density due to strong electron-electron interaction.