Tuning Valley Magnetic Moment in Bilayer MoS2 via Symmetry Control

Monolayer MoS2 provides the opportunity to explore the coupled spin-valley physics arising from broken inversion symmetry. Although inversion symmetry is present in pristine bilayer MoS2, it can be broken by applying a perpendicular electric field. It offers the remarkable possibility of switching on/off and continuously tuning the physical properties of the Dirac valleys, such as valley magnetic moment and Berry curvature, by reversible electrical control. In this work, we employ polarization-resolved photoluminescence (PL) to investigate this effect using bilayer and monolayer MoS2 field effect transistors. We find that in bilayer MoS2 the circularly polarized PL can be continuously tuned from -15{\%} to 15{\%} as a function of gate voltage, whereas in structurally non-centrosymmetric monolayer MoS2 the PL polarization is gate-independent. The observations are well explained as resulting from the continuous variation of orbital magnetic moments between positive and negative values via symmetry control.