Optical control of the valley Zeeman effect through many-exciton interactions

Charge carriers in two-dimensional transition metal dichalcogenides (TMDs), such as WSe 2 , have their spin and valley-pseudospin locked into an optically addressable index that is proposed as a basis for future information processing 1 , 2 . The manipulation of this spin–valley index, which carries a magnetic moment 3 , requires tuning its energy. This is typically achieved through an external magnetic field ( B ), which is practically cumbersome. However, the valley-contrasting optical Stark effect achieves valley control without B , but requires large incident powers 4 , 5 . Thus, other efficient routes to control the spin–valley index are desirable. Here we show that many-body interactions among interlayer excitons (IXs) in a WSe 2 /MoSe 2 heterobilayer (HBL) induce a steady-state valley Zeeman splitting that corresponds to B ≈ 6 T. This anomalous splitting, present at incident powers as low as microwatts, increases with power and is able to enhance, suppress or even flip the sign of a B -induced splitting. Moreover, the g -factor of valley Zeeman splitting can be tuned by ~30% with incident power. In addition to valleytronics, our results could prove helpful to achieve optical non-reciprocity using two-dimensional materials. Many-body interactions amongst interlayer excitons in a WSe 2 /MoSe 2 heterobilayer give rise to a strong and tunable effective magnetic field enabling the control of the valley pseudospin.