in High Magnetic Fields*

The strong Coulomb interaction in 2D-TMDCs provides an outstanding platform for investigating the Rydberg exciton physics. In this study, we observed for the first time excitonic luminescence of up to the 4s excited state in ultrahigh quality BN/1L-WSe₂/BN heterostructures in a strong out-of-plane magnetic field. By analyzing the diamagnetic shift of the ground and excited exciton states, the radii of the 2s and 3s excitons are found to be 3.4 and 6 times larger comparing with the 1s exciton. Moreover, the Zeeman splitting measurement shows the monotonic increase of g factor from -4.4 to -4.8 for 1s to 3s, indicating existence of nontrivial differences of magnetic moment and effective mass between different Rydberg exciton states. Complementary to PLE and absorption measurements in literature, our results provide an alternative method to optically investigate tightly-bound electron-hole pairs and strong Coulomb interaction in 2D excitonic systems.