Observation of B 1s trion and A 2s trion in 2d limit

The distinct excitonic effect in two-dimensional (2d) layered material attracts lot of attentions in recent years. The largely reduced screening effect in 2d materials allows tightly bonding exciton. With gate tunable photoluminescence spectrum, we observe B 1s trion and A 2s trion in h-BN capsuled MoSe₂. The two states show much larger valley polarization compared with their low energy counterparts A 1s exciton and trion.