A transition metal dichalcogenides device includes a substrate, a bottom layer of boron nitride, a tungsten diselenide monolayer on the bottom layer of boron nitride, a top layer of boron nitride on the tungsten diselenide monolayer such that the bottom and top layers of boron nitride at least partially encapsulate the tungsten diselenide monolayer, a source electrode on the substrate, a drain electrode on the substrate, and a top gate electrode on the top layer of boron nitride. The tungsten diselenide monolayer is configured to reveal excitons when at least one of a K valley and a K′ valley of the tungsten diselenide monolayer is exposed to excitation photon energy and an external magnetic field. The excitons are giant valley-polarized Rydberg excitons in excited states ranging from 2s to 11s when the external magnetic field is in the range of about −17 T to about 17 T.