Spatial variations of valley splitting in monolayer transition metal dichalcogenide

Abstract

In monolayer group‐VI transition metal dichalcogenides (TMDs), valley splitting features have received a lot of attention since it can be potentially utilized for information storing and processing. Among the known two‐dimensional (2D) TMDs, monolayer WSe2 or MoSe2 has been mostly selected for excitonic and valleytronic physics studies because of its sharp and well‐resolved excitonic spectral features. Meanwhile, their high optical quality leads to a tremendous desire for developing promising WSe2‐ and MoSe2‐based valleytronic devices. Toward this goal, exploring the uniformity of valley features crossing an entire piece of monolayer becomes necessary and critical. Here, we performed the systematic magneto‐photoluminescence mapping measurements on mechanically exfoliated monolayer WSe2 and observed unconventional spatial variations of valley splitting. The observed nonuniformity is attributed to the modulated doping, which is probably due to the different distributions of unintentional absorbates across the sample. Such an unexpected doping effect shows the nonnegligible influence on the valley Zeeman splitting of the trion emission (XT) while affecting that of the neutral exciton emission (X0) trivially, evidencing for the large valleytronic sensitivity of the charged exciton. This work not only enriches the understanding of the doping effect on valley splitting but also is meaningful for developing 2D valleytronics.