Abstract
AbstractIn 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.image
Highlights
Besides the direct-bandgap nature of ML MX2, the inversion symmetry breaking of ML MX2 leads to a large spin-orbit coupling (SOC),[15,16,17] which further results in the splitting of valance bands at K and K0 valleys
In addition to the strong SOC in ML transition metal dichalcogenides (TMDs), K and K0 valleys are energy-degenerated but inequivalent due to the time-reversal symmetry.[18,19]. This energy degeneracy can be lifted upon an out-of-plane external magnetic field due to the time-reversal symmetry breaking.[20,21,22,23,24,25]
There are some works studying the doping influence on the valley splitting by applying electric field,[23,26,27] studies of valley splitting variations crossing the ML TMDs are still rare
Summary
Beyond the evolution of PL peaks along spatial locations, valley splitting behaviors of XT and X0 emissions are studied at the center and the edge of the exfoliated WSe2.
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