Valley phonons and exciton complexes in a monolayer semiconductor.
basic_science · Level V
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- Record sourced from PubMed, PMID 32001715.
- Also identified by DOI 10.1038/s41467-020-14472-0 and PMC identifier 6992782.
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Abstract
The coupling between spin, charge, and lattice degrees of freedom plays an important role in a wide range of fundamental phenomena. Monolayer semiconducting transitional metal dichalcogenides have emerged as an outstanding platform for studying these coupling effects. Here, we report the observation of multiple valley phonons - phonons with momentum vectors pointing to the corners of the hexagonal Brillouin zone - and the resulting exciton complexes in the monolayer semiconductor WSe<sub>2</sub>. We find that these valley phonons lead to efficient intervalley scattering of quasi particles in both exciton formation and relaxation. This leads to a series of photoluminescence peaks as valley phonon replicas of dark trions. Using identified valley phonons, we also uncover an intervalley exciton near charge neutrality. Our work not only identifies a number of previously unknown 2D excitonic species, but also shows that monolayer WSe<sub>2</sub> is a prime candidate for studying interactions between spin, pseudospin, and zone-edge phonons.