English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

We examine a mechanism by which excitons are generated via the LO(longitudinal optical) phonon-assisted scattering process after opticalexcitation of monolayer transition metal dichalcogenides. The exciton formationtime is computed as a function of the exciton center-of-mass wavevector,electron and hole temperatures, and carrier densities for known values of theFr\"ohlich coupling constant, LO phonon energy, lattice temperature, and theexciton binding energy in layered structures. For the monolayer MoS$_2$, weobtain ultrafast exciton formation times on the sub-picosecond time scale atcharge densities of 5 $\times$ 10$^{11}$ cm$^{-2}$ and carrier temperaturesless than 300 K, in good agreement with recent experimental findings ($\approx$0.3 ps). While excitons are dominantly created at zero center-of-masswavevectors at low charge carrier temperatures ($\approx$ 30 K), the excitonformation time is most rapid at non-zero wavevectors at higher temperatures($\ge $ 120 K) of charge carriers. The results show the inverse square-lawdependence of the exciton formation times on the carrier density, consistentwith a square-law dependence of photoluminescence on the excitation density.Our results show that excitons are formed more rapidly in exemplary monolayerselenide-based dichalcogenides (MoSe$_2$ and WSe$_2$) than sulphide-baseddichalcogenides (MoS$_2$ and WS$_2$).

Exciton formation assisted by longitudinal optical phonons in monolayer transition metal dichalcogenides