| SM ISO690:2012|
MITIOGLU, Anatolie; ANGHEL, Sergiu; BUHOT, Jonathan; PŁOCHOCKA, Paulina; KULIUC, Leonid; CHRISTIANEN, Peter. Magneto-optical investigation of strained 2D WSe2 Monolayers. In: Materials Science and Condensed Matter Physics. Editia a 8-a, 12-16 septembrie 2016, Chişinău. Chişinău: Institutul de Fizică Aplicată, 2016, p. 216. ISBN 978-9975-9787-1-2.
|Materials Science and Condensed Matter Physics
Editia a 8-a, 2016
Conferința "International Conference on Materials Science and Condensed Matter Physics" |
8-th Edition, Chişinău, Moldova, 12-16 septembrie 2016
Monolayer transition metal dichalcogenides (TMDs), such as MoS2, MoSe2, WS2 and WSe2, are novel two dimensional materials with a direct bandgap located at two degenerate valleys (K+ and K-) at the corners of the hexagonal Brillouin zone. The energy bandgap lies in the visible spectral range, which gives rise to efficient light emission and absorption. The optical spectra in monolayer TMDCs are dominated by excitonic effects due to strong 2D confinement and electron-hole exchange . Strong spin-orbit interaction and optical selection rules enable the creation of excitons in a specific valley using circularly polarized light. In addition, linearly polarized illumination leads to excitons, whose states are a superposition of those of K+ and K- valleys, which also emit linearly polarized light due to valley coherence. The micro-photoluminescence (PL) spectra of TMDs are dominated by sharp neutral and charged exciton (trions) lines. Recently, we reported that under an applied magnetic field both exciton and trion emission lines of WSe2 shift in position with magnetic field and split up into two lines of opposite circular polarization (Valley splitting). This behavior was explained using a single-electron picture and a massive Dirac model . As a result, we found an effective valley g-factor of 4 and a Fermi velocity of 0.51x106 cm2/s. However, also significantly different g-factor values have been reported . Possible origins for the spread in g-factors are the effects of doping or strain, although Li and co-workers  claimed that doping does not influence the effective g-factor. Recent theoretical work confirmed that moderate strain together with e-h exchange leads to a splitting of the exciton peak . Our recent experiments on WSe2 monolayers, using high resolution micro-PL, reveal that some flakes exhibit a PL spectrum with a splitted exciton peak (see figure). The splitting is due to a moderate intrinsic strain, which is confirmed by concomitent Raman measurements on the same flake. The amount of strain varies from flake-to flake. We have performed detailed polarized-resolved PL measurements in fields up to 30 T for a series of WSe2 monolayer flakes, where the amount of strain of each sample have been determined by Raman measurements. Our results elucidate the influence of the combined effect of strain and electron-hole exchange on the exciton energy structure and the resulting effective g-factors.