Phonon-assisted oscillatory exciton dynamics in monolayer MoSe2

Abstract

In monolayer semiconductor transition metal dichalcogenides, the exciton-phonon interaction strongly affects the photocarrier dynamics. Here, we report on an unusual oscillatory enhancement of the neutral exciton photoluminescence with the excitation laser frequency in monolayer MoSe 2 . The frequency of oscillation matches that of the M-point longitudinal acoustic phonon, LA(M), suggesting the significance of zone-edge acoustic phonons and hence the deformation potential in exciton-phonon coupling in MoSe 2 . Moreover, oscillatory behavior is observed in the steady-state emission linewidth and in time-resolved PLE data, which reveals variation with excitation energy in the exciton lifetime. These results clearly expose the key role played by phonons in the exciton formation and relaxation dynamics of two-dimensional van der Waals semiconductors.

Direct band-gap crossover in epitaxial monolayer boron nitride

“…For monolayer MoSe 2 , PL excitation spectroscopy has provided evidence for the prominent effect of longitudinal acoustic phonon modes at the M point, labelled LA(M), in the resonant excitation of phonon modes 47 . This result is consistent with ab initio calculations in MoS 2 and WS 2 , predicting the strongest electron–phonon interaction for LA phonons in the vicinity of the M points 47 . In mBN, the LA(M) energy is calculated to be at 150 ± 5 meV 45,46 .…”

Guide to optical spectroscopy of layered semiconductors

“…In PLE experiments on MoSe 2 monolayers, a periodic oscillation in energy is observed over an energy range without any expected exciton resonance (roughly constant absorption 166 ). These maxima are all equally spaced in energy by longitudinal acoustic phonons at the M point of the Brillouin zone, LA(M), revealing the efficient energy relaxation of excitons through emission of LA(M) phonons 125,167 . This experimental observation was possible owing to the spectrally narrow excitation source, which could resolve fine separations between different peaks related to phonon emission 125,168 .…”

Unusual Exciton–Phonon Interactions at van der Waals Engineered Interfaces

“…Figure 1b,c show PLE intensity plots from WSe 2 /SiO 2 and hBN/WSe 2 /SiO 2 samples, respectively, in which the X 0 and trion (X -) emission peaks are indicated. In both cases, the response of X 0 luminescence to the excitation laser energy features pronounced resonances, while that of Xis monotonic 15 . As Figure 1b shows, there are three prominent peaks in the X 0 PLE of the WSe 2 /SiO 2 sample, as indicated by white arrows.…”