Observation of exciton-phonon coupling in MoSe2 monolayers

Abstract

We study experimentally and theoretically the exciton-phonon interaction in MoSe2 monolayers encapsulated in hexagonal BN, which has an important impact on both optical absorption and emission processes. The exciton transition linewidth down to 1 meV at low temperatures makes it possible to observe high energy tails in absorption and emission extending over several meV, not masked by inhomogeneous broadening. We develop an analytical theory of the exciton-phonon interaction accounting for the deformation potential induced by the longitudinal acoustic phonons, which plays an important role in exciton formation. The theory allows fitting absorption and emission spectra and permits estimating the deformation potential in MoSe2 monolayers. We underline the reasons why exciton-phonon coupling is much stronger in two-dimensional transition metal dichalcodenides as compared to conventional quantum well structures. The importance of excitonphonon interactions is further highlighted by the observation of a multitude of Raman features in the photoluminescence excitation experiments. arXiv:1804.06340v1 [cond-mat.mtrl-sci]

Temperature dependence of the double‐resonance Raman bands in monolayer MoS2

“…Moreover, the strong spin–orbit interaction splits the valence band, giving rise to the so‐called A and B excitons, at 1.89 and 2.06 eV, respectively . The strong coupling between A and B excitons with the acoustic phonons has been revealed by several studies of transition metal dichalcogenides (TMDs) specially with Raman spectroscopy …”

Quantum Interference Effect on Exciton Transport in Monolayer Semiconductors

“…The product k B T τ / = M s 2 τ 0 / is also temperature independent and on the order of unity in TMDC MLs meaning that the criterion (2) does not, strictly speaking, hold. It is also experimentally confirmed by the thermal broadening of exciton resonance [27,29,30]. Furthermore, at the room temperature the exciton interaction with the optical and zone-edge phonons becomes significant which reduces τ and violates the condition (2) even stronger.…”

“…Effect of acoustic phonons. (a) Exciton scattering times as functions of temperature calculated for the parameters typical for TMDC MLs: deformation potential difference |Ξc − Ξv| = 7 eV, exciton translational mass M = 0.5m0 with m0 being free electron mass, mass density ρ = 4.46 × 10 −7 gm/cm 2 , speed of sound s = 4.1 × 10 5 cm/s[1,29,45,46]. Dotted curve shows /(kBT ) for comparison.…”

Theory of the absorption line shape in monolayers of transition metal dichalcogenides

“…Monolayers of transition metal dichalcogenides (TMDCs) are intensely studied direct semiconductors with tightly bound excitons [1][2][3][4][5] and exceptionally strong exciton-phonon interaction [6][7][8][9]. Remarkable signatures of these traits are strongly inhomogeneous lineshapes in absorption spectra and pronounced phonon-assisted transitions in photoluminescence [6][7][8]10]. This gives rise to the question how to theoretically describe the combined exciton and phonon physics.…”

“…There the lineshape of the excitonic resonance is usually incorporated phenomenologically as a Lorentzian. Because the origin of lineshapes are diverse [24], a few works are devoted to the description of the influence of excitonphonon interaction on spectra [6,8,25]. In Refs.…”