Fig. 1: Photoluminescence and time-resolved Kerr rotation measurements on WSe2/MoSe2 heterobilayers with small twist angles towards a crystallographic stacking order. | npj 2D Materials and Applications

Fig. 1: Photoluminescence and time-resolved Kerr rotation measurements on WSe2/MoSe2 heterobilayers with small twist angles towards a crystallographic stacking order.

From: Twist angle dependent interlayer transfer of valley polarization from excitons to free charge carriers in WSe2/MoSe2 heterobilayers

Fig. 1

a Schematic device structure of the heterobilayer devices. Only STA device #1 and LTA devices #1 and #3 have a graphite gate, whereas STA device #2 is gated via the Si++/SiO2 (285 nm) wafer. c Calculated band structure in case of the RhX-stacking (i.e., a twist angle of zero), in which the amount of hybridization is color-coded. The bands at the K-point only show negligible hybridization and a type-II band alignment. The bands at the Q- and Γ-valleys are strongly hybridized and, depending on parameters like stacking order or twist angle, shift in energy with respect to the band maxima at the K-point (see Supplementary Note 4). b, g Photoluminescence (PL) spectra as a function of gate voltage Vgate for two different devices plotted with a logarithmic color scale and (d, f) respective line-cuts plotted on a linear scale along the black dashed lines in (b) and (g) (white dashed lines are guides to the eye). The features with the highest PL intensities are the intralayer neutral exciton (X0) and the trion (X−) emission of MoSe2. For STA device #1, the interlayer exciton (IX) emission consists of several sub-peaks (see fits in the inset of d), which can be attributed to transitions involving Q- and Γ-valleys. As these features are absent in STA device #2 (see inset in f), we assume that in STA device #2 both Q- and Γ-valleys are energetically further away from the K-valleys decreasing phonon-assisted scattering between the valleys (see schematic in the inset of e). This assumption is consistent to the TRKR data shown in (e, h). For STA device #1, we observe surprisingly short lifetimes of around 200 ps and extremely small amplitudes. Instead, Kerr rotation lifetimes and amplitudes of STA device #2 are one order of magnitude larger. All measurements were conducted at 10 K, pump and probe energies are the trion energies of the specified TMD unless stated otherwise.

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