Modulation of Phonons and Excitons Due to Moiré Potentials in Twisted Bilayer of WSe₂/MoSe₂

Abstract

The application of two-dimensional materials has been expanded by introducing the twisted bilayer (TBL) system. However, the landscape of the interlayer interaction in hetero-TBLs has not yet been fully understood, while that in homo-TBLs has been extensively studied, with the dependence on the twist angle between the constituent layers. Here, we present detailed analyses on the interlayer interaction that depends on the twist angle in WSe 2 /MoSe 2 hetero-TBL via Raman and photoluminescence studies combined with first-principles calculation. We observe interlayer vibrational modes, moiréphonons, and the interlayer excitonic states that evolve with the twist angle and identify different regimes with distinct characteristics of such features. Moreover, the interlayer excitons that appear strong in the hetero-TBLs with twist angles near 0°or 60°have different energies and photoluminescence excitation spectra for the two cases, which results from different electronic structures and carrier relaxation dynamics. These results would enable a better understanding of the interlayer interaction in hetero-TBLs.

Modification of interlayer interaction in bilayer MoS2 due to monolayer WSe2 in heterostructures

“…This mode has been reported to exhibit strong dependence on the twist angle in WSe 2 homobilayers [39]. We observed small additional peaks in the highfrequency Raman spectra of some samples, which may be due to moiré phonons of the intralayer vibration modes (see figure S5) [2,17,21,24].…”

“…Interlayer shear modes appear only for small twist angles near 0 • (3R-stacking type) or 60 • (2H-stacking type) [17,20]. In hetero-bilayers, moiré phonons of the higherfrequency intralayer vibration modes are observed in MoSe 2 /WSe 2 and WSe 2 /WS 2 heterostructures [21][22][23][24] and the evolution of the low-frequency interlayer vibration modes was also reported [24].…”

Raman‐Active Interlayer Phonons and Moiré Phonons in Twisted Thin‐Layer MoTe2

“…Notably, the separation of the two modes exhibits an avoided crossing behavior at the twist angle of around 4°, resulting from the coupling of the folded acoustic phonon modes with the LB mode, as discussed in previous literatures. [10,27] Besides the interlayer phonon modes, we have discovered two series of small peaks in the low-frequency Raman spectra, falling within the range of 30-100 cm −1 . Figure 3a,b is the low-frequency Stokes and anti-Stokes Raman spectra of the bilayers, covering twist angles from 0°to 55°, under parallel (XX) and cross (XY) polarization configurations, respectively.…”

“…Notably, the Moiré superlattices not only change the electronic bands but also lead to the folding of phonon bands, [5] a distinctive spectroscopic feature of twisted bilayers. Phonon modes activated by Moiré superlattices have been observed in various systems, including twisted bilayer graphene, [6][7][8] twisted bilayer MoS 2 , [5] WSe 2 , [9] and MoSe 2 /WSe 2 [10,11] heterojunctions. In the case of twisted bilayer graphene, Moiré phonons encompass both the activated acoustic [8] and optical modes, [6,12] emerging within different twisted angle ranges and exhibiting distinct dependencies on resonant excitation conditions.…”

Advance in twisted transition metal dichalcogenides: synthesis, characterization, and properties

“…Additionally, Lim et al obtained monolayers of WSe 2 and MoSe 2 through mechanical exfoliation method, and stacked the WSe 2 monolayer on MoSe 2 using a PDMS-assisted dry pressing method. The resulting WSe 2 /MoSe 2 has 2H-like and 3R-like twist angles [43]. Similarly, Debnath et al described the preparation method for the MoS 2 /WS 2 heterojunction, and the micro-manipulation platform they used can precisely control the twist angle with an accuracy of 0.1 • [44].…”