Hybridization and localized flat band in the WSe₂/MoSe₂ heterobilayer

Abstract

Nearly localized moiré flat bands in momentum space, arising at particular twist angles, are the key to achieve correlated effects in transition-metal dichalcogenides. Here, we use angle-resolved photoemission spectroscopy (ARPES) to visualize the presence of a flat band near the Fermi level of van der Waals (vdW) WSe2/MoSe2 heterobilayer grown by molecular beam epitaxy. This flat band is localized near the Fermi level and has a width of several hundred meVs. By combining ARPES measurements with density functional theory (DFT) calculations, we confirm the coexistence of different domains, namely the reference 2H stacking without layer misorientation and regions with arbitrary twist angles. For the 2H-stacked heterobilayer, our ARPES results show strong interlayer hybridization effects, further confirmed by complementary micro- Raman spectroscopy measurements. The spin-splitting of the valence band at K is determined to be 470 meV. The valence band maximum (VBM) position of the heterobilayer is located at the Γ point. The energy difference between the VBM at Γ and the K point is of -60 meV, which is a stark difference compared to individual 1L WSe2 and 1L WSe2, showing both a VBM at K.

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

“…Depending on stacking order, interlayer distance, or twist angle, theoretical studies come to different conclusions about whether the valence band maximum lies either at the Γor the K-valley 44,[46][47][48][49] . Interestingly, even experimental ARPES studies come to different conclusions: Whereas one of the first reported measurements claims that the Γ-valley lies below the K-valley 76 , a more recent measurement claims the opposite 77 . As we cannot conduct ARPES measurements on the devices with a top hexagonal boron nitride (hBN) layer (see Fig.…”

Stacking Order Engineering of Two-Dimensional Materials and Device Applications

“…In addition to CVD, twist angles may be generated between layers grown sequentially by molecular beam epitaxy (MBE). Many studies have revealed moiré patterns in MBE grown stacks, originating from lattice mismatch and arbitrary rotation between layers. − For example, in a recent study, Khalil et al grew WSe 2 /MoSe 2 heterobilayers on top of a graphene substrate by MBE and found coexistence of domains with arbitrary interlayer twist angles up to 4°, leading to a flat band observed by angle-resolved photoemission spectroscopy. As with CVD, control of the interlayer twist during MBE growth of stacked layers would greatly advance the scalability of moiré based heterostructures …”