Hybridization and localized flat band in the WSe2/MoSe2 heterobilayer grown by molecular beam epitaxy

TL;DR

This study visualizes a localized flat band near the Fermi level in WSe2/MoSe2 heterobilayers grown by molecular beam epitaxy, revealing strong interlayer hybridization and domain coexistence, which are crucial for correlated electronic effects.

Contribution

It provides direct experimental visualization and theoretical confirmation of flat bands and hybridization effects in WSe2/MoSe2 heterobilayers grown by MBE, highlighting the role of stacking domains.

Findings

Presence of a flat band near the Fermi level localized at the K point.

Strong interlayer hybridization effects confirmed by ARPES and Raman.

Valence band spin-splitting of 470 meV and VBM at Gamma point.

Abstract

Nearly localized moire 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 K point of the Brillouin zone 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 Gamma point. The energy difference between the VBM at Gamma 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.