Polarization-dependent electronic structure of Ag quantum well states on the MoS2 (0001) surface using ARPES and DFT studies

Abstract

The electronic band structure of clean and Ag-induced quantum well states on the ${\mathrm{MoS}}_{2}$(0001) surface has been investigated using polarization-dependent angle-resolved photoemission spectroscopy (ARPES) along with first-principle-based density functional theory (DFT) calculations. Using selective linearly polarized light, the orbital symmetry and $k$ dispersion of the surface localized electronic states have been unambiguously determined. The quantum well states (QWS) originating from the Ag ${p}_{z}$ orbitals are confined within the Ag overlayer, while the quantum well resonance states (QWRS) are hybridized with substrate Mo $4{d}_{{z}^{2}}$ and S $3{p}_{z}$ orbitals. The photon energy dependence of the dispersion characteristics confirms the two-dimensional (2D) nature of these quantum states while their momentum dependence is a consequence of the finite lateral coherence length of the electrons. Our ARPES experiments using incident circularly polarized light on ${\mathrm{MoS}}_{2}$(0001) surface show circular dichroism effects (CD-ARPES), similar to recent studies where it is used to probe the initial state orbital angular momentum or the Berry curvature. While the QWS on the Ag overlayer does not exhibit any intensity asymmetry with the helicity of the incident light, the Ag QWRS show circular dichroism characteristics. The observed circular dichroism from the QWRS is attributed to the hybridization of these quantum states to the substrate states. We compare our ARPES results with the calculated orbital projected band structure to obtain a microscopic insight into the electronic behavior, which is critically important for manipulating wave functions for potential device applications.