Beyond Twisted Bilayers: Engineering Interfacial Quantum Well States in Twisted MoS₂ Bilayers on Bi(111)

Twisted bilayer transition metal dichalcogenides (twBL-TMDs) have emerged as an ideal platform for engineering quantum well states (QWS) with spatially varying potentials. Interlayer coupling between twBL-MoS₂ and Bi(111) induces a Bi-thickness-dependent electron effective mass, providing a new degree of freedom to control the spatial QWS configurations. However, resolving QWS configurations demands atomic-scale microscopy and electronic spectroscopy. Here, we employ low-temperature scanning tunneling microscopy/spectroscopy (LT-STM/S) to examine twBL-MoS₂/Bi(111), demonstrating twBL-MoS₂ moiré-assisted quantum confinement. Our results confirm that these phenomena arise from Bi(111) interfacial QWS that are vertically confined within the semimetallic film and laterally localized by twBL-MoS₂ moiré potential. Varying the Bi(111) thickness to tune the electron effective mass will systematically modify the charge confinement patterns from molecular-like to Kagome-like configurations. Our findings demonstrate that, in addition to twBL-TMD, semimetallic film engineering provides a rational materials design for modulating artificial atomic arrays in 2D/semimetal systems, establishing a new paradigm for interface-controlled quantum materials.