Interlayer Coupling of MoS2 and Future 2D Materials

Interlayer coupling offers the opportunity to observe new physical phenomena and new strategies for modulating the electronic and optoelectronic properties of two-dimensional (2D) van der Waals (vdW) materials for practical device applications. This provides a good foundation for the future of molybdenum disulfide (MoS₂) structural interlayer coupling and 2D materials.

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Stacking two comparable semiconductor monolayers at distorted angles induces new physical phenomena, including moiré excitons and associated electronic phases, which are moiré superlattice formed due to modulation of the periodic coupling between the layers. Therefore, it is necessary to explore the underlying coupling mechanisms between atomic layers to understand these new phenomena.

A study published in Physical Review X proposes interlayer coupling between the valence and conduction bands of two different layers. Its basic mechanism is determined on the basis of the Berry phase winding associated with the layers. The type II band arrangement at the K point was found by optical spectroscopic study of three rhombohedral (R)-molybdenum disulfide bilayers in a two-gate device.

In addition, spontaneous polarization and potentially asymmetric interlayer coupling in 3R-MoS₂ are quantified by revealing their contribution to band shifts. This study reveals the physical basis for the stacking-induced ferroelectricity of transition metal dichloride (TMD) homostructures, which play a key role in the molar physics of two-dimensional semiconductors.

TMDs are two-dimensional semiconductor materials with unique electrical, mechanical and optical properties. Mixing and matching of single layers of 2D materials provides a fruitful platform for exploring new quantum phenomena in vdW-based material systems. When two-dimensional materials are stacked individually, lattice mismatches or distorted angles may occur between layers. Regardless of their occurrence (natural or designed), moiré superlattices, an interference pattern in the atomic lattice structure, appear.

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Interlayer coupling is prevalent in vdW materials and provides flexibility to tune the electronic band structure of 2D materials. Tuning the layer orientation of artificial 2D assemblies can bring about periodically tuned interlayer coupling in the molar superlattice, leading to singularities that appear different from their monolayer counterparts.

In TMD 2D semiconductors, the moire potential quenches the kinetic energy of the electron and locates it at the energy local minimum of the moire superlattice, yielding a new platform for simulating various related physics and creating arrays of quantum emitters.

The low density of states of single-layer MoS₂ crystals may limit their practical applications. MoS₂ bilayers are particularly attractive for applications in logic devices and sensors because of their high density of states, carrier mobility, and stability at room temperature.

Reference: Liang, J., Yang, D., Wu, J., Dadap, J. I., Watanabe, K., Taniguchi, T., Ye, Z. (2022). Optically Probing the Asymmetric Interlayer Coupling in Rhombohedral-Stacked MoS₂ Bilayer. Physical Review X. https://journals.aps.org/prx/abstract/10.1103/PhysRevX.12.041005

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