Topology Hierarchy of Transition Metal Dichalcogenides Built from Quantum Spin Hall Layers

The evolution of the physical properties of 2D material from monolayer limit to the bulk reveals unique consequences from dimension confinement and provides a distinct tuning knob for applications. Monolayer 1T'-phase transition metal dichalcogenides (1T'-TMDs) with ubiquitous quantum spin Hall (QSH) states are ideal 2D building blocks of various 3D topological phases. However, the stacking geometry has been previously limited to the bulk 1T'-WTe2 type. Here, the novel 2M-TMDs consisting of translationally stacked 1T'-monolayers are introduced as promising material platforms with tunable inverted bandgaps and interlayer coupling. By performing advanced polarization-dependent angle-resolved photoemission spectroscopy as well as first-principles calculations on the electronic structure of 2M-TMDs, a topology hierarchy is revealed: 2M-WSe2, MoS2, and MoSe2 are weak topological insulators (WTIs), whereas 2M-WS2 is a strong topological insulator (STI). Further demonstration of topological phase transitions by tunning interlayer distance indicates that band inversion amplitude and interlayer coupling jointly determine different topological states in 2M-TMDs. It is proposed that 2M-TMDs are parent compounds of various exotic phases including topological superconductors and promise great application potentials in quantum electronics due to their flexibility in patterning with 2D materials.

Automated summary

The evolution of physical properties in 2D materials from monolayer to bulk introduces unique effects due to dimension confinement and provides a tuning knob for applications. The novel 2M-TMDs, consisting of translationally stacked 1T'-monolayers, exhibit tunable inverted bandgaps and interlayer coupling, making them promising as building blocks for various topological phases. By using advanced spectroscopy and calculations, a topology hierarchy is revealed, showing different topological insulator states in 2M-WSe2, MoS2, MoSe2, and 2M-WS2 due to band inversion amplitude and interlayer coupling. These 2M-TMDs are proposed as parent compounds for exotic phases and have great potential in quantum electronics due to their flexibility in patterning with 2D materials.