Properties and interplay of carrier and exciton in moiré system

Abstract

The development of moiré systems based on various materials such as magnetic topological materials, transition metal dichalcogenides (TMDs), hexagonal boron nitride (h-BN) and graphene has generated significant interest. These systems are considered promising platforms for investigat- ing charge carrier properties and exciton properties in moiré potential and the corresponding many-body correlation phenomena in a flexible manner. This thesis explores three distinct moiré systems, namely, MnBi2Te4 with spin texture from twisted magnetic substrate, twisted h-BN as the substrate and twisted bilayer TMDs. We investigate various aspects in these systems, including charge carrier properties, formation of moiré potential near the twisted interface, and the impact of the charge carrier-exciton interaction. Regarding MnBi2Te4 spin texture, we established that for magnetization textures with closed domain wall geometries, the formed superlattice mini- band is a gapped Dirac cone. This cone features orbital magnetization from the current circulation in the closed loops of chiral channels. In con- trast, magnetization textures with open domain wall geometries result in gapless mini-Dirac cones. Through our investigations of twisted h-BN, we observed that the interface creates a universal superlattice potential and electric field in various 2D materials placed on top of it. We then general- ized this idea to AB-stacked h-BN subject to torsion with adjacent layers all twisted with an angle in the same direction. This enabled scalability of the potential and field strength with film thickness, ultimately saturating to a quasi-periodic structure with chiral features. Lastly, in the twisted bilayer TMDs system, we found that through the Coulomb exchange between mo- bile interlayer excitons and charge carriers, the interlayer exciton bath could mediate both Heisenberg and Dzyaloshinskii-Moriya type spin interactions between moiré trapped charge carriers. These interactions were control- lable by exciton density and exciton spin current, respectively. We showed that the strong Heisenberg interactions and the extraordinarily long-ranged Dzyaloshinskii-Moriya interactions could establish robust spin spiral mag- netic orders in Mott-Wigner crystal states at various filling factors, with the spiral direction controlled by the exciton current.