二硫化鉬/二硫化鎢異質雙層材料的第一原理研究

Abstract

With distinctive properties, heterostructures comprising semiconducting transition metal dichalcogenides (TMDs) have gained prominence recently owing to their prospects in versatile electronic and optoelectronic applications, as well as as a platform for studying valley physics. The weakness of van der Waals interaction between adjacent layers enables the variability in stacking configuration, which may induce variation in interlayer coupling and thereby the modification of structural and electronic properties. To systematically explore the stacking effects in MoS_2/WS_2 heterobilayers, we perform first-principles calculations for comprehensive different stacking configurations, including six coherent and twelve twisted ones. Three coherent stackings are confirmed to be most stable and expected to be predominant upon growth, in agreement with previous experimental reports. Further, all the most stable stackings are shown to exhibit indirect band gap regardless of the presence of spin-orbit coupling (SOC). Intriguingly, we find for all stackings a significant correlation between the interlayer coupling and the equilibrium interlayer distance, the latter of which depends largely on the atomic registry. This is consistent with another finding that while the interlayer distance and coupling as well as the structural stability vary among different coherent stackings, they all remain nearly unchanged in twisted systems despite the presence of disorder in atomic registry. Such invariance against rotation could stem from the subtle balance achieved by the average of spatially varying interlayer interaction over the Moire unit cell. For angles approaching 0/60 degree, the concomitant emergence of local regions featuring high-symmetry stackings may serve to characterize the structural and electronic properties in twisted systems. We demonstrate the evolution of corrugation over rotation angle and argue that the modulation amplitude should not grow beyond 0.3 angstrom. For all twisted systems, the inclusion of SOC modifies the global VBM from Gamma to K point. We observe that the charge density of Gamma-VBM shows no spatial variation until 7.3/52.7 degree, where the corrugation is more pronounced. The present study may suggest the general behaviors of semiconducting TMDs heterobilayers, as well as shed light on future experiments.