Emergent Inhomogeneity and Nonlocality in a Graphene Field-Effect Transistor on a Near-Parallel Moiré Superlattice of Transition Metal Dichalcogenides.

At near-parallel orientation, twisted bilayers of transition metal dichalcogenides exhibit interlayer charge transfer-driven out-of-plane ferroelectricity. Here, we report detailed electrical transport in a dual-gated graphene field-effect transistor placed on a 2.1° twisted bilayer WSe2. We observe hysteretic transfer characteristics and an emergent charge inhomogeneity with multiple local Dirac points evolving with an increasing electric displacement field (D). Concomitantly, we also observe a strong nonlocal voltage signal at D ∼ 0 V/nm that decreases rapidly with increasing D. A linear scaling of the nonlocal signal with longitudinal resistance suggests edge mode transport, which we attribute to the breaking of valley symmetry of graphene due to the spatially fluctuating electric field from the underlying polarized moiré domains. A quantitative analysis suggests the emergence of finite-size domains in graphene that modulate the charge and the valley currents simultaneously. This work underlines the impact of interfacial ferroelectricity that can trigger a new generation of devices.

Band structure sensitive photoresponse in twisted bilayer graphene proximitized with WSe2.

The ability to tune the twist angle between different layers of two-dimensional (2D) materials has enabled the creation of electronic flat bands artificially, leading to exotic quantum phases. When a twisted blilayer of graphene (tBLG) is placed at the van der Waals proximity to a semiconducting layer of transition metal dichalcogenide (TMDC), such as WSe2, the emergent phases in the tBLG can fundamentally modify the functionality of such heterostructures. Here we have performed photoresponse measurements in few-layer-WSe2/tBLG heterostructure, where the mis-orientation angle of the tBLG layer was chosen to lie close to the magic angle of 1.1°. Our experiments show that the photoresponse is extremely sensitive to the band structure of tBLG and gets strongly suppressed when the Fermi energy was placed within the low-energy moiré bands. Photoresponse could however be recovered when Fermi energy exceeded the moiré band edge where it was dominated by the photogating effect due to transfer of charge between the tBLG and the WSe2 layers. Our observations suggest the possibility of the screening effects from moiré flat bands that strongly affect the charge transfer process at the WSe2/tBLG interface, which is further supported by time-resolved photo-resistance measurements.