E. Li
Unveristy of Texas at Austin,
United States
Summary:
Moiré superlattices are typically created by stacking and twisting two functional layers, such as graphene and transition metal dichalcogenides (TMDs). Simultaneous changes in electronic and photonic properties as a function of the twist angle often impose undesirable constraints. We have measured the periodic electrostatic potential on the top surface of a twisted hexagonal boron nitride (hBN) substrate and found it to range between 50-400 meV. Furthermore, the inversion symmetry breaking at the interface leads to ferroelectricity. We propose both periodic potential and ferroelectricity of the twisted hBN can be used to modulate the properties of an adjacent functional layer, drastically expanding the range of materials susceptible to moiré engineering. Here, we demonstrate the properties of a semiconductor monolayer MoSe2 can be controlled by the twisted hBN substrate in several ways. First, the in-plane electric field at the FE domain walls leads to a Stark-shifted exciton resonance, similar to those found in semiconductor p-n junctions. Secondly, excitons within the FE domains become localized. Finally, an electric gate can be used to switch the FE domains, manifested in the optical spectra. The light emission from the MoSe2 layer exhibits hysteresis behavior, characteristic of the ferroelectric substrate. These results establish twisted hBN as a versatile platform to modulate the properties of an adjacent functional layer.