RESUMO
Breaking the symmetry in the out-of-plane direction in two-dimensional materials to trigger distinctive electronic properties has long been predicted. Inspired by the recent progress in the experimental synthesis of a sandwiched S-Mo-Se structure (Janus SMoSe) at the monolayer limit [Zhang et al., ACS Nano, 2017, 11, 8192-8198], we investigate the transport and electronic structure of two-faced XMoY monolayers (X, Y = O, S, Se and Te) through first-principles calculations. It is found that all the monolayers are semiconductors except OMoTe, which is metallic. Interestingly, the "parents" of OMoTe (MoO2 and MoTe2) are both semiconductors. Further analysis shows that it is the out-of-plane asymmetry-induced strain that results in the metal-semiconductor transition between Janus OMoTe and its parents. By increasing the ratio of O atoms in one face of MoTe2, a progressive decreasing trend of the bandgap, as well as the transition to metallic, is found. In addition, a transition from the direct band gap semiconductor to the indirect one is also observed in the process. This could be used as an effective way to precisely control electronic structures, e.g., the bandgap. Different from other methods, this method uses the intrinsic features of the material, which can persist without the need of additional equipment. Moreover, such a modulating method is expected to be extended to many other transition-metal chalcogenides, showing great application potential.
RESUMO
Bernal-stacked bilayer graphene has rich ground states with various broken symmetries, allowing the existence of magneto-optical (MO) effects even in the absence of an external magnetic field. Here we report controllable Faraday rotation (FR) of bilayer graphene induced by electrostatic gate voltage, whose value is 10 times smaller than the case of single layer graphene with a magnetic field. A proposed bilayer graphene-based microcavity configuration enables the enhanced FR angle due to the large localized electromagnetic field. Our results offer unique opportunities to apply bilayer graphene for MO devices.
RESUMO
A magneto-optical tunable device based on a one-dimensional magnetophotonic crystal infiltrated with a nematic liquid crystal has been proposed. By applying a tunable electric field the voltage-induced reorientation of the director results in an alternating magneto-optical effect. The transfer matrix method was performed to verify the controllable magneto-optical properties. The present results may be useful for future application of liquid crystal-based tunable magneto-optical devices.
RESUMO
A tunable optical Tamm state is investigated in a magnetophotonic crystal with nematic liquid crystals. It is revealed that the intra-Brillouin-zone bandgaps exist and clearly depend on the applied voltages. We find that the optical Tamm state does occur at the boundary between two photonic crystals, one of which is composed of two dielectric materials and the other that consists of a nematic liquid crystal and a magnetic material. A shift of the optical Tamm state with the applied voltage, which stems from the change in the dielectric permittivity of the nematic liquid crystal, is observed. This novel scheme offers a possibility of controlling the optical Tamm state in magnetophotonic crystals induced by nematic liquid crystals.