Klein-tunneling-enhanced directional coupler for Dirac electron wave in graphene

Using the coupled-mode theory in guided-wave optics and electronics, we explore a directional coupling structure composed of two parallel waveguides electrostatically induced by the split-gate technique in bulk graphene. Our results show that Klein tunneling can greatly enhance the coupling strength of the structure. By adjusting a gate voltage, the probability density of Dirac electron wave function initially in one waveguide can be completely transferred into the other waveguide within several hundred nanometers. Our findings could not only lead to functional coherent coupling devices for quantum-based electronic signal processing and on-chip device integration in graphene, but also shrink the size of the devices to facilitate the fabrication of graphene-based large-scale integrated logic circuits.