Electron Flow in Circular n-p Junctions of Bilayer Graphene

TL;DR

This paper theoretically investigates electron wave functions in circular n-p junctions of bilayer graphene, revealing caustic formations and differences from monolayer graphene due to Klein tunneling effects.

Contribution

It provides a detailed analysis of wave function behavior in bilayer graphene n-p junctions, highlighting differences from monolayer graphene and explaining the underlying physics.

Findings

Wave functions form caustics inside the circular region.

Shape of caustics described by geometrical optics with negative refractive index.

Strong focusing effect is absent in bilayer graphene.

Abstract

We present a theoretical study of electron wave functions in ballistic circular n-p junctions of bilayer graphene. Similarly to the case of a circular n-p junction of monolayer graphene, we find that (i) the wave functions form caustics inside the circular region, and (ii) the shape of these caustics are well described by a geometrical optics model using the concept of a negative refractive index. In contrast to the monolayer case, we show that the strong focusing effect is absent in the bilayer. We explain these findings in terms of the angular dependence of Klein tunneling at a planar n-p junction.