Confinement and edge effects on atomic collapse in graphene nanoribbons

TL;DR

This paper investigates how atomic collapse phenomena in graphene nanoribbons are influenced by edge types and confinement, revealing distinct behaviors in armchair and zig-zag configurations with implications for nanoscale electronic properties.

Contribution

It provides a detailed analysis of atomic collapse in graphene nanoribbons, highlighting the effects of edges and multiple energy bands, which differ from monolayer graphene.

Findings

Armchair nanoribbons show bound states transforming into collapse states with increased impurity charge.

Zig-zag nanoribbons exhibit multiple quasi-one-dimensional bound states from edge states.

Edge states in zig-zag ribbons relocalize from edges to impurity sites as charge increases.

Abstract

Atomic collapse in graphene nanoribbons behaves in a fundamentally different way as compared to monolayer graphene, due to the presence of multiple energy bands and the effect of edges. For armchair nanoribbons we find that bound states gradually transform into atomic collapse states with increasing impurity charge. This is very different in zig-zag nanoribbons where multiple quasi-one-dimensional \emph{bound states} are found that originates from the zero energy zig-zag edge states. They are a consequence of the flat band and the electron distribution of these bound states exhibits two peaks. The lowest energy edge state transforms from a bound state into an atomic collapse resonance and shows a distinct relocalization from the edge to the impurity position with increasing impurity charge.