Edge-dependent optical absorption of silicene nanoribbons in an in-plane magnetic field

We theoretically study the low energy electronic structures and optical conductivities of silicene nanoribbons (SiNRs) with zigzag and armchair edges in the presence of an in-plane magnetic field. It is found that the absorption spectrum exhibits a rich structure and remarkably depends on the edge types and the width of the SiNRs. In particular, the helical edge states for the zigzag SiNRs is gapped by the magnetic field, whereas those for the wide armchair SiNRs remain gapless, which could be demonstrated by the optical absorption measurement in experiments.