Majorana fermions in narrow zigzag honeycomb nanoribbons

In this work, we study the generation of Majorana fermions in narrow zigzag honeycomb nanoribbons (ZHNR) deposited over an 's' superconductor. We study the system using an effective minimal model that consists of the first nearest neighbor hopping, Rashba spin-orbit interaction, triplet superconducting pairing between the magnetic moments of the ZHNR edges and an external exchange magnetic field [1].

We present results of the band structure, density of states and conductance for the infinite case as well as the energy spectrum as a function of the chemical potential for the finite one. In the infinite case, the band structure exhibits several topological phase transitions associated with spin-up or spin-down Majorana fermions. The results for the finite ZHNR show an energy spectrum with zero-energy modes at the chemical potential, which are the signature of Majorana fermions. A striking result of the work is that the nanoribbon spins polarize the Majorana fermions, generating regions of chemical potential where there are only spin-up or spin-down zero-energy modes. The results show that the system could develop Majorana half-metallic behavior.

[1] J. H. Correa et.al. PRB 98, 045419 (2018).