Tunable persistent currents in a spin-orbit coupled pseudospin-1 fermionic quantum ring

Abstract: We conduct a thorough study of the persistent currents in a spin-orbit coupled ${\alpha}-T_3$ pseudospin-1 fermionic quantum ring (QR) that smoothly interpolates between graphene (${\alpha} = 0$, pseudospin-1/2) and a dice lattice (${\alpha} = 1$, pseudospin-1). In particular, we have considered both intrinsic spin-orbit coupling (ISOC) and Rashba spin-orbit coupling (RSOC) in addition to an external magnetic field, and have systematically enumerated their individual and combined effects on the charge, valley and the spin-polarized persistent currents. The energy levels of the system comprise of the conduction bands, valence bands, and flat bands which show non-monotonic dependencies on the ring radius, R of the QR, in the sense that, for small R, the energy levels vary as 1/R, while the variation is linear in R for large R. The cases corresponding to zero magnetic fields are benchmarked with those for finite external fields. Further, it is noted that the flat bands demonstrate dispersive behavior, and hence can contribute to the transport properties only when ISOC is non-zero. Moreover, the RSOC yields spin-split bands, thereby contributing to the spin-resolved currents, together with distinct degeneracies for different spin branches. The persistent currents in the charge, valley, and spin sectors for each of these cases oscillate as a function of the magnetic field with a period equal to the flux quantum, as they should be, and depend upon the spin-orbit coupling terms. Further, we have explored the role played by the parameter ${\alpha}$ in our entire analysis to ascertain the effect of the flat bands.