Generic model with unconventional Rashba bands and giant spin galvanic effect

In a two-dimensional system, Rashba spin-orbit coupling can lift spin degeneracy and give the opposite spin chirality to two split Fermi circles from two Rashba bands. Here, we propose a generic model that can produce unconventional Rashba bands. In such cases, the two Fermi circles from the two bands exhibit the same spin chirality. When various interactions are taken into account, many unique physics can emerge in systems with unconventional Rashba bands compared to those with conventional Rashba bands. For instance, we study the spin galvanic effect by considering two cases: one with potential impurity scattering and the other with magnetic impurity scattering. In both cases, we find that the efficiency of the spin galvanic effect is strongly enhanced in unconventional Rashba bands compared to conventional Rashba bands. More intriguingly, we find that the efficiency of conventional Rashba bands is insensitive to either potential or magnetic impurity scattering. However, the efficiency of unconventional Rashba bands can be further enhanced by magnetic impurity scattering compared to the potential impurity scattering. Thus, unconventional Rashba bands can produce giant spin galvanic effect. These results demonstrate that this model is useful for exploring abnormal physics in systems with unconventional Rashba bands.