Influence of Rashba spin-orbit coupling on the Kondo effect

An Anderson model for a magnetic impurity in a two-dimensional electron gas with bulk Rashba spin-orbit interaction is solved using the numerical renormalization group under two different experimental scenarios. For a fixed Fermi energy, the Kondo temperature T-K varies weakly with Rashba coupling lambda(R), as reported previously. If instead the band filling is low and held constant, increasing lambda(R) can drive the system into a helical regime with exponential enhancement of T-K. Under either scenario, thermodynamic properties at low temperatures T exhibit the same dependencies on T/T-K as are found for lambda(R) = 0. Unlike the conventional Kondo effect, however, the impurity exhibits static spin correlations with conduction electrons of nonzero orbital angular momentum about the impurity site. We also consider a magnetic field that Zeeman splits the conduction band but not the impurity level, an effective picture that arises under a proposed route to access the helical regime in a driven system. The impurity contribution to the system's ground-state angular momentum is found to be a universal function of the ratio of the Zeeman energy to a temperature scale that is not T-K (as would be the case in a magnetic field that couples directly to the impurity spin), but rather is proportional to T-K divided by the impurity hybridization width. This universal scaling is explained via a perturbative treatment of field-induced changes in the electronic density of states.