Electrical control of the Kondo effect in a helical edge liquid

Abstract

Magnetic impurities affect the transport properties of the helical edge states of quantum spin Hall insulators by causing single-electron backscattering. We study such a system in the presence of a Rashba spin-orbit interaction induced by an external electric field, showing that this can be used to control the Kondo temperature, as well as the correction to the conductance due to the impurity. Surprisingly, for a strongly anisotropic electron-impurity spin exchange, Kondo screening may get obstructed by the presence of a non-collinear spin interaction mediated by the Rashba coupling. This challenges the expectation that the Kondo effect is stable against time-reversal invariant perturbations.Comment: 7 pages, 2 figures. Expression for the current operator corrected. (Conclusions unaffected.) Erratum to be publishe

Electrically tunable two-channel Kondo fixed points in helical liquids

“…17 Moreover, the HgTe quantum wells exhibit some of the largest known Rashba couplings of any semiconductor heterostructures. 18 In fact, it was found very recently 12 that the presence of a Rashba coupling has profound effects on both the Kondo temperature and the transport properties of the helical liquids in the presence of a single magnetic impurity.…”

Generic helical edge states due to Rashba spin-orbit coupling in a topological insulator

“…By diagonalization, we see that this often used [31,32] simple model does not introduce a k-dependent B k , since all matrix elements are linear in momentum k. Thereby, it does not give rise to energy-dependent spin orientation and to GHESs, i.e., T s = 0. This is consistent with the lack of the lowest-order inelastic backscattering due to a linear spin-orbit coupling combined with a phonon exchange [23].…”

“…Most studies of inelastic backscattering combine some energyexchange mechanism (e.g., phonons [24] or electron-electron interactions [21,22,24,27]) with a way to manipulate the spin (often some form of spin-orbit coupling [24,26,27]). Scattering of localized spins [29][30][31][32][33] such as magnetic impurities or nuclear spins [34] has also been analyzed.…”

Magnetic ac control of the spin textures in a helical Luttinger liquid

“…Fractional charge in antiparallel magnetic domains [20,21] and the emergence of spin-density waves in the presence of magnetic impurities [22][23][24] represent a strong signature of helical systems. Also the peculiar Kondo screening in the presence of impurity spins has been extensively discussed [1,[25][26][27][28][29][30]. The extreme sensitivity to TR breaking couplings and the fundamental role played by the spin degree of freedom require a careful study of the spin response of helical Luttinger liquids to magnetic perturbations.…”