Tunable unconventional Kondo effect on topological insulator surfaces

Abstract

We study Kondo physics of a spin-1 2 impurity in electronic matter with strong spin-orbit interaction, which can be realized by depositing magnetic adatoms on the surface of a three-dimensional topological insulator. We show that magnetic properties of topological surface states and the very existence of Kondo screening strongly depend on details of the bulk material, and specifics of surface preparation encoded in time-reversal preserving boundary conditions for electronic wavefunctions. When this tunable Kondo effect occurs, the impurity spin is screened by purely orbital motion of surface electrons. This mechanism gives rise to a transverse magnetic response of the surface metal, and spin textures that can be used to experimentally probe signatures of a Kondo resonance. Our predictions are particularly relevant for STM measurements in PbTe-class crystalline topological insulators, but we also discuss implications for other classes of topological materials.

Topological phases of topological-insulator thin films

“…Within this layer the wave function varies rapidly satisfying the exact boundary conditions of the full Hamiltonian. This complex behavior can be absorbed into the linearized low energy theory 23,[29][30][31] by imposing a boundary condition that is consistent with particle conservation (so that the resulting Hamiltonian is self-adjoint in the half-space), time-reversal, and inversion symmetry. This boundary condition takes the form Bψ| edge = 0, where the matrix…”

A non-perturbative treatment of quantum impurity problems in real lattices

“…In overall agreement with Ref. [200], Isaev et al [206] demonstrated that strong SOI leads to an unconventional Kondo effect, despite being of the SU(2) kind, with an impurity spin screened by purely orbital motion of surface electrons. At low energies, the impurity spin forms a singlet state with the total electron angular momentum, and the system exhibits an emergent SU(2) symmetry, which is responsible for the Kondo resonance.…”

Rashba-induced Kondo screening of a magnetic impurity in a two-dimensional superconductor

“…For example, the Dzyaloshinsky-Moriya (DM) interaction introduced by Rashba SOC leads to an exponential enhancement of the Kondo temperature, which originates from the exchange coupling between magnetic impurity and conduction electrons with different orbit angular momentum. 33 Similarly, the Kondo screening originating from purely orbital states was predicted for a magnetic impurity on the surface of topological insulator with strong spin-orbit coupling 35 . Different to these papers, in the present work we found that the Rashba interaction not only suppresses the superconducting energy gap, but also introduces an novel Kondo screening channel.…”

“…The Rashba enhanced Kondo screening of magnetic impurity in normal metal has been predicted in many works [33][34][35]40,53,54 . For example, the Dzyaloshinsky-Moriya (DM) interaction introduced by Rashba SOC leads to an exponential enhancement of the Kondo temperature, which originates from the exchange coupling between magnetic impurity and conduction electrons with different orbit angular momentum.…”