Experimental Demonstration of a Magnetically Induced Warping Transition in a Topological Insulator Mediated by Rare-Earth Surface Dopants

Magnetic topological insulators constitute a novel class of materials whose topological surface states (TSSs) coexist with long-range ferromagnetic order, eventually breaking time-reversal symmetry. The subsequent bandgap opening is predicted to co-occur with a distortion of the TSS warped shape from hexagonal to trigonal. We demonstrate such a transition by means of angle-resolved photoemission spectroscopy on the magnetically rare-earth (Er and Dy) surface-doped topological insulator Bi2Se2Te. Signatures of the gap opening are also observed. Moreover, increasing the dopant coverage results in a tunable p-type doping of the TSS, thereby allowing for a gradual tuning of the Fermi level toward the magnetically induced bandgap. A theoretical model where a magnetic Zeeman out-of-plane term is introduced in the Hamiltonian governing the TSS rationalizes these experimental results. Our findings offer new strategies to control magnetic interactions with TSSs and open up viable routes for the realization of the quantum anomalous Hall effect.

Automated summary

Magnetic topological insulators with long-range ferromagnetic order and tunable p-type doping of the topological surface states are demonstrated using angle-resolved photoemission spectroscopy on magnetically rare-earth doped topological insulator Bi2Se2Te. The transition from hexagonal to trigonal shape of the TSS and the opening of a bandgap are observed. The experimental results are rationalized by a theoretical model introducing a magnetic Zeeman out-of-plane term in the governing Hamiltonian of the TSS, providing new strategies for controlling magnetic interactions with TSSs and realizing the quantum anomalous Hall effect.