Domain wall induced spin-polarized flat bands in antiferromagnetic topological insulators

E K Petrov,V K Dugaev,T V Menshchikova,I P Rusinov,M Hoffmann,E V Chulkov,V N Men'Shov,A Ernst,M M Otrokov

doi:10.1103/physrevb.103.235142

Abstract

A flat band in fermionic system is a dispersionless single-particle state with a diverging effective mass and nearly zero group velocity. These flat bands are expected to support exotic properties in the ground state, which might be important for a wide range of promising physical phenomena. For many applications it is highly desirable to have such states in Dirac materials, but so far they have been reported only in non-magnetic Dirac systems. In this work we propose a realization of topologically protected spin-polarized flat bands generated by domain walls in planar magnetic topological insulators. Using first-principles material design we suggest a family of intrinsic antiferromagnetic topological insulators with an in-plane sublattice magnetization and a high N\'eel temperature. Such systems can host domain walls in a natural manner. For these materials, we demonstrate the existence of spin-polarized flat bands in the vicinity of the Fermi level and discuss their properties and potential applications.

Highlights

The modern technology proposals require the consideration of quantum effects, which will significantly expand the functionality of new spintronic devices
Total energy calculations show ferromagnetic configuration to be preferable of the three considered magnetic configurations, ferromagnetic (FM), collinear antiferromagnetic and non-collinear antiferromagnetic
These results are supported by the calculated exchange coupling parameters (Fig. 1b), which are mostly positive for the intralayer interaction (J0,i) indicating FM order, whereas the interlayer exchange parameters J⊥0,i are mostly negative, which is a distinct feature of the interlayer AFM order

Summary

INTRODUCTION

The modern technology proposals require the consideration of quantum effects, which will significantly expand the functionality of new spintronic devices. Of great importance is realization of such physical phenomena as various Hall effects[1,2,3], a gate-tunable topological valley transport[4,5,6,7,8] and superconductivity[9,10,11,12,13] In many cases, it can be attained using specific electron states – flat bands – which can arise either because of strong electronic correlations[14,15,16,17] or due to specific structural deformations[18,19]. We propose a way to generate flat bands in magnetic topological insulators (TIs) surfaces, where massless Dirac states and the exchange fields can serve as a platform to create spin-polarized dispersionless states. The latter can appear due to magnetic domain walls (DWs) at the surface. In view of the unique combination of two distinctive properties, flat bands and planar magnetic TIs, we suggest several potential applications such as optical spin manipulations, anomalous Hall effect and superconductive coupling between the neighboring DWs

RESULTS AND DISCUSSION

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CONCLUSION