Charge transfer and absence of magnetic proximity effect in EuS(111)/Bi₂Se₃ heterostructures from ab initio calculations

Heterostructures made from magnetic and topological insulators (TIs) promise to form excellent platforms for new electronic and spintronic functionalities. The ferromagnet EuS has emerged as a leading candidate for realizing magnetic proximity effect in these systems. However, detailed understanding EuS/TI interfaces is still lacking. 

To address this, we study the proximity effect in a periodic EuS(111)/Bi₂Se₃ heterostructure with Bi₂Se₃  containing seven quintuple layers (QLs), using density functional theory calculations that include both van der Waals and spin-orbit interactions. Our results show no appreciable magnetic anisotropy at the interface due to spin-orbit interactions. Even though the linear dispersion of the topological surface state (TSS) is gapless, a partial charge transfer from Eu to Se atoms occurs, leading to a 0.4 eV downshifting of the Dirac cone relative the Fermi energy. The associated electrostatic screening moves the TSS from the first to the second QL of the TI. Our analysis indicates no substantial magnetic proximity effect on the TSS.  These results agree with recent experimental measurements. Lastly, we discuss the implications of our findings on the search for materials that enable robust magnetic proximity effect in topological heterostructures.