We investigate a magnetic proximity effect on Dirac surface states of topological insulator (TI) induced by a Bi2Se3/EuS interface, using density-functional theory (DFT) and a low-energy effective model, motivated by a recent experimental realization of the interface. We consider a thin ferromagnetic insulator EuS film stacked on top of Bi2Se3(111) slabs of three or five quintuple layers (QLs) with the magnetization of EuS normal to the interface (z axis), which breaks both time-reversal and inversion symmetry. It is found that a charge transfer and surface relaxation makes the Dirac cones electron-doped. For both 3 and 5 QLs, the top-surface Dirac cone has an energy gap of 9 meV, while the bottom surface Dirac cone remains gapless. This feature is due to the short-ranged induced magnetic moment of the EuS film. For the 5 QLs, an additional Dirac cone with an energy gap of 2 meV is formed right below the bottom-surface Dirac point, while for 3 QLs, there is no additional Dirac cone. We also examine the spin-orbital texture of the Dirac surface states with broken inversion symmetry, using DFT and the effective model. We find that the pz orbital is coupled to the z component of the spin moment in the opposite sign to the px and py orbitals. The pz and radial p orbitals are coupled to the in-plane spin texture in the opposite handedness to the tangential p orbital. The result obtained from the effective model agrees with our DFT calculations. The calculated spin-orbital texture may be tested from spin-polarized angle-resolved photoemission spectroscopy.
@article{arxiv.1407.6268,
title = {Magnetic proximity effect at Bi$_2$Se$_3$/EuS interface with broken inversion symmetry},
author = {Alex Taekyung Lee and Myung Joon Han and Kyungwha Park},
journal= {arXiv preprint arXiv:1407.6268},
year = {2014}
}