posted on 2021-06-07, 18:36authored byTiancong Zhu, Alexander J. Bishop, Tong Zhou, Menglin Zhu, Dante J. O’Hara, Alexander A. Baker, Shuyu Cheng, Robert C. Walko, Jacob J. Repicky, Tao Liu, Jay A. Gupta, Chris M. Jozwiak, Eli Rotenberg, Jinwoo Hwang, Igor Žutić, Roland K. Kawakami
The
intrinsic magnetic topological insulators MnBi2Te4 and MnBi2Se4 support novel topological
states related to symmetry breaking by magnetic order. Unlike MnBi2Te4, the study of MnBi2Se4 has been inhibited by the lack of bulk crystals, as the van der
Waals (vdW) crystal is not the thermodynamic equilibrium phase. Here,
we report the layer-by-layer synthesis of vdW MnBi2Se4 crystals using nonequilibrium molecular beam epitaxy. Atomic-resolution
scanning transmission electron microscopy and scanning tunneling microscopy
identify a well-ordered vdW crystal with septuple-layer base units.
The magnetic properties agree with the predicted layered antiferromagnetic
ordering but disagree with its predicted out-of-plane orientation.
Instead, our samples exhibit an easy-plane anisotropy, which is explained
by including dipole–dipole interactions. Angle-resolved photoemission
spectroscopy reveals the gapless Dirac-like surface state, which demonstrates
that MnBi2Se4 is a topological insulator above
the magnetic-ordering temperature. These studies show that MnBi2Se4 is a promising candidate for exploring rich
topological phases of layered antiferromagnetic topological insulators.