Distinguishing surface and bulk electromagnetism via their dynamics in an intrinsic magnetic topological insulator

Project Summary: The indirect exchange interaction between local magnetic moments via surface electrons has been long
predicted to bolster the surface ferromagnetism in magnetic topological insulators (MTIs), which facilitates the quantum anomalous
Hall effect. This unconventional effect is critical to determining the operating temperatures of future topotronic devices. The experimental confirmation of this mechanism remains elusive, especially in intrinsic MTIs. The Yang group at University of Chicago, in collaboration with the 2DCC external user Zhang group at University of Florida and 2DCC, have unveiled the unique electromagnetism at the surface of an intrinsic MTI MnBi2Te4 by combining two advanced time-domain spectroscopies: time- and angle-resolved photoemission spectroscopy (trARPES) and time-resolved magneto-optical Kerr effect (trMOKE). By combining these surface- and bulk-sensitive techniques with the theoretical support, the team has identified a unique 2D Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction on the surface of MnBi2Te4. This mechanism directly explains the sizable gap in the quasi-2D electronic state and the nonzero residual magnetization in even-layer MnBi2Te4. These findings open up new possibilities for the effective manipulation of magnetism and topological orders in future topotronic devices.

Publication: Khanh Duy Nguyen et al., Science Advances 10, eadn5696 (2024).

2DCC Role:This research resulted from a close collaboration between 2DCC, Prof. Zhang and Prof. Yang. The 2DCC’s ability of growing high-quality MnBi2Te4 crystals made this impactful work possible.