Skimming the Surface of Magnetic Topological Insulators

Combining topology and magnetism promises a wealth of new phenomena, such as the quantum anomalous Hall effect and axion electrodynamics (see 24 November 2008 Viewpoint). Some of these “goodies” have been observed but only at impractically cold temperatures. Recent efforts have turned toward intrinsically magnetic topological insulators, likeMnBi2Te4, which have the potential to exhibit exotic effects at room temperature. However, three new papers have analyzed the surface states of MnBi2Te4 and found that they lack a feature needed for novel topological behavior: a magnetically induced gap between electronic energy bands. The results suggest that more work is needed to get the right combination of magnetism and topology.