The quantum anomalous Hall (QAH) phase is a two-dimensional bulk ferromagnetic insulator with a nonzero Chern number in the presence of spin-orbit coupling (SOC) but in the absence of applied magnetic fields. Associated metallic chiral edge states host dissipationless current transport in electronic devices and thus promise great applications in low-power-consumption electronic and spintronic devices. This intriguing QAH phase has recently been observed in magnetic impurity-doped topological insulators, albeit, at extremely low temperatures. By first-principles density functional calculations, Guang-Yu Guo (Distinguished Center Scientist & Professor of NTU-Physics) and his collaborators recently demonstrated in a paper published in the Physical Review Letters[1] that layered rhodium oxide K0.5RhO2 in the noncoplanar antiferromagnetic state is anunconventional three-dimensional QAH insulator with a large band gap and a Néel temperature of a few tens of Kelvins. Furthermore, this unconventional QAH phase is revealed to be the exotic quantum topological Hall effect caused by nonzero scalar spin chirality due to the topological spin structure in the system and without the need of net magnetization and SOC.
[1] [1] J. Zhou et al., Phys. Rev. Lett. 116, 256601 (2016)
Figure caption: Atomic and magnetic structures as well as bulk and edge energy bandsof K0.5RhO2, together with anomalous Hall conductivity (sAH) as a function of Fermi energy which shows the quantized conductance within the insulating gap. Also shown are the four noncoplanar magnetic moments within onelayer unit cell that span a sphere and thus generate a Berry phase of 2p (Chern number of 1.0).
