Nonlocal transport in Cr-doped (Bi,Sb)₂Te₃: Absence of nonchiral edge states

The quantum anomalous Hall effect shows great promise for the realization of the ohm without the need for an external magnetic field. The most mature material platform is magnetically doped topological insulators. In these materials, precise quantization is limited to low temperatures, with the activation energy for dissipative transport typically in the range of 1 K. One potential source of dissipative transport is nonchiral edge states. These states are expected to be present in sufficiently thick samples. In this work, we perform extensive Hall and nonlocal resistance measurements in a Hall bar geometry at 2 K. We perform 15 distinct measurements on a single device, each independent with respect to device symmetry and Onsager reciprocity. By comparing the results to different transport models, we find that the system behavior is well described by a simple continuum Ohm's law model. The addition of nonchiral edge states to the model does not significantly improve the fitting, and we conclude that there is not strong evidence for these states. We discuss the implications of our results for the prospect of a high-temperature quantized anomalous Hall effect in these materials.