  Achieving metrological precision of quantum anomalous Hall resistance
quantization at zero magnetic field so far remains limited to temperatures of
the order of 20 mK, while the Curie temperature in the involved material is as
high as 20 K. The reason for this discrepancy remains one of the biggest open
questions surrounding the effect, and is the focus of this article. Here we
show, through a careful analysis of the non-local voltages on a multi-terminal
Corbino geometry, that the chiral edge channels continue to exist without
applied magnetic field up to the Curie temperature of bulk ferromagnetism of
the magnetic topological insulator, and that thermally activated bulk
conductance is responsible for this quantization breakdown. Our results offer
important insights on the nature of the topological protection of these edge
channels, provide an encouraging sign for potential applications, and establish
the multi-terminal Corbino geometry as a powerful tool for the study of edge
channel transport in topological materials.
