  The beauty of quantum Hall (QH) effect is the metrological precision of Hall
resistance quantization that originates from the topological edge states.
Understanding the factors that lead to quantization breakdown not only provides
important insights on the nature of the topological protection of these edge
states, but is beneficial for device applications involving such quantized
transport. In this work, we combine conventional transport and real space
conductivity mapping to investigate whether the quantization breakdown is tied
to the disappearance of edge state in the hotly studied MnBi2Te4 system. Our
experimental results unambiguously show that topological edge state does exist
when quantization breakdown occurs. Such edge state is dissipative in nature
and could lead to a quantization breakdown due to its diffusive character
causing overlapping with bulk and other edge states in real devices. Our
findings bring attentions to issues that are generally inaccessible in the
transport study of QH, but can play important roles in practical measurements
and device applications.
