  We propose a magnetic topological transistor based on MnBi$_{2}$Te$_{4}$, in
which the "on" state (quantized conductance) and the "off" state (zero
conductance) can be easily switched by changing the relative direction of two
adjacent electric fields (parallel vs. antiparallel) applied within a
two-terminal junction. We explain that the proposed magnetic topological
transistor relies on a novel mechanism due to the interplay of topology,
magnetism, and layer degrees of freedom in MnBi$_{2}$Te$_{4}$. Its performance
depends substantially on film thickness and type of magnetic order. We show
that "on" and "off" states of the transistor are robust against disorder due to
the topological nature of the surface states. Our work opens an avenue for
applications of layer-selective transport based on the topological van der
Waals antiferromagnet MnBi$_{2}$Te$_{4}$.
