Macroscopic channel-size effect of nonequilibrium electron distributions in quantum Hall conductors.

We have studied the channel-size dependence of nonequilibrium electrons excited into higher Landau levels in a quantum Hall conductor, by mapping cyclotron emission in Hall bars of different sizes. The images obtained reveal that the spatial evolution of the nonequilibrium electrons with current density significantly depends on the channel width of the Hall bar on a macroscopic scale of several hundred microms. This observation provides clear evidence of a macroscopic channel-size effect, which can be reasonably understood as originating from a very long equilibrium length of the excited electrons.