  Usually the conductivity is quantized as the inverse of the resistivity,
\rho=hc/ie^2, \sigma=ie^2/hc and the velocity versus the electric field is
linear, v=\mu E where \mu is the mobility of the electrons.However,when the
applied electric field exceeds a certain value, microwaves are emitted and the
relation v=\mu E breaks down so that the velocity actually reduces as E
increases. In this region, when magnetic field is applied, the conductivity
quantizes like the magnetic field, i.e., in units of hc/e which is different
from the usual quantization. Because of the flux quantization, the resistivity
will touch zero in the region of high electric field. Factors like 4/5 arise
due to new spin dependence of the effective charge.
