Short-range impurity in a magnetic field: The conductance of a narrow channel

We consider a single short-range impurity in a two-dimensional electron-gas channel in a magnetic field. The conductance scrG of the channel with impurity is calculated in terms of the Green's function of the channel without impurity and the impurity scattering length. It is found that a series of downward dips in the graph of scrG versus Fermi energy E exist due to quasibound states with wave functions localized near the impurity. In a strong magnetic field such states exist also for a repulsive impurity and not only below the band bottom of each transverse mode, but also above it.