  We have developed a method for electrical polarization of nuclear spins in
quantum Hall systems. In a breakdown regime of odd-integer quantum Hall effect
(QHE), excitation of electrons to the upper Landau subband with opposite spin
polarity dynamically polarizes nuclear spins through the hyperfine interaction.
The polarized nuclear spins in turn accelerate the QHE breakdown, leading to
hysteretic voltage-current characteristics of the quantum Hall conductor.
