  We have observed hysteresis between the forward and reverse sweeps of a
common mode bias applied to the two in-plane side gates of an asymmetrically
biased GaAs quantum point contact. The size of the hysteresis loop increases
with the amount of bias asymmetry between the two side gates and depends on the
polarity of the bias asymmetry. It is argued that hysteresis may constitute
another indirect proof of spontaneous spin polarization in the narrow portion
of the quantum point contact.
