Anomalous asymmetry of magnetoresistance in NbSe${}_3$ single crystals

A pronounced asymmetry of magnetoresistance with respect to the magnetic field direction is observed for NbSe${}_3$ crystals placed in a magnetic field perpendicular to their conducting planes. It is shown that the effect persists in a wide temperature range and manifests itself starting from a certain magnetic induction value $B_0$, which at $T=4.2$ K corresponds to the transition to the quantum limit, i.to the state where the Landay level splitting exceeds the temperature.