Effects of high magnetic fields on charge-density waves inNbSe3

The magnetotransport properties of ${\mathrm{NbSe}}_3$ in the temperature range below the second charge-density-wave (CDW) onset of 59 K have been studied in magnetic fields up to 230 kG. At liquid-helium temperatures giant magnetoquantum oscillations caused by magnetic breakdown (MB) between the normal Fermi surface (FS) and open orbits on the nested sheets of the FS dominate the magnetotransport and are extremely sensitive to the pinned CDW configuration. Spatial variations in the phase of the pinned CDW change the local Fermi level and CDW gap, giving rise to a distribution of FS cross-sectional areas. These variations in FS cross section and CDW gap produce frequency shifts, amplitude modulations, and beat structures in the quantum oscillations observed in both the magnetoresistance and Hall effect. A model conductivity tensor has been developed describing the open-orbit network and MB interference as well as the closed-orbit contribution. The adjustable parameters of the model are the frequency of oscillation, the frequency-distribution spread ΔF, and critical MB parameter ${\omega }_0$τ.