Oscillatory magnetotransport in NbSe3and TaSe3

Abstract

Shubnikov-de Haas oscillations in Nb${\mathrm{Se}}_3$ and Ta${\mathrm{Se}}_3$ have been observed in the field range 0-170 kG using both ac and dc techniques. The Fermi-surface sections have been tracked over a substantial angular range and the observed anisotropies are consistent with elongated ellipsoids. In Nb${\mathrm{Se}}_3$ a single section with a minimum frequency of 0.28 MG dominates the oscillatory behavior and develops a strong harmonic content at high fields. Fits of the data to expressions including the spin splitting of the Landau levels gives a minimum $g$ factor of 3.2 and a Dingle temperature of $T_D=2.3\mathrm{}$ K. The temperature dependence of the amplitude gives an effective mass of 0.24 for this section. The Hall effect has also been measured in Nb${\mathrm{Se}}_3$ and shows a sign change from positive to negative as the temperature is decreased below the 59-K transition in Nb${\mathrm{Se}}_3$. No significant change is observed near the 145-K transition. In Ta${\mathrm{Se}}_3$ at least 20 frequencies in the range 0.7-22 MG have been observed and these exhibit a distribution of fairly strong amplitudes with no single frequency dominating. The crystals of Nbs${\mathrm{Se}}_3$ and Ta${\mathrm{Se}}_3$ are of comparable quality and resistance ratio so the results indicate that the Fermi surfaces have quite different parameters in the two metals.