Oscillatory magnetotransport in the layer compounds 4Hb-TaS2 and 2H-TaSe2

Abstract

Quantum oscillations have been observed in the magnetoresistance and Hall effect of $4Hb$-Ta${\mathrm{S}}_2$ and $2H$-Ta${\mathrm{Se}}_2$ in fields up to 230 kG. For magnetic fields perpendicular to the layers at least twelve frequencies in the range 0.044 to 8.2 MG have been observed in $4Hb$-Ta${\mathrm{S}}_2$. Eleven frequencies in the range 1.6 to 44.6 MG have been observed in $2H$-Ta${\mathrm{Se}}_2$. The angular dependence of the frequencies generally follows functions of the form $\frac{{\omega }_{\perp }}{sin\theta }$, where ${\omega }_{\perp }$ is the frequency observed for field perpendicular to the layers and $\theta$ is the angle between the field and the layers. The angular dependence is consistent with that expected for a nearly two-dimensional cylindrical Fermi surface and the small cross sections corresponding to the observed frequencies indicate that the Fermi-surface sections result from the $3a_0\times 3a_0\times c_0$ charge-density-wave superlattice. Maxima in the magnetoresistance rotation diagrams indicate the presence of open orbits along the $c$ axis in both materials. Features in the field dependence of the magnetoresistance and Hall effect of $4Hb$-Ta${\mathrm{S}}_2$ suggest the presence of magnetic breakdown while the field dependence observed in $2H$-Ta${\mathrm{Se}}_2$ is well behaved although magnetic breakdown may play a role in the orbits associated with the highest frequencies.