Shubnikov-de Haas oscillations and Fermi surfaces in transition-metal pentatellurides ZrTe₅and HfTe₅

Abstract

Shubnikov-de Haas (SdH) oscillations are reported for well characterised crystals of the anisotropic conductors ZrTe5, HfTe5 and Hf0.88Zr0.12Te5. In each material, only one cross sectional frequency dominates the oscillations below the temperature of the resistivity anomaly. Shapes of the Fermi surface (FS) are deduced from the dependence of the extremal FS cross sections on the angle between the crystallographic axes of the sample and the magnetic field. The FS obtained is a long cigar-shaped ellipsoid, which indicates the quasi-two-dimensional character of the electronic properties in these pentatellurides. The temperature dependence (0.32<T<4.2 K) of the amplitudes of the SdH oscillations has been studied to determine the cyclotron effective masses for dominant FS cross sections. The high-field Hall coefficient at 1.2 K shows clearly that at least two types of electrons contribute to the low-temperature conduction. The observed FSS in ZrTe5 and HfTe5 supply 78 and 68% of the total carriers estimated from the high-field Hall coefficient. The conductivity calculated by using the values of the carrier density and the Dingle temperature is the major part of the conductivity at low temperatures in ZrTe5 and HfTe5. Low-temperature electronic band structure is discussed on the basis of the electronic band calculation of Whangbo et al. (1982).