We have observed Shubnikov-de Haas oscillations in the longitudinal magnetoresistance of SnTe, a cubically symmetric, extrinsic ptype semiconductor. 1 " 5 The measurements were made in steady magnetic fields up to 155 kG. Oscillations were detected between 40 and 155 kG, and were seen in samples with carrier concentrations 6 /) between 5xl0 19 and 5xl0 20 cm" 3 . It is very unusual to have observed the Shubnikov-de Haas effect over such a wide range of carrier concentrations. Moreover, the upper limit is some 25 times larger than the highest concentration at which such oscillations have been detected previously in an extrinsic material. 7 It was possible to observe the oscillations at such large carrier concentrations because of the high magnetic field intensities available, and because of the extraordinarily weak "ionized impurity" scattering 8 in SnTe.The results presented here already suggest (1) the orientation of the Fermi surfaces, (2) the presence of a second, lower-lying valence band, and (3) an explanation for several puzzling electrical and elastic measurements obtained earlier. 2 ' 6 ' 9For our as-pulled single crystals, />«5xl0 20 cm"" 3 . We obtained lower p values by diffusion techniques to be described elsewhere. The crystallographic orientations studied included [001], [114], [112], [111], and [110] directions. Measurements were made at 4.2 and 1.4°K. The high, steady magnetic fields were produced in a li-inch inner diameter modified Bitter-type solenoid. 10

Samples of TlBiTe2 and TlTe were prepared and characterized by x-ray powder diffraction, differential thermal analysis, scanning-electron-microscope and electron-microprobe studies, and transport measurements.The two materials were found to be distinctly different with regard to melting point, crystal structure, temperature dependence of the resistivity and Hall coefficient, and sign of the Hall coefficient and thermoelectric power. The Hall mobilities (in cm /V aec) are -84 and +3 at 300 K and -128 and+1120 at 4.2 K for T1BiTet and TlTe, respectively. The temperature dependence of these mobilities, combined with the apparently large carrier densities, suggests that TlBiTe2 is a highly degenerate n-type semiconductor, while TlTe is more likely to be a semimetal. Discontinuities in the resistivity and Hall-coefficient data of TlTe at 170 K suggest the occurrence of a phase change at that temperature.The two sets of results were compared with data on material which had been described by Hein and Swiggard as TlBiTe2, a new nonmetallic superconductor.But the normal-state properties of a portion of this material closely resemble those of T1Te, not TlBiTe2. A search for superconductivity in further samples of both compounds is needed to clarify this situation.

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We have used the de Haas-van Alphen effect and Shubnikov-de Haas effect at temperatures from 1.6 to 7. 9 K to investigate the Fermi surface of SnTe. Nine samples were studied covering a range in carrier concentration from 5&& 10~t o 5&& 10 o cm" . The nature of the data is such that they divide into two regions in carrier concentration, a normal one at or above 3.6x 10 cm and an anomalous one at or below 2.1 x 10 cm" . In the normal region one extremal cross section was observed at each orientation describing a pocket elongated in a (111)direction and located at the L point. In addition, oscillations describing a second set of pockets elongated in a (100) direction were observed. At a carrier concentration of 3.6x 10 cm 3, Dingle temperatures and cyclotron masses of 21.6 K and 0.125nzo and 17.3 K and 0.094mo were measured for the (111) and (100) pockets, respectively. At about this carrier concentration a density of states of 6 x 10 ' (eV cm )~was computed from the data and is in fair agreement with the density of states computed from heat-capacity measurements. In the anomalous region a number of extremal cross sections describing one pocket at the L point were observed at each orientation. The shapes of the constant-energy surfaces described by the data are in poor agreement with the results of existing band calculations.

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