We have used electrical resistivity and X-ray diffraction measurements to study SmTe2_ x (x ~0.1)... more We have used electrical resistivity and X-ray diffraction measurements to study SmTe2_ x (x ~0.1). The crystal structure is highly two-dimensional, but no evidence was found at room temperature for either charge density wave or ordered defect structures. Unlike the previously studied Sm polytellurides, the electrical resistivity of SmTel 9 is insulating, but displays a similar large electronic anisotropy.
We have carried out angle resolved photoemission spectroscopy of SmTe 3 , a quasi-two-dimensional... more We have carried out angle resolved photoemission spectroscopy of SmTe 3 , a quasi-two-dimensional material with an incommensurate high-temperature charge density wave (CDW). This is the first direct experimental view of the full detail of an imperfectly nested Fermi surface, and the momentum space gap anisotropy, for an incommensurate CDW. [S0031-9007(98)06715-5]
We report the presence of charge-density waves ͑CDW's͒ in the planar square lattices of the layer... more We report the presence of charge-density waves ͑CDW's͒ in the planar square lattices of the layered compounds LaTe 2Ϫx Sb x for 0рxр1, which we have studied through electron microprobe analysis, powderand single-crystal x-ray diffraction, and transmission electron microscopy. We have identified superlattice reflections with wave vectors spanning large parallel sheets of Fermi surfaces derived from extended-Hückel tight-binding band calculations performed on two-dimensional Te square sheets. As Sb substitutes for Te in LaTe 2 , the band filling of the square sheets is continuously decreased, with essentially no deviation from the LaTe 2 substructure. Through the series, the CDW wave vector follows the changes in the Fermi surface. The CDW's are observed at room temperature and we see no evidence of significant disorder effects with Sb doping. This work establishes LaTe 2Ϫx Sb x as a family of materials in which the CDW is dependent on Fermi-surface energetics, in contrast to other CDW materials in which lattice strain forces the structural distortion to remain commensurate. ͓S0163-1829͑96͒00140-3͔
We demonstrate that the rare-earch polychalcogenides Sm2Te5 and SmTe3 are metals and despite opti... more We demonstrate that the rare-earch polychalcogenides Sm2Te5 and SmTe3 are metals and despite optimal Fermi surface nesting contain undistorted tellurium square lattice sheets. Our resistivity measurements reveal a n extremely large electrical anisotropy for both Sm polytellurides. Single-crystal X-ray structure refinements of both phases show highly isotropic metallic tellurium atoms. Magnetic susceptibility measurements reveal that the Sm valence is close to 3. For SmTe3 and SmzTe5 the resistivity perpendicular to the plane of the layers is quadratic in temperature, with P coefficients which are 5-6 orders of magnitude larger t h a n those of simple metals. These results firmly establish that the rareearth polychalcogenides as a family span the metal-insulator boundary.
We have used electrical resistivity and X-ray diffraction measurements to study SmTe2_ x (x ~0.1)... more We have used electrical resistivity and X-ray diffraction measurements to study SmTe2_ x (x ~0.1). The crystal structure is highly two-dimensional, but no evidence was found at room temperature for either charge density wave or ordered defect structures. Unlike the previously studied Sm polytellurides, the electrical resistivity of SmTel 9 is insulating, but displays a similar large electronic anisotropy.
We have carried out angle resolved photoemission spectroscopy of SmTe 3 , a quasi-two-dimensional... more We have carried out angle resolved photoemission spectroscopy of SmTe 3 , a quasi-two-dimensional material with an incommensurate high-temperature charge density wave (CDW). This is the first direct experimental view of the full detail of an imperfectly nested Fermi surface, and the momentum space gap anisotropy, for an incommensurate CDW. [S0031-9007(98)06715-5]
We report the presence of charge-density waves ͑CDW's͒ in the planar square lattices of the layer... more We report the presence of charge-density waves ͑CDW's͒ in the planar square lattices of the layered compounds LaTe 2Ϫx Sb x for 0рxр1, which we have studied through electron microprobe analysis, powderand single-crystal x-ray diffraction, and transmission electron microscopy. We have identified superlattice reflections with wave vectors spanning large parallel sheets of Fermi surfaces derived from extended-Hückel tight-binding band calculations performed on two-dimensional Te square sheets. As Sb substitutes for Te in LaTe 2 , the band filling of the square sheets is continuously decreased, with essentially no deviation from the LaTe 2 substructure. Through the series, the CDW wave vector follows the changes in the Fermi surface. The CDW's are observed at room temperature and we see no evidence of significant disorder effects with Sb doping. This work establishes LaTe 2Ϫx Sb x as a family of materials in which the CDW is dependent on Fermi-surface energetics, in contrast to other CDW materials in which lattice strain forces the structural distortion to remain commensurate. ͓S0163-1829͑96͒00140-3͔
We demonstrate that the rare-earch polychalcogenides Sm2Te5 and SmTe3 are metals and despite opti... more We demonstrate that the rare-earch polychalcogenides Sm2Te5 and SmTe3 are metals and despite optimal Fermi surface nesting contain undistorted tellurium square lattice sheets. Our resistivity measurements reveal a n extremely large electrical anisotropy for both Sm polytellurides. Single-crystal X-ray structure refinements of both phases show highly isotropic metallic tellurium atoms. Magnetic susceptibility measurements reveal that the Sm valence is close to 3. For SmTe3 and SmzTe5 the resistivity perpendicular to the plane of the layers is quadratic in temperature, with P coefficients which are 5-6 orders of magnitude larger t h a n those of simple metals. These results firmly establish that the rareearth polychalcogenides as a family span the metal-insulator boundary.
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Papers by Enzo Dimasi