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We present a detailed ARPES investigation of the RTe 3 family, which sets this system as an ideal "textbook" example for the formation of a nesting driven Charge Density Wave (CDW). This family indeed exhibits the full range of phenomena that can be associated to CDW instabilities, from the opening of large gaps on the best nested parts of Fermi Surface (FS) (up to 0.4eV), to the existence of residual metallic pockets. ARPES is the best suited technique to characterize these features, thanks to its unique ability to resolve the electronic structure in k-space. An additional advantage of RTe 3 is that the band structure can be very accurately described by a simple 2D tight-binding (TB) model, which allows one to understand and easily reproduce many characteristics of the CDW. In this paper, we first establish the main features of the electronic structure, by comparing our ARPES measurements with Linear Muffin-Tin Orbital band calculations. We use this to define the validity and limits of the TB model. We then present a complete description of the CDW properties and, for the first time, of their strong evolution as a function of R. Using simple models, we are able to reproduce perfectly the evolution of gaps in k-space, the evolution of the CDW wave vector with R and the shape of the residual metallic pockets. Finally, we give an estimation of the CDW interaction parameters and find that the change in the electronic density of states n(E f ), due to lattice expansion when different R ions are inserted, has the correct order of magnitude to explain the evolution of the CDW properties.

The Fermi surface of rare-earth tri-tellurides (RTe3) is investigated in terms of the nesting driven charge-density wave formation using positron annihilation and first-principles LMTO calculations. Fermi surface nesting is revealed as a strong candidate for driving charge-density wave formation in these compounds. The nesting vector obtained from positron annihilation experiments on GdTe3 is determined to be q = (0.28 ± 0.02, 0, 0) a * , (a * = 2π/a), in excellent agreement with previous experimental and theoretical studies.

The charge density wave transition is investigated in the bi-layer family of rare earth tritelluride RTe3 compounds (R = Sm, Gd, Tb, Dy, Ho, Er, Tm) via high resolution x-ray diffraction and electrical resistivity. The transition temperature increases monotonically with increasing lattice parameter from 244(3) K for TmTe3 to 416(3) K for SmTe3. The heaviest members of the series, R = Dy, Ho, Er, Tm, are observed to have a second transition at a lower temperature, which marks the onset of an additional CDW with wavevector almost equal in magnitude to the first, but oriented in the perpendicular direction.

We report the simultaneous measurement of the structural and electronic components of the metal-insulator transition of VO2 using electron and photoelectron spectroscopies and microscopies. We show that these evolve over different temperature scales, and are separated by an unusual monoclinic-like metallic phase. Our results provide conclusive evidence that the new monoclinic-like metallic phase, recently identified in high-pressure and nonequilibrium measurements, is accessible in the thermodynamic transition at ambient pressure, and we discuss the implications of these observations on the nature of the MIT in VO2.PACS numbers: 71.30.+h, 71.27.+a, 79.60.-i The metal-insulator transition (MIT) of VO 2 is one of the most intensively studied examples of its kind, and yet it continues to surprise and inform us: some recent examples include the observation of its solid-state triplepoint, which is remarkably found to lie at the ambient pressure transition temperature, 1 and the peculiar nanosized striped topographical pattern that has been found in strained VO 2 films.2,3 Moreover, the phase transition itself faces renewed questions as to its origin and mechanism following the discovery at high pressure, and in nonequilibrium experiments, of a metallic state of monoclinic symmetry, 4-6 which beforehand had universally been the reserve of the insulating state in experiments. Very recently, the decoupling of the structural and electronic phase transitions has been confirmed in the related compound, V 2 O 3 .7 In part, the widespread interest that VO 2 has attracted is owed to the accessibility of its sharp, 8 ultrafast 9 transition, occurring in the bulk at 65• C at ambient pressures, coupled with the rich tunability of its properties with alloying and strain 10-12 and flexibility in fabrication 13 that make it a promising candidate for device application. 14In the bulk, the MIT of VO 2 is accompanied by a large structural distortion that has added to the difficulties in unraveling its origins. The high temperature metallic phase resides in the tetragonal rutile structure (isostructural with TiO 2 ). Below the first-order transition temperature, V-V dimers form, accompanied by the twisting of the VO 6 octahedra, as the structure is distorted into the insulating monoclinic M 1 phase. A second insulating monoclinic structure (M 2 ), in which one-half of the V atoms dimerize, is accessible through Cr doping 10 and strain.12 On the one hand, the dimerization has been considered a hallmark of the Peierls transition, in which the rearrangement of the lattice plays the key role. On the other hand, several experiments have made it clear that electron-electron correlations cannot be ignored, 15 and should be considered on at least an equal footing. 16We report the direct observation of the structural and electronic components of the transition in strained VO 2 by simultaneously combining powerful spatial and energy resolved probes of the crystal and electronic structure. We further show that the recently-observed monoclinic ...