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Current-voltage characteristics, voltage oscillations and NMR on the same Rb0.30MoO3 crystal at 77 K are presented. The 1/2,-1/2; transition at V0=80 MHz of 87Rb nuclei broadened by the CDW modulation is motionally narrowed for bias currents exceeding threshold for non-linear conduction. Calculation of the lineshapes, assuming a partial depinning of the sample, leads to excellent agreement with experiment. An estimate of the ratio of the average current density and voltage oscillation frequency in the depinned region agrees roughly with phenomenological models. A CDW phase correlation time of single domains is deduced to be τ=200 μS.

The molybdenum bronzes A0·30MoO3, A0·9Mo6O17 and Mo4O11 oxides all show low-dimensional electronic properties, due to anisotropic crystal structures, which lead to charge-density-wave (CDW) instabilities. In the CDW states of the quasi-one-dimensional blue bronzes, non-linear transport properties are attributed to the sliding of the CDW. A lock-in transition from an incommensurate to a commensurate CDW is found in the best crystals. The non-linear properties are associated with noise voltage at both low (around 1 Hz) and high (around 10 kHz) frequencies as well as with hysteresis and time-dependent phenomena, showing the importance of metastability. The purple bronzes A0·9Mo6O17 and the oxides η-MO4O11 and γ-Mo4O11 have quasi-two-dimensional properties and quasi-cylindrical Fermi surfaces. In the CDW state, galvano-magnetic studies indicate the presence of small electron and/or hole pockets induced by the CDW gap openings. In the bronze Li0·9Mo6O17, the low-temperature properties reflect the comp...

The purple molybdenum bronze K0–9Mo6O17 is a trigonal, quasi-two-dimensional metal which shows an electronic transition at 120 K. In this paper are reported specific-heat data which provide evidence that a second-order phase transition takes place at this temperature, with an entropy change of the order of 0·5 J mol−1 K−1. Both X-ray diffuse scattering and electron diffraction studies have established that this transition is accompanied by a structural transition towards a commensurate 2a × 2a × c state. All the results are consistent with a model of a Fermi-surface-driven instability. The temperature dependence of the charge-density-wave gaps, as well as the nature of the nesting at the Fermi surface, are also discussed.

Far-infrared reflectance of ${\mathrm{Rb}}_{0.3}$${\mathrm{MoO}}_{3}$ for both polarizations (E\ensuremath{\parallel}b) and (E\ensuremath{\perp}b) at 300 K and at 9 K, below the Peierls transition temperature, are presented. Models of the frequency-dependent optical conductivity are used to fit the data. At 9 K, for the (E\ensuremath{\parallel}b) polarization, the existence of a Peierls gap and midgap states are observed along with phase phonons. For the (E\ensuremath{\perp}b) polarization, 41 phonons are detected at 9 K. Comparison with the phonons detected at 300 K shows that some of them have their oscillator strength affected by the onset of the charge-density wave.

In order to study the modification of the transport properties of NaxWO3 by substitution in the WO3 sublattice, single crystals of tantalum-substituted tungsten bronzes of formula NaxTayW1−yO3 have been grown by electrolytic reduction of fused Na2WO4WO3Ta2O5 mixtures. The lattice constant of their cubic perovskite like structure increases with Ta content. Electric conductivity measurements on NaxTayW1−yO3 single crystals characterize a metal-non metal transition when x-y, i.e. the number of d electrons, decreases. This transition seems to be of Anderson type.

The magnetic properties, the Mossbauer resonance between 2 K and 300 K, the low temperature specific heat have been studied on Eu 0.08 MoO 3 : a new molybdenum bronze. The magnetic transition which takes place at 4.3 K is due to the ordering of the Mo V spin and not to the europium which stays in a trivalent state in the explored temperature range.

Current-voltage characteristics, voltage oscillations and NMR on the same Rb0.3MoO3 crystal at 77 K are presented. The 1 2 , − 1 2 transition at ν0=80 MHz of 87Rb nuclei broadened by the CDW modulation is motionallu narrowed for bias currents exceeding threshold for non-linear conduction. Calculation of the lineshapes, assuming a partial depinning of the sample, leads to excellent agreement with experiment. An estimate of the ratio of the average current density and voltage oscillation frequency in the depinned region agrees roughly with phenomenological models. A CDW phase correlation time of single domain is deduced to be τ=200 μS.

International audience; We present recent results obtained using angle-resolved photoemission spectroscopy performed on 1T-TiSe2. Emphasis is put on the peculiarity of the bandstructure of TiSe2 compared to other transition metal dichalcogenides, which suggests that this system is an excellent candidate for the realization of the excitonic insulator phase. This exotic phase is discussed in relation to the BCS theory, and its spectroscopic signature is computed via a model adapted to the particular bandstructure of 1T-TiSe2. A comparison between photoemission intensity maps calculated with the spectral function derived for this model and experimental results is shown, giving strong support for the exciton condensate phase as the origin of the charge density wave transition observed in 1T-TiSe2. The temperature-dependent order parameter characterizing the exciton condensate phase is discussed, both on a theoretical and an experimental basis, as well as the chemical potential shift occurring in this system. Finally, the transport properties of 1T-TiSe2 are analyzed in the light of the photoemission results.

Magnetoresistance, magnetization and 57 Fe Mossbauer studies in K 0.9 Mo 6 O 17 single crystals are reported. A large and positive magnetoresistance, sigmoidal magnetization curves and a quadrupole splitting of the Mossbauer spectrum are found at low temperatures. The results are discussed in relation with the onset of a charge density wave below 120 K.

Transport properties, electrical resistivity, thermopower and magnetoresistance, have been studied of Li 0.9 Mo 6 O 17 single crystals, which show a superconducting transition at 1.9 K. The thermopower is found hole-like, decreasing with increasing temperature above 50 K. The upper critical field and its anisotropy is also obtained from resistivity measurements.