Spontaneous Breaking of Isotropy Observed in the Electronic Transport of Rare-Earth Tritellurides

International audienceWe show that the isotropic conductivity in the normal state of rare-earth tritelluride RTe3 compounds is broken by the occurrence of theunidirectional charge density wave (CDW) in the (a, c) plane below the Peierls transition temperature. In contrast with quasi-one-dimensional systems, the resistivity anomaly associated with the CDW transition is strong in the direction perpendicular to the CDW wave vector Q (a axis) and very weak in the CDW wave vector Q direction (c axis). We qualitatively explain this result by calculating the electrical conductivity for the electron dispersion with momentum-dependent CDW gap as determined by angle-resolved photoemission spectroscopy. Similar measurements of in-plane conductivity may uncover the gap anisotropy in other compounds for which angle-resolved photoemission spectroscopy is not available

Strong Effects of Weak Localization in Charge Density Wave/Normal Metal Hybrids

Collective transport through a multichannel disordered conductor in contact with charge-density-wave electrodes is theoretically investigated. The statistical distribution function of the threshold potential for charge-density wave sliding is calculated by random matrix theory. In the diffusive regime weak localization has a strong effect on the sliding motion.Comment: To be published in Physical Review

Optical investigation of the charge-density-wave phase transitions in NbSe3NbSe_{3}

We have measured the optical reflectivity $R(\omega)$ of the quasi one-dimensional conductor $NbSe_{3}$ from the far infrared up to the ultraviolet between 10 and 300 $K$ using light polarized along and normal to the chain axis. We find a depletion of the optical conductivity with decreasing temperature for both polarizations in the mid to far-infrared region. This leads to a redistribution of spectral weight from low to high energies due to partial gapping of the Fermi surface below the charge-density-wave transitions at 145 K and 59 K. We deduce the bulk magnitudes of the CDW gaps and discuss the scattering of ungapped free charge carriers and the role of fluctuations effects

Coherent-noncoherent tunneling crossover in NbSe3-NbSe3 point contacts

International audienceCurrent-voltage (IV) characteristics of NbSe3-NbSe3 artificial contacts (point contacts) formed along the a(*) axis have been investigated in a wide range of contact resistances and temperatures. Depending on the contact resistance, two types of IV characteristics have been observed: the first type observed for low contact resistance demonstrates a conducting peak at zero bias, while the second one for large contact resistance is characterized by a large resistance maximum near the zero bias voltage. Below the second charge-density wave (CDW) transition (T < 59 K), CDW energy gap singularities were observed in the IV characteristics of both types of junctions at V=Delta(p1)/e and V=2 Delta(p2)/e, while the singularity at V=Delta(p2)/e corresponding to the single particle tunneling of carriers noncondensed into the low-temperature CDW is absent. The experimental results are discussed in the frame of the model of interlayer coherent tunneling of the remaining charge carriers that are not condensed into the CDW

Point-contact spectroscopy probing the NbSe3_3 CDW gap in different crystallographic orientations

We have measured the differential current-voltage characteristics of normal metal-NbSe$_3$ direct point contacts (without insulating barrier) formed along different crystallographic orientations under applied magnetic field with different orientations. At low temperature two energy gaps, $\Delta_{p1}$ and $\Delta_{p2}$, corresponding to the high and the low-temperature CDW were observed simultaneously as a singulanty of the excess resistance which is attributed to an analog of Andreev reflection, in which the incident electron reflects on the Peierls energy gap barriers with its charge unchanged. An applied magnetic field up to 8.5 T does not lead to a change in the density of states and in the Peierls energy gaps, suggesting that the large magnetoresistance observed in NbSe$_3$ might not result from the change in the CDW order parameter with magnetic field but rather from the increase of scattering of non-condensed to CDW carriers

Effect of commensurability on the CDW deformation near a point contact

The results of investigation of normal metal(Cu, Au)-CDW (K$_{0.3}$MoO$_3$) point-contacts (PCs) in a wide range of temperature are reported. At ${\rm T}>80$ K the contact characteristics are adequately described by the semiconducting model of CDW. At $T<70$ K the $I-V$ characteristics of PCs Cu-K$_{0.3}$MoO$_3$ demonstrate a strain-compress asymmetry of the CDW. The observed behavior is likely to reveal the lock-in transition (incommensurate-commensurate) due to the electric-field induced strain of the CDW

Transverse voltage in a quasi-one-dimensional NbSe3 conductor with a charge density wave in zero magnetic field

International audienceTransverse voltage in a quasi-one-dimensional NbSe3 conductor with a charge density wave in zero magnetic fiel

Unidirectional charge-density-wave sliding in two-dimensional rare-earth tritellurides

Nonlinear transport properties in the layered TbTe3 and GdTe3 rare-earth tritellurides with a charge- density-wave( CDW) transition above room temperature have been studied along different crystal- lographic orientations.The pronounced effect of collective CDW motion is observed along c-axis andi s absent completely in the perpendicular direction demonstrating the unidirectional character of the CDW.In contrast to one-dimensiona lCDWs the threshold electric field for CDW sliding is linearly temperature dependent in a wide range of temperature

Hall effect in the pinned and sliding charge density wave state of NbSe3

International audienceResults of Hall effect measurements are reported both below and above the threshold electric field, E-t, for depinning the low temperature charge density wave (CDW) in NbSe3 in a wide temperature range. At low electric fields, below E-t, we have observed a change in the sign of the Hall voltage at all temperatures lower than T-p2. Comparison between the Hall effect and the magnetoresistance behavior indicates that the n-type conductivity in the low magnetic field range differs qualitatively from the p-type conductivity in the high field range. We demonstrate that at low temperature the CDW motion significantly alters the Hall voltage. These results indicate that, in NbSe3, the CDW in the sliding state interacts essentially with holes. Possible mechanisms of this effect are discussed

Unusual magnetotransport properties of NbSe3_{3} single crystals at low temperature

A parallel to ($b-c$) plain field Negative magnetoresistance was found at low temperature with the magnetic field applied parallel to ($b,c$) plane of NbSe$_3$ single crystals with a thickness less than some critical value determined by the Larmor diameter. The effect observed is qualitatively explained by a size effect near the transition to the quantum limit