Luttinger liquid behaviour of Li0.9Mo6O17 studied by scanning tunnelling microscopy
Scanning tunnelling spectroscopy (STS) was used to study the Luttinger liquid behaviour of the purple bronze Li0.9Mo6O17 in the temperature range 5 K < T < 300 K. In the entire temperature range the suppression of the density of states at the Fermi energy can be fitted very well by a model describing the tunnelling into a Luttinger liquid at ambient temperature. The power-law exponent extracted from these fits reveals a significant increase above 200 K. It changes from α = 0.6 at low temperature to α = 1.0 at room temperature.
Probing Localization Effects in Li0.9Mo6O ;17 Purple Bronze: An Optical-Properties Investigation
We report the polarized reflectance and optical conductivity of the quasi-one-dimensional conductor ${\mathrm{Li}}_{0.9}{\mathrm{Mo}}_{6}{\mathrm{O}}_{17}$ as a function of temperature. The compound displays an unusual (non-Drude-type) mobile carrier response at low-energy, with partially screened vibrational features along the highly conducting b axis. In addition, we observe Mo $\stackrel{\ensuremath{\rightarrow}}{d}d$ transitions near 0.42, 0.57, and 1.3 eV, and an O $\stackrel{\ensuremath{\rightarrow}}{p}\mathrm{Mo}d$ charge-transfer band near 4 eV. Perpendicular to the b axis, ${\mathrm{Li}}_{0.9}{\mathrm{Mo}}_{6}{\mathrm{O}}_{17}$ exhibits semiconducting behavior with an optical gap of 0.4 eV and electronic structure similar to that of the b axis at higher energies. The substantial temperature dependence of the vibrational modes in this direction reveals that the lattice of ${\mathrm{Li}}_{0.9}{\mathrm{Mo}}_{6}{\mathrm{O}}_{17}$ is not rigid. However, no noticeable change in the lattice through the 25 K metal-insulator transition is observed. Comparing x-ray and infrared data for several model materials, we establish an upper bound on the size of any lattice distortion in ${\mathrm{Li}}_{0.9}{\mathrm{Mo}}_{6}{\mathrm{O}}_{17}.$ Based upon these combined results, we argue that localization effects dominate the bulk and microscopic properties of this material.
Long Ceramic Beam Tubes for Accelerator Magnets
The ceramic beam tubes for the fast and abort kickers and the bucker and pinger magnets used at Fermilab must meet a number of exacting requirements. The tubes must be long and sufficiently straight so as not to limit magnet design. They must have wall strength capable of withstanding the atmospheric and mechanical forces encountered during construction and operation. Vacuum tight ceramic to stainless steel transitions must be of reasonable cost; they must also withstand high temperature processing and remain vacuum tight to the 10/sup -9/ Torr range. To remove the possibility of static charge buildup each tube must have a surface coating of indium oxide applied to the inner wall. This thin coating is difficult to achieve and requires the most careful attention to detail. The methods used at Fermilab to achieve these goals are presented in this paper.