Abstract

Quasi one-dimensional (Q1d) systems are strongly correlated materials exhibiting some of the most fasci- nating phenomena in condensed matter physics, scal- ing from commensurate/incommensurate spin/charge or- ders/waves to singlet/triplet superconductivities. The building blocks of these materials are chains of atoms or (planar) molecules (case of organic conductors) with large orbital overlaps along a favored direction result- ing in a broad partially filled electronic band. The rich physical properties arising from the weak interactions enhanced by the low dimensionality of the band have been thoroughly investigated over the last 4 decades resulting in deep understanding of the underlying physics.

An appealing way of putting new elements into the problem is by crossing the broad Q1d band by a partially filled narrow band. If the interactions are weak with respect to the broad band but strong with respect to the narrow band, a whole new field of physical varieties results from the fine interplay between the two sets of electrons. We will demonstrate that the BaVS3 family of materials is ideally suited for studying such a complex array of physical properties. It is a Q1d system consisting of V-3d1 chains, which displays a unique collection of correlation-driven phenomena, including a metal- insulator transition driven by the charge-density wave and/or the spin-density wave as well as a pressure- dependent crossover between the non-Fermi-liquid and Fermi-liquid behaviors. In an attempt to understand better these and many other properties, we have undertaken a systematic experimental study of BaVS3 and related compounds. The primary measurements carried out were those of the transport properties, resistivity and thermo-electric power (TEP) as functions of temperature (from 2 to 600 K), pressure (up to 3 GPa) and magnetic field (up to 12 T). In addition to the transport measurements, the strong changes in the electrical and magnetic properties of the system around TMI were followed by magnetic susceptibility, angle-resolved photoelectron spectroscopy (ARPES) and frequency-dependent conductivity. As a result we are suggesting a p-T phase diagram. Observed physical properties are interpreted in the framework of the two band model i.e. by the subtle interplay between the two sets of electrons.