METAL-SEMICONDUCTOR TRANSITION AND LUTTINGER-LIQUID BEHAVIOR IN QUASI-ONE-DIMENSIONAL BAVS3 STUDIED BY PHOTOEMISSION SPECTROSCOPY

The quasi-one-dimensional conductor BaVS3 exhibits successive phase transitions at approximately 240 K (linear chains to zigzag chains), approximately 70 K (metallic to semiconducting), and approximately 35 K (paramagnetic to antiferromagnetic). We have made high-resolution ultraviolet-photoemission-spectroscopy (UPS), x-ray-photoemission-spectroscopy, electrical-resistivity, and magnetic-susceptibility measurements on BaVS3. UPS spectra near the Fermi level of the metallic phase exhibit a power-law dependence on the electron binding energy, indicating that conduction electrons in BaVS3 behave as a Luttinger liquid. The power-law exponent is large ( < approximately 1), indicating that electron-electron interaction is long ranged and possibly that electron-phonon interaction is also important. The spectra exhibit gradual changes with temperature. In particular, a semiconducting gap starts to open well above the metal-to-semiconductor transition temperature and fully develops below it. We propose that the gradual orthorhombic distortion of the Jahn-Teller type below approximately 240 K lowers one of the d levels, d(xy), and that below approximately 70 K electrons are fully transferred to the d(xy) band. The d(xy) band then becomes half-filled, resulting in the opening of a Mott-Hubbard gap.