Magnetic and transport studies of barium ruthenate

BaRuO₃ is a quasi-one-dimensional material with segmented chains of RuO₆ octahedra along the c-axis. Well-characterized single crystals of the four-layer hexagonal (4H) and nine-layer rhombohedral (9R) crystallographic forms of BaRuO₃ were studied under a wide range of physical conditions. Measurements of the electrical resistivity and magnetization were made over the temperature range 20mK–1040K in magnetic fields ranging from 0–18T. Both materials are metallic above T_MI = 40K (4H) or 118K (9R) Based on optical measurements, the 4H material shows the onset of a charge density wave (CDW) state at T_CDW = 240K and an opening of a pseudogap in the Fermi surface. However, the system remains metallic above T_MI due to incomplete gapping at the Fermi surface. The 9R system, while showing signs of being on the verge of a CDW state, does not order. The transition from metallic to non-metallic behavior in this system is driven by a reduction in the concentration exceeding the enhancement of the mean free path of free charge carriers. Shubnikov-de Haas and de Haas-van Alphen oscillations are observed in the 4H material. The results indicate frequencies of oscillation of 400, 650 and 9300 T, a cyclotron mass of 2.25 m_o, and a Dingle temperature of 1.91 K.