Observation of an anomalous quasi-one-dimensional behavior in Na2Ru4O9-delta single crystals

The magnetic susceptibility chi(parallel to)(H parallel to b), chi(perpendicular to)(H perpendicular to b) (2 less than or equal to T less than or equal to 700 K) and electrical resistivity rho(T) (2 less than or equal to T less than or equal to 300 K) of single crystals Na2Ru4O9-delta (delta greater than or equal to 0) with various oxygen content were measured. The crystal structure is monoclinic with single, double, and triple chains along the b axis. The most striking feature is the drastically large anisotropy reflected in the resistivity which exhibits metallic behavior along chains and semiconducting behavior perpendicular to the chains. The resistivity ratio for these two directions rho(perpendicular to)/rho(parallel to) is larger than 10(5). This ratio is exceptionally large, indicating that the anisotropy of the bandwidth is substantial. While the magnetic susceptibility chi(parallel to)(H parallel to b) undergoes a drastic change due to oxygen removal, the electrical resistivity along the conducting chains rho(parallel to)(T) alters only slightly, however, the resistivity perpendicular to the chain rho(perpendicular to)(T) changes more significantly at low temperatures. It is argued that the different sensitivity to oxygen content reflected in magnetic and transport properties may indicate decoupling of spin and charge, and can be attributed the complexity of the crystal structure.