Transport properties of quasi-one-dimensional KRu4 O8

We report resistivity, thermopower, Hall coefficient, and magnetic susceptibility of the quasi-one-dimensional (Q1D) hollandite oxide KRu4 O8 with RuO2 zigzag chains made of edge-shared RuO6 octahedra. The resistivity along the chain direction (ρ) is evaluated to be 1.1. μΩcm at 4.2 K, which corresponds to a mean-free path along the chain direction of 2800Å and implies that this material is one of the cleanest systems in Q1D oxides. ρ is found to be proportional to T2.7 below 62 K indicating a strong electron-electron Umklapp scattering. The temperature dependence of the thermopower is also found to derive from the expected conventional T -linear dependence and is approximately proportional to T2 below 156 K. We discuss these peculiar transport properties using several theories for Q1D systems and also make a comparison to three-dimensional systems.