Magnetotransport Properties of the Orbital-Ordered State of Ba^sub 1−x^Sr^sub x^V^sub 13^O^sub 18

Magnetotransport properties were investigated for single crystals of Ba1−xSrxV13O18 (x = 0,0.05,0.2,1), which exhibit an anomalous orbital-ordered state with electrical conduction at low temperatures. It was found that a positive magnetoresistance, which is 30% at a magnetic field of 14 T, appears only in the low-temperature region (T < 10 K) with an anisotropy negligible in the direction of the magnetic field but a small anisotropy in the direction of the electric current. The behavior of the magnetoresistance hardly changes with x, except for a systematic decrease in its absolute value with increasing x. The fitting of the magnetoresistance by a two-carrier model reveals the existence of carriers with a relatively high mobility (∼103 cm2·V−1·s−1). It was also found by Hall measurement that the majority carriers in the orbital-ordered state are electrons and the number of carriers is much larger than that estimated from the magnetoresistance. On the basis of these experimental results, it was speculated that the ground state of this series of compounds is a semimetallic state with a small number of intrinsic electrons and holes with a high mobility, together with an additional larger number of electrons with a lower mobility.