Normal-state transport properties of slightly overdoped YBa2Cu3Oy crystals prepared by a crystal-pulling technique

Anisotropic transport properties of high-temperature superconductors were extensively investigated for YBa2Cu3Oy crystals prepared by a crystal-pulling technique. Since the crystals are as large as 4X4x2 mm(3), we have successfully measured their resistivity, Hall coefficient, and thermopower along both the in-plane and out-of-plane directions, by using samples cut from the same crystal. The measured in-plane data have revealed that our samples are slightly overdoped when highly oxygenated. This means that our samples have the least anisotropic resistivities between the in-plane and out-of-plane directions among high-T-c cuprates. The Hall coefficient and the thermopower along the out-of-plane direction qualitatively agree with the band calculation, but the scattering time along the out-of-plane direction is anomalously short. Thus, it is concluded that the two-dimensional nature in the electronic states of high-T-c cuprates is mainly characterized by the anomalously short scattering time along the out-of-plane direction, not by the anisotropic effective masses.