Vanishingly small Maki-Thompson superconducting fluctuation in the magnetoresistance of high-T-c superconductors

The magnetoresistance (MR) of high-T-c cuprate superconductors (HTSC's) is Studied. We have shown that the Zeeman term of the Maki-Thompson (MT) process could not be detected in the longitudinal MR of 90 K YBCO crystals. We show here that the MT process is thought to be also negligible in the transverse MR of 90 K and Zn-doped YBCO crystals. The MR, which has been assigned previously to a MT-orbital process, is more naturally understood as normal-state orbital MR that is proportional to the square of the Hall angle. We conclude that the MT-fluctuation is vanishingly small, at least above T-c, in these HTSC's. In addition to the Hall measurements, MR measurements also support the hypothesis of two distinct relaxation times in HTSC's.