NORMAL-STATE MAGNETOTRANSPORT IN SUPERCONDUCTING TL2BA2CUO6+DELTA TO MILLIKELVIN TEMPERATURES

We report a study of the normal-state Hall effect and magnetoresistanc e of single crystals of Tl2Ba2CuO6-delta. Using samples with T-c<15 K, we can suppress the superconductivity down to low temperatures with m agnetic fields of 16 T, and can thus study the normal state properties over three decades of temperature, extending into the T-->0 limit whe re it is possible to make a reliable estimate of k(F) similar to 0.7 A ngstrom(-1) from the Hall effect in the elastic-scattering regime. The temperature dependence of the Hall coefficient, R(H), below 30 K rule s out models in which R(H)(T) is taken as a measure of a real temperat ure-dependent change in the carrier concentration. The two scattering rates (probed by the resistivity and the cotangent of the Hall angle) which characterize normal-state transport in the cuprates also appear in this overdoped material for T greater than or equal to 30 K. Howeve r, as T-->0, we observe only a single scattering rate, whose temperatu re dependence is dominated by low power terms, in contrast to the T-2 dependence predicted for a Fermi liquid. The relationship between thes e findings and anomalous behavior previously reported for the upper cr itical field is discussed.