The temperature dependence of the Hall coefficient is measured with high accuracy in a series of ${\mathrm{YBa}}_2({\mathrm{Cu}}_{1-z}{\mathrm{Zn}}_z{)}_3{\mathrm{O}}_{6.78}$ crystals with $0<~z<~\mathrm{0.013.}$ We found that the cotangent of the Hall angle, $\cot {\theta }_H,$ starts to deviate upward from the $T^2$ dependence below $T_0\left(\sim 130\hspace{0.5em}\mathrm{K}\right),$ regardless of the Zn concentration. We discuss that this deviation is caused by the pseudogap; the direction of the deviation and its insensitivity to the Zn doping suggest that the pseudogap affects $\cot {\theta }_H$ through a change in the effective mass, rather than through a change in the Hall scattering rate.

• Received 19 May 1999

DOI:https://doi.org/10.1103/PhysRevB.60.R15055