Hall Coefficient of High-T_c Superconductors in aModified Bipolaron Model

Using non-rigid bipolaron model modified with the correction of pseudogap effect, we have studied the temperature (T) dependence of the Hall coefficient (R_H) in the normal state of several typical high-T_c superconductors (e.g. YBa₂Cu₃O_7-δ). The results are in agreement with experiments. It is suggested that the positive maximum in the R_H-T diagram corresponds to a point near the bottom of the pseudogap. We have also found that for these high-T_c superconductors, W-T can be scaled into a single universal function form, where W is the bandwidth of the non-rigid bipolaron system.