Effects of the pseudogap and the Fermi surface on the rapid Hall-coefficient changes in cuprates

High-$T_c$ cuprates are characterized by strong spin fluctuations, which give rise to antiferromagnetic and pseudogap phases and may be key to the high superconducting critical temperatures observed in these materials. Experimental studies have revealed significant changes in the Hall coefficient $R_H$ across these phases, a phenomenon closely related to both spin fluctuations and changes in the Fermi surface morphology. Using the perturbation correction to Gaussian approximation (PCGA), we investigate the two-dimensional(2D) square-lattice single-band Hubbard model and obtain the self-energy with a finite imaginary part due to scattering. We calculate the density dependence of the Hall number $n_H=1/(qR_H)$. For small hole (or electron) doping $p$ (or $x$), our numerical results show that $n_H$ transitions from $p$ to $1+p$ for hole-doped systems, and from $-x$ to $1-x$ for electron-doped systems -- both in agreement with experimental findings. Furthermore, we discuss the correlation between phase boundaries and the observed peculiar changes in the Hall number.