Universal scaling behavior of pseudogap with doping in high Tc cuprates;   temperature and doping dependence of spectral intensity
  Based on our improved SU(2) slave-boson approach (Phys. Rev. B 64, 052501(2001)) to the t-J Hamiltonian, we report a scaling behavior of pseudogap with doping and the temperature and doping dependence of spectral functions. In addition we discuss the cause of hump and quasi-particle peak in the observed spectral functions of high Tc cuprates. It is demonstrated that the sharpening of the observed quasi-particle peak below Tc is attributed to the bose condensation of holon pair. From the computed ratios of pseudogap $\Delta_0$ to both the superconducting temperature Tc and the pseudogap temperature $T^*$ as a function of hole doping concentration x, we find that there exists a universal scaling of these ratios with doping, that is, the hyperbolic scaling behavior of the former, $\frac{2 \Delta_0}{k_B T_c} \sim x^{-\alpha}$ with $\alpha \sim 2$ and near doping independence of the latter, $\frac{2 \Delta_0}{k_B T^*} \approx 4 \sim 6$ are found. 
Sung-Sik Lee and Sung-Ho Suck Salk