Thermal excitation relevant to the pseudo-gap phenomenon in the normal state of high temperature superconductors

The thermal excitation spectrum relevant to the pseudo gap phenomenon is established from the conductivity measurement results. The plot of the logarithmic deviation in the conductivity, with respect to the normal state conductivity, against the inverse temperature shows some characteristic temperatures T* and T-S, at which the pseudo-gap is opened and the saturation temperature of the created quasi-particles in the pseudo gap level. There is another characteristic temperature T-F, which close to the onset critical temperature of the superconductivity. There is a crossover from the strange metallic state to the pseudo-gap state within the temperature interval DeltaT = T* - T-S. In the temperature interval DeltaT = T-S - T-F, the plot of ln[1/rho (T) - 1/rho (N)(T)] vs. 1/T exhibits linear relationship. The slope of this linear relationship represents the magnitude of the pseudo-gap Delta (SP)/k(B). The conductivity deviation can be expressed in term of the number of quasi-particles.