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 es tablished from the conductivity measurement results. The plot of the logari thmic deviation in the conductivity, with respect to the normal state condu ctivity, against the inverse temperature shows some characteristic temperat ures T* and T-S, at which the pseudo-gap is opened and the saturation tempe rature of the created quasi-particles in the pseudo gap level. There is ano ther characteristic temperature T-F, which close to the onset critical temp erature of the superconductivity. There is a crossover from the strange met allic 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 o f this linear relationship represents the magnitude of the pseudo-gap Delta (SP)/k(B). The conductivity deviation can be expressed in term of the numb er of quasi-particles.