THE UNIVERSALITY OF PSEUDOGAP PHENOMENON IN THE NORMAL STATE OF HIGH TEMPERATURE CUPRATE SUPERCONDUCTORS

Abstract

The pseudogap phenomenon in the normal state of Sn-, Mg- and Cd-doped Hg-1223 ceramic superconductors was studied based on the results of resistivity versus temperature measurement. By using the data obtained in the resistivity measurement a logarithmic deviation of the conductivity versus inverse temperature, i.e. ln [σ(T)-σ N (T)] versus 1/T was constructed to study the pseudogap which is opened at T* far above the critical temperature T C of the superconductors. The magnitude of the pseudogap was measured through the slope of the linear part in these plots. It is surprising that the differentiation of these plots with respect to the inverse temperature shows a constant within very wide temperature range. Similar as in the energy gap measurement in the semiconductors, this constant should represent the pseudogap of the normal state for the materials interested. The occurrence of the characteristic temperatures T*, T S and T F can be interpreted by our microscopic theory. The physical significances of the variation in the magnitude of the pseudogap Δ PG with respect to temperature are related to the kinetic energy of the quasiparticles involved in the system. The plot of T* against the molar fraction of the Sn-doping x is linear. However, the data of T* for the other doping elements Mg and Cd are scattered from the linear relationship for the Sn-doped ( Hg 1-x, Sn x)-1223 system. However, when we plot the relationship between T* against T C , the data of T* for different doping elements fall on the same curve of bend finger-like shape. This indicates that the intrinsic parameters T* and T C satisfy a universal relationship. The ratio Δ PG /(k B T F ) is expressible as a linear function of T C when the critical temperature is below ~ 129 K; while for samples that have critical temperature greater than 129 K this ratio is expressible as a quadratic polynomial function of T C . The universality relationship is also hold for this ratio against T C .