Changes in the transport properties and the suppression of superconductivity in La 2-x-y Nd y Ba x CuO4 at x=1/8

Abstract

Superconductivity of La2-xBaxCuO4 is severely suppressed in a narrow range of xaround 1/8, accompanied by a low-temperature structural phase transition at the temperature T d2. In this study, a series of polycrystalline samples of La2-x-y NdyBaxCu04 was prepared with a fixed value of x (x=1/8) and varied values of y. The interplay among the transport properties, superconductivity and structure was investigated by electrical resistivity, thermoelectric power and diamagnetic susceptibility, as well as by low-temperature powder X-ray diffraction. The results show a sharp decrease of thermopower below the temperature (T min) at which the resistivity takes the minimum. With increasing Nd concentration T d2 increases from 65K (y=0) up to 135K (y=0.60). In contrast, T min shows a much weaker /dependence. From these results, it is clear that the anomalies of the transport properties do not occur at the structural phase transition temperature T d2. This behavior is consistent with the formation of charge density waves in the TLT phase, as suggested from the recent neutron diffraction as well as from electron diffraction experiments.