Transport properties and low temperature structural phase transition around x=0.125 in La 2−x−yRE ySr xCuO 4 (RENd, Sm, Gd, Tb)

Abstract

In La 1.9−itxGd 0.1Sr x CuO 4, a prominent change of the thermoelectric power S below ∼80K is observed in a narrow region of x around 0.12 although the structural phase transition to the tetragonal low-temperature (TLT) phase is observed at ∼ 115K in a wide region of x. These results suggest that the anomalous behaviors of the transport properties below ∼80K are responsible for the change of the electronic state itself. In La 1.875− y Gd y Sr 0.125CuO 4, T u ittd β, which is the structural phase transition temperature to the TLT pahse, increases with increasing y. The temperature where S begins to decrease rapidly is close to T u dβ in y≤0.04. In y≥0.05, a prominent change of S is observed below a lower temperature than T u dβ and an obvious sign reversal of S appears appears at ∼40K. These results indicate that the change of the electronic state is enhanced in the TLT phase.