Transport and NQR Studies of Nd _1.6-xCe _xSr _0.4CuO ₄ with T* Structure

Transport and Cu-NQR studies have been carried out for the T*-type high temperature superconducting Cu oxide Nd _1.6-xCe _xSr _0.4CuO ₄ with single layered CuO ₅ planes formed by CuO ₅ pyramids. No anomaly related to the static or quasi static "stripe" order has been observed in the temperature T and x dependence of the thermoelectric powers S. We have not found such kind of anomaly in the x dependence of the superconducting transition temperature T _c, either. Although the decrease of the Cu NQR intensity with decreasing T (wipeout) has been observed in this system, it can be understood by considering the loss of the itinerant nature of the electrons, which takes place in the proximity region of the metal-insulator phase boundary, and cannot be connected with the static or quasi static "stripe" order.