The main topic of this thesis is an inquiry into the origin of low-energy excitations of the electron-doped high-temperature superconductor Nd 2 _xCexCu0 4 (0 :::; x :::; 0.23) which lead to anomalously high electronic contributions 1 to the specific heat. Apart from studies on the temperature and magnetic-field dependence of the specific heat at various Cerium concentrations, especially electrical transport properties of normal conducting, overdoped single crystals and thin films have been

more »

... stigated down to mK temperatures in magnetic fields up to 11 T. Sampie quality played a crucial role and is reported in detail. For all Ce-doped samples (x 2:: 0.05) a linear term 1T was found at temperatures below 300 mK, with 0.3 J /K 2 :::;