vorgelegt von

Crucial to the development of a microscopic theory of high transition temperature (high-Tc) superconductivity in the cuprates is the knowledge of the symmetry of the order parameter characterizing the pairing of electrons in the superconducting state. Cuprate superconductors with various crystal structures are known; however, all of them exhibit a common feature, the copper oxide (CuO2) plane where Cooper pairs form. A cuprate essentially consisting of CuO2 planes is therefore of special interest because secondary effects, possibly stemming from too complex crystal structures, can be ruled out in advance. This thesis explores the order parameter symmetry of such a simple cuprate, the electron-doped infinite-layer cuprate Sr1−xLaxCuO2 (SLCO), denoted as the parent structure of high-Tc superconductors. Four kinds of samples were fabricated and investigated, SLCO thin films, SLCO/gold/niobium planar tunnel junctions (PTJs), SLCO grain boundary Josephson junctions (GBJs), and an SLCO tetracrystal superconducting quantum interference device (SQUID). Strong evidence for a predominant dx2−y2-wave (d-wave) symmetry of the orde