Time resolved X ray diffraction study on superconducting YBa2Cu3O7 epitaxially grown on SrTiO3 This thesis addresses the lattice response of a compound consisting of a thin superconducting lm and a single crystalline substrate to an ultrafast breaking of superconductivity. The lattice response is investigated by means of time resolved X ray diraction. As X ray source a laser produced plasma is used that emits sub ps Ka bursts. This thesis is organized in the following way: After an introduction to important issues of the physics of high temperature superconductors and SrTiO3 as well as their lattice response the experimental and theoretical methods used in this work are briey introduced. In the following section the experiment is discussed in more detail. Further results from both static and time resolved experiments are presented. For a theoretical discription of the experimental results several models are developed.