For getting a first overview of the topic and the published materials, “Google Scholar” is a good start. However, the next step should be the library portal Primo where you can search the catalogues of all university libraries in Berlin and possibly also find online resources. (Tip: It’s worth searching also other university’s libraries as they might possess more specific literature.)
The following pages might be useful as well:
You might also ask your supervisor for help with your search for papers. On the one hand, s/he can mention some introductory material to you, on the other hand, s/he might have extended access to resources that are not free accessible for students.