Search for supersymmetric partners of the top quark in events with two leptons in the final state with the ATLAS experiment at the LHC

The search for Supersymmetric extensions of the Standard Model (SUSY) remains a hot topic in high energy physics in the light of the discovery of the Higgs boson with mass of 125 GeV. Supersymmetric particles can cancel out the quadratically-divergent loop corrections to the Higgs boson mass and can explain presence of Dark Matter in the Universe. Moreover, SUSY can unify the gauge couplings of the Standard Model (SM) at high energy scales. Under certain theoretical assumptions, the supersymmetric partner of the top quark, i.e. the top squark, is preferred to be lighter than one TeV and its discovery can thus be accessible at the LHC. This thesis describes a search for pair production of top squarks in final states with two leptons with the ATLAS experiment at the LHC, using 4.7 inverse fb and 20.3 inverse fb of proton-proton collisions at a center of mass energy of 7 TeV and 8 TeV, respectively. No excess over the SM predictions has been observed and results of the searches are used to place exclusion limits on the parameters of the models.