[Excerpt] Within the Standard Model flavour changing neutral currents (FCNC) are forbidden at tree level and much smaller than the dominant decay mode (t → bW) at one loop level. Nonetheless, several Standard Model extensions predict higher branching fractions (BR) for the top quark FCNC decays [1], making the search for FCNC processes an important probe for new physics in the top quark sector. In the present analysis [2], the t → qZ decay channel is searched for by looking for top quark pair production with one top quark decaying through FCNC (t → qZ) and the other through the Standard Model dominant mode (t → bW). Only the leptonic decays of the Z and W bosons were considered (Z → e+e−,µ+µ− and W → eν,µν) as signal. ATLAS data collected at a centre-of-mass energy of √s = 7 TeV during 2010 and corresponding to an integrated luminosity of 35 pb−1 are used. Presently, the most stringent experimental limits on BR(t → qZ) were obtained by the DO Collaboration: BR(t → qZ) < 3.2% at 95% confidence level (CL) [3]. [...]