The results of a search for direct pair production
of top squarks in events with two opposite-charge leptons
(electrons or muons) are reported, using 36.1 fb−1 of integrated
luminosity from proton–proton collisions at √s = 13
TeV collected by the ATLAS detector at the Large Hadron
Collider. To cover a range of mass differences between the
top squark t
˜ and lighter supersymmetric particles, four possible
decay modes of the top squark are targeted with dedicated
selections: the decay t
˜ → bχ˜
±
1 into a b-quark and the lightest
chargino with χ˜
±
1 → Wχ˜
0
1 , the decay t
˜ → tχ˜
0
1 into an
on-shell top quark and the lightest neutralino, the three-body
decay t
˜ → bWχ˜
0
1 and the four-body decay t
˜ → bνχ˜
0
1 .
No significant excess of events is observed above the Standard
Model background for any selection, and limits on top
squarks are set as a function of the t
˜ and χ˜
0
1 masses. The
results exclude at 95% confidence level t
˜ masses up to about
720 GeV, extending the exclusion region of supersymmetric
parameter space covered by previous searches.