  A measurement of spin correlation in $t\bar{t}$ production is presented using
data collected with the ATLAS detector at the Large Hadron Collider in
proton-proton collisions at a center-of-mass energy of 8 TeV, corresponding to
an integrated luminosity of 20.3 fb$^{-1}$. The correlation between the top and
antitop quark spins is extracted from dilepton $t\bar{t}$ events by using the
difference in azimuthal angle between the two charged leptons in the laboratory
frame. In the helicity basis the measured degree of correlation corresponds to
$A_{helicity} = 0.38 \pm 0.04$, in agreement with the Standard Model
prediction. A search is performed for pair production of top squarks with
masses close to the top quark mass decaying to predominantly right-handed top
quarks and a light neutralino, the lightest supersymmetric particle. Top
squarks with masses between the top quark mass and 191 GeV are excluded at the
95% confidence level.
