  We compute the rational $\mathfrak{sl}_2$ $R$-matrix acting in the product of
two spin-$\ell\over 2$ (${\ell \in \mathbb{N}}$) representations, using a
method analogous to the one of Maulik and Okounkov, i.e., by studying the
equivariant (co)homology of certain algebraic varieties. These varieties, first
considered by Nekrasov and Shatashvili, are typically singular. They may be
thought of as the higher spin generalizations of $A_1$ Nakajima quiver
varieties (i.e., cotangent bundles of Grassmannians), the latter corresponding
to $\ell=1$.
