Efficient cycles of hyperbolic manifolds

Let $N$ be a complete finite-volume hyperbolic $n$-manifold. An efficient cycle for $N$ is the limit (in an appropriate measure space) of a sequence of fundamental cycles whose ${\mathrm{\ell }}^1$-norm converges to the simplicial volume of $N$. Gromov and Thurston’s smearing construction exhibits an explicit efficient cycle, and Jungreis and Kuessner proved that, in dimension $n\ge 3$, such cycle actually is the unique efficient cycle for a huge class of finite volume hyperbolic manifolds, including all the closed ones. In this paper we prove that, for $n\ge 3$, the class of finite-volume hyperbolic manifolds for which the uniqueness of the efficient cycle does not hold is exactly the commensurability class of the figure-8 knot complement (or, equivalently, of the Gieseking manifold).