Minimal translation surfaces in the Heisenberg group Nil3
  A translation surface in the Heisenberg group $\mathrm{Nil}_3$ is a surface constructed by multiplying (using the group operation) two curves. We completely classify minimal translation surfaces in the Heisenberg group $\mathrm{Nil}_3$. 
J.-I. Inoguchi, R. L\'opez and M.I. Munteanu
math.DG