Ladders of compactly generated triangulated categories and preprojective algebras

In this paper we characterize when a recollement of compactly generated triangulated categories admits a ladder of some height going either upwards or downwards. As an application, we show that the derived category of the preprojective algebra of Dynkin type ${\mathbb{A}}_n$ admits a periodic infinite ladder, where the one outer term in the recollement is the derived category of a differential graded algebra.