  Let $X$ be a proper Hadamard space and $\Gamma< Isom(X)$ a non-elementary
discrete group of isometries with a rank one isometry. We discuss and prove
Hopf-Tsuji-Sullivan dichotomy for the geodesic flow on the set of parametrized
geodesics of the quotient of $X$ by $\Gamma$ and with respect to Ricks' measure
introduced in [MR3628926]. This generalizes previous work of the author and J.
C. Picaud on Hopf-Tsuji-Sullivan dichotomy in the analogous manifold setting
and with respect to Knieper's measure.
