Finite-dimensional pointed Hopf algebras over finite simple groups of   Lie type IV. Unipotent classes in Chevalley and Steinberg groups
  We show that all unipotent classes in finite simple Chevalley or Steinberg groups, different from PSL_n(q) and PSp_{2n}(q), collapse (i.e. are never the support of a finite-dimensional Nichols algebra), with a possible exception on one class of involutions in PSU_n(2^m). 
Nicol\'as Andruskiewitsch, Giovanna Carnovale and Gast\'on Andr\'es   Garc\'ia
math.QA math.GR