Dense point spectrum and absolutely continuous spectrum in spherically symmetric Dirac operators. Karl Michael Schmidt — 1995 Forum mathematicum
On the essential spectrum of Dirac operators with spherically symmetric potentials. Karl Michael Schmidt — 1993 Mathematische Annalen
On the genericity of nonvanishing instability intervals in periodic Dirac systems Karl Michael Schmidt — 1993 Annales de l'I.H.P. Physique théorique
A discrete Hardy-Laptev-Weidl-type inequality and associated Schrödinger-type operators. Desmond W. Evans; Karl Michael Schmidt — 2009 Revista Matemática Complutense