  Doorway states, which are related to the strength function phenomenon and
giant resonances, arise when two systems interact, one with a high density
eigenvalue spectrum and the other with a comparatively low density. These
concepts, first studied in nuclear physics in the 40's, are here analyzed from
a theoretical point of view in special and simple graphene structures, obtained
after applying appropriate voltages to a graphene sheet. The influence of the
doorway states on the electronic transport in these systems is also studied. To
analyze these effects we consider a two-dimensional model of two potential
barriers of equal height but very different widths separated by a well.
