  The Coulomb gap in the single particle density of states (DOS) is a universal
consequence of electron-electron interaction in disordered systems with
localized electron states. Here we show that in arrays of monodisperse metallic
nanocrystals, there is not one but three identical adjacent Coulomb gaps, which
together form a structure that we call a "Coulomb gap triptych." We calculate
the DOS and the conductivity in two- and three-dimensional arrays using a
computer simulation. Unlike in the conventional Coulomb glass models, in
nanocrystal arrays the DOS has a fixed width in the limit of large disorder.
The Coulomb gap triptych can be studied via tunneling experiments.
