Coulomb gap in the quantum Hall insulator

We calculate numerically the spectrum of disordered electrons in the lowest Landau level at filling factor 1/5 using the self-consistent Hartree-Fock approximation for systems containing up to 400 flux quanta. Special attenti on is paid to the correct treatment of the q = 0 component of the Coulomb i nteraction. For sufficiently strong disorder, the system is an insulator at this filling factor. We observe numerically a Coulomb gap in the single-pa rticle density of states (DOS). The DOS agrees quantitatively with the pred ictions for classical point charges.