Tunneling measurements of the Coulomb pseudogap in a two-dimensional electron system in a quantizing magnetic field

We study the Coulomb pseudogap for tunneling into the two-dimensional elect ron system of high-mobility (Al,Ga)As/GaAs heterojunctions subjected to a q uantizing magnetic field at filling factor v less than or equal to 1. Tunne l current-voltage characteristics show that for the double maximum observed in the tunnel resistance at v approximate to 1 the pseudogap is linear in energy with a slope that depends on filling-factor, magnetic field, and tem perature. We give a qualitative account of the filling-factor dependence of the pseudogap slope, and we confirm the recently reported appearance of an other relaxation time for tunneling at v approximate to 1. For the tunnel r esistance peaks at v = 1/3 and 2/3 a completely different behavior of the c urrent-voltage curves is found and interpreted as manifestation of the frac tional gap.