While CeCu6 is a Pauli-paramagnetic heavy-fermion (HF) system, Au doping introduces long-range incommensurate antiferromagnetism for x>xc≈0.1. At the critical concentration xc, the system experiences a quantum phase transition (QPT). Here, both unusual magnetic fluctuations, studied by inelastic neutron scattering, and non-Fermi-liquid behavior, i.e. to anomalous low-temperature thermodynamic and transport properties have been observed. We report on Hall effect measurements that probe the electronic structure of heavy fermions across the critical concentration xc of the QPT.