Since this is an unlikely process, the germanium crystal still acts as an insulator. What Dubon, Walukiewicz and Haller found was that pressure applied along one direction changed the electron orbitals around the copper atoms, effectively enlarging these orbitals enough so that even at low concentrations they overlapped and permitted conduction. The overlapping orbitals of the dopant atoms themselves form their own separate band, with properties that depend on charge and electron spin. Uniaxially stressed copper-doped germanium is free of these problems and represents a pristine case of isolated Hubbard bands. The placement of the copper is random, but its electronic structure is a completely delocalized extended state.
Random systems are much more difficult to study than crystals, but also much more common.
Haller agrees that the possibilities are numerous. We have seen this huge physical effect, an increase in conductivity of many orders of magnitude achieved simply by applying pressure. And it is intrinsically interesting to be able to study the Hubbard band in a new state, clearly separated from the valence band of germanium. We can do that for the first time.