In a metal the resistivity at low temperatures is dominated by electron–electron scattering in combination with umklapp scattering. For a Fermi liquid, the resistivity from this mechanism varies as T 2 , which is often taken as an experimental check for Fermi liquid behaviour (in addition to the linear temperature-dependence of the specific heat), although it only arises in combination with the lattice. In certain cases, umklapp scattering is not required. For example, the resistivity of compensated semimetals scales as T 2 because of mutual scattering of electron and hole. This is known as the Baber mechanism.