  Distinctive normal-state properties of cuprate superconductors follow from
their charge carriers forming a large-bipolaron liquid. The very weak
scattering of the slow-moving heavy-massed excitations of the liquid by
acoustic phonons yields a scattering rate that is less than the Debye
frequency. The moderate liquid mobility, greater than 1 cm2/V-sec at 300 K,
results as the weak scattering of the liquid compensates for its large mass. In
resolution of a long-standing dilemma, the dc resistivity resulting from
scattering by acoustic phonons remains nearly proportional to temperature to
well below the Debye temperature. Above the Debye frequency the
frequency-dependent conductivity is dominated by excitation and
photo-ionization of the self-trapped electronic carriers of the
large-bipolarons. Below the Debye frequency the frequency-dependent
conductivity is dominated by the Drude-like collective motion of the
large-bipolaron liquid. The gap between these two domains sharpens with
decreasing temperature as phonon scattering of the liquid diminishes. The
high-frequency electronic excitations survive in the superconducting state.
