An extended infrared study of the p, T phase diagram of the p-doped Cu-O plane

The ab-plane optical conductivity of 11 single crystals, belonging to the families Sr(2-x)CuO(2)Cl(2), Y(1-x)Ca(x)Ba(2)Cu(3)O(6), Bi(2)Sr(2-x)La(x)CuO(6) and Bi(2)Sr(2)CaCu(2)O(8), has been measured with hole concentrations p between 0 and 0.18 and for 6 K <= T <= 500 K to obtain an infrared picture of the p, T phase diagram of the Cu-O plane. At extreme dilution (p = 0.005), a narrow peak is observed at 1570 cm(-1) (195 meV), which we assign to a single-hole bound state. For increasing doping, that peak broadens into a far-infrared (FIR) band whose low-energy edge sets the insulating gap. The insulator-to-metal transition (IMT) occurs when the softening of the FIR band closes the gap, thus evolving into a Drude term. In the metallic phase, a multi-band analysis identifies a mid-infrared band which weakly depends on temperature and softens for increasing p, while the extended-Drude analysis leads to an optical scattering rate larger than the frequency, as was found in other cuprates. The infrared spectral weight W(T) is consistent with a Fermi liquid renormalized by strong correlations, provided that the T(4) term of the Sommerfeld expansion is included above 300 K. In the superconducting phase, the optical response of single-layer Bi(2)Sr(2-x)La(x)CuO(6) at optimum doping is similar to that of the corresponding optimally doped bilayer Bi(2)Sr(2)CaCu(2)O(8).