Dragging excitation characteristics from thermoelectric power in Bi-2(Sr2-yLay)CuO6+delta single crystals

The ab-plane thermoelectric power (S) of Bi-2201 single crystals is used to establish the superconducting phase diagram that shows two branches, one m atching the general curve for cuprates and a singular one, apparently linke d to structural disorder. The low maximum T-c of 18 K allows us to follow t he sequence S(T) curves over a large absolute temperature range in the norm al state for both the under- and overdoped regions. The results support a d rag mechanism. A simplified model is used to make a quantitative characteri zation of the dragging excitations through their effective number of modes as well as the temperature dependence of their specific heat. This analysis points out relations between the phase diagram and the spectral shift and rearrangement of the excitation modes.