Figure 2

Figure 2: (a) The “preformed pairs” picture of cuprate superconductivity. Here the pairing energy scale (Tp) falls but the phase coherence energy scale (Tθ) rises with increasing doping. The zero resistance Tc is set by the smaller of the two energy scales, so optimal Tc is defined by the crossing of the two lines. (b) The “2-gap” picture of cuprate superconductivity is supported by the authors’ previous work showing that the d-wave gap saturates in underdoped cuprates, while a larger gap in a different region of k-space continues to grow with underdoping [15]. ( Panel (b) adapted from A. Pushp et al. [15].)