Fig. 2: The figure presents a prototypical phase diagram of strongly coupled superconductors and the associated pair chemical potential of these states.

a Shows a prototypical phase diagram for superconductors with strong pairing, in this case for the cuprate⁵⁹. Indicated is the T_c dome, along with the pairing onset temperature T^*. The latter reflects the size of the attractive interaction. This figure represents the effect of changing the attractive interaction (at small T^*/T_c) so that (as in the brown arrow) a state shown by the red triangle can be transformed to a state associated with the blue triangle (at larger T^*/T_c) while keeping the temperature the same. The left-hand edge of the dome corresponds to a relatively strong interaction strength. b Shows the behavior of the bosonic chemical potential for the analogous superconductors associated with the same color codes as for the triangles in (a). Note that systems with larger attraction (larger T^*/T_c) have smaller ∣μ_pair∣ over a more extended range of temperatures.