Figure 6. Schematic pairing gap evolution based on our ARPES results.

(a) Temperature variation of the point nodal d-wave pairing gap. The energy gap has a BCS-type function (inset curve) with the same onset at T_pair regardless of directions (φ) along the Fermi surface. Temperatures for each curve are indicated in the inset with coloured circles. The gapped Fermi surface with a point node below T_c (b) persists beyond T_c (c) up to the temperature of pair formation (T_pair). (d) Emergence of the gapless Fermi arc centered at the node due to the pseudogap evolution around the antinode9,27; while the antinodal region is not observable at the low photon energies like 7 eV, the studies with higher energy photons have demonstrated that the competing pseudogap state emerges at |φ|>25° in the optimal doping9.