Figure 4. Evidence for the point nodal gap surviving above T_c revealed by means of the energy shift of spectral leading edge.

(a) The temperature evolution of ARPES spectra (EDCs) at the gap node for OP92K, normalized to the peak intensity of each curve. (b–d) The same spectra as a, but measured off the node (colour circles in the inset of e). (e–h) Temperature dependence of the spectral leading edge, ɛ_LE(T), defined as energies where the spectral peaks become half in intensity (marked by arrows in a–d). The bottom panels of f–h plot the difference of ɛ_LE(T) from the T-linear behaviours (red dashed lines), which are fit to ɛ_LE(T) at high temperatures. The onset temperatures of the deviation from T-linear behaviour are around 135 K for all the k_F points off the node (dashed circles). A kink is seen in the difference curve for f (small black arrow) because the thermally populated Bogoliubov peaks in the unoccupied side significantly affect the shapes of leading edge specially at k_Fs close to the node with small gaps. The inset of e shows the Fermi surface with the examined k_F points. The bold orange arrow indicates the momentum region where the Fermi arc was previously claimed to emerge at T_c.