Nodal quasiparticle meltdown in ultrahigh-resolution pump-probe angle-resolved photoemission

High-transition-temperature cuprate superconductors are characterized by a strong momentum-dependent anisotropy between the low-energy excitations along the Brillouin zone diagonal (nodal direction) and those along the Brillouin zone face (antinodal direction)-the most striking example of which is the d-wave superconducting gap, with the largest magnitude found in the antinodal direction and no gap in the nodal direction. Furthermore, whereas antinodal quasiparticle excitations occur only below the transition temperature (T c), superconductivity is thought to be indifferent to nodal excitations that are regarded as robust and insensitive to T c. Here we reveal an unexpected link between nodal quasiparticles and superconductivity using high-resolution time-and angle-resolved photoemission on optimally doped Bi₂Sr ₂CaCu₂O₈₊₈. We observe a suppression of the nodal quasiparticle spectral weight following pump laser excitation, and measure its recovery dynamics. This suppression is greatly enhanced in the superconducting state. These results reduce the nodal-antinodal dichotomy and challenge the conventional view of nodal excitation neutrality in superconductivity.