  In nodal-line semimetals linearly dispersing states form Dirac loops in the
reciprocal space, with high degree of electron-hole symmetry and
almost-vanishing density of states near the Fermi level. The result is reduced
electronic screening and enhanced correlations between Dirac quasiparticles.
Here we investigate the electronic structure of ZrSiSe, by combining time- and
angle-resolved photoelectron spectroscopy with ab initio density functional
theory (DFT) complemented by an extended Hubbard model (DFT +U +V). We show
that electronic correlations are reduced on an ultrashort timescale by optical
excitation of high-energy electrons-hole pairs, which transiently screen the
Coulomb interaction. Our findings demonstrate an all-optical method for
engineering the band structure of a quantum material.
