Studying ultrafast hot electron dynamics in topological nodal-line semimetal ZrSiS using XUV-based time- and angle-resolved photoemission spectroscopy*

We study the ultrafast hot electron cooling process on topological nodal-line semimetal ZrSiS using an advanced XUV-based time- and angle-resolved photoemission spectroscopy (trARPES) with sub-30 meV energy resolution and 320 fs time resolution. By scanning the delay, the transient ARPES spectra on the nodal-line bulk states and surface states are measured, separately. We find that the relaxation decay of the transient electronic temperature in the nodal-line bulk states (around 700 fs) is longer than the surface states (around 320 fs). More interestingly, the relaxation process of the hot electron temperature in the nodal-line bulk states contains contributions from multiple channels. Our studies reveal the unique ultrafast properties of the hot electrons in the nodal-line semimetal ZrSiS.