Study of hot electrons in topological nodal-line semimetal ZrSiS using time- and angle-resolved photoemission spectroscopy*

We have studied 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. The transient ARPES spectra in the vicinity of the nodal-line bulk states and surface states are individually measured using pump-probe scans employing 1.2 eV pump and 21.8 eV probe pulses. Our data reveals 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). Furthermore, the relaxation process of the hot electrons in the nodal-line bulk states exists not only a fast decay of ~700 fs, but also a second slow decay (> 6 ps) process, which indicates the existence of a second filling channel in the nodal-line bulk states. Our studies reveal the unique ultrafast properties of the hot electrons in the nodal-line semimetal ZrSiS.