Observation of bulk nodal lines in topological semimetal ZrSiS

Topological nodal-line semimetals are characterized by protected band crossings along one-dimensional route in the Brillouin zone. Crystalline ZrSiS is the most intensively studied topological nodal-line semimetal candidate, which is proposed to host multiple nodal lines in its bulk electronic structure. However, previous angle-resolved photoemission spectroscopy (ARPES) experiments with vacuum ultraviolet lights mainly probed the surface states. Here using soft X-ray ARPES, we acquire the bulk electronic states of ZrSiS without any interference from surface states, unambiguously demonstrating the existence of bulk nodal lines in ZrSiS. Furthermore, our results show that the whole Fermi surfaces are composed of the Dirac nodal lines on high-symmetry planes, as enforced to pin at the Fermi level by carrier compensation. This means that the carriers in ZrSiS are entirely contributed by Dirac nodal-line fermions, suggesting that ZrSiS is a remarkable platform for studying physical properties related to nodal lines.