Quantum transport evidence of isolated topological nodal-line fermions

Topological nodal-line semimetals have been shown interesting anomalous transport responses, dictated by the nontrivial band topology, with rich topological structures. However, their transport signatures have often been masked by the complexity in band crossings or the coexisting topologically trivial states. Here we show that, in slightly hole-doped SrAs₃, the single-loop nodal-line states are well-isolated from the trivial states and entirely determine the transport responses. Shubnikov-de Hass oscillations in SrAs₃ confirm dominant charge conduction by nodal-line fermions and identify its tubular Fermi surface, thinnest among those of known nodal-line semimetals, and the characteristic smoke-ring-type pseudospin texture. These unique characters of nodal-line fermions lead to the significantly enhanced quantum interference effect, resulting in the largest weak antilocalization contribution to electric conduction among topological semimetals, making the isolated nodal-line fermions in SrAs₃ desirable for novel devices based on their topological charge and spin transport.