Unusual magnetotransport from Si-square nets in topological semimetal HfSiS

The class of topological semimetals comprises a large pool of compounds. Together they provide a wide platform to realize exotic quasiparticles, for example, Dirac, nodal-line Dirac, and Weyl fermions. In this Rapid Communication, we report the Berry phase, Fermi-surface topology, and anisotropic magnetoresistance of HfSiS which has recently been predicted to be a nodal-line semimetal. This compound contains a large carrier density, higher than most of the known semimetals. Massive amplitudes of de Haas-van Alphen and Shubnikov-de Haas oscillations up to 20 K in 7 T assist us in witnessing a nontrivial π-Berry phase, which is a consequence of topological Dirac-type dispersion of bands originating from the hybridization of p_x+p_y and d_x²-y² orbitals of square-net plane of Si and Hf atoms, respectively. Furthermore, we establish the three-dimensional Fermi surface which consists of very asymmetric water caltroplike electrons and barley seedlike hole pockets which account for the anisotropic magnetoresistance in HfSiS.