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Abstract

Three-dimensional (3D) Dirac and Weyl semimetals are quantum states that have emerged in physics recently. But their intrinsic transport properties are quite elusive because of either the coexistence of Schrödinger fermions or the deviation of linear dispersion at Fermi level in previously proposed Dirac and Weyl semimetals. Here, we provide the theoretical and experimental evidences of an intrinsic Dirac state in the quaternary chalcogenide Cu₂HgSnSe₄ that has bared linear dispersions in conduction bands. Scanning tunneling spectroscopy reveals the quadratic energy-dependent density of states within an extremely large energy range (∼400meV) on conduction bands of Cu₂HgSnSe₄, which is self-consistent with linear dispersion detected by angle-resolved photoemission spectroscopy. In electron-doped Cu₂HgSnSe₄, positive magnetoresistance at low magnetic field B(<2.5T) and negative magnetoresistance under high B are observed, which is attributed to the chiral anomaly effect. However, conventional negative magnetoresistance is observed in hole-doped Cu₂HgSnSe₄, which is attributed to weak localization broken by B. Remarkably, the carrier mobility has a 10⁵-fold decrease when the Fermi level is adjusted from conduction to valence bands. Our results suggest that Cu₂HgSnSe₄ not only provides a playground for exploring intrinsic properties of 3D Dirac fermions but also is promising for developing high-speed, low-dissipation electronic devices.