Theoretical and experimental evidence for the intrinsic three-dimensional Dirac state in Cu2HgSnSe4

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 Schr\"odinger 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 $\mathrm{C}{\mathrm{u}}_{2}\mathrm{HgSnS}{\mathrm{e}}_{4}$ 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 $(\ensuremath{\sim}400\phantom{\rule{0.16em}{0ex}}\mathrm{meV})$ on conduction bands of $\mathrm{C}{\mathrm{u}}_{2}\mathrm{HgSnS}{\mathrm{e}}_{4}$, which is self-consistent with linear dispersion detected by angle-resolved photoemission spectroscopy. In electron-doped $\mathrm{C}{\mathrm{u}}_{2}\mathrm{HgSnS}{\mathrm{e}}_{4}$, positive magnetoresistance at low magnetic field $B(<2.5\phantom{\rule{0.16em}{0ex}}\mathrm{T})$ 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 $\mathrm{C}{\mathrm{u}}_{2}\mathrm{HgSnS}{\mathrm{e}}_{4}$, which is attributed to weak localization broken by $B$. Remarkably, the carrier mobility has a ${10}^{5}$-fold decrease when the Fermi level is adjusted from conduction to valence bands. Our results suggest that $\mathrm{C}{\mathrm{u}}_{2}\mathrm{HgSnS}{\mathrm{e}}_{4}$ 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.