Observation of well-defined quasiparticles at a wide energy range in a quasi-two-dimensional system

We report an observation of a highly anisotropic Dirac-cone structure, and its unconventional electronic behaviors, in high quality SrMnBi₂ crystal by angle-resolved photoemission spectroscopy measurement. We observed a well-defined sharp quasiparticle peak in a wide energy range, linearly dispersive, forming a highly anisotropic holelike Dirac cone (v_F₁/v_F₂~5--6). The density of state remains linear, and the scattering rate of the quasiparticle increases linearly as a function of binding energy up to higher binding energy. The results contrast with the expectation for a two-dimensional (2D) or three-dimensional (3D) Fermi-liquid theory and rather suggest the existence of a two-dimensional electron gas system in this 3D material, making SrMnBi₂ a potentially useful 2D-electron-gas-encapsulated material.