Electronic band structures in solids stem from a periodic potential reflecting the structure of either the crystal lattice or electronic order. In the stoichiometric ruthenate Ca₃Ru₂O₇, numerous Fermi surface-sensitive probes indicate a low-temperature electronic reconstruction. Yet, the causality and the reconstructed band structure remain unsolved. Here, we show by angle-resolved photoemission spectroscopy, how in Ca₃Ru₂O₇ a C₂-symmetric massive Dirac semimetal is realized through a Brillouin-zone preserving electronic reconstruction. This Dirac semimetal emerges in a two-stage transition upon cooling. The Dirac point and band velocities are consistent with constraints set by quantum oscillation, thermodynamic, and transport experiments, suggesting that the complete Fermi surface is resolved. The reconstructed structure—incompatible with translational-symmetry-breaking density waves—serves as an important test for band structure calculations of correlated electron systems.

固体中的电子能带结构源自反映晶格或电子顺序结构的周期性电势。在化学计量的钌酸盐Ca ₃ Ru ₂ O _7中，许多费米表面敏感探针指示低温电子重构。然而，因果关系和重构的带结构仍未解决。在这里，我们通过角分辨光发射光谱显示了在Ca ₃ Ru ₂ O ₇ a C _2中如何对称的块状狄拉克半金属是通过布里渊区保留电子重构实现的。这种狄拉克半金属在冷却时分两步出现。狄拉克点和能带速度与量子振荡，热力学和输运实验所设定的约束条件一致，表明可以分辨出完整的费米表面。重建的结构与打破平移对称性的密度波不兼容，是相关电子系统能带结构计算的重要测试。