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 C-2-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.

Electronic band structures in solids stem from a periodic potential reflecting the structure of either the crystal lattice or an electronic order. In the stoichiometric ruthenate Ca_3Ru_2O_7, 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 Ca_3Ru_2O_7 a C_2-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.

M. Horio, Q. Wang, V. Granata, 3 K. P. Kramer, Y. Sassa, S. Jöhr, D. Sutter, A. Bold, L. Das, Y. Xu, R. Frison, R. Fittipaldi, 3 T. K. Kim, C. Cacho, J. E. Rault, P. Le Fèvre, F. Bertran, N. C. Plumb, M. Shi, A. Vecchione, 3 M. H. Fischer, and J. Chang Physik-Institut, Universität Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland CNR-SPIN, I-84084 Fisciano, Salerno, Italy Dipartimento di Fisica ”E.R. Caianiello”, Università di Salerno, I-84084 Fisciano, Salerno, Italy Department of Physics, Chalmers University of Technology, SE-412 96 Göteborg, Sweden Center for X-ray Analytics, Swiss Federal Laboratories for Materials Science and Technology (Empa), Überlandstrasse 129, CH-8600 Dübendorf, Switzerland Diamond Light Source, Harwell Campus, Didcot, OX11 0DE, United Kingdom Synchrotron SOLEIL, Saint-Aubin-BP 48, F-91192 Gif sur Yvette, France Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland