Electronic reconstruction forming a $C_2$-symmetric Dirac semimetal in Ca$_3$Ru$_2$O$_7$

TL;DR

This paper reveals that Ca$_3$Ru$_2$O$_7$ hosts a $C_2$-symmetric Dirac semimetal formed through an electronic reconstruction, confirmed by ARPES and consistent with various experimental constraints, providing insights into correlated electron systems.

Contribution

It demonstrates the realization of a $C_2$-symmetric Dirac semimetal via a Brillouin-zone preserving electronic reconstruction in Ca$_3$Ru$_2$O$_7$, a novel finding in correlated materials.

Findings

Identification of a $C_2$-symmetric Dirac semimetal in Ca$_3$Ru$_2$O$_7$

The Dirac point and band velocities match quantum oscillation and transport data

The reconstructed structure does not involve translational-symmetry-breaking density waves

Abstract

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$_3$Ru$_2$O$_7$, 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$_3$Ru$_2$O$_7$ 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.