Quantum oscillations in monoclinic SrIrO$_3$: non-trivial topology and strong electron correlations in a three-dimensional Dirac semimetal.

We report the observation of Shubnikov-de Haas oscillations in bulk single crystals of monoclinic SrIrO$_3$ in magnetic fields up to 35 T. Analysis of the oscillations reveals a Fermi surface comprising multiple small pockets with effective masses up to five times larger than the calculated band mass. Phase analysis of the oscillations indicates non-trivial topological character of the dominant orbit while ab-initio calculations reveal robust linear band-crossings at the Brillouin zone boundary. These collective findings, coupled with knowledge of the evolution of the electronic state across the Ruddlesden-Popper iridate series, establishes monoclinic SrIrO$_3$ as a topological semimetal on the boundary of the Mott metal-insulator transition.