Topological crystalline metal in orthorhombic perovskite iridates

Since topological insulators were theoretically predicted and experimentally observed in semiconductors with strong spin–orbit coupling, increasing attention has been drawn to topological materials that host exotic surface states. These surface excitations are stable against perturbations since they are protected by global or spatial/lattice symmetries. Following the success in achieving various topological insulators, a tempting challenge now is to search for metallic materials with novel topological properties. Here we predict that orthorhombic perovskite iridates realize a new class of metals dubbed topological crystalline metals, which support zero-energy surface states protected by certain lattice symmetry. These surface states can be probed by photoemission and tunnelling experiments. Furthermore, we show that by applying magnetic fields, the topological crystalline metal can be driven into other topological metallic phases, with different topological properties and surface states. Topological insulators are insulators in the bulk, but can support conducting states on their surface. Here, Chen et al. predict orthorhombic perovskite iridates to be topological crystalline metals, exhibiting bulk metallic behaviour and surface states protected by certain crystal symmetries.