Surface States of Perovskite Iridates AIrO$_3$; Signatures of Topological Crystalline Metal with Nontrivial $\mathbb{Z}_2$ Index

Heung-Sik Kim, Yige Chen, Hae-Young Kee

Published 2014-11-05Version 1

Motivated by a recent proposal of topological crystalline metal in perovskite iridates, we perform first-principles calculations for epitaxially stabilized orthorhombic perovskite iridates with $Pbnm$ symmetry. In the presence of spin-orbit coupling, a ring-shape nodal Fermi surface composed of a set of Dirac points exists, hinting intriguing surface states. Two types of distinct topological surface states are found depending on the surface direction. On the side surfaces, flat surface states protected by the mirror symmetry emerge manifesting the topological crystalline character. On the top surface where mirror symmetry is broken, a Dirac cone appears indicating a non-trivial topology of the nodal metal. Indeed, there is a well-defined two dimensional topological $\mathbb{Z}_2$ index associated with time reversal symmetry leading to the Dirac surface state. Transitions to weak and strong topological insulators and implications of different surface states in light of angle resolved photoemission spectroscopy are also discussed.