Density Response of Surface States in a Topological Crystalline Metal

Orthorhombic perovskite iridates are predicted to realize a new class of metals called topological crystalline metals (TCMs). For particular terminations, these materials support zero energy surface states which are protected by a certain lattice symmetry. Despite experimental efforts, a direct signature of these surface states has remained elusive. Apart from difficulty in their synthesis, this is partly due to the lack of an appropriate probe which is able to distinguish between surface and metallic bulk contributions. We studied the density fluctuations of surface modes, and found that symmetry properties of the surface states allow for unique consequences for the electron-phonon interaction. Experimental implications are also discussed.