LAUSR

We performed a combined study of the (001)-cleavage plane of lanthanum hexaboride $({\mathrm{LaB}}_{6})$ using scanning tunneling microscopy and density-functional theory (DFT). Experimentally, we found a $(2\ifmmode\times\else\texttimes\fi{}1)$ reconstructed surface on a local scale. The reconstruction is only short-range ordered and tends to order perpendicularly to step edges. At larger distances from surface steps, the reconstruction evolves to a labyrinthlike pattern. These findings are supported by low-energy electron diffraction experiments. Slab calculations within the framework of DFT show that the atomic structure consists of parallel lanthanum chains on top of boron octahedra. Scanning tunneling spectroscopy shows a prominent spectral feature at $\ensuremath{-}0.6\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$. Using DFT, we identify this structure as a surface resonance of the $(2\ifmmode\times\else\texttimes\fi{}1)$ reconstructed ${\mathrm{LaB}}_{6}$ (100) surface which is dominated by boron dangling bond states and lanthanum $d$ states.