Surface resonance of the (2×1) reconstructed lanthanum hexaboride (001)-cleavage plane: A combined STM and DFT study

Abstract

We performed a combined study of the (001)-cleavage plane of lanthanum hexaboride (LaB6) using scanning tunneling microscopy (STM) and density functional theory (DFT). Experimentally, we found a (2×1) 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 labyrinth-like pattern. These findings are supported by low-energy electron diffraction (LEED) experiments. Slab calculations within the framework of DFT shows that the atomic structure consists of parallel lanthanum chains on top of boron octahedra. Scanning tunneling spectroscopy (STS) shows a prominent spectral feature at −0.6 eV. Using DFT, we identify this structure as a surface resonance of the (2×1) reconstructed LaB6 (100)-surface which is dominated by boron dangling bond-states and lanthanum d-states.

Comparative Scanning Tunneling Microscopy Study on Hexaborides

“…[ 28,30,39 ] The reconstruction was also observed by low‐energy electron diffraction, [ 36,40,41 ] as well as by STM on LaB 6 . [ 42 ] Clearly, if we assume that the reconstruction results from each second row of Sm atoms missing on top of an otherwise B‐terminated surface, such a reconstruction is energetically favorable compared with an unreconstructed polar surface. Yet, other STM studies did not report this reconstruction [ 29 ] or interpreted it differently.…”

An STM Perspective on Hexaborides: Surface States of the Kondo Insulator SmB6

“…At positive bias, the La d ‐orbitals contribute to dd V . [ 158 ] The B dangling bonds are speculated to also lead to a feature at −0.2 eV on PrB 6 surfaces. [ 159 ] In addition, a peak at −0.7 eV is observed in dd V for the Pr‐terminated surface of Figure 10d, which is related to the 4 f states.…”

Ultrafast Probing and Coherent Vibrational Control of a Surface Structural Phase Transition

“…The following chapter gives an overview of the capabilities of ULEED. From proofof-principle experiments [217] to the observation and control of surface-specific structural dynamics [53], the technique has demonstrated its potential in various fields of surface science, including polymer and molecular dynamics at surfaces [217,219], surface reconstructions on the µm scale [231], as well as ultrafast structural transitions and phase ordering kinetics in CDW systems [18,53,55]. Of crucial importance for all these experiments is the high temporal and momentum resolution of the two ultrafast electron guns, which will be reviewed first for this reason.…”

“…Considering that many materials can often only be synthesised in the form of sub-mm single crystals, the small spot diameters of the miniaturised electron guns offer a decisive advantage over standard LEED setups. Furthermore, even single crystals cleaved in-situ potentially exhibit surface inhomogeneities on a µm length scale, as exemplified by the case of the (001) surface of LaB 6 [231] (see Fig. 3.10).…”

“…g, STM topography of the surface, showing areas with (left) and without (right) a rather long-range ordered reconstruction. h, 2D Fourier transform of the STM topography.Adapted with permission from Ref [231]…”