Surface analysis of the PrB6 (001) cleavage plane by scanning tunneling microscopy and spectroscopy

Scanning tunneling microscopy and spectroscopy were performed on the (001) cleavage plane of praseodymium hexaboride ($\mathrm{Pr}{\mathrm{B}}_{6}$). We found three different ordered morphologies, namely, a chainlike ($2\ifmmode\times\else\texttimes\fi{}1$) reconstruction and two uniform terminations. The chainlike ($2\ifmmode\times\else\texttimes\fi{}1$) reconstruction is rationalized as parallel Pr rows on top of a complete ${\mathrm{B}}_{6}$ network. The two uniform terminations are identified as complete Pr or ${\mathrm{B}}_{6}$ layers. Although the uniform terminations could be expected to be simply ($1\ifmmode\times\else\texttimes\fi{}1$) reconstructed, one of them shows a rather stripelike atomic corrugation for close tip-sample distances. All morphologies share two spectral features at $\ensuremath{-}0.2$ and $+0.2$ eV around ${E}_{\text{F}}$. In addition, one uniform termination shows an additional peak in the differential conductance at $\ensuremath{-}0.7\phantom{\rule{0.28em}{0ex}}\mathrm{eV}$. Similarly, the chainlike ($2\ifmmode\times\else\texttimes\fi{}1$) reconstruction reveals a feature in the differential conductance at $\ensuremath{-}1.1\phantom{\rule{0.28em}{0ex}}\mathrm{eV}$ when moving the tip closer to the surface. The distance dependency points towards rather localized electronic states, which we tentatively attribute to a $4f$-related feature.