Visualizing crystal twin boundaries of bismuth by high-spatial-resolution ARPES

We have performed micro-/nanofocused angle-resolved photoemission spectroscopy (ARPES) on cleaved single-crystal surfaces of bismuth to clarify the spatially resolved electronic states. While the dominant area of the cleaved surface was found to display the well-known Rashba-spin-split surface state with the (111)-surface origin, the steplike region with a typical width of $\sim 10\text{–}20$ $\mu \mathrm{m}$ shows distinctly different band structure and fermiology originating from the hard-to-cleave (100) surface. This unexpected mixture of the (100)-derived electronic states in a tiny area of the cleaved (111) surface is attributed to the crystal planes separated by a twin boundary, as supported by laser microscopy and electron backscatter diffraction measurements. The present study paves a pathway toward investigating electronic states associated with inhomogeneities and coexisting phases of hard-to-cleave crystal planes and complex materials by spatially resolved ARPES, making this technique a powerful method to investigate the interplay between local electronic states and crystal structures when combined with structural characterization techniques.