ELECTRONIC ORIGIN OF THE LOW-SYMMETRY SCANNING-TUNNELING-MICROSCOPY IMAGE OF THE LAYERED TRANSITION-METAL HALIDE ALPHA-RUCL3

Scanning tunneling microscopy (STM) and atomic force microscopy (AFM) images of the layered transition-metal halide alpha-RuCl3 show striking differences. The AFM image shows a hexagonal symmetry of the surface Cl layer, while the STM images at various tunneling conditions exhibit a strong deviation from the hexagonal symmetry. The STM image was examined by calculating the partial electron density rho(r0,e(f)), and the AFM image by calculating the total electron density rho(r0), of a single RuCl3 layer. The patterns of the rho(r0,e(f)) and rho(r0) plots are similar to those of the STM and AFM images, respectively. The STM images of alpha-RUCl3 for the surface-to-tip and tip-to-surface tunneling processes are similar, because alpha-RuCl3 is a magnetic semiconductor with d5 ions so that the partially filled levels lying at the top portion of the t2g-block bands are involved in both tunneling processes.