Electronic origin of the low-symmetry scanning tunneling microscopy image of the layered transition-metal halide .alpha.-ruthenium(III) chloride

Abstract

Scanning tunneling microscopy (STM) and atomic force microscopy (AFM) images of the layered transition-metal halide [alpha]-RuCl[sub 3] show striking differences. The AFM image show 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](r[sub 0],e[sub f]), and the AFM image by calculating the total electron density [rho](r[sub 0]), of a single RuCl[sub 3] layer. The patterns of the [rho](r[sub 0],e[sub f]) and [rho](r[sub 0]) plots are similar to those of the STM and AFM images, respectively. The STM images of [alpha]-RuCl[sub 3] for the surface-to-tip and tip-to-surface tunneling processes are similar, because [alpha]-RuCl[sub 3] is a magnetic semiconductor with d[sup 5] ions so that the partially filled levels lying at the top portion of the t[sub 2g]-block bands are involved in both tunneling processes. 19 refs., 6 figs., 1 tab.