A Systematic Investigation of the Coupling between One-Dimensional Edge States of a Topological Crystalline Insulator.

The interaction of spin-polarized one-dimensional (1D) topological edge modes localized along single-atomic steps of the topological crystalline insulator $Pb_{0.7}Sn_{0.3}Se(001)$ has been studied systematically by scanning tunneling spectroscopy. Our results reveal that the coupling of adjacent edge modes sets in at a step{to{step distance $d_{ss} < 25$ nm, resulting in a characteristic splitting of a single peak at the Dirac point in tunneling spectra. Whereas the energy splitting exponentially increases with decreasing $d_{ss}$ for single-atomic steps running almost parallel, we find no splitting for single-atomic step edges under an angle of $90^{o}$. The results are discussed in terms of overlapping wave functions with $p_x; p_y$ orbital character.