Strong Electron Confinement By Stacking-fault Induced Fractional Steps on Ag(111) Surfaces

TL;DR

This study reveals that stacking-fault induced fractional steps on Ag(111) surfaces strongly confine electrons, maintaining high reflection amplitudes over a broad energy range, with subsurface faults playing a key role.

Contribution

It provides the first detailed experimental and theoretical analysis of electron reflection at stacking-fault fractional steps, highlighting their significant impact on surface state confinement.

Findings

Reflection amplitude remains high (0.6-0.8) from 0 to 0.5 eV

Phase shifts at descending steps are larger than at ascending steps by ~0.4π

Subsurface stacking faults significantly enhance electron reflection

Abstract

The electron reflection amplitude $R$ at stacking-fault (SF) induced fractional steps is determined for Ag(111) surface states using a low temperature scanning tunneling microscope. Unexpectedly, $R$ remains as high as $0.6 \sim 0.8$ as energy increases from 0 to 0.5 eV, which is in clear contrast to its rapidly decreasing behavior for monatomic (MA) steps [L. B{\"u}rgi et al., Phys. Rev. Lett. \textbf{81}, 5370 (1998)]. Tight-binding calculations based on {\em ab-initio} derived band structures confirm the experimental finding. Furthermore, the phase shifts at descending SF steps are found to be systematically larger than counterparts for ascending steps by $\approx 0.4 \pi$. These results indicate that the subsurface SF plane significantly contributes to the reflection of surface states.