Topological boundary states in engineered quantum-dot molecules on the InAs(111)A surface

TL;DR

This study demonstrates the creation of topological boundary states in engineered quantum-dot chains on InAs(111)A surfaces, revealing how atomic-scale design can realize and probe topological phases predicted by the SSH model.

Contribution

The paper reports the experimental realization of topological boundary states in quantum-dot molecules with atomic precision, including the effects of charged dots on the SSH model.

Findings

Boundary states observed at chain ends and domain walls.

Probability density found on both sublattices, deviating from ideal SSH predictions.

Onsite potential variation shifts boundary state energies away from midgap.

Abstract

Atom manipulation by scanning tunneling microscopy was used to construct quantum dots on the InAs(111)A surface. Each dot comprised six ionized indium adatoms. The positively charged adatoms create a confining potential acting on surface-state electrons, leading to the emergence of a bound state associated with the dot. By lining up the dots into N-dot chains with alternating tunnel coupling between them, quantum-dot molecules were constructed that revealed electronic boundary states as predicted by the Su-Schrieffer-Heeger (SSH) model of one-dimensional topological phases. Dot chains with odd N were constructed such that they host a single end or domain-wall state, allowing one to probe the localization of the boundary state on a given sublattice by scanning tunneling spectroscopy. We found probability density also on the forbidden sublattice together with an asymmetric energy spectrum of the chain-confined states. This deviation from the SSH model arises because the dots are charged and create a variation in onsite potential along the chain - which does not remove the boundary states but shifts their energy away from the midgap position. Our results demonstrate that topological boundary states can be created in quantum-dot arrays engineered with atomic-scale precision.