Tailoring topological states of core-shell nanoparticles

TL;DR

This paper explores spherical core-shell nanoparticles with topological insulator shells, revealing topologically protected midgap states and showing how shell thickness can tune energy levels for potential electronic applications.

Contribution

It introduces a model for core-shell nanoparticles with topological insulator shells, demonstrating the existence of robust midgap states and the tunability of energy levels via shell thickness.

Findings

Support for midgap bound states at interfaces due to band inversion

Topologically protected states are robust against perturbations

Shell thickness allows fine-tuning of energy levels

Abstract

In this work we investigate novel spherical core-shell nanoparticles with band inversion. The core and the embedding medium are normal semiconductors while the shell material is assumed to be a topological insulator. The envelope functions are found to satisfy a Dirac-like equation that can be solved in a closed form. The core-shell nanoparticle supports midgap bound states located at both interfaces due to band inversion. These states are robust since they are topologically protected. The energy spectrum presents mirror symmetry due to the chiral symmetry of the Dirac-like Hamiltonian. As a major result, we show that the thickness of the shell acts as an additional parameter for the fine tuning of the energy levels, which paves the way for electronics and optoelectronics applications.