Equally Spaced Quantum States in van der Waals Epitaxy-Grown Nanoislands

TL;DR

This paper presents experimental evidence of equally spaced quantum well states in Pb(111) nanoislands, attributed to confined relativistic electrons, with implications for topological materials and quantum devices.

Contribution

It demonstrates the existence of equally spaced quantum states in nanoislands, supported by STM, simulations, and first-principles calculations, revealing relativistic electron confinement.

Findings

Observation of sharp, densely distributed QWSs near Fermi energy.

QWSs explained as quantized energies of confined linearly dispersive electrons.

Spin-orbit coupling enhances relativistic electron behavior.

Abstract

Pursuing the confinement of linearly dispersive relativistic fermions is of interest in both fundamental physics and potential applications. Here, we report strong STM evidence for the equally spaced, strikingly sharp, and densely distributed quantum well states (QWSs) near Fermi energy in Pb(111) nanoislands, van-der-Waals epitaxially grown on graphitized 6H-SiC(0001). The observations can be explained as the quantized energies of confined linearly dispersive [111] electrons, which essentially 'simulate' the out-of-plane relativistic quasiparticles. The equally spaced QWSs with an origin of confined relativistic electrons are supported by phenomenological simulations and Fabry-Perot fittings based on the relativistic fermions. First-principles calculations further reveal that the spin-orbit coupling strengthens the relativistic nature of electrons near Fermi energy. Our finding uncovers the unique equally spaced quantum states in electronic systems beyond Landau levels, and may inspire future studies on confined relativistic quasiparticles in flourishing topological materials and applications in structurally simpler quantum cascade laser.