Observation of discrete energy levels in a quantum confined system

TL;DR

This study used low temperature STM to observe discrete energy levels in subnanometer Pb clusters, revealing quantum confinement effects and resonant tunneling phenomena consistent with random matrix theory.

Contribution

First direct observation of discrete energy levels in subnanometer Pb clusters using STM, linking experimental data to random matrix theory predictions.

Findings

Discrete energy levels observed as current peaks in I-V characteristics

Peak voltage spacings follow Wigner-Dyson distribution

Peak current heights follow Porter-Thomas distribution

Abstract

Low temperature scanning tunneling microscope images and spectroscopic data have been obtained on subnanometer size Pb clusters fabricated using the technique of buffer layer assisted growth. Discrete energy levels were resolved in current-voltage characteristics as current peaks rather than current steps. Distributions of peak voltage spacings and peak current heights were consistent with Wigner-Dyson and Porter-Thomas distributions respectively, suggesting the relevance of random matrix theory to the description of the electronic eigenstates of the clusters. The observation of peaks rather than steps in the current-voltage characteristics is attributed to a resonant tunneling process involving the discrete energy levels of the cluster, the tip, and the states at the interface between the cluster and the substrate surface.