Break-down of the density-of-states description of scanning tunneling spectroscopy in supported metal clusters

TL;DR

This paper investigates how scanning tunneling spectroscopy measurements of supported metal clusters deviate from their actual density of states, explaining experimental observations and proposing energy-resolved imaging for accurate characterization.

Contribution

It provides a quantum transport theoretical analysis showing the discrepancy between conductance curves and density of states, and suggests imaging techniques for better state identification.

Findings

Conductance spectra show fewer peaks than the density of states.

Realistic tunneling tips significantly affect the measured spectra.

Energy-resolved images enable unambiguous cluster state characterization.

Abstract

Low-temperature scanning tunneling spectroscopy allows to probe the electronic properties of clusters at surfaces with unprecedented accuracy. By means of quantum transport theory, using realistic tunneling tips, we obtain conductance curves which considerably deviate from the cluster's density of states. Our study explains the remarkably small number of peaks in the conductance spectra observed in recent experiments. We demonstrate that the unambiguous characterization of the states on the supported clusters can be achieved with energy-resolved images, obtained from a theoretical analysis which mimics the experimental imaging procedure.