Manifestation of the Verwey Transition in the Tunneling Spectra of Magnetite Nanocrystals

TL;DR

This study demonstrates the Verwey transition at the nanoscale in magnetite nanocrystals through tunneling spectroscopy, revealing temperature-dependent changes in electronic structure and resistance that shed light on charge ordering mechanisms.

Contribution

It provides direct tunneling evidence of the Verwey transition in individual magnetite nanocrystals, highlighting the evolution of electronic states with temperature at the nanoscale.

Findings

Resistance increases abruptly around 100 K.

Tunneling spectra show a gap below transition temperature.

Transition from insulator gap to peak structure with temperature.

Abstract

Tunneling transport measurements performed on single particles and on arrays of Fe3O4 (magnetite) nanocrystals provide strong evidence for the existence of the Verwey metal-insulator transition at the nanoscale. The resistance measurements on nanocrystal arrays show an abrupt increase of the resistance around 100 K, consistent with the Verwey transition, while the current-voltage characteristics exhibit a sharp transition from an insulator gap to a peak structure around zero bias voltage. The tunneling spectra obtained on isolated particles using a Scanning Tunneling Microscope reveal an insulator-like gap structure in the density of states below the transition temperature that gradually disappeared with increasing temperature, transforming to a small peak structure at the Fermi energy. These data provide insight into the roles played by long- and short-range charge ordering in the Verwey transition.