STS Observations of Landau Levels at Graphite Surfaces

TL;DR

This study uses scanning tunneling spectroscopy to observe Landau levels on graphite surfaces, revealing field-dependent peaks and fixed levels near the Fermi energy, enhancing understanding of graphite's electronic structure.

Contribution

First direct observation of almost field independent Landau levels at graphite surfaces, linking spectral features to graphite's crystalline structure and thickness.

Findings

Landau levels grow with magnetic field strength.

Fixed Landau levels near the Fermi energy are characteristic of graphite.

Kish graphite identified as bulk, HOPG as finite-thickness graphite.

Abstract

Scanning tunneling spectroscopy measurements were made on surfaces of two different kinds of graphite samples, Kish graphite and highly oriented pyrolytic graphite (HOPG), at very low temperatures and in high magnetic fields. We observed a series of peaks in the tunnel spectra, which grow with increasing field, both at positive and negative bias voltages. These are associated with Landau quantization of the quasi two-dimensional electrons and holes in graphite in magnetic fields perpendicular to the basal plane. Almost field independent Landau levels fixed near the Fermi energy, which are characteristic of the graphite crystalline structure, were directly observed for the first time. Calculations of the local density of states at the graphite surfaces allow us to identify Kish graphite as bulk graphite and HOPG as graphite with finite thickness effectively.