Quantum-Hall activation gaps in graphene

TL;DR

This study measures quantum-Hall activation gaps in graphene at various magnetic fields and temperatures, revealing different behaviors at filling factors ν=2 and ν=6, and suggesting a Landau level narrowing effect.

Contribution

It provides the first detailed measurements of quantum-Hall activation gaps in graphene at high magnetic fields and temperatures, highlighting the Landau level narrowing phenomenon.

Findings

The ν=6 gap fits a model with broadened Landau levels of 400 K width.

The ν=2 gap is highly temperature and field dependent, approaching sharp Landau level behavior at high B and T.

Evidence suggests a narrowing of the lowest Landau level at high magnetic fields.

Abstract

We have measured the quantum-Hall activation gaps in graphene at filling factors $\nu=2$ and $\nu=6$ for magnetic fields up to 32 T and temperatures from 4 K to 300 K. The $\nu =6$ gap can be described by thermal excitation to broadened Landau levels with a width of 400 K. In contrast, the gap measured at $\nu=2$ is strongly temperature and field dependent and approaches the expected value for sharp Landau levels for fields $B > 20$ T and temperatures $T > 100$ K. We explain this surprising behavior by a narrowing of the lowest Landau level.