The zero-energy state in graphene in a high magnetic field

TL;DR

This study investigates the behavior of the charge-neutral Dirac point in graphene under high magnetic fields at very low temperatures, revealing a transition to an insulating state with unusual properties.

Contribution

It provides new insights into the high-field insulating state in graphene and the nature of charge excitations at the Dirac point.

Findings

Resistance at the Dirac point diverges with magnetic field in small V_0 samples

The resistance saturates to a T-independent value below 2 K

Evidence of gapless charge excitations in the insulating state

Abstract

The fate of the charge-neutral Dirac point in graphene in a high magnetic field $H$ has been investigated at low temperatures ($T\sim$ 0.3 K). In samples with small $V_0$ (the gate voltage needed to access the Dirac point), the resistance $R_0$ at the Dirac point diverges steeply with $H$, signalling a crossover to an insulating state in intense field. The approach to the insulating state is highly unusual. Despite the steep divergence in $R_0$, the profile of $R_0$ vs. $T$ in fixed $H$ saturates to a $T$-independent value below 2 K, consistent with charge carrying gapless excitations.