Insulating behavior at the neutrality point in dual-gated, single-layer graphene

TL;DR

This study investigates the insulating behavior at the charge-neutrality point in single-layer graphene at very low temperatures, revealing a divergence in resistivity linked to broken valley symmetry and quantum Hall effects.

Contribution

It demonstrates that the insulating behavior at the neutrality point persists down to 20 mK and is associated with broken valley symmetry, providing new insights into graphene's low-temperature electronic phases.

Findings

Resistivity diverges as temperature approaches 20 mK

Insulating state transitions to broken-valley-symmetry quantum Hall state under magnetic field

Behavior suggests broken valley symmetry causes insulating phase

Abstract

The fate of the low-temperature conductance at the charge-neutrality (Dirac) point in a single sheet of graphene is investigated down to 20 mK. As the temperature is lowered, the peak resistivity diverges with a power-law behavior and becomes as high as several Megohms per square at the lowest temperature, in contrast with the commonly observed saturation of the conductivity. As a perpendicular magnetic field is applied, our device remains insulating and directly transitions to the broken-valley-symmetry, nu=0 quantum Hall state, indicating that the insulating behavior we observe at zero magnetic field is a result of broken valley symmetry. Finally we discuss the possible origins of this effect.