Temperature dependance of the tunneling density of states in sub-micron planar metal / oxide / graphene junctions

TL;DR

This study investigates how the tunneling density of states in metal/oxide/graphene junctions varies with temperature, revealing a gap that disappears at lower temperatures than predicted by theory, likely due to phonon effects.

Contribution

It demonstrates the temperature dependence of the tunneling gap in graphene junctions and introduces vibrational phonon effects as an explanation for the earlier disappearance of the gap.

Findings

The gap remains gate independent up to room temperature.

The gap disappears at temperatures much lower than the theoretical $T_{c}$.

Vibrational out-of-plane phonon modes influence the gap's temperature dependence.

Abstract

We present tunneling measurements of sub-micron metal/insulator/graphene planar tunnel junctions up to room temperature. We observe a gate independent gap, as previously observed only by low temperature STM[Y. Zhang et al., Nat. Phys. 4, 627 (2008)]. No gap appears at temperatures above 150K, which is four times smaller than the theoretically expected $T_{c}$, from the accepted mean field model[T. O. Wehling et al. Phys. Rev. Lett. 101, 216803 (2008)]. We show that taking into account an additional vibrational effect of out-of-plane phonon soft modes the gap may disappear from the measurements at temperatures much lower than the calculated $T_{c}$.