Characterizing wave functions in graphene nanodevices: electronic transport through ultrashort graphene constrictions on a boron nitride substrate

TL;DR

This study investigates electronic transport in ultrashort graphene constrictions on boron nitride, revealing that charge localization extends beyond the constriction, primarily along imperfect edges, challenging previous assumptions about bulk localization.

Contribution

The paper provides new insights into charge localization mechanisms in graphene constrictions, emphasizing the role of edge states over bulk localization, supported by experimental data and tight-binding simulations.

Findings

Charge localization can be larger than the constriction area.

Localized states mainly extend along device edges.

Bulk mobility on boron nitride does not align with Coulomb-blockade localization length.

Abstract

We present electronic transport measurements through short and narrow (30x30 nm) single layer graphene constrictions on a hexagonal boron nitride substrate. While the general observation of Coulomb-blockade is compatible with earlier work, the details are not: we show that the area on which charge is localized can be significantly larger than the area of the constriction, suggesting that the localized states responsible for Coulomb-blockade leak out into the graphene bulk. The high bulk mobility of graphene on hexagonal boron nitride, however, seems not consistent with the short bulk localization length required to see Coulomb-blockade. To explain these findings, charge must instead be primarily localized along the imperfect edges of the devices and extend along the edge outside of the constriction. In order to better understand the mechanisms, we compare the experimental findings with tight-binding simulations of such constrictions with disordered edges. Finally we discuss previous experiments in the light of these new findings.