Tunneling Spectroscopy of Two-Dimensional Materials Based on Via Contacts

Qingrui Cao, Evan J. Telford, Avishai Benyamini, Ian Kennedy, Amirali Zangiabadi, Kenji Watanabe, Takashi Taniguchi, Cory R. Dean, Benjamin M. Hunt

Published 2022-03-14Version 1

We introduce a novel planar tunneling architecture for van der Waals heterostructures based on via contacts, namely metallic contacts embedded into through-holes in hexagonal boron nitride (hBN). We use the via-based tunneling method to study the single-particle density of states of two different two-dimensional (2D) materials, superconducting NbSe$_2$ and monolayer graphene in zero magnetic field as well as in the quantum Hall regime. In NbSe$_2$ devices, we characterize the barrier strength and interface disorder, within the Blonder-Tinkham-Klapwijk model, for tunnel barrier thicknesses of 0, 1 and 2 layers of hBN and study the area dependence of the tunneling contacts down to $30^2$ nm$^2$, demonstrating that the effect of interface disorder can be suppressed in the small-area limit. Additionally, we demonstrate that for 0 layers of hBN, we cross over from diffusive to point contacts in the small-area limit. In graphene, we show that reducing the tunneling area can suppress the effects of phonon-assisted tunneling and defects in the hBN barriers. These via-based tunneling devices overcome limitations of other planar tunneling designs and can be used to produce high-quality, ultra-clean tunneling structures from a variety of 2D materials.