Signatures of phonon and defect-assisted tunneling in planar metal-hexagonal boron nitride-graphene junctions

Abstract

Electron tunneling spectroscopy measurements on van der Waals heterostructures consisting of metal and graphene (or graphite) electrodes separated by atomically thin hexagonal boron nitride tunnel barriers are reported. The tunneling conductance dI/dV at low voltages is relatively weak, with a strong enhancement reproducibly observed to occur at around |V| ~ 50 mV. While the weak tunneling at low energies is attributed to the absence of substantial overlap, in momentum space, of the metal and graphene Fermi surfaces, the enhancement at higher energies signals the onset of inelastic processes in which phonons in the heterostructure provide the momentum necessary to link the Fermi surfaces. Pronounced peaks in the second derivative of the tunnel current, are observed at voltages where known phonon modes in the tunnel junction have a high density of states. In addition, features in the tunneling conductance attributed to single electron charging of nanometer-scale defects in the boron nitride are also observed in these devices. The small electronic density of states of graphene allows the charging spectra of these defect states to be electrostatically tuned, leading to Coulomb diamonds in the tunneling conductance.

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• Gate-controlled reversible rectifying behaviour in tunnel contacted atomically-thin MoS${}_2$ transistor
• Planar and van der Waals heterostructures for vertical tunnelling single electron transistors
• Tunnel spectroscopy of localised electronic states in hexagonal boron nitride
• Measuring Phonon Dispersion and Electron-Phason Coupling in Twisted Bilayer Graphene with a Cryogenic Quantum Twisting Microscope
• Universal model for electron thermal-field emission from two-dimensional semimetals
• Twisted monolayer and bilayer graphene for vertical tunneling transistors
• Tunneling spectroscopy of localized states of ${\mathrm{WS}}_2$ barriers in vertical van der Waals heterostructures
• Observation of Giant Quantized Phonon Modes in Graphene via Tunneling Spectra
• Valley-polarised tunnelling currents in bilayer graphene tunnelling transistors
• A non-invasive sub-surface electrical probe to encapsulated layers in van der Waals heterostructures
• Charge transfer due to defects in hexagonal boron nitride/graphene heterostructures: an ab initio study
• Shot noise detection in hBN-based tunnel junctions
• A magnetically-induced Coulomb gap in graphene due to electron-electron interactions
• Probing the Electronic Structure of Graphene Near and Far from the Fermi Level via Planar Tunneling Spectroscopy
• Enhanced Phonon-Assisted Tunneling in Metal -- Twisted Bilayer Graphene Junctions
• Hard superconducting gap and vortex-state spectroscopy in NbSe${}_2$ van der Waals tunnel junctions