A new twist on conductive atomic force microscopy: cryogenic tunneling microscopy of van der Waals materials
Scanning probe microscopy techniques have been indispensable in unraveling the rich physics of van der Waals materials. Yet mapping ground-state electronic structures over large fields of view, in gated devices on insulating substrates or through phase-transitions remains a persistent challenge.
Here we demonstrate cryogenic conductive atomic force microscopy (CAFM) as a platform for tunneling microscopy and spectroscopy with nanoscale resolution through two experiments. First, we image atomic defects in monolayer graphene on hexagonal boron nitride, resolving their local electronic signatures through spatially resolved tunneling spectroscopy. Second, we turn to moiré materials, where relevant electronic textures can span few nanometers up to hundreds of nanometers — length scales that are readily accessible by CAFM. Focusing on minimally twisted mono-bilayer graphene, we image electronic resonances at structural domain walls and confinement of electronic modes within domains, demonstrating that domain wall scattering plays a role beyond a perturbative correction. Together, these results establish low-temperature CAFM as a powerful and versatile addition to the scanning probe toolkit for van der Waals quantum materials.