Controlling sliding ferroelectricity and coulomb screening with novel scanning probes

2D van der Waals materials provide unique opportunities to study the interplay of crystal symmetry, band topology, and electron-electron interactions due to breadth of configurations enabled by layered stacking and because of their broad electrostatic tunability. Observations of sliding ferroelectricity in hBN, WTe2, and MoTe2, as well as numerous correlated states in flat-band multi-layered graphene systems highlight the richness of physics accessible in van der Waals materials. They also highlight an opportunity for new methods to tune system parameters to better investigate the underlying physics: sliding ferroelectricity invites us to contemplate controlling interlayer shear forces, and flat-band physics encourages us to seek new ways to tune coulomb interactions.

In this talk, I will discuss our ongoing efforts to build new scanning probe-based techniques that enable in situ control of sliding ferroelectricity and coulomb screening. In the case of sliding ferroelectricity, we have implemented a soft-polymer based scanning probe approach for applying shear forces to van der Waals devices and demonstrate the ability to tune the coercive field in parallel stacked hBN. In the case of screening in flat-band systems, I will discuss the development of an atomically-flat planar-probe-based millikelvin scanning gate microscope that we use to tune coulomb interactions in magic-angle twisted bilayer graphene via precise in situ control of gate-sample distance.