Imaging sliding charge order and atomic-scale movement of topological defects using a scanning tunneling microscope

The charge density wave (CDW) emerges in low-dimensional materials below a critical temperature due to electron-phonon coupling and/or band nesting, known as the Peierls instability model. External in-plane electric fields can drive the collective CDW to move, or slide, in these materials. While the CDW response to an external field has been captured macroscopically through diffraction, transport, and optical methods, the direct atomic-scale imaging of CDW phase dynamics and sliding is still lacking. In this talk, we discuss our results using in situ external electric fields to control the microscopic surface CDW order parameter by combining scanning tunneling microscope/microscopy (STM/STS) with an in-plane driving current. Specifically, I will show how atomic-scale topological defects in the CDW order parameter couple and evolve with increasing electric field in a prototypical quasi-1D material, potassium blue bronze (K0.3MoO3), in general agreement with long-held microscopic theory models of CDW de-pinning and sliding. I will conclude with more recent measurements using an external electric field to tune the surface CDW order parameter in quasi-2D van der Waals materials where bulk sliding is notoriously absent.