Probing Valence Electron Distributions at Subatomic Resolution in a Charge Density Wave Material

Probing the internal electronic structure of complex materials with atomic spatial resolution has remained an outstanding challenge in condensed-matter science. A promising approach is convergent-beam electron diffraction (CBED) in four-dimensional scanning transmission electron microscopy (4D-STEM). Here, we apply 4D-STEM CBED to the charge-density-wave (CDW) material 1T-TaS2. We demonstrate a qualitative breakdown of the conventional independent atom model (IAM) in reproducing the experimental CBED patterns. A robust low-angle intensity maximum is systematically absent in IAM-based simulations but is consistently reproduced in simulations that use electrostatic potentials derived from density functional theory. A comparison of CBED patterns with projected charge densities reveals a remarkable correspondence between the local real-space valence charge distribution and diffracted intensities, reflecting site-dependent charge density variations within the CDW structure. These results establish atomic-resolution CBED as an experimental probe of valence electron contributions to the scattering potential and open a route to resolving complex electronic ordering phenomena.