Imaging a nematic electronic domain wall and its edge modes on the surface of bismuth*

Nematic electronic phases, whose wave functions spontaneously break the rotational symmetry of the underlying lattice, are susceptible to the formation of domains. In this talk, I will describe scanning tunneling microscope measurements that allow us to directly visualize the evolution of local nematic order across a domain wall on the surface of bismuth. Coulomb interactions in this material lift the degeneracy of six anisotropic hole valleys to produce nematic quantum Hall states [1]. Spatially resolved spectroscopy shows that the resulting exchange gap between Landau levels closes in the vicinity of the domain wall, where there is an abrupt switch in which valleys are occupied, as seen by imaging the orientation of anisotropic wave functions on either side. The data match well to theoretical simulations where the boundary is predicted to support counter-propagating valley-polarized edge modes, forming an extended topological defect. While we observe enhanced low-energy conductance at the boundary, atomic-scale defects allow for scattering between valleys that partially localizes the one-dimensional electronic states.

[1] B. E. Feldman et al., Science, 354, 316 (2016).