Symmetry protected Luttinger liquids in Quantum Hall Ferromagnets on the surface of Bi(111).

Quantum Hall Ferromagnets are a unique platform to study the confluence of symmetry-broken order parameter and topology. Recent experiments by Feldman et al.[1] observe clear signatures of valley-polarized Quantum Hall Ferromagnets on the surface of Bi(111) in the presence of strong magnetic fields. The tunneling conductance shows a discrete spectrum indicating the formation of Landau levels while individual nematic Landau level orbits pinned to impurities indicate selective occupation of certain valleys. Further recent experiments[2] observe domain wall states between such nematic domains. Most curiously, domain walls between these domains appear to host low energy excitations that appear to be gapped/gapless depending upon the filling fraction of the nematic quantum Hall states. We explain[3] these observations both qualitatively and quantitatively by highlighting the role of interactions and symmetries in engendering such exotic Luttinger liquids.

[1] B. Feldman et al., Science 2016
[2] M. T. Randeria, KA et al., Nature 2018
[3] KA et al., ArXiv:1807.10293