Scanning tunneling microscopy observation of symmetry breaking in Landau levels at the ZrSiS surface

Christopher Butler^1*, M. Murase², S. Sawada², D. Hashizume¹, T. Hanaguri¹, T. Sasagawa²

¹CEMS, RIKEN, Wako, Saitama, Japan
²Laboratory for Materials and Structures, Tokyo Institute of Technology, Tokyo, Japan

* Presenter:Christopher Butler, email:christopher.butler@riken.jp

The observation of an electronic state that breaks underlying crystal symmetries might indicate the discovery of a new quantum liquid crystal phase. Using scanning tunneling microscopy, we discover an example of such symmetry breaking at the surface of ZrSiS. We observe Landau levels in this material’s unusual ‘floating’ surface band, and image quasiparticle interference within each Landau level. These observations reveal a lowering of symmetry from the expected C₄ down to C₂, and the orientation of the C₂-symmetric pattern alternates from each Landau level to the next. Using state-of-the-art Landau level spectroscopy techniques and analysis, we distinguish two separate Landau level series resulting from a lifting of valley degeneracy. Finally, we discuss possible underlying mechanisms of the lifted degeneracy, in particular considering the role of external strain, which could offer a lever to control the Landau level anisotropy.

Keywords: Scanning tunneling microscopy, Dirac semimetal, surface states, Landau levels, symmetry breaking