Imaging Electronic Liquid Crystal Phase and Dirac Nodal Lines in Topological Semimetals

Abstract: Strongly correlated electron systems, in which various order parameters compete or intertwine with each other, exhibit rich quantum states of matter such as high Tc superconductivity and heavy fermion systems. Electronic liquid crystal phases, which originate from strong electron correlation, break the underlying crystalline symmetry and play a crucial role in cuprates, iron-based superconductors and quantum Hall states. Topological materials, which host symmetry protected Dirac or Weyl fermions with highly linear dispersion, however, are mostly weakly correlated. Therefore, the search for correlated topological phases has attracted great attentions. Here, we report the first direct visualization of electronic smectic and nematic phases in a Dirac nodal line semimetal by using scanning tunneling microscopy. The temperature and magnetic field dependent measurements rule out spin as the origin of the electronic liquid crystal phases. We propose the nearby charge density wave instability due to quenched disorder plays the key role. Our results demonstrate these topological semimetals provide a fertile playground to study novel phenomena of correlated Dirac electrons.