RQMP Research Seminar

Imaging nematic quantum Hall states and their interacting boundary modes

Mallika Randeria

MIT

Two-dimensional quantum Hall systems offer a versatile platform to explore the interplay between topology and symmetry breaking facilitated by Coulomb interactions. In this talk, I will discuss novel phenomena that arises from spontaneous valley ordering of bismuth surface states in a large magnetic field. Specifically, we observe the emergence of a nematic phase which breaks the rotational symmetry of the underlying crystal and a ferroelectric phase that carries an in-plane electric dipole moment. We use a scanning tunneling microscope to identify and directly image the wavefunctions of these broken-symmetry quantum Hall phases. Furthermore, we explore the boundary between distinct nematic quantum Hall domains, which host counter-propagating 1D modes. By changing the valley flavor and number of modes, we realize strikingly different regimes where the boundary is either metallic or insulating, constrained by Coulomb interactions between these 1D modes.