Seminar By Xiaomeng Liu, Cornell University

Title: Uncovering Hidden Quantum Phenomena: From Emergent Quasiparticles to Electron Crystals

Series: Condensed Matter Sciences Seminar

Host: Cyprian Lewandowski

Abstract: In this talk, I will present two examples of using scanning tunneling microscopy and spectroscopy to investigate correlated and topological states in two-dimensional materials. First, I will discuss the real-space investigation of quantum Hall effects in graphene. We identify charged defects in graphene and hBN whose Coulomb potentials allow us to image Landau orbitals and localize individual quasiparticles. The distinct spatial and spectroscopic structures reveal the presence and number of quasiparticles bound to these defects in both integer and fractional quantum Hall states. Second, I will present the surprising observation of electron crystals in rhombohedral hexalayer graphene. As the carrier density is tuned, the crystal evolves from a honeycomb lattice to a near-square oblique lattice through a first-order phase transition. Its response to magnetic field suggests that the honeycomb and oblique lattices possess distinct internal magnetic structures, which we interpret as a metallic anomalous Hall crystal and an orbital-antiferromagnetic electron crystal, respectively. This points toward the exciting possibility that spontaneous electron crystallization can provide a route to emergent topological bands.