Description:

Title: Studying Electron Tunneling into Insulators: Observation of a Long-Range Ordered “Electron Crystal” in a Two-Dimensional Electronic System

Speaker: Ray Ashoori, MIT

Abstract: In a system of free electrons, both the Coulomb repulsion and quantum kinetic energies diminish as the electron density is decreased. Since the kinetic energy diminishes faster than the Coulomb energy, it becomes energetically favorable for electrons to localize into a crystal known as a “Wigner Crystal". In the case of 2D systems, applying a quantizing magnetic field favors crystal formation by further freezing out the kinetic energy into Landau levels. Theory predicts that a Wigner crystal of quasiparticles in a Landau level exists near integer quantum Hall states as an insulating phase with an expected transition temperature in the range of a few hundred millikelvin or below. As the state in insulating, it is very difficult to probe it. Using a refined pulsed tunneling method, capable of probing insulating phases, we are able to measure tunneling current directly into the electronic crystal. I will present high-resolution tunneling measurements that reveal very sharp structure arising from the vibrational spectrum of the spatially ordered electronic structure. This observation conclusively demonstrates the existence of a Wigner Crystal with long correlation length and opens the door to using tunneling to probe and detect a wide variety of ordered electronic phases.

Host: Anupam Garg

Speaker Schedule

Keywords: Physics, Astronomy, colloquium