University of Minnesota
School of Physics & Astronomy

Physics and Astronomy Calendar

Wednesday, October 19th 2016
2:30 pm:
Condensed Matter Seminar in Physics 110 PAN
Speaker: Raymond Ashoori, MIT
Subject: Studying Tunneling into Insulators: Observation of a Long-Range Ordered Wigner-Crystal in a Two-Dimensional Electronic System

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. Finally, I will also show results from a related tunneling method that we have developed that permits quantitative determination of spectral function of the 2D electron system as a function of both energy and momentum.

Faculty Host: Vlad Pribiag

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