Sharp Tunneling Resonance from the Vibrations of an Electronic Wigner Crystal

TL;DR

This paper reports the discovery of a sharp tunneling resonance in a 2D electron system, attributed to vibrational modes of a Wigner crystal, providing new insights into electron ordering at low temperatures and high magnetic fields.

Contribution

It introduces a novel pulsed tunneling method to detect vibrational modes of a Wigner crystal, revealing a sharp resonance indicative of long-range electron order.

Findings

Observation of a sharp tunneling resonance consistent with Wigner crystal vibrations

Evidence of long-range electron correlation in a 2D system

Validation of a new probing technique for insulating electron phases

Abstract

Photoemission and tunneling spectroscopies measure the energies at which single electrons can be added to or removed from an electronic system. Features observed in such spectra have revealed electrons coupling to vibrational modes of ions both in solids and in individual molecules. Here we report the discovery of a sharp resonance in the tunneling spectrum of a 2D electron system. Its behavior suggests that it originates from vibrational modes, not involving ionic motion, but instead arising from vibrations of spatial ordering of the electrons themselves. In a two-dimensional electronic system at very low temperatures and high magnetic fields, electrons can either condense into a variety of quantum Hall phases or arrange themselves into a highly ordered Wigner crystal lattice. Such spatially ordered phases of electrons are often electrically insulating and delicate and have proven very challenging to probe with conventional methods. Using a unique pulsed tunneling method capable of probing electron tunneling into insulating phases, we observe a sharp peak with dependencies on energy and other parameters that fit to models for vibrations of a Wigner crystal. The remarkable sharpness of the structure presents strong evidence of the existence of a Wigner crystal with long correlation length.