Dynamics of electrons in the quantum Hall bubble phases

TL;DR

This paper investigates the phase transitions and collective excitations of bubble states in Landau levels of a 2D electron gas under a magnetic field, predicting measurable discontinuities in physical properties.

Contribution

It provides a detailed analysis of phase transitions between bubble states and their collective excitation spectra, including higher-energy modes, in quantum Hall systems.

Findings

Discontinuous changes in density of states and magnetization at phase transitions.

Identification of higher-energy collective modes beyond the pinned phonon.

Predictions of measurable frequency discontinuities in microwave absorption experiments.

Abstract

In Landau levels N > 1, the ground state of the two-dimensional electron gas (2DEG) in a perpendicular magnetic field evolves from a Wigner crystal for small filling of the partially filled Landau level, into a succession of bubble states with increasing number of guiding centers per bubble as the filling increases, to a modulated stripe state near half filling. In this work, we show that these first-order phase transitions between the bubble states lead to measurable discontinuities in several physical quantities such as the density of states and the magnetization of the 2DEG. We discuss in detail the behavior of the collective excitations of the bubble states and show that their spectra have higher-energy modes besides the pinned phonon mode. The frequencies of these modes, at small wavevector k, have a discontinuous evolution as a function of filling factor that should be measurable in, for example, microwave absorption experiments.