Charge Excitations in Easy-Axis and Easy-Plane Quantum Hall Ferromagnets

Abstract

We study charge excitations in quantum Hall ferromagnets realized in a symmetric quantum well. Landau levels (LLs) with different subband and orbital indices crossing at the Fermi level act as up and down pseudospin levels. The activation energy measured as a function of the pseudospin Zeeman energy, ${\ensuremath{\Delta}}_{Z}$, reveals easy-plane and easy-axis ferromagnetism for LL filling of $\ensuremath{\nu}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}3$ and 4, respectively, for which the crossing levels have parallel and antiparallel spin. For $\ensuremath{\nu}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}4$, we observe a sharp reduction in the gap for ${\ensuremath{\Delta}}_{Z}\ensuremath{\rightarrow}0$, which we discuss in terms of a topological excitation in domain walls akin to Skyrmions.