Fractional Quantum Hall Effect Measurements at Zero g Factor

Abstract

Fractional quantum Hall effect energy gaps have been measured as a function of Zeeman energy. The gap at $\ensuremath{\nu}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1/3$ decreases as the $g$ factor is reduced by hydrostatic pressure. This behavior is similar to that at $\ensuremath{\nu}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1$ and shows that the excitations are spinlike. At small Zeeman energy, the excitation is consistent with the reversal of 3 spins and may be interpreted as a small composite Skyrmion. At 20 kbar, where $g$ has changed sign, the $1/3$ gap appears to increase again.