Surface Acoustic Waves Probe of the Spin Phase Transition at $\nu$=2/3 in n-GaAs/AlGaAs structure

TL;DR

This study uses surface acoustic waves to investigate the spin phase transition at filling factor 2/3 in a high-mobility GaAs/AlGaAs quantum well, revealing a minimum in activation energy indicative of a spin transition.

Contribution

It introduces a contactless acoustic method to probe the spin phase transition at fractional quantum Hall states in high-mobility quantum wells.

Findings

Observed a minimum in activation energy at the 2/3 filling factor.

Demonstrated the ability to control the spin phase transition via magnetic field tilt.

Provided evidence for a spin unpolarized-polarized phase transition.

Abstract

High frequency (ac) conductivity in the single quantum well AlGaAs/GaAs/AlGaAs with high mobility was investigated by contactless acoustic methods in the fractional quantum Hall effect regime in perpendicular and tilted magnetic fields. We studied the dependence of ac conductivity $\sigma^{ac}=\sigma_1 - i\sigma_2$ on both the temperature and magnetic field tilt angle. Tilting the magnetic field relative to the sample surface enabled us to change the position of the conductivity oscillation minimum at $\nu$=2/3. We measured the temperature dependence of ac conductivity for each tilt angle and for the 2/3 state we calculated the activation energy $\Delta E$ which was derived by constructing the Arrhenius plot ln $\sigma_1$ against 1/$T$. Analyzing behavior of the activation energy in total magnetic field for the filling factor 2/3 we observed a distinct minimum which can be interpreted as the spin unpolarized-polarized phase transition.