High-sensitive optical measurement of spin polarization in a quantum Hall system

Spin polarization measurement is important for the study of a variety of spin states in quantum Hall system. Kerr rotation is proportional to spin polarization, so we developed a high sensitive measurement of Kerr rotation by using homodyne detection and a variety of modulation techniques. Furthermore, we developed Kerr rotation spectra measurement system base on the multi-channel homodyne detection, which enables the assignment of the optical transitions and semi-quantitative estimation of spin polarization by integrating the spectra over the specific optical transition. The spin polarization presents a rapid spin depolarization on both sides of ν= 1 due to Skyrmionic excitation. However the top of spin polarization presents a narrow flat region. Furthermore the spin polarization around ν=3 also shows a rapid spin depolarization which suggest the existence of Skyrmion at higher odd filling factor.