Observation of a new phase transition between fully and partially polarized quantum Hall states with charge and spin gaps at $ν= 2/3$
The average electron spin-polarization $\cal P$ of two-dimensional electron gas confined in $\rm GaAs/GaAlAs$ multiple quantum-wells was measured by nuclear magnetic resonance (NMR) near the fractional quantum Hall state with filling factor $ν={2/3}$. Above this filling factor (${2/3} \leq ν< 0.85$), a strong depolarization is observed corresponding to two spin flips per additional flux quantum. The most remarkable behavior of the polarization is observed at $ν={2/3}$, where a quantum phase transition from a partially polarized (${\cal P} \approx {3/4}$) to a fully polarized (${\cal P} = 1$) state can be driven by increasing the ratio between the Zeeman and the Coulomb energy above a critical value $η_{c} = \frac{Δ_{Z}}{Δ_{C}} = 0.0185$.
cond-mat.mes-hall↗