New phase transition between partially and fully polarized quantum Hall states with charge and spin gaps at ν=2/3 -: art. no. 136801

The average electron spin polarization P of a two-dimensional electron gas confined in GaAs/GaAlAs multiple quantum wells was measured by NMR near the fractional quantum Hall state with filling factor nu =2/3. Above this filling factor (2/3 less than or equal to nu <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 <nu>=2/3, where a quantum phase transition from a partially polarized (P approximate to3/4) to a fully polarized (P = 1) state can be driven by increasing the ratio between the Zeeman and the Coulomb energy above a critical value eta (c) = Deltaz/Deltac = 0.0185.