One-component to two-component transitions of fractional quantum Hall states in a wide quantum well

Abstract

We report measurements of the quasi-particle excitation gaps for different fractional quantum Hall (FQH) states of a low-disorder, symmetric electron system in a 770 Å wide GaAs quantum well as a function of density, N s. At filling factor v = 1 2 , the electron system undergoes phase transitions from a compressible (metallic) state to an incompressible (FQH) state and then to an insulating phase as N s is increased. The v = 1 2 FQH state, observed in the range 1.0 × 10 11 N s{1.4 × 10 11cm −2}, is remarkably strong and its excitation gap reaches≅0.9 K at N s = 1.16 × 10 11cm−2. Our data suggest that this 1 2 FQH state has a two-component origin. We also observe a dramatic transition from a one-component to a two-component FQH state at v = 2 3 as N s is increased.