Inelastic light scattering in the fractional quantum Hall regime: Collapse of the intersubband energy

Low-temperature inelastic-light-scattering experiments reveal a collapse of the intersubband transition energy in the regime of the fractional quantum Hall effect. The collapse has a pronounced dependence on temperature, Landau filling factor, and light intensity. Changes in the intersubband energy remain observable at extremely low light intensities and temperatures down to T=0.05 K. Simultaneous conductivity measurements under illumination also reveal a depletion of the electron density at similar fields and temperatures. Self-consistent calculations of the subbands indicate a common mechanism for both effects.