Magneto-optical evidence of the percolation nature of the   metal-insulator transition in the 2D electron system
  We compare the results of the transport and time-resolved magneto-luminescence measurements in disordered 2D electron systems in GaAs-AlGaAs heterostructures in the extreme quantum limit, in particular, in the vicinity of the metal-insulator transition (MIT). At filling factors $\nu <1$, the optical signal has two components: the single-rate exponentially decaying part attributed to a uniform liquid and a power-law long-living tail specific to a microscopically inhomogeneous state of electrons. We interprete this result as a separation of the 2D electron system into a liquid and localized phases, especially because the MIT occurs strikingly close to those filling factors where the liquid occupies ${1\over 2}$ of the sample area (the percollation threshold condition in two-component media). 
I.V. Kukushkin (ISSP, Chernogolovka), Vladimir I. Fal'ko (Lancaster   Univ.), R.J. Haug (Univ. of Hannover), K. v. Klitzing,...