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).Comment: 5 pages RevTex + 4 fig., to appear in PRB, Rapid Com

Splitting of Landau levels of a 2D electron due to electron-phonon interactions

We show that in a very strong magnetic field $B$ electron-phonon interaction gives rise to a splitting of Landau levels of a 2D electron into a series of infinitely degenerate sublevels. We provide both qualitative and quantitative description of this phenomenon. The cases of interaction with acoustic and polar optical phonons are considered. The energy distance between nearest sublevels in both cases tends to zero as $B^{-1/2}$ at large $B$.Comment: 4 pages, LaTe

Extra Spin-Wave mode in Quantum Hall systems. Beyond the Skyrmion Limit

We report on the observation of a new spin mode in a quantum Hall system in the vicinity of odd electron filling factors under experimental conditions excluding the possibility of Skyrmion excitations. The new mode having presumably zero energy at odd filling factors emerges at small deviations from odd filling factors and couples to the spin-exciton. The existence of an extra spin mode assumes a nontrivial magnetic order at partial fillings of Landau levels surrounding quantum Hall ferromagnets other then the Skyrmion crystal.Comment: 9 pages, 4 figure

The Cyclotron Spin-Flip Mode as the Lowest-Energy Excitation of Unpolarized Integer Quantum Hall States

The cyclotron spin-flip modes of spin unpolarized integer quantum Hall states ($\nu =2,4$) have been studied with inelastic light scattering. The energy of these modes is significantly smaller compared to the bare cyclotron gap. Second order exchange corrections are held responsible for a negative energy contribution and render these modes the lowest energy excitations of unpolarized integer quantum Hall states.Comment: Published: Phys. Rev. B 72, 073304 (2005