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Abstract:

Magnetotransport measurements have been performed in strongly coupled two-dimensional electron-hole gases in an InAs Gash heterostructure in the presence of antidot potentials of different strengths. We have observed commensurability features in the magnetoresistance that we attribute to high mobility electrons. It is proposed that they can be observed due to magnetic breakdown, despite the fact that the electron-hole mixing is found to play an important role. (C) 2002 Elsevier Science B.V. All rights reserved.

Abstract:

We report a study of cyclotron resonance (CR) in a bilayer-bipolar InAs/GaSb structure and the influence of the spatial separation between the electrons and holes. At low magnetic fields we find that the cyclotron mass of the electrons can double when the electrons and holes have a very small separation. At higher cyclotron energies we find that the CR lines are split by a series of resonances which are due to interband coupling, and which also increase rapidly in magnitude when the electron-hole separation is decreased. At very high fields, in the quantum limit a new series of couplings is observed, with the resonances being split by energies in the range of 3-12 meV. (C) 2002 Elsevier Science B.V. All rights reserved.

Abstract:

We report a study of the spin polarisation of 2D electrons around an occupancy v = 1 for a series of quantum wells with widths ranging from 250 to 51 A in which the electron g-factor passes through zero, Our data are inconsistent with present theoretical pictures of the quantum Hall ferromagnet at v = 1 and suggest that a robust collective state forms in the region of v = 1 but that this state does not correspond to full spin polarisation of the system at values of g-factor less than similar to 0.5. (C) 2002 Elsevier Science B.V. All rights reserved.

Abstract:

We examine the quantum Hall effect in an electron-hole system and its current-driven breakdown, We find that samples with closely matched electron and hole concentrations have vastly reduced critical cur-rents while those with many more electrons than holes show much larger critical currents, though still smaller than those reported for single-carrier type systems, The channel width dependence shows two regimes of behaviour. States with larger critical cur-rents ( > 5 muA) have linear width dependence. while for narrower channel widths where the critical current is smaller, the critical current has a superlinear relationship with the channel width. (C) 2002 Elsevier Science B.V. All rights reserved.

Abstract:

We report a study of the spin polarization of the Composite Fermion system in the occupancy range 1 < v(e) < 2 equivalent to the occupancy range 1 > v(h) > 0 of Composite Fermion holes, Polarized magneto-reflectivity is used to measure the polarization of the unoccupied states in the lowest Landau level. We observe the existence of spin polarized and unpolarized states at v(e) = 5/3 = 2 - 1/3 and v(e) = 4/3 = 2 - 2/3. We measure the polarization of the Composite Fermion gas at v(e) = 3/2 = 2 - 1/2 from which we can deduce the Composite Fermion mass. (C) 2002 Elsevier Science B.V. All rights reserved.