Robin Nicholas

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.