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Abstract:

Fractional Quantum Hall Effect measurements in 50 T pulsed magnetic fields, are analysed in the Composite Fermion (CF) model. Energy gaps of all fractions in the principal series around nu=1/2 show a simple, sample independent, increase with the CF effective field following root B*. The spin polarised state at nu=5/3 follows exactly the same behaviour, but for mixed spin states like 4/3 the energy gap collapses when B*>1 T.

Abstract:

We have performed magnetotransport measurements on InAs/(Ga,In)Sb heterostructures under hydrostatic pressure. The system has a cross gap band alignment which leads to the formation of co-existent 2D electron-hole gases. The amount of overlap and thus the electron and hole concentrations can be tuned by the application of hydrostatic pressure. The samples studied here have nearly equal electron and hole concentrations and show large oscillatory quantum Hall features. Measurements of the band overlap Delta and its rate of change with pressure d(Delta)/dP provides evidence that both the growth direction and also the composition of the interface layer play an important role in determining the band line-up.