Robin Nicholas

Abstract:

The quantum Hall effect has been measured in an intrinsic semimetallic superlattice with almost equal electron and hole densities. Giant oscillations are seen in the Hall resistivity, and at high fields and pressures a zero-resistance state is observed where the Hall resistivity goes to zero due to compensation of the Hall fields of the two carrier types. This behaviour is interpreted in terms of the limiting properties of rho(xx) and rho(xy)

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.