5/2 state in high election density gallium arsenide/aluminum gallium arsenide quantum well
Master of Science thesis
This Master of Science Thesis is concerned with electronic transport in the higher Landau levels (LL) in a two-dimensional electron system, where novel many-body electronic phases have been observed. Particular attention is paid to the even-denominator fractional quantum Hall states at LL filling factors 5/2 and 7/2, and the anisotropic states at 9/2 and 11/2. In a high electron density (n = 6.3 x 10 11cm-2), high mobility (mu = 1 x 107cm2/Vs) modulation-doped GaAs/Al0.24Ga 0.76As quantum well, we observed the nu = 5/2 quantum Hall plateau at a high magnetic field B = 10 T. In contrast to previous findings in a lower density system, electronic transport at nu = 9/2 and nu = 11/2 is essentially isotropic. Anisotropic transport at 9/2 and 11/2 can be induced by an in-plane magnetic field, B//. Depending on the B// direction, the nu = 5/2 diagonal resistances in a high B// either remain isotropic or become strongly anisotropic. Our data suggest a new regime for electronic transport in higher LLs.
Condensed matter physics