Electron transport in confined structures in very high mobility GaAs in perpendicular magnetic fields

In this thesis we study properties of two-dimensional electron transport through constrictions in perpendicular magnetic fields. We present two sets of experiments, one focusing on properties in the integer quantum Hall effect the second looking at properties in the fractional quantum Hall effect at filling fraction v = 5/2. Both sets of experiments employ electrostatically defined quantum point contacts (QPCs) fabricated on a high mobility GaAs/AlGaAs two-dimensional electron gas (2DEG). In the first set of experiments, we study the suppression of the spin splitting of the Landau levels in QPCs compared to the bulk 2DEG. By using QPCs with different lithographic widths and varying the voltage applied on the gates, we can control the width of the conduction channel from ~3000 to ~100 nm. The width of the channel is estimated from the low magnetic field dependence of the conductance through the QPC. We study the suppression of the spin-splitting of the Landau levels as a function of the effective width of the QPC and measure the number of channels of conduction Ns, above which the spin-splitting is no longer observed. We find that Ns is approximately half of the number of quantized channels in the QPC for all widths less than approximately 1200 nm. For the same width range, we show that the cyclotron diameter at the lowest magnetic field where the spin splitting is resolved is half of the effective width of the QPC. In the second set of experiments, in the fractional quantum Hall regime at v = 5/2, QPCs are used to bring counter-propagating edge states close enough that quasiparticles can tunnel between them.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Physics.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2009

Author dc:creator

• Radu, Iuliana

Advisor dc:contributor.advisor

• Marc A. Kastner.

• Physics.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/53208

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/53208