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Quantum Hall Effect

Quantum Hall Effect. Tim Morgan. The Setup. V l. V H. I. The Experiment. Extreme Conditions: Large magnetic field (8-20 T) Low temperatures (< 4K) Material: Si MOSFET, GaAl/AlGaAs, or just about any 2DEG in the shape of a hall bar Procedure: Cool down and apply constant current

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Quantum Hall Effect

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  1. Quantum Hall Effect Tim Morgan

  2. The Setup Vl VH I NQHE 1.16.07

  3. The Experiment • Extreme Conditions: • Large magnetic field (8-20 T) • Low temperatures (< 4K) • Material: Si MOSFET, GaAl/AlGaAs, or just about any 2DEG in the shape of a hall bar • Procedure: • Cool down and apply constant current • Sweep magnetic field while measuring Hall and parallel voltages NQHE 1.16.07

  4. The Observations • Hall Resistance shows plateaus (top) • Parallel resistance shows 0 valleys (bottom) NQHE 1.16.07

  5. The Explaination WHO KNOWS?! NQHE 1.16.07

  6. Well, let’s at least try… • DOS for a 2DEG is a series of delta spikes • Spikes at Landau levels are broadened because of defects • Result: localized & non-localized states • As the Fermi energy changes with the magnetic field, it will shift into various regions of the broadened spikes causing the plateaus NQHE 1.16.07

  7. What Can You Do with This? • You can • Accurately measure • Establish Hall Resistance (25.813 k-ohms) • Independent of material parameters • Uncertainty < 5 x 10-8 from various samples • Determine the Fine Structure Constant NQHE 1.16.07

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