Quasiparticle charge in the nu=5/2 fractional quantum Hall state
Abstract
The fractional quantum Hall effect is a prime example of collective behavior of strongly interacting electrons. Its excitations (quasiparticles) carry a fractional charge, and are expected to obey fractional statistics. While odd denominator fractional states are expected to have abelian statistics, the newly discovered 5=2 even denominator state is expected to have a non-abelian statistics. Moreover, a large number of emerging proposals predict that the latter state can be employed for topological quantum computation. The main goal of this work was to study the quasiparticles of the nu = 5=2 quantum Hall state, focusing on their charge. As a first step, a growth technique for 2D electron gases, which supports the fragile nu = 5=2 state was developed. Shot noise measurements at different quantum Hall states allowed us to deduce the quasiparticle charge. In particular, the nu = 5=2 quasiparticles were found to carry a charge of e/4, providing the first experimental support to the theory that is conjectured to explain the nu = 5=2 quantum Hall effect: the Moore-Read theory. This is of significant importance, since based on the Moore-Read theory, the nu = 5=2 state is a prime candidate for a physical system in which the quasiparticles obey a special statistics, known as non-abelian statistics. An improvement of our experimental methods enabled us to perform more recent measurements at lower excitation energies. The results obtained under the improved conditions were unexpected: Although e/4 quasiparticles were measured at higher excitation energies, agreeing with our previous work, in the limit of extremely low energies (extremely low temperatures and impinging currents) and very weak backscattering, the backscattered quasiparticle charge seemed to increase toward a full electron charge. This result was found to be consistent also at other fractional quantum Hall states, such as nu = 7=3 and nu = 1=3. As this limit of low energies and weak backscattering is of great interest from both theoretical and experimental point of views, these results affect not only our current understanding of the nature of the nu = 5=2 quasiparticles, but also the main proposals for experiments aimed at detecting their statistics.
- Publication:
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Ph.D. Thesis
- Pub Date:
- 2011
- Bibcode:
- 2011PhDT.......196D
- Keywords:
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- Physics, Quantum;Physics, Elementary Particles and High Energy