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Title: Quantised charge pumping in a perpendicular magnetic field
Author: Wright, Samuel James
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2010
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There are seven base units in the International System of Units; the metre, kilogram, second, kelvin, ampere, mole and candela. Quantum metrology aims to redefine these quantities in terms of fundamental constants of nature such as the Planck, A vogadro and Boltzmann constants. In the electrical domain, the quantum Hall effect and Josephson effect provide quantum standards for resistance and voltage, respectively. Combining them through Ampere's law yields an indirect quantum standard for current. However, a quantum metrological redefinition of the ampere requires a stand-alone source of current that is quantised for values directly related to fundamental constants. Quantised charge transport devices fabricated in semiconductor heterostructure materials are the most promising candidates for a redefinition of the ampere. Our observations of the quantised current produced by a tunable-barrier GaAs/ AlGaAs electron pump in the presence of a perpendicular magnetic field are documented in detail in this thesis. Perhaps the most important observation is an enhancement of the quantisation as a result of the applied field. To determine the accuracy of the quantisation we applied novel measurement techniques and compared the pumped current with an accurate current generated using primary electrical standards. The reader will find an account of our extensive study, demonstrating the most accurate quantised current source for a current greater than 50 pA. By operating multiple pumps in parallel the current is increased without any noticeable loss of accuracy. Our results have motivated the incorporation of tunable-barrier GaAs/ AlGaAs electron pumps into a system for performing the Quantum Metrological Triangle Experiment at the National Physical Laboratory.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral