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Title: The capacity and NMR investigation of two dimensional helium mixtures adsorbed on grafoil
Author: Ziouzia, Fanoula.
ISNI:       0000 0001 3577 985X
Awarding Body: Royal Holloway, University of London
Current Institution: Royal Holloway, University of London
Date of Award: 2004
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The subject of this thesis is the investigation of two dimensional helium mixtures adsorbed on Grafoil. Heat capacity and Nuclear Magnetic Resonance (NMR) measurements were used in the temperature range of 1 mK to 90 mK. This work represents the first systematic study of monolayer fluid helium mixtures adsorbed in Grafoil at low mK temperatures, extends previous experimental observations on solid helium mixtures and explores the ground state of 3He on top of three layers of 4He. The experimental setup consists of a dilution refrigerator with a nuclear de magnetisation stage with the possibility to achieve ultra low temperatures of 0.3 mK. An NMR setup was constructed to perform continuous wave NMR measurements and was satisfactorily used to obtain data for this thesis. A series of automated, computer controlled data acquisition programmes was also developed to measure and analyse the signals. The study involved the investigation of three different types of mixtures on the second and third layer of Grafoil. The study of fluid mixtures lead for the first time, to evidence of finite solubility of 2D 3He in fluid 4He. It was also possible to explore, within the data collected, the phenomenon of phase separation within a monolayer mixture. Furthermore, the possibility of 3He condensation and stratification effects in this system were also argued as an alternative scenario. A study of solid helium mixtures supported previous observations of delocalised 3He tunnelling excitations and a model was constructed to interpret the data. Additional data in this mixture at various 3He concentrations provided evidence of finite solubility of 3He in 2D solid 4He. Finally, additional measurements were undertaken on 3He on top of three layers of 4He. A number of new and interesting features were observed. The new data suggest the possibility of a phase transition below 10 mK
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available