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Title: A torsional oscillator study of solid helium
Author: Nichols, George
ISNI:       0000 0004 8497 6480
Awarding Body: Royal Holloway, University of London
Current Institution: Royal Holloway, University of London
Date of Award: 2014
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A compound two-mode torsional oscillator is used to investigate the 'supersolid' signature in polycrystaline 4He. We observe a change in the resonant period of both torsion modes below 200mK, accompanied by dissipation peaks, consistent with the original observation of Kim and Chan. By careful analysis of the sensitivity of the two modes of the torsional oscillator we are able to account for contributions from changes in the shear modulus of the 4He sample proposed by Beamish et al and Maris, and the viscoelastic behaviour discussed by Yoo and Dorsey. We find that a zero-frequency period shift remains unaccounted for, corresponding to a velocity-dependant decoupling of 0.14% of the sample with a critical velocity of ~100 µm/s. We examine the results of Aoki et al and apply the same corrections to their work, finding a decoupling of 0.017% Extensive repair work performed on the cryostat during the experiment is also described.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Helium ; supersolid ; torsional oscillator