Type of Document	Dissertation
Author	Wierschem, Keola
Author's Email Address	kjw7591@fsu.edu
URN	etd-07122010-185540
Title	Role of Defects in Possible Superfluidity of Spatially Ordered Helium
Degree	Doctor of Philosophy
Department	Physics, Department of
Advisory Committee	Advisor Name Title Efstratios Manousakis Committee Chair David Van Winkle Committee Member Mark Riley Committee Member Nicholas Bonesteel Committee Member Wei Yang University Representative
Keywords	Supersolid KTHNY Condensed Matter Physics Computational Physics
Date of Defense	2010-06-29
Availability	unrestricted
Abstract A path integral Monte Carlo investigation of the role of defects in ordered helium-4 systems has been conducted. We find that interstitial defects in two- and three-dimensional solid helium-4 can lead to a small but non-zero superfluid fraction, while still maintaining the original solid ordering. Furthermore, a helium-3 impurity atom initially placed as an interstitial defect is found to relax onto the solid lattice through the promotion of a helium-4 atom to the interstitial space. We also study the melting transition of pure helium-4 in two dimensions, where thermally excited defects give rise to unique phases with quasi-long-range order. Finite-size scaling techniques, initially applied to a classical system of Lennard-Jones particles, are found to be able to distinguish two separate melting temperatures. Additionally, coexistence of superfluid and diagonal order was observed in several of our finite-sized samples, raising the possibility that such real- and momentum-space ordering could be held simultaneously by quantum systems in two dimensions.
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