Generalized Rotational Susceptibility Studies of Solid [superscript 4]He
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10909_2012_Article_650.pdf
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Author(s)
Gadagkar, V.
Pratt, E. J
Yamashita, M.
Graf, M. J
Balatsky, A. V
Davis, J. C
Pratt, E. J.
Graf, M. J.
Balatsky, A. V.
Davis, J. C.
Alternative Title
Generalized Rotational Susceptibility Studies of Solid 4He
Date Issued
July 2012
Journal
Journal of Low Temperature Physics
Publisher
Springer US
Citation
Gadagkar, V. et al. “Generalized Rotational Susceptibility Studies of Solid 4He.” Journal of Low Temperature Physics 169.3–4 (2012): 180–196.
Version
Author's final manuscript
Abstract
Using a novel SQUID-based torsional oscillator (TO) technique to achieve increased sensitivity and dynamic range, we studied TO’s containing solid [superscript 4]He. Below ∼250 mK, the TO resonance frequency f increases and its dissipation D passes through a maximum as first reported by Kim and Chan. To achieve unbiased analysis of such [superscript 4]He rotational dynamics, we implemented a new approach based upon the generalized rotational susceptibility χ[subscript 4He][superscript -1](ω,T). Upon cooling, we found that equilibration times within f(T) and D(T) exhibit a complex synchronized ultraslow evolution toward equilibrium indicative of glassy freezing of crystal disorder conformations which strongly influence the rotational dynamics. We explored a more specific χ[subscript 4He][superscript -1](ω,τ(T)) with τ(T) representing a relaxation rate for inertially active microscopic excitations. In such models, the characteristic temperature T* at which df/dT and D pass simultaneously through a maximum occurs when the TO angular frequency ω and the relaxation rate are matched: ωτ(T*)=1. Then, by introducing the free inertial decay (FID) technique to solid [superscript 4]He TO studies, we carried out a comprehensive map of f(T,V) and D(T,V) where V is the maximum TO rim velocity. These data indicated that the same microscopic excitations controlling the TO motions are generated independently by thermal and mechanical stimulation of the crystal. Moreover, a measure for their relaxation times τ(T,V) diverges smoothly everywhere without exhibiting a critical temperature or velocity, as expected in ωτ=1 models. Finally, following the observations of Day and Beamish, we showed that the combined temperature-velocity dependence of the TO response is indistinguishable from the combined temperature-strain dependence of the [superscript]4He shear modulus. Together, these observations imply that ultra-slow equilibration of crystal disorder conformations controls the rotational dynamics and, for any given disorder conformation, the anomalous rotational responses of solid [superscript 4]He are associated with generation of the same microscopic excitations as those produced by direct shear strain.
MIT Department
Massachusetts Institute of Technology. Department of Physics
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DOI of Published Version
https://doi.org/10.1007/s10909-012-0650-3
