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The Anomalous Behavior of Solid He in Porous Vycor Glass
The low temperature properties of solid He contained in porous Vycor
glass have been investigated utilizing a two-mode compound torsional
oscillator. At low temperatures, we find period shift signals for the solid
similar to those reported by Kim and Chan \cite{ref1}, which were taken at the
time as evidence for a supersolid helium phase. The supersolid is expected to
have properties analogous to those of a conventional superfluid, where the
superfluid behavior is independent of frequency and the ratio of the superfluid
signals observed at two different mode periods will depend only on the ratio of
the sensitivities of the mode periods to mass-loading. In the case of helium
studies in Vycor, one can compare the period shift signals seen for a
conventional superfluid film with signals obtained for a supersolid within the
same Vycor sample. We find, contrary to our own expectations, that the signals
observed for the solid display a marked period dependence not seen in the case
of the superfluid film. This surprising result suggests that the low
temperature response of solid He in a Vycor is more complex than previously
assumed and cannot be thought of as a simple superfluid.Comment: 4 pages, 5 figure
Bubble Nucleation of Spatial Vector Fields
We study domain-walls and bubble nucleation in a non-relativistic vector
field theory with different longitudinal and transverse speeds of sound. We
describe analytical and numerical methods to calculate the orientation
dependent domain-wall tension, . We then use this tension to
calculate the critical bubble shape. The longitudinally oriented domain-wall
tends to be the heaviest, and sometime suffers an instability. It can
spontaneously break into zigzag segments. In this case, the critical bubble
develops kinks, and its energy, and therefore the tunneling rate, scales with
the sound speeds very differently than what would be expected for a smooth
bubble.Comment: version 4, correction in the citation
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