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Torsional oscillator and synchrotron X-Ray experiments on solid 4He in aerogel
N Mulders1, J T West, M H W Chan
1Department of Physics and Astronomy, University of Delaware, Newark, DE 19716, USA.
Physical Review Letters
|November 13, 2008
Summary
Solid helium-4 (4He) in aerogel exhibits a highly polycrystalline structure. Unexpectedly, it shows minimal supersolid behavior, similar to pure crystals, challenging prior expectations for disordered solids.
Area of Science:
- Condensed Matter Physics
- Quantum Materials
Background:
- Solid helium-4 (4He) is a quantum fluid.
- Aerogel confinement influences material properties.
- Supersolid behavior in 4He is a key area of research.
Purpose of the Study:
- To investigate the structural and supersolid properties of solid 4He confined within an aerogel matrix.
- To compare the behavior of 4He in aerogel to bulk solid 4He.
- To understand the impact of disorder on supersolidity.
Main Methods:
- X-ray diffraction experiments were used to determine the crystal structure and crystallite size.
- Torsional oscillator measurements were employed to quantify the supersolid fraction and onset temperature.
Main Results:
- Solid 4He in aerogel forms highly polycrystalline structures with hexagonal close-packed (hcp) crystal symmetry.
- Crystallite size was found to be approximately 100 nm.
- Torsional oscillator measurements revealed a low supersolid fraction (approximately 3 x 10^-4) and an onset temperature around 100 mK, similar to pure 4He crystals.
Conclusions:
- Despite the disordered aerogel environment, solid 4He maintains a well-defined hcp structure.
- The observed low supersolid fraction contradicts expectations for highly disordered systems, suggesting structural order plays a dominant role.
- These findings provide new insights into the relationship between disorder, structure, and supersolidity in quantum systems.
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