Equilibrium shape of (4)He crystal under zero gravity below 200 mK.
Takuya Takahashi1, Haruka Ohuchi1, Ryuji Nomura1
1Department of Physics, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo 152-8551, Japan.
Science Advances
|November 25, 2015
Summary
Researchers observed the equilibrium crystal shape of helium-4 (4He) quantum crystals in a superfluid under zero gravity. These crystals rapidly relaxed to their lowest energy state, revealing unique properties of quantum crystal surfaces.
Area of Science:
- Quantum physics
- Materials science
- Low-temperature physics
Background:
- Equilibrium crystal shape (ECS) is the lowest energy configuration, typically difficult to achieve due to slow relaxation in ordinary crystals.
- Helium-4 (4He) quantum crystals in superfluid are theoretically expected to exhibit rapid growth and relaxation at low temperatures.
- Gravity distorts macroscopic crystals, masking their true equilibrium shape, necessitating a microgravity environment for observation.
Purpose of the Study:
- To investigate the relaxation processes and equilibrium crystal shape of macroscopic (4)He crystals in a superfluid under zero gravity.
- To overcome gravitational deformation and observe the intrinsic equilibrium shape of (4)He quantum crystals.
- To determine Wulff's construction parameters and interfacial free energies for different crystal facets.
Main Methods:
- Experiments conducted on macroscopic (4)He crystals in a superfluid at temperatures below 200 mK.
- Utilized a parabolic flight of a jet plane to achieve a temporary zero-gravity environment.
- Observed crystal shape evolution and relaxation dynamics after removal of gravitational effects.
Main Results:
- (4)He crystals rapidly transformed into a shape with flat surfaces upon removal of gravity.
- Despite initial condition dependency, crystals ultimately relaxed to a homothetic shape, confirming equilibrium.
- Successfully determined Wulff's origin, c-facet size, vicinal surface profiles, and interfacial free energies for a- and s-facets.
Conclusions:
- Macroscopic (4)He crystals in superfluid can rapidly achieve their equilibrium shape in microgravity.
- The observed equilibrium shape provides insights into the Wulff construction and surface properties of quantum crystals.
- Facet-like surfaces observed were identified as vicinal surfaces, with extremely small c-facet sizes in these quantum crystals.
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