Positive ion induced solidification of 4He

Area of Science:

• Low-temperature physics
• Condensed matter physics
• Quantum fluids

Background:

• Superfluid helium-4 (4He) exhibits unique quantum properties.
• Solid helium structures can coexist with superfluid helium below the solidification pressure.
• The stability of these solid structures against melting has been a subject of investigation.

Purpose of the Study:

• To investigate the role of charged particles in the solidification of 4He.
• To provide experimental evidence for the stabilization mechanism of solid helium structures.
• To determine the charge density within the observed solid helium structures.

Main Methods:

• Extraction of positive alkali ions from alkali-doped solid He into superfluid 4He using a static electric field.
• Observation of bulk solidification of 4He induced by nucleation on these ions.
• Determination of charge density using two independent experimental methods.

Main Results:

• Observed bulk solidification of 4He nucleated by positive alkali ions.
• Confirmed the existence of charged particles within the solid He structure.
• Provided evidence that Coulomb interactions and surface tension stabilize the solid structure.

Conclusions:

• Positive alkali ions act as nucleation sites for 4He solidification.
• Charged particles, specifically ions and potentially electron bubbles, are crucial for the stability of solid helium structures.
• The study quantifies charge density, contributing to a deeper understanding of matter at extreme conditions.