Observation of mixed fermionic-bosonic helium clusters by transmission grating diffraction

Area of Science:

• Atomic and Molecular Physics
• Quantum Fluids
• Low-Temperature Physics

Background:

• Investigating weakly bound clusters of helium isotopes (4He and 3He) is crucial for understanding quantum phenomena.
• Previous theoretical models predicted the existence of various exotic cluster structures, but experimental verification remained challenging.

Purpose of the Study:

• To experimentally identify and characterize small, weakly bound boson-fermion clusters of helium-3 (3He) and helium-4 (4He).
• To confirm the existence of predicted exotic molecular complexes, such as halo and pseudo-Borromean structures.

Main Methods:

• Utilized nondestructive transmission grating diffraction to probe clusters formed in a free jet expansion.
• Employed a sudden freeze model incorporating theoretical binding energies to analyze cluster formation temperatures.

Main Results:

• Confirmed the existence of more than 11 tenuous helium-3/helium-4 complexes.
• Observed specific structures including the three-body halo molecule (4He2 3He) and the pseudo-Borromean complex (4He2 3He2).
• Demonstrated a smooth increase in effective cluster formation temperatures with increasing cluster size, supporting theoretical binding energy calculations.

Conclusions:

• The experimental observations provide strong evidence for the existence of numerous weakly bound helium clusters.
• The findings validate theoretical predictions for exotic molecular structures in helium systems.
• The study confirms the applicability of the sudden freeze model for describing cluster growth dynamics.