Molecular superfluid: nonclassical rotations in doped para-hydrogen clusters

Area of Science:

• Quantum fluid dynamics
• Low-temperature physics
• Molecular clusters

Background:

• Theoretical predictions suggested para-hydrogen (pH₂) clusters could exhibit superfluidity.
• Experimental observation of this phenomenon in pH₂ clusters has been challenging.

Purpose of the Study:

• To investigate the size evolution of the superfluid response in para-hydrogen clusters doped with carbon dioxide (CO₂).
• To determine the conditions under which molecular superfluidity emerges in para-hydrogen.

Main Methods:

• Combined experimental techniques with theoretical simulations.
• Analyzed the size-dependent superfluid response of CO₂-doped pH₂ clusters.

Main Results:

• Observed a reduction in effective inertia when CO₂ dopants were surrounded by the pH₂ solvent.
• This reduction signifies the onset of molecular superfluidity in para-hydrogen.
• Found a correlation between the fractional occupation of solvation rings around CO₂ and enhanced superfluid response in specific cluster sizes.

Conclusions:

• This study provides the first direct evidence of molecular superfluidity in para-hydrogen clusters.
• The findings demonstrate that doping with CO₂ can induce and modulate superfluid behavior in pH₂.
• The results offer insights into the quantum behavior of molecular clusters and the factors influencing superfluidity.