Condensate-free superfluid induced by the frustrated proximity effect

Area of Science:

• Condensed Matter Physics
• Quantum Fluids
• Low-Temperature Physics

Background:

• The relationship between Bose condensation and superfluidity in bosonic systems has been a long-standing debate.
• Typically, superfluidity in dimensions D≥2 is associated with Bose-Einstein condensation in the ground state.
• Experimental systems, including ultracold atoms in optical lattices, usually exhibit condensation alongside superfluidity.

Purpose of the Study:

• To investigate the possibility of achieving superfluidity in a two-dimensional (2D) bosonic system without Bose condensation at zero temperature (T=0).
• To explore the properties of such a condensate-free superfluid, specifically its correlation functions.

Main Methods:

• Populating a 2D layer of bosons via a frustrated proximity effect from a coexisting superfluid reservoir.
• Theoretical analysis of the resulting 2D bosonic gas.

Main Results:

• A 2D gas of bosons that is not condensed at T=0 was successfully achieved.
• This condensate-free bosonic fluid was demonstrated to be superfluid.
• The superfluid exhibited incommensurate correlations.

Conclusions:

• Superfluidity can exist in 2D bosonic systems even in the absence of Bose-Einstein condensation at absolute zero.
• This finding challenges the conventional understanding linking ground-state condensation to superfluidity in 2D.
• The study opens new avenues for exploring quantum fluids with exotic properties.