Spin Susceptibility above the Superfluid Onset in Ultracold Fermi Gases

Area of Science:

• Condensed matter physics
• Ultracold atomic gases
• Quantum simulation

Background:

• Ultracold atomic Fermi gases exhibit phenomena analogous to the cuprate pseudogap.
• Fermi liquid theory successfully describes some thermodynamic properties of spin-imbalanced normal states.

Purpose of the Study:

• Investigate spin susceptibility in ultracold Fermi gases across interaction strengths and temperatures.
• Explore the validity of analogies with cuprates and Fermi liquid theory.

Main Methods:

• Utilized a novel radio frequency technique for spin susceptibility measurements.
• Employed ultracold Lithium-6 (⁶Li) gases.
• Analyzed data across a wide interaction strength-temperature phase diagram.

Main Results:

• Observed reduced spin susceptibility compared to noninteracting Fermi gases at all conditions.
• Extracted integrated spin susceptibility at unitarity, finding it lower than theoretical predictions at high temperatures.
• Data at low temperatures align with theoretical predictions and a simple mean-field model.

Conclusions:

• Spin susceptibility in ultracold Fermi gases is consistently reduced.
• The findings provide insights into the normal state properties of strongly interacting Fermi gases.
• A simple one-parameter mean-field model effectively describes the observed spin susceptibility.