Boiling a Unitary Fermi Liquid.

Area of Science:

• Atomic, Molecular, and Optical Physics
• Condensed Matter Physics
• Quantum Gases

Background:

• Understanding the thermal evolution of quantum degenerate Fermi gases is essential for exploring many-body physics.
• Highly spin-imbalanced Fermi gases exhibit complex phenomena, including polaron formation and transitions to classical gas behavior.

Purpose of the Study:

• To investigate the thermal evolution of a homogeneous, spin-imbalanced Fermi gas with unitarity-limited interactions.
• To characterize Fermi polarons and their properties across different temperature regimes, from quantum degenerate to classical.

Main Methods:

• Utilized radio-frequency spectroscopy to probe the energy, lifetime, and correlations of Fermi polarons at low temperatures.
• Performed density measurements in a harmonic trap to study the dressing cloud and polaron effective mass.

Main Results:

• Observed a T^2 dependence of spectral width at low temperatures, consistent with Fermi liquid theory.
• Found the spectral width decreases as T^-1/2 at high temperatures, matching the classical Boltzmann gas behavior.
• Identified a maximum spectral width in the transition region, indicating a breakdown of quasiparticle description.

Conclusions:

• The study maps the thermal evolution from a Fermi liquid of polarons to a classical Boltzmann gas.
• Fermi polaron properties, including effective mass and compressibility, were determined.
• The transition region highlights the limits of quasiparticle descriptions in strongly interacting Fermi gases.