Using photoemission spectroscopy to probe a strongly interacting Fermi gas

Area of Science:

• Quantum physics
• Ultracold atomic gases
• Many-body systems

Background:

• Ultracold atomic gases serve as model systems for many-body quantum physics.
• Fermi gases exhibit a phase transition to a superfluid state with strong interactions, realizing the BCS-BEC crossover.
• Measuring the single-particle excitation spectrum, a fundamental property, has been a key challenge.

Purpose of the Study:

• To directly probe elementary excitations and energy dispersion in a strongly interacting Fermi gas.
• To measure the occupied density of single-particle states across the BCS-BEC crossover.
• To compare results with a nearly ideal Fermi gas and theoretical predictions.

Main Methods:

• Utilized photoemission spectroscopy on ultracold (40)K Fermi gas.
• Employed radio-frequency photons for spin-flip transitions to eject atoms.
• Measured the density of occupied single-particle states at and near the BCS-BEC crossover.

Main Results:

• Demonstrated a dramatic alteration of the single-particle spectral function near the critical temperature.
• Observed results consistent with a large pairing gap in the strongly interacting Fermi gas.
• Showcased the potential for comparing ultracold atomic gas data with high-transition-temperature superconductors.

Conclusions:

• Photoemission spectroscopy directly probes low-energy excitations in ultracold atomic gases, revealing excitation gaps and pseudogaps.
• The technique offers an analogue to angle-resolved photoemission spectroscopy for studying anisotropic systems.
• This method provides a new avenue for investigating complex many-body quantum phenomena.