Attractive and repulsive Fermi polarons in two dimensions

Area of Science:

• Quantum Many-Body Physics
• Condensed Matter Physics
• Atomic, Molecular, and Optical Physics

Background:

• Polarons, quasiparticles formed by an impurity interacting with a bath, are crucial in condensed matter systems like superconductors.
• While polarons in bosonic baths are well-understood, mobile impurities in fermionic baths (Fermi polarons) are a recent focus.
• Fermi polarons are key to understanding quantum phases in spin-imbalanced Fermi gases, relevant to Bose-Einstein condensates and superfluids.

Purpose of the Study:

• To experimentally investigate Fermi polarons in a two-dimensional (2D), spin-imbalanced Fermi gas.
• To probe the spectral function and properties of these polarons under attractive and repulsive interactions.
• To explore the stability and observability of quantum phases potentially realized in 2D Fermi gases.

Main Methods:

• Creation and manipulation of Fermi polarons in a 2D spin-imbalanced Fermi gas.
• Measurement of the quasiparticle spectral function using momentum-resolved photoemission spectroscopy.
• Systematic investigation across attractive and repulsive interaction regimes.

Main Results:

• Evidence for a disputed pairing transition between polarons and tightly bound dimers in the attractive interaction regime.
• Observation of novel repulsive polarons in the repulsive interaction regime.
• Characterization of the lifetime of repulsive polarons, impacting the stability of repulsively interacting Fermi systems.

Conclusions:

• The study provides crucial insights into the elementary pairing mechanism in imbalanced, strongly coupled 2D Fermi gases.
• The findings shed light on the properties and potential applications of Fermi polarons in 2D systems.
• This work advances the understanding of quantum phases and quasiparticle behavior in interacting Fermi gases.