BCS-BEC crossover in 2D Fermi gases with Rashba spin-orbit coupling

Area of Science:

• Condensed Matter Physics
• Quantum Gases
• Many-Body Physics

Background:

• The Bardeen-Cooper-Schrieffer (BCS) to Bose-Einstein Condensation (BEC) crossover describes the transition between fermionic superfluidity and bosonic condensation.
• Spin-orbit coupling (SOC) significantly influences the properties of quantum gases, particularly in two dimensions.
• Understanding these phenomena is crucial for developing novel quantum technologies.

Purpose of the Study:

• To theoretically investigate the BCS-BEC crossover in two-dimensional Fermi gases with Rashba spin-orbit coupling (SOC).
• To analyze the impact of SOC on bound state formation, ground-state properties, and the Berezinskii-Kosterlitz-Thouless (BKT) transition temperature.
• To elucidate the distinct behaviors of condensate and superfluid densities under SOC.

Main Methods:

• Exact two-body problem solution for attractive short-range interactions.
• Many-body theoretical analysis of dilute Fermi gases.
• Analytical calculations for ground-state properties and BKT transition temperature in various limits.

Main Results:

• SOC enhances bound state formation, increasing binding energy E(B) and effective mass m(B).
• A dilute Fermi gas transitions from BCS superfluid to Bose condensation of molecules as SOC increases.
• BKT transition temperature recovers that of a Bose gas with effective mass m(B) for large SOC.
• Condensate density is enhanced by SOC, while superfluid density is suppressed due to nontrivial molecule effective mass.

Conclusions:

• Rashba SOC plays a critical role in the BCS-BEC crossover of 2D Fermi gases.
• SOC modifies the fundamental properties of fermionic superfluids and molecular condensates.
• The interplay between SOC and interactions offers a tunable pathway to control quantum gas phases.