Thermal BCS-BEC Crossovers in Finite Systems

Area of Science:

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

Background:

• The Bardeen-Cooper-Schrieffer (BCS) to Bose-Einstein Condensate (BEC) crossover describes the transition in interacting quantum gases.
• Conventional BCS-BEC crossover is typically tuned by interaction strength.

Purpose of the Study:

• Investigate the thermal evolution of fermionic pairings in a finite-size SU(2) × SU(2) complex model.
• Explore temperature as a sole driver for a BCS-like to BEC-like state transition.

Main Methods:

• Utilized an exactly solvable model with a finite number of fermions.
• Analyzed eigenstate structures, pairing correlations, and thermodynamic response functions.
• Examined the role of thermal fluctuations and multiplet structures.

Main Results:

• Demonstrated that temperature alone can induce a smooth transition from weakly bound Cooper pairs (BCS-like) to tightly bound dimers (BEC-like).
• Showcased that different multiplet structures, defined by quasi-spin quantum numbers, become thermally accessible.
• Observed crossover behavior analogous to that in ultracold Fermi gases.

Conclusions:

• Thermal fluctuations play a significant role in quantum pairing phenomena.
• Temperature-induced crossover offers alternative routes for exploring crossover physics in mesoscopic and strongly correlated systems.
• The study provides a novel perspective on controlling quantum states via thermal evolution.