The BKT transition and its dynamics in a spin fluid

Area of Science:

• Condensed Matter Physics
• Statistical Mechanics
• Computational Physics

Background:

• Understanding phase transitions in systems with mobile particles is crucial.
• Spin fluids exhibit complex behaviors influenced by particle interactions and dynamics.
• The 2D XY model and BKT universality class provide a theoretical framework for such transitions.

Purpose of the Study:

• To investigate the impact of particle mobility on phase transitions in a 2D spin fluid.
• To determine if the system exhibits a BKT universality class transition.
• To analyze both static and dynamic properties around the critical temperature.

Main Methods:

• Off-lattice computer simulations of particles with purely repulsive interactions.
• Analysis of static correlation functions and finite-size scaling.
• Investigation of dynamic aspects, including spin autocorrelation functions and spin wave dynamics.

Main Results:

• A phase transition belonging to the BKT universality class was identified.
• A critical temperature T_BKT = 0.17(1) was determined.
• Static correlations transitioned from power-law to exponential decay at T_BKT.
• Dynamic behavior showed agreement with Nelson-Fisher predictions at short times but differed at long times compared to the static XY model.
• Spin wave dynamics were consistent with hydrodynamic theory, though particle mobility increased damping.

Conclusions:

• Particle mobility significantly affects spin wave damping in 2D spin fluids.
• Despite enhanced damping, the model remains within the dynamic universality class of the standard XY model.
• The study confirms the presence of a BKT-type phase transition in this off-lattice model.