Magnetic Tuning of the Relativistic BCS-BEC Crossover

TL;DR

This paper explores how magnetic fields influence the transition between BEC and BCS pairing regimes in relativistic fermion systems, revealing that strong magnetic fields favor the BCS state regardless of initial conditions.

Contribution

It demonstrates that magnetic fields can tune the BCS-BEC crossover in relativistic systems, a process distinct from atomic systems, linked to Landau level occupation rather than Feshbach resonances.

Findings

Magnetic fields can induce a transition to a pure BCS regime in relativistic fermion systems.

The tuning mechanism is related to Landau level occupation, not Feshbach resonances.

The system always reaches a BCS state at high magnetic fields, regardless of initial state.

Abstract

The effect of an applied magnetic field in the crossover from Bose-Einstein condensate (BEC) to Bardeen-Cooper-Schrieffer (BCS) pairing regimes is investigated. We use a model of relativistic fermions and bosons inspired by those previously used in the context of cold fermionic atoms and in the magnetic-color-flavor-locking phase of color superconductivity. It turns out that as with cold atom systems, an applied magnetic field can also tune the BCS-BEC crossover in the relativistic case. We find that no matter what the initial state is at B=0, for large enough magnetic fields the system always settles into a pure BCS regime. In contrast to the atomic case, the magnetic field tuning of the crossover in the relativistic system is not connected to a Feshbach resonance, but to the relative numbers of Landau levels with either BEC or BCS type of dispersion relations that are occupied at each magnetic field strength.