Mechanism of the second-threshold effective-field onset

Determine the detailed underlying self-consistent dynamical mechanism responsible for the experimentally observed onset of the state-dependent effective-field contribution above the second threshold in dense cesium vapor under strong spin exchange.

Background

The phenomenological model describes branch-dependent effective-field behavior through an anisotropic coupling between the primary alignment tensor and the collective orientation. It reproduces the qualitative hysteresis and bistability associated with the observed effective-field contribution, but it does not derive the microscopic or fully self-consistent dynamics responsible for the emergence of that contribution above the second threshold.

The unresolved issue concerns why the effective-field behavior begins above a distinct threshold and what qualitative change in the coupled collective and single-atom dynamics produces it. The paper explicitly states that the detailed mechanism is not determined by the present treatment.