Absence of spin superradiance in resonatorless magnets

TL;DR

This paper demonstrates through quantum-mechanical analysis that molecular magnets with dipole interactions do not exhibit superradiance without a resonant circuit, emphasizing the negligible effect of radiation on their spin dynamics.

Contribution

The study provides a detailed quantum derivation showing the absence of superradiance in resonatorless molecular magnets, clarifying the conditions needed for superradiance to occur.

Findings

Radiation effects on spin dynamics are negligible.

No superradiance occurs in resonatorless molecular magnets.

Superradiance requires coupling to a resonant electric circuit.

Abstract

A spin system is considered with a Hamiltonian typical of molecular magnets, having dipole-dipole interactions and a single-site magnetic anisotropy. In addition, spin interactions through the common radiation field are included. A fully quantum-mechanical derivation of the collective radiation rate is presented. An effective narrowing of the dipole-dipole attenuation, due to high spin polarization is taken into account. The influence of the radiation rate on spin dynamics is carefully analysed. It is shown that this influence is completely negligible. No noticeable collective effects, such as superradiance, can appear in molecular magnets, being caused by electromagnetic spin radiation. Spin superradiance can arise in molecular magnets only when these are coupled to a resonant electric circuit, as has been suggested earlier by one of the authors in Laser Phys. {\bf 12}, 1089 (2002).