Multiphoton antiresonance in large-spin systems

TL;DR

This paper investigates the nonlinear response of large-spin systems with easy-axis anisotropy, revealing sharp features in their response during multiphoton resonance sweeps, with implications for molecular magnet dynamics.

Contribution

It introduces a detailed analysis of multiphoton antiresonance phenomena in large-spin systems, highlighting the role of symmetry and anisotropy in their nonlinear response.

Findings

Sharp dips or peaks occur at multiphoton resonances.

Higher-order anisotropy causes sharp steps in response.

Response shape depends on modulation amplitude.

Abstract

We study nonlinear response of a spin $S>1/2$ with easy-axis anisotropy. The response displays sharp dips or peaks when the modulation frequency is adiabatically swept through multiphoton resonance. The effect is a consequence of a special symmetry of the spin dynamics in a magnetic field for the anisotropy energy $\propto S_z^2$. The occurrence of the dips or peaks is determined by the spin state. Their shape strongly depends on the modulation amplitude. Higher-order anisotropy breaks the symmetry, leading to sharp steps in the response as function of frequency. The results bear on the dynamics of molecular magnets in a static magnetic field.