Decoherence window and electron-nuclear cross-relaxation in the molecular magnet V 15

TL;DR

This study investigates decoherence mechanisms in V15 single molecule magnets, revealing a resonant damping peak caused by electron-nuclear cross-relaxation at specific microwave frequencies, with implications for understanding spin dynamics in similar SMMs.

Contribution

It demonstrates the first observation of rapid electron-nuclear cross-relaxation decoherence in SMM V15 within a specific microwave frequency window, linking it to energy dissipation and suggesting universality in other proton-containing SMMs.

Findings

Damping peak occurs when Rabi frequency matches proton Larmor frequency.

Decoherence time is significantly shorter than phase coherence time.

Cross-relaxation effects are likely present in other proton-rich SMMs.

Abstract

Rabi oscillations in the V_15 Single Molecule Magnet (SMM) embedded in the surfactant DODA have been studied at different microwave powers. An intense damping peak is observed when the Rabi frequency Omega_R falls in the vicinity of the Larmor frequency of protons w_N, while the damping time t_R of oscillations reaches values 10 times shorter than the phase coherence time t_2 measured at the same temperature. The experiments are interpreted by the N-spin model showing that t_R is directly associated with the decoherence via electronic/nuclear spin cross-relaxation in the rotating reference frame. It is shown that this decoherence is accompanied with energy dissipation in the range of the Rabi frequencies w_N - sigma_e < Omega_R < w_N, where sigma_e is the mean super-hyperfine field (in frequency units) induced by protons at SMMs. Weaker damping without dissipation takes place outside this dissipation window. Simple local field estimations suggest that this rapid cross-relaxation in resonant microwave field observed for the first time in SMMV_15 should take place in other SMMs like Fe_8 and Mn_12 containing protons, too.