Incoherent Landau-Zener-Stuckelberg Transitions in Single-Molecule Magnets

TL;DR

This paper demonstrates that Landau-Zener-Stuckelberg transitions in single-molecule magnets are fully incoherent due to nuclear and dipolar interactions, revising the theoretical understanding of spin-flip probabilities.

Contribution

It identifies the main sources of decoherence in SMMs and shows that a recent formula better describes the incoherent LZS transitions than the traditional one.

Findings

Transitions are fully incoherent in experiments.

Nuclear spins and dipolar couplings cause decoherence.

The Kayanuma formula better describes spin-flip probabilities.

Abstract

It is shown that in experiments on single molecule magnets (SMM's) in which transitions between two lowest spin states are induced by sweeping the applied magnetic field along the easy axis, the transitions are fully incoherent. Nuclear spins and the dipolar coupling of molecular spins are identified as the main sources of decoherence, and the form of the decoherence is calculated. The Landau-Zener-Stuckelberg (LZS) process is examined in light of this decoherence, and it is shown that the correct formula for the spin-flip probability is better given by a more recent formula of Kayanuma's than that of LZS. The two formulas are shown to be identical in the limit of rapid sweeps. An approximate way of incorporating the molecular spin dipole field into the rate equations for this process is developed.