EPR spectrum via entangled states for an Exchange-Coupled Dimer of Single-Molecule Magnets

TL;DR

This paper analyzes the EPR spectrum of a supermolecular dimer of single-molecule magnets, revealing entangled states and quantifying exchange interactions, thus confirming quantum mechanical coupling in the system.

Contribution

It introduces a perturbation method including high-order corrections to analyze the EPR spectrum, demonstrating entangled eigenstates and accurately determining anisotropy and exchange constants.

Findings

Eigenvectors are entangled states of two molecules.

Calculated EPR peak positions match experimental data.

Confirmed antiferromagnetic exchange coupling in the dimer.

Abstract

Multi-high-frequency electron paramagnetic resonance(EPR) spectrum for a supermolecular dimer $[ Mn_4]_2$ of single-molecule magnets recently reported [S. Hill, R. S. Edwards, N. Aliaga-Alcalde and G. Christou(HEAC), Science 302, 1015 (2003)] is studied in terms of the perturbation method in which the high-order corrections to the level splittings of degenerate states are included. It is shown that the corresponding eigenvectors are composed of entangled states of two molecules. The EPR-peak positions are calculated in terms of the eigenstates at various frequencies. From the best fit of theoretical level splittings with the measured values we obtain the anisotropy constant and exchange coupling which are in agreement with the corresponding values of experimental observation. Our study confirms the prediction of HEAC that the two $Mn_4$ units within the dimer are coupled quantum mechanically by the antiferromagnetic exchange interaction and the supermolecular dimer behaviors in analogy with artificially fabricated quantum dots.