Quantum Phase Interference and Parity Effects in Magnetic Molecular Clusters
W. Wernsdorfer,
1*
R. Sessoli
2
An experimental method based on the Landau-Zener model was
developed to measure very small tunnel splittings in molecular clusters
of eight iron atoms, which at low temperature behave like a nanomagnet
with a spin ground state of S = 10. The observed oscillations of the tunnel splittings as a function of the magnetic field applied along the hard anisotropy axis are due to topological quantum interference of two tunnel paths of opposite windings. Transitions between quantum numbers M = 
S
and (S n), with n even or odd,
revealed a parity effect that is analogous to the suppression of
tunneling predicted for half-integer spins. This observation is direct
evidence of the topological part of the quantum spin phase (Berry
phase) in a magnetic system.
1 Laboratoire Louis Néel, CNRS, BP166,
38042 Grenoble, France.
2 Department of Chemistry,
University of Florence, Via Maragliano 75/77, 50144 Firenze, Italy.
*
To whom correspondence should be addressed. E-mail:
wernsdor{at}labs.polycnrs-gre.fr
