Quantum phase interference and parity effects in magnetic molecular clusters
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.
Wernsdorfer
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Laboratoire Louis Neel, CNRS, BP166, 38042 Grenoble, France. Department of Chemistry, University of Florence, Via Maragliano 75/77, 50144 Firenze, Italy.
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