Quantum tunneling and dissipation in nanometer-scale magnets

Loss, D. and Divincenzo, D. P. and Grinstein, G. and Awschalom, D. D. and Smyth, J. F.. (1993) Quantum tunneling and dissipation in nanometer-scale magnets. Physica. B, Condensed matter, Vol. 189, H. 1-4. pp. 189-203.

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Official URL: http://edoc.unibas.ch/dok/A5254794

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We summarize recent low-temperature noise and AC magnetic susceptibility measurements on the nanometer-scale magnetic protein horse-spleen ferritin. The experiments show a narrow resonance peak at about 10(6) Hz, which is discussed in the framework of recently-developed theories of macroscopic quantum coherence and tunneling in antiferromagnets; theory and experiment are argued to agree qualitatively, though quantitative discrepancies remain. We also review the recent analysis of a rather general spin-parity effect for tunneling in magnetic systems: systems with appropriate symmetry may exhibit quantum tunneling for integer spin, but not for half-odd-integer spin, where destructive interference between different tunneling paths suppresses the tunneling. Finally, we study the effect on this spin-parity phenomenon caused by dissipation, i.e. coupling to an environment consisting of a bath of harmonic oscillators. Using the real-time, Feynman-Vernon path integral formalism, we find models where an arbitrarily small amount of ohmic dissipation completely destroys the spin-parity effect (i.e., produces as much tunneling for half-odd-integer spins as for integer spins), and others where the effect appears to disappear gradually with increasing dissipation. Surprisingly, however, there is a sense in which the spin-parity effect is preserved in both types of models: a Caldeira-Leggett type of analysis shows that neither experiences any tunnel splitting of its ground state. We present simple arguments for how this intriguing paradox might be resolved.
Faculties and Departments:05 Faculty of Science > Departement Physik > Physik > Theoretische Physik Mesoscopics (Loss)
UniBasel Contributors:Loss, Daniel
Item Type:Article, refereed
Article Subtype:Research Article
Note:Publication type according to Uni Basel Research Database: Journal article
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Last Modified:22 Mar 2012 14:26
Deposited On:22 Mar 2012 13:53

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