BEGIN:VCALENDAR VERSION:2.0 CALSCALE:GREGORIAN PRODID:UW-Madison-Physics-Events BEGIN:VEVENT SEQUENCE:0 UID:UW-Physics-Event-1888 DTSTART:20110204T220000Z DURATION:PT1H0M0S DTSTAMP:20260407T161720Z LAST-MODIFIED:20110124T205909Z LOCATION:2241 Chamberlin Hall (coffee at 3:30 pm) SUMMARY:Multiferroic Vortices and Graph Theory\, Physics Department Co lloquium\, Sang-Wook Cheong\, Rutgers Center for Emergent Materials DESCRIPTION:The fascinating concept of topological defects permeates u biquitously our understanding of the early-stage universe\, hurricanes \, quantum matters such as superfluids and superconductors\, and also technological materials such as liquid crystals and magnets. Large-sca le spatial configurations of these topological defects have been inves tigated only in a limited degree. Exceptions include the cases of supe rcurrent vortices or liquid crystals\, but they tend to exhibit either trivial or rather-irregular configurations.Hexagonal REMnO3 (RE= rare earths) with RE=Ho-Lu\, Y\, and Sc\, is an improper ferroelectric whe re the size mismatch between RE and Mn induces a trimerization-type st ructural phase transition\, and this structural transition leads to th ree structural domains\, each of which can support two directions of f erroelectric polarization. We reported that domains in h-REMnO3 meet i n cloverleaf arrangements that cycle through all six domain configurat ions [1]\, Occurring in pairs\, the cloverleafs can be viewed as vorti ces and antivortices\, in which the cycle of domain configurations is reversed. Vortices and antivortices are topological defects: even in a strong electric field they won't annihilate. Recently we have found i ntriguing\, but seemingly irregular configurations of a zoo of topolog ical vortices and antivortices in h-REMnO3 [2]. These configurations c an be neatly analyzed in terms of graph theory and this graph theoreti cal analysis reflects the nature of self-organized criticality in comp lexity phenomena as well as the condensation and eventual annihilation processes of topological vortex-antivortex pairs.
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\n[1] In sulating Interlocked Ferroelectric and Structural Antiphase Domain Wal ls in Multiferroic YMnO3\, T. Choi\, Y. Horibe\, H. T. Yi\, Y. J. Choi \, Weida. Wu\, and S-W. Cheong\, Nature Materials 9\, 253-258 (2010).
\n[2] Self-Organization\, Condensation and Annihilation of Topolo gical Vortices and Antivortices in a Multiferroic\, S. C. Chae\, Y. Ho ribe\, D. Y. Jeong\, S. Rodan\, N. Lee\, and S.-W. Cheong\, PNAS\, in print. URL:https://www.physics.wisc.edu/events/?id=1888 END:VEVENT END:VCALENDAR