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PRODID:UW-Madison-Physics-Events
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UID:UW-Physics-Event-1888
DTSTART:20110204T220000Z
DURATION:PT1H0M0S
DTSTAMP:20240328T150028Z
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.
\n
\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
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