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ics Colloquium
Friday, February 15, 2002
4:00 PM
Physics Building, Room 204
Note special time.
Despina Louca [Host: T. Gallagher]
University of Virginia
"Lattice Effects and Jahn-Teller Fluctuations in Crystals"
In many systems i.e. magnetoresistive and superconducting oxides, the atomic structure couples strongly to the electronic degrees of freedom. In CMR crystals, Jahn-Teller effects are strongly related to the metal-insulator transition, for instance. The manganites are one example where the JT distortions are static and are important ingredients to the polaron lattice formation. In cuprates, when static distortions are present it usually means superconductivity is killed, while dynamic effects prevailing in the SC phase are sometimes too fast to observe. (La/Sr)CoO3 serves as a prototype for studying the crossover from static to dynamic effects. With the pair density function analysis and inelastic S(Q,w) measurements, it was determined that dynamical JT fluctuations induce a distorted atomic structure. The S(Q,w) clearly shows the presence of localized phonon modes most likely due to JT excitations, while the local structure transforms to an unusually glassy state that is intermediate to the manganites and cuprates.

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