Speaker: Dr. Sunil Sinha, UCSD/ Los Alamos Natl. Laboratory

Title: " Diffuse scattering studies of lattice modulations and lattice distortions in complex oxides "

Date: Monday, May 3, 2004

Time: 4:10 p.m.

Place: 55 Roessler Hall

Host: Liu

We shall discuss recent synchrotron X-ray scattering studies of the layered LaSrMn₂O₇ manganite compounds and the high-Tc YBa₂Cu₃O_7-x superconducting compounds. In the former, diffuse X-ray scattering studies have revealed directly the formation of Jahn-Teller-driven polarons associated with oxygen displacements around the Mn3+ ions. These collapse below Tc with the onset of double-exchange-driven ferromagnetism, while above Tc they form a polaron-liquid with stripe-like short-range order. In the underdoped compound YBa₂Cu₃O_6.62, we see short-range order due to oxygen vacancy ordering in the chains which induces stripe-like lattice modulations of period 5a along the a-axis in the CuO₂ planes and two neighboring planes as the temperature is lowered, but which appear to saturate below Tc. Similar modulations are also seen in the optimally doped compound YBa₂Cu₃O_6.92, but with period 4a.

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Refreshments

3:50 p.m., Physics Bldg. Entrance

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