Condensed-Matter Physics & Materials Science Seminar

"Direct ARPES Studies on Strained High-Tc Films"

Presented by Davor Pavuna, Laboratory for Physics of Functional Matter, Switzerland

Friday, July 28, 2006, 1:30 pm — Bldg. 480, conference room

Following the original concept of Ivan Bozovic (BNL), we systematically perform direct ARPES on in-situ grown thin (<30nm) cuprate films. Specifically we probe low energy electronic structure and properties of high-Tc superconductors (HTSC) under different degree of epitaxial (compressive vs tensile) strain. In overdoped and underdoped in-plane compressed 10nm thin La2-xSrxCuO4 (LSCO) films (the strain is induced by the choice of substrate) we almost double Tc to 40K, from 20K and 24K, respectively, yet the Fermi surface (FS) remains essentially 2-dimensional (and appears as if we performed an effective ‘overdoping’). In contrast, ARPES data under tensile strain show the measured dispersion that is 3-dimensional, yet Tc drastically decreases. It seems that the in-plane compressive strain tends to push the apical oxygen far away from the CuO2 plane, enhances the 2-dimensional character of the dispersion and increases TC, while the tensile strain seems to act exactly in the opposite direction and the resulting dispersion is 3-dimensional. We have established the shape of the FS for both cases, and all our data are consistent (also with other ongoing studies, like EXAFS). Our data essentially rule out all oversimplified 2-dimensional mean field models.

Hosted by: Ivan Bozovic

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