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Berlin 2012 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 43: Correlated Electrons: Metal-Insulator Transition 2

TT 43.3: Talk

Thursday, March 29, 2012, 15:30–15:45, H 3010

Response of acoustic phonons to charge and orbital order in LaSr2Mn2O7 — •Frank Weber1,2, Stephan Rosenkranz2, John-Paul Castellan2, Ray Osborn2, Hong Zheng2, John F. Mitchell2, Ying Chen3,4, Songxue Chi3,4, Jeffrey W. Lynn3, and Dmitry Reznik1,51Karlsruhe Institute of Technology, Institute of Solid State Physics, Karlsruhe, Germany — 2Materials Science Division, Argonne National Laboratory, Argonne IL, USA — 3NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg MD, USA — 4Department of Materials Science and Engineering, University of Maryland, USA — 5Department of Physics, University of Colorado, USA

The acoustic phonons in the 50% doped bilayer manganite LaSr2Mn2O7 exhibiting CE type charge order were investigated using inelastic neutron scattering. At the onset of charge ordering, we observe an abrupt increase(decrease) of the energies(linewidths) of the transverse acoustic phonon along (110), which crosses the CE ordering wavevector. This effect is, however, not localized at the CE ordering wave vector, but is observed over an extended range of momentum transfers, for which the phonon energy is lower than 15 meV. These observations indicate a reduced electron-phonon coupling due to a partial removal of the Fermi surface and provide direct evidence for a link between electron-phonon coupling and charge order in manganites. However, the observed response is not consistent with a standard charge-density-wave mechanism, clearly showing that the transition is unconventional.

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