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 Weber^1,2, Stephan Rosenkranz², John-Paul Castellan², Ray Osborn², Hong Zheng², John F. Mitchell², Ying Chen^3,4, Songxue Chi^3,4, Jeffrey W. Lynn³, and Dmitry Reznik^1,5 — ¹Karlsruhe 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.