Berlin 2008 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 18: Correlated Electrons: Low-dimensional Systems - Materials 2

TT 18.6: Talk

Tuesday, February 26, 2008, 16:30–16:45, H 2053

Effect of composition on phonon anomalies in Na_xCoO₂ · yH₂O — •Peter Lemmens^1,2, Dietrich Wulferding¹, Patric Scheib¹, Kwang-Yong Choi³, Vladimir Gnezdilov⁴, Fangcheng Chou⁵, Chengtian Lin², and Bernhard Keimer² — ¹IPKM, TU Braunschweig — ²MPI-FKF, Stuttgart — ³NHMFL, Florida — ⁴B.I. Verkin Inst. for Low Temp. Phys., NASU, Kharkov — ⁵CMSE, MIT, Cambridge, USA

A quantitative analysis of phonon frequencies for nonsuperconducting and superconducting cobaltates Na_xCoO₂ · yH₂O shows pronounced phonon anomalies in the proximity of the charge ordering instabilities in Na_0.5CoO₂. Furthermore, as function of Na doping a systematic shift of a high energy out-of-plane oxygen phonon is observed in a wide doping range. The corresponding in-plane mode does not show any appreciable anomaly.

Work supported by DFG, ESF-HFM and MRSEC Program of NSF under award number DMR 02-13282.