Regensburg 2004 – scientific programme

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TT: Tiefe Temperaturen

TT 14: FV-internes Symposium ”Orbital Physics”

TT 14.13: Talk

Tuesday, March 9, 2004, 18:25–18:40, H18

Excitation spectrum of the cobaltite Na_xCoO₂ yH₂O as function of Na content and hydration — •P. Lemmens^1,2, K.-Y. Choi², V. Gnezdilov³, N.N. Kovaleva¹, H. Sakurai⁴, K. Takada⁴, T. Sasaki⁴, E. Takayama-Muromachi⁴, F.C. Chou⁵, C.T. Lin¹, and B. Keimer¹ — ¹MPI for Solid State Research, D-70569 Stuttgart — ²2. Phys. Inst., RWTH Aachen, D-52056 Aachen — ³B.I. Verkin Inst. for Low Temp. Phys., NASU, 61164 Kharkov — ⁴Superconducting Mat. Center and Advanced Mat. Lab., NIMS, Tsukuba, Ibaraki 305-0044 — ⁵Center for Material Science and Engineering, MIT, Cambridge, MA 02139

We report on a Raman scattering study on the superconducting cobaltite Na_xCoO₂ yH₂O as function of Na content and hydration (x≈1/3, 3/4 and y≈0, 2/3, 4/3). The observed phonon scattering is analyzed in terms of lattice strain due to the structural misfit and disorder. Hydration, due to the intercalation of H₂O layers, releases a part of this strain. We will show experimental evidence for a pseudo gap formation in the electronic scattering continuum. Furthermore, our Raman data suggest a connection between disorder on the partly occupied Na sites, the split off of the a_1g level from the other t_2g states of Co⁴⁺ and superconductivity. Work supported by DFG SPP1073, NATO PST.CLG.9777766, INTAS 01-278, CREST of JST (Japanese Science and Technology Corporation) and MRSEC Program of NSF under award number DMR 02-13282.