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21世紀COEセミナー「Probing Gaps and Pseudogaps in Cuprates by Infrared Spectroscopy」

日時 平成18年(2006年)11月22日(水)10:30〜12:00
場所 理学研究科H棟6階 中セミナー室(H601)
講師 Nicole Bontemps 教授 (CNRS (UPR5) - ESPCI)
現 東京大学大学院 新領域創成科学研究科 客員教授
題目 Probing Gaps and Pseudogaps in Cuprates by Infrared Spectroscopy
概要 Identifying how remote high critical temperature superconductors are from conventional metals is an important clue for these materials. Infrared spectroscopy can provide a model independent insight about the properties of these “strange metals”. Indeed the optical conductivity integrated up to a set of cut-off frequencies (spectral weight) has clear signatures when studied versus temperature and cut-off frequency, for a metal (full Fermi surface) or a partially gapped state.
We will first present our data deduced from in-plane reflectivity measurements, in electron doped cuprates (Pr2-xCexCuO4, x = 0.11, 0.13, 0.15, 0.17). There, we find a clear spectroscopic signature of the onset of a pseudogap up to x = 0.15. Recent infrared results in a reduced (superconducting) sample and an oxidized non superconducting sample for x = 0.17, together with inelastic neutron scattering data, point towards a magnetic origin of the pseudogap. In contrast, in hole doped materials (two layers cuprate Bi2Sr2CaCuO8+δ), the pseudogap is hardly seen in the in-plane conductivity. This may imply that the pseudogap in electron doped and hole doped compounds has a different origin.

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