講演題目：　 Revisiting NMR of La2-xSrxCuO4 Superconductors :
　　　　　　　　Can we see charge stripes ?

講　師　：　Dr. Marc-Henri Julien 
　　　　　　(Laboratoire de Spectrometrie Physique, Saint Martin d'Heres, France)

日　時　：　平成12年10月17日（火）　15:00−
場　所　：　北海道大学大学院理学研究科物理学専攻　大学院講義室
　　　　　　　理学部　2号館（2−11号室）

要　旨　：
　Introducing a few percents of charge carriers into insulating copper-oxides is sufficient to make them superconducting at high temperature. Long-range antiferromagnetic order is concomitantly destroyed by these few holes. This however does not imply that magnetism has disappeared in superconducting compounds. On the contrary, various experiments have demonstrated that short-range antiferromagnetic correlations remain, actively contributing the very　peculiar electronic properties of these materials, possibly including superconductivity itself. 
In this talk, I shall mainly describe recent NMR experiments on La and Cu nuclei in a single crystal of La1.90Sr0.10CuO4, a high-Tc superconductor with Tc=27 K. It is found that magnetic fluctuations slow down on cooling, without any influence from the superconducting transition. Still, superconductivity, as well as the magnetic freezing, concerns the whole sample. Thus this sample exhibits at low temperature superconductivity microscopically coexisting with a frozen magnetic state, which resembles a spin-glass with AF local order.
Why so strong local antiferromagnetism has been overlooked before, and how these results may be, or may not be, connected to the presence of charge stripes will be discussed.

世話人　古川裕次　（北海道大学大学院理学研究科）
　　　　　　(011-706-4424、furu@phys.sci.hokudai.ac.jp)