报告题目：Evidence for superconducting correlations above Tc in iron-based superconductors observed by inelastic neutron scattering measurements

报 告 人： Jinsheng Wen，加州大学伯克利分校

报告时间：9月23日14：30

报告地点：理科楼三楼报告厅（理科楼C-302）

报告摘要：Interplay between magnetism and superconductivity is key to understanding unconventional superconductors. In the newly discovered iron-based superconductors, there are compelling evidences showing the unconventional nature of the superconductivity with magnetism playing an essential role. Take Fe1+yTe1-xSex (11 system) as an example: first, superconductivity is in close vicinity to antiferromagnetism; the neutron-spin resonance manifests itself like a superconducting order parameter from the temperature and magnetic-field dependence; magnetic excitations close to the in-plane wave vector (π, 0) are correlated with static magnetic order, which competes with superconductivity, while those near (π, π) are coupled with superconductivity.

Our recent inelastic neutron scattering measurements have added new information into these understandings---we have observed that superconducting correlations persist well above the superconducting temperature, Tc. In particular, the anisotropic low-energy magnetic excitations maintain the “hour-glass” shape across Tc, and change to two “waterfalls” at a higher temperature. Such change appears to be universal among the superconducting samples, while in the non-superconducting ones, a waterfall shape is observed in the whole temperature range, suggesting that it is related to superconductivity. Our results demonstrate that, superconducting fluctuations, commonly observed in cuprate superconductors at temperatures much higher than Tc, also exist in iron-based superconductors. Therefore, the “normal-sate” properties should also be important in understanding the superconductivity of iron-based superconductors.