报告人简介：Jinsheng Wen received his B.S.  in materials science from Tsinghua University in 2005.  He got his PhD in Materials Science from Stony Brook University in 2010.  He was a Research Assistant at  Brookhaven Natl. Lab from 2006-2010, then joined Department of physics, University of California at Berkeley in 2010 as a Post Doctoral Researcher.  His research interests are the following:
 Large-size, high-quality, single crystal growth on copper- and iron-based high-temperature;
Superconductors, layered copper oxide materials, and multiferroics, using floating-zone, Bridgman and flux technique;
 Neutron scattering and transport studies on the interplay between magnetism and superconductivity in copper- and iron-based high-temperature superconductors;
Exploring how local inhomogeneities affect the properties of relaxor ferroelectrics using neutron and x-ray scattering technique;
Understanding magnetic and electrical control of the charge and magnetic structures in multiferroics with neutron and transport measurements.

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.