报告题目1： Muon Spin Relaxation (MuSR) Studies of Unconventional Superconductors

报告人1： Prof. Yasutomo J. Uemura, Physics Department, Columbia University, USA

报告题目2： NMR and μSR Investigation of Fe-based superconductors and Diluted Ferromagnetic Semiconductors

报告人2： Prof. Fanlong Ning（宁凡龙）, Department of Physics, Zhejiang University

时间： 1月13日，下午14：00

地点： 散裂园区A1-104

主持人： 唐靖宇 研究员

报告1简介：

Muon spin relaxation (MuSR) measurements have made significant contributions in studies of high-Tc cuprate, FeAs, Alkali-doped C60, Sr2RuO4, heavy fermions and other unconventional superconductors. MuSR can determine the magnetic field penetration depth, from which one can derive the superfluid density (superconducting carrier density ns/ effective mass m*). The temperature dependence of the superfluid density reflects the structure of the superconducting gap and symmetry of the superconducting pairing. The absolute values of the superfluid density will allow energy-scale arguments of the condensation process of unconventional superconductors.

I would like to present a brief review on MuSR studies of superconducting systems, focusing particularly on the relationship between the superconducting Tc and the superfluid density at T → 0. The accumulated results on this study indicate possibilities that condensation mechanisms of many unconventional superconductors are fundamentally different from BCS condensation, and possibly closer to Bose Einstein Condensation of preformed pairs. I will also discuss relationship with other signatures of non-BCS behaviors observed in: a) spin, charge and ARPES pseudogap behavior; (b) vortex-like Nernst effect pioneered by N. P. Ong and Yayu Wang, and (c) photo-excited optical conductivity pioneered by Andrea Cavalleri.

报告人1简介：

Prof. Yasutomo Uemura obtained his Doctor of Science in 1982 from Tokyo University under the supervision of Prof. Toshimitsu Yamazaki. During 1983-88, he worked at Brookhaven National Laboratory with the neutron scattering group lead by Dr. Gen Shirane. He moved to Columbia University as an Associate Professor in 1988, and since then has been active in μSR studies. By applying muSR, Prof. Uemura discovered a strong correlation between Tc and the superfluid density of HTSC systems in 1988-89, which has been often referred to as ‘Uemura plot’ among HTSC researchers.

Prof. Uemura has published 340 scientific papers, including 5 in Nature, 44 in Physical Review Letters, and 85 in Physical Review B, with a total citation >13000 and H-index = 56. He has presented more than 200 invited talks at international conferences and workshops.

Prof. Uemura was elected as a Fellow of Americal Physical Society in 1999, and has received several world-known prizes. One is the Yamazaki Prize for his outstanding, sustained work in μSR with long term impact on scientific applications. His scientific interests cover topics as heavy-fermion physics, frustrated magnetism, superconductivity and topology.

报告2简介：

NMR (Nuclear Magnetic Resonance) is a local, site-selective microscopic experimental probe. In this talk, I will introduce some work done on the Fe-based high temperature superconductor Ba(Fe1-xCox)2As2 , especially the spin dynamics in the narrow regime between TS and TSDW. I will then introduce how we extended our research from Fe-based superconductors into diluted ferromagnetic semiconductors (DMS). I will show a series of bulk form DMS materials synthesized by our collaboration team. Among them, the Curie temperature TC of 122-type bulk form (Ba,K)(Mn,Zn)2As2 DMS has reached to 230 K, which is higher than the record value 200 K of (Ga,Mn)As. Furthermore, through the doping of Co onto Zn sites in BaZn2As2, we obtained an n-type DMS with TC as high as 45 K. μSR measurements confirm that the ferromagnetism is homogenous in these bulk form DMSs, and indicate that the mechanism responsible for ferromagnetic ordering in (Ba,K)(Mn,Zn)2As2 and other bulk DMSs is the same as that of (Ga,Mn)As.

报告人2简介：

Professor Fanlong Ning received his Bachelor’s degree at Jilin University in 2000, and his Ph.D at McMaster University, Canada in 2009. He then become a postdoctoral research fellow at Columbia University, USA. He was appointed as a tenure-tracked professor at Zhejiang University since 2010 and promoted to a full professorship in 2014. His research is mainly focusing on the study of strongly correlated system by two local experimental techniques, one is the site-selective NMR and the other is the volume-sensitive μSR. He has published ~50 papers in Nature Communications, Physical Review Letters, Physical Review B and other journals with a total citation more than 2000 times.