中国科学技术大学物理系呈献|加州大学伯克利分校宋宇

题目：   Intertwined Magnetism and Nematicity in Semiconducting KFe_0.8Ag_1.2Te₂(KFAT)

报   告   人：宋宇

单 位：加州大学伯克利分校

时 间：   2019-06-13

地 点：中国科学技术大学

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Strongly correlated materials often adopt electronic ground states that break rotational-symmetry of their underlying crystal structures, analogous to nematic liquid crystals. Such states are found in close proximity to and are an essential aspect of iron-based superconductors. Important questions in these materials concern the nature of their nematic and magnetic orders, whether the magnetism is due to local moments or itinerant electrons, and whether the nematic order is driven by the magnetic or the orbital degree of freedom. Using scattering techniques we demonstrate the presence of intertwined nematic and stripe-type magnetic orders in semiconducting KFe_0.8Ag_1.2Te₂, a structural analogue of iron-based superconductors. A small strain induces sizeable magnetic anisotropy above the magnetic and nematic transition temperatures, indicating a large nematic susceptibility while realizing a strain-induced spin-nematic state. Because KFe_0.8Ag_1.2Te₂is a semiconductor devoid of a Fermi surface, its magnetic and nematic orders likely arise from interactions between local moments. Such interactions should be important for systems containing Fe-pnitogen/ chalcogen planes in general, including iron-based superconductors. Our results suggest several aspects of the phenomenology of iron-based superconductor result from the unique geometry of the iron-pnictogen/ chalcogen planes.

Yu Song obtained his PhD from Rice University in 2017, after receiving a Bachelor's degree from Zhejiang University in 2010. After a brief appointment as a RCQM/ Smalley-Curl Postdoctoral Fellow in Quantum Materials at Rice University, he moved to UC Berkeley in 2017 as a postdoctoral fellow. His past research focused on the interplay between magnetism, nematicity and superconductivity in iron-based superconductors, as well as the magnetic excitations in heavy fermion superconductors. His interests also include frustrated magnetism in low-dimensional magnetic systems and itinerant magnetism.