报告题目：Gap structure, hidden quantum criticality and nematic transition in BaFe2As2-based superconductors

报 告 人：Yuji Matsuda，Department of Physics, Kyoto University

报告时间：4月26日（周四） 11:00

报告地点：物理系三楼报告厅

报告摘要：BaFe2As2-based materials are a prototypical family of iron-based high transition temperature superconductors. Among them, the isovalent pnictogen substituted system BaFe2(As1-xPx)2appears to be the most suitable system to discuss many physical properties, because it can be grown in a wide substitution range, where very clean and homogeneous single crystals are available. We here discuss three topics related to the unusual electronic properties of this system. First is the superconducting gap structure. In contrast to the electron- and hole-doped systems, BaFe2(As1-xPx)2has line node. We discuss the detailed nodal structure of this system, which is still controversial. Second is the issue of a quantum critical point (QCP) . An important question is whether high-transition temperature superconductivity is driven by an underlying QCP separating different ground states. We show the presence of the QCP deep inside the superconducting dome by systematic measurements of the superfluid density. Third is unusual electronic state in the normal state. We provide thermodynamic evidence that an electronic nematic phase, a unidirectional self-organized state which breaks rotational symmetry of underlying lattice, develops well above the structural transition and persists to the nonmagnetic superconducting regime. Based on these results, we propose a new phase diagram of iron-pnictide superconductors.