报告人简介：
杨帆是北京理工大学物理学院教授。2002年博士毕业于北京大学物理学院，2004年从清华大学高等研究中心博后出站，之后加入北京理工大学物理学院。2010年至2011年公派访问美国加州大学伯克利分校。2013年被聘为教授。杨帆的主要研究方向为强关联和超导理论。曾长期在铜基超导、量子自旋液体和铁基超导领域展开研究。近期的研究兴趣集中在魔角石墨烯、准晶电子态和镍基超导等领域。发表论文80余篇，被引3000余次。

讲座摘要：

The high-temperature superconductivity discovered recently in the Ruddlesden-Popper (RP) phase multilayer superconductors has aroused great research interests. In this talk, I will first make a brief introduction over the experimental progress, and then report our series of works obtained through adopting both weak-coupling approach and strong-coupling one, for the bilayer 𝐿𝑎3𝑁𝑖2𝑂7, the trilayer 𝐿𝑎4𝑁𝑖3𝑂10 and the alternating bilayer-monolayer 𝐿𝑎5𝑁𝑖3𝑂11. In the weak-coupling aspect, we adopt the random-phase approximation approach to study the pairing symmetry and magnetic properties both at ambient pressure and under high pressure, with part of the results consistent with experiments. In the strong-coupling aspect, we propose that the SC under high pressure is carried by the 𝑑_(𝑥^2−𝑦^2 ) orbital, and that the 𝑑_(𝑧^2 ) orbital also plays an important role through the Hund’s rule coupling. Based on this viewpoint, we construct the 𝑑_(𝑥^2−𝑦^2 )orbital bilayer 𝑡−𝐽−𝐽_⊥ model for 𝐿𝑎3𝑁𝑖2𝑂7, and generalized it to 𝐿𝑎4𝑁𝑖3𝑂10. These studies lead us to predict possible way to enhance the Tc by element substitution, partly confirmed by experiment. Finally, we discuss the relation between the results of the two approaches.

邀请人：蒋易凡，齐彦鹏