报告题目： Pairing mechanism for the high-temperature superconductivity in La₃Ni₂O₇ under pressure

报告人：杨帆教授  北京理工大学

报告时间：2024.7.22 上午10：00

报告地点：物理科技楼155

报告邀请人：蒋密

报告摘要：The recently discovered high-temperature superconductivity in La₃Ni₂O₇ under pressure has attracted a great deal of interests. In this talk, I will introduce our recent studies on this system from combined weak-coupling and strong-coupling viewpoints.  In the weak-coupling perspective, we adopted a random-phase-approximation (RPA) approach based study on the system. Our calculations reveal an s^+- wave pairing symmetry driven by spin fluctuations. We further found the emergence of local moments in the vicinity of apical-oxygen deficiencies, which significantly suppresses the T_c. In the strong-coupling perspective, we built up a single d_x2-y2-orbital bilayer t-J model, in which the two layers are coupled via the super-exchange interaction transferred from the d_z2-orbital assisted by the Hund’s coupling. Our slave-boson-mean-field approach based study reveal that the effective interlayer super-exchange not only changes the pairing symmetry from d-wave to s-wave, but also strongly enhance the T_c. The connection between the two viewpoints is also discussed at the end.

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。2013年被聘为教授。获得教育部“新世纪优秀人才“称号。杨帆的主要研究方向为强关联和超导理论。集中关注各类强关联电子材料当中的非常规超导。在铜基超导、铁基超导、镍基超导、量子自旋液体、魔角石墨烯、准晶电子态等领域从事研究多年。发表论文70余篇，引用2500余次。