讲座题目：The s^±-Wave Pairing and the Destructive Role of Oxygen Deficiencies in La₃Ni₂O₇

时间：3 月 29 日 上午 10：00

地点：理学楼A301

报告人：杨帆 教授

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、量子自旋液体、魔角石墨烯、镍基超导等领域从事研究多年。发表论文80余篇，其中包括10篇Phys. Rev. Lett.，引用2000余次。

讲座内容：Recently, the bilayer perovskite nickelate La3Ni2O7 has been reported to show evidence of high-temperature superconductivity (SC) under a moderate pressure of about 14 GPa. To investigate the superconducting mechanism, pairing symmetry, and the role of apical-oxygen deficiencies in this material, we perform a random-phase-approximation based study on a bilayer model consisting of the $d_{x^2-y^2}$ and $d_{3z^2-r^2}$ orbitals of Ni atoms in both the pristine crystal and the crystal with apical-oxygen deficiencies. Our analysis reveals an s+- wave pairing symmetry driven by spin fluctuations. The crucial role of pressure lies in that it induces the emergence of the $\gamma$-pocket, which is involved in the strongest Fermi-surface nesting. We further found the emergence of local moments in the vicinity of apical-oxygen deficiencies, which significantly suppresses the TC. Therefore, it is possible to significantly enhance the TC by eliminating oxygen deficiencies during the synthesis of the samples.

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2024年3月25日