报告题目：Interlayer coupling driven high-temperature superconductivity in La3Ni2O7 under pressure
报告人：杨帆 教授 （北京理工大学）
The newly discovered high-temperature superconductivity in La3Ni2O7 under pressure has attracted a great deal of interests. The essential ingredient characterizing the electronic properties is the bilayer NiO2 planes, in which the two layers couple with each other from the bonding of Ni-3dz2 orbital through the intermediate oxygen-atoms. In the strong coupling limit, an intralayer antiferromagnetic spin-exchange interaction J// between 3dx2−y2 orbitals and an interlayer one J⊥ between 3dz2 orbitals are generated. Taking into account the Hund’s rule at each site and integrating out the 3dz2 spin of freedom, the system reduces to a single-orbital bilayer t-J model of the 3dx2−y2 . Based on the slave-boson approach, the self-consistent equation for the hopping and pairing order parameters is solved. Near the relevant 1/4 -filling regime (doping δ = 0.3 ∼ 0.5), the inter-layer coupling J⊥ tunes the conventional single-layer d-wave superconducting state to the s-wave one. A strong J⊥ could enhance the intra-layer superconducting order, leading to a dramatically increased Tc. Interestingly, there could exist a finite regime in which an s + id state emerges.
Fan Yang is a professor of physics in Beijing Institute of Technology. He got the Ph.D of physics from Peking University in 2002, and afterwards became post doctor at the Institute of Advanced Study in Tsinghua University. He joined Beijing Institute of Technology in 2004, and was promoted as full professor in 2013. Fan Yang's research area is theoretical strongly-correlated systems and superconductivity. He has contributed in the research areas including the high-temperature cuprates superconductors, the iron-based superconductors, the twisted-bilayer graphene and the quantum spin liquid. In 2013, he was selected into the "New Century Outstanding Talents Program" by the Ministry of Education of China, and has published more than 70 papers, including 7 Phys. Rev. Lett., with more than 2000 citations,