Joint colloquium of CQT and Physics department

Speaker: Academician Ting-Kuo Lee (李定國院士), Department of Physics, National Sun Yat-sen University
Time：2022/2/23  1:30PM-3:00PM
Place：Lecture room 124, Dept. of Phys. 
Title : A new pairing order in the copper-oxide high temperature superconductor
Abstract: 
Since the discovery of copper-oxide (or cuprate) high temperature superconductors about thirty-five years ago, experiments have continuously reported many exotic properties, like broken Fermi surfaces, the pseudogap at normal state, and two energy gaps at the superconducting state, etc. More surprises have been reported recently about the breaking of four fold rotation symmetry and translation symmetry of the copper-oxide square lattice and the presence of various charge density wave (CDW) or spin density wave (SDW) in different cuprate families. These states are seen in the superconducting and normal phases. It has also been observed inside a vortex halo. In this talk, the microscopic model of cuprates is shown to naturally provide a solution to resolve many of these puzzles. The Cooper pair in this solution has a finite center of mass momentum. This state has been searched for more than half a century since the work of Fulde-Ferrell (FF) and Larkin-Ovchinnikov(LO). However, the mechanism of forming such a state in cuprates is completely different. In real space this state has a modulation of pairing order, which is called a pair density waves (PDW). The relation of this state with pseudogap, CDW, SDW and magnetic vortex will be discussed. In addition, an experimental method to unequivocally determine the existence of this state will be proposed.