College of Sciences (Colloquium)

A new superconducting phase in the copper-oxide high temperature superconductor?

Speaker : 講座教授 / 中央研究院院士 李定國 (國立中山大學物理系)
Location :
Time : 2021 / 04 / 23 14:10
Since the discovery of copper-oxide (or cuprate) high temperature superconductors about thirty 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 of the copper-oxide square lattice and the presence of various charge density waves or spin density waves in different cuprate families.  These states are seen in the superconducting and normal phases. 

In this talk, I will try to show theoretically that most of these complicated and seemingly contradictory results could actually point to the presence of a possible new superconducting phase.  This novel phase, that the Cooper pair with a non-zero center of mass momentum, has been searched for about half a century since the work of Fulde-Ferrell and Larkin-Ovchinnikov.  In real space this state with a modulation of pairing order is also called pair density waves. The mechanism of forming such a state in cuprates is completely different. The implication of this state will be discussed also.