Exchange interaction in singlet and triplet superconductors

Chih-Kai Yang^1*, Chi-Hsuan Lee¹

* Presenter:Chih-Kai Yang, email:ckyang@nccu.edu.tw

FeTe0.55Se0.45 is an iron-based superconductor with critical temperature (Tc) at 14.5 K. It exhibits an s-wave superconducting gap associated with topological surfaces states. Using density functional calculations for electrons and phonons and the Bardeen-Cooper-Schrieffer theory for superconductivity, it can be shown that the exchange interaction is behind the formation of singlet Cooper pairs in FeTe0.5Se0.5. Furthermore, the calculation shows that Tc and superconducting gap for FeTe0.5Se0.5 soars under increasing compression, consistent with the results of experiment. UTe2 is an example of triplet superconductors. We will discuss how exchange interaction affects its Tc and other physical properties.

Keywords: Iron-based superconductor, Topological surfaces states, Pairing mechanism, UTe2