Special Condensed Matter Seminar, Hong Ding, Strong and local pairing in iron-based superconductors as seen by photoelectrons"

Thu, Jul 10, 2014, 2:00 pm to 3:30 pm
PCTS Seminar Room
Iron-based superconductors (Fe-SCs), with their highest transition temperature (Tc) at 57K, have been added since 2008 to the family of high-Tc superconductors which has been solely occupied by copper-based superconductors (Cu-SCs) for more than 20 years. Both Fe-SCs and Cu-SCs, with a transition element playing crucial roles in their superconductivity, share a similar phase diagram where the superconducting phase is adjacent to a magnetic order phase, and are clearly beyond of the scope of BCS superconductors. In this talk I will report our extensive and some new ARPES results on Fe-SCs, which demonstrate unequivocally that a strong pairing gap is determined by its location in the momentum space, basically following a coskxcosky function which is likely determined by the local next-nearest-neighboring antiferromagnetic exchange J2, in much the same way that the d-wave gap of cuprates is caused by its nearest-neighboring exchange J1. In an example of Li(Fe,Co)As, the low-energy spin fluctuations, while sensitive to the Fermi surface nesting condition, are found not directly tie to its superconductivity. We conclude that a same pairing mechanism, at least phenomenologically if not microscopically, must be in work for both Fe- and Cu-SCs.