講師：Prof. Eun-Gook Moon (Korea Advanced Institute of Science and Technology (KAIST), Korea)
タイトル：Exotic phenomena in superconductors : topological superconductivity and unconventional nematicity
Superconducting material may host exotic behaviors of physical quantities. For example, recent experiments in cuprates such as YBCO and Hg1201 show unconventional nematicity behaviors. In the first part of the seminar, we consider a topological superconductor with Fermi surfaces of Bogoliubov quasi-particles, so-called Bogoliubov Fermi surfaces, and discuss its instability. Implication to correlated systems such as FeSe and Sr2RuO4 is pointed out. In the second part, we discuss nematicity of Fe-based superconducting material with tetragonal symmetry, Ba1−xRbxFe2As2, by using a microscopic model with two orbitals. Limitation of a conventional phenomenological theory is emphasized, and plausible theories for the exotic nematicity are introduced.