Bezghuba V. Iron-based superconductors as search platform for topological superconductivity

The thesis focuses on the study of the electronic structure of iron-based superconductors using angle-resolved photoemission spectroscopy (ARPES). As part of the work methods for analysing data from ARPES experiments were developed and improved. For the first time, the dependence of the obtained ARPES spectra from the polarization of light at the Г-point for optimally doped Ba(1-x)K(x)Fe2As2 (x=0.4) was revealed, which indicates additional splitting of bands due to the nematicity in this compound. It was first established that FeTe0.55Se0.45 is a superconducting 3D Dirac semimetal hosting Dirac points of both type-I and type-II, that no topological states are present in its electronic structure. It is shown that the inverted band gap in FeTe(1-x)Se(x) can possibly be realized by further increase of Te content, but strong correlations reduce it to a sub-meV size, making the experimental detection of the gap and corresponding topological surface states very challenging. The work lays the foundations of the method for detecting topological states in other iron-based superconductors.