Lay summary

The superconducting state is a special phase of matter with the features of vanishing electric resistivity and the expulsion of external magnetic flux. Uncovering the mechanism of the high-temperature superconductivity in complex materials, such as iron- and copper-based superconducting compounds, has essential importance in their potential industrial applications, e.g. building power-distribution cables and powerful motors. The aim of this project is to study the electronic structure and the low-energy electronic excitations of 1111 iron-pnictides, which have the highest superconducting transition temperature among the newly discovered iron-based superconductors. This will advance our understanding of various exotic properties of this class of materials and shed light on the microscopic origin of the high-temperature superconductivity in iron-pnictides.

Because the physical properties in solids are govern by the interactions between multiple degrees of freedom, an essential piece of knowledge is how the electronic states and excitation spectra change from one phase to another. In this project we shall concentrate our studies on the electronic structure and charge excitations of iron-pnictides. By using high-resolution angle-resolved photoemission spectroscopy (ARPES) and soft X-ray ARPES stations at Swiss Light Source (SLS), we will investigate how the electronic structure evolves under the structural transition from a tetragonal structure to an orthorhombic one, and under phase transitions from an antiferromagnetically ordered phase (AFM) to a superconducting state, and from a normal state to a superconducting state. We shall also investigate the relation between the superconducting phase and other instabilities in this class of materials. These studies will provide essential ingredients for uncovering the mechanism for the emergence of the high-temperature superconductivity in this class of materials.