An Overview on the Local Atomic Displacements and Electronic Structures in BiS₂/BiSe₂-Based Superconductors

Superconductivity with layered structure has attracted intensive research interests due to their exotic superconducting properties. In 2012, a new family of BiS₂-based superconductor with their desired layered structure has been discovered. Recently, the isostructural superconductor with the substitution of Se for all S ions in BiS₂-based compounds is recognized as the BiSe₂-based superconductors. To date, enormous efforts were dedicated to explore the physical properties of this new family. Among them, synchrotron radiation-based X-ray absorption spectroscopy (XAS) contributed significantly to the understanding of local atomic structure and the electronic structure of BiS₂/BiSe₂-based systems. This article reviewed the progresses in the study of the new BiS₂/BiSe₂-based materials revealed by the unique technique XAS, including the determination of valence state, local atomic displacements, as well as the different structural distortion between BiS₂-based and BiSe₂-based systems. The superconductivity of BiS₂- and BiSe₂-based system is indeed intimately related to valence states and local atomic displacements. Further development of microscopic mechanism of superconductivity in BiS₂/BiSe₂-based materials requires synergetic endeavors integrating new experimental, numerical, and theoretical techniques.