FeSe, which has the simplest crystal structure among the Fe based superconductors, and related chalcogenide superconductors are ideal candidates for investigating the detailed mechanism of the iron-based superconductors. Here, we summarize recent studies on the Fe-chalcogenides, with the goal to address some unresolved questions such as what is the influence of chemical stoichiometry on the phase diagram, what is the exact parent phase of FeSe system, and why can Tcs be so dramatically enhanced in FeSe based superconductors? Recent developments in novel synthesis to prepare chalcogenide crystals, nano-materials and thin films allow the community to begin to address these issues. Then we review physical properties of the Fe chalcogenides, specifically focusing on optical properties, scanning tunneling spectroscopy and angle-resolved photoemission spectroscopy (ARPES) results. These measurements along with recent theories provide a framework for better understanding the origin of superconductivity in FeSe and Fe-chalcogenides.
Chang, C-C., Chen, T. K., Lee, W. C., Lin, P. H., Wang, J. M., Wen, Y. C., Wu, M. P., & Wu, M. K. (2015). Superconductivity in Fe-chalcogenides: Superconducting Materials: Conventional, Unconventional and Undetermined. Physica C: Superconductivity and its Applications, 514, 423-434. https://doi.org/10.1016/j.physc.2015.02.011